System and method for micro-electromechanical operating of an interferometric modulator

CROSS-REFERENCE TO RELATED APPLICATIONS

0001This application is a continuation-in-part of the following: <patcit id="pcit0001" dnum="US90922804A"><text>U.S. Application Serial No. 10/909,228, filed July 29, 2004</text></patcit>; and <patcit id="pcit0002" dnum="US04866205A"><text>U.S. Application Serial No. 11/048,662, filed January 27, 2005</text></patcit>; both of which are hereby incorporated by reference in their entireties. This application also claims priority to the following: <patcit id="pcit0003" dnum="US61346604P"><text>U.S. Provisional Application No. 60/613,466, filed September 27, 2004</text></patcit>; <patcit id="pcit0004" dnum="US61349904P"><text>U.S. Provisional Application No. 60/613,499, filed September 27, 2004</text></patcit>; and <patcit id="pcit0005" dnum="US65886705P"><text>U.S. Provisional Application No. 60/658,867, filed March 4, 2005</text></patcit>; all of which are hereby incorporated herein by reference in their entireties.

BACKGROUND

Field of the Invention

0002This invention relates to microelectromechanical systems for use as interferometric modulators. More particularly, this invention relates to systems and methods for improving the micro-electromechanical operation of interferometric modulators.

Description of the Related Art

0003Microelectromechanical systems (MEMS) include micro mechanical elements, actuators, and electronics. Micromechanical elements may be created using deposition, etching, and or other micromachining processes that etch away parts of substrates and/or deposited material layers or that add layers to form electrical and electromechanical devices. One type of MEMS device is called an interferometric modulator. As used herein, the term interferometric modulator or interferometric light modulator refers to a device that selectively absorbs and/or reflects light using the principles of optical interference. In certain embodiments, an interferometric modulator may comprise a pair of conductive plates, one or both of which may be transparent and/or reflective in whole or part and capable of relative motion upon application of an appropriate electrical signal. In a particular embodiment, one plate may comprise a stationary layer deposited on a substrate and the other plate may comprise a metallic membrane separated from the stationary layer by an air gap. As described herein in more detail, the position of one plate in relation to another can change the optical interference of light incident on the interferometric modulator. Such devices have a wide range of applications, and it would be beneficial in the art to utilize and/or modify the characteristics of these types of devices so that their features can be exploited in improving existing products and creating new products that have not yet been developed.

Summary

0004The system, method, and devices of the invention each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of this invention, its more prominent features will now be discussed briefly. After considering this discussion, and particularly after reading the section entitled "Detailed Description of Certain Embodiments" one will understand how the features of this invention provide advantages over other display devices.

0005One aspect of the invention provides an interferometric modulator, which includes a first layer, a second layer and a member. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion located substantially parallel to the first reflective planar portion. The second layer is movable between a first position and a second position. The first position is located at a first distance from the first layer. The second position is located at a second distance from the first layer. The second distance is greater than the first distance. The member includes a surface that is located between the first layer and second layer. The member defines one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member.

0006Another aspect of the invention provides a microelectromechanical device, which includes a first surface, a second surface and a third surface. The second surface is located substantially parallel to the first surface. The second surface is movable between a first position and a second position. The first position is located at a first distance from the first surface. The second position is located at a second distance from the first surface. The second distance is greater than the first distance. The third surface is located between the first surface and the second surface. The third surface defines one or more gap regions between the first surface and the second surface when the second surface is in the first position, wherein the second surface in the one or more gap regions does not contact either the first surface or the third surface.

0007Another aspect of the invention provides a microelectromechanical device, which includes a first layer; a second layer and a plurality of members. The second layer is located substantially parallel to the first layer. The second layer is movable between a first position and a second position. The first position is a first distance from the first layer. The second position is a second distance from the first layer. The second distance is greater than the first distance. Each of the plurality of members includes a surface located between the first layer and second layer. The plurality of members define one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the plurality of members.

0008Still another aspect of the invention provides a microelectromechanical device, which includes a first surface, a second surface and at least one structure on at least one of the first surface and the second surface. The second surface is located substantially parallel to the first surface. The second surface is movable relative to the first surface between a driven position and an undriven position. The driven position is closer to the first surface than is the undriven position. The at least one structure is compressed by the first surface and the second surface when the second surface is in the driven position. The at least one structure provides a force to the second surface when the second surface is in the driven position. The force assists movement of the second surface from the driven position toward the undriven position.

0009Still another aspect of the invention provides a method of making an interferometric modulator. The method includes: providing a first layer, forming a second layer and forming a member comprising a surface. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion. The second reflective planar portion is located substantially parallel to the first reflective planar portion. The second layer is movable between a first position and a second position. The first position is at a first distance from the first layer. The second position is at a second distance from the first layer. The second distance is greater than the first distance. The surface of the member is located between the first layer and the second layer. The member defines one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member.

0010A further aspect of the invention provides a microelectromechanical device produced by a method. The method includes: providing a first layer, providing a second layer and providing a member comprising a surface. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion. One of the first reflective planar portion and the second reflective planar portion may be partially reflective. The second reflective planar portion is located substantially parallel to the first reflective planar portion. The second layer is movable between a first position and a second position. The first position is at a first distance from the first layer. The second position is at a second distance from the first layer. The second distance is greater than the first distance. The surface of the member is located between the first layer and the second layer. The member defines one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member.

0011A further aspect of the invention provides a method of operating a microelectromechanical device. Here, the device includes a first layer, a second layer and a member. The second layer of the device is located substantially parallel to the first layer. The member includes a surface intervening between the first layer and second layer. The surface of the member is located between only portions of the first layer and the second layer. The method of operating the device includes moving the second layer relative to the first layer from an undriven position to a driven position. The driven position is closer to the first layer than is the undriven position. The method further includes contacting the member with at least one of the first layer and the second layer so as to stop the movement of the second layer at the driven position, the member defining one or more gap regions between the first layer and the second layer when the second layer is in the driven position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member..

0012A further aspect of the invention provides a microelectromechanical device. The device includes first means for partially reflecting and partially transmitting incident light and second means for substantially reflecting incident light. The device further includes means for moving the first means relative to the second means between a driven position and an undriven position. The device further includes means for providing a separation between the first means and the second means when the second means is in the driven position. The driven position is closer to the first means than is the undriven position. The first means may include, for example, a partial mirror surface. The second means may include, for example, a full mirror surface. The means for moving may include, for example, a deformable layer. The means for providing separation may include, for example, at least one of a bump, a landing pad or a spring clip

0013A further aspect of the invention provides a microelectromechanical device. The device includes: first means for partially reflecting and partially transmitting incident light and second means for substantially reflecting incident light. The device further includes means for moving the first means relative to the second means between a driven position and an undriven position, and means for applying a force on the second means in a direction toward the undriven position when the second means is in the driven position. The first means may include, for example, a partial mirror surface. The second means may include, for example, a full mirror surface. The means for moving may include, for example, a deformable layer. The means for applying force may include, for example, a spring clip, or, as another example, a bump or a landing pad that includes an elastomeric material.

0014A still further aspect of the invention provides an interferometric modulator. The interferometric modulator includes a first layer, a second layer and at least one bump on the at least one of the first layer and the second layer. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion that is located substantially parallel to the first reflective planar portion. The second layer is movable between a driven position and an undriven position. The driven position is closer to the first layer than the undriven position. The at least one bump is configured to prevent the first layer and the second layer from contacting each other.

0015A still further aspect of the invention provides an interferometric modulator, which includes a first layer, a second layer and at least one landing pad located between the first layer and the second layer. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion that is located substantially parallel to the first reflective planar portion. The second layer is movable between a driven position and an undriven position. The driven position is closer to the first layer than the undriven position. The at least one landing pad includes a contact area where one of the first layer and the second layer contacts while not contacting the other when the second layer is in the driven position.

0016A still further aspect of the invention provides an interferometric modulator. The interferometric modulator includes a first layer, a second layer and at least one spring member placed between the at least one of the first layer and the second layer. The first layer includes a first reflective planar portion. The second layer includes a second reflective planar portion that is located substantially parallel to the first reflective planar portion. One of the first reflective planar portion and the second reflective planar portion may be partially reflective. The second layer is movable between a driven position and an undriven position. The driven position is closer to the first layer than the undriven position. The at least one spring member is compressible by at least one of the first layer and second layer as the second layer moves toward the driven position. The at least one spring member is configured to apply force to the second layer in a direction toward the undriven position when the second layer is in the driven position.

0017Another embodiment provides a display system comprising an interferometric modulator, a display, a processor and a memory device. The processor is in electrical communication with the display and configured to process image data. The memory device is in electrical communication with the processor.

0018Another embodiment provides a method of making a MEMS device, such as a MEMS device that includes an interferometric modulator. The method includes forming a first electrode, depositing a dielectric material over at least a portion of the first electrode, then removing a portion of the dielectric material from over the first electrode, thereby forming a variable thickness dielectric layer. The method further includes forming a second electrode over at least a portion of the variable thickness dielectric layer. In an embodiment, a sacrificial layer is deposited over at least a portion of the dielectric material that is over the first electrode. The sacrificial layer and at least a portion of the dielectric material may be removed during a later etching step. Another embodiment provides an interferometric modulator made by such a method.

0019Another embodiment provides a method of making an interferometric modulator. The method includes forming a first electrode and depositing a dielectric layer over at least a portion of the first electrode. The method further includes removing a portion of the dielectric layer to form a variable thickness dielectric layer, depositing a sacrificial layer over the variable thickness dielectric layer, planarizing the sacrificial layer, and forming a second electrode over the sacrificial layer. Another embodiment provides an interferometric modulator made by such a method.

0020Another embodiment provides a method of making an interferometric modulator. The method includes forming a first electrode and depositing a dielectric layer over at least a portion of the first electrode. The method further includes removing a portion of the dielectric layer to form a variable thickness dielectric layer, depositing a sacrificial layer over the variable thickness dielectric layer, depositing a planarization layer over the sacrificial layer, and forming a second electrode over the planarization layer. Another embodiment provides an interferometric modulator made by such a method.

Brief Description of the Drawings

0021<figref idref="f0001">FIG. 1</figref> is an isometric view depicting a portion of one embodiment of an interferometric modulator display in which a movable reflective layer of a first interferometric modulator is in a relaxed position and a movable reflective layer of a second interferometric modulator is in an actuated position.

0022<figref idref="f0002">FIG. 2</figref> is a system block diagram illustrating one embodiment of an electronic device incorporating a 3x3 interferometric modulator display.

0023<figref idref="f0003">FIG. 3</figref> is a diagram of movable mirror position versus applied voltage for one exemplary embodiment of an interferometric modulator of <figref idref="f0001">FIG. 1</figref>.

0024<figref idref="f0003">FIG. 4</figref> is an illustration of a set of row and column voltages that may be used to drive an interferometric modulator display.

0025<figref idref="f0004">FIGS. 5A and 5B</figref> illustrate one exemplary timing diagram for row and column signals that may be used to write a frame of display data to the 3x3 interferometric modulator display of <figref idref="f0002">FIG. 2</figref>.

0026<figref idref="f0005">FIGS. 6A and 6B</figref> are system block diagrams illustrating an embodiment of a visual display device comprising a plurality of interferometric modulators.

0027<figref idref="f0006">FIG. 7A</figref> is a cross section of the device of <figref idref="f0001">FIG. 1</figref>.

0028<figref idref="f0006">FIG. 7B</figref> is a cross section of an alternative embodiment of an interferometric modulator.

0029<figref idref="f0006">FIG. 7C</figref> is a cross section of another alternative embodiment of an interferometric modulator.

0030<figref idref="f0007">FIG 7D</figref> is a cross section of yet another alternative embodiment of an interferometric modulator.

0031<figref idref="f0007">FIG. 7E</figref> is a cross section of an additional alternative embodiment of an interferometric modulator.

0032<figref idref="f0008">Figure 8</figref> is a perspective view of an interferometric modulator array which uses micro-electromechanical system technology.

0033<figref idref="f0009">Figure 9A</figref> is a schematic cross-sectional view of the interferometric modulator array of <figref idref="f0006 f0007">Figure 7</figref> taken along line 8A-8A of <figref idref="f0006 f0007">Figure 7</figref>.

0034<figref idref="f0009">Figure 9B</figref> is a schematic cross-sectional view of another embodiment of the interferometric modulator array utilizing micro-electromechanical system technology.

0035<figref idref="f0010">Figure 10A</figref> is a side cross-sectional view of an embodiment of the interferometric modulator including landing pads with the modulator shown in the undriven state.

0036<figref idref="f0010">Figure 10B</figref> is a side cross-sectional view of the embodiment of <figref idref="f0009">Figure 9A</figref> in the driven state.

0037<figref idref="f0010 f0011 f0012 f0013">Figures 10C-10I</figref> are side cross-sectional views of embodiments of the interferometric modulator, illustrating various configurations of landing pads.

0038<figref idref="f0013">Figure 10J</figref> is a top cross-sectional view of an embodiment of the interferometric modulator taken along line 9J-9J of <figref idref="f0009">Figure 9A</figref> and illustrating various shapes of landing pads.

0039<figref idref="f0014">Figure 11</figref> is a flowchart illustrating a method of manufacturing a MEMS device having a variable thickness dielectric layer.

0040<figref idref="f0015">Figure 12</figref> is a cross-sectional view schematically illustrating an alternative embodiment of a MEMS device having a variable thickness dielectric layer.

0041<figref idref="f0015">Figure 13</figref> is a cross-sectional view schematically illustrating the formation of a lower electrode <b>502</b> in accordance with an embodiment.

0042<figref idref="f0015">Figure 14</figref> is a cross-sectional view schematically illustrating the formation of a dielectric layer <b>540</b> (including a lower portion <b>550</b> and an upper portion <b>560)</b> on the stationary layer <b>502</b> and over the substrate <b>500</b> of <figref idref="f0015">Figure 13</figref>.

0043<figref idref="f0016">Figures 15 and 16</figref> are cross-sectional views schematically illustrating the formation of a variable thickness dielectric layer <b>570</b> (including "stops" <b>565)</b> on the stationary layer 502 of <figref idref="f0015">Figure 13</figref> by removing parts of the upper portion <b>560</b> of dielectric layer <b>540</b> of <figref idref="f0015">Figure 14</figref>.

0044<figref idref="f0017">Figure 17</figref> is cross-sectional views schematically illustrating the formation of a sacrificial layer <b>710,</b> support structures <b>720,</b> and an upper electrode <b>730</b> of an interferometric modulator.

0045<figref idref="f0018">Figure 18</figref> is a cross-sectional view schematically illustrating the removal of the sacrificial layer <b>710</b> and the removal of parts of the lower portion <b>550</b> of the dielectric layer <b>570</b> of <figref idref="f0017">Figure 17</figref>.

0046<figref idref="f0019">Figure 19</figref> shows cross-sectional views schematically illustrating an interferometric modulator <b>1800</b> comprising a stationary layer <b>502,</b> a deformable layer <b>506,</b> and a variable thickness dielectric layer <b>920</b> that substantially prevents contact between the first electrode <b>502</b> and the second electrode <b>506.</b>

0047<figref idref="f0020">Figure 20</figref> shows cross-sectional views schematically illustrating the formation of a sacrificial layer <b>710,</b> support structures <b>720,</b> and an upper electrode <b>731</b> of an interferometric modulator.

0048<figref idref="f0021">Figure 21</figref> is a cross-sectional view schematically illustrating an interferometric modulator.

0049<figref idref="f0021">Figure 22A</figref> is a side cross-sectional view of an embodiment of the interferometric modulator with bumps showing the modulator in the undriven state.

0050<figref idref="f0021">Figure 22B</figref> is a side cross-sectional view of the embodiment of <figref idref="f0021">Figure 22A</figref> in the driven state.

0051<figref idref="f0022">Figures 22C-22E</figref> are side cross-sectional views of embodiments of the interferometric modulator illustrating various configurations of bumps.

0052<figref idref="f0023">Figure 23A</figref> is a side cross-sectional view of an embodiment of the interferometric modulator with spring clips showing the modulator in the undriven state.

0053<figref idref="f0023">Figure 23B</figref> is a side cross-sectional view of the embodiment of <figref idref="f0023">Figure 23A</figref> in the driven state.

0054<figref idref="f0023 f0024">Figures 23C-23F</figref> are side cross-sectional views of embodiments of the interferometric modulator illustrating various configurations of spring clips.

0055<figref idref="f0025">Figure 24A</figref> is a side cross-sectional view of one embodiment of a three state interferometric modulator in the undriven state.

0056<figref idref="f0025">Figure 24B</figref> is a side cross-sectional view of the three state interferometric modulator of <figref idref="f0025">Figure 24A</figref> in the driven state.

0057<figref idref="f0025">Figure 24C</figref> is a side cross-sectional view of the three state interferometric modulator of <figref idref="f0025">Figure 24A</figref> in the reverse driven state.

0058<figref idref="f0026">Figure 24D</figref> is a side cross-sectional view of another embodiment of the interferometric modulator in the undriven state.

0059<figref idref="f0026">Figure 24E</figref> is a side cross-sectional view of another embodiment of the interferometric modulator in the undriven state.

0060<figref idref="f0027">Figure 25A</figref> is a side cross-sectional view of an alternative embodiment of an interferometric modulator shown in the undriven state.

0061<figref idref="f0027">Figure 25B</figref> is a top plan view of the interferometric modulator of <figref idref="f0027">Figure 25A</figref>, shown in the undriven state.

0062<figref idref="f0027">Figure 25C</figref> is a side view of the interferometric modulator of <figref idref="f0027">Figure 25A</figref>, shown in the driven state.

0063<figref idref="f0027">Figure 25D</figref> is a top plain view of the interferometric modulator of <figref idref="f0020">Figure 20C</figref>, shown in the driven state.

Detailed Description of Preferred Embodiments

0064The following detailed description is directed to certain specific embodiments of the invention. However, the invention can be embodied in a multitude of different ways. In this description, reference is made to the drawings wherein like parts are designated with like numerals throughout. As will be apparent from the following description, the embodiments may be implemented in any device that is configured to display an image, whether in motion (e.g., video) or stationary (e.g., still image), and whether textual or pictorial. More particularly, it is contemplated that the embodiments may be implemented in or associated with a variety of electronic devices such as, but not limited to, mobile telephones, wireless devices, personal data assistants (PDAs), handheld or portable computers, GPS receivers/navigators, cameras, MP3 players, camcorders, game consoles, wrist watches, clocks, calculators, television monitors, flat panel displays, computer monitors, auto displays (e.g., odometer display, etc.), cockpit controls and/or displays, display of camera views (e.g., display of a rear view camera in a vehicle), electronic photographs, electronic billboards or signs, projectors, architectural structures, packaging, and aesthetic structures (e.g., display of images on a piece of jewelry). MEMS devices of similar structure to those described herein can also be used in non-display applications such as in electronic switching devices.

0065Driving an interferometric modulator may result in contact between a deformable layer and a stationary layer. Such contact may be undesirable and may result in damage to the device, potentially resulting in performance degradation. Various embodiments provides structures (such as landing pads, bumps and spring clips) and methods for reducing such damage.

0066One interferometric modulator display embodiment comprising an interferometric MEMS display element is illustrated in <figref idref="f0001">Figure 1</figref>. In these devices, the pixels are in either a bright or dark state. In the bright ("on" or "open") state, the display element reflects a large portion of incident visible light to a user. When in the dark ("off" or "closed") state, the display element reflects little incident visible light to the user. Depending on the embodiment, the light reflectance properties of the "on" and "off" states may be reversed. MEMS pixels can be configured to reflect predominantly at selected colors, allowing for a color display in addition to black and white.

0067<figref idref="f0001">Figure 1</figref> is an isometric view depicting two adjacent pixels in a series of pixels of a visual display, wherein each pixel comprises a MEMS interferometric modulator. In some embodiments, an interferometric modulator display comprises a row/column array of these interferometric modulators. Each interferometric modulator includes a pair of reflective layers positioned at a variable and controllable distance from each other to form a resonant optical cavity with at least one variable dimension. In one embodiment, one of the reflective layers may be moved between two positions. In the first position, referred to herein as the relaxed position, the movable reflective layer is positioned at a relatively large distance from a fixed partially reflective layer. In the second position, referred to herein as the actuated position, the movable reflective layer is positioned more closely adjacent to the partially reflective layer. Incident light that reflects from the two layers interferes constructively or destructively depending on the position of the movable reflective layer, producing either an overall reflective or non-reflective state for each pixel.

0068The depicted portion of the pixel array in <figref idref="f0001">Figure 1</figref> includes two adjacent interferometric modulators <b>12a</b> and <b>12b.</b> In the interferometric modulator <b>12a</b> on the left, a movable reflective layer <b>14a</b> is illustrated in a relaxed position at a predetermined distance from an optical stack <b>16a,</b> which includes a partially reflective layer. In the interferometric modulator <b>12b</b> on the right, the movable reflective layer <b>14b</b> is illustrated in an actuated position adjacent to the optical stack <b>16b.</b>

0069The optical stacks <b>16a</b> and <b>16b</b> (collectively referred to as optical stack <b>16),</b> as referenced herein, typically comprise of several fused layers, which can include an electrode layer, such as indium tin oxide (ITO), a partially reflective layer, such as chromium, and a transparent dielectric. The optical stack <b>16</b> is thus electrically conductive, partially transparent and partially reflective, and may be fabricated, for example, by depositing one or more of the above layers onto a transparent substrate <b>20.</b> In some embodiments, the layers are patterned into parallel strips, and may form row electrodes in a display device as described further below. The movable reflective layers <b>14a, 14b</b> may be formed as a series of parallel strips of a deposited metal layer or layers (orthogonal to the row electrodes of <b>16a, 16b)</b> deposited on top of posts <b>18</b> and an intervening sacrificial material deposited between the posts <b>18.</b> When the sacrificial material is etched away, the movable reflective layers <b>14a, 14b</b> are separated from the optical stacks <b>16a, 16b</b> by a defined gap <b>19.</b> A highly conductive and reflective material such as aluminum may be used for the reflective layers <b>14,</b> and these strips may form column electrodes in a display device.

0070With no applied voltage, the cavity <b>19</b> remains between the movable reflective layer <b>14a</b> and optical stack <b>16a,</b> with the movable reflective layer <b>14a</b> in a mechanically relaxed state, as illustrated by the pixel <b>12a</b> in <figref idref="f0001">Figure 1</figref>. However, when a potential difference is applied to a selected row and column, the capacitor formed at the intersection of the row and column electrodes at the corresponding pixel becomes charged, and electrostatic forces pull the electrodes together. If the voltage is high enough, the movable reflective layer <b>14</b> is deformed and is forced against the optical stack <b>16.</b> A dielectric layer (not illustrated in this Figure) within the optical stack <b>16</b> may prevent shorting and control the separation distance between layers <b>14</b> and <b>16,</b> as illustrated by pixel <b>12b</b> on the right in <figref idref="f0001">Figure 1</figref>. The behavior is the same regardless of the polarity of the applied potential difference. In this way, row/column actuation that can control the reflective vs. non-reflective pixel states is analogous in many ways to that used in conventional LCD and other display technologies.

0071<figref idref="f0002 f0003 f0004">Figures 2 through 5</figref> illustrate one exemplary process and system for using an array of interferometric modulators in a display application.

0072<figref idref="f0002">Figure 2</figref> is a system block diagram illustrating one embodiment of an electronic device that may incorporate aspects of the invention. In the exemplary embodiment, the electronic device includes a processor <b>21</b> which may be any general purpose single- or multi-chip microprocessor such as an ARM, Pentium^®, Pentium II^®, Pentium III^®, Pentium IV^®, Pentium^® Pro, an 8051, a MIPS^®, a Power PC^®, an ALPHA^®, or any special purpose microprocessor such as a digital signal processor, microcontroller, or a programmable gate array. As is conventional in the art, the processor <b>21</b> may be configured to execute one or more software modules. In addition to executing an operating system, the processor may be configured to execute one or more software applications, including a web browser, a telephone application, an email program, or any other software application.

0073In one embodiment, the processor <b>21</b> is also configured to communicate with an array driver <b>22.</b> In one embodiment, the array driver <b>22</b> includes a row driver circuit <b>24</b> and a column driver circuit <b>26</b> that provide signals to a display array or panel <b>30.</b> The cross section of the array illustrated in <figref idref="f0001">Figure 1</figref> is shown by the lines 1-1 in <figref idref="f0002">Figure 2</figref>. For MEMS interferometric modulators, the row/column actuation protocol may take advantage of a hysteresis property of these devices illustrated in <figref idref="f0003">Figure 3</figref>. It may require, for example, a 10 volt potential difference to cause a movable layer to deform from the relaxed state to the actuated state. However, when the voltage is reduced from that value, the movable layer maintains its state as the voltage drops back below 10 volts. In the exemplary embodiment of <figref idref="f0003">Figure 3</figref>, the movable layer does not relax completely until the voltage drops below 2 volts. There is thus a range of voltage, about 3 to 7 V in the example illustrated in <figref idref="f0003">Figure 3</figref>, where there exists a window of applied voltage within which the device is stable in either the relaxed or actuated state. This is referred to herein as the "hysteresis window" or "stability window." For a display array having the hysteresis characteristics of <figref idref="f0003">Figure 3</figref>, the row/column actuation protocol can be designed such that during row strobing, pixels in the strobed row that are to be actuated are exposed to a voltage difference of about 10 volts, and pixels that are to be relaxed are exposed to a voltage difference of close to zero volts. After the strobe, the pixels are exposed to a steady state voltage difference of about 5 volts such that they remain in whatever state the row strobe put them in. After being written, each pixel sees a potential difference within the "stability window" of 3-7 volts in this example. This feature makes the pixel design illustrated in <figref idref="f0001">Figure 1</figref> stable under the same applied voltage conditions in either an actuated or relaxed pre-existing state. Since each pixel of the interferometric modulator, whether in the actuated or relaxed state, is essentially a capacitor formed by the fixed and moving reflective layers, this stable state can be held at a voltage within the hysteresis window with almost no power dissipation. Essentially no current flows into the pixel if the applied potential is fixed.

0074In typical applications, a display frame may be created by asserting the set of column electrodes in accordance with the desired set of actuated pixels in the first row. A row pulse is then applied to the row 1 electrode, actuating the pixels corresponding to the asserted column lines. The asserted set of column electrodes is then changed to correspond to the desired set of actuated pixels in the second row. A pulse is then applied to the row 2 electrode, actuating the appropriate pixels in row 2 in accordance with the asserted column electrodes. The row 1 pixels are unaffected by the row 2 pulse, and remain in the state they were set to during the row 1 pulse. This may be repeated for the entire series of rows in a sequential fashion to produce the frame. Generally, the frames are refreshed and/or updated with new display data by continually repeating this process at some desired number of frames per second. A wide variety of protocols for driving row and column electrodes of pixel arrays to produce display frames are also well known and may be used in conjunction with the present invention.

0075<figref idref="f0003">Figures 4</figref> and <figref idref="f0004">5</figref> illustrate one possible actuation protocol for creating a display frame on the 3x3 array of <figref idref="f0002">Figure 2</figref>. <figref idref="f0003">Figure 4</figref> illustrates a possible set of column and row voltage levels that may be used for pixels exhibiting the hysteresis curves of <figref idref="f0003">Figure 3</figref>. In the <figref idref="f0003">Figure 4</figref> embodiment, actuating a pixel involves setting the appropriate column to -V_bias, and the appropriate row to +ΔV, which may correspond to -5 volts and +5 volts respectively Relaxing the pixel is accomplished by setting the appropriate column to +V_bias, and the appropriate row to the same +ΔV, producing a zero volt potential difference across the pixel. In those rows where the row voltage is held at zero volts, the pixels are stable in whatever state they were originally in, regardless of whether the column is at +V_bias, or -V_bias. As is also illustrated in <figref idref="f0003">Figure 4</figref>, it will be appreciated that voltages of opposite polarity than those described above can be used, e.g., actuating a pixel can involve setting the appropriate column to +V_bias, and the appropriate row to -ΔV. In this embodiment, releasing the pixel is accomplished by setting the appropriate column to -V_bias, and the appropriate row to the same -ΔV, producing a zero volt potential difference across the pixel.

0076<figref idref="f0004">Figure 5B</figref> is a timing diagram showing a series of row and column signals applied to the 3x3 array of <figref idref="f0002">Figure 2</figref> which will result in the display arrangement illustrated in <figref idref="f0004">Figure 5A</figref>, where actuated pixels are non-reflective. Prior to writing the frame illustrated in <figref idref="f0004">Figure 5A</figref>, the pixels can be in any state, and in this example, all the rows are at 0 volts, and all the columns are at +5 volts. With these applied voltages, all pixels are stable in their existing actuated or relaxed states.

0077In the <figref idref="f0004">Figure 5A</figref> frame, pixels (1,1), (1,2), (2,2), (3,2) and (3,3) are actuated. To accomplish this, during a "line time" for row 1, columns 1 and 2 are set to -5 volts, and column 3 is set to +5 volts. This does not change the state of any pixels, because all the pixels remain in the 3-7 volt stability window. Row 1 is then strobed with a pulse that goes from 0, up to 5 volts, and back to zero. This actuates the (1,1) and (1,2) pixels and relaxes the (1,3) pixel. No other pixels in the array are affected. To set row 2 as desired, column 2 is set to -5 volts, and columns 1 and 3 are set to +5 volts. The same strobe applied to row 2 will then actuate pixel (2,2) and relax pixels (2,1) and (2,3). Again, no other pixels of the array are affected. Row 3 is similarly set by setting columns 2 and 3 to -5 volts, and column 1 to +5 volts. The row 3 strobe sets the row 3 pixels as shown in <figref idref="f0004">Figure 5A</figref>. After writing the frame, the row potentials are zero, and the column potentials can remain at either +5 or -5 volts, and the display is then stable in the arrangement of <figref idref="f0004">Figure 5A</figref>. It will be appreciated that the same procedure can be employed for arrays of dozens or hundreds of rows and columns. It will also be appreciated that the timing, sequence, and levels of voltages used to perform row and column actuation can be varied widely within the general principles outlined above, and the above example is exemplary only, and any actuation voltage method can be used with the systems and methods described herein.

0078<figref idref="f0005">Figures 6A and 6B</figref> are system block diagrams illustrating an embodiment of a display device <b>40.</b> The display device <b>40</b> can be, for example, a cellular or mobile telephone. However, the same components of display device <b>40</b> or slight variations thereof are also illustrative of various types of display devices such as televisions and portable media players.

0079The display device <b>40</b> includes a housing <b>41,</b> a display <b>30,</b> an antenna <b>43,</b> a speaker 45, an input device <b>48,</b> and a microphone <b>46.</b> The housing <b>41</b> is generally formed from any of a variety of manufacturing processes as are well known to those of skill in the art, including injection molding, and vacuum forming. In addition, the housing <b>41</b> may be made from any of a variety of materials, including but not limited to plastic, metal, glass, rubber, and ceramic, or a combination thereof. In one embodiment the housing <b>41</b> includes removable portions (not shown) that may be interchanged with other removable portions of different color, or containing different logos, pictures, or symbols.

0080The display <b>30</b> of exemplary display device <b>40</b> may be any of a variety of displays, including a bi-stable display, as described herein. In other embodiments, the display <b>30</b> includes a flat-panel display, such as plasma, EL, OLED, STN LCD, or TFT LCD as described above, or a non-flat-panel display, such as a CRT or other tube device, as is well known to those of skill in the art. However, for purposes of describing the present embodiment, the display <b>30</b> includes an interferometric modulator display, as described herein.

0081The components of one embodiment of exemplary display device <b>40</b> are schematically illustrated in <figref idref="f0005">Figure 6B</figref>. The illustrated exemplary display device <b>40</b> includes a housing <b>41</b> and can include additional components at least partially enclosed therein. For example, in one embodiment, the exemplary display device <b>40</b> includes a network interface <b>27</b> that includes an antenna <b>43</b> which is coupled to a transceiver <b>47.</b> The transceiver <b>47</b> is connected to a processor <b>21,</b> which is connected to conditioning hardware <b>52.</b> The conditioning hardware <b>52</b> may be configured to condition a signal (e.g. filter a signal). The conditioning hardware <b>52</b> is connected to a speaker <b>45</b> and a microphone <b>46.</b> The processor <b>21</b> is also connected to an input device <b>48</b> and a driver controller <b>29.</b> The driver controller <b>29</b> is coupled to a frame buffer <b>28,</b> and to an array driver <b>22,</b> which in turn is coupled to a display array <b>30.</b> A power supply <b>50</b> provides power to all components as required by the particular exemplary display device <b>40</b> design.

0082The network interface <b>27</b> includes the antenna <b>43</b> and the transceiver <b>47</b> so that the exemplary display device <b>40</b> can communicate with one ore more devices over a network. In one embodiment the network interface <b>27</b> may also have some processing capabilities to relieve requirements of the processor <b>21.</b> The antenna <b>43</b> is any antenna known to those of skill in the art for transmitting and receiving signals. In one embodiment, the antenna transmits and receives RF signals according to the IEEE 802.11 standard, including IEEE 802.11(a), (b), or (g). In another embodiment, the antenna transmits and receives RF signals according to the BLUETOOTH standard. In the case of a cellular telephone, the antenna is designed to receive CDMA, GSM, AMPS or other known signals that are used to communicate within a wireless cell phone network. The transceiver <b>47</b> pre-processes the signals received from the antenna <b>43</b> so that they may be received by and further manipulated by the processor <b>21.</b> The transceiver <b>47</b> also processes signals received from the processor <b>21</b> so that they may be transmitted from the exemplary display device <b>40</b> via the antenna <b>43.</b>

0083In an alternative embodiment, the transceiver <b>47</b> can be replaced by a receiver. In yet another alternative embodiment, network interface <b>27</b> can be replaced by an image source, which can store or generate image data to be sent to the processor <b>21.</b> For example, the image source can be a digital video disc (DVD) or a hard-disc drive that contains image data, or a software module that generates image data.

0084Processor <b>21</b> generally controls the overall operation of the exemplary display device 40. The processor <b>21</b> receives data, such as compressed image data from the network interface <b>27</b> or an image source, and processes the data into raw image data or into a format that is readily processed into raw image data. The processor <b>21</b> then sends the processed data to the driver controller <b>29</b> or to frame buffer <b>28</b> for storage. Raw data typically refers to the information that identifies the image characteristics at each location within an image. For example, such image characteristics can include color, saturation, and gray-scale level.

0085In one embodiment, the processor <b>21</b> includes a microcontroller, CPU, or logic unit to control operation of the exemplary display device <b>40.</b> Conditioning hardware <b>52</b> generally includes amplifiers and filters for transmitting signals to the speaker <b>45,</b> and for receiving signals from the microphone <b>46.</b> Conditioning hardware <b>52</b> may be discrete components within the exemplary display device <b>40,</b> or may be incorporated within the processor <b>21</b> or other components.

0086The driver controller <b>29</b> takes the raw image data generated by the processor <b>21</b> either directly from the processor <b>21</b> or from the frame buffer <b>28</b> and reformats the raw image data appropriately for high speed transmission to the array driver <b>22.</b> Specifically, the driver controller <b>29</b> reformats the raw image data into a data flow having a raster-like format, such that it has a time order suitable for scanning across the display array <b>30.</b> Then the driver controller <b>29</b> sends the formatted information to the array driver <b>22.</b> Although a driver controller <b>29,</b> such as a LCD controller, is often associated with the system processor <b>21</b> as a stand-alone Integrated Circuit (IC), such controllers may be implemented in many ways. They may be embedded in the processor <b>21</b> as hardware, embedded in the processor <b>21</b> as software, or fully integrated in hardware with the array driver <b>22.</b>

0087Typically, the array driver <b>22</b> receives the formatted information from the driver controller <b>29</b> and reformats the video data into a parallel set of waveforms that are applied many times per second to the hundreds and sometimes thousands of leads coming from the display's x-y matrix of pixels.

0088In one embodiment, the driver controller <b>29,</b> array driver <b>22,</b> and display array <b>30</b> are appropriate for any of the types of displays described herein. For example, in one embodiment, driver controller <b>29</b> is a conventional display controller or a bi-stable display controller (e.g., an interferometric modulator controller). In another embodiment, array driver <b>22</b> is a conventional driver or a bi-stable display driver (e.g., an interferometric modulator display). In one embodiment, a driver controller <b>29</b> is integrated with the array driver <b>22.</b> Such an embodiment is common in highly integrated systems such as cellular phones, watches, and other small area displays. In yet another embodiment, display array <b>30</b> is a typical display array or a bi-stable display array (e.g., a display including an array of interferometric modulators).

0089The input device <b>48</b> allows a user to control the operation of the exemplary display device <b>40.</b> In one embodiment, input device <b>48</b> includes a keypad, such as a QWERTY keyboard or a telephone keypad, a button, a switch, a touch-sensitive screen, a pressure- or heat-sensitive membrane. In one embodiment, the microphone <b>46</b> is an input device for the exemplary display device <b>40.</b> When the microphone <b>46</b> is used to input data to the device, voice commands may be provided by a user for controlling operations of the exemplary display device <b>40.</b>

0090Power supply <b>50</b> can include a variety of energy storage devices as are well known in the art. For example, in one embodiment, power supply <b>50</b> is a rechargeable battery, such as a nickel-cadmium battery or a lithium ion battery. In another embodiment, power supply <b>50</b> is a renewable energy source, a capacitor, or a solar cell, including a plastic solar cell, and solar-cell paint. In another embodiment, power supply <b>50</b> is configured to receive power from a wall outlet.

0091In some implementations control programmability resides, as described above, in a driver controller which can be located in several places in the electronic display system. In some cases control programmability resides in the array driver <b>22.</b> Those of skill in the art will recognize that the above-described optimization may be implemented in any number of hardware and/or software components and in various configurations.

0092The details of the structure of interferometric modulators that operate in accordance with the principles set forth above may vary widely. For example, <figref idref="f0006 f0007">Figures 7A-7E</figref> illustrate five different embodiments of the movable reflective layer 14 and its supporting structures. <figref idref="f0006">Figure 7A</figref> is a cross section of the embodiment of <figref idref="f0001">Figure 1</figref>, where a strip of metal material <b>14</b> is deposited on orthogonally extending supports <b>18.</b> In <figref idref="f0006">Figure 7B</figref>, the moveable reflective layer <b>14</b> is attached to supports at the corners only, on tethers <b>32.</b> In <figref idref="f0006">Figure 7C</figref>, the moveable reflective layer <b>14</b> is suspended from a deformable layer <b>34,</b> which may comprise a flexible metal. The deformable layer <b>34</b> connects, directly or indirectly, to the substrate <b>20</b> around the perimeter of the deformable layer <b>34.</b> These connections are herein referred to as support posts. The embodiment illustrated in <figref idref="f0007">Figure 7D</figref> has support post plugs <b>42</b> upon which the deformable layer <b>34</b> rests. The movable reflective layer <b>14</b> remains suspended over the cavity, as in <figref idref="f0006">Figures 7A-7C</figref>, but the deformable layer <b>34</b> does not form the support posts by filling holes between the deformable layer <b>34</b> and the optical stack <b>16.</b> Rather, the support posts are formed of a planarization material, which is used to form support post plugs <b>42.</b> The embodiment illustrated in <figref idref="f0007">Figure 7E</figref> is based on the embodiment shown in <figref idref="f0007">Figure 7D</figref>, but may also be adapted to work with any of the embodiments illustrated in <figref idref="f0006">Figures 7A-7C</figref> as well as additional embodiments not shown. In the embodiment shown in <figref idref="f0007">Figure 7E</figref>, an extra layer of metal or other conductive material has been used to form a bus structure <b>44.</b> This allows signal routing along the back of the interferometric modulators, eliminating a number of electrodes that may otherwise have had to be formed on the substrate <b>20.</b>

0093In embodiments such as those shown in <figref idref="f0006 f0007">Figure 7</figref>, the interferometric modulators function as direct-view devices, in which images are viewed from the front side of the transparent substrate <b>20,</b> the side opposite to that upon which the modulator is arranged. In these embodiments, the reflective layer <b>14</b> optically shields the portions of the interferometric modulator on the side of the reflective layer opposite the substrate <b>20,</b> including the deformable layer <b>34.</b> This allows the shielded areas to be configured and operated upon without negatively affecting the image quality. Such shielding allows the bus structure <b>44</b> in <figref idref="f0007">Figure 7E</figref>, which provides the ability to separate the optical properties of the modulator from the electromechanical properties of the modulator, such as addressing and the movements that result from that addressing. This separable modulator architecture allows the structural design and materials used for the electromechanical aspects and the optical aspects of the modulator to be selected and to function independently of each other. Moreover, the embodiments shown in <figref idref="f0006 f0007">Figures 7C-7E</figref> have additional benefits deriving from the decoupling of the optical properties of the reflective layer <b>14</b> from its mechanical properties, which are carried out by the deformable layer <b>34.</b> This allows the structural design and materials used for the reflective layer <b>14</b> to be optimized with respect to the optical properties, and the structural design and materials used for the deformable layer <b>34</b> to be optimized with respect to desired mechanical properties.

0094<figref idref="f0008">Figure 8</figref> schematically illustrates a portion of an exemplary interferometric modulator array <b>501.</b> The interferometric modulator array <b>501</b> is formed on a substrate <b>500,</b> which is transparent for a predetermined light spectrum and has a bottom surface <b>400.</b> Although not limited thereto, the substrate <b>500</b> is preferably made of glass. A single layer or stack of layers <b>502</b> is formed over the substrate <b>500.</b> The single layer <b>502</b> or at least one sub-layer (not shown) of the stack of layers <b>502</b> is made of a conductive material. The layer <b>502</b> or a sub-layer serves as a partial mirror as it both reflects and transmits some of the light incident thereto. For the sake of convenience, the term "stationary layer <b>502"</b> is used to refer to the single layer or stack of layers <b>502</b> unless the specific terms are used. Deformable layers <b>506</b> are located over the stationary layer <b>502.</b> Support posts <b>504</b> are formed between the substrate <b>500</b> and the layers <b>506,</b> separating the deformable layers <b>506</b> from the substrate <b>500</b> and the stationary layer <b>502.</b> The deformable layers <b>506</b> lie in a generally parallel plane to that of the stationary layer <b>502.</b> The surface of the deformable layers <b>506</b> facing the stationary layer <b>502</b> is highly reflective of the predetermined light spectrum and serves as a full mirror.

0095This interferometric modulator array <b>501</b> is operated by applying or not applying an electric potential difference between the conductive portion of the stationary layer <b>502</b> and the deformable layers <b>506.</b> By applying a certain electric potential difference between them, for example 7 volts, the deformable layer <b>506</b> is driven to deform toward and contact the stationary layer <b>502</b> as in the case of the interferometric modulator <b>501b.</b> In this driven state, the interferometric modulator <b>501b</b> is, for example, in an induced absorption mode, in which most of the light incident to the substrate <b>500</b> is absorbed by the interferometric modulator <b>501b.</b> If the interferometric modulator <b>501b</b> is designed to operate in the visible light spectrum, the bottom surface <b>400</b> of the substrate <b>500</b> corresponding to the area of interferometric modulator <b>501b</b> turns to black at the driven state.

0096The interferometric modulator <b>501a,</b> on the other hand, is illustrated in the configuration produced when no voltage is applied between the deformable layer <b>506</b> and the stationary layer <b>502.</b> This configuration is referred to as "the undriven state." In this state, the deformable layer <b>506</b> is maintained separate from the stationary layer <b>502,</b> forming a space <b>499</b> referred to as an "interferometric cavity" between them. More accurately, the interferometric cavity <b>499</b> is defined as the distance between the reflective surface of the deformable layer <b>506</b> and the partial mirror surface of the stationary layer <b>502.</b> Light that is incident to the interferometric modulator <b>501a</b> through the substrate <b>500</b> is interferometrically modulated via the cavity <b>499.</b> Depending on the depth of the cavity <b>499,</b> which is the distance between the partial mirror surface of the stationary layer <b>502</b> and the full mirror surface of the deformable layer <b>506,</b> the interferometric modulation selects a certain wavelength of the light, which is reflected from the bottom surface <b>400</b> of the substrate <b>500.</b> If the selected wavelength of the light is visible, the bottom surface <b>400</b> of the substrate <b>500</b> displays a visible light corresponding to the wavelength. One of ordinary skill in the art will well appreciate the interferometric modulation produced in the interferometric modulator <b>501.</b>

0097<figref idref="f0009">Figure 9A</figref> is a cross-sectional view of the interferometric modulator <b>501</b> of <figref idref="f0008">Figure 8</figref> taken along lines 9A-9A. <figref idref="f0009">Figure 9A</figref> illustrates additional interferometric modulators <b>501c-501e</b> arranged in the lateral direction of the interferometric modulator <b>501b.</b> In the illustrated embodiment, the stationary layer <b>502</b> is comprised of three sub-layers, for example, including a dielectric layer <b>413,</b> a mirror layer <b>415</b> and a conductor layer <b>417.</b> As illustrated, the deformable layer <b>506</b> is laterally spaced by the posts <b>504</b> and substantially parallel with the stationary layer <b>502,</b> creating an interferometric cavity <b>418</b> between them. Although not illustrated, additional layers may be formed over the deformable layer <b>506.</b> The overall micro-structure formed over the substrate <b>500</b> constitutes an array of interferometric modulators or array <b>411.</b> The interferometric modulator <b>501c</b> is illustrated in an undriven state, which generally reflects a certain light through the substrate <b>500</b> depending upon the depth of the interferometric cavity <b>418.</b> Again, this depth determines the wavelength of light reflected on the surface <b>400.</b> The interferometric modulator <b>501b</b> is illustrated in a driven state, which generally reflects no light on the surface <b>400.</b> The operation of the interferometric modulators <b>501b</b> and <b>501c</b> will be well appreciated by one of ordinary skill in the art.

0098<figref idref="f0009">Figure 9B</figref> illustrates the micro-construction of another embodiment of the interferometric modulator <b>501.</b> In this embodiment, the deformable layer <b>506</b> is connected to a mirror <b>419,</b> which is located between the deformable layer <b>506</b> and the stationary layer <b>502.</b> All of the other features are the same as in the embodiment of <figref idref="f0009">Figure 9A</figref>. In one embodiment, the mirror <b>419</b> is substantially rigid and has a highly reflective surface facing the stationary layer <b>502.</b> The deformable layer <b>506</b> functions to control the location of the mirror <b>419</b> with respect to the stationary layer <b>502,</b> and the rigid mirror <b>419</b> does not experience any significant bending or deformation in this process. In this embodiment, the interferometric cavity <b>418</b> is defined by the space between the mirror <b>419</b> and the stationary layer <b>502,</b> and more accurately the mirror layer <b>415.</b> The interferometric modulator <b>501c</b> is illustrated in an undriven state, while the interferometric modulator <b>501b</b> is illustrated in a driven state.

0099In the embodiments illustrated in <figref idref="f0009">Figures 9A and 9B</figref>, the stationary layer <b>502</b> may be formed by a single layer functioning as both a conductor and a mirror. Alternatively, the stationary layer <b>502</b> may be formed of two layers, for example the pair of a mirror layer and a conductive layer, the pair of a dielectric layer and a bi-functional layer of electrode and mirror. Further, in other embodiments, one or more additional layers may be formed over the stationary layer <b>502</b> or in between the layers <b>413, 415</b> and <b>417.</b> Also, although not illustrated, the deformable layer <b>506</b> or the mirror <b>419</b> of the embodiments of <figref idref="f0009">Figures 9A and 9B</figref> may have a laminated construction. For example, a dielectric layer may be formed on a surface of the deformable layer <b>506</b> (<figref idref="f0009">Figure 9A</figref>) or the mirror <b>419</b> (<figref idref="f0009">Figure 9B</figref>), particularly the surface facing the stationary layer <b>502.</b> The dielectric layer on the deformable layer <b>506</b> (<figref idref="f0009">Figure 9A</figref>) or the mirror <b>419</b> (<figref idref="f0009">Figure 9B</figref>) may be useful when the stationary layer <b>502</b> has the construction that does not include the dielectric layer <b>413.</b> One of ordinary skill in the art will appreciate the formation of various films or layers making the stationary layer <b>502</b> and/or the additional layers that can be formed on the deformable layer <b>506</b> or mirror <b>419.</b>

0100In a typical construction, as illustrated in <figref idref="f0008">Figures 8</figref>, <figref idref="f0009">9A and 9B</figref>, the deformable layer <b>506</b> or the mirror <b>419</b> may physically contact the stationary layer <b>502</b> during its operation, particularly when the interferometric modulator <b>501</b> is in its driven state. Physical contact or interaction between the two layers may cause some adverse results, particularly if it is between the surfaces defining the interferometric cavity, which are mirror surfaces of the stationary layer <b>502</b> and the deformable layer <b>506</b> (or mirror <b>419).</b> The dielectric layer <b>413</b> over the mirror layer <b>415</b> is provided to minimize or reduce the mechanical and/or electrical interactions between the surfaces forming the interferometric cavity. For the same reason, a dielectric layer (not shown) can be formed on the surface of the deformable layer <b>506</b> or the mirror <b>419.</b> However, repeated changes between the driven and undriven states can eventually result in degradation of such dielectric layers mechanically and/or electrically.

0101Also, the dielectric layers may contain some charges in them due to, not limited to, imperfection of the manufacturing processes. The charges in the dielectric layers may create attractive forces between the deformable layer <b>506</b> (or mirror <b>419)</b> and the stationary layer <b>502.</b> Some additional force may be needed to separate the deformable layer <b>506</b> (or the mirror <b>419)</b> from the stationary layer <b>502</b> when a unit of the interferometric modulator <b>501</b> is operating from its driven state to undriven state. Also, when the dielectric layer <b>413</b> contacts the deformable layer <b>506</b> (or the mirror <b>419),</b> there may be some other form of attractive force between the materials of the two contacting layers. Furthermore, even in an embodiment where the stationary layer <b>502</b> does not contact the deformable layer <b>506</b> (or the mirror <b>419)</b> in the driven state, the gap between them is generally very small, for example, in the order of 200 Å (20 nm). In certain conditions, moisture from the surrounding environment may condense in the small gap and form a liquid layer. To separate the layers in that condition, additional force overcoming the surface tension of the liquid layer is needed.

0102The degradation of the dielectric layer(s) and the need for additional forces may be overcome by various techniques and features of embodiments described herein, which include use of components such as landing pads, bumps and springs. Although introduced in light of the degradation of the dielectric layer and the associated need for the additional force, the below-described technical features may be used in any constructions of the interferometric modulator utilizing the MEMS technology without such degradation or need of additional force. For the sake of simplicity, the below-described embodiments of the interferometric modulators have the general architecture illustrated in <figref idref="f0008">Figures 8</figref> and <figref idref="f0009">9A</figref>. However, all of the features can be applied to any other architecture of the interferometric modulators, including the embodiment illustrated in <figref idref="f0009">Figure 9B</figref>.

0103An embodiment provides an interferometric modulator, comprising: a first layer comprising a first reflective planar portion; a second layer comprising a second reflective planar portion located substantially parallel to the first reflective planar portion, the second layer movable between a first position and a second position, the first position being a first distance from the first layer, the second position being a second distance from the first layer, the second distance being greater than the first distance; and a member having a surface located between the first layer and the second layer, the member defining one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member. Various aspects of this embodiment are described in greater detail below.

Landing Pads

0104<figref idref="f0010">Figures 10A and 10B</figref> illustrate an embodiment of the interferometric modulator <b>301</b> which includes landing pads <b>513.</b> In the illustrated embodiment, the landing pads <b>513</b> extend from the substrate <b>500</b> through the stationary layer <b>502</b> beyond the top surface of the stationary layer <b>502.</b> Accordingly, when the interferometric modulator <b>301</b> is driven from its undriven state (<figref idref="f0010">Figure 10A</figref>) to the driven state (<figref idref="f0010">Figure 10B</figref>), travel of the deformable layer <b>506</b> is interrupted by the landing pads <b>513,</b> which operate to prevent further travel of the deformable layer <b>506</b> toward the stationary layer <b>502,</b> and thus to prevent the physical contact between those layers <b>502</b> and <b>506,</b> and to maintain a desired separation distance between the layers <b>506</b> and <b>502.</b> As discussed above with reference to <figref idref="f0009">Figures 9A and 9B</figref>, the stationary layer <b>502</b> can be formed of a single layer or multiple layers. Also, the stationary layer <b>502</b> may or may not include a dielectric layer <b>413.</b> It will be recognized that the landing pads <b>513</b> are examples of members having a surface <b>514</b> located between the deformable layer <b>506</b> and the stationary layer <b>502.</b> The landing pads <b>513</b> define a gap region <b>418a</b> between the deformable layer <b>506</b> and the stationary layer <b>502</b> when the interferometric modulator <b>301</b> is in the driven state (<figref idref="f0010">Figure 10B</figref>). The deformable layer <b>506</b> in the gap region <b>418a</b> does not contact either the stationary layer <b>502</b> or the landing pads <b>513.</b>

0105In another embodiment as illustrated in <figref idref="f0010">Figure 10C</figref>, the landing pads <b>513</b> may be formed on the top surface of the stationary layer <b>502.</b> In another embodiment as illustrated in <figref idref="f0011">Figure 10D</figref>, the landing pads <b>513</b> may extend from a sub-layer <b>415</b> of the stationary layer <b>502</b> through one or more other sub-layers <b>413.</b> In still another embodiment as illustrated in <figref idref="f0011">Figure 10E</figref>, the landing pads <b>513</b> may be integrally formed with the substrate <b>500</b> and extend through the stationary layer <b>502.</b> In a further embodiment, as illustrated in <figref idref="f0011">Figure 10F</figref>, the landing pad <b>513</b> may extend from below the interface between the substrate <b>500</b> and the stationary layer <b>502</b> and through both the substrate <b>500</b> and the stationary layer <b>502.</b>

0106In another embodiment as illustrated in <figref idref="f0012">Figure 10G</figref>, the landing pads <b>513</b> may be formed on the deformable layer <b>506</b> or mirror <b>419</b> (not shown). In other embodiments as illustrated in <figref idref="f0012">Figures 10H</figref> and <figref idref="f0013">10I</figref>, the landing pads <b>513</b> may be formed on both the deformable layer <b>506</b> and the stationary layer <b>502.</b> In the foregoing embodiments where one or more landing pads <b>513</b> are formed on the deformable layer <b>506,</b> although not illustrated, the landing pads <b>513</b> may extend from various sub-layers, if any, of the deformable layer <b>506,</b> as the landing pads <b>513</b> may extend from various sub-layers of the stationary layer <b>502</b> or substrate <b>500</b> illustrated in <figref idref="f0010 f0011">Figures 10A-10F</figref>.

0107The landing pads <b>513</b> can be positioned in various locations on the stationary layer <b>502</b> or the deformable layer <b>506,</b> or both within the interferometric cavity <b>418.</b><figref idref="f0013">Figure 10J</figref> is a top cross-sectional view of the embodiment of <figref idref="f0010">Figure 10A</figref> taken along line 10J-10J (<figref idref="f0010">Figure 10A</figref>). In the illustrated embodiment of <figref idref="f0013">Figure 10J</figref>, for example, the landing pads <b>513</b> are located generally on peripheral portions of the stationary layer <b>502</b> and/or deformable layer <b>506</b> within the interferometric cavity <b>418.</b> Optionally, the landing pads <b>513</b> are positioned on the portions of the stationary layer <b>502</b> and/or deformable layer <b>506</b> where the existence of the landing pads <b>513</b> would not affect the optical characteristics of the interferometric modulator <b>301.</b> In another embodiment (not illustrated), the landing pads <b>513</b> can be positioned on a central portion of the stationary layer <b>502</b> and/or deformable layer <b>506</b> within the interferometric cavity <b>418.</b> In still another embodiment (not illustrated), the landing pads <b>513</b> can be positioned on both the central and peripheral portions of the stationary layer <b>502</b> and/or deformable layer <b>506</b> within the interferometric cavity <b>418.</b> In a further embodiment (not illustrated), the landing pads <b>513</b> can be located where the deformable layer <b>506</b> first contacts the stationary layer <b>502.</b>

0108Referring again to <figref idref="f0010">Figures 10A</figref> and <figref idref="f0012">10G</figref>, it is seen that the landing pads <b>513</b> extend beyond the surface of the stationary layer <b>502</b> (<figref idref="f0010">Figure 10A</figref>) or the deformable layer <b>506</b> (<figref idref="f0012">Figure 10G</figref>) by a height indicated at <b>519.</b> In one embodiment, the landing pad height <b>519</b> is selected so as to prevent physical contact between the deformable layer <b>506</b> and the stationary layer <b>502.</b> In another embodiment, the height <b>519</b> is selected to not only prevent such contact, but to define the depth of the interferometric cavity <b>418</b> in the driven state of the interferometric modulator <b>301,</b> and so as to enable production of the desired optical characteristics of the interferometric modulator <b>301.</b> In one embodiment, the landing pads <b>513</b> are configured to precisely define the distance between the two layers <b>506</b> and <b>502.</b> Thus, the landing pads <b>513</b> can be used to control the minimal size of the interferometric cavity <b>418</b> with a high degree of accuracy and precision.

0109In one embodiment of interferometric modulator <b>301</b> for use as a display element, the interferometric cavity depth at the driven state is short enough to absorb most, if not all, of the visible light. In another embodiment of interferometric modulator <b>301</b> for use as a display element, the interferometric cavity depth at the driven state reflects a selected visible wavelength of incident light. Since the interferometric cavity depth at the driven state is determined by the thickness of various layers and/or structures positioned between the reflective surfaces of the layers <b>502</b> and <b>506,</b> the height <b>519</b> of the landing pad <b>513</b> is designed in view of the color to be displayed on the substrate <b>500.</b> In such display embodiments, the height <b>519</b> is, for example, from about 50 Å to about 1500 Å, and preferably from about 100 Å to about 300 Å.

0110In one embodiment, the landing surface <b>514</b> of the landing pads <b>513</b> is substantially planar, as illustrated in <figref idref="f0010">Figure 10A</figref>. Also as in the embodiment illustrated in <figref idref="f0010">Figure 10A</figref>, the landing surface <b>514</b> may be substantially parallel to the surface of the deformable layer <b>506</b> or the stationary layer <b>502</b> that lands on the landing surface <b>514.</b> In this embodiment, the size of the landing surface <b>514</b> is from about 0.1 micron to about 25 microns, and preferably from about 3 microns to about 10 microns. In another embodiment as illustrated in <figref idref="f0010">Figure 10C</figref>, the landing surface <b>514</b> of the landing pads <b>513</b> may be rough, bumpy or embossed. In another embodiment as illustrated in <figref idref="f0011">Figure 10F</figref>, the landing surface <b>514</b> of the landing pads <b>513</b> may be tilted from the plane parallel to the counterpart surface landing on the landing surface <b>514.</b> In still another embodiment as illustrated in <figref idref="f0011">Figure 10D</figref>, the landing surface <b>514</b> may be substantially round.

0111The landing pads <b>513</b> can be made from various materials, including, but not limited to, a metal, an alloy, a dielectric material, and an elastomeric material. For example, such materials may include metals including aluminum, semiconductors, oxides of metals or semiconductors, nitrides of metals or semiconductors, and oxynitrides of metals or semiconductors. Preferably, the materials forming landing pads <b>513</b> are those that substantially do not or only insignificantly affect the electrical or optical characteristics of the interferometric modulator 301.

0112In one embodiment, the landing pads <b>513</b> are optically transparent for the light spectrum which the interferometric modulator <b>301</b> can select. Optionally, in the case where the light spectrum includes visible light, the transparent material that can be used for the landing pads <b>513</b> includes, for example, oxides of metals or semiconductors, nitrides of metals or semiconductors, and oxynitrides of metals or semiconductors. In another embodiment, the landing pads <b>513</b> may be made of a material that absorbs the light spectrum which the interferometric modulator <b>301</b> can select. In another embodiment, the landing pads <b>513</b> may be covered with the light absorbing material. Optionally, in the case where the light spectrum includes visible light, the light absorbing material that can be used for the landing pads <b>513</b> includes, for example, polymeric materials or metals, such as chrome, nickel, titanium, molybdenum, etc. In still another embodiment, the landing pads <b>513</b> may be made of a material that reflects the light spectrum which the interferometric modulator <b>301</b> can select. In still another embodiment, the landing pads <b>513</b> may be covered with the light reflecting material. Optionally, in the case where the light spectrum includes visible light, the light reflecting material that can be used for the landing pads <b>513</b> includes, for example, polymeric materials or metals, such as silver, aluminum, gold, platinum, etc.

0113In a unit of the interferometric modulator <b>301,</b> multiple landing pads <b>513</b> can be used. Thus, 2, 3, 4, 5, 6 or more landing pads <b>513</b> can be fabricated to provide the landing surfaces of the layers of the interferometric modulator <b>301.</b> Preferably, the multiple landing pads <b>513</b> have substantially the same heights <b>519.</b> Optionally, the multiple landing pads <b>513</b> are arranged as remote as possible from one another on the stationary layer <b>502</b> or the deformable layer <b>506.</b> In one embodiment, a single landing pad <b>513</b> per unit of the interferometric modulator <b>301</b> can be used.

0114The landing pads <b>513</b> may be positioned in any cross-sectional shape lying in a plane parallel to the stationary layer <b>502.</b> In the embodiment illustrated <figref idref="f0013">Figure 10J</figref>, the cross-sectional shape of the landing pads <b>513</b> is substantially circular, oval, rectangular and pentagonal, although not limited thereto.

0115The landing pads <b>513</b> can be fabricated in various configurations and made of various compounds as discussed above, utilizing the presently existing techniques of depositing and selectively etching a material. In one embodiment, the landing pads <b>513</b> can also be created from deformations of the layers of the interferometric modulator <b>301.</b> In another embodiment, the landing pads <b>513</b> can be created using conventional semiconductor manufacturing techniques.

0116MEMS devices often comprise an array of individual elements activated by application of a voltage potential. The elements may comprise many different types of structures, including mirrors, switches, gears, motors, etc. The application of the voltage potential may be done by applying the potential directly to the structure, or by manipulation of electrical or magnetic fields around the structure. For example, an element may be activated by electrostatic attraction between the element and another structure to which the voltage is applied. For purposes of this discussion, the structure to which the voltage is applied will be referred to as an electrode.

0117In this type of device, there is generally a gap between the element and the electrode. This gap may give rise to capacitive charge between the element and the electrode. For most MEMS devices with this type of structure, the performance of the device will be improved by lowering the capacitance in the gap. This reduction of capacitance produces more predictable performance, and there is a lowered risk of capacitive discharge, which can damage the element or the neighboring elements.

0118In a bi-chrome display, such as a display that switches between black and white, one interferometric modulator element might correspond to one pixel. In a color display, three or more interferometric modulator elements may make up each pixel, e.g., one each for red, green and blue. The individual interferometric modulator elements are controlled separately to produce the desired pixel reflectivity. Typically, a voltage is applied to the movable wall, or element, of the cavity, causing it to be electrostatically attracted to the other electrode, resulting in a change in the color of the pixel seen by the viewer.

0119The interferometric modulator is merely one type of an active MEMS device that has an element separated from an electrode, where the electrode is used to activate the device. Another example may be a MEMS switch. These devices may suffer from high capacitance that may affect their operation. If a device has high capacitance in the mechanically relaxed state, it may take longer for the attractive charge to activate the device, slowing the device response time.

0120The capacitance of the device can be approximated by the capacitance of an idealized parallel-plate capacitor, given by C = ε A/d, where ε is the electrical permittivity of the material between the movable wall and the electrode, A is the surface area of the electrode, and d is the gap distance between the movable wall and the electrode. The electrical permittivity ε of a material is equal to the dielectric constant κ of the material multiplied by the electrical permittivity ε₀ of vacuum. In various embodiments, the capacitance between the movable wall and the electrode is reduced by increasing the size of the gap between the electrode and the movable wall and/or by lowering the dielectric constant of the material within the gap (that is, by decreasing ε in the above equation). For example, the gap can comprise a material with a low dielectric constant, such as a gas or a mixture of gases (e.g., air). This use of a material within the gap with a reduced dielectric constant has the effect of lowering the capacitive charging of the dielectric surface, thereby lowering the capacitance.

0121An embodiment of a processing flow for a MEMS device is shown in <figref idref="f0014">Figure 11</figref>. In that embodiment, an electrode is formed on a substrate at step <b>150.</b> A multilayer dielectric stack is deposited at step <b>152,</b> and patterned at step <b>154.</b> Portions of the multilayer dielectric stack, e.g., a thin oxide stop layer, are removed at step <b>156.</b> The MEMS device then undergoes its appropriate processing at step <b>158,</b> where the processing includes the use of a sacrificial layer to form the gap. The sacrificial layer, and portions of the multilayer dielectric stack not under the oxide stops, are removed at step <b>160.</b> In another embodiment, a graded dielectric material is deposited at step <b>152</b> instead of the multilayer dielectric stack. The remainder of the process illustrated in <figref idref="f0014">Figure 11</figref> continues in a similar manner, including removing upper portions of the graded dielectric material at step <b>156,</b> and removing lower portions of the graded dielectric material at step <b>160,</b> along with the sacrificial layer.

0122An embodiment of an interferometric modulator having a multilayer dielectric stack is shown in <figref idref="f0015">Figure 12</figref>. In this embodiment the portions of the dielectric stack <b>513</b> not removed appear across the device <b>140,</b> rather than just under the support posts <b>18.</b> The process of forming the oxide stops can be modified as desired to leave portions of the dielectric stack wherever desired.

0123<figref idref="f0015 f0016 f0017 f0018 f0019">Figures 13-19</figref> illustrate an embodiment of a process for the fabrication of an interferometric modulator that includes landing pads <b>513,</b> using conventional semiconductor manufacturing techniques such as photolithography, deposition, masking, etching (e.g., dry methods such as plasma etch and wet methods), etc. Deposition includes "dry" methods such as chemical vapor deposition (CVD, including plasma-enhanced CVD and thermal CVD) and sputter coating, and wet methods such as spin coating. <figref idref="f0015">Figure 13</figref> illustrates the formation of a stationary layer <b>502,</b> which can be a single layer structure or multiple sub-layer structure as described above. In a single layer structure where the layer <b>502</b> functions as both electrode and mirror, the layer <b>502</b> is formed by deposition of an electrode material <b>410</b> on the substrate <b>500</b> and subsequent patterning and etching. The electrode material <b>410</b> is conductive and may be a metal or a semiconductor (such as silicon) doped to have the desired conductivity. In one embodiment (not shown in <figref idref="f0015">Figure 13</figref>), the electrode layer <b>410</b> (and the corresponding first electrode <b>502)</b> is a multilayer structure comprising a transparent conductor (such as indium tin oxide) and a primary mirror (such as chromium).

0124<figref idref="f0015">Figure 14</figref> illustrates the formation of a dielectric layer <b>540</b> on the substrate <b>500</b> and the stationary layer <b>502</b> by deposition, preferably by CVD. The lower or "bulk" portion <b>550</b> of the dielectric layer <b>540</b> need not be a dielectric material and is preferably a material that may be removed in a later etching step, and thus may be molybdenum, a silicon-containing materials (e.g., silicon, silicon nitride, silicon oxide, etc.), tungsten, or titanium, preferably silicon oxide. The upper or "stop" portion <b>560</b> of the dielectric layer <b>540</b> is preferably a material that is more resistant to a later etching step than the bulk portion <b>550,</b> and may be a metal (e.g., titanium, aluminum, silver, chromium) or a dielectric material, preferably a metal oxide, e.g., an aluminum oxide. Aluminum oxide may be deposited directly or by deposition of an aluminum layer followed by oxidation. The upper and lower portions <b>550, 560</b> of the dielectric layer <b>540</b> may be composed of the same material or may be different materials. Additional layers, e.g., intermediate layers, may also be formed over the stationary layer <b>502.</b> For example, in an embodiment (not shown), an intermediate layer is formed over at least a portion of the stationary layer <b>502,</b> and the dielectric layer <b>540</b> is formed over the intermediate layer and over the stationary layer <b>502</b> underlying the intermediate layer. Such intermediate layer(s) formed between the stationary layer <b>502</b> and the dielectric layer <b>540</b> may be utilized for various purposes. For example, the intermediate layer may be an optical layer, a barrier layer and/or a non-conductive layer (such as a second dielectric layer). In an embodiment, in any particular dielectric layer <b>540,</b> at least one of the portions <b>550, 560</b> is an electrical insulator.

0125The upper portion <b>560</b> may be thinner or thicker than the lower portion <b>550.</b> For example, in one embodiment the upper portion <b>560</b> may have a thickness in the range of about 50 Å to about 500 Å, and the lower portion <b>550</b> may have a thickness in the range of about 200 Å to about 3000 Å. As described in greater detail below, the upper or "stop" portion <b>560</b> may serve as an etch barrier (e.g., functioning in a manner somewhat analogous to a photomask) during a later process step, and a part of the lower portion <b>550</b> may serve as a "sacrificial" layer that is removed. In this embodiment, the upper portion <b>560</b> is more resistant to removal (e.g. by etching) than the lower portion <b>550.</b> In a particular embodiment, the upper portion <b>560</b> is aluminum oxide and the lower portion <b>550</b> is silicon oxide. The upper and lower portions <b>550, 560</b> need not be distinct layers and thus the dielectric layer <b>540</b> may be a graded layer. For example, the dielectric layer <b>540</b> may be compositionally graded so that the composition varies as a function of position (e.g., as a function of vertical position in <figref idref="f0015">Figure 14</figref>) within the dielectric layer. For example, the dielectric layer <b>540</b> may be a graded silicon nitride layer in which the relative amounts of silicon and nitrogen vary on going from the upper surface <b>420, 421</b> to the interface <b>421, 422</b> with the first electrode layer <b>502</b> and the substrate <b>500.</b> In one embodiment, for example, the graded silicon nitride layer is enriched in silicon at the interface <b>421</b> with the first electrode <b>502</b> relative to the overall composition of the graded silicon nitride. In another embodiment, the dielectric layer <b>540</b> may be a graded silicon oxide layer in which the relative amounts of silicon and oxygen vary on going from the upper surface <b>420, 421</b> to the interface <b>421, 422</b> with the first electrode layer <b>502</b> and the substrate <b>500.</b> In one embodiment, for example, the graded silicon oxide layer is enriched in silicon at the interface <b>421</b> with the first electrode <b>502</b> relative to the overall composition of the graded silicon oxide.

0126<figref idref="f0016">Figure 15</figref> shows that parts of the upper portion <b>560</b> are then removed to form "stops" <b>565</b> by masking the upper portion <b>560</b> with a photomask <b>610,</b> then etching to selectively remove the exposed part of the upper portion <b>560</b> of the dielectric layer <b>540</b> to form a variable thickness dielectric layer <b>570</b> as illustrated in <figref idref="f0016">Figure 16</figref>. The etching is carried out to expose part of the lower portion <b>550</b> of the dielectric layer <b>540.</b> The etching is controlled so that a substantial portion of the lower portion <b>550</b> of the dielectric layer <b>540</b> remains. For example, a small part of the lower portion <b>550</b> may be removed during etching, but most of the lower portion <b>550</b> preferably remains until it is removed during subsequent processing as described below, thereby increasing the unevenness of the dielectric layer and increasing the average peak-to-valley surface variation of the dielectric layer.

0127The fabrication process continues as illustrated in <figref idref="f0017">Figure 17</figref>, including formation of a sacrificial layer <b>710</b> (which is later removed to form the interferometric cavity <b>418)</b> by deposition, patterning and etching; formation (and optional planarization) of the posts <b>504;</b> and formation of the deformable layer <b>506</b> by deposition, patterning and etching. Sacrificial layer 710 is preferably molybdenum. In an embodiment, the deformable layer <b>506</b> is an upper electrode. Because these steps are carried out over variable thickness dielectric layer <b>570,</b> the interface between sacrificial layer <b>710</b> and deformable layer <b>506</b> may not be completely flat. For example, in the illustrated embodiment, the lower surface contour <b>741, 742</b> of the deformable layer <b>506</b> tends to substantially parallel the contours of the layers beneath it, e.g., the steps in the variable thickness dielectric layer <b>570.</b> However, those skilled in the art will understand that variable thickness dielectric layer <b>570</b> may have a thickness of only 100 Å, and thus <figref idref="f0017">Figure 17</figref> (not to scale) may exaggerate the undulations in the lower contour <b>741, 742.</b>

0128<figref idref="f0018">Figure 18</figref> illustrates etching with an etchant to remove the "sacrificial" layers, sacrificial layer <b>710</b> and the exposed part of the lower portion <b>550.</b> As the etchant, XeF₂, F₂ or HF may be used alone or in combination. The upper or "stop" portion <b>565</b> substantially protects the part of the lower portion <b>550</b> that is beneath it from being removed by etching, functioning in a manner somewhat analogous to a photomask. The resulting interferometric modulator <b>1800</b> illustrated in <figref idref="f0019">Figure 19</figref> includes the interferometric cavity <b>418,</b> a portion <b>910</b> of the stationary layer <b>502</b> that is not covered by a variable thickness dielectric layer <b>920</b> (comprising the upper variable thickness dielectric layer <b>565</b> and a variable thickness lower portion <b>925).</b> The lower portion <b>550</b> need not be completely removed by etching, and thus part of the lower portion <b>550</b> may remain over the stationary layer <b>502,</b> preferably where the stationary layer <b>502</b> is a single conductor layer.

0129This invention is not limited by theory, but it is believed that XeF₂ serves as a convenient source of F₂ gas. Other etchants such as F₂ and HF may be used in place of or in addition to XeF₂. In an embodiment, the etchant removes the lower portion <b>550</b> at an etch rate that is higher than an etch rate for removing the upper portion <b>565.</b> Thus, in an embodiment, the difference in average thickness variation between the lower surface contour <b>741, 742</b> of the deformable layer <b>506</b> and the upper contour of the variable thickness dielectric layer <b>570</b> tends to increase as etching proceeds, e.g., as the variable thickness dielectric layer <b>570</b> is etched to form the variable thickness dielectric layer <b>920.</b>

0130The variable thickness dielectric layer <b>920</b> comprises landing pads <b>513.</b> The landing pads <b>513</b> project upward from the stationary layer <b>502</b> and substantially prevent contact between the stationary layer <b>502</b> and the deformable layer <b>506,</b> during both the driven and undriven states. The variable thickness dielectric layer may be a discontinuous layer, e.g., as illustrated by dielectric layer <b>920</b> in <figref idref="f0019">Figure 19</figref>, or may be a continuous layer in which the thickness variation is manifested as peaks and valleys on the surface of the layer.

0131It will be appreciated by those skilled in the art that the variable thickness dielectric layer <b>920</b> may comprise multiple columns of dielectric material that project upward from the bottom electrode and substantially prevent contact between the first and second electrode, during both the driven and undriven states, e.g., as illustrated in <figref idref="f0015">Figure 12</figref>. Thus, the remaining surface area of the bottom electrode (e.g., the surface portion <b>910</b> not covered by such a column) need not be coated or covered by an insulating layer. A substantial improvement in capacitance is thus obtained, because the dielectric constant of air (about 1) is lower than that of insulating materials such as metal oxides disclosed in <patcit id="pcit0006" dnum="US5835255A"><text>U.S. Patent No. 5,835,255</text></patcit>. The variable thickness dielectric layer may be a discontinuous layer, e.g., as illustrated by dielectric layer <b>920</b> in <figref idref="f0016">Figure 15</figref>, or may be a continuous layer in which the thickness variation is manifested as peaks and valleys on the surface of the layer. In either case, the distance between the top of the landing pad 513, for example, and the bottom of the valley or gap <b>910,</b> for example, is preferably about 50 Å or greater, more preferably in the range of about 100 Å to about 3,000 Å.

0132Those skilled in the art will appreciate that, in the illustrated embodiment of <figref idref="f0018">Figure 18</figref>, the upper or "stop" portion <b>565</b> that is patterned above the lower or "bulk" portion <b>550</b> prevents the bulk layer from being completely etched away by the XeF₂ (similar to any masking step used to pattern previous layers). The areas of the bulk layer <b>550</b> that are not protected by the stop portion <b>565</b> form a sacrificial portion that is later removed, and the portions of the bulk material <b>925</b> below the stop <b>565</b> remain, forming a variable thickness dielectric layer <b>920</b> (comprising an upper layer <b>565</b> and a lower layer <b>925),</b> e.g., comprising one or more islands or columns of multilayer dielectric material that substantially prevent contact between the first and second electrodes. Although the lower contour <b>741, 742</b> of the underside of the deformable layer <b>506</b> illustrated in <figref idref="f0018">Figure 18</figref> tends to substantially parallel the upper contour of the variable thickness dielectric layer <b>570,</b> it does not substantially parallel the upper contour of the variable thickness dielectric layer <b>920</b> illustrated in <figref idref="f0019">Figure 19</figref> because etching removes at least a part of the lower portion <b>550</b> that is not protected by the upper portion <b>565</b> of the variable thickness dielectric layer <b>570.</b> This etching to remove the exposed part of the lower portion <b>550</b> creates extra space between the lower contour <b>742</b> of the deformable layer <b>506</b> and the surface portion <b>910</b> of the stationary layer <b>502.</b>

0133<figref idref="f0019">Figure 19</figref> illustrates an actuated interferometric modulator <b>1801.</b> During actuation, the lower contour <b>741</b> of the actuated deformable layer <b>506a</b> may contact the top of the stops <b>565,</b> e.g. at the landing pads <b>513</b> in the illustrated embodiment, thereby creating regions in which the lower contour <b>741</b> of the deformable layer <b>506</b> is spaced from the surface portion <b>910</b> of the lower electrode <b>502.</b> These regions include a low dielectric constant gap <b>418a</b> between the lower contour <b>742</b> of the actuated deformable layer <b>506a</b> and the surface portion <b>910</b> of the stationary layer <b>502.</b> Thus, as illustrated in <figref idref="f0019">Figure 19</figref>, the profile of the underside of the actuated deformable layer <b>506a</b> is different from the profile of the upper side of the variable thickness dielectric layer <b>920,</b> so that the low dielectric constant gap <b>418a</b> exists between the actuated deformable layer <b>506a</b> and the stationary layer <b>502</b> during operation. Thus, the lower surface of the deformable layer <b>506</b> has a surface profile variation <b>741, 742</b> that is less than a surface profile variation of the variable thickness dielectric layer <b>920.</b> In certain embodiments, the surface profile variation is equal to the average peak-to-valley surface profile variation. The average peak-to-valley surface profile variation of the lower surface of the upper electrode may be in the range of about 50 Å to about 200 Å. The average peak-to-valley surface profile variation of the variable thickness dielectric layer may be in the range of about 200 Å to about 1000 Å. Average peak-to-valley surface profile variation may be determined by scanning electron microscopy and/or atomic force microscopy. In certain embodiments, the average peak-to-valley surface profile variation is the difference between the average peak heights and the average valley depths of the layer over a selected area.

0134It will be recognized that the landing pads <b>513</b> are examples of members having an upper surface located between the deformable layer <b>506</b> and the stationary layer <b>502.</b> The landing pads <b>513</b> define a gap region <b>418a</b> between the deformable layer <b>506a</b> and the stationary layer <b>502</b> when the interferometric modulator <b>1801</b> is in the driven state (<figref idref="f0019">Figure 19</figref>). The lower surface contour <b>742</b> of the deformable layer <b>506a</b> in the gap region <b>418a</b> does not contact either the stationary layer <b>502</b> or the landing pads <b>513.</b>

0135<figref idref="f0020">Figure 20</figref> illustrates another embodiment in which the sacrificial layer is planarized before deposition of the upper electrode. The structure <b>1900</b> illustrated in <figref idref="f0020">Figure 20</figref> may be formed from the structure <b>1600</b> illustrated in <figref idref="f0017">Figure 17</figref> by planarizing the sacrificial layer <b>710</b> to produce a relatively planar surface <b>746.</b> In an alternative embodiment (not illustrated), the relatively planar surface is formed by depositing a planarization layer over the sacrificial layer <b>710,</b> instead of or in addition to planarizing the sacrificial layer <b>710.</b> A deformable layer <b>506</b> is then formed over the surface <b>746</b> as illustrated in <figref idref="f0016">Figure 16</figref>. In an embodiment, the deformable layer <b>506</b> is an upper electrode. The sacrificial layer <b>710</b> may then be removed to form a gap <b>418</b> as illustrated in <figref idref="f0021">Figure 21</figref> in a manner generally similar to that illustrated in <figref idref="f0018">Figure 18</figref>. Removal of the part of the lower portion <b>550</b> that is not protected by the upper portion <b>565</b> of the variable thickness dielectric layer <b>570</b> (as illustrated in <figref idref="f0018">Figure 18</figref>) is optional for the configuration illustrated in <figref idref="f0020 f0021">Figures 20-21</figref> because the lower contour <b>747</b> of the deformable layer <b>506</b> is relatively planar. Thus, the profile of the underside of the deformable layer <b>506</b> is different from the profile of the upper side of the variable thickness dielectric layer <b>570</b> (regardless of whether the part of the lower portion <b>550</b> that is not protected by the upper portion <b>565</b> of the variable thickness dielectric layer <b>570</b> is removed or not) so that a low dielectric constant gap(s) exists between the upper deformable layer <b>506</b> and lower stationary layer <b>502</b> during operation. Thus, the lower contour <b>747</b> of the deformable layer <b>506</b> has a surface profile variation that is less than a surface profile variation of the variable thickness dielectric layer <b>570.</b>

0136In the illustrated embodiments, the variable thickness dielectric layer <b>920</b> is formed over the stationary layer <b>502</b> (in this context, "over" refers to the relative location for the orientation illustrated in <figref idref="f0019">Figure 19</figref>). A variable thickness dielectric layer may be formed elsewhere in the cavity <b>418,</b> e.g., under the deformable layer <b>506.</b> Thus, for example, a variable thickness dielectric layer may be formed on the first electrode and/or on the second electrode of an interferometric modulator. Those skilled in the art will also appreciate that an interferometric modulator may contain three or more electrodes, and thus may contain two or more variable thickness dielectric layers, e.g., a variable thickness dielectric layer between each of the electrodes.

0137In the illustrated embodiment, portions of the cavity may contain a low dielectric constant material, e.g., some or all of the interior walls of the cavity <b>418</b> may optionally be coated or covered with a low dielectric constant material. For example, after etching to form the interferometric modulator illustrated in <figref idref="f0019">Figure 19</figref>, a layer of low dielectric constant material (not shown) may be formed on the surface portion <b>910</b> of the stationary layer <b>502.</b> Preferably, any such layer of low dielectric constant material is relatively thin, such that a gap remains between the top electrode and the low dielectric constant material during both the driven and undriven states. Other interior walls of the cavity <b>418</b> that may coated with a low dielectric constant material include the deformable layer <b>506</b> (which may be an upper electrode) and the variable thickness dielectric layer <b>565.</b>

0138Silicon dioxide has a dielectric constant of approximately 3.8. Preferred low dielectric constant materials have a dielectric constant less than that of silicon oxide, i.e., less than 3.8. Exemplary materials compatible with embodiments described herein include, but are not limited to, porous dielectric materials (e.g., aerogels) and modified silicon oxides. See, e.g., <patcit id="pcit0007" dnum="US6171945B"><text>U.S. Patent Nos. 6,171,945</text></patcit> and <patcit id="pcit0008" dnum="US6660656B"><text>6,660,656</text></patcit>, both of which describe low dielectric constant materials and methods for making them which are compatible with embodiments described herein. Preferred low dielectric constant materials have a dielectric constant of about 3.3 or less, more preferably about 3.0 or less, and most preferably about 2.0 or less.

0139In another embodiment (not illustrated), a variable thickness dielectric layer is formed by depositing a dielectric layer having a relatively uniform thickness on the first and/or second electrodes (e.g., over the stationary layer <b>502</b> as shown in <figref idref="f0015">Figure 13</figref>), then continuing the fabrication process as shown in <figref idref="f0015 f0016">Figures 14-16</figref> but without the masking step shown in <figref idref="f0016">Figure 15</figref>. Then, during subsequent etching (e.g., as illustrated in <figref idref="f0018 f0019">Figures 18-19</figref>), the flow of the etchant is controlled so that the dielectric layer having a relatively uniform thickness is etched to a greater extent in some areas than others, resulting in a variable thickness dielectric layer.

0140It will be appreciated by those skilled in the art that a variable thickness dielectric layer, e.g., comprising multiple columns of dielectric material that project upward from the bottom electrode, may also reduce damping of the interferometric modulator during operation, and thus may provide increased device switching speed by facilitating escape of the damping medium (e.g., air) from the cavity. It will also be appreciated that the variable thickness dielectric layer has a reduced dielectric constant as compared to a comparable uniform thickness dielectric layer of the same overall thickness as the variable thickness dielectric layer. The reduced dielectric constant may advantageously reduce the RC time constant of the interferometric device into which it is incorporated, based on the relationship time = resistance x capacitance, thus increasing device switching speed. Certain embodiments provide an interferometric modulator made by a process described herein, wherein the interferometric modulator comprises a variable thickness dielectric layer. Such an interferometric modulator may have a lower capacitance than a comparable interferometric modulator having a uniform thickness dielectric layer in place of the variable thickness dielectric layer. Such an interferometric modulator may also have increased performance (e.g., increased switching speed resulting from reduced damping and/or from a reduced RC time constant) than a comparable interferometric modulator having a uniform thickness dielectric layer in place of the variable thickness dielectric layer. It will also be appreciated that use of a variable thickness dielectric layer as described herein may result in reduced contact area between moving parts of the MEMS device, e.g., a reduced contact area between the dielectric layer and the movable electrode. This reduction in contact area may result in increased mechanical reliability and/or reduced wear. Electrical reliability may also be improved by use of a variable thickness dielectric layer that results in reduced electrical contact area with the moveable electrode. Such reduced electrical contact area may result in reduced electrical charging of the dielectric layer.

Bumps

0141<figref idref="f0021">Figures 22A and 22B</figref> illustrate an embodiment of an interferometric modulator <b>401</b> that includes bumps <b>511.</b> In the illustrated embodiment, a plurality of bumps <b>511</b> is formed on the top surface of the stationary layer <b>502.</b> Accordingly, when the interferometric modulator <b>401</b> is driven from its undriven state (<figref idref="f0021">Figure 22A</figref>) to the driven state (<figref idref="f0021">Figure 22B</figref>), the deformable layer <b>506</b> contacts the bumps <b>511,</b> which act to prevent or minimize the physical contact between the deformable layer <b>506</b> and the stationary layer <b>502.</b> Further, with the existence of the bumps, the area of contact between the deformable layer <b>506</b> and the stationary layer <b>502</b> can be reduced.

0142As discussed above with reference to <figref idref="f0009">Figures 9A and 9B</figref>, the stationary layer <b>502</b> includes at least one conductive layer but can be formed of a single layer or multiple layers. In any of the constructions of the stationary layer <b>502,</b> the bumps <b>511</b> are preferably located on the top surface of the stationary layer <b>502.</b> In one embodiment, the top surface is made of a dielectric material and the bumps <b>511</b> are located on the dielectric surface. In another embodiment, the top surface of the stationary layer <b>502</b> is made of a conductive layer, and the bumps <b>511</b> are located on the conductive surface.

0143In another embodiment as illustrated in <figref idref="f0022">Figure 22C</figref>, the bumps <b>511</b> may be located on the deformable layer <b>506</b> or mirror <b>419</b> (not shown). Again, the deformable layer <b>506</b> (or mirror <b>419)</b> may include multiple sub-layers. In any of the constructions, the bumps <b>511</b> are preferably located on the surface of the deformable layer <b>506</b> (or mirror <b>419)</b> facing the stationary layer <b>502.</b> In another embodiment as illustrated in <figref idref="f0022">Figure 22D</figref>, the bumps <b>511</b> may be located on both the deformable layer <b>506</b> and the stationary layer <b>502.</b>

0144The plurality of bumps <b>511</b> can be positioned in various locations on the stationary layer <b>502</b> and/or the deformable layer <b>506</b> within the interferometric cavity <b>418.</b> In one embodiment, the bumps <b>511</b> are located throughout the surface of the stationary layer <b>502</b> and/or the deformable layer <b>506.</b> In another embodiment, the bumps <b>511</b> are located primarily on a central portion of the stationary layer <b>502</b> or the deformable layer <b>506.</b> In the area where the bumps <b>511</b> are located, the bumps <b>511</b> may be regularly, sporadically or randomly arranged on the surface of the stationary layer <b>502</b> or the deformable layer <b>506.</b>

0145The bumps <b>511</b> may be fabricated in various shapes. In an embodiment as illustrated in <figref idref="f0022">Figure 22E</figref>, the bumps <b>511</b> may not have a regular shape and may comprise irregular protrusions from the stationary layer <b>502</b> or the deformable layer <b>506.</b> In other embodiments, the bumps <b>511</b> may have one or more regular shapes as illustrated in <figref idref="f0021 f0022">Figures 22A-22D</figref>. In the embodiments of regularly shaped bumps, the bumps <b>511</b> may have a distal surface <b>512</b> (<figref idref="f0021">Figure 22A</figref>). In the illustrated embodiments, the distal surface <b>512</b> is substantially planar and parallel to the counterpart surface of the deformable layer <b>506</b> (or the stationary layer <b>502</b> in the embodiment of <figref idref="f0022">Figure 22C</figref> or the counterpart bumps in the embodiment of <figref idref="f0022">Figure 22D</figref>). In another embodiment, the distal surface <b>512</b> may be planar but tilted with reference to the counterpart surface (not illustrated). In still another embodiment, the distal surface <b>512</b> of the bumps <b>511</b> may be round or rough (not illustrated).

0146The bumps <b>511</b> protrude from the stationary layer <b>502</b> or the deformable layer <b>506</b> by a height indicated at <b>515</b> of <figref idref="f0021">Figure 22A</figref>. The height <b>515</b> of a bump <b>511</b> is defined as the distance between the distal end (distal surface <b>512</b> in <figref idref="f0021">Figure 22A</figref>) of the bump <b>511</b> and the surface from which the bump <b>511</b> protrudes. In some situations where the bumps are formed of the same material as the underlying layer and are shaped irregularly, the reference surface may be difficult to determine. In such cases, the height <b>515</b> of a bump <b>511</b> is the farthest distance between the distal end of the bump and the surface of the stationary layer <b>502</b> and/or the deformable layer <b>506.</b> In some embodiments, the bumps <b>511</b> have substantially the same height <b>515.</b> In other embodiments, each of the bumps <b>511</b> may have a different height.

0147In one embodiment, the height <b>515</b> is selected so as to prevent physical contact between the deformable layer <b>506</b> and the stationary layer <b>502.</b> In another embodiment, the height <b>515</b> is selected not only to prevent such contact, but to define the depth of the interferometric cavity <b>418</b> in the driven state of the interferometric modulator <b>401,</b> so as to enable production of the desired optical characteristics of the interferometric modulator <b>401.</b> In the embodiments of interferometric modulator <b>401</b> for use as a display element, the interferometric cavity depth at the driven state is designed to be short enough to absorb most, if not all, of the visible light. Although not so limited, the height <b>515</b> of the bumps <b>511</b> can be substantially smaller than the height <b>519</b> of the landing pads <b>513.</b> The height <b>511</b> is from about 50 Å to about 500 Å, and preferably from about 100 Å to about 200 Å.

0148In a unit of the interferometric modulator <b>401,</b> a number of bumps <b>511</b> can be provided. As noted above, the bumps <b>511</b> are provided to prevent the stationary layer <b>502</b> and the deformable layer <b>506</b> from directly contacting each other, and also to reduce the contact area of the two layers <b>502</b> and <b>506.</b> The number of the bumps <b>511</b> in a unit of the interferometric modulator <b>401</b> is determined in view of the height <b>515</b> thereof. For example, if the height <b>515</b> of the bump <b>511</b> is significantly large, only very few bumps <b>511</b> are necessary to effectively prevent the contact between the stationary layer <b>502</b> and the deformable layer <b>506</b> because it is unlikely that the deformable layer <b>506</b> in contact with the tall bumps <b>511</b> can also contact the stationary layer <b>502.</b> On the other hand, when the height <b>515</b> of the bumps <b>511</b> is small, more bumps <b>511</b> may be needed.

0149The plurality of bumps <b>511</b> can be fabricated from various materials. In one embodiment, the bumps <b>511</b> are made of a dielectric material. If the bumps <b>511</b> extend from a dielectric surface of the stationary layer <b>502</b> or the deformable layer <b>506,</b> the bumps <b>511</b> may be made of the same dielectric material. Alternatively, the bumps <b>511</b> may be formed of another dielectric material of the surface from which they extend. In another embodiment, the bumps <b>511</b> are made of a conductive material. Preferably, the materials used to form for the bumps <b>511</b> are those that do not significantly affect the electrical or optical characteristics of the interferometric modulator. For example, materials for the bumps <b>511</b> may include oxides, nitrides and oxynitrides. Preferably, the bumps <b>511</b> are substantially transparent to predetermined wavelengths of light.

0150The bumps <b>511</b> can be produced in a number of ways. In one embodiment, the bumps <b>511</b> are formed by the process described above for the production of landing pads <b>513.</b> In one embodiment, a material is deposited over the stationary layer <b>502</b> or the deformable layer <b>506,</b> and the material is etched to form the bumps <b>511</b> on the layer <b>502</b> or <b>506.</b> The layer to be etched to form the bumps may comprise the same material as the top or sole layer of the stationary layer <b>502</b> or layer <b>506.</b> For example an exposed SiO₂ layer formed over the stationary layer <b>502</b> may be etched with an etchant to produce a rough surface, thereby forming bumps <b>511.</b> The etching process can be random, or the etching can be further directed into particular shapes through the use of particular etching barriers. This can allow one to control the size and shape of the bumps and create patterns which may be optimized for reducing or preventing the adverse impact created by contact of the deformable layer <b>506</b> with the stationary layer <b>502.</b>

Spring Clips

0151<figref idref="f0023 f0024">Figures 23A-23F</figref> illustrate embodiments of an interferometric modulator <b>501</b> including spring clips <b>509.</b> In typical constructions of the interferometric modulator e.g., as illustrated in <figref idref="f0008">Figures 8</figref>, <figref idref="f0009">9A and 9B</figref>, the deformable layer <b>506</b> has a tension in its deformed (driven) state <b>501b</b> and has a tendency to return to its non-deformed (undriven) state <b>501c</b> to reduce the tension. The tension of the deformable layer <b>506</b> in its deformed state creates a mechanical restoring force that is exerted on that layer <b>506</b> in the direction away from the stationary layer <b>502.</b> The deformable layer <b>506</b> returns from its deformed state <b>501b</b> to the undeformed state <b>501c</b> when the mechanical restoring force overcomes the attractive force created by the electrical potential applied between the deformable layer <b>506</b> and the stationary layer <b>502.</b> As will be described below in detail, the spring clips <b>509</b> are provided to help the recovery of the deformable layer <b>506</b> from its driven state to the undriven state by applying an additional element of force onto the deformable layer <b>506</b> in the direction away from the stationary layer <b>502.</b> When combined with the mechanical restoring force of the deformable layer <b>502,</b> the additional element of force can increase the likelihood and/or speed of the return of the deformable layer <b>506</b> to the driven state when the return is desired.

0152In the illustrated embodiment of <figref idref="f0023">Figures 23A and 23B</figref>, the spring clips <b>509</b> are provided on the stationary layer <b>502</b> of the interferometric modulator <b>501.</b> Referring to <figref idref="f0023">Figure 23A</figref> which illustrates the undriven state, a portion of the spring clip <b>509</b> is located on the top surface of the stationary layer <b>502,</b> and the tip <b>510</b> of the spring clip <b>509</b> is bent so as to extend into the interferometric cavity <b>418</b> toward the deformable layer <b>506.</b> In this undriven state, the spring clips <b>509</b> are in their normal configuration as no force is applied thereto. When this interferometric modulator <b>501</b> is driven, the deformable layer <b>506</b> deforms into the driven state illustrated in <figref idref="f0023">Figure 23B</figref>. As the deformable layer <b>506</b> is deforming to its deformed state, the deformable layer <b>506</b> first contacts the tip <b>510</b> of the clips <b>509</b> and compresses the tip <b>510</b> into the substantially flat configuration as shown in <figref idref="f0023">Figure 23B</figref>. The spring clips <b>509</b> in their flat configuration have a tendency to return to their normal configuration. This tendency produces a force that is exerted by the tips <b>510</b> on the deformable layer <b>506.</b> When actuating the deformed layer <b>506</b> from the deformed state to its flat state, the force of the spring clips <b>509</b> exerted on the deformable layer <b>506</b> can help the actuation and increase the likelihood and/or speed of the recovery of the deformable layer <b>506.</b>

0153The embodiment illustrated in <figref idref="f0023">Figures 23C</figref> and <figref idref="f0024">23D</figref> is the same as the embodiment of <figref idref="f0023">Figures 23A and 23B</figref> except that the spring clips <b>509</b> are formed on the deformable layer <b>506.</b> In the embodiments of <figref idref="f0023 f0024">Figures 23A-23D</figref>, the spring clips <b>509</b> can also serve as the above-described landing pads and/or bumps that maintain a desired distance between the stationary layer <b>502</b> and the deformable layer <b>506.</b>

0154<figref idref="f0024">Figures 23E and 23F</figref> illustrate another embodiment of the interferometric modulator <b>501</b> that includes the spring clips <b>509.</b> Referring to <figref idref="f0024">Figure 23E</figref> which illustrates the interferometric modulator <b>501</b> in the undriven state, the stationary layer <b>502</b> has a recess <b>520</b> and the spring clip <b>509</b> has a portion contained in and attached to the recess <b>520.</b> The tip <b>510</b> of the spring clip <b>509</b> is bent with respect to the portion of the clip <b>509</b> contained in the recess <b>520</b> and extends upwardly beyond the top surface of the stationary layer <b>502</b> into the interferometric cavity <b>418.</b> Referring to <figref idref="f0024">Figure 23F</figref> illustrating the driven state, the tip <b>510</b> of the spring clip <b>509</b> is substantially flattened by the deformable layer <b>506</b> and the stationary layer <b>502.</b> Again, this tip <b>510</b> has the tendency to return to its normal configuration shown in <figref idref="f0024">Figure 23E</figref> and thus exerts a force on the deformable layer <b>506</b> that is in the direction away from the stationary layer <b>502.</b>

0155In the embodiment of <figref idref="f0024">Figures 23E and 23F</figref>, the thickness <b>521</b> of the spring clip <b>509</b> is substantially the same as or smaller than the depth of the recess <b>520.</b> As a result, the deformable layer <b>506</b> contacts the top surface of the stationary layer <b>502</b> in the driven state as shown in <figref idref="f0024">Figure 23F</figref>. In another embodiment, the thickness <b>521</b> of the spring clip <b>509</b> at the tip <b>510</b> and/or in the portion contained in the recess <b>520</b> may be greater than the depth of the recess <b>520.</b> In such an embodiment, in the driven state of the interferometric modulator <b>501,</b> the deformable layer <b>506</b> contacts the spring clip <b>509</b> particularly at the area thereof that has the thickness <b>521</b> greater than the depth of the recess <b>520,</b> while not contacting the stationary layer <b>502.</b> In this configuration, the spring clips <b>509</b> serve as the above-described landing pads and/or bumps as well as the spring clips <b>509</b> prevent direct contact between the stationary layer <b>502</b> and the deformable layer <b>506.</b>

0156As will be appreciated by one of skill in the art, the spring clips <b>509</b> may not have the exact configuration as illustrated in <figref idref="f0023 f0024">Figures 23A-23F</figref>. Also, many different types of biasing mechanisms and springs may be employed in lieu of the clips <b>509.</b> Additionally, materials with biasing characteristics can also be employed. For example a landing pad that includes one or more elastomeric materials may also be employed in lieu of the clips <b>509.</b> For the sake of convenience, the term "spring clip" refers to any and all mechanisms having the function of exerting a force on the deformable layer <b>506</b> in the direction toward its undriven state. Although two spring clips <b>509</b> are illustrated in <figref idref="f0023 f0024">Figures 23A-23F</figref>, a single spring clip or more than two spring clips may be employed. Optionally, two or more spring clips <b>509</b> are arranged in the interferometric cavity <b>418</b> such that the forces exerted on the deformable layer <b>506</b> by the spring clips <b>509</b> are substantially balanced with one another, rather than focusing the forces on a local area of the deformable layer <b>506.</b>

0157As will be appreciated by one of skill in the art, the size, placement and strength of the spring or biasing elements can all be varied according to the desired characteristics of the interferometric modulator. The stronger the spring, the faster and the more reliably the deformable layer <b>506</b> will return to its undriven planar position. Of course, this may also require one to adjust the initial voltage input in order to drive the interferometric modulator <b>501</b> to its fully driven state, as the deformable layer <b>506</b> will tend to have an increased amount of resistance against the spring clips <b>509</b> during its approach towards the stationary layer <b>502.</b>

0158In some embodiments, the spring clips <b>509</b> are useful in overcoming stictional forces (static friction) that may develop when the deformable layer <b>506</b> comes in close proximity to or contacts the stationary layer <b>502.</b> These forces can include Van der Waals or electrostatic forces, as well as other possibilities as appreciated by one of skill in the art. The stictional forces in nature hinder the separation of the deformable layer <b>506</b> from the stationary layer <b>502.</b> Since the spring clips <b>509</b> provide additional force to separate the deformable layer <b>506</b> from the stationary layer <b>502,</b> the force of the spring clips <b>509</b> can balance or overcome the stictional forces.

0159In some embodiments, the stictional forces between the deformable layer <b>506</b> and the stationary layer <b>502</b> can be reduced by coating the layers with a polymer that reduces static friction with or without the spring clips. For example, the layers can be coated by an anti-stiction polymer coating, which can reduce the degree of adhesion between the deformable layer 506 and the stationary layer <b>502.</b> In one embodiment, this coating is applied to other aspects of the device, such as the spring clips <b>509,</b> bumps <b>511</b> or landing pad <b>513.</b>

0160As will be appreciated by one of skill in the art, the above features of landing pads <b>513,</b> bumps <b>511</b> and spring clips <b>509</b> may be employed individually or may be employed together in a single embodiment. For example, an interferometric modulator may have one, two or all three of these features. Also, as described, certain features can serve both to assist in the return of the deformable layer <b>506</b> to its undriven state and to reduce the likelihood that the deformable layer <b>506</b> and the stationary layer <b>502</b> adversely contact each other, as landing pads <b>513</b> and spring clips <b>509</b> might function.

Multi-State Interferometric Modulators

0161In some embodiments, the interferometric modulator provides more than two states (driven and undriven). An example of this is illustrated in the embodiment shown in <figref idref="f0025">Figures 24A-24C</figref>. In this embodiment, the interferometric modulator is not only capable of a deflection of the deformable layer <b>506</b> towards the layer <b>503,</b> in the driven state as shown in <figref idref="f0025">Figure 24B</figref>, but the interferometric modulator is also capable of reversing the direction of the deflection of layer <b>506</b> in the opposite direction, as illustrated in <figref idref="f0025">Figure 24C</figref>. This "upwardly" deflected state may be called the "reverse driven state."

0162As will be appreciated by one of skill in the art, this reverse driven state can be achieved in a number of ways. In one embodiment, the reverse driven state is achieved through the use of an additional stationary layer <b>502'</b> that can pull the deformable layer <b>506</b> in the upward direction, as depicted in <figref idref="f0025">Figure 24C</figref>. In this particular embodiment, there are basically two interferometric modulators positioned symmetrically around a single layer <b>506.</b> This allows each of the stationary layers <b>502</b> and <b>502'</b> to attract the layer <b>506</b> in opposite directions. Thus, while an initial voltage command may send layer <b>506</b> into the normal driven state (<figref idref="f0025">Figure 24B</figref>), the next voltage command can accelerate the recovery of the deformable layer <b>506</b> by driving that layer towards the reverse driven state. In this mode, the deformable layer <b>506</b> is then attracted in the opposite direction to the stationary layer <b>502'.</b> In this embodiment, the stationary layers <b>502</b> and <b>502'</b> may be in various constructions as described earlier in the disclosure, and do not have to be in the same construction at the same time. For example, the stationary layers <b>502</b> and <b>502'</b> can be in a single layer construction or in multiple sub-layer construction. In the illustrated embodiment, a support surface <b>500'</b> is maintained some distance above the deformable layer <b>506</b> through a second set of supports 504'.

0163As will be appreciated by one of skill in the art, not all of these elements will be required in every embodiment. For example, if the precise relative amount of upward deflection, such as that shown in <figref idref="f0025">Figure 24C</figref> compared to <figref idref="f0025">Figures 24A or 24B</figref>, is not relevant in the operation of the device, then the stationary layer <b>502'</b> can be positioned at various distances from the deformable layer <b>506.</b> Thus, there may be no need for support elements <b>504'</b> or a separate substrate <b>500'.</b> In these embodiments, it is not necessarily important how far upward the deflection of the deformable layer <b>506</b> extends, but rather that the stationary layer <b>502'</b> is configured to attract the deformable layer <b>506</b> at the appropriate time. In other embodiments, the position of the deformable layer <b>506</b> as shown in <figref idref="f0025">Figure 24C</figref> may alter optical characteristics of the interferometric modulator. In these embodiments, the precise distance of deflection of layer <b>506</b> in the upward direction can be relevant in improving the image quality of the device.

0164As will be appreciated by one of skill in the art, the materials used to produce the stationary layer <b>502'</b> (or its sub-layers) and substrate <b>500'</b> need not be similar to the materials used to produce the corresponding layer <b>502</b> and substrate <b>500.</b> For example, in some embodiments, light need not pass through the layer <b>500'</b> while it may be necessary for light to be able to pass through the layer <b>500.</b> Additionally, if layer <b>502'</b> is positioned beyond the reach of layer <b>506</b> in its deformed upward position, then a dielectric sub-layer may not be needed in the stationary layer <b>502'</b> as there is little risk of layer <b>506</b> contacting the conductive portion of the layer <b>502'.</b> Accordingly, the voltages applied to layers <b>502'</b> and <b>506</b> can be different based on the above differences.

0165As will be appreciated by one of skill in the art, the voltage applied to drive the deformable layer <b>506</b> from the driven state shown in <figref idref="f0025">Figure 24B</figref> to the undriven state shown in <figref idref="f0025">Figure 24A</figref>, may be different from that required to drive the deformable layer <b>506</b> from the state shown in <figref idref="f0025">Figure 24A</figref> to the upward or reverse driven state shown in <figref idref="f0025">Figure 24C</figref>, as the distance between plates <b>502'</b> and <b>506</b> is different in the two states. Thus, the amount of voltage to be applied is determined based upon the desired application and amounts of deflection.

0166In some embodiments, the amount of force or the duration that a force is applied between the layer <b>502'</b> and the layer <b>506</b> is limited to that is necessary to merely increase the rate at which the interferometric modulator transitions between the driven state and the undriven state. Since the deformable layer <b>506</b> can be made to be attracted to either the layer <b>502</b> or <b>502'</b> which are located on opposite sides of the layer <b>506,</b> a very brief driving force can be provided to weaken the interaction of the layer <b>506</b> with the opposite layer. For example, as the layer <b>506</b> is driven to interact with the layer <b>502,</b> a pulse of energy to the opposite layer <b>502'</b> can be used to weaken the interaction of the layer <b>506</b> with the layer <b>502'</b> and thereby make it easier for the deformable layer <b>506</b> to move to the undriven state.

Controlling Offset Voltages

0167Traditionally, interferometric modulator devices have been designed such that there is a minimum, or no, fixed electrical charge associated with each layer. However, as current fabrication techniques have not been able to achieve a "no fixed charge standard," it is frequently desirable to have the resulting fixed charge considered and compensated for when selecting the operational voltages used to control the deformable layer <b>506.</b>

0168Through testing various configurations of layers and various deposition techniques, the amount of fixed electrical charge that is associated with each layer can be modeled and used as design criteria to select materials and layer configurations that minimize the amount of total offset voltage imparted to the interferometric modulator. For example, one or more materials can be replaced in the interferometric modulator layers to change the electrical characteristics of the overall interferometric modulator device.

0169Referring now to <figref idref="f0026">Figure 24D</figref>, in some embodiments, the dielectric sub-layer <b>413</b> or another sub-layer of the stationary layer <b>502</b> is modified with a charged component in order to obtain a neutrally charged system. In the illustrated embodiment, the stationary layer <b>502</b> is in a two sub-layer construction, a dielectric sub-layer <b>413</b> is located on a sub-layer <b>416</b> that serves as mirror and conductive electrode, and the dielectric sub-layer <b>413</b> contains charged components <b>514.</b> Again, the stationary layer <b>502</b> can be in various constructions as described above.

0170The incorporation of the charged component <b>514</b> can be achieved in a number of ways. For example, additional charged components <b>514</b> can be added to the dielectric material when the dielectric sub-layer <b>413</b> is being formed on the underlying sub-layer <b>416.</b> As will be appreciated by one of skill in the art, there are a variety of charged components that can be used, the amount and particular characteristics of these charged components can vary depending upon the desired properties of the interferometric modulator. Examples can include, forming a dielectric layer in a sputter tool (which can be negative) as compared to a chemical vapor deposition process (which can be positive), or altering the amount of hydrogen in the layer.

0171In some embodiments, the control of the amount of charged components <b>514</b> in the interferometric modulator can also be achieved through altering the method of deposition of the layers or adding entirely new layers. In another embodiment, one selects particular materials with the goal of optimizing the electrochemical characteristics of the materials. Thus, one can use various work function differences to control the final offset voltage of the interferometric modulator or change the charge accumulation rate within the device during operation of the device. For example, the deformable layer <b>506</b> can have a surface that can contact the stationary layer <b>502,</b> the surface can have a high work function to minimize the transfer of electrons between the layers. In another embodiment, one can modify a sacrificial material used in the creation of the interferometric modulator so that as the sacrificial material is being removed, one is not imparting charge to the deformable layer <b>506</b> and/or the stationary layer <b>502.</b> In another embodiment, materials to be used to connect the layers <b>502</b> and <b>506</b> during processing can be selected on the basis of their work function properties. In another embodiment, the material selected for the connector rod <b>333</b> (<figref idref="f0027">Figures 25A and 25B</figref>) is based on its work function characteristics.

0172In one embodiment, during the creation of the interferometric modulator, the stationary layer <b>502</b> and the deformable layer <b>506</b> are electrically connected so as to minimize the charge difference between the two layers. This can allow for higher yield in production and higher reliability in the final interferometric modulator. This electrical connection can be removed to allow the device to properly function. In one embodiment, this connection between the two layers is created from the same material as that from which the deformable layer 506 is created.

Reducing the Movement of the deformable layer <b>506</b>

0173In some embodiments, the supports <b>504</b> interact with the deformable layer <b>506</b> through direct contact of the top end <b>37</b> of the supports <b>504</b> and the bottom surface of layer <b>506.</b> In certain situations, sliding or slippage of the deformable layer <b>506</b> along the top <b>37</b> of support <b>504</b> may occur. This movement can be decreased in a number of ways. In one embodiment, the movement is decreased by altering the surface characteristics of the top <b>37</b> of the support <b>504.</b> For example, one can roughen the deformable layer <b>506</b> and/or the support <b>504</b> at the point <b>505</b> where the two interact, as shown in <figref idref="f0026">Figures 24D and 249E</figref>. For example, this can be done by oxygen plasma burn down of the support or by sputter etching before the deposition of the deformable layer <b>506.</b>

Alternative Forces for Driving Recovery from the Driven State

0174In some embodiments, the manner of deformation of the deformable layer <b>506</b> may be altered for improved functionality. In a traditional interferometric modulator <b>501,</b> the deformable layer <b>506</b> is a single contiguous sheet stretched taut across the support members <b>504.</b> Because the layer is stretched taut, the residual stress in the layer allows the layer to "spring" or "snap back" from the driven state to the undriven state. However, this particular arrangement can be sensitive to process variability.

0175Instead of relying upon the tautness of the deformable layer <b>506</b> (to create residual stress), one can instead rely upon the elastic modulus of the material, which is a constant based upon the material, rather than on primarily how the material is arranged or processed. Thus, in one aspect, the deformable layer <b>506</b> retains and provides its elasticity through a material constant of the material from which it is made. In one embodiment, this is similar to that of a cantilever spring, rather than a taut stretched film. An example of such a design is shown in <figref idref="f0027">Figures 25A-25D. Figure 25A</figref> shows a side view, and <figref idref="f0027">Figure 25B</figref> shows a top view of one embodiment of an interferometric modulator <b>501</b> in the undriven state. <figref idref="f0027">Figure 25C</figref> shows a side view and <figref idref="f0027">Figure 25D</figref> shows a top view of the interferometric modulator <b>501</b> in a driven state.

0176In this embodiment, the deformable layer <b>506</b> has been divided into two separate parts, a load bearing part <b>506a</b> that is responsible for providing the flexibility and resilience for the movement of the layer through its elastic modulus, and a substantially planar part <b>506b,</b> which functions as the secondary mirror for the interferometric modulator. The two parts <b>506a</b> and <b>506b</b> are connected to each other via a connector rod <b>333.</b> In one embodiment, the connector rod <b>333</b> is made of the same material as the load bearing part <b>506a</b> and/or the substantially planar part <b>506b.</b> In another embodiment, the connector rod <b>333</b> is made of a material different from the load bearing part <b>506a</b> and the substantially planar part <b>506b.</b> In some embodiments, the connector rod <b>333,</b> rather than the load bearing structure <b>506a,</b> is the part that provides flexibility and resilience to the system. In some embodiments, the load bearing structure <b>506a</b> is thicker than the deformable layer <b>506</b> in the previous embodiments.

0177As shown in <figref idref="f0027">Figure 25B</figref>, the load bearing part <b>506a</b> is configured in an "X" shape that is supported at its four corners <b>70, 71, 72,</b> and <b>73</b> to provide its elastomeric properties. In the driven state, the load bearing part <b>506a</b> bends downward and towards the stationary layer <b>502</b> through the pull from the planar part <b>506b</b> of the deformable layer <b>506.</b> As will be appreciated by one of skill in the art, the particular material or materials used to provide the elasticity for the system can vary depending upon the particularly desired characteristics of the system.

0178The above-described modifications can help remove process variability and lead to a more robust design and fabrication. Additionally, while the above aspects have been described in terms of selected embodiments of the interferometric modulator, one of skill in the art will appreciate that many different embodiments of interferometric modulators may benefit from the above aspects. Of course, as will be appreciated by one of skill in the art, additional alternative embodiments of the interferometric modulator can also be employed. The various layers of interferometric modulators can be made from a wide variety of conductive and non-conductive materials that are generally well known in the art of semi-conductor and electromechanical device fabrication.

0179While the above detailed description has shown, described, and pointed out novel features of the invention as applied to various embodiments, it will be understood that various omissions, substitutions, and changes in the form and details of the device or process illustrated may be made by those skilled in the art without departing from the spirit of the invention. As will be recognized, the present invention may be embodied within a form that does not provide all of the features and benefits set forth herein, as some features may be used or practiced separately from others.

Alternative Embodiments

0180Alternative embodiments set out in following clauses: <ul id="ul0001" list-style="none" compact="compact"><li>Clauses: <ol id="ol0001"><li>1. An interferometric modulator, comprising: a first layer comprising a first reflective planar portion; a second layer comprising a second reflective planar portion located substantially parallel to the first reflective planar portion, the second layer movable between a first position and a second position, the first position being a first distance from the first layer, the second position being a second distance from the first layer, the second distance being greater than the first distance; and a member having a surface located between the first layer and the second layer, the member defining one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member.</li><li>2. The interferometric modulator of Clause 1, wherein the member separates the first layer and the second layer when the second layer is in the first position.</li><li>3. The interferometric modulator of Clause 1, wherein the first reflective planar portion is partially reflective and partially transmissive to light in a predetermined wavelength range.</li><li>4. The interferometric modulator of Clause 1, wherein the second planar portion is substantially reflective to light in a predetermined wavelength range.</li><li>5. The interferometric modulator of Clause 1, further comprising a third layer between the first layer and the second layer, the third layer substantially transparent to light in a predetermined wavelength range, wherein the third layer comprises a dielectric layer.</li><li>6. The interferometric modulator of Clause 5, wherein the second layer in the one or more gap regions does not contact at least a portion of the third layer when the second layer is in the first position.</li><li>7. The interferometric modulator of Clause 1, wherein the member is spaced from the second layer when the second layer is in the second position, and is contacted by the second layer when the second layer is in the first position.</li><li>8. The interferometric modulator of Clause 1, wherein the member comprising a biased portion.</li><li>9. The interferometric modulator of Clause 8, wherein when the second layer is in the first position, the biased portion applies force on the second layer toward the second position.</li><li>10. The interferometric modulator of Clause 1, wherein the member is located at a discrete location on the at least one of the first layer and the second layer.</li><li>11. The interferometric modulator of Clause 1, wherein the member comprises a plurality of discrete members.</li><li>12. A microelectromechanical device, comprising: a first surface having a first surface area; a second surface having a second surface area, the second surface being located substantially parallel to the first surface, the second surface movable between a first position and a second position, the first position being a first distance from the first surface, the second position being a second distance from the first surface, the second distance being greater than the first distance; and a third surface located between the first surface and the second surface, the third surface defining one or more gap regions between the first surface and the second surface when the second surface is in the first position, wherein the second surface in the one or more gap regions does not contact either the first surface or the third surface.</li><li>13. The microelectromechanical device of Clause 12, wherein the third surface provides a contact area which contacts at least one of the first surface and the second surface when the second surface is in the first position.</li><li>14. The microelectromechanical device of Clause 12, wherein the third surface comprises a surface of a member that is positioned on a peripheral portion of at least one of the first surface and the second surface.</li><li>15. The microelectromechanical device of Clause 14, wherein the third surface contacts the second surface when the second surface is m the first position.</li><li>16. The microelectromechanical device of Clause 15, wherein the third surface comprises a material different from a material which comprises either the first or second surfaces</li><li>17. The microelectromechanical device of Clause 15, wherein the third surface comprises a material which also comprises either the first or second surfaces.</li><li>18. The microelectromechanical device of Clause 14, wherein the third surface comprises a substantially non-transparent material.</li><li>19. The microelectromechanical device of Clause 14, wherein the third surface comprises a substantially transparent material.</li><li>20. The microelectromechanical device of Clause 14, wherein the third surface contacts the first surface when the second surface is in the first position.</li><li>21. The microelectromechanical device of Clause 12, wherein the third surface comprises a surface of a member that is located on a central portion of at least one of the first layer and the second layer.</li><li>22. The microelectromechanical device of Clause 21, wherein the third surface comprises a substantially transparent material.</li><li>23. The microelectromechanical device of Clause 12, wherein the third surface comprises a surface of a spring which is compressed when the second surface is in the first position</li><li>24. The microelectromechanical device of Clause 12, further comprises one or more additional discrete third surfaces between the first surface and the second surface.</li><li>25. A microelectromechanical device, comprising: a first layer; a second layer located substantially parallel to the first layer, the second layer movable between a first position and a second position, the first position being a first distance from the first layer, the second position being a second distance from the first layer, the second distance being greater than the first distance; and a plurality of members, each member comprising a surface located between the first layer and the second layer, the plurality of members defining one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the plurality of members.</li><li>26. The microelectromechanical device of Clause 25, wherein the plurality of members are positioned on either the first layer or the second layer.</li><li>27. The microelectromechanical device of Clause 25, wherein the plurality of members are positioned on both the first layer and the second layer.</li><li>28. A microelectromechanical device, comprising: a first surface; a second surface located substantially parallel to the first surface, the second surface movable relative to the first surface between a driven position and an undriven position, wherein the driven position is closer to the first surface than is the undriven position; and at least one structure on at least one of the first surface and the second surface, wherein the at least one structure is compressed by the first surface and the second surface when the second surface is in the driven position, and wherein the at least one structure provides a force to the second surface when the second surface is in the driven position, the force assisting movement of the second surface from the driven position toward the undriven position.</li><li>29. A microelectromechanical device of Clause 28, wherein the at least one structure is a spring.</li><li>30. A microelectromechanical device of Clause 28, wherein the at least one structure comprises a body and a tip extended from the body, the body connected to at least one of the first surface and the second surface, the tip bent away from the surface to which the body is connected when the second surface is in the undriven position.</li><li>31. A microelectromechanical device of Clause 30, wherein the tip is compressed and substantially flattened when the second surface is in the driven position.</li><li>32. A method of making an interferometric modulator, the method comprising: providing a first layer comprising a first reflective planar portion; forming a second layer comprising a second reflective planar portion, the second reflective planar portion located substantially parallel to the first reflective planar portion, the second layer movable between a first position and a second position, the first position being a first distance from the first layer, the second position being a second distance from the first layer, the second distance being greater than the first distance; and forming a member comprising a surface located between the first layer and the second layer, the member defining one or more gap regions between the first layer and the second layer when the second layer is in the first position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member.</li><li>33. The method of Clause 32, wherein the member separates the first layer from the second layer when the second layer is in the first position.</li><li>34. The method of Clause 32, wherein the member is on at least one of the first layer and second layer.</li><li>35. The method of Clause 32, wherein the member comprises a bump.</li><li>36. The method of Clause 32, wherein the member comprises a landing pad.</li><li>37. The method of Clause 32, wherein the member comprises a spring.</li><li>38. The method of Clause 32, further comprising forming one or more additional members, wherein each additional member comprises a surface located between the first layer and the second layer.</li><li>39. A microelectromechanical device produced by the method of Clause 32.</li><li>40. A method of operating a microelectromechanical device, wherein the device comprises a first layer, a second layer located substantially parallel to the first layer and a member comprising a surface located between the first layer and the second layer, the method comprising: moving the second layer relative to the first layer from an undriven position towards a driven position, wherein the driven position is closer to the first layer than is the undriven position; and contacting the member with at least one of the first layer and the second layer so as to stop the movement of the second layer at the driven position, the member defining one or more gap regions between the first layer and the second layer when the second layer is in the driven position, wherein the second layer in the one or more gap regions does not contact either the first layer or the member.</li><li>41. The method of Clause 40, wherein the member separates the second layer from the first layer when the second layer reaches the driven state.</li><li>42. The method of Clause 40, wherein the member comprises a biased portion facing one of the first layer and second layer, and wherein as the second layer moves toward the undriven position, the biased portion contacts the at least one of the first layer and second layer.</li><li>43. The method of Clause 42, wherein after the biased portion first contacts the at least one of the first layer and second layer, the second layer further moves toward the driven position, and wherein the biased portion is compressed by the further movement of the second layer.</li><li>44. The method of Clause 42, wherein when the second layer is in the driven position, the biased portion exerts force on the second layer m a direction toward the undriven position.</li><li>45. The method of Clause 40, wherein the member comprises a plurality of discrete members.</li><li>46. A microelectromechanical device, comprising: first means for partially reflecting and partially transmitting incident light; second means for substantially reflecting incident light; means for moving the first means relative to the second means between a driven position and an undriven position, the driven position being closer to the first means than is the undriven position; and means for providing a separation between the first means and the second means when the second means is in the driven position.</li><li>47. The microelectromechanical device of Clause 46, wherein the means for providing separation comprises at least one of a bump, a landing pad or a spring clip.</li><li>48. The microelectromechanical device of Clause 46, wherein the means for providing separation is located between the first means and second means.</li><li>49. The microelectromechanical device of Clause 46, wherein the first means comprises a partial mirror surface.</li><li>50. The microelectromechanical device of Clause 46, wherein the second means comprises a full mirror surface.</li><li>51. The microelectromechanical device of Clause 46, wherein the means for moving comprises a deformable layer.</li><li>52. A microelectromechanical device, comprising: first means for partially reflecting and partially transmitting incident light; second means for substantially reflecting incident light; means for moving the first means relative to the second means between a driven position and an undriven position, the driven position being closer to the first means than is the undriven position; and means for applying a force on the second means in a direction toward the undriven position when the second means is in the driven position.</li><li>53. The microelectromechanical device of Clause 52, wherein the means for applying force comprises a spring clip.</li><li>54. The microelectromechanical device of Clause 52, wherein the means for applying force comprises a bump or a landing pad, which comprises an elastomeric material.</li><li>55. The microelectromechanical device of Clause 52, wherein the means for applying a force is in contact with both the first layer and the second layer when the second means is in the driven position.</li><li>56. The microelectromechanical device of Clause 52, wherein the first means comprises a partial mirror surface.</li><li>57. The microelectromechanical device of Clause 52, wherein the second means comprises a full mirror surface.</li><li>58. The microelectromechanical device of Clause 52, wherein the means for moving comprises a deformable layer.</li><li>59. An interferometnc modulator, comprising: a first layer comprising a first reflective planar portion; a second layer comprising a second reflective planar portion located substantially parallel to the first reflective planar portion, the second layer movable between a driven position and an undriven position, the driven position being closer to the first layer than the undriven position; and at least one bump on at least one of the first layer and the second layer, the at least one bump configured to prevent the first layer and the second layer from contacting each other.</li><li>60. The microelectromechanical device of Clause 59, wherein the at least one bump is located on a central portion of at least one of the first layer and the second layer.</li><li>61. The microelectromechanical device of Clause 59, wherein the at least one bump comprises a substantially transparent material.</li><li>62. The microelectromechanical device of Clause 59, wherein the at least one bump is located on the second layer.</li><li>63. An interferometnc modulator, comprising: a first layer comprising a first reflective planar portion; a second layer comprising a second reflective planar portion located substantially parallel to the first reflective planar portion, the second layer movable between a driven position and an undriven position, the driven position being closer to the first layer than the undriven position; and at least one landing pad located between the first layer and the second layer, the at least one landing pad comprising a contact area where a first portion of at least one of the first layer and the second layer contacts the landing pad when the second layer is in the driven position.</li><li>64. The interferometnc modulator of Clause 63, wherein the at least one landing pad comprises a material different from a material which comprises the at least one of the first layer and the second layer.</li><li>65. The interferometric modulator of Clause 63, wherein the at least one landing pad is positioned on a peripheral portion of at least one of the first layer and the second layer.</li><li>66. The microelectromechanical device of Clause 63, wherein the at least one landing pad is located on the first layer.</li><li>67. An interferometric modulator, comprising: a first layer comprising a first reflective planar portion; a second layer comprising a second reflective planar portion located substantially parallel to the first reflective planar portion, the second layer movable between a driven position and an undriven position, the driven position being closer to the first layer than the undriven position; and at least one spring member placed between at least one of the first layer and the second layer, the at least one spring member compressed as the second layer moves toward the driven position, the at least one spring member configured to apply force to the second layer in a direction toward the undriven position when the second layer is in the driven position.</li><li>68. The interferometric modulator of Clause 67, wherein the at least one spring member is positioned on a peripheral portion of at least one of the first layer and the second layer.</li><li>69. The microelectromechanical device of Clause 67, wherein the spring member is in contact with at least one of the first layer and the second layer when the second layer is in the driven position.</li><li>70. A microelectromechanical device of Clause 67, wherein the at least one spring member comprises a body and a tip extended from the body, the body attached to at least one of the first layer and the second layer, the tip bent away from the layer to which the body is attached when the second layer is in the undriven position.</li><li>71. A display system comprising: the interferometric modulator of Clause 1; a display; a processor that is in electrical communication with the display, the processor being configured to process image data, and a memory device in electrical communication with the processor.</li><li>72. The display system of Clause 71, further comprising: a first controller configured to send at least one signal to the display, and a second controller configured to send at least a portion of the image data to the first controller.</li><li>73. The display system of Clause 71, further comprising: an image source module configured to send the image data to the processor.</li><li>74. The display system of Clause 73, wherein the image source module comprises at least one of a receiver, transceiver, and transmitter.</li><li>75. The display system of Clause 71, further comprising: an input device configured to receive input data and to communicate the input data to the processor.</li><li>76. A method of making a microelectromechanical system (MEMS) device, comprising: forming a first electrode; depositing a dielectric material over at least a portion of the first electrode; removing a portion of the dielectric material from over the first electrode, thereby forming a variable thickness dielectric layer; and forming a second electrode over at least a portion of the variable thickness dielectric layer.</li><li>77. The method of Clause 76, further comprising depositing a sacrificial layer over at least a portion of the dielectric material.</li><li>78. The method of Clause 77, in which the MEMS device comprises an interferometric modulator.</li><li>79. The method of Clause 77, in which the second electrode comprises a surface facing the variable thickness dielectric layer, the surface of the second electrode facing the variable thickness dielectric layer having an average peak-to-valley surface profile variation that is less than an average peak-to-valley surface profile variation of the variable thickness dielectric layer.</li><li>80. The method of Clause 76, in which the dielectric material comprises at least a first layer and a second layer.</li><li>81. The method of Clause 80, in which the first layer has a first thickness that is greater than a second thickness of the second layer.</li><li>82. The method of Clause 81, in which the first thickness is m the range of about 200 Å to about 3000 Å.</li><li>83. The method of Clause 81, in which the second thickness is in the range of about 50 Å to about 500 Å.</li><li>84. The method of Clause 80, further comprising patterning the dielectric material to define stops.</li><li>85. The method of Clause 84, in which removing a portion of the dielectric material comprises removing a portion of the second layer of the dielectric material such that the stops remain.</li><li>86. The method of Clause 85, further comprising depositing a sacrificial layer over at least a portion of the dielectric material.</li><li>87. The method of Clause 86, further comprising removing the sacrificial layer and at least a portion of the first layer of the dielectric material.</li><li>88. The method of Clause 87, in which removing the sacrificial layer and the at least a portion of the first layer of the dielectric material further comprises etching with an etchant.</li><li>89. The method of Clause 88, in which etching further comprises removing the first layer of the dielectric material at a first etch rate that is higher than a second etch rate for removing the second layer.</li><li>90. The method of Clause 76, in which the dielectric material is compositionally graded.</li><li>91. The method of Clause 90, in which the dielectric material is a graded dielectric material selected from the group consisting of graded silicon oxide and graded silicon nitride.</li><li>92. The method of Clause 91, in which the graded dielectric material at an interface with the first electrode is enriched in Si relative to the overall composition of the graded dielectric material.</li><li>93. The method of Clause 76, further comprising depositing an intermediate layer over the at least a portion of the first electrode.</li><li>94. The method of Clause 93, in which the intermediate layer comprises at least one of an optical layer, a barrier layer or a non-conductive layer.</li><li>95. The method of Clause 93, comprising depositing the dielectric material over the intermediate layer.</li><li>96. An interferometric modulator made by the method of Clause 76.</li><li>97. The interferometric modulator of Clause 96, having a lower capacitance than a comparable interferometric modulator having a uniform thickness dielectric layer in place of the variable thickness dielectric layer.</li><li>98. The interferometric modulator of Clause 97, having increased switching speed as compared to the comparable interferometric modulator.</li><li>99. The interferometric modulator of Clause 97, having reduced damping as compared to the comparable interferometric modulator.</li><li>100. A method of making an interferometric modulator, comprising: forming a first electrode; depositing a dielectric layer over at least a portion of the first electrode; removing a portion of the dielectric layer to form a variable thickness dielectric layer; depositing a sacrificial layer over the variable thickness dielectric layer; planarizing the sacrificial layer; and forming a second electrode over the sacrificial layer.</li><li>101. The method of Clause 100, further comprising forming a planarization layer over the sacrificial layer.</li><li>102. The method of Clause 100, further comprising removing the sacrificial layer.</li><li>103. The method of Clause 100, in which the variable thickness dielectric layer comprises at least one stop.</li><li>104. The method of Clause 100, in which the second electrode comprises a lower surface at an interface with the sacrificial layer, the lower surface of the second electrode having an average peak-to-valley surface profile variation that is less than an average peak-to-valley surface profile variation of the variable thickness dielectric layer.</li><li>105. An interferometric modulator made by the method of Clause 100.</li><li>106. A method of making an interferometric modulator, comprising: forming a first electrode; depositing a dielectric layer over at least a portion of the first electrode; removing a portion of the dielectric layer to form a variable thickness dielectric layer; depositing a sacrificial layer over the a variable thickness dielectric layer; depositing a planarization layer over the sacrificial layer; and forming a second electrode over the planarization layer.</li><li>107. The method of Clause 106, further comprising removing the sacrificial layer.</li><li>108. The method of Clause 106, further comprising planarizing the sacrificial layer.</li><li>109. The method of Clause 106, in which the variable thickness dielectric layer comprises at least one stop.</li><li>110. The method of Clause 106, in which the second electrode comprises a lower surface at an interface with the planarization layer, the lower surface of the second electrode having an average peak-to-valley surface profile variation that is less than an average peak-to-valley surface profile variation of the variable thickness dielectric layer.</li><li>111. An interferometric modulator made by the method of Clause 106.</li></ol></li></ul>