Electrowetting display element

The present invention relates to a display device, and more particularly to the field of a passive display device.

Many companies are actively striving to create easily manufactured display devices using roll-to-roll coating techniques. These display elements are active, such as LEDs, OLEDs, PLEDs, ELs, etc., that emit light, or passive, such as LCDs, CLC, e-inks, etc., that is, light passage, reflection, or refraction. It can be either influential. Some passive systems are bistable and can be switched and remain switched even after power is removed. Many of the configurations disclosed so far can be easily adapted to the color function.

Various electrowetting display devices are known in the prior art.

U.S. Pat. No. 6,647,492 discloses a fluid element device that dislocates a fluid within a capillary. A voltage is used to move the fluid to the desired level within the capillary. U.S. Patent Application Publication No. 2002/0080920 discloses a filter device with an array of elements based on U.S. Patent No. 6473492 for use with X-ray imaging devices. U.S. Patent Application Publication No. 2003/0085850 discloses an electronic device that modifies the meniscus shape to change the focal length of the device.

U.S. Pat. No. 6449081 describes focusing devices based on the electrowetting phenomenon. WO2 / 002099527 describes a display device with a defined prismatic structure that contains two immiscible fluids with electrodes so that the fluids dislocate with the cell.

<patcit num="1"><text>U.S. Pat. No. 6,634,492</text></patcit><patcit num="2"><text>U.S. Patent Application Publication No. 2002/0080920</text></patcit><patcit num="3"><text>U.S. Pat. No. 6,634,492</text></patcit><patcit num="4"><text>U.S. Patent Application Publication No. 2003/0085850</text></patcit><patcit num="5"><text>U.S. Pat. No. 6,449,081</text></patcit><patcit num="6"><text>International Publication No. WO2 / 002099527 Pamphlet</text></patcit>

<p> In display devices based on liquid dislocation, it is advantageous to ensure liquid capture by capillary force. This is achieved by making the element smaller. Therefore, current technology is not easy to handle requirements for large pixel areas. Furthermore, current technology describes structures that inevitably require microfabrication and therefore relatively complex assembly methods that are not transitionable to roll-to-roll manufacturing.</p><p> It is an object of the present invention to provide a new bistable device based on a combination of mechanisms not previously intended. Devices of this class, described below for monochromatic devices, can be adapted for color applications. This display element is capacitive in nature and therefore has low power consumption and can be switched by low voltage. This device modifies the reflectance of their surface.</p>

<p> According to the present invention, a display element including at least two conductive porous layers and a conductive liquid is provided, and the conductive porous layer is insulated from the conductive liquid by a dielectric and sparse cover. Including a plurality of connected conductive particles, the display element further includes a means for individually connecting at least two porous layers and a voltage across the liquid, so that the voltage is transferred to each conductive layer. The liquid shifts from one location to another when sequentially applied to the layers, and the liquid returns to its original location only when the alternating voltages are applied.</p><p> Preferably, at least one additional layer is provided adjacent to at least two conductive porous layers, the liquid has a contact angle of less than 60 ° with the material of this additional layer, and the thickness of this additional layer. The thickness is greater than the thickness of each of the conductive porous layers, but smaller than the combined thickness of the two conductive porous layers.</p>

<p> The present invention is simple to manufacture over large areas from the stochastic structure of the device and can be manufactured via the roll-to-roll technique. This meets the requirement of capturing small liquid elements by the capillary. However, the switching time of the element is not limited by its area. Addresses and drives are also simple via a properly patterned passive or active matrix type backplane.</p><p> The bistable nature of this device makes it possible to maintain one state until power is applied and the device is switched to another state.</p><p> Hereinafter, the present invention will be described with reference to the accompanying drawings.</p>

FIG. 1 is a schematic view of a display element according to the present invention. The present invention relates to a passive display device.

Throughout this description and claims, the expression upper side defines the side on which the device will be viewed. The expression lower defines the opposite side of the upper. The upper and lower sides should not be taken as limiting the orientation of the device according to the present invention in any way.

The device shown in Figure 1 is based on a 4-layer porous system. Layers 6, 8, 10, and 12 are stacked and arranged in sequence, with layer 6 at the top. Between each layer, a conductor 14 for connecting with the liquid is provided. This conductor can be composed of wire filaments. Separate conductors 20 and 22 are provided in association with layer 8 and layer 10, respectively. The element is enclosed by the upper substrate 24 and the lower substrate 26. These substrates can be flexible and conductive. The upper substrate should be made of a transparent material.

The upper layer 6 contains a plurality of particles 28 such as silicon dioxide. As will be appreciated by those skilled in the art here, this silicon dioxide is just one example of a usable material. Any other arsenic material that can be matched to the index of refraction of the liquid used can be used. The particle size is in the 30 nm to 2 μm range.

The liquid 18 exists in the pore space of the upper layer 6. This liquid can be water, but as will be appreciated by those skilled in the art, it is not essential that the liquid be water. However, this liquid must be conductive. Conductive liquids can be created by adding ions to the solvent. Instead, the conductive liquid may be an ionic liquid. The index of refraction of the particles 28 in the upper layer 6 should be substantially the same as the index of refraction of the liquid 18. The size of the particles 28 should effectively be a fraction of the wavelength of light, eg 200 nm. The refractive index of the liquid is substantially similar to that of the particles, effectively making the upper layer invisible.

Layer 8 contains a plurality of particles 30. The particles 30 need to be similar in size or smaller than the particles 28 in the upper layer 6. These particles may be colored to provide colored pixels, or may provide black pixels as black. Alternatively, an intermediate layer 50 of colored or black particles may be provided between the upper layer 6 and the layer 8. An embodiment of the type is shown in FIG. The particles in the intermediate layer differ in that they are colored, and have substantially the same characteristics as the particles in the upper layer 6 in terms of material, size, shape, and the like. When such intermediate layers are used, the color of the particles in layer 8 does not matter because they are not visible. Another option is to use the colored liquid 18. The liquid can be colored by the addition of dyes or pigments. Conductor 20 is associated with layer 8.

The liquid 18 has a contact angle greater than 90 ° with the particles 30. Particle 30 is conductive. These particles may be solid metal particles, or only their shells may be conductive. If these particles have a shell, the thickness of the shell can be selected to produce particles of a particular color. The explanation is given by Zhong-jie Jiang and Chun-yan Liu, "Seed-Mediated Growth Techniques for the Preparation of a Silver." Seed-mediated Growth Techniques for the Preparation of a Silver Nanoshell on a Silica Sphere Journal of Physical Chemistry B 2003, 107, p12411 ~ Can be found at 12415.

A thin layer or cover of leasable material with low contact angle hysteresis, no matter what type of particle is used<u style="single">54</u>Need to cover them with. This sparse material needs to be an insulator. Suitable particles would be conductive silver particles wrapped in a sparse and dielectric mercaptan. As will be appreciated by those skilled in the art, this is only an example, and any conductive material and sparse and dielectric cover can be used within the conditions of the present invention. Figure 5 illustrates possible core-shell configurations for particles. core<u style="single">56</u>Can be an inexpensive insulator particle such as silicon dioxide. Metal shell 36 is each core<u style="single">56</u>Wrap up. A layer of leaching material with particles wrapped in those shells<u style="single">54</u>Surrounds. layer<u style="single">54</u>Can be made, for example, from macromolecules. Other materials that can be used include polymer electrolytes, fluoropolymers, self-assembled monolayers (SAM), or inorganic shells. However, the present invention is not construed as being limited to these materials. layer<u style="single">8</u>The metallic components of the particles 30 inside must be connected and cover their structure with a sparse liquid.<u style="single">54</u>Wraps up completely.

Layer 10 contains a plurality of particles 32. Particle 32 is substantially the same as particle 30 in layer 8. Liquid 18 has a contact angle greater than 90 ° with particle 32. These particles are conductive and are accompanied by a thin cover of sparse material as described above. Conductor 22 is associated with layer 10.

The lowermost layer 12 contains a plurality of particles 34. These particles can include any arsenic material. The particles need to be substantially similar to the particles in layer 6 in terms of contact angle, size, etc. with the liquid. The particle size is in the 30 nm to 2 μm range.

The volume of liquid 18 must be equal to or greater than the volume available in the upper layer 6 or in the lower layer 12. This available volume is therefore thickness x area x porosity. The porosity thickness of layers 6, 8, 10, and 12 can be defined by multiplying their actual (mechanical) thickness by the porosity of the material. The expression of thickness as used in the description of this application and in the claims should be construed as the thickness of the porous material as defined above.

Each layer 8 and 10 has a smaller thickness than that of layer 6 or 12. However, the thickness of the combined layers 8 and 10 is greater than that of the layers 6 or 12 alone.

As mentioned above, the liquid 18 has a contact angle greater than 90 ° with the particles 30 in layer 8. Therefore, the capillary pressure in the layer 8 is such that the liquid 18 does not enter the layer 8 from the upper layer 6. Therefore, when no voltage is applied to the device, the liquid 18 stays in the upper layer 6. Since the liquid 18 and the particles 28 have similar refractive indexes, the upper layer 6 is essentially transparent or translucent. The particles 30 in layer 8 scatter light. As a result, the color of the particles 30 in layer 8 can be seen. In the embodiment of the present invention including the intermediate layer illustrated in FIG. 6, the color of the particles forming the intermediate layer can be seen.

FIG. 2 illustrates what happens when a voltage is applied to the device. The applied voltage is in the 2 volt range and is intended for up to 20 V.

A voltage is applied between the liquid 18 and the conductor 20. This brings about an effect called electrowetting. Electrowetting is described in Blake et al. Langmuir 2000, 16, p2928-2935. The electrowetting effect reduces the contact angle of the liquid 18 with layer 8. The general electrowetting formula shown in the following formula (1) can be used. cos (θ) = cos (θ)₀) + εε₀V²/ 2dγ (1)

In this, θ is the contact angle in the presence of voltage, θ₀Is the contact angle when there is no voltage, V is the voltage, ε is the dielectric constant of the sparse layer, ε₀Is the permittivity of the free space, γ is the surface tension of the liquid, and d is the thickness of the sparse layer. The capillary pressure ΔP in the pore system can be defined by the following equation (2). ΔP = γcos (θ) / a (2) In this, a is the average radius of the pores in the porous structure. Here, if the upper layer 6 is defined as A, the layer 8 is defined as B, the layer 10 is defined as C, and the layer 12 is defined as D. ΔP_A&lt;ΔP_BIf so, the liquid moves from upper layer 6 to layer 8, ΔP_A&lt;ΔP_B&lt;ΔP_CIf so, the liquid moves from layer 8 to 10, ΔP_B&lt;ΔP_C&lt;ΔP_DIf so, the liquid moves from layer 10 to layer 12.

As those skilled in the art will recognize, reversing the capillary pressure will cause the liquid to move in the opposite direction.

If V = 0, ΔP_AIs positive, ΔP_BBecomes negative. Therefore, this capillary pressure is not suitable for the transfer of liquid 18 from upper layer 6 to layer 8. Sufficient voltage is applied, ΔP_BBut ΔP_AAs it increases to a larger size, then the liquid 18 will move to layer 8.

When the anterior surface of the liquid meniscus reaches the interface between layers 8 and 10, it stops there because layer 10 is still sparse. There, a higher voltage applied through the conductor 20 is applied between the liquid 18 and the conductor 22. The voltage applied through the conductor 20 can be removed at this point. Layer 10 then changes to lipophilic, and the difference in capillary pressure between layers 8 and 10 draws liquid 18 further down. Liquid 18 retracts from upper layer 6. At this point, the upper layer is virtually empty, scattering light strongly and appearing white. The liquid will stop when the front meniscus reaches the interface between layers 10 and 12. Capillary pressure in layers 8 and 10 changes again in response to subsequent removal of voltage from conductors 20 and 22, and liquid 18 is drawn into and stays in layer 12. Therefore, it can be understood that this device is bistable. The device remains white even after the voltage has been removed.

To return to the original color, reverse the application of voltage between the liquid and conductors 20 and 22. First, a voltage is applied between the liquid and the conductor 22. Layer 10 becomes liquid-friendly, reducing the contact angle between liquid 18 and particle 32. As a result, the liquid 18 is drawn from layer 12 to layer 10. When the liquid passes through layer 10 and reaches the interface with layer 8, a higher voltage is applied between the liquid and the conductor 20 and the voltage applied between the liquid and the conductor 22 is removed. Differences in the voltage applied through the conductors 22 and 20 change the capillary pressure in layer 8 relative to the capillary pressure in layer 10, and the liquid is drawn into layer 8. At this point, all liquid 18 is removed from layer 12. The anterior surface of the meniscus reaches the interface between layers 6 and 8. Removing the voltage supply to conductors 20 and 22 will draw the liquid into the upper layer 6. When the liquid completely fills layer 6, the original color reappears on this device.

FIG. 3 illustrates an element according to a second embodiment of the present invention.

The device illustrated in FIG. 3 is based on a three-layer porous system.

This embodiment is in many ways similar to that shown in FIG. The layers of the three particles are substantially the same as the layers 6, 8 and 10 illustrated in FIG. 1 and are therefore labeled the same. Between each phase there is a conductor 14 for connecting with the liquid. This conductor can be composed of wire filaments. Conductors 20 and 22 are associated with layers 8 and 10 as described above. Lowermost layer<u style="single">10</u>An insulating layer 16 is arranged on the lower side. This element is enclosed by the upper substrate 24 and the lower substrate 26. The upper substrate must be a transparent material.

Each layer 8 and 10 has a thickness smaller than that of layer 6. However, the thickness of the combined layers 8 and 10 is greater than that of the layer 6 alone.

This device works in essentially the same manner as the device shown in FIG.

In the absence of voltage application, the liquid remains in the upper layer 6. Therefore, as described above, the upper layer becomes invisible. As a result, as described in relation to the embodiment shown in FIG. 1, the color of the particles in layer 8 or, if an intermediate layer, is provided, the color is visible. When a voltage is applied between the liquid and the conductor 20, the electrowetting effect reduces the contact angle between the liquid and layer 8. Therefore, the liquid is started to be drawn into the layer 8 and the front meniscus reaches the interface between the layers 8 and 10. When a higher voltage is applied between the liquid and the conductor 22, layer 10 also becomes positivity, and the difference in capillary pressure between layers 8 and 10 in turn draws liquid 18 further down. All liquid withdraws from layer 6 and remains within layers 8 and 10, primarily within layer 10. As mentioned above, removing the liquid 18 from the layer 6 results in an optical change in that layer.

When the voltage is removed from the conductors 20 and 22, layers 8 and 10 return to sparse. However, the liquid does not return from layers 8 and 10 because the liquid meniscus is not at the interface between layers 6 and 8 and the capillary pressure is in equilibrium within layers 8 and 10. Therefore, it can be seen that the device shown in FIG. 3 is bistable.

To restore the original color, a voltage is applied between the liquid and the conductor 20. At this time, the liquid 18 rises until the meniscus reaches the interface between the layers 6 and 8 due to the difference in capillary pressure appearing in the layers 8 and 10. When the voltage is turned off there, the difference in capillary pressure between layers 6 and 8 causes the liquid to rise into the upper layer 6. When the liquid completely fills layer 6, the original color reappears on this device.

In the embodiments illustrated in FIGS. 1 and 2, the upper layer 6 can also include, for example, a photonic crystal structure such as opal, inverted opal, etc. instead of a random porous structure. This crystal structure acts as a diffraction grating and reflects only light of a specific wavelength. When the gaps in the crystal structure are filled with liquid, the photonic nature of the layer is removed and the layer becomes transparent or translucent. As a result, the color from the lower layer is visible. However, when the liquid is discharged from the layer, the layer is strongly reflected at the wavelength defined by the structure of the photonic crystal and the spacing dimensions.

FIG. 4 illustrates an element according to a third embodiment of the present invention.

The device illustrated in FIG. 4 is based on a two-layer porous system. The layers of the two particles are substantially the same as the layers 8 and 10 illustrated in FIG. 1 and are therefore labeled the same.

As mentioned above, the two layers 8 and 10 contain multiple conductor particles. These particles can be conductors of only solid metal particles or their shells. Regardless of the type of particles used, they need to be wrapped by a thin layer of sparse electrical insulating material, as described above. The particle size and composition of the particles should be the same within layers 8 and 10, respectively. The porous volume and pore size of each layer 8 and 10 should also be the same. These layers have the same thickness.

At the ends of each layer 8 and 10, two electrodes 38 and 40 are provided, respectively. These electrodes allow the application of voltage to the particles in each layer. Insulating substrates 42 and 44 are provided on the top and bottom of the device. The insulating substrate 42 must be transparent. These substrates seal the element.

When this device is made, the use of static electricity pushes the conductive liquid 46 into layer 8. This is achieved by applying a voltage between the layer and the liquid, resulting in an increase in capillary pressure due to a decrease in the contact angle of the liquid on the particle surface. When the volume of liquid absorbed in the layer becomes the same as the available volume in the pores of layer 8, the upper transparent substrate is placed, thereby sealing the device.

When the voltage is removed, the liquid 46 stays in layer 8. If the liquid is colored, that color will be visible. It is preferable to use a colored liquid. This provides the greatest optical contrast between the on and off states. When a voltage is applied between the layer 10 and the liquid via the electrode 40, the layer becomes lipophilic and the difference in capillary pressure between the layers 8 and 10 draws the liquid 46 into the layer 10. Turn off the voltage after the liquid has been completely absorbed into layer 10. Since there is no difference in capillary pressure within layers 8 and 10, the liquid remains within layer 10 even after the voltage has been removed. Therefore, it can be seen that the device illustrated in FIG. 4 is bistable. If you look at this element from above when there is liquid in layer 10, you can see the color of the particles in layer 8. If the lower substrate 44 is transparent, the color of the liquid can be seen when looking at this element through the lower substrate 44. In this way, the opposite image can be seen from either side of this element.

To return to the original color, a voltage is applied to layer 8 through the electrode 38. This makes layer 8 positivity, and the difference in capillary pressure between layers 8 and 10 allows the liquid 46 to be drawn into layer 8 and revert to its original color.

This device can be made using coating technology. First, a substrate containing an electrode pattern is prepared by printing or the like. This is followed by placing a porous layer using a multi-layer coating or one or more multi-layer coatings. The coating process of choice can be uniform and is preferably pre-weighed. It is well known in coating techniques that a porous particle layer is produced via a single-layer or multi-layer coating process. Subsequently, these layers are dried. After that, the liquid can be coated, and since the top layer is liable, the liquid fills the upper layer without penetrating into the lower layer. The final encapsulation layer will then be provided by coating or lamination and will include electrodes that connect to the liquid layer.

A matrix or multiple elements can be assembled to form a display device.

The elements of the display device contain the liquid and are environmentally sealed to prevent the ingress of moisture and the leakage of the liquid.

The present invention has been described in detail with reference to the preferred embodiments thereof. As will be appreciated by those skilled in the art, modifications and modifications can be made within the scope of the present invention.

<figref num="1">It is the schematic of the element according to this invention.</figref><figref num="2">It is explanatory drawing which illustrated the switching of an element.</figref><figref num="3">It is the schematic of another element according to this invention.</figref><figref num="4">It is a schematic diagram of yet another element according to the present invention.</figref><figref num="5">It is explanatory drawing which illustrated the core-shell composition of the particle in an element.</figref><figref num="6">It is the schematic of the element including an intermediate layer.</figref>