Liquid crystal reflective display

Liquid crystal reflective display

The present invention relates to a liquid crystal display device comprising at least one retardation film, a nematic liquid crystal layer and a reflective cholesteric color filter layer.

The market share of liquid crystal displays (LCDs) continues to increase at the cost of other display technologies, and this development is believed to continually improve size and performance and reduce the price of the panel. LCDs designed for portable applications such as mobile phones and demanding applications such as PDAs are quite different from LCD designs for advanced terminal applications such as monitors and televisions. Low cost and low power are important for displays for telecom applications, such as the quality of the displayed image. Further improving the properties of LCDs remains a challenge, and performance issues must be improved, such as the color quality of the reflective passive matrix display originally described. For the absorption color filter layer, it is very attractive to select such a display panel based on a cholesteric color filter layer.

According to the prior art, a passive matrix display with a reflective color filter layer is described in patent document US 5 555 114. This document discloses a liquid crystal display including a cholesteric liquid crystal layer for selecting a reflective circularly polarized light having a specific wavelength. The display of one embodiment of the present invention basically comprises a polarizing plate, a quarter-wavelength plate, a liquid crystal layer and a cholesteric color filter layer. The driven liquid crystal layer can be a ferroelectric layer, a twisted nematic or a super twisted nematic liquid crystal.

However, for super-twisted nematic liquid crystals, the display as described in the patent document US 5 555 114 is problematic because a high contrast display covering the overall range of the clear spectrum cannot be obtained.

Therefore, the object of the present invention is to provide a display device having a twisted nematic liquid crystal to overcome the problems of the prior art, but still maintain quite Simple structure.

These and other objects are achieved by a liquid crystal display device comprising a polarizing plate, at least one retardation film, a nematic liquid crystal layer comprising an electro-optical unit, and an optimal cross-combination, light reflecting cholesterol type color a filter layer for reflecting a substantially circular or rightward circularly polarized light to the left, wherein the liquid crystal layer is a super twisted nematic liquid crystal layer having a twist angle of 180-270 degrees apart, and The retardation film or the total retardation R of the retardation film and the liquid crystal layer corresponds to about R = (3 + 2n) λ / 4, where n = 0, 1, 2, 3.... A variety of displays have been achieved due to the use of super-twisted nematic liquid crystals in the display.

Further, the retardation film or such retardation films are preferably disposed between the aforementioned polarizing plate and the super twisted nematic liquid crystal layer.

Preferably, the retardation film comprises a broadband quarter wave plate. It is appropriate to form the broadband quarter-wavelength plate from a quarter-wavelength plate in combination with a half-wavelength plate, and therefore, it is possible to standardly use components of the complete test layer. The aforementioned polarizing plate, the retardation film or the retardation film, the liquid crystal layer and the reflection cholesteric color filter layer are appropriately disposed in order of each other.

According to a preferred embodiment of the present invention, the apparatus further includes an additional retardation layer which is a twisted nematic polymeric film disposed between the front substrate and the super twisted nematic layer, the twisted nematic polymeric layer There is a twisting direction opposite to the super twisted nematic layer.

Further preferred embodiments of the present invention are described in the scope of the appended claims.

The presently preferred embodiment of the present invention will now be described in more detail with reference to the associated drawings.

Figure 1 is a cross-sectional view of a display in accordance with the present teachings.

Figure 2 shows an optical schematic block diagram of the display according to Figure 1.

Figure 3a shows the computer simulated optics principle of a display in this creation, optimized to obtain a high-brightness structure.

Figure 3b is a transmission diagram showing the wavelength of incident light in accordance with the display device of Figure 3a.

Figure 4a shows the computer simulated optics principle of a display in this creation, optimized to obtain a high contrast structure.

Figure 4b is a transmission diagram showing the wavelength of incident light in accordance with the display device of Figure 4a.

1 is a schematic cross-sectional view of a portion of a liquid crystal reflective display device, in this case, including a display unit including a super twisted nematic liquid crystal layer 5, also referred to as an LC layer, having a twist angle not exceeding an interval of 180 °-270°, and substantially sandwiched between two glass substrates, which are the front substrate 7 and the rear substrate 8. On the face of the front substrate facing the liquid crystal layer 5, a polarizing layer 1 and one or more retardation films 4 are disposed. Further, the combination of the retardation film 4 includes a half-wavelength plate 2 and a quarter-wavelength plate 3. The first electrode layer 10 and the LC positioning layer 12 are sequentially disposed between the front substrate 7 and the super twisted nematic liquid crystal layer 5. Further, between the high twisted nematic liquid crystal layer 5 and the rear substrate 8, the LC positioning layer 13, the second electrode layer 11, and the reflection cholesteric color filter layer 6 are sequentially disposed. An absorbing layer 9 is disposed on the surface of the rear substrate 8 facing the cholesteric color filter layer 6. The first and second electrode layers 10, 11 and the alignment layers 12, 13 formed in the supertwisted nematic display according to the prior art will not be described in detail herein. However, in order to be familiar with the party itself An electric field is generated in the super twisted nematic liquid crystal layer 5 to establish an open and closed state of the display, and thus the first and second electrode layers 10 are made of a penetrable material such as indium tin oxide (ITO). 11, and connected to the power source 14. In order to provide the desired reliable positioning to the super twisted nematic liquid crystal layer 5, such positioning layers are provided on both sides of the super twisted nematic liquid crystal layer. The positioning layer 12, 13, such as PI, may comprise a polymer according to prior art processing.

The reflective cholesterol type color filter layer 6 described above substantially combines a reflector function, a polarizing plate function, and a color filter function. The cholesteric liquid crystal phase is an optical intermediate phase having a natural law, and the liquid crystals are arranged in a spiral shape. In the material, the birefringent product of the cholesteric material and the law of the liquid crystal are commensurate with the wavelength of the light, ie λ=n. p (where λ is the wavelength of the incident light, n is the reflectivity of the material, and p is the spacing of the material) is reflected by the Bragg reflection device. In addition, a liquid crystal such as a spiral is not in the right direction to the left. Therefore, the cholesteric liquid crystal is determined to be leftward or rightward to reflect circular or polarized light to the left or right. Usually, the cholesteric layer only reflects between pn_eWith pn_oBetween the wavelengths of light, where n_eAnd n_oThey are the special and common reflectivity of a single axis positioning phase. The reflection cholesteric color filter layer is preferably based on a photosensitive cholesteric material. For this type of material, the curvature of the cholesteric phase can be reflected by UV light. And the cholesteric color filter layer is exposed to UV light in a compositional pattern, and has a gray scale scale. Since only one exposure step is required, this process facilitates the production of colors as described in the patent document WO/0034808. For subsequent deposition of red, green and The blue filter layer, as described above, is much more simplified than conventional absorption color filtering, which typically involves three lithography steps.

As described above, the retardation film 4 (also referred to as a retardation layer) includes two films of a half-wavelength plate 2 and a quarter-wavelength plate 3, and together constitutes a broadband quarter-wavelength plate 4, resulting in better The overall dark state.

Figure 2 is a diagram showing more generally the main optically active components of the display.

A first embodiment of the present creation, which is shown in Figures 3a and 3b, will be described below. This configuration, as shown schematically in Figure 3a, includes a twisted nematic layer with a 0.76 μm optical thickness turned 240° to the right. The display is of the normal black type. In this mode, the off-state of the driven LC layer 5 is dark, while the on-state is bright. Although the embodiment described is a normal black mode, the configuration of the normal white mode can also be made. The aforementioned two retardation films 2, 3 are inserted between the polarizing plate 1 and the front substrate 7 described above. The retardation film 3 having a thickness of 140 nm is combined with a polarizing plate to produce a circular polarized light. By adding a half-wavelength sheet 2 having a thickness of 280 nm in the middle, a wide-band quarter-wavelength sheet is created, resulting in a better overall dark state. The slow axis of the film 3 adjoining the substrate forms an angle of 30 with the vertical y-axis of the device. The half-wavelength sheet 2 forms an angle of 170 with the vertical y-axis. The absorption axis of the polarizing plate forms an angle of 110 with the vertical y-axis. LC layer 5 is converted to 315 nm (<img file="TWM250176U_D0001.tif" />1/2. λ). Above the rear substrate 8, a color filter layer that turns to the left is used. By using the previously configured display, the best highest brightness of the on-state is obtained, see Figure 3b. The curves shown in Figure 3 are used to indicate the transmittance of the on-state (upper curve) and off-state (lower curve) of the different wavelengths in the visible spectrum, respectively.

The second embodiment shown in Figures 4a and 4b will be described below. The configuration shown schematically in Figure 4a includes a twisted nematic layer with a 0.76 μm optical thickness twisted 240° to the right. The display is of the normal black type. In this mode, the off-state of the driven LC layer 5 is dark, while the on-state is bright. Although the embodiment described is a normal black mode, the configuration of the normal white mode can also be made. The aforementioned two retardation films 2, 3 are inserted between the polarizing plate 1 and the front substrate 7 described above. The film 3 having a thickness of 140 nm is combined with a polarizing plate to produce a circular polarized light. By adding a half-wavelength sheet 2 having a thickness of 280 nm in the middle, a wide-band quarter-wavelength sheet is created, resulting in a better overall dark state. The slow axis of the film 3 adjoining the substrate forms an angle of 30 with the vertical y-axis of the device. The half-wavelength sheet 2 forms an angle of 0 with the vertical y-axis. The absorption axis of the polarizing plate forms an angle of 120 with the vertical y-axis. LC layer 5 is converted to 315 nm (<img file="TWM250176U_D0002.tif" />1/2. λ). Above the rear substrate 8, a color filter layer that turns to the left is used. The best contrast ratio is obtained by using the display of the aforementioned configuration, see Figure 4b. The curves shown in Figure 4 are used to indicate the transmittance of the on-state (upper curve) and off-state (lower curve) of the different wavelengths in the visible spectrum, respectively.

According to a third embodiment of the present creation (not shown), the single super twisted nematic LC layer described above is replaced with two super twisted nematic LC layers having opposite twist directions. In this particular example, a first layer disposed adjacent to the polarizer includes a twisted nematic layer having a optical thickness of 0.75-0.85 μm (eg, 0.79 μm) twisted 230-250° (eg, 245°) to the right, A second layer disposed adjacent to the cholesteric color filter layer includes a twisted nematic layer having a 0.82 μm optical thickness twisted 240° to the left. However, there may be many other configurations as well. The display is of the normal black type. In this mode, the off-state of the driven LC layer 5 is dark, while the on-state is bright. Although the embodiment described is a normal black mode, it can also be made. Make a normal white mode configuration. The aforementioned two retardation films 2, 3 are inserted between the polarizing plate 1 and the front substrate 7 described above. The retardation film 3 having a thickness of 140 nm is combined with a polarizing plate to produce a circular polarized light. A wide frequency quarter wave plate is created by adding a half wavelength plate 2 having a thickness of 280 nm in the middle to produce a better overall dark state. The slow axis of the film 3 adjoining the substrate forms an angle of 40 with the vertical y-axis. The half-wavelength sheet 2 forms an angle of 12 with the vertical y-axis. The absorption axis of the polarizing plate forms an angle of 100° with the vertical y-axis. Above the rear substrate 8, a color filter layer that turns to the left is used.

The present teachings should not be considered limited to the embodiments described above, and all possible variations are covered by the fields defined by the scope of the appended claims. The combination of many twist angles and optical thickness is suitable for reflective STNs having a cholesteric color filter layer, which may be optimized for different uses in addition to those described above. Therefore, the creation is by no means limited to a twist angle of 240°. However, other configurations using different twist angles and optical thicknesses can also be combined with a cholesteric color filter layer to produce a normal black or normal white versatile reflective color display.

Moreover, it should be understood that the angles specified above, delays, and the like are not absolute and that a distance change of at least about 10% can be used.

<p>1. . . Polarizer</p><p>2. . . Half-wavelength</p><p>3. . . Quarter wave plate</p><p>4. . . Delay film</p><p>5. . . Liquid crystal layer</p><p>6. . . Reflective cholesterol color filter</p><p>7. . . Front substrate</p><p>8. . . Back substrate</p><p>9. . . Absorbing layer</p><p>10. . . First electrode layer</p><p>11. . . Second electrode layer</p><p>12. . . Positioning layer</p><p>13. . . Positioning layer</p><p>14. . . power supply</p>