JPH1152364A - Reflective liquid crystal display - Google Patents

Abstract

(57) [Problem] To provide a reflection type liquid crystal display element having a high aperture ratio, a high brightness, a high contrast, a high display quality, and a multi-gradation / multi-color display with good color purity. SOLUTION: A transparent first insulating substrate provided on a light incident side and having a pixel electrode and a driving circuit formed thereon, and a light reflecting layer and / or a color filter layer provided on the other surface and facing A reflective liquid crystal display device having a second insulating substrate on which electrodes are formed, and a dimming layer in which liquid crystal is sandwiched between the first and second insulating substrates, wherein On the light control layer side, a low reflection film, an insulating film, and a drive electrode are arranged in this order from the light incident side, and further, a pixel electrode is arranged in an opening of the low reflection film.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display device which is of a direct viewing type and does not use a backlight.
More specifically, office automation equipment such as notebook personal computers and word processors, personal use information equipment such as portable information terminals,
The present invention relates to a reflective liquid crystal display device suitable for various video information devices, game devices, and the like.

[0002]

2. Description of the Related Art In recent years, there has been a demand for the development of a full-color display and a multi-gradation / multi-color display in accordance with the type of information to be displayed, the sophistication of the content, and the increase in the number of functions. Further, even in a reflection type liquid crystal display device which has been attracting attention as a light weight, thin and low power consumption liquid crystal display device, a multi-grayscale / multi-color display is realized, while taking advantage of its low power consumption. It can be applied to a wide range of product fields.

[0003] For example, in a reflection type liquid crystal display in which multi-gradation and multi-color display can be performed by an active element such as a TFT or MIM, an organic insulating film is applied on an active driving element, and a smooth uneven surface is formed thereon. A reflection type liquid crystal display device and the like in which a phase change type guest-host liquid crystal is sandwiched between an insulating substrate formed with a reflection electrode having a transparent electrode and an opposite side substrate formed with a transparent electrode and an absorption type color filter have been developed. (S. Mitui, Y. Shiamada et al., SID'92 pp437-44
0). A so-called single-polarizer type, in which a twisted nematic liquid crystal is used as the dimming layer, a phase compensator and a polarizer are arranged on the light-incident side substrate of the liquid crystal element, and the response due to voltage application is detected by the polarizer. TN mode has also been developed (E. Sakai, H. Nakamura, K. Yoshida, Y. Ugai,
Hoshiden IDW'96 pp329-332). In these reflective liquid crystal display devices, usually, a light absorbing color filter is arranged on an insulating substrate on the light incident side, and a light reflecting film is formed on the substrate on the opposite side via an active element and an organic insulating film. ing.

[0004] In the case of the single-sheet polarizer type TN device, light incident through the polarizer and the optical phase compensator passes through the absorption type color filter layer and the liquid crystal light control layer and then to the light reflection film. The light is again reflected, passes through the liquid crystal layer, the absorption type color filter layer, and the optical phase compensator, and is detected by the polarizer. That is, when a voltage is applied to the liquid crystal layer,
Since the alignment state of the liquid crystal molecules changes and the light that has passed through the liquid crystal changes in accordance with the change, the light intensity detected by the polarizer changes to enable multi-gradation display. Further, multicolor display is possible by installing RGB three primary color absorption type color filters between the light passage paths.

In the liquid crystal display mode using a guest-host liquid crystal in which a dichroic dye is added to a liquid crystal as the dimming layer, the dichroic property in which the alignment direction changes with the alignment of the liquid crystal in the electric field direction. Since light absorption and transmission by the dye are used, the above-described polarizer and optical phase compensator are not required, and a bright display can be achieved in principle.

Furthermore, as a reflective type color liquid crystal element capable of brighter multi-gradation and multi-color display, separation of the three primary colors of RGB utilizing multiple interference by laminating two types of dielectric thin films having different refractive indices. Japanese Patent Application Laid-Open No. 7-287115 also discloses a bright reflective color liquid crystal display device having a high light use efficiency by using a reflective color filter for performing the above.

[0007]

However, in the case of display using the above-mentioned light-absorbing color filter, light passes through the color filter twice, so that the light use efficiency is reduced. Further, when the transmittance of the color filter is improved in order to increase the light use efficiency, there is a problem that the color purity is reduced. In addition, in the display using a polarizer, the display is further darkened because light is absorbed by the polarizer. That is, in order to realize a reflective color liquid crystal display device capable of multi-tone and multi-color display, display using a multi-interference micro color filter using a dielectric mirror or the like is advantageous as a bright display device. It is desirable to use an active driving element such as a TFT element for driving.

For example, a dichroic mirror used as a dielectric mirror has a multilayer structure of dielectric thin films having different refractive indexes, and it is necessary to increase the number of layers in order to increase the reflection wavelength width and improve the reflection efficiency. And its film thickness is 2
About 4 μm is required. Therefore, the dielectric mirror is set to T
It is difficult to form active elements such as FT elements on the same substrate. Also, in consideration of the problem of parallax such as double reflection of characters on the display surface, it is desirable to arrange a reflection type color filter using a dielectric mirror inside the liquid crystal element.

When a display element is formed using a reflective color filter having a multilayer structure of an active element such as a TFT element and a dielectric thin film, a transparent insulating substrate on which an active driving element is formed is placed on the light incident side, and the substrate is placed on the transparent insulating substrate. It is necessary to arrange an insulating substrate on which a dielectric mirror is formed on the opposite side of the substrate. In that case, the light incident on the liquid crystal element is Al,
The light is reflected by the active drive element made of a metal film having a relatively high reflectivity such as Ta or Ti, the signal wiring and the scanning wiring connected thereto, and the surface of the auxiliary capacitor section.

When the TFT element is an active driving element, the area ratio of the signal wiring, the scanning wiring, the driving element, and the auxiliary capacitor part in one pixel is required to be about 15 to 20%, and the reflection utilizing the reflection of ambient light is required. In the case of the type display device, the reflection of the above-mentioned portion causes a significant decrease in visibility. In addition, when used in places with high ambient light illuminance, such as outdoors, the reflection of light from the above-mentioned driving parts greatly reduces color purity and visibility, so a reflective liquid crystal display element for multicolor color display. Is a fatal problem.

The present invention has been made in order to solve the above-mentioned problem, and is a high-quality reflective liquid crystal display element aiming at full-color display.
It is an object of the present invention to obtain a reflective display element capable of multicolor display and having good visibility.

[0012]

In order to achieve the above object, a reflection type liquid crystal display element according to the present invention is provided on a light incident side, and is provided with a pixel electrode and a driving circuit. A first insulating substrate, a second insulating substrate disposed on the other surface and having a light reflecting layer and / or a color filter layer and a counter electrode formed thereon, and a first and a second insulating substrate A reflection type liquid crystal display device having a light control layer having a liquid crystal interposed therebetween, comprising a low reflection film, an insulation film, and a drive electrode on the first insulating substrate and on the light control layer side from the light incident side. The pixel electrodes are arranged in this order, and the pixel electrodes are arranged in the openings of the low reflection film.

With this configuration, the active driving element, the signal wiring, the scanning wiring, and the transparent substrate on the light incident side (observer side) are formed on the low reflection film (so-called black matrix) via the inorganic insulating film. A driving circuit such as an auxiliary capacitor can be provided, reflection of ambient light on the surface of the driving element and the driving circuit portion can be suppressed, and visibility such as contrast and color purity can be improved.

Preferably, the low-reflection film disposed on the first insulating substrate is an organic resin film mixed with a black pigment or a black dye, a multilayer metal film, a metal oxide film, or the like. It is a film formed by at least one of the films.

By using an organic resin film as the low reflection film in this manner, it is possible to form a film by a relatively simple and inexpensive method such as spin coating or roll coating, and to simplify the process. it can. further,
By using a multilayer metal film, it is possible to further reduce the reflection. In addition, by using a metal oxide film, it can be manufactured with a small film thickness, and it becomes possible to planarize the surface unevenness of the TFT substrate surface.

Preferably, as set forth in claim 3, a reflection type color filter or a holographic color filter of an organic resin, which is disposed on the second insulating substrate and has a multilayer structure of dielectric thin films having different refractive indices. Wherein the light reflection layer and the color filter layer are formed.

Preferably, the surface of the light reflection layer disposed on the second insulating substrate is a metal reflection film having a flat mirror surface or smooth irregularities. And

The reflection type liquid crystal display device according to claim 5, wherein at least one polarizing plate is arranged on the light incident side of the reflection type liquid crystal display device, and the nematic liquid crystal is twist-aligned between the substrates. The light control layer is characterized in that a good contrast is obtained and the gradation display is easy.

Further, according to the present invention, there is provided a reflection type liquid crystal display element, wherein a light control layer utilizing light scattering and light transmission comprising a mixture of a liquid crystal and a polymer or a liquid crystalline polymer is provided between the substrates. Alternatively, it is a light control layer using a guest-host phase change type liquid crystal to which a dichroic dye is added. The light control layer enables a brighter display due to light scattering or the need for a polarizing plate.

Preferably, as set forth in claim 7, at least one optical phase compensation member is disposed between the polarizing plate according to claim 5 and the light control layer. Thereby, a better contrast can be obtained as compared with the configuration related to only the polarizer.

Preferably, a light scattering optical member is disposed on the light incident side of the reflection type liquid crystal display element. The light scattering effect can be given to the observer, and the visibility can be improved.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to the drawings. <Embodiment 1> In this embodiment, a reflection type liquid crystal display element using a TFT element as an active drive element and a phase change type guest-host liquid crystal added with a dichroic dye as a dimming layer will be described. FIG. 1 is a schematic cross-sectional view of the liquid crystal display element, and FIG. 2 is an enlarged view of a driving element portion.

First, a CrOx (chromium oxide) film 12 is formed as a low-reflection film on a transparent insulating substrate 11 so as to have a thickness of about 200 °, and photolithography using a resist and etching with hydrofluoric acid are performed. By the processing, a pattern having a shape with a matrix-shaped opening was formed. The CrOx film can be formed by sputtering using chromium oxide as a target or by depositing chromium oxide. Further, in a sputtering method using Cr as a target, an oxidation reaction is caused by supplying an oxygen gas at a predetermined flow rate and pressure at the time of vapor deposition of Cr, and a CrOx
It can also be formed as a film. Although any of the above methods can be used, the formed CrOx film is made of CrO ₂ , Cr ₂ O ₅ , C
r ₅ O ₁₂ shows black, Cr ₂ O ₅ shows dark green, CrO ₅
In the blue color. In the case of a reflection type liquid crystal display element utilizing the reflection of ambient light, the color of the low reflection film is desirably a color close to an achromatic color like a black matrix.

The thickness of the low reflection film varies depending on what material is used.
The rOx film may have a thickness of 200 to 1000 °. For example, an organic resin film such as an acrylic resin film, a polycarbonate resin, or a polyimide resin containing carbon particles may have a thickness of about 1 μm. The reflectance should be set appropriately so as to obtain a reflectance of preferably 3% (Y value) or less in a wavelength range of 380 to 780 nm.

Next, as the insulating film 13, a SiO ₂ film is
A film was formed so as to have a thickness of 2,000 mm, and a TFT element 16 was formed thereon by a usual method. Further, the IT device is connected to one terminal (drain terminal) of the TFT element.
After an O film (thickness 3000 °) is formed by sputtering, patterning is performed, and then an ultraviolet curable acrylic resin 18 is formed on the TFT element and the ITO film by spin coating so as to have a thickness of about 3 μm. did. After the resin was cured by ultraviolet irradiation, a contact hole for connecting the transparent pixel electrode and the TFT element was formed in the acrylic resin by patterning.

On the acrylic resin, an ITO (indium tin oxide) film 17 was formed by sputtering to a film thickness of about 3000 °, and was patterned into a pixel shape. This pixel is patterned with a gap of 3 μm between adjacent pixels to prevent leakage between pixels. However, it is necessary for the conventional TFT element having no interlayer film made of acrylic resin to reduce the stray capacitance accumulated between the wiring and the pixel electrode which causes signal delay and disturbance of liquid crystal molecular alignment. In the element structure according to the present embodiment, a gap of about 3 μm in the horizontal direction between the signal wiring and the scanning wiring is provided in the vertical direction by the thickness of the acrylic resin.
The shape of the pixel electrode can be designed to overlap the signal wiring and the scanning wiring. Therefore, the gap between the wiring and the pixel electrode is theoretically unnecessary, and the TFT element substrate according to the present invention has a high aperture ratio of about 85%.

Next, a Si film 22 is formed as a light absorbing layer on the insulating substrate 21 on the opposite side, and SiO ₂ (refractive index n = 1.4) and TiO ₂ (n = 2.4) are formed thereon. The specific wavelength reflection type color filter 23 having a multilayer structure of two types of metal oxide films having different refractive indices of (1) and (2) is formed into pixels so as to have reflection spectra of RGB primary colors. On the color filter, an ITO film 24 was formed by sputtering to a film thickness of about 3000 ° to form a common electrode.

Each of the TFT element substrate 11 and the color filter substrate 21 has a polyimide alignment film (Sun Ever 15).
0: manufactured by Nissan Chemical Industries, Ltd.) was applied by spin coating to a film thickness of about 600 ° and baked to form a film.

Next, a rubbing treatment is applied to each substrate so that the liquid crystal molecules are twist-aligned, and the gap material (PB-
45: made by Nippon Electric Glass Co., Ltd., and bonded together via a thermosetting sealing material (Struct Bond: made by Mitsui Toatsu Chemicals) to produce a liquid crystal cell having a cell thickness of 4.5 μm. As a mixture to be sealed in a liquid crystal cell, a liquid crystal (ZLI23)
2: a dichroic dye (S-497, M-61) mixed with 4.5% by weight of a chiral substance (manufactured by Merck) and liquid crystal with respect to the liquid crystal to give a black color.
8, Y-710: manufactured by Mitsui Toatsu)
The solution dissolved by weight% was injected into a liquid crystal cell by a vacuum injection method.

When no electric field is applied, the reflection type liquid crystal panel obtained in this way looks black due to absorption of dichroic dyes. When an electric field of an effective voltage of about 5 V is applied to all the pixels, the liquid crystal molecules and the dichroic dye molecules rise in the direction of the electric field, and the light from the dichroic mirror on the opposing substrate is reflected and looks bright. However, since the dichroic mirror is basically a mirror, the visibility as a display element is poor as it is. In the present embodiment, the performance as a display element was confirmed by disposing a scattering film in which fine particles were dispersed in a resin on a substrate on the light incident side.

As shown in FIG. 3, CrOx in the present embodiment has a visible sensitivity within a wavelength range of 380 to 780 nm.
Since it is about 5% to 3% (Y value), and the reflection of ambient light on the wiring and the driving element can be greatly reduced, the phenomenon that the display becomes whitish due to the reflection on the wiring surface during black display is suppressed.
It was found that the contrast could be improved.

In this embodiment, CrOx is used as the low reflection film formed on the TFT element substrate. However, a metal oxide film such as TaN, a metal nitride film, or an acrylic organic resin to which a black pigment or a black dye is added is also used. The same effect was obtained. However, a metal film is preferable in terms of reflectance and film thickness, and CrOx is most preferable in terms of reflectance.

FIG. 4 shows the reflection spectrum characteristics of the red, green, and blue colors in the bright state (ON state) of the liquid crystal panel according to the present embodiment. FIG. 5 shows, as a comparative example, a low reflection on the TFT substrate. 9 shows reflection spectrum characteristics of red, green, and blue in a bright state (ON state) of the liquid crystal panel when no liquid crystal panel is provided.
As can be seen from a comparison between FIG. 4 and FIG. 5, in FIG. 5, the reflection of the bus line and the metal film of the element portion causes extra reflection in the spectrum of each color of RGB, which causes a decrease in color purity. all right. That is, according to the present embodiment, the color purity is greatly improved.

FIG. 6 is a CIE chromaticity diagram showing the color reproduction area of each of the liquid crystal panels according to FIGS. 4 and 5. According to this result, it was found that the liquid crystal panel provided with the low-reflection film has a larger triangle representing the color reproduction area, which is about twice as large as the liquid crystal panel without the low-reflection film.

<Second Embodiment> Next, as a second embodiment of the present invention, FIG. 7 is a schematic cross-sectional view of a reflection type liquid crystal display device using an MIM device as an active device, and FIG. As shown in FIG. First, as in the first embodiment,
Low reflection film 1 made of CrOx on transparent insulating substrate 11
2 was created. Next, an insulating film is formed of SiO ₂ 13 so as to have a thickness of 3000 °, and an MIM element 31 is formed thereon by an ordinary method.

Next, as in the first embodiment, a UV-curable acrylic resin 18 is formed by spin coating to a thickness of 1 μm. After the resin was cured by ultraviolet irradiation, a contact hole for connecting the transparent pixel electrode and the MIM element was opened in the acrylic resin by patterning. On this resin, an ITO (indium tin oxide) film 1
7 was formed by sputtering at a film thickness of about 3000 °, and was patterned into a pixel shape.

On the counter substrate 21 side, as in the first embodiment, the Si film 22 and the RGB reflection color filter layer 23 are formed.
Was formed, and an ITO film 24 was formed thereon, followed by patterning to form a pixel electrode. A polyimide-based alignment film (San Eva 150: manufactured by Nissan Chemical Industries, Ltd.) 19 is spin-coated on the element substrate and the counter substrate at a film thickness of 600 ° to form a film.
After performing a rubbing treatment so that the liquid crystal cell is twisted, a gap material (PB-45: manufactured by Nippon Electric Glass Co., Ltd.) is sprayed, and bonded via a sealing material (Struct Bond: manufactured by Mitsui Toatsu Chemicals) to form a liquid crystal cell. Created. The same liquid crystal material and dichroic dye material as those used in Embodiment 1 were used for injection.

The reflection type liquid crystal display device using the MIM device manufactured as described above was able to suppress the reflected light at the signal data line and the drive element portion. The contrast (reflectance in the case of white display / reflectance in the case of black display) was 4 when the wiring portion did not have a low reflection film, but the contrast was improved to 5.5 by providing a black matrix. I was able to.

In the present invention, a phase-transition type guest-host liquid crystal to which a dichroic dye is added is used as a liquid crystal mode. However, a twist nematic liquid crystal is used as another dimming layer, and one sheet is formed on an incident side substrate. A single polarizer type TN mode having a polarizer, or a PDLC (Polymer Disper) using a liquid crystal and a polymer or a liquid crystalline polymer as a light control layer.
It is needless to say that the present invention can be applied to a reflective liquid crystal display device using a second liquid crystal (second liquid crystal) mode or the like.

[0040]

As described above, according to the present invention, an element substrate having an active driving element formed on the light incident side (observer side) is provided on the opposite side, and multiple interference reflection is performed by a multilayer structure of a dielectric thin film on the opposite side. In the reflection type liquid crystal display device with a configuration in which a color filter is arranged, the drive element, signal wiring, scanning wiring, auxiliary capacitor, etc. on the element substrate are formed under a low reflection film (as viewed from the observer side). Thus, the reflection type liquid crystal display device of high display quality can be obtained by eliminating the so-called reflection due to ambient light, improving the contrast and improving the color purity.

[Brief description of the drawings]

FIG. 1 is a structural sectional view of a liquid crystal display element according to a first embodiment.

FIG. 2 is a structural sectional view of a driving element unit according to the first embodiment.

FIG. 3 is a graph (based on Al) of a spectral reflection characteristic of the low-reflection CrOx film according to the first embodiment.

FIG. 4 is a reflection spectrum characteristic diagram of each color of red, green, and blue in a bright state (ON state) of the liquid crystal panel according to the first embodiment.

FIG. 5 is a reflection spectrum characteristic diagram of each color of red, green, and blue in a bright state (ON state) of a liquid crystal panel according to a comparative example in which a TFT substrate is not provided with low reflection.

6 is a CIE chromaticity diagram showing a color reproduction area of each of the liquid crystal panels according to FIGS. 4 and 5. FIG.

FIG. 7 is a structural cross-sectional view of a liquid crystal display element according to a second embodiment.

FIG. 8 is a structural sectional view of a driving element section according to the second embodiment.

[Explanation of symbols]

 11, 21 Insulating substrate 12 Low-reflection black matrix 13 Inorganic insulating film 14 Scan wiring 15 Auxiliary capacitor 16 TFT drive element 17 Pixel electrode 18 Acrylic resin film 19 Alignment film 22 Light absorbing layer 23 Reflective color filter layer (RGB) 24 Counter electrode REFERENCE SIGNS LIST 31 MIM drive element 32 scanning wiring 33 inorganic insulating film 41 liquid crystal layer 42 liquid crystal

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification code FI G02F 1/137 500 G02B 1/10 A

Claims (8)

[Claims] 1. A transparent first insulating substrate disposed on a light incident side and having a pixel electrode and a driving circuit formed thereon, and a light reflecting layer and / or a color filter layer disposed on another surface and disposed on the other surface. A reflective liquid crystal display device comprising: a second insulating substrate on which a counter electrode is formed; and a light control layer having a liquid crystal sandwiched between the first and second insulating substrates, wherein the first insulating substrate is provided. On the light control layer side, a low reflection film, an insulating film, and a drive electrode are arranged in this order from the light incident side, and further, a pixel electrode is arranged in an opening of the low reflection film. Liquid crystal display element. 2. The method according to claim 1, wherein the low-reflection film disposed on the first insulating substrate is at least one of an organic resin film mixed with a black pigment or a black dye, a multilayer metal film, and a metal oxide film.
2. The reflection type liquid crystal display device according to claim 1, wherein the reflection type liquid crystal display device is a film formed by one of the above. 3. The light reflection layer and the color filter provided by a reflection type color filter having a multilayer structure of dielectric thin films having different refractive indices and being disposed on the second insulating substrate or a holographic color filter of an organic resin. 2. The reflective liquid crystal display device according to claim 1, wherein a layer is formed. 4. The reflection type according to claim 1, wherein the surface of the light reflection layer disposed on the second insulating substrate is a metal reflection film having a flat mirror surface or smooth irregularities. Liquid crystal display element. 5. The light-modulating layer according to claim 1, wherein at least one polarizing plate is disposed on the light incident side of the reflective liquid crystal display element, and a nematic liquid crystal having a twist orientation is sandwiched between the substrates. A reflective liquid crystal display device according to any one of the above. 6. A light-modulating layer made of a mixture of a liquid crystal and a polymer or a liquid crystalline polymer between the substrates using light scattering and light transmission, or a guest-host phase transition type liquid crystal to which a dichroic dye is added. The reflective liquid crystal display element according to claim 1, wherein the reflective liquid crystal display element is a light control layer using 7. A reflection type liquid crystal display device comprising at least one optical phase compensation member disposed between the polarizing plate according to claim 5 and a light control layer. 8. A light scattering optical member is arranged on a light incident side of the reflection type liquid crystal display element.
5. The reflective liquid crystal display device according to any one of items 1 to 4.