JPH05341276A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide the liquid crystal display element having the high reliability to enable the element to withstand long-term use even if a high-luminance light source is used by obviating the degradation in a contrast ratio and the generation of nonuniformity by generation of heat and the deterioration of polarizing plates, a liquid crystal layer etc. CONSTITUTION:Since light transmissive ceramic is used for substrates 1, the heat diffusion and release within the liquid crystal display element are rapidly effected and, therefore, the temp. rise is suppressed. The deterioration of the polarizing plate 41, etc., is suppressed if the ceramics is used particularly for the substrate which is drastically deteriorated by heat and is stuck with the polarizing plate and, therefore, such use is effective. Namely, the heat generated in the polarizing plate 41, etc., is diffused into the liquid crystal display element and is released to the outside of the liquid crystal display element and, therefore, the temp. rise is suppressed even if light is made incident over a long period of time.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art Liquid crystal display devices are actively used as display devices for personal OA equipment such as Japanese word processors and desktop personal computers, and as image display devices for televisions and the like, by taking advantage of the features of thinness, light weight, and low power consumption. Has been.

Particularly, the projection type liquid crystal display device is a conventional CRT.
In recent years, development has been actively carried out because a large screen image that could not be realized with can be realized with a small device.

In the projection type liquid crystal display device, an active matrix type liquid crystal display element is mainly used. In this active matrix type liquid crystal display element, a scanning line and a signal line are provided on one of a pair of glass substrates facing each other so as to be orthogonal to each other, and a switching element and a pixel electrode are connected at each intersection thereof to form a switching element array. It is formed as a substrate, and the other glass substrate is provided with a common electrode and is formed as a counter substrate. As a switching element used as a means for driving and controlling each pixel, a thin film transistor (TFT), which is a semiconductor switch, is usually used because a transmissive display is possible and a large area is easy. Used.
A thin film transistor is a type of insulated gate field effect transistor, in which the gate is a scanning line, the drain is a signal line,
The source is connected to the pixel electrode.

When a scanning pulse is applied to the gate of the thin film transistor, the resistance between the source and the drain of the thin film transistor becomes low and the source and the drain become conductive, and the potential of the pixel electrode to which the source electrode is connected. Has the same potential as the signal line to which the drain electrode is connected at that time. When no pulse is applied to the gate,
A high resistance state is established between the source and the drain of the thin film transistor, and a non-conduction state is established between the source and the drain. Since the liquid crystal functions as a capacitor in an electric circuit, the potential difference between the pixel electrode and the electrode on the common substrate is maintained if the resistance of the thin film transistor and the liquid crystal is sufficiently high.

In addition to the above, the array substrate may be provided with a storage capacitor in order to sufficiently increase the discharge time constant of the capacitance of the liquid crystal serving as the load of the thin film transistor of each pixel. Usually, one end of the storage capacitor is connected to the pixel electrode and the other end is connected to the storage capacitor line.

The projection type liquid crystal display device has the above-mentioned TF.
A twisted nematic (TN) liquid crystal display element driven by T and having a positive dielectric anisotropy is used as a light valve to control the transmission of light from a light source provided on the back surface of the liquid crystal display element, and This is a device for projecting an image on a screen or the like for display via an optical system including a diloic mirror and a lens provided.

As liquid crystal display elements used in such a device, there are a total of three liquid crystal display elements, one for each of the colors corresponding to the three primary colors of light such as red (R), green (G) and blue (B). Is used as a valve.

As described above, the liquid crystal display element used in this projection type liquid crystal display device has a T having a positive dielectric anisotropy.
It has an N-type liquid crystal and two polarizing plates arranged so that their polarization axes are orthogonal to each other, and transmits light in a normal state where no voltage is applied to the liquid crystal cell. The one that uses the so-called normally white mode is the mainstream.

The contrast ratio of such a light-transmissive liquid crystal display element is determined by the ratio of the light transmittance when the voltage applied to the liquid crystal is on and when it is off. In the case of a normally white mode liquid crystal display element, the light transmittance becomes the light transmittance peculiar to the liquid crystal when the applied voltage is off, and the light transmittance decreases according to the applied voltage when the applied voltage is on, resulting in a dark display. In order to increase the contrast ratio, it is necessary to apply a high applied voltage to reduce the light transmittance of dark display.

However, the threshold voltage and the saturation voltage of the liquid crystal have unique values for each liquid crystal display element, and the liquid crystal display has a change in the transmittance caused by changing the value of the voltage applied to the liquid crystal. Since each element has its own limit, there is also a limit to increasing the contrast ratio by setting the applied voltage.

Therefore, in the conventional projection type liquid crystal display device, the brightness of the light source has been increased to obtain a bright and clear projected image, and a metal halide lamp or the like having a brightness of 10,000 lux to 30,000 lux, etc. Using the high brightness light source. Further, also in the direct-view type liquid crystal display device, there is a similar tendency to increase the brightness of such a light source.

[0013]

However, the brighter the light source, the more heat it generates, which causes various problems in practical use, which is a serious problem.

First, since the light from the light source is absorbed by the polarizing plate by about 50%, there is a problem that the polarizing plate is deteriorated by heat. In the case of a commonly used iodine-based polarizing plate, for example, in an environment of 65 ° C and 97% RH, the polarizing plate deteriorates after about 100 hours and its polarization rate decreases, and after about 400 hours, the polarization rate decreases. It will be almost zero.

The intensity of light emitted from the light source to the liquid crystal display element varies depending on the position of the liquid crystal display element on the screen due to the difference in the incident angle and the light path. The generated heat also becomes non-uniform, and as a result, the applied voltage-light transmittance characteristics of the liquid crystal display element become non-uniform within the screen of the same liquid crystal display element, and the contrast ratio becomes non-uniform.

In the conventional projection type liquid crystal display device, in order to suppress the above-mentioned adverse effects of heat, air cooling by attaching a cooling fan or cooling by a liquid flow system is performed, but both of them have the structure of the device. However, there is a problem that the contrast ratio varies within the same liquid crystal display element and the deterioration of the liquid crystal layer and the polarizing plate in the element does not occur. It was

The present invention has been made to solve such a problem, and an object thereof is to solve the problems of deterioration of contrast ratio and nonuniformity due to heat generation and deterioration of polarizing plate, liquid crystal layer and the like. Therefore, it is an object of the present invention to provide a liquid crystal display element having high reliability that can be used for a long time even when a light source of high brightness is used.

[0018]

A liquid crystal display device according to the present invention comprises a pair of transparent substrates, at least one of which is transparent, and a liquid crystal layer sandwiched between the pair of substrates. In the above, at least one of the pair of substrates is made of translucent ceramics.

As the above-mentioned translucent ceramics, those having higher thermal conductivity are preferable, and the value thereof is 10 W /
It is preferably mK or more. As a translucent ceramic material satisfying such conditions, specifically, Y ₂ O is used.
₃ , PLZT, MgAl ₂ O ₄ , sapphire, BeO,
ThO ₂ , MgF, CaF ₂ , ZnS, ZnCe, Lu
calox (product of GE) and the like are preferable.

[0020]

The transmissive ceramic has a higher thermal conductivity than that of the glass used as the transparent substrate of the conventional liquid crystal display element, and has a higher thermal diffusion efficiency. Since the liquid crystal display element of the present invention uses the transparent ceramics on at least one of the substrates,
Since the heat diffusion and the heat release in the liquid crystal display element are performed quickly, the temperature rise can be suppressed. In particular, when it is used for a substrate on which a polarizing plate, which has been a serious problem of deterioration due to heat, is attached, the deterioration of the polarizing plate can be suppressed, which is more effective. That is, since the heat generated by the polarizing plate and the like diffuses into the liquid crystal display element and is emitted to the outside of the liquid crystal display element, the temperature rise can be suppressed even if light is incident for a long time. Therefore, deterioration of the polarizing plate can be prevented, and the voltage-light transmittance characteristics within the same panel become uniform, and problems such as deterioration and nonuniformity of the contrast ratio and deterioration of the liquid crystal layer and the like are solved.

[0021]

Embodiments of the liquid crystal display device according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a plan view showing the structure of an array substrate 100 of a liquid crystal display device according to an embodiment of the present invention, and FIG.
It is a -B sectional view. This liquid crystal display element is an array substrate 1
00, the counter substrate 200, and the liquid crystal layer 300 sandwiched between the array substrate 100 and the counter substrate 200.

First, the array substrate 100 will be described. The substrate 1 is a substrate made of translucent ceramics such as Y ₂ O ₃ . On this substrate 1, a pixel electrode 3 made of ITO, a thin film transistor (hereinafter abbreviated as TFT) 5 using amorphous silicon, and a signal storage capacitance line 7 made of metal such as MoTa are formed. TFT5 is Mo
A gate electrode 9, a drain electrode 11, and a source electrode 13, which are made of a metal such as Ta, Al, and Mo, SiO _x 15, SiN _x 17 as an insulating film, a semiconductor film 19 made of amorphous silicon, and low-resistance semiconductor films 21 and 23. ,
The etching stopper 25 constitutes the main part, and the upper part thereof is covered with an insulating film 27 made of SiN _x . Further, an alignment film 29 made of polyimide is formed so as to cover the entire surface of the array substrate 100 facing the liquid crystal layer.

On the other hand, the counter substrate 200 is a glass substrate 31.
A light-shielding film 33 made of a metal such as Cr, a color filter 35 having predetermined R (red), G (green), and B (blue) formed for each pixel, a common electrode 37 made of ITO, and an alignment made of polyimide. The film 39 is formed in order. Further, the polarizing plate 41 is provided on the surface opposite to the surface on which the array of the TFTs 5 is provided, and the polarizing plate 41 is provided on the surface opposite to the surface on which the common electrode 37 of the counter substrate is provided. On the other hand, a polarizing plate 43 is attached so that the angle formed by the polarization directions is 90 degrees. Such array substrate 100 and counter substrate 20
The liquid crystal layer 300 is sandwiched in the space between the liquid crystal layer 300 and zero.

As for the structure of the TFT 5, as shown in FIG. 1, the gate electrode 9 is the address line 45 and the drain electrode 11 is
Is connected to the signal line 47, and the source electrode 13 is connected to the pixel electrode 3. SiO _x 15, Si as insulating film
N _x 17 is formed so as to cover the gate electrode 9 of the TFT 5 and the address line 45.

This liquid crystal display device was manufactured as follows.

Sumitomo Electric Y ₂ O ₃ (Average grain size
100μm, thermal conductivity 15.4W / mK) Thickness 0.6mm above,
A MoTa film was formed by sputtering, and the gate electrode 9, the signal storage capacitance line 7, and the address line 45 were formed by photolithography.

Next, SiO _x , SiN _x , a-Si, Si
Each film of N _x is formed by a CVD method and formed into a predetermined pattern by photolithography, and SiO _x 15 and SiN _x 17 as a gate insulating film and the semiconductor layer 1 are formed, respectively.
9, the etching stopper 25 was obtained. The n ⁺ a-Si film was formed by CVD, and the low resistance semiconductor films 21 and 23 were formed by photolithography.

Next, an ITO film was formed by sputtering and then patterned by photolithography to obtain a pixel electrode 3. Further, Mo and Al are formed by sputtering and photolithography to obtain the drain electrode 11 and the source electrode 13, and a SiN _x film is formed by the CVD method to form the insulating film 2.
It was set to 7. In this way, the signal line 47 and the address line 4
5 was formed in a matrix, and an array substrate 100 having 100 pixels vertically and 100 pixels in total was produced.

Next, a polyimide thin film was formed on the surface of the array substrate 100 facing the liquid crystal layer 300, and then rubbing treatment was performed to form an alignment film 29.

On the other hand, the counter substrate 200 is the glass substrate 31.
Cr was formed thereon by sputtering and photolithography to form a light-shielding film 33, and a color filter 35 having predetermined R, G, and B formed on each pixel was formed. An ITO film was formed on almost the entire surface by sputtering to obtain a common electrode 37.
After forming a polyimide thin film on this, rubbing treatment was performed to form an alignment film 39. After this, the counter substrate 20
An epoxy-based adhesive as an adhesive was printed along the periphery of the alignment film 39 of No. 0 except the injection port (not shown).

Next, micropearls having a particle size of 6 μm manufactured by Sekisui Fine Chemical Co., Ltd. were sprayed on the surface of the counter substrate 200 as a gap material (not shown). Next, the array substrate 100 and the counter substrate 200 were arranged so that the alignment films 29 and 39 were opposed to each other and the rubbing directions were 90 degrees, and the adhesive was cured by heating to bond them together.

Next, as the liquid crystal layer 300, ZLI-1565 is used.
A liquid crystal composition obtained by adding 0.1 wt% of S811 to (E. Merck Co., Ltd.) was injected from an injection port by a usual method, and then the injection port was sealed with an ultraviolet curable resin.

After that, the polarizing plates 41 and 43 were attached to the array substrate 100 and the counter substrate 200, and the short ring (not shown) on the surface of the array substrate 100 was cut off to manufacture an active matrix liquid crystal display element. In addition, Sumitomo Electric Y ₂ O ₃ (average grain size 3μ
m, thermal conductivity 15.1 W / mK), and the same MgAl ₂ O ₃ (thermal conductivity 16.9 W / mK) were used.

When an active matrix type liquid crystal display element as described above was used as a light valve and a metal halide lamp was used as a light source for continuous display for 100 hours, the contrast ratio was 60, which remained at such a high value. I was able to maintain.

On the other hand, as a comparative example, the array substrate 10 is used.
A glass (heat conductivity 1.1 W / mK) was used for the substrate of No. 0, and a liquid crystal display element similar to the liquid crystal display element of this example was manufactured in other configurations, and 100-hour continuous display similar to the above was performed. After about 3 hours, the center of the screen was bright and the periphery was dark. This is because the voltage-transmittance changes due to the heat accumulated in the glass substrate due to the light from the light source and the radiant heat, and the contrast characteristics are spatially nonuniform within the screen of the liquid crystal display element.

The present invention is not limited to the above-mentioned embodiment, and as the translucent ceramic substrate, other than this, sapphire, PLZT, sapphire, BeO,
ThO ₂ , MgF, CaF ₂ , ZnS, ZnCe, Lu
calox (product of GE) or the like may be used, and a translucent ceramic may be used for the counter substrate.

Further, translucent ceramics may be used as the substrate for the polarizing plate. That is, the substrate 1 may be a substrate formed by stacking two thin plate substrates, and one of the thin plate substrates may be made of translucent ceramic, and the polarizing film may be attached to the surface thereof. In this way, the formation of the polarizing plate and the formation of the TFT can be separated. Further, as described below, two thin plate substrates may be arranged so as to have a predetermined gap, and a cooling liquid may be caused to flow in the gap for more effective cooling. An example of such a liquid crystal display device is shown below.

First, the color filter 35 and the polarizing plate 4
A projector corresponding to R, G, and B is formed by forming three liquid crystal display elements similar to those in the first embodiment except that Nos. 1 and 43 are not formed on the counter substrate. And a liquid crystal display device.

Next, an iodine-based polarizing plate manufactured by Kayapora Co., Ltd. was used as a thin substrate on Y ₂ O ₃ (average grain size 100 μm, thermal conductivity 15.4 W / mK) manufactured by Sumitomo Electric Industries, with an adhesive layer interposed. It was stuck and used as a polarizing plate. This polarizing plate
For example, by arranging the liquid crystal display device at a distance of 0.3 mm from the above-mentioned liquid crystal display device, and by making a fluid such as a liquid such as water or a gas such as air flow through the gap, a polarizing plate and a liquid crystal display A liquid crystal display device having a structure for cooling the element was manufactured.

When a projector was manufactured using this liquid crystal display device, deterioration of the polarizing plate was not recognized even after 10,000 hours. A metal halide lamp was used as the light source. On the other hand, as a comparative example, when a projector similar to the above was manufactured except that the polarizing plate was formed on a glass plate, the polarization rate of the polarizing plate dropped after 1000 hours, and the polarization rate was almost zero after 2000 hours. Became.

In addition to the above, the present invention is also suitable for a liquid crystal display element integrated with a driving circuit using a p-SiTFT. By applying the technique of the present invention to a liquid crystal display element integrated with a drive circuit using a p-SiTFT, it can be said that it is extremely effective because not only the display portion but also the drive circuit portion can be prevented from accumulating heat.

[0043]

As is apparent from the above detailed description, the liquid crystal display device of the present invention solves the problems of deterioration of the contrast ratio and nonuniformity due to heat generation and deterioration of the polarizing plate, liquid crystal layer and the like. Thus, the liquid crystal display element has high reliability that can withstand long-time use even with a high-luminance light source.

[Brief description of drawings]

FIG. 1 is a plan view showing a structure of a liquid crystal display element according to the present invention.

FIG. 2 is a sectional view showing the structure of a liquid crystal display element according to the present invention.

[Explanation of symbols]

1 ... Substrate, 31 ... Glass substrate, 41, 43 ... Polarizing plate, 1
00 ... Array substrate, 200 ... Counter substrate, 300 ... Liquid crystal layer

Claims (1)

[Claims] 1. A liquid crystal display device comprising a pair of substrates, at least one of which is transparent and opposed to each other, and a liquid crystal layer sandwiched between the pair of substrates, wherein at least one of the pair of substrates is transparent. A liquid crystal display device comprising a photo-ceramic.