JPH0682786A - Liquid crystal display element and its manufacture - Google Patents

Abstract

PURPOSE:To enhance the aperture ratio of a picture element part and provide a wide visual angle by differing the pretilt angle of a liquid crystal between two opposed bases. CONSTITUTION:Onto a color filter base having color filter 2 of RGB and black matrix 3 arranged on a glass base 1 and a counter electrode 4 formed thereon, a polyimide the liquid crystal of which shows a pretilt angle of 1 deg. is applied by printing, and rubbed after heating. To a TFT base having picture element electrode 11 and TFT 12 arranged on the glass base 1, a polyimide the liquid crystal of which shows a pretilt angle of 4 deg. is applied, and rubbed after heating. These color filter base and TFT base are continued to each other by a transfer 6, and superposed with keeping a determined gap by use of a seal material 8. Since the pretilt angle of the liquid crystal on one base side is differed from the pretilt angle of the liquid crystal of the opposed base, progress of disclination can be suppressed.

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 and a manufacturing method thereof, and more particularly to an active matrix liquid crystal display device and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, color display technology using liquid crystals has become popular.
It has been put to practical use in various fields such as LCD TVs, large-screen projectors, personal computers, and car navigation systems. In order to realize a higher-definition color display device using liquid crystal, it is necessary to consider the aperture ratio, the contrast and the viewing angle of the display unit so that disclination does not occur in the display unit. For that purpose, control of the pretilt angle of the liquid crystal becomes important.

In a conventional liquid crystal display device, a color filter 2 and a black matrix 3 are arranged on a glass substrate 1 as shown in FIG. 2, and an ITO (Indium Tin) is formed thereon.
TFT 1 on a color filter (CF) substrate and a glass substrate 1 on which a counter electrode 4 typified by an oxide is formed.
2 is formed on the TFT substrate on which the pixel electrode 11 and the pixel electrode 11 are arranged by rubbing treatment as an alignment film 5, and a liquid crystal is sandwiched between the substrates with a sealing material 8 keeping a gap of 5 to 10 μm. There is. The liquid crystal molecules 9 at the interface between the alignment film 5 and the liquid crystal 7 at this time have a molecular alignment that maintains a certain angle (pretilt angle) with the plane of the alignment film 5. The pretilt angle is the same for both substrates and is 2 ° in the example of FIG.

The pretilt angle of the liquid crystal is pre-im.
In the case of the ide type alignment film, the solvent is removed by heating to form a polyimide, and then a rubbing treatment is performed, and a polyimide is formed by baking like an imidation type alignment film, and then a rubbing treatment is performed. Two methods are commonly used, which are obtained by rubbing.

[0005]

In the conventional liquid crystal display element, in order to prevent the disclination line from appearing in the pixel area, the black matrix is used to shield the light, thereby suppressing the deterioration of contrast and the occurrence of display defects. However, as the screen size of the display unit and the projection size of the projector are increased, higher definition is required, and therefore it is necessary to improve the aperture ratio and reduce the visual dependency of contrast. However, when the aperture ratio of the pixel portion is increased, disclination appears, so that there is a problem that the contrast is lowered and a display defect occurs. In order to solve this problem, it is effective to increase the pretilt angle of the liquid crystal, but if it is too high, another problem that the visual dependence of the contrast becomes large (viewing angle reduction) occurs. Therefore, it is difficult to suppress the occurrence of disclination, increase the aperture ratio of the pixel portion, and widen the viewing angle.

[0006]

According to the present invention, in a liquid crystal display device having a structure in which a liquid crystal is sandwiched between two substrates, one of the substrates and the other counter substrate have different pretilt angles of the liquid crystal. Is characterized by. Different pretilt angles can be achieved by different firing conditions for the alignment film.

[0007]

[Function] One of the pretilt angles (≧ 1
By making the angle (°) higher than the pretilt angle of the counter substrate by 1 ° or more, disclination is suppressed on one substrate side and a wide viewing angle is obtained on the counter substrate side.

[0008]

The present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram showing a first embodiment of the present invention.
This embodiment is an example using two kinds of polyimides having different pretilt angles. The alignment film 5 is a pre-imide type polyimide, and is used as a solvent by heating.
An alignment film is formed by skipping butyl lactone. An actual wide-viewing-angle liquid crystal display device is manufactured by arranging a color filter 2 of RGB and a black matrix 3 on a glass substrate 1 and using a polyimide having a liquid crystal pretilt angle of 1 ° on a color filter substrate on which a counter electrode 4 is formed. Apply by printing method,
After heating at 180 ° C. for 2 hours, rubbing treatment is performed. In addition, the TF in which the pixel electrode 11 and the TFT 12 are arranged on the glass substrate 1.
A polyimide having a liquid crystal pretilt angle of 4 ° is applied to the T substrate, heated at 180 ° C. for 2 hours, and then rubbed. The color filter substrate and the TFT substrate are electrically connected by a transfer 6 and are overlapped with each other by using a sealing material 8 while keeping a gap of 6 μm.

The liquid crystal display device manufactured in this manner is shown in FIGS. 3 (a) to 3 (d), and the conventional examples (a) and (c) are used.
Then, the distance of the disclination 13 from the gate line advanced to the region of 7 μm at the maximum and entered the pixel electrode 11, but in the present embodiments (b) and (d), the disclination line reaches the distance of 3 μm. Since it retreated and did not enter the pixel electrode 11, the contrast was improved and the occurrence of display defects was eliminated. As a result, the aperture ratio of the pixel portion can be increased to about 2.5 times that of the conventional one, and since the pretilt angle on the color filter substrate side is as low as 1 °, the contrast in the direction of 30 ° to the left and right of the liquid crystal display element surface is high. Compared with the conventional example (FIG. 2), the viewing angle was about 1.5 times wider and a wider viewing angle could be obtained.

Next, the second aspect of the present invention for controlling the pretilt angle by changing the polyimide production conditions.
An example will be described. The alignment film 5 is a baking type polyimide, and baking conditions are set to obtain an arbitrary pretilt angle, and polyimide is formed from polyamic acid. An actual wide-viewing-angle liquid crystal display device has a color filter substrate similar to that of the first embodiment coated with polyamic acid at 170 ° C.
It is baked for 2 hours, and then a rubbing treatment is performed. Also, T
Similarly, the FT substrate is coated with polyamic acid, baked at 200 ° C. for 1.5 hours, and then subjected to rubbing treatment.
The same as in the above example.

The high-viewing-angle liquid crystal display device manufactured in this manner has a liquid crystal pretilt angle of 1 ° on the color filter substrate side and 4 ° on the TFT substrate side, which is the same as in the first embodiment. The effect is that the receding receding, the aperture ratio is increased, the contrast is increased, and a high viewing angle can be obtained. In addition, in this example, since polyimide is formed from polyamic acid of both substrates jointly having one composition, polyimide printing can be performed using the same apparatus,
It is not necessary to clean the coating device as in the first embodiment. Therefore, the time for each lot (20p) is shortened by 40 minutes.

[0012]

As described above, in the present invention, the pretilt angle of the liquid crystal on one substrate side is different from the pretilt angle of the liquid crystal on the counter substrate. In particular, the structure is such that the difference between the pretilt angles (≧ 1 °) of one liquid crystal and the pretilt angle of the liquid crystal on the opposite side is 1 ° or more. As a result, as can be seen from the experimental result shown in FIG. 4B, the influence of the electrode (TFT, MIM side) on the one substrate side where the lateral electric field is strong is reduced, so that the progress of disclination can be suppressed. You can
Therefore, the aperture ratio of the pixel portion can be increased. In addition, from the experimental result shown in FIG. 4A, on the counter substrate side,
Since the pretilt angle of the liquid crystal is lower than that of one of the substrates, it is possible to realize a wide viewing angle by suppressing the visual dependence of the contrast due to the increase in the pretilt angle.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a first embodiment of the present invention.

FIG. 2 is a schematic sectional view showing a general conventional color liquid crystal display device.

FIG. 3 is a diagram comparing the degree of progress of the disclination line of the present invention and the conventional example, (a) and (b) are plan views seen from the color filter substrate side, and (c) and (d) are TFT
It is the top view seen from the substrate side.

4A is a diagram showing a relationship between a pretilt angle and cotrust, and FIG. 4B is a diagram showing a relationship between a pretilt angle difference and a disclination generation distance.

[Explanation of symbols]

 1 glass substrate 2 color filter 3 black matrix 4 counter electrode 5 alignment film 6 transfer 7 liquid crystal 8 sealant 9 liquid crystal molecule 10 pretilt angle 11 pixel electrode 12 TFT

Claims (3)

[Claims] 1. A liquid crystal display device having a structure in which a liquid crystal is sandwiched between two substrates, wherein a pretilt angle of one liquid crystal of the substrate is different from a pretilt angle of a liquid crystal of an opposite substrate. 2. The liquid crystal display element according to claim 1, wherein the difference between the pretilt angle of the liquid crystal on one substrate and the pretilt angle of the liquid crystal on the counter substrate is 1 ° or more. 3. A method of manufacturing a liquid crystal display device, wherein the pretilt angle of the liquid crystal is controlled by making one substrate and the counter substrate have different firing conditions for the alignment film.