JPH06160858A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To increase the stability of orientation of a liquid crystal molecule by increasing the pretilt angle of the liquid crystal molecule by forming the surface roughness of the horizontal oriented film of a substrate at least on one side in specific irregular surface film. CONSTITUTION:A pair of transparent substrates 1, 2 consisting of glass, etc., are adhered via a frame shape sealing material 3, and liquid crystal 8 is sealed in an area enclosed with the sealing material 3 between both substrates 1, 2. Transparent electrodes 4, 5 for display are provided on the inner plane of both substrates 1, 2, respectively, and the horizontal oriented film 6, 7 to orient the liquid crystal molecule horizontally are provided on the electrodes. The horizontal oriented film 6, 7 are formed with a horizontal orientation material such as polyimide, etc., and rubbing processing is applied to the film surfaces of them. The oriented film 6, 7 are formed in fine irregular surface film, and height difference between a projecting part and a recessed part i.e., the surface roughness is set at a valued >=10nm.

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 in which liquid crystal molecules are horizontally aligned with a certain pretilt angle.

[0002]

2. Description of the Related Art A liquid crystal display device in which liquid crystal molecules are horizontally aligned has a TN (twisted nematic) mode, an S mode.
There are a TN (super twisted nematic) mode, a horizontal alignment type of ECB (electric field control type birefringence) mode, a type using a ferroelectric liquid crystal or an antiferroelectric liquid crystal, and the like.

In these liquid crystal display elements, a transparent electrode and a horizontal alignment film for horizontally aligning liquid crystal molecules are formed on the surfaces of a pair of transparent substrates facing each other with a liquid crystal layer in between, which face each other. Has become. Some liquid crystal display devices using ferroelectric liquid crystal or antiferroelectric liquid crystal have a horizontal alignment film provided on only one substrate.

The horizontal alignment film provided on the substrate of these liquid crystal display elements is generally formed by forming a film of a horizontal alignment material such as polyimide on the substrate and rubbing the film surface in one direction. Thus, the liquid crystal molecules are horizontally aligned with a certain pretilt angle with respect to the substrate surface.

The pretilt angle is an important factor that influences the stability of the alignment of the liquid crystal molecules, and if the pretilt angle is increased to some extent, the stability of the alignment of the liquid crystal molecules due to the alignment regulating force of the alignment film is improved. You can

By the way, the pretilt angle of liquid crystal molecules in the above liquid crystal display device is mainly determined by the material of the alignment film, but the horizontal alignment material currently being developed is more reliable when a relatively large pretilt angle is obtained. When the alignment film is formed with such an alignment material, the display stability of the liquid crystal display element is deteriorated, and defects such as display unevenness occur with long-term use.

For this reason, the alignment film of the liquid crystal display element uses a highly reliable horizontal alignment material which can improve the display stability of the liquid crystal display element although the pretilt angle is not so large. There is.

[0008]

However, in the conventional liquid crystal display device in which the alignment film is formed of the above-mentioned highly reliable horizontal alignment material, the pre-tilt angle of the liquid crystal molecules is small, so that the initial alignment state of the liquid crystal molecules is large. Becomes uneven,
Therefore, there is a problem in that the liquid crystal display element has low quality with display unevenness.

An object of the present invention is to increase the pretilt angle of liquid crystal molecules to improve the stability of the alignment of liquid crystal molecules, and to form a display by forming the alignment film from a highly reliable horizontal alignment material. An object of the present invention is to provide a liquid crystal display device that can improve stability.

[0010]

According to the present invention, in a liquid crystal display device in which liquid crystal molecules are horizontally aligned with a certain pretilt angle, the horizontal alignment film of at least one substrate is an uneven surface film having a surface roughness of 10 nm or more. It is characterized by having done.

[0011]

As described above, when the alignment film is the uneven surface film having a surface roughness of 10 nm or more, the liquid crystal molecules aligned by this alignment film are aligned with a pretilt angle larger than the pretilt angle according to the material of the alignment film. Even if the alignment film is formed of a horizontal alignment material that does not have a large pretilt angle of the liquid crystal molecules, the actual pretilt angle of the liquid crystal molecules can be increased to improve the stability of the alignment of the liquid crystal molecules. Further, since the horizontal alignment material has high reliability although the pretilt angle of liquid crystal molecules is not large, the display stability can be improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 2 is a cross-sectional view of the liquid crystal display device, FIG.
FIG. 3 is an enlarged view of a portion I in FIG.

First, the overall structure of the liquid crystal display element will be described. In this liquid crystal display element, as shown in FIG. 2, a pair of transparent substrates 1 and 2 made of glass or the like are adhered to each other via a frame-shaped sealing material 3 and surrounded by the sealing material 3 between the substrates 1 and 2. The liquid crystal 8 is enclosed in a closed area, and transparent electrodes 4 and 5 for display are provided on the inner surfaces of both substrates 1, respectively.
On top of that, horizontal alignment films 6 and 7 for horizontally aligning liquid crystal molecules are provided.

The horizontal alignment films 6 and 7 are formed of a horizontal alignment material such as polyimide, and the film surfaces thereof are subjected to rubbing treatment. As shown in FIG. 1, these alignment films 6 and 7 are uneven surface films having fine unevenness, and the height difference between the convex portion and the concave portion, that is, the surface roughness (R
a) is set to 10 nm or more.

The orientation films 6 and 7 have a surface roughness of 10 n on the surface on which the orientation films are formed, that is, the surfaces of the transparent electrodes 4 and 5.
The uneven surface film as described above is formed by forming the uneven surface of m or more.

The transparent electrodes 4 and 5 are formed by forming a transparent conductive film, for example, an ITO film on the substrates 1 and 2 by a vacuum deposition method,
This ITO film is formed by patterning by the photolithography method, and the surface roughness of the film formed by the vacuum evaporation method increases as the deposition thickness increases. In the example, the ITO
The film is formed to have a film thickness such that the surface roughness is 10 nm or more,
The ITO film is patterned to form the electrodes 4 and 5 having the above surface roughness.

The alignment films 6 and 7 are formed on the electrodes 4 and 5, respectively.
Is formed with a substantially uniform film thickness on top of the
When the alignment films 6 and 7 are formed on the electrodes 4 and 5 whose surfaces are uneven to have a substantially uniform film thickness, the alignment films 6 and 7 have a surface roughness almost the same as that of the electrodes 4 and 5. It becomes an uneven surface film.

The thickness of the alignment films 6 and 7 is 500 to
When the thickness of the alignment films 6 and 7 is 1000 nm, the surface roughness of the alignment films 6 and 7 is almost the same as the surface roughness of the electrodes 4 and 5.

That is, in the above liquid crystal display element, the surfaces of the transparent electrodes 4 and 5 provided on both the substrates 1 and 2 are uneven surfaces having a surface roughness of 10 nm or more, and the electrodes 4 and 5 are substantially uniform. By forming the alignment films 6 and 7 in the film thickness, the alignment films 6 and 7 are uneven surface films having a surface roughness of 10 nm or more. When the alignment films 6 and 7 are such uneven surface films, The liquid crystal molecules aligned by the alignment films 6 and 7 are aligned with a pretilt angle larger than the pretilt angle according to the material of the alignment films 6 and 7. In FIG. 1, arrow a indicates the pretilt direction of the liquid crystal molecules, and θ indicates the pretilt angle of the liquid crystal molecules with respect to the substrate surface.

In the following [Table 1], three types of liquid crystal display devices having different surface roughnesses of the transparent electrodes 4 and 5 were prototyped, and the pretilt angle (average value) of liquid crystal molecules was examined for each of these devices. The results are shown.

Here, the electrode surface roughness of each element is 8.2 nm (electrode film thickness 100 nm) and 9.5 n, respectively.
m (electrode thickness 140 nm), 13.2 nm (electrode thickness 2
60 nm). As the alignment film, four kinds of alignment films having different peculiar pretilt angles of liquid crystal molecules are selected, and these alignment films have the same film thickness (500 to 600 n) for each element.
m).

[0022]

[Table 1]

As shown in [Table 1], the element 1 having the electrode surface roughness of 8.2 nm (the surface roughness of the alignment film is the same)
Has a pretilt angle of 3.0 ° when the alignment film A is used,
The pretilt angle when the alignment film B is used is 2.4 °, the pretilt angle when the alignment film C is used is 4.2 °, the alignment film D
The pretilt angle in the case of using is 4.5 °, and these pretilt angles are almost the same as the peculiar pretilt angle of each alignment film (the pretilt angle when the alignment film surface is not an uneven surface). This also applies to the element 2 in which the electrode surface roughness is 9.5 nm (the surface roughness of the alignment film is the same).

On the other hand, the electrode surface roughness is set to 13.2n.
The element 3 having a larger m (the same in surface roughness of the alignment film) is
The pretilt angle when the alignment film A is used is 3.2 °, the pretilt angle when the alignment film B is used is 2.6 °, and the alignment film C is used.
The pretilt angle in the case of using (1) is 4.7 °, and the pretilt angle in the case of using the alignment film D is 4.9 °, which is larger than those of the elements 1 and 2.

This is because the surface roughness of the alignment films 6 and 7 is 10n.
It is shown that when it is m or more, the liquid crystal molecules are aligned with a pretilt angle larger than the pretilt angle depending on the material of the alignment films 6 and 7.

In the above liquid crystal display device, since the alignment films 6 and 7 of the substrates 1 and 2 are uneven surface films having a surface roughness of 10 nm or more, a horizontal alignment material that cannot secure a large pretilt angle of liquid crystal molecules. Even if the alignment film is formed, the actual pretilt angle θ of the liquid crystal molecules can be increased to improve the stability of the alignment of the liquid crystal molecules. Therefore, the initial alignment state of the liquid crystal molecules can be made uniform and the display can be improved. The quality can be improved.

Further, since the horizontal alignment material does not have a large pretilt angle of liquid crystal molecules but has high reliability, the display stability is good, and defects such as display unevenness occur with long-term use. There is nothing to do.

Further, in the above embodiment, in order to make the surfaces of the transparent electrodes 4 and 5 uneven surfaces having a surface roughness of 10 nm or more,
Although the thickness of the electrodes 4 and 5 (the thickness of the deposited ITO film) is increased, if the thickness of the electrodes 4 and 5 is increased in this way,
As shown in the above [Table 1], the sheet resistance of the electrodes becomes small, so that it is possible to obtain the effect that the voltage drop at the electrodes 4 and 5 can be made small.

In the liquid crystal display element of the above-mentioned embodiment, the alignment films 6 and 7 are formed on the transparent electrodes 4 and 5, but in the present invention, the transparent electrodes 4 and 5 are made of SiN (silicon nitride). ) Or SiO ₂ (silicon oxide) or the like and covered with a transparent insulating film to form the alignment films 6 and 7 on the transparent insulating film. The film may be formed so as to have a surface roughness of 10 nm or more (formed by a plasma CVD apparatus).

Further, in the above embodiment, the surface on which the alignment film is formed (the surface of the transparent electrodes 4 and 5) is an uneven surface having a surface roughness of 10 nm or more, and the alignment films 6 and 7 are formed thereon to have a substantially uniform film thickness. By forming the alignment films 6 and 7 as the uneven surface film having the above surface roughness, the means for using the alignment films 6 and 7 as the uneven surface film is not limited to the above-mentioned embodiment.

Further, in the above embodiment, the alignment films 6 and 7 of both substrates 1 and 2 of the liquid crystal display element are uneven surface films having a surface roughness of 10 nm or more, but the alignment film of one of the substrates is Also, a surface-roughened film having a surface roughness of less than 10 nm may be used, or a flat film having almost no surface unevenness may be used.

Further, the liquid crystal display element of the above-mentioned embodiment has the horizontal alignment films 6 and 7 provided on both substrates 1 and 2, but the present invention provides the horizontal alignment film only on one substrate. The present invention can also be applied to existing liquid crystal display devices (liquid crystal display devices using ferroelectric liquid crystal or antiferroelectric liquid crystal).

[0033]

According to the liquid crystal display element of the present invention, since the horizontal alignment film of at least one of the substrates is an uneven surface film having a surface roughness of 10 nm or more, the pretilt angle of the liquid crystal molecule is increased to increase the liquid crystal molecule. The stability of the alignment can be improved, and the stability of the display can be improved by forming the alignment film with a highly reliable horizontal alignment material.

[Brief description of drawings]

FIG. 1 is an enlarged view of portion I of FIG.

FIG. 2 is a sectional view of a liquid crystal display element.

[Explanation of symbols]

 1, 2 ... Substrate 3 ... Sealing material 4, 5 ... Electrodes 6, 7 ... Alignment film 8 ... Liquid crystal a ... Pretilt direction of liquid crystal molecules θ ... Pretilt angle

Claims (2)

[Claims] 1. A liquid crystal display device in which liquid crystal molecules are horizontally aligned with a certain pretilt angle, wherein the horizontal alignment film of at least one substrate is an uneven surface film having a surface roughness of 10 nm or more. element. 2. The liquid crystal display element according to claim 1, wherein the horizontal alignment film is formed in a substantially uniform film thickness on the alignment film formation surface having a surface roughness of 10 nm or more.