JPH11281983A - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-response liquid crystal display which uses vertical orientation mode liquid crystal to realize display of not only a high contrast but also a wide field angle and which is produced with a low cost. SOLUTION: A liquid crystal layer 5 is held between a pair of substrates 1 and 4, and a signal voltage is applied to an electrode 7 formed on at least one of the pair of substrate 1 and 4 to display a picture. A wall structure 2 whose section in the normal direction of substrates is trapezoidal when viewed from at least one direction and an orienting film 3 which is adjacent to the wall structure 2 and is arranged on the liquid crystal layer 5 side are provided between the pair of substrates 1 and 4, and the angle formed by the direction of the major axis of liquid crystal molecules on the surface of the orienting film 3 and the pair of substrates 1 and 4 is 45 deg. to 90 deg..

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 more particularly to a liquid crystal display device having a vertically aligned mode liquid crystal sandwiched between a pair of substrates.

[0002]

2. Description of the Related Art In recent years, a liquid crystal display device compatible with multimedia has been required to satisfy all requirements such as high contrast, high speed response, wide viewing angle, and low cost. Research and development are being performed to meet these requirements.

For example, in recent years, attention has been paid to a liquid crystal display utilizing vertical alignment as one method for obtaining high contrast. For example, K. Ohmu
ro et al. (SID 97 DIGEST, p845 (1997)) use vertical alignment to make the light transmittance in the black state almost equal to that of the cross-polarizer, and a high contrast of 300: 1 or more is obtained. Announced what can be achieved. Here, the response speed is 25 msec, which is a high-speed response.

[0004] In addition, due to the recent demand for obtaining a wider viewing angle, the viewing angle obtained in this mode is not sufficient in the vertical alignment mode in which a wide viewing angle is conventionally obtained. There is a need to introduce technology.

Conventionally, in order to improve the viewing angle dependency, as described in, for example, JP-A-64-88520, an alignment process is performed with a predetermined alignment region patterned with a resist. Accordingly, a method of forming two or more pretilt angle regions in a pixel and dividing the pixel into pixels is performed. And as another solution,
K. Ohmuro et al. Use a method in which the inside of a pixel is divided into domains and the orientation of each domain is made different.

Japanese Patent Application Laid-Open No. 9-90434 discloses that
An amorphous vertical alignment cell using an alignment in which the azimuth of the substrate surface is random (so-called amorphous) is disclosed. Further, Japanese Patent Application Laid-Open No. Hei 7-230097 discloses a method of controlling an inclination direction of liquid crystal molecules by providing an alignment control electrode.

[0007]

However, the method disclosed in JP-A-64-88520 and the method by K. Ohmuro et al. Increase the number of manufacturing steps such as a patterning step using a resist, Since different orientation treatments must be performed on the domains, a problem arises in that the manufacturing time and the manufacturing process increase.

The method disclosed in Japanese Patent Application Laid-Open No. 9-90434 has the advantage that rubbing treatment is not necessary for determining the direction (azimuth) at which liquid crystal molecules are inclined when an electric field is applied. It is not controlled whether or not the molecules tilt. Therefore, there is a disadvantage that the average tilt of the liquid crystal molecules differs for each pixel. Further, JP-A-7-2300
The method disclosed in Japanese Patent Publication No. 97 has a possibility of causing problems such as a decrease in aperture ratio and a decrease in yield.

Therefore, the present invention has been made to solve such a problem, and realizes not only a high contrast but also a wide viewing angle display by using a vertical alignment mode liquid crystal, and furthermore, corresponds to a high speed response. It is an object to provide a liquid crystal display device which can be manufactured at low cost.

[0010]

In order to achieve the above object, a liquid crystal display device according to a first aspect of the present invention includes a liquid crystal layer sandwiched between a pair of substrates and at least one of the pair of substrates. In a liquid crystal display device that displays an image by applying a signal voltage to an electrode, a wall structure having a trapezoidal cross section in a normal direction of the substrate between a pair of substrates when viewed from at least one direction; An alignment film adjacent to the structure and disposed on the liquid crystal layer side, wherein an angle between a long axis direction of liquid crystal molecules on the alignment film surface and the pair of substrates is not less than 45 degrees and not more than 90 degrees. It is characterized by.

Preferably, the angle between the major axis direction of the liquid crystal molecules on the surface of the alignment film and the pair of substrates is not less than 85 degrees and not more than 90 degrees. It is characterized by.

According to a third aspect of the present invention, in the liquid crystal display device, the upper surface of the trapezoidal wall structure disposed on one of the pair of substrates is interposed with the other substrate via an alignment film. It is characterized by being adhered. With this configuration, the shock resistance of the liquid crystal display device can be improved.

In a liquid crystal display device according to a fourth aspect of the present invention, the liquid crystal layer sandwiched between the pair of substrates is a liquid crystal material having a negative dielectric anisotropy. The liquid crystal display device according to claim 5, wherein the liquid crystal layer sandwiched between the pair of substrates is a liquid crystal material having a positive dielectric anisotropy. Characterized in that an electrode is provided on only one of the substrates.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A method for controlling the alignment of a liquid crystal in the present invention will be described below with reference to FIG. FIG. 1 is a schematic sectional view of a liquid crystal display device according to the present invention. In the figure,
1 is a substrate, 2 is a trapezoidal wall structure, 3 is an alignment film, 4 is a counter substrate, 5 is a liquid crystal layer, 6 is a sealant such as an injection port, and 7 is an electrode. The present invention is characterized in that a wall structure 2 is provided on the substrate 1 and in the liquid crystal cell, and a cross section of the wall structure in a direction normal to the substrate has a trapezoidal shape. Here, the alignment film 3 is characterized in that a so-called vertical alignment film having a pretilt angle of 45 to 90 degrees is used, and preferably a film having a pretilt angle of 85 degrees or more is used.

First, consider the case where the pretilt angle is 90 degrees. In the liquid crystal cell, at the interface with the substrate having no wall structure, the major axis direction of the liquid crystal molecules is oriented perpendicular to the substrate without applying a voltage. However, with respect to the wall structure, an orientation film provided in the wall structure tends to be oriented perpendicular to the wall surface. This situation is shown as a schematic diagram in FIG. 2A, where a, b, and c are 15 μm, 2 μm, 4 μm, respectively.
m represents a state where no voltage is applied.

When a nematic liquid crystal having a negative dielectric anisotropy is used as the liquid crystal, the liquid crystal molecules tend to become parallel to the substrate by application of an electric field. As shown in (1), since the substrate is tilted to a certain degree with respect to the substrate when no voltage is applied, a force that tends to fall in the direction of the tilt acts more. This is shown in FIG. Therefore, one pixel is sandwiched between at least one or more trapezoidal wall structures, or is arranged within one pixel, so that at least two or more regions having different inclination directions of liquid crystal molecules in one pixel. The present inventors have found that a liquid crystal display device having a wide viewing angle can be obtained as a result.

Various investigations were made on the arrangement of the trapezoidal wall structure in the liquid crystal cell. As a result, it was found that the arrangement should be made as shown in FIGS. That is, as shown in FIG. 3A, a configuration in which wall structures are arranged on both sides of each pixel, or FIG.
As shown in FIG. 4C, a configuration in which the pixels are arranged so as to surround four sides thereof, or as shown in FIGS. 4A, 4B, and 4C, a configuration in which the pixels are arranged in various shapes inside the pixels, and the like. Can be applied, and further, these can be applied in combination.

Here, the pretilt angle of liquid crystal molecules was also studied. In the present application, perfect vertical alignment (90 degrees) is most preferable, but it is needless to say that it is not necessarily limited to 90 degrees. For example, in FIG. 1, by arranging two regions having different pretilt directions in a direction perpendicular to the paper surface in a pixel, a region in which liquid crystal molecules tilt in different directions when an electric field is applied is combined with a wall structure. , Can be further manufactured.

It is needless to say that different alignment films can be used between the two substrates. However, if the same alignment film having a pretilt angle of 90 degrees is used for both the upper and lower substrates, the liquid crystal molecules in the absence of an electric field are applied to the substrates. Being vertical, higher contrast can be realized.

When a nematic liquid crystal having negative dielectric anisotropy as described above is used as a liquid crystal material, a high-speed black-and-white response can be achieved by reducing the cell thickness to 3 μm or less. In addition, it goes without saying that a smectic A liquid crystal or the like may be used. Nematic liquid crystal having positive dielectric anisotropy or smectic A
Using a liquid crystal or the like, switching can be performed by a horizontal electric field. Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.

Embodiment 1 A first embodiment of the present invention will be described below with reference to FIG. As shown in FIG. 5A, a photosensitive resin, for example, a negative photosensitive resin V-259PA (manufactured by Nippon Steel Chemical Co., Ltd.) or the like is applied on the substrate 1 by a spin coating method, and is coated with a photomask.
Exposure is performed at a proximity gap of μm, and then development is performed to form a wall 2 having a stripe shape and a trapezoidal cross section (height: 1.5 μm, trapezoidal lower side width: 15 μm, trapezoidal upper side width: 10 μm). did.

Next, as shown in FIG. 5B, a vertical alignment film 3 is formed on the substrate. Here, the vertical alignment film ODS-E manufactured by Chisso was used.
Next, the opposing substrates 4 were bonded together, the liquid crystal 5 was sandwiched between the substrates, and both ends were sealed with a sealant 6.

Here, since a vertical alignment film is used as the alignment film 3, the angle between the major axis direction of the liquid crystal molecules on the surface of the alignment film 3 and the substrate 1 or 4 is set to approximately 90 degrees. Is done. On the other hand, in the inclined portion of the wall 2, since the orientation is substantially perpendicular to the inclined surface, the orientation is inclined with respect to the substrate 1 or 4. Note that the angle between the major axis direction of the liquid crystal molecules on the surface of the alignment film 3 and the substrate is not substantially 90 degrees but may be between 45 and 90, but from the viewpoint of contrast, , 85 ° or more. Needless to say, an alignment film may also be formed on the counter substrate 4.

In order to drive the liquid crystal display device, electrodes are required on at least one of the substrates, but they are omitted in FIG. A method for switching the liquid crystal in combination with the electrodes will be described in Embodiment 4 and thereafter.

<< Embodiment 2 >> A second embodiment of the present invention will be described below with reference to FIG. A wall, a vertical alignment film, and the like were formed on the substrate 1 in the same manner as in the first embodiment.
The difference from the first embodiment is that the substrate 1 and the substrate 4 are in contact with each other and bonded together, whereby the wall structure 2 also has a role of a spacer between the substrates, and the height of the wall structure Thus, the cell thickness can be controlled.

Furthermore, since it is not necessary to use a spherical spacer conventionally used, there is no problem that the orientation is disturbed around the spherical spacer and the contrast is lowered. Also, if the wall according to the present invention is used as a spacer and formed outside the pixel, even if the orientation is disturbed near the wall, the portion is hidden by a black matrix or the like so that the display is not adversely affected. Is also possible.

<< Embodiment 3 >> A third embodiment of the present invention will be described below with reference to FIG. A wall, a vertical alignment film, and the like were formed on the substrate 1 in the same manner as in the first embodiment.
After that, the present embodiment differs from the first embodiment only in that an adhesive 7 is arranged on the wall 2 to be bonded to the counter substrate 4. As in the second embodiment, the cell thickness can be controlled by the height of the wall. According to the present embodiment, the wall is bonded to the opposing substrate using an adhesive, so that the mechanical strength is increased, and it is possible to prevent display disturbance or the like that has occurred in a pen input type display or the like. Becomes

<< Embodiment 4 >> The optimum electrode arrangement, alignment film, and liquid crystal material for driving the liquid crystal display element shown in Embodiments 1 to 3 as a display device will be described below with reference to FIG. Will be described. A stripe electrode 11 is formed on a substrate 1, and a wall 2 and a vertical alignment film 3 are formed on the electrode. The wall 2 structure has a trapezoidal cross section perpendicular to the longitudinal direction of the electrode.

On the counter substrate 4, a TFT element 8 and a pixel electrode 9 connected to the TFT element 8 are formed, and a vertical alignment film 10 is formed so as to cover the TFT element and the pixel electrode. It goes without saying that the alignment film 10 on the pixel electrode may be made of an organic silane, a photo-alignment film, a chromium carboxylate complex, or the like, in addition to those used in the above embodiment. Next, the substrate 1 and the substrate 4 are bonded together via an adhesive 7, and the liquid crystal 5 is sandwiched. Finally, the liquid crystal injection port is bonded with a sealant 6, thereby obtaining a liquid crystal display device.

As the liquid crystal injected in the present invention, for example, a nematic liquid crystal having a negative dielectric anisotropy is used. Alternatively, a smectic A liquid crystal or a liquid crystal having a positive dielectric anisotropy may be used. It goes without saying that you can do it. However, when a liquid crystal having a positive dielectric anisotropy is used, an electrode is not formed as shown in FIG. 8, but a counter electrode is eliminated, and one substrate (in FIG. 8, the substrate on which the TFT is formed) is used. 4), both electrodes (the electrode bonded to the TFT and the counter electrode) must be formed and driven by the lateral electric field method.

Here, FIG. 9 shows the alignment state of the liquid crystal in one pixel of the liquid crystal display device according to the present embodiment. The pixel is sandwiched between two walls 2, and liquid crystal molecules are inclined with respect to the substrates 1 and 4 in the vicinity of the wall structure 2. Therefore, the directions of slightly tilting the liquid crystal molecules on both sides of one pixel are reversed. here,
When an electric field is applied, the liquid crystal molecules that have been vertically aligned tend to be aligned in parallel with the substrates 1 and 4. This situation is shown in FIG.
These are indicated by reference numerals 12 and 13. That is, since the liquid crystal molecules are tilted to some extent by the wall structure, arrows 12 and 13
As shown in the above, the directions in which the liquid crystal molecules incline on the left and right sides of the pixel are reversed. This makes it possible to obtain a liquid crystal display device having a wide viewing angle. By setting the cell thickness to 3 μm or less, the electric field strength can be increased, and a high-speed response can be achieved.

[0032]

As described above, according to the present invention, it is possible to realize not only a high contrast but also a display with a wide viewing angle by using the vertical alignment mode liquid crystal. Further, unlike the related art, the liquid crystal display device of the present invention can be manufactured by a relatively easy method without increasing the number of manufacturing steps and without performing complicated processing, so that cost reduction can be achieved. . In addition, by setting the cell thickness appropriately, it is possible to respond to a high-speed response.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a liquid crystal display device according to the present invention.

FIG. 2 shows a state of liquid crystal molecules with respect to a wall structure, (a)
FIG. 3 is a schematic diagram in a state where no voltage is applied, and FIG. 3B is a schematic diagram in a state where a voltage is applied.

FIGS. 3A, 3B, and 3C are schematic diagrams each showing a layout configuration of a trapezoidal wall structure in a liquid crystal cell.

FIGS. 4A, 4B, and 4C are schematic diagrams showing the arrangement of a trapezoidal wall structure in a liquid crystal cell.

FIGS. 5A and 5B are schematic cross-sectional views of the liquid crystal display device according to the first embodiment.

FIG. 6 is a schematic sectional view of a liquid crystal display device according to a second embodiment.

FIG. 7 is a schematic sectional view of a liquid crystal display device according to a third embodiment.

FIG. 8 is a schematic sectional view of a liquid crystal display device according to a fourth embodiment.

FIG. 9 is a schematic diagram illustrating an alignment state of liquid crystal in one pixel of a liquid crystal display device according to a fourth embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Wall structure 3, 10 Alignment film 4 Substrate 5 Liquid crystal 6 Sealant 7, 9, 11 Electrode 8 TFT 12, 13 Inclination direction of molecule

Claims (5)

[Claims] A liquid crystal layer sandwiched between a pair of substrates; and a liquid crystal display device that displays an image by applying a signal voltage to electrodes formed on at least one of the pair of substrates. A cross-sectional shape in the normal direction of the substrate includes a wall structure having a trapezoidal shape when viewed from at least one direction, and an alignment film adjacent to the wall structure and disposed on the liquid crystal layer side, and the alignment film surface The angle between the major axis direction of the liquid crystal molecules and the pair of substrates is 45 degrees or more and 90 degrees or less. 2. A liquid crystal display device which sandwiches a liquid crystal layer held between a pair of substrates and a signal voltage applied to electrodes formed on at least one of the pair of substrates to display an image. The cross-sectional shape in the normal direction of the substrate includes a wall structure having a trapezoidal shape when viewed from at least one direction, and an alignment film arranged adjacent to the wall structure, and the liquid crystal molecules on the alignment film surface have The angle between the long axis direction and the pair of substrates is
A liquid crystal display device characterized by being at least 85 degrees and at most 90 degrees. 3. The device according to claim 1, wherein an upper surface of the trapezoidal wall structure disposed on one of the pair of substrates is bonded to the other substrate via an alignment film.
Or the liquid crystal display device according to claim 2. 4. The liquid crystal display device according to claim 1, wherein the liquid crystal layer sandwiched between the pair of substrates is a liquid crystal material having negative dielectric anisotropy, and each of the pair of substrates has A liquid crystal display device comprising an electrode. 5. The liquid crystal display device according to claim 1, wherein the liquid crystal layer sandwiched between the pair of substrates is a liquid crystal material having a positive dielectric anisotropy, and is provided on one of the pair of substrates. A liquid crystal display device comprising only electrodes.