JPH0798457A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain good orientation stability and visual angle characteristic and to enable driving with a low driving voltage without making stages intricate and difficult and making reliability and durability low by using an oriented film having good stability and low pretilt angle and forming projecting parts. CONSTITUTION:A transparent electrode 2 is formed as a counter common electrode on a glass substrate 1 and an SiOX film 3 is sputtered thereon. A positive type photosensitive resist film 4 is applied thereon and is subjected to drying and prebaking. Mask patterns are transferred on this resist film 4 by using a photomask 5 and executing exposing by i rays. The nearly hemispherical projecting parts 6 using the SiOX film 3 as a material are formed by etching the SiOX film 3 of the parts exposed without being covered by the resist patterns. A high polymer film consisting of, for example, a polyimide, is formed to cover nearly the entire surface of the front surface of the glass substrate 1 including the projecting parts 6 and the surface thereof is subjected to a rubbing treatment, by which the oriented film 7 is formed.

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 particular, the present invention relates to a liquid crystal display device that realizes wide viewing angle characteristics.

[0002]

2. Description of the Related Art In recent years, liquid crystal display elements having the features of thinness, light weight, and low power consumption have been widely used as display elements for OA equipment such as Japanese word processors and desktop personal computers. Among such liquid crystal display devices, a liquid crystal display device called a nematic liquid crystal, which uses a light modulation characteristic due to a twisted arrangement of liquid crystal molecules, is generally put into practical use. The display method can be roughly classified into two methods, that is, an optical rotation mode and a birefringence mode.

The LCD in the optical rotation mode is, for example, a twisted nematic (TN) having a molecular arrangement twisted by 90 degrees.
Type liquid crystal, which basically displays black and white from the operating principle, shows a high contrast ratio and good gradation display performance, and has a fast response speed (about several 10 ms), A segment type digital display panel, an image display panel driven by an active matrix drive equipped with a simple matrix drive or a switching element for each pixel used as a display device of OA equipment, and a full color display in combination with a color filter It has been applied to liquid crystal televisions and the like. On the other hand, the liquid crystal display element of the birefringence mode display method generally has a molecular arrangement twisted by 90 degrees or more and has steep electro-optical characteristics, so that it is not necessary to form a switching element such as a TFT element or a diode element for each pixel. In addition, even with a structure in which electrodes are arranged opposite to each other on a simple matrix, a large capacity display can be easily realized by the next division driving. A liquid crystal of such a mode is generally called a super twisted nematic type liquid crystal (STN type liquid crystal), but in order to display such a liquid crystal display element uniformly over the entire screen, liquid crystal molecules are evenly distributed over the entire surface of the substrate. Orientation is required.

At this time, in the liquid crystal display device, the liquid crystal composition is sandwiched between the electrodes of the two substrates, and a voltage is applied from the electrodes of the two substrates to the liquid crystal composition for display. Therefore, it is necessary to give a pretilt angle to liquid crystal molecules in advance in order to perform uniform display when a voltage is applied.

In order to give such a pretilt angle to the liquid crystal molecules, a technique is generally used in which an alignment film having a surface in contact with the liquid crystal molecules is subjected to an alignment treatment on the substrate surface. As such an alignment film, an organic polymer thin film typified by polyimide is formed on a substrate by a method such as spin coating or printing, and the upper surface of the film is lightly rubbed with a cloth or the like to impart liquid crystal alignment ability. The rubbing method is generally used as a technique suitable for mass production. Improvement of yield in the alignment treatment step by such a rubbing method and suppression of tilt reverse alignment failure,
In order to reduce the driving voltage of the liquid crystal display element, it is desirable to increase the pretilt angle to some extent.

However, in order to obtain such a relatively large pretilt angle, a polymer material having a long-chain alkyl, for example, is preferably used as the alignment film material. There is a problem that the stability against humidity and humidity is relatively low and the reliability is poor, and the workability of coating on the substrate is extremely poor.

Alternatively, a method of controlling the pretilt angle by changing the manufacturing conditions such as the forming temperature of the alignment film and the rubbing treatment conditions has been proposed. However, in such a method, the control range of the pretilt angle is small, and There is a problem that its reproducibility is poor.

Further, a method of obtaining a large pretilt angle by, for example, making two regions having different alignment capabilities separately on a substrate and vertically aligning one of them (Japanese Patent Laid-Open No. 63-141).
23, 63-14124) has been proposed, but such a method has a problem that it is extremely unpractical because it requires complicated steps for manufacturing an alignment film and alignment treatment.

Further, in the prior art, the pretilt angle is set to be almost the same on any part of the substrate. For example, in the case of a TN type liquid crystal display element, the viewing angle characteristics are asymmetric with respect to the viewing direction because the rising directions of liquid crystal molecules when the same voltage is applied are almost the same in any part of the display area on the substrate. Therefore, there is a problem that the luminance distribution is biased and the viewing angle dependency is large.

For the purpose of solving this problem, one pixel of the liquid crystal display element is divided into a plurality of regions and the pretilt angle between the upper and lower substrates is made different for each of the plurality of regions, so that the liquid crystal molecules of the liquid crystal molecules under voltage application are A method has been proposed in which the rising direction is made different for each divided region and the viewing angle characteristics are made symmetrical with respect to the viewing direction to reduce the viewing angle dependency.

[0011]

However, in the above-mentioned conventional technique, it is actually extremely difficult to form a plurality of regions having different pretilt angles on the same substrate. That is, it is extremely difficult to form two types of alignment films, an alignment film having a low pretilt angle and an alignment film having a high pretilt angle, due to the problems of process matching and solvent resistance. In addition, by forming an alignment film with a high pretilt angle, that part becomes less durable than an alignment film with a low pretilt angle, and the quality of the liquid crystal display device is improved in terms of reliability and durability of the completed liquid crystal display device. There is a problem of decrease.

The present invention has been made to solve such a problem, and its object is to use an alignment film having a low stability and a low pretilt angle which is used as a conventional alignment film material. An image quality that achieves a high pretilt angle, has good alignment stability, and can be driven at a low drive voltage without complicating and complicating the process and reducing the reliability and durability of the liquid crystal display element. To realize a high-performance liquid crystal display device.

[0013]

A liquid crystal display element of the present invention is a device in which two substrates each having an electrode and an alignment film formed on the surface of the substrate are opposed to each other with a gap between the alignment films and the electrode is In a liquid crystal display element, which is arranged so as to face each other to form a pixel, and the liquid crystal composition is sandwiched by sealing the periphery in the gap, the liquid crystal composition of at least one of the two substrates. An alignment film having a plurality of protrusions and a plurality of grooves for inducing alignment with respect to the liquid crystal composition is provided on the surface side in contact with the alignment film.

Further, in the liquid crystal display element of the present invention, two substrates having electrodes and alignment films formed on the surfaces of the substrates are opposed to each other with the alignment films having a gap and the electrodes are opposed to each other. In a liquid crystal display element in which the liquid crystal composition is sandwiched between the two substrates by arranging so as to form pixels, and the liquid crystal composition is sandwiched in the gap, the liquid crystal composition is in contact with at least one of the two substrates. A plurality of protrusions formed on the surface side, and a plurality of grooves that are formed so as to cover the substrate including the plurality of protrusions and that induces alignment with respect to the liquid crystal composition. And an alignment film. Here, the protrusion may be formed integrally with the alignment film as a part of the alignment film, or it may be formed separately from the alignment film on the substrate and the alignment film may be formed on the alignment film to form the alignment film. The upper surface of the film may be formed to have a surface protruding in a shape along the protrusion.

Alternatively, a plurality of regions having different sizes and arrangement densities of the protrusions may be provided, and regions having different alignment pretilt angles of the liquid crystal composition may be provided in the substrate.

Further, in the liquid crystal display element of the present invention, two substrates having an electrode and an alignment film formed on the surface of the substrate are opposed to each other with a gap between the alignment films and the electrodes are opposed to each other. In the liquid crystal display element, which is arranged so as to form a pixel, and the liquid crystal composition is sandwiched by sealing the periphery in the gap, each pixel is divided into a plurality of regions, and the bottom surface is substantially isosceles. A triangular truncated pyramid shape or a truncated triangular pyramid-shaped projection obtained by cutting the upper part of the triangular pyramid in a plane substantially parallel to the bottom surface, and a vertical bisector of the base of the isosceles triangle of the bottom surface is generally Alignment in which the projections are aligned in one direction and the orientations of the isosceles triangles on the bottom surface are arranged in 180 ° opposite directions with the base of the isosceles triangle as the axis of symmetry for each divided region of each pixel. A film on each of the two substrates It is characterized in that it is provided on the surface side in contact with the liquid crystal composition.

Further, in the liquid crystal display element of the present invention, two substrates having electrodes and an alignment film formed on the surface of the substrates are opposed to each other with the alignment films having a gap and the electrodes are opposed to each other. In the liquid crystal display element, which is arranged so as to form each pixel and has a liquid crystal composition sandwiched by sealing the periphery of the gap, each pixel is divided into a plurality of regions, and the plurality of divided regions are divided. Is an alignment film in which a plurality of triangular pyramid-shaped projections each having an isosceles triangle bottom surface different in shape are arranged, and the rubbing alignment treatment is performed in a direction substantially perpendicular to the base of the isosceles triangle of the bottom surface. It is characterized in that an alignment film having an alignment groove formed by, for example, is provided on the surface side of each of the two substrates in contact with the liquid crystal composition.

Further, the liquid crystal display element of the present invention is characterized in that, in the above-mentioned liquid crystal display element, the projections are arranged so that the area ratios are equal in each of the plurality of divided regions.

The projection may be formed in a hemispherical shape, for example. Alternatively, the side surface may be formed in a convex shape having a tapered shape (that is, a trapezoidal cross section).
Alternatively, it may be formed in an elongated shape in a direction along the long axis direction of the liquid crystal molecules.

Needless to say, the height of the protrusion is smaller than the gap between the two substrates, but the retardation of the liquid crystal layer is affected particularly with respect to the cell gap (that is, the thickness of the liquid crystal layer). It is desirable to keep the height to a level that does not give Since the cell gap of a practical liquid crystal display element is generally about several μm, it is desirable that the height of the protrusion is within about 1 μm. Further, it is effective that the arrangement density of the protrusions is about 10 ² pieces / mm ² to 10 ⁷ pieces / mm ² .

[0021]

The present inventors have found that the angle (pretilt angle) formed by the liquid crystal molecules and the alignment film on the substrate is regulated to some extent by the material of the triangular pyramid, the surface energy, the density, etc., but the isosceles triangle of the bottom surface with respect to the rubbing direction. It was found that it depends most strongly on the orientation and the shape of the isosceles triangle of the base. Specifically, for example, when the protrusions having the same density are provided, the pretilt angle when the isosceles triangle of the bottom surface is an acute triangle is larger than that when it is an obtuse triangle, and the isosceles triangle of the bottom surface is larger. It was found that the pretilt angle is larger when the rubbing is performed from the bottom to the apex angle than when the rubbing is performed from the apex to the bottom. Therefore, the orientation pretilt angle of the liquid crystal molecules can be controlled by changing the direction of the isosceles triangle of the bottom surface or the shape of the isosceles triangle of the bottom surface with respect to the rubbing direction.

According to the present invention using such a technique,
While using an alignment film with a low pretilt angle on a flat surface, which is conventionally used, it is possible to align a liquid crystal molecule with a large pretilt angle by a plurality of protrusions formed on the alignment film. Therefore, a liquid crystal display device having high display quality can be obtained. Further, as described above, the tilt direction of the liquid crystal molecules when a voltage is applied can be changed for each pixel, and a wide viewing angle can be obtained.

Further, by enlarging the pretilt angle, it is possible to drive at a low driving voltage, and it is possible to improve the durability and reliability, and to increase the yield at the time of manufacturing the liquid crystal display panel.

Furthermore, the pretilt angle can be changed for each divided area by dividing one pixel into a plurality of divided areas and changing the shape, size, density, etc. of the protrusions for each divided area. Specifically, for example, one pixel is divided into a plurality of regions, and the shape of the isosceles triangle of the bottom surface is formed in each of the divided regions to have different shapes such as an acute triangle and an obtuse triangle. Alternatively, by arranging the isosceles triangles on the bottom surface in 180 ° opposite directions in multiple areas, a rubbing treatment is applied to the alignment film material in which different pyramidal protrusions are formed in each of these multiple areas. By doing so, it is possible to realize liquid crystal alignment in which the magnitude or direction of the pretilt angle is different between the plurality of regions. As a result, for example, in the liquid crystal display element of splay alignment, the viewing angle direction can be different by 180 ° for each region, and a liquid crystal display element with a wide viewing angle can be obtained. Alternatively, the pretilt angle can be changed for each of the divided areas by providing the protrusion in some of the divided areas and omitting it in the other divided areas.

By thus providing a plurality of divided areas in which the shape and arrangement of the protrusions are changed, a plurality of areas in which the pretilt angle is changed can be formed, and the liquid crystal at the time of voltage application is formed in each pixel. Regions having different tilt directions of molecules can be provided. As a result, the viewing angle can be effectively widened, the viewing angle characteristics of the liquid crystal display element can be improved, and the display quality can be improved.

Further, according to the present invention, since the protrusions made of the same kind of material are provided in a plurality of regions in each pixel with substantially the same density on each of the two substrates, the bias of the liquid crystal applied voltage is generated between the two substrates. It is possible to prevent the occurrence of display defects such as an afterimage due to image sticking due to the bias of the liquid crystal applied voltage.

As a method of forming a plurality of minute projections as described above, a film made of an inorganic substance such as SiO _x or SiN _x or a polymer compound is formed on a substrate, and the film is formed thereon. Apply a resist made of a photosensitive polymer material such as photosensitive acrylic used in general photolithography, transfer the pattern by exposing the resist using a photomask, and use the resist with this pattern formed. The film made of the above-mentioned inorganic substance or polymer such as SiO _x or SiN _x can be manufactured by a method such as patterning using etching (etching solution for wet etching, etching gas for dry etching). it can.

[0028]

Embodiments of the liquid crystal display device according to the present invention will be described below in detail with reference to the drawings. (Embodiment 1) FIG. 1 is a view showing the structure of a liquid crystal display element according to the present invention. Here, for simplification of the description, an alignment film having protrusions will be mainly described.

As shown in FIG. 1, this liquid crystal display device is
A transparent electrode 2 is formed on the glass substrate 1 as a counter common electrode. The SiO _x film 3 is sputtered thereon to form a thickness of 0.1 μm. Further, a positive type photosensitive resist film 4 made of photosensitive polyimide is spin-coated on the SiO _x film 3 by a spin coater and dried.
Prebaked. And this resist film 4 has a diameter
The mask pattern is transferred by performing exposure with i-line using the photomask 5 in which circular repeating patterns of 10 μm are formed. Then, the resist film 4 is developed to form a resist pattern having a shape almost equal to the baked pattern, and the exposed portion of the SiO _x film 3 which is not covered with the resist pattern is exposed to CF ₄ O ₂ gas. Etching is performed to form substantially hemispherical projections 6 made of the SiO _x film 3. The shape of such a protrusion 6 is shown in FIG.

As described above, the hemispherical projection 6 is formed on the glass substrate 1.
A large number are regularly arranged on the upper transparent electrode 2. This is shown in FIG. Needless to say, various conditions for the above-mentioned etching using CF ₄ O ₂ gas are set in advance so that the hemispherical projection 6 can be formed.

A polymer film such as polyimide is formed so as to cover almost the entire upper surface of the glass substrate 1 including the protrusions 6, and the surface is subjected to a rubbing treatment to form an alignment film 7. . As the material of the alignment film 7, AL-1051 (manufactured by Japan Synthetic Rubber Co., Ltd.) was used in this embodiment. A conventional rubbing method can be used as the above rubbing method.

On the other hand, the TF is formed on the TFT substrate (hereinafter not shown) arranged to face the glass substrate 1 on which the protrusions 6 are formed.
A transparent electrode connected to T is formed corresponding to each pixel, and a large number of hemispherical projections 6 similar to those described above are arranged thereon. Then, AL-1051 (manufactured by Japan Synthetic Rubber Co., Ltd.) is formed so as to cover almost the entire upper surface of the TFT substrate on which the hemispherical projection 6 is formed.
Is formed and the surface thereof is rubbed to form an alignment film similar to the alignment film 7 formed on the glass substrate 1 on the opposite substrate side.

On the opposite substrate side (on the glass substrate 1)
In order that the liquid crystal molecules are twisted by 90 degrees between the alignment film 7 and the alignment film on the TFT substrate which faces the alignment film 7, the alignment films are arranged so as to face each other, and the periphery thereof is sealed with a sealing material. Then, ZLI-1132 (manufactured by E. Merck) as a liquid crystal composition is injected into the substrate gap supported by the spacer,
The liquid crystal display element of the first embodiment according to the present invention is formed.

In the present embodiment, the hemispherical projection 6 has a shape of 1
^They were arranged at a density of × 10 ⁶ pieces / cm ² (1 × 10 ⁴ pieces / mm ² ). The diameter of each of the protrusions 6 was about 2 μm, and the height (thickness) thereof was about 1 μm.

As described above, in the liquid crystal display device of the present invention, the plurality of projections 6 are formed on the transparent electrode 2 on the substrate 1, and the alignment film 7 such as polyimide for horizontally aligning the liquid crystal molecules is further formed thereon. When the liquid crystal composition is brought into contact with such an alignment film 7, liquid crystal molecules are rubbed on the flat alignment film. The present inventors have confirmed that they are aligned with a larger pretilt angle as compared with.

When rubbing is performed on the alignment film 7 in the portion where the protrusion 6 is formed as described above, the groove 8 on the surface of the alignment film 7 in the rubbing entering portion is formed as shown in FIG. 4A. Being influenced by the protrusion 6, the shape rises and is inclined with respect to the substrate surface in the rubbing direction. Therefore, at the rubbing entry portion, the pretilt angle θ ₂ due to the groove 11 of the flat alignment film 10 formed on the conventional flat substrate surface 9 as shown in FIG. 4B.
The liquid crystal molecules 12 are aligned with a larger pretilt angle θ ₁ .

On the other hand, in the region on the opposite side of the rubbing entrance portion, that is, in the region where the rubbing passes from the protrusion 6, the groove 13 due to the rubbing is influenced by the protrusion 6 and is directed to the substrate surface in the rubbing direction. It is conceivable that the rubbing will have a downwardly sloping shape, but in reality, the portion through which such rubbing passes becomes a shadow portion with respect to the rubbing orientation treatment due to the protrusion 6, so that the orientation treatment is performed. Since it is performed only shallowly, it has almost no effect on the orientation of the liquid crystal molecules 12 in the pixel and the pretilt angle.

Therefore, it is considered that the substrate as a whole is strongly subjected to the control of the alignment direction and the control of the pretilt angle in the rubbing entry region of the protrusion 6. Therefore, the controllability of the alignment direction of the liquid crystal molecules 12 and the controllability of the pretilt angle θ ₁ by the alignment film 7 in the liquid crystal display element of the present invention are the same as those of the flat alignment film 10 in which the rubbing alignment is performed on the flat substrate 1. It is stronger than the pretilt angle θ ₂ . Moreover, since it is possible to control correspondingly the pretilt angle theta ₁ by changing the setting of the height and shape of the projection 6, it is also possible to heighten the degree of freedom in the pretilt angle theta ₁ configuration.

As described above, according to the present invention, a large pretilt angle is obtained by the action of the projection 6 while using an alignment film material having a low pretilt angle on a flat surface which is conventionally used. In addition, durability, reliability, and yield can be improved. Further, it is possible to drive with a low drive voltage, and it is possible to obtain a liquid crystal display element having a high display image quality.

The pretilt angle of the liquid crystal molecules in the liquid crystal display element of the first embodiment as described above was about 4.0 degrees. Further, the direction of this pretilt was a direction substantially following the rubbing direction of the alignment film 7. When the alignment state of the liquid crystal molecules in the liquid crystal layer between the cell gaps was examined, it was confirmed that a uniform alignment of 90 ° twist was realized.

The liquid crystal display device according to the present invention as described above was connected to a drive circuit system and actually driven to display a test pattern, and the display performance was verified. It was confirmed that no display defect due to the above-mentioned alignment defect was observed, and a good display without tilt reverse was obtained.

(Embodiment 2) In the above first embodiment, the first glass substrate having 480 transparent electrodes formed in the X direction on the glass substrate 1 and the glass substrate 1 are different from each other. Using the second glass substrate (not shown) in which 640 transparent electrodes are formed in the Y direction so as to be orthogonal to the X direction on the glass substrate, the first embodiment described above is performed on both substrates. A hemispherical protrusion 6 similar to that of the example is formed, and an alignment film 7 is formed so as to cover the entire surface of the substrate including the protrusion 6 in the same manner as in the first embodiment. The two substrates are arranged so as to face each other with a gap so that the liquid crystal molecules 12 are twisted by 240 ° to the left between the two glass substrates, the periphery is sealed, and the liquid crystal composition is injected into the gap. A simple matrix type liquid crystal display device using STN type liquid crystal was manufactured.

In the liquid crystal display device of the second embodiment having such a structure, the pretilt angle of the liquid crystal molecules 12 on the surface of the alignment film 7 was examined in the same manner as in the first embodiment. Became. Further, when the alignment state of the liquid crystal molecules 12 between the facing alignment films (that is, between the cell gaps) was examined, it was confirmed that a uniform 240 ° twist alignment was realized in the screen.

As a result of driving such a liquid crystal display device and verifying its display performance, it was confirmed that no display defect due to an alignment defect was found and a good display was obtained.

As described above, the present invention is an effective technique for an active matrix type liquid crystal display element using a TN type liquid crystal and a simple matrix type liquid crystal display element using an STN type liquid crystal. Or in addition to this,
Generally, it is effective in a liquid crystal display device that requires pretilt of liquid crystal molecules.

Although the projection 6 is formed in a hemispherical shape in the above embodiments, the present invention is not limited to this. In addition to this, for example, it may be formed in an elongated shape in the direction along the long axis direction of the liquid crystal molecules. Alternatively, the side surface may be formed in a convex shape having a tapered shape (that is, a trapezoidal cross section).

Needless to say, the height of the protrusion 6 is smaller than the gap (cell gap) between the two substrates, but especially with respect to the cell gap (that is, the thickness of the liquid crystal layer). It is desirable to suppress the height so as not to affect the retardation of the liquid crystal layer. Since the cell gap of a practical liquid crystal display device is generally about several μm, it is desirable to set the height of the protrusion 6 to within about 1 μm as in the above embodiment. This height may be set to an appropriate value depending on the cell gap of the liquid crystal display device, the viewing angle characteristics and the retardation characteristics of the liquid crystal composition used.

The arrangement density of the protrusions 6 is as follows.
About 10 ² pieces / mm ² to 10 ⁷ pieces / mm ² is effective.

In the above embodiment, the projection 6 is formed on the substrate 1.
The alignment film 7 is formed separately from the alignment film 7, and the alignment film 7 is formed on almost the entire surface of the substrate including the protrusion 6, and the upper surface of the alignment film 7 is projected in a shape along the protrusion 6. Although it is formed to have a surface, the protrusion 6 may be formed integrally with the alignment film 7 as a part of the alignment film 7 in addition to this. That is, according to the above-described embodiment, the SiO _x film 3 is formed thick in advance and half-etched to form the protrusion 6 at a height of about 1/2 of the film thickness. The SiO _x film 3 having a thickness of about 1/2 of the remaining portion where the portion 6 is not formed may be left solid. And in this case, S
By forming the iO _x film 3 from a material that can also be used as an alignment film, the rubbing alignment treatment is directly applied to the upper surface of the SiO _x film 3 to form the protrusion 6 itself. It can also be used as the alignment film 7. This is preferable because the formation of the alignment film 7 different from the SiO _x film 3 can be omitted.

Furthermore, by dividing one pixel into a plurality of divided areas and changing the shape, size, density, etc. of the projections 6 for each divided area, the pretilt angle can be changed for each divided area. it can. Alternatively, the pretilt angle can be changed for each divided region by providing the protrusion 6 in some divided regions and omitting it in the other divided regions. By providing a plurality of divided regions in which the formation state of the protrusion 6 is changed to form a plurality of regions having different pretilt angles in this way, the viewing angle can be effectively expanded, and the viewing angle as a liquid crystal display device can be increased. It is also possible to further improve the corner characteristics and further improve the display quality. In this case, in the conventional technique, the complicated process of performing different rubbing alignment treatments for each of the divided areas is required. However, according to the present invention, the shape and arrangement state of the protrusions 6 are set to the mask pattern. Since the change can be made only by changing or changing the etching conditions, it is possible to extremely easily create a plurality of regions in which the pretilt angle for changing the viewing angle is changed.

In addition, it goes without saying that various changes can be made to the material for forming each part of the liquid crystal display device of the present invention without departing from the scope of the present invention. (Comparative Example 1) A liquid crystal display device was formed by omitting the protrusions 6 formed on the glass substrate 1 and the TFT substrate in the first embodiment, and a test similar to that of the first embodiment was conducted on such a liquid crystal display device. When a pattern was displayed and the display performance was verified, alignment defects due to tilt reverse occurred in a part of the display area, and the visibility was significantly reduced.

(Comparative Example 2) A liquid crystal display element in which the projection 6 in the second embodiment 2 is omitted is prepared, and the same test pattern as that of the second embodiment is displayed on the liquid crystal display element to verify the display performance. As a result, tilt reverse occurred and the visibility deteriorated.

(Embodiment 3) FIG. 5 is a diagram showing the outline of the structure of a liquid crystal display element according to the present invention. For simplification of the description, the description will focus on two substrates on which the alignment film according to the present invention is formed. The same parts as those in the first and second embodiments are designated by the same reference numerals.

As shown in FIG. 5, in the two substrates of the liquid crystal display device of the third embodiment, an electrode layer 2 made of a transparent conductive film such as ITO is formed on a glass substrate 1,
An alignment film 500 is formed so as to cover it. The alignment film 500 is formed by using a polyimide film as a material. Then, on the surface of the alignment film 500, triangular pyramidal protrusions 501 having a base of about 5 μm and a bottom of an isosceles triangle having a vertical angle of about 10 μm from the bottom are arranged in a row. In this protrusion 501, the perpendicular bisector of the isosceles triangle on the bottom surface, in other words, the ridgeline 503 of the triangular pyramid is arranged in line so that the edge side of the glass substrate 1 forms an angle of 45 °. ing. In addition, this protrusion 501 is a ridgeline 50 of the triangular pyramid.
The angle formed by 3 with the bottom is about 6 °. Such a triangular pyramid-shaped protrusion 501 is shown in FIG.

Such a protrusion 501 is 110 μm wide × longitudinal
A 330 μm pixel is divided into two, and one region and the other region are arranged so that they are opposite by 180 °. At this time, the protrusions 501 are formed to have a substantially uniform density in each of the regions and the two substrates. Then, rubbing alignment treatment is performed on almost the entire surface of the alignment film 500 including the protrusion 501. This rubbing alignment treatment is performed in a direction parallel to the vertical bisector of the bottom surface, in other words, in a direction parallel to the ridge line 503 to form an alignment groove (not shown). Then, two substrates having the alignment film 500 on which such a protrusion 501 is formed are combined so that the alignment directions intersect each other by 90 ° to form a splay array cell, and the periphery is sealed to seal both substrates. A liquid crystal composition is injected into a gap (cell gap) and sandwiched as a liquid crystal layer (not shown) to form a liquid crystal cell. Then, two polarizing plates (not shown) of crossed Nicols are attached to the upper and lower sides of the liquid crystal cell so as to sandwich the liquid crystal cell from above and below, thereby forming the liquid crystal display element according to the present invention. There is.

The pretilt angle in the first region in one pixel in the liquid crystal display element having such a structure is about 4
The pretilt angle in the first region was about 6 °.

At this time, the rising directions of the liquid crystal molecules in the two regions were opposite to each other.

By controlling the pretilt angle and direction of the liquid crystal molecules in this way, it is possible to perform display with good viewing angle characteristics.

Next, a method of manufacturing such a liquid crystal display device will be described with reference to FIG.

As a material for forming the alignment film 500, polyimide (Probimide 400 series: manufactured by Ciba-Geigy) is used. This polyimide is applied on the glass substrate 1 with a uniform film thickness by a spin coater or the like to form a polyimide film 505.
To form. Then, using a photomask 5 on which a repeating pattern of an isosceles triangle having a base of 5 μm and a height of 10 μm is drawn, exposure is performed by i-line, and a polyimide film 505 that is a forming material of the alignment film 500 is coated so as to cover the polyimide film 505. The repetitive pattern of the photomask 5 is transferred to the resist 4 thus formed. This is performed using so-called backside exposure, in which the backside of the resist 4 is exposed through the glass substrate 1.

Then, etching is performed by diluting the etching solution to one tenth of the concentration generally used. The etching performed at this time is the polyimide film 50 for forming the alignment film 500 from the surface side on which the resist 4 is deposited.
5 is not removed by etching over the entire film thickness direction, but the progress of etching is stopped midway, that is, so-called half etching is performed, so that a protrusion having a substantially triangular pyramid shape is formed in the portion covered with the resist pattern. Fifty
1 is formed, the exposed portion is etched up to the middle thickness, but a part of the film thickness of the polyimide film 505 is left and a flat upper surface portion of the alignment film 500 can be formed. Various conditions such as the etching time of the above half etching are set in advance so that the alignment film 500 formed by performing such half etching has a film thickness and a shape of a protrusion that function as a desired alignment film. Needless to say.

Actually, when the liquid crystal display element as described above was driven to display the test pattern, it was confirmed that the display with good viewing angle characteristics can be realized as is clear from the isocontrast curve in FIG. Was done.

In the third embodiment described above, one pixel is
Although it is divided into two areas, it is also possible to further divide into a plurality of areas.

(Embodiment 4) Instead of the protrusion 501 in the liquid crystal display element of the third embodiment, as shown in FIG. 9, in two regions in one pixel 900, the direction of the vertical bisector of the bottom side is changed. Are in the same direction, the bottom is 5 μm and the height of the apex is 10 μm
Triangular pyramid-shaped protrusion 90 having a sharp-angled isosceles triangle on the bottom
1 (a) is formed in the first region 902 (a), while a triangular pyramid-shaped protrusion 901 (b) having an obtuse isosceles triangle with a base of 10 μm and a vertex height of 5 μm as the bottom is formed on the second region 902 (a). Area 9
No. 02 (b), and the rubbing alignment treatment is performed in the same direction as the third embodiment in a direction parallel to the ridgeline 903 of the triangular pyramid of the protrusions 901 (a) and 901 (b). Membrane 90
5 was formed. This is shown in FIG.

As a result, in the first region 902 (a), the pretilt angle of the liquid crystal molecules is about 6 °, and in the second region 902.
In (b), the pretilt angle was about 4.5 °. In this way, different shapes of triangular pyramids are formed in different areas,
Such triangular pyramid-shaped protrusions 901 (a) and 901 (b)
By subjecting the formed alignment film to rubbing alignment treatment in the same direction, it is possible to form the alignment film 905 having different pretilt angle alignment capabilities for each region.

A substrate on which such an alignment film 905 was formed was assembled as a liquid crystal cell having a 90 ° splay structure, a drive circuit was attached and driven to display a test pattern, and the image display quality was verified. It was confirmed that a good display can be realized with uniform viewing angle characteristics as in the third embodiment.

In the above embodiment, the protrusion 50
Although the shape of the bottom surface of each of the triangular pyramids 1 and 901 is an isosceles triangle, the shape is not necessarily limited to an accurate isosceles triangle. If the ridge lines of the triangular pyramid are aligned in a substantially parallel direction as a whole, the shape of the bottom surface of the triangular pyramid of the protrusion 901 is not necessarily a geometrically accurate isosceles triangle, but is good as in the above-described embodiments. Orientation control can be performed.

[0068]

As is clear from the detailed description above, according to the present invention, it is possible to obtain an alignment film having a low pretilt angle while having good stability, which is used as a conventional alignment film material. While using it, by controlling the pretilt angle by forming a protrusion, the process becomes complicated and difficult,
Alternatively, a liquid crystal display element that has good alignment stability and can be driven with a low drive voltage without lowering the reliability or durability of the liquid crystal display element, has good viewing angle characteristics, and has high image display quality is realized. can do.

[Brief description of drawings]

FIG. 1 is a diagram showing a structure of a liquid crystal display element according to a first embodiment of the present invention at a stage before a projection is formed.

FIG. 2 is a diagram showing an example of the shape of a protrusion of the liquid crystal display element according to the first embodiment of the present invention.

FIG. 3 is a diagram partially showing a counter substrate having a protrusion according to the first embodiment of the present invention.

FIG. 4A is a diagram showing the orientation state of the alignment film in the vicinity of the protrusions of the first embodiment and the orientation of the liquid crystal molecules controlled by the orientation (a), and the orientation of the liquid crystal molecules on the conventional flat orientation film. The figure (b) which shows a state.

FIG. 5 is a diagram showing a structure of both substrates on which protrusions according to a third embodiment of the present invention are formed.

FIG. 6 is a diagram showing a protrusion according to a third embodiment of the present invention.

FIG. 7 is a diagram showing a layer structure of a liquid crystal display device of a third embodiment before an exposure process for forming protrusions according to the present invention.

FIG. 8 is a diagram showing isocontrast curves of the liquid crystal display element of the third embodiment according to the present invention.

FIG. 9 is a diagram showing a shape of a pixel portion and a protrusion of an alignment film of a liquid crystal display element according to a fourth embodiment of the present invention.

[Explanation of symbols]

1 ... Glass substrate, 2 ... Transparent electrode, 3 ... SiO _x film, 4 ...
Positive type photosensitive resist film, 5 ... Photomask, 6 ... Protrusion,
7 ... Alignment film

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Yasue Moriizumi 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock company, Toshiba Yokohama Works (72) Inventor Ren Hato 8 Shinsugita-cho, Isogo-ku, Yokohama, Kanagawa Company Toshiba Yokohama Office (72) Inventor Akira Kubo 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Stock Company Toshiba Yokohama Office

Claims (6)

[Claims] 1. A pair of substrates each having an electrode and an alignment film formed on the surface of the substrate are arranged so that the alignment films face each other with a gap and the electrodes face each other to form a pixel. In a liquid crystal display element that is arranged and has a liquid crystal composition sandwiched by surrounding the gap, a plurality of protrusions are provided on the surface side of at least one of the two substrates in contact with the liquid crystal composition. A liquid crystal display device comprising: an alignment film having a plurality of alignment grooves formed therein, the alignment film having a plurality of alignment grooves that induce alignment in the liquid crystal composition. 2. A pair of substrates each having an electrode and an alignment film formed on the surface of the substrate are arranged so that the alignment films face each other with a gap and the electrodes face each other to form a pixel. In a liquid crystal display element, which is disposed and has a liquid crystal composition sandwiched by sealing the periphery in the gap, a plurality of liquid crystal display devices formed on at least one of the two substrates, the surface side being in contact with the liquid crystal composition. A protrusion, and an alignment film formed to cover the substrate including the plurality of protrusions, the alignment film having a plurality of grooves that induce alignment with respect to the liquid crystal composition. Characteristic liquid crystal display element. 3. The liquid crystal display element according to claim 1, wherein a plurality of regions having different sizes and arrangement densities of the protrusions are provided in the substrate, and a plurality of regions having different alignment pretilt angles of the liquid crystal composition are provided. A liquid crystal display device having a region. 4. Two substrates, each having an electrode and an alignment film formed on the surface of the substrate, are formed so that the alignment films face each other with a gap and the electrodes face each other to form a pixel. In a liquid crystal display element, which is arranged and has a liquid crystal composition sandwiched around the gap and sandwiching a liquid crystal composition, each pixel is divided into a plurality of regions, and a bottom surface is an isosceles triangular triangular pyramid shape or the bottom surface. It is a truncated triangular pyramid-shaped protrusion that is obtained by cutting out the upper part of the triangular pyramid in a plane substantially parallel to, and the perpendicular bisectors of the base of the isosceles triangle of the bottom face are aligned in substantially one direction, and The orientation film of the isosceles triangle is formed in each of the divided areas of the pixels by 180 ° in opposite directions with the base of the isosceles triangle as a symmetrical axis. Are provided on the surface side in contact with the liquid crystal composition of A liquid crystal display device characterized by the above. 5. The two substrates each having an electrode and an alignment film formed on the surface of the substrate are arranged so that the alignment films face each other with a gap and the electrodes face each other to form each pixel. In the liquid crystal display element, wherein each of the pixels is divided into a plurality of regions, each of which has a different shape. An alignment film in which a plurality of protrusions having a triangular pyramid shape or a truncated triangular pyramid shape having an equilateral triangular bottom surface are arranged, and the liquid crystal is aligned in a direction substantially perpendicular to the base of the isosceles triangle of the bottom surface. A liquid crystal display device, comprising: an alignment film having alignment grooves for controlling directions, which are respectively provided on the surfaces of the two substrates in contact with the liquid crystal composition. 6. The liquid crystal display element according to claim 1, wherein the projections are arranged so that the area ratios are equal in each of the plurality of divided areas. .