JP2001281662A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vertical alignment mode liquid crystal display device with improved display quality and capable of displaying by utilizing reflected light. SOLUTION: The liquid crystal display device has a liquid crystal layer 23, containing liquid crystal molecules with negative dielectric constant anisotropy and is equipped with a reflection layer 3 for reflective mode display. With respect to a first alignment layer 30a and a second alignment layer 30b, arranged to control alignment of the liquid crystal molecules, only the second alignment layer 30b, arranged on the side of the substrate without the reflection layer 4, is subjected to photo aligning treatment.

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, and more particularly, to a vertical alignment mode liquid crystal display capable of performing display utilizing reflected light.

[0002]

2. Description of the Related Art A liquid crystal display device is characterized by its thinness and low power consumption, and is characterized by OA equipment such as a word processor and a personal computer, portable information equipment such as an electronic organizer, or a camera body equipped with a liquid crystal monitor. Widely used for VTRs and the like. In many of these liquid crystal display devices, a liquid crystal material having a positive dielectric anisotropy is horizontally oriented with respect to a substrate, and 90% of liquid crystal molecules exist between upper and lower substrates.
This is a liquid crystal display device of a TN (twisted nematic) mode that takes a twisted alignment state.

In recent years, since a display having a higher contrast ratio than that of the TN mode can be realized, a liquid crystal material having a negative dielectric anisotropy is vertically aligned with respect to a substrate. Aligned Phase)
Mode ". The development of the liquid crystal display device has been actively carried out. However, the vertical alignment mode has a streak-like luminance in the direction in which a rubbing process in which the surface of the alignment film is rubbed with a cloth in order to define the alignment direction of liquid crystal molecules when a voltage is applied is different from the TN mode. Unevenness (hereinafter referred to as "rubbing streaks") is likely to occur, and there is a problem that display quality is deteriorated.

On the other hand, as an alignment treatment method that does not require a rubbing treatment method, a light alignment treatment method using a light polarization storage film is known (for example, Japanese Patent Application Laid-Open Nos. 7-56173 and 9-61826). And JP-A-9-318946, and "Takezoe et al., Japanese Society of Liquid Crystal Society, Proceedings, 2D03, pp. 400-401, 199
9 "). In these photo-alignment treatment methods, for example, a polyvinyl 4-methoxycinnamate (PVC) film is irradiated with linearly polarized light to impart an orientation force to the PVC film (see JP-A-7-56173 and JP-A-9-56173). −61
No. 826). Further, by irradiating the polyimide film with non-polarized light from an oblique direction, an orientation force is given to the polyimide film (see Japanese Patent Application Laid-Open No. 9-318946). In addition, a non-polarized light is irradiated from an oblique direction to an alignment film obtained by adding lecithin to a polyimide having an azo group in the main chain, and an alignment force is imparted by using a photoisomerization reaction. Proceedings of lectures).

The alignment films obtained by these methods define the alignment direction of the liquid crystal molecules and give a pretilt angle to the liquid crystal molecules. In addition, unlike the rubbing treatment method, the optical alignment treatment method does not apply a physical force to the surface of the alignment film, so that display defects such as rubbing streaks do not occur and uniform orientation can be obtained. .

[0006]

However, a photo-alignment treatment method using an optical polarization storage film has been applied to a reflection type liquid crystal display device of a vertical alignment mode or a transflective type liquid crystal display device (for example, Japanese Patent Application Laid-Open No. 11-101992). Disclosure is generated when applied to a vertical alignment mode liquid crystal display device capable of performing display using reflected light, such as
The present inventor has found that there is a problem that uniform orientation cannot be obtained.

[0007] The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to improve display quality.
It is an object of the present invention to provide a vertical alignment mode liquid crystal display device capable of performing display using reflected light.

[0008]

A liquid crystal display device according to the present invention comprises a first substrate, a second substrate, the first substrate and the second substrate.
A liquid crystal layer provided between the substrate and the substrate, the liquid crystal layer including liquid crystal molecules having negative dielectric anisotropy, and a plurality of picture element regions for performing display, wherein the first substrate Includes a first electrode, a reflective layer, and a first electrode in the plurality of pixel regions.
A first electrode provided on the liquid crystal layer side of the electrode and the reflective layer;
An alignment film, the second substrate has a second electrode in the plurality of picture element regions, and a second alignment film provided on the liquid crystal layer side of the second electrode; The first alignment film is a vertical alignment film that does not define the alignment of the liquid crystal molecules in the azimuthal direction, and the second alignment film is provided with an alignment control force that gives a pretilt angle to the liquid crystal molecules by a photo alignment process. This is a vertical alignment film, whereby the above object is achieved.

[0009] The first electrode may be a reflective electrode functioning as the reflective layer, or the first electrode has a reflective electrode functioning as the reflective layer and a transparent electrode made of a transparent conductive layer. It may be configured.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present inventor has set forth the cause of the above-mentioned problem which occurs when a photo-alignment processing method using a light polarization storage film is applied to a reflective liquid crystal display device or a transflective liquid crystal display device. Elucidation, and as a result, led to the present invention. First, the cause of the above problem is considered as follows.

The light alignment light treatment using the light polarization storage film disclosed in the above publication is, for example, as shown in FIG.
An optical polarization storage film (for example, PVC) formed on the substrate 10
The film 30 is irradiated with linearly polarized light from a direction inclined with respect to the substrate normal (the inclination angle is represented by θ), thereby giving an alignment regulating force that gives a pretilt angle in a direction parallel to the polarization direction P. A film is formed (for example, see JP-A-7-5
No. 6173, FIG. 4). In addition, Japanese Patent Application Laid-Open No. 9-6
FIG. 4 (B) of JP-A-1826 and Japanese Patent Application Laid-Open No. 9-318946.
As disclosed in FIG. 1A of Japanese Patent Application Laid-Open Publication No. H10-209, all of the above-described methods irradiate light (linearly polarized light or non-polarized light) from a direction inclined with respect to the substrate normal line to obtain a desired azimuth direction. An alignment film having an alignment regulating force giving a pretilt angle of?

When these light alignment treatment methods are performed on the light polarization storage layer 30 formed on the reflection layer 32 as shown in FIG. 1, light incident on the light polarization storage layer 30 from the light source side is reduced. Are reflected by the reflection layer 32 and again enter the light polarization storage layer 30. Therefore, light enters the reflective layer 30 from two directions forming an angle of 2θ with each other. As a result, it is considered that the direction of the alignment regulating force applied to the alignment film by the optical alignment treatment is not constant. Of course, a desired pretilt angle cannot be obtained.

FIG. 1 shows a case where light is specularly reflected (specular reflection) by the reflection layer 32 for the sake of simplicity. However, the reflection layer for displaying a reflection mode has a characteristic of diffusing and reflecting incident light. (In an appropriate light distribution), the angle at which the reflected light enters the light polarization storage film 30 has a distribution. As a result, the azimuthal direction of the alignment regulating force provided by the optical alignment process further varies.

Although FIG. 1 shows a configuration in which the reflective layer 32 is formed on the substrate 10, the same applies to a configuration in which the reflective layer is provided outside the substrate (the lower side in FIG. 1).

Some of the reflective layers 32 having a diffuse reflection characteristic have an uneven surface. The light polarization storage film 30 formed on the uneven surface of the reflective layer 32 is formed along the surface shape. Therefore, the light obliquely incident is
It becomes difficult to uniformly irradiate the light polarization storage film 30.

Further, the transflective liquid crystal display device exemplified in the embodiment has a transparent region and a reflective region for each picture element region, and electrodes (typically, transmissive electrodes and reflective electrodes) in the respective regions. Are different from each other in height from the surface of the substrate. This is to optimize the thickness of the liquid crystal layer for transmitted light and the thickness of the liquid crystal layer for reflected light, respectively. Therefore, for example, the difference between the height of the transparent electrode and the height of the reflective electrode is several μm. It is difficult to irradiate the light polarization storage film 30 on the electrodes formed at different heights from a diagonal direction with a uniform intensity distribution.

In view of the above, the inventor of the present application has studied to perform a photo-alignment treatment only on the light polarization storage film 30 provided on a substrate having no reflective layer. Further, when a vertical alignment film is formed on the optical polarization storage film 30 provided on the substrate having the reflective layer according to a conventional method without performing the alignment treatment, a uniform alignment having a pretilt angle can be realized. Do you get it.

The liquid crystal display device of the present invention is a liquid crystal display device having a liquid crystal layer containing liquid crystal molecules having a negative dielectric anisotropy and a reflective layer for displaying a reflection mode. Of the first alignment film and the second alignment film provided for regulating the alignment of molecules, the optical alignment treatment is performed only on the second alignment film provided on the substrate (the second substrate) having no reflective layer. It has been subjected.

Since the second substrate does not have a reflective layer, light applied to the vertical alignment film for imparting an alignment regulating force for giving a pretilt angle to the liquid crystal molecules is reflected by the base of the vertical alignment film. The problem that the incident direction of the light applied to the vertical alignment film is not constant does not occur. Therefore, the vertical alignment film is uniformly photo-aligned, and the obtained second
The alignment film can uniformly align the liquid crystal molecules in a predetermined azimuthal direction at a predetermined pretilt angle. On the other hand, the first alignment film provided on the first substrate having the reflective layer is a vertical alignment film that does not define the azimuthal orientation of the liquid crystal molecules, and does not require a rubbing process or a photo alignment process. It is only necessary to form a film made of a film material.

The liquid crystal molecules in the vicinity of the second alignment film are uniformly aligned in a predetermined azimuth direction at a predetermined pretilt angle in accordance with the uniform alignment regulating force of the second alignment film. On the other hand, the liquid crystal molecules in the vicinity of the first alignment film do not receive the alignment control force in the azimuthal direction from the first alignment film, and thus the alignment is controlled by the first alignment film through the interaction between the liquid crystal molecules. Align to align with liquid crystal molecules. Therefore, since the liquid crystal molecules of the entire liquid crystal layer are uniformly aligned, when a voltage is applied to the liquid crystal layer, the liquid crystal molecules uniformly tilt (rotate) in a predetermined azimuth direction. As a result, high-quality display is realized.

FIG. 2 is a plan view of the liquid crystal display device according to the embodiment of the present invention, and FIG. 3 is a sectional view taken along line AA 'in FIG.

This liquid crystal display device is a transflective liquid crystal display device, in which a reflection portion (reflection electrode 4) that reflects external light to one picture element region and a transmission portion (transmission) that transmits light from a backlight. Electrode 3) and has both functions of a reflection type and a transmission type. The liquid crystal layer 23 is a vertical alignment mode liquid crystal display device including a liquid crystal material having a negative dielectric anisotropy.
Further, the polarizing plates 20 and 22 are arranged so that their polarization axes are orthogonal to each other, and display in a normally black mode. Quarter-wave plates 19 and 21 are provided with liquid crystal layer 23.
Is provided for converting the polarized light incident (or emitted) to the linearly polarized light from the linearly polarized light or from the circularly polarized light to the linearly polarized light.

The TFT substrate is a substrate on which a thin film transistor (hereinafter, referred to as TFT) 5 is formed on a glass substrate 10. A plurality of gate bus lines 1 as scanning lines and source bus lines 2 as signal lines are alternately provided. In a region surrounded by each gate bus line 1 and each source bus line 2, for example, ITO
Transparent electrode 3 made of and reflective electrode 4 made of, for example, Al
And are arranged. The transmissive electrode 3 and the reflective electrode 4 constitute a picture element electrode. In order to optimize the display in the transmission mode and the display in the reflection mode, the thickness of the liquid crystal layer 23 is adjusted so that the thickness dt of the transmission region is approximately twice the thickness dr of the reflection region. And reflective electrode 4
Are formed.

A TFT 5 is arranged at a corner of the area where the picture element electrodes are arranged (which defines the picture element area of the liquid crystal display device). The TFT 5 has a gate electrode 6, a source electrode 7, and a drain electrode 8, and the gate bus line 1 is connected to the gate electrode 6, and the source bus line 2 is connected to the source electrode 7. Picture element electrode (transmission electrode 3 and reflection electrode 4)
Is connected to the drain electrode 8 at a contact hole 9 provided in the resin film 14 described later.

Further, a gate insulating film 12 is formed on the glass substrate 10, and a transparent electrode 13 is patterned. Under the reflective electrode 15, a photosensitive resin film 14 having a continuous wavy uneven surface is formed. The reflection electrode 15 formed on the resin film 14 also has a continuous wavy uneven surface, and as a result, functions as a reflection layer having good light distribution characteristics. As a material of the photosensitive resin film 14, for example, OFPR-800 manufactured by Tokyo Ohka Co., Ltd. is used.

This TFT substrate has a vertical alignment film 30a formed so as to cover almost the entire surface (at least the entire display area). The vertical alignment film 30a is formed using a known vertical alignment film material. For example, JSR
It is obtained by printing JASL 204 manufactured by the company so that the film thickness becomes, for example, 100 nm, and baking it at 180 ° C. for 2 hours. No treatment such as a rubbing treatment or a photo-alignment treatment for giving a force to regulate the orientation in the azimuthal direction to the orientation film is performed.

The color filter substrate comprises a color filter layer 16 and a black matrix 17, and a transparent electrode (counter electrode) 18 is formed on the surface of the substrate. The transparent electrode 18 is formed using, for example, ITO. This color filter substrate has an alignment film 30b formed so as to cover almost the entire surface (at least the entire display area).

The alignment film 30b is a vertical alignment film material and
A material to which a pretilt angle is given in a predetermined azimuthal direction by a predetermined optical alignment process is selected. Since the polarization direction and the pretilt direction are different depending on the optical alignment processing method, a combination of the material and the alignment processing method is appropriately selected.

For example, by irradiating linearly polarized light from an inclined direction, a polymer film in which liquid crystal molecules are uniformly aligned in one direction with pretilt is spin-coated so that the film thickness becomes 50 nm, Dried for 10 minutes.

Next, as shown in FIG. 4, linearly polarized ultraviolet rays (300 to 350 nm) were irradiated for 6 seconds from a direction inclined 45 ° from the vertical direction of the color filter substrate so as to generate pretilt. The amount of light at this time is, for example, about 1.0 J / cm ² .

A nematic liquid crystal material having a negative dielectric anisotropy (for example, Merck liquid crystal) is attached to a liquid crystal cell formed by bonding the color filter substrate and the TFT substrate obtained as described above with a predetermined gap therebetween. Company: MLC-6
608, Δn = 0.0830) according to a conventional method,
The liquid crystal display device is obtained by forming the vertical alignment liquid crystal layer 23.

In the liquid crystal display device manufactured as described above, since no rubbing treatment is performed, uniform alignment can be obtained without rubbing streaks. On the TFT substrate side, no vertical alignment film is applied, and no alignment treatment is performed. Therefore, pretilt does not occur, and the liquid crystal molecules are aligned at approximately 90 degrees with respect to the alignment film surface.

On the other hand, since the color filter substrate irradiates the linearly polarized ultraviolet light at an angle of 45 ° from the vertical direction of the color filter, a pretilt of about 2 to 3 ° with respect to the normal direction is uniformly generated. This mechanism is considered as follows.

In the alignment film used here, before the alignment treatment is performed, the molecular chains defining the alignment direction of the liquid crystal molecules are aligned almost perpendicularly to the substrate surface. Strictly, this molecular chain is inclined at a pretilt angle of 2 to 3 ° with respect to the substrate normal, but since the azimuth of the inclination is random, the liquid crystal molecules are vertically aligned as a whole. For example, when the alignment film has a property that a molecular chain regulating the alignment is decomposed by light having a polarization direction orthogonal to the molecular chain, a direction inclined to the alignment film (for example, the above-described 45 °) Irradiates linearly polarized light from, the molecular chains oriented in a direction parallel to the polarization direction of the linearly polarized light (a direction close to parallel) remain without being decomposed, so that the azimuthal direction is pretilt angle of 2 ° to 3 ° It is decided uniquely.

Therefore, in this liquid crystal display device, the liquid crystal molecules in the vicinity of the color filter substrate are uniformly inclined in the pretilt direction without causing the directions in which the liquid crystal molecules fall when a voltage is applied, and match the liquid crystal molecules. As described above, the liquid crystal molecules in the vicinity of the TFT substrate can also be tilted uniformly, so that disclination does not occur and high-quality display can be realized.

In the above description, the photo-alignment treatment is performed by using a method of irradiating linearly polarized light obliquely. In addition, the above-mentioned Japanese Patent Application Laid-Open No. 7-56173 and Japanese Patent Application Laid-Open No. 9-618
No. 26, Japanese Patent Application Laid-Open No. 9-318946, and a method for photo-alignment treatment disclosed in a collection of lectures by Takezoe et al.

The present invention is not limited to a transflective liquid crystal display device but can be widely applied to a liquid crystal display device having a reflective layer. For example, the present invention can be applied to a reflective liquid crystal display device shown in FIG. The picture element electrode of this liquid crystal display is the reflection electrode 4. Other configurations are practically the same as those of the liquid crystal display device shown in FIG.

[0038]

According to the present invention, of the first alignment film and the second alignment film provided for regulating the alignment of the liquid crystal molecules, the second alignment film provided on the substrate side having no reflective layer is provided. Only the photo-alignment treatment is performed. Since the second substrate does not have a reflective layer, light applied to the vertical alignment film to provide an alignment control force for giving a pretilt angle to liquid crystal molecules is reflected by the base of the vertical alignment film, and as a result, the vertical alignment film is formed. The problem that the incident direction of the light applied to the light source is not constant does not occur. On the other hand, the first alignment film provided on the first substrate having the reflective layer is a vertical alignment film that does not define the azimuthal alignment of the liquid crystal molecules.

The liquid crystal molecules in the vicinity of the second alignment film are uniformly aligned in a predetermined azimuth direction at a predetermined pretilt angle in accordance with the uniform alignment control force of the second alignment film. On the other hand, the liquid crystal molecules in the vicinity of the first alignment film do not receive the alignment control force in the azimuthal direction from the first alignment film, and thus the alignment is controlled by the first alignment film through the interaction between the liquid crystal molecules. Align to align with liquid crystal molecules. Therefore, since the liquid crystal molecules of the entire liquid crystal layer are uniformly aligned, when a voltage is applied to the liquid crystal layer, the liquid crystal molecules uniformly tilt (rotate) in a predetermined azimuth direction. As a result, a reflective or transflective vertical alignment mode liquid crystal display device with improved display quality is provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a problem when a light distribution processing method is applied to a light polarization storage film formed on a substrate having a reflective layer.

FIG. 2 is a plan view schematically showing a liquid crystal display device according to an embodiment of the present invention.

FIG. 3 is a cross-sectional view schematically illustrating a liquid crystal display device according to an embodiment of the present invention.

FIG. 4 is a diagram schematically showing a light distribution processing method used in an embodiment according to the present invention.

FIG. 5 is a plan view schematically showing another liquid crystal display device according to the embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Gate bus line 2 Source bus line 3 Transparent electrode 4 Reflection electrode 5 TFT 6 Gate electrode 7 Source electrode 8 Drain electrode 9 Contact hole 10 Glass substrate 11 Glass substrate 12 Gate insulating film 14 Resin film 16 Color filter 17 Black matrix 18 Transparent electrode 19 Quarter-wave plate 20 Polarizer 21 Quarter-wave plate 22 Polarizer 23 Liquid crystal layer 24 Linearly polarized UV 25 Color filter substrate 30a Alignment film (vertical alignment film) 30b Alignment film subjected to photo-alignment treatment (optical polarization storage film) )

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H090 KA04 LA01 LA04 MA01 MA10 MA12 MB12 2H091 FA14Y GA02 GA06 HA06 LA18 2H092 GA19 HA04 HA05 JA24 JB07 JB08 NA01 PA02 PA12 5C094 AA03 AA15 AA22 BA03 BA44 CA19 EA04 EA09

Claims (3)

[Claims] A first substrate, a second substrate, and a liquid crystal layer provided between the first substrate and the second substrate, the liquid crystal layer including liquid crystal molecules having negative dielectric anisotropy; A liquid crystal display device having a plurality of picture element regions for performing display, wherein the first substrate includes a first electrode, a reflection layer, a first electrode, and a reflection layer in the plurality of picture element regions. A first alignment film provided on the liquid crystal layer side of a layer, wherein the second substrate is provided on the liquid crystal layer side of the second electrode in the plurality of picture element regions. A second alignment film, wherein the first alignment film is a vertical alignment film that does not define the azimuthal alignment of the liquid crystal molecules, and the second alignment film has a pretilt angle for the liquid crystal molecules. A liquid crystal display device, which is a vertical alignment film to which an alignment regulating force to be given is given by a light alignment process. 2. The liquid crystal display device according to claim 1, wherein the first electrode is a reflection electrode that functions as the reflection layer. 3. The liquid crystal display device according to claim 1, wherein the first electrode has a reflective electrode functioning as the reflective layer and a transparent electrode made of a transparent conductive layer.