JPH10213794A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electro-optical display device capable of removing hysteresis to be a fault at the time of gradation display and capable of attaining half tone display with respect to an electro-optical display element using liquid crystal(LC) layer structure of a high twist angle exceeding 270 deg.. SOLUTION: An irregular and fine rugged face is constituted on the LC layer side surface of at least one of 1st and 2nd transparent electrodes 3, 4 arranged through an LC layer 7. When the surface of the 2nd transparent electrode 4 e.g. is ruggedly formed, the layer thickness of the layer 7 is formed so as to be partially different like d1, d2 and the electric field strength of the layer 7 is made partially different. Thereby the hysteresis of each part is offset by a '0' part and the hysteresis of the whole LC layer 7 is removed and half tone display is attained.

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 improved halftone reproducibility.

[0002]

2. Description of the Related Art The principle of operation of a conventionally used liquid crystal display device using a twisted nematic structure will be described with reference to FIG. FIG. 1 is a schematic sectional view of the structure of this type of liquid crystal display device. Here, assuming that light is incident from the upper side to the lower side of the drawing, the first polarizing plate 1 that transmits only the vibration component in a certain direction through the incident light in order from the light incident side, and is polished so that the surface becomes flat Transparent substrate 2, a first transparent electrode 3 typified by ITO (indium tin oxide) applied on the transparent substrate 2, a liquid crystal layer 7 made of a birefringent substance, a first transparent It has a structure in which a second transparent electrode 4 arranged to face the electrode 3, a flat second transparent substrate 5 on which the second transparent electrode 4 is applied, and a second polarizing plate 6 are superposed. The liquid crystal layer 7 is interposed between the first transparent electrode 3 and the second transparent electrode 4 between the gaps d, and the layer structure of the liquid crystal molecules constituting the liquid crystal layer 7 includes the first transparent electrode 3 and the second transparent electrode 3. It has a layer structure twisted between the transparent electrodes 4.

The principle of operation of this twisted nematic liquid crystal display device is that when no voltage is applied to the first transparent electrode 3 and the second transparent electrode 4, light is incident from the outside (first It is assumed that the light enters from the polarizing plate 1)
The incident natural light is converted into linearly polarized light by the first polarizing plate 1, passes through the first transparent substrate 2 and the first transparent electrode 3, and enters the liquid crystal layer 7. The light incident on the liquid crystal layer 7 reaches the second transparent electrode 4 facing the first transparent electrode 3 while changing the plane of polarization due to the birefringence of the liquid crystal. Thereafter, the light passes through the second transparent electrode 4 and the second transparent substrate 5 and the second polarizer 6
Creates a first optical state by cutting off light components in arbitrary directions. On the other hand, when a voltage is applied to the first transparent electrode 3 and the second transparent electrode 4, the liquid crystal molecules constituting the liquid crystal layer 7 are aligned according to the applied voltage due to the dielectric anisotropy of the liquid crystal molecules. To change. for that reason,
When the birefringence of the liquid crystal layer 7 changes and the light transmitted through the liquid crystal layer 7 reaches the second transparent electrode 4, the polarization plane of the light applies a voltage to the first transparent electrode 3 and the second transparent electrode 4. The second optical state can be created because it is different from the case in which the second optical state is not performed. Therefore, it is possible to change between the first optical state and the second optical state by the magnitude of the voltage applied to the first transparent electrode 3 and the second transparent electrode 4, so that light can be switched. Become.

[0004]

In such a conventional liquid crystal display device, the twist angle of the liquid crystal layer is increased.
It is known that when the angle is larger than 0 degree, the tilt angle that can be taken by the molecules at the center of the liquid crystal layer due to the electric field applied from the outside takes an S-shaped locus depending on the magnitude of the voltage applied to the liquid crystal layer. If the tilt angle of the liquid crystal molecules follows an S-shaped trajectory as described above, different arrangement states of the liquid crystal molecules occur when the voltage is raised and lowered, and as a result of the two states intermingling, an alignment defect called finger texture is generated. To be observed. FIG. 20 shows a photograph showing a state in which an alignment defect has occurred. This alignment defect is not observed when a sufficient voltage is applied or when no voltage is applied, and can be observed only when an intermediate voltage is applied. As a result, a large hysteresis occurs in the optical response as a whole as shown in FIG. When such hysteresis exists, two or more stable points are generated even at the same voltage. Therefore, even if a certain voltage is applied to the liquid crystal element, the arrangement state of the liquid crystal molecules obtained is two or more states. In other words, the transmittance cannot be uniquely determined with respect to the applied voltage, and there is a problem that halftone display cannot be performed.

[0005] In order to solve this problem, regarding the elimination of the hysteresis effect in a guest-host liquid crystal having a twist angle of 300 degrees, "May 1996, SID '96 Digest Technical Paper, p. 35 (SID'96 Diges
t of Technical Paper, P35, 1996) ”
Although there is a proposal of a method using N, in this method, a process of giving initial alignment to liquid crystal molecules such as a rubbing process is not performed in order to make the alignment of the liquid crystal amorphous. Therefore, in this method, there is a problem that the liquid crystal alignment is likely to occur at the time of injecting the liquid crystal, and it is not suitable for production with a high yield due to strict temperature control during the injection.

An object of the present invention is to provide a liquid crystal display device having a liquid crystal layer having a twist angle larger than 270 degrees where the molecular tilt angle at the center of the liquid crystal layer is theoretically S-shaped. An object of the present invention is to provide a liquid crystal display device which has no hysteresis, improves reproducibility of halftones, and does not cause alignment failure even at the time of liquid crystal injection at room temperature so that production is easy.

[0007]

According to the present invention, at least one of the transparent electrodes is provided between a first electrode and a second electrode.
In a liquid crystal display device in which a liquid crystal layer having a layer structure twisted by 0 ° or more is interposed, an electric field intensity generated in the liquid crystal layer by a voltage applied between the first electrode and the second electrode partially occurs within one pixel. It is characterized in that it is configured to be different. For example, at least one of the first electrode and the second electrode is 1
Irregularities are formed on the surface in the pixel, and the layer thickness of the liquid crystal layer is partially changed due to the irregularities. Alternatively, at least one of the first electrode and the second electrode has an uneven surface formed in one pixel, and an organic or inorganic substance having a dielectric constant equal to or lower than the dielectric constant of the liquid crystal layer is formed in the concave portion. The liquid crystal layer is embedded so as to have a uniform thickness. In this case, the electrode having the uneven surface is formed on the surface of the substrate having the uneven surface, or has an inorganic or organic film on a flat substrate. The film is formed on the uneven surface of the surface formed by changing the thickness of this film. When a voltage is applied between the first electrode and the second electrode to the liquid crystal element having such a configuration, the electric field intensity applied to the liquid crystal layer changes by one pixel because the thickness of the liquid crystal layer changes. Due to the difference in thickness within the pixel, the pixel partially differs within one pixel. As a result, the threshold voltage and the saturation voltage of the liquid crystal partially differ within one pixel, and when measuring the voltage versus transmittance characteristics as one pixel, the hysteresis is eliminated regardless of the twist angle at which the hysteresis occurs. Display becomes possible.

The present invention also provides a liquid crystal display device comprising a liquid crystal layer having a layer structure twisted by 270 degrees or more between a first electrode and at least one transparent electrode. The liquid crystal is characterized in that the initial alignment state of the liquid crystal on one or both electrode surfaces of the electrode and the second electrode is non-uniform in the pixel, and that the rising direction of the liquid crystal molecule is different in one pixel when a voltage is applied. For example, a rubbing direction is provided in at least two directions in one pixel on one surface of the first electrode or the second electrode. Alternatively, one of the first electrode and the second electrode has fine irregularities formed on its surface, and the alignment film formed on the irregularities is rubbed to align the liquid crystal along the minute irregularities. The tilt angles of the liquid crystal molecules caused by the above are different in one pixel. In this configuration, when an electric field is applied between the first electrode and the second electrode, there are a plurality of portions (regions) in which the rising direction of the liquid crystal molecules differs in one pixel due to the difference in the initial alignment state. In addition, an area boundary is generated between the areas due to the reverse tilt. The size of this region is substantially equal to the pitch of the unevenness formed on the substrate. That is,
When the adjacent regions rise in the same direction when a voltage is applied, the apparent size of the region becomes large because the two are fused. The change in the alignment state of the liquid crystal molecules generated in one region cannot affect another region beyond the boundary of the region. Therefore, when a plurality of regions exist in one pixel, even if hysteresis occurs in each region, the transmittance of the entire pixel increases or decreases without a hysteresis with respect to the voltage applied from the outside, and the liquid crystal element exceeds 270 degrees. The hysteresis effect peculiar to the above can be eliminated.

According to the structure of the present invention, the liquid crystal molecules filled between the first electrode and the second electrode are given an initial alignment state from the alignment film. No initial alignment failure occurs due to the flow of the liquid crystal generated when the liquid crystal panel is pressed. Therefore, it is possible to omit the annealing process performed for the purpose of stabilizing the initial alignment state of the liquid crystal after the liquid crystal is injected.

According to the present invention, the first electrode or the second electrode is formed as a transparent electrode, formed on the opposing surfaces of the first transparent substrate and the second transparent substrate, respectively, and configured as a transmission type liquid crystal display device. One of the first and second electrodes is configured as a transparent electrode, and the other is configured as a reflective electrode, and can be configured as a reflective liquid crystal display device.

As described above, in the present invention, 270
In order to eliminate the hysteresis phenomenon peculiar to the liquid crystal element having a twist angle exceeding the degree, at least one of the first electrode and the second electrode, characterized in that minute irregularities are formed on the surface, Through detailed experiments, it has been clarified that a slight difference in the shape of the minute unevenness causes a difference in the degree of the effect of eliminating the hysteresis. That is, in the present invention, the fine unevenness formed on at least one of the first electrode and the second electrode does not have a long continuous valley line in the uneven shape, and particularly the concave portion among the individual concave portions and the convex portions is formed. It has been found that a shape separated from each other by a ridge-like convex portion is preferable. Unlike such a preferable uneven shape, if the uneven shape has a long valley line, the above-mentioned alignment defect called finger texture appears along the valley line, and the hysteresis is not completely eliminated. . On the other hand, in the preferred concavo-convex shape according to the present invention, since the individual concave portions are separated from each other by the ridge-shaped convex portions, alignment defects do not appear in a long row, and therefore, hysteresis can be eliminated.

Further, as described above, the concave and convex shape does not have a long continuous valley line, and the individual concave portions are separated from each other by the ridge-like convex portions. It has been found that more preferable gradation display is performed when the depths of the individual concave portions included in the inside are configured to have a random wide distribution. The threshold voltage that induces a change in the alignment state of the liquid crystal in a region corresponding to each concave portion is determined according to the depth of the concave portion. Therefore, as described above, when the depth of each concave portion is configured to have a random wide distribution, the threshold value in each concave portion is widely distributed, so that the gradation characteristic becomes smooth, and the display is accordingly performed. The number of possible gradations can be increased.

In the present invention, when one of the first electrode and the second electrode is configured as a transparent electrode and the other is configured as a reflective electrode, and is configured as a reflective liquid crystal display device, the electrode having the fine irregularities described above is used. As a reflective electrode. In a reflection type liquid crystal display device, the surface shape of the reflector and the reflection characteristics (the relationship between the incident angle and the detection angle of light and the reflectance) based on the surface shape greatly affect the brightness of the display, and therefore, are particularly important. Importantly, in the present invention, it is possible to make the surface shape of the reflective electrode a shape that can realize a bright display after the shape is preferable for eliminating the above-described hysteresis.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION

[First Embodiment] Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic sectional view showing the configuration of the first embodiment of the present invention. This liquid crystal display device includes a first polarizing plate 1, a first transparent substrate 2, a first transparent electrode 3,
It has a structure in which a liquid crystal layer 7, a second transparent electrode 4, a second transparent substrate 5, and a second polarizing plate 6 are superposed in this order. In this structure, the first polarizing plate 1, the first transparent substrate 2, the first transparent electrode 3, and the second polarizing plate 6 have the same structure as the conventional example. The liquid crystal layer 7 has a twist angle of 270 degrees or more and less than 450 degrees between the first transparent electrode 3 and the second transparent electrode 4. On the other hand, the second transparent substrate 5 has a structure in which at least the surface in contact with the liquid crystal layer 7 is roughened. For example, the second transparent substrate 5 is processed by a method such as etching, sandblasting, or polishing. This realizes a rough surface. Here, the surface is roughened so as to have a continuous corrugated cross section. A second transparent electrode 4 is obtained by forming a transparent electrode such as ITO on the roughened surface by a method such as vapor deposition, sputtering, or coating. Then, the transparent substrate 2 having the first transparent electrode 3 is opposed to the second transparent electrode 4 and the second transparent substrate 5 so as to form a gap d1 at the convex portion of the unevenness, and a liquid crystal layer is provided between the two. The liquid crystal display device is constructed by producing a structure with the interposition of.

According to this configuration, the liquid crystal layer 7 has a gap between the first and second transparent electrodes 3 and 4 according to the corrugations formed on the surface of the second transparent substrate, that is, the thickness of the liquid crystal layer 7. Is continuously changed from d1 to d2.
Therefore, for example, light incident from the first polarizing plate 1 side is
When transmitted through the first polarizing plate 1, the light is changed from natural light having any polarization plane to linearly polarized light, and further transmitted through the first transparent electrode 3 to enter the liquid crystal layer 7. The polarization plane of the light incident on the liquid crystal layer 7 is rotated by the refractive index anisotropy of the liquid crystal molecules constituting the liquid crystal layer 7. Thereafter, the light passes through the second transparent electrode 4 and the second transparent substrate 5 and reaches the second polarizing plate 6. Then, in the second polarizing plate 6, display can be performed by cutting the plane of polarization rotated in the liquid crystal layer 7 at an arbitrary angle.

Here, the thickness of the liquid crystal layer 7 is the same as that of the second transparent substrate 5.
The film thickness changes from d1 to d2 depending on the location due to a plurality of irregularities existing in one pixel formed on the surface of. Therefore, the intensity of the electric field applied to the liquid crystal layer 7 is different for each portion corresponding to the unevenness. As a result, the electric field distribution in the liquid crystal layer 7 is dispersed according to the difference in the thickness of the liquid crystal layer 7, and a partial change occurs in the threshold voltage and the saturation voltage of the liquid crystal. For this reason, although the same hysteresis occurs in each part as in the related art, the above-described phenomenon caused by this hysteresis is averaged due to the existence of a number of parts having different threshold voltages in one pixel. , Resulting in 1
As seen from the whole pixel, the hysteresis is reduced as shown in FIG. Therefore, even in a liquid crystal having a twist angle exceeding 270 degrees, in which a halftone cannot be displayed conventionally, the state is uniquely determined by an externally applied voltage, so that a stable halftone can be obtained. ,
It is possible to improve the display of the halftone. This makes it possible to create a full-color liquid crystal display by combining a multi-tone display and a color filter.

[Second Embodiment] In the first embodiment, the second transparent substrate 5 is used to change the thickness of the liquid crystal layer 7.
The surface of the second transparent substrate 5 is made of an inorganic or organic material (e.g., as shown in a schematic cross-sectional view of FIG. 3). For example, a film of polyimide or acrylic resin) is formed as needed, and the surface of the film is roughened to form a roughened film 8. A second transparent electrode is formed on the surface of the roughened film 8. 4 may be formed. Also in this configuration, asperities are formed on the surface of the second transparent electrode 4 and the thickness of the liquid crystal layer 7 is partially changed in the range from d1 to d2, so that the hysteresis is similar to the first embodiment. Can be substantially eliminated to improve the display of halftones.

[Third Embodiment] FIG. 4 is a schematic sectional view showing a third embodiment of the present invention. In this embodiment, the dielectric constant of the liquid crystal molecules constituting the liquid crystal layer 7 is equal to or less than the dielectric constant of the liquid crystal molecules in the concave and convex portions formed on the surface of the second transparent electrode 4 in the first embodiment. However, the leveling film 9 is formed by embedding an organic or inorganic substance having a low dielectric constant. As a result, in this configuration, the thickness of the liquid crystal layer 7 becomes uniform regardless of the unevenness of the surface of the second transparent electrode 4. Therefore,
In this configuration, in a portion where the leveling film 9 is formed thick, an externally applied voltage is applied to the gap d2.
And d3, the driving voltage is substantially reduced, and the intensity of the electric field applied to the liquid crystal layer 7 can be changed. As described above, the halftone display can be improved. On the other hand, since the thickness of the liquid crystal layer 7 itself is constant, the alignment of the liquid crystal does not become uneven, and the influence on the display due to the disorder of the alignment of the liquid crystal can be eliminated. is there.

Also in this third embodiment, as shown in a schematic cross-sectional view of FIG. 5, a second transparent substrate 5 is a flat substrate, on which a roughened film 8 is formed to form an uneven surface. Is provided thereon, and the second transparent electrode 4 is formed thereon, and the concave and convex portions have a dielectric constant equal to or lower than the dielectric constant of the liquid crystal molecules constituting the liquid crystal layer 7. It is also possible to adopt a configuration in which the leveling film 9 is formed by embedding an organic or inorganic substance. In the embodiment shown in FIG. 5, the second transparent electrode 4 is formed on the roughened film 8, but the dielectric constant of the liquid crystal molecules is equal to or higher than that of the liquid crystal molecules on the second transparent electrode 4. A structure in which the roughened film 8 is formed of an organic or inorganic substance having a dielectric constant lower than the dielectric constant is also possible. In this case, the voltage applied to the liquid crystal layer 7 is such that the gap becomes d1 in the concave portion of the roughened film 8 and the voltage applied between the first transparent electrode 3 and the second transparent electrode 4 remains unchanged. Applied to 7. On the other hand, in the convex portion of the roughened film 8, the thickness of the roughened film 8 and the voltage applied to the liquid crystal layer 7 are divided by d2 and d3, so that the effective voltage applied to the liquid crystal layer 7 is increased. Decreases. Therefore, the intensity of the electric field applied to the liquid crystal layer 7 is different between the concave portions and the convex portions of the roughened film, and the display of the halftone can be improved as described above.

In the above description, the case where light is incident from the first polarizing plate 1 is described. However, the same operation and effect can be obtained even if the light is incident from the second polarizing plate 6. Can be. In each embodiment, the liquid crystal layer 7
Although a liquid crystal having a twisted nematic structure is used, a guest-host type liquid crystal obtained by mixing a dichroic dye with a nematic liquid crystal in the liquid crystal layer 7 can also be used. In this case, it is possible to omit the first polarizing plate 1 and the second polarizing plate 6 in each of the above-described embodiments, and to simplify the configuration, while providing a brighter display than a method requiring a polarizing plate. There is also the effect that it is possible to obtain.

[Fourth Embodiment] FIG. 6 is a schematic sectional view of a fourth embodiment of the present invention. In this embodiment,
This is an embodiment applied to a reflection type liquid crystal display by changing the second transparent electrode 4 in each of the above embodiments to a light reflection plate and electrode 10 made of a metal such as aluminum. Here, minute irregularities are formed on the surface of the second transparent substrate 5, and aluminum is vapor-deposited on the surface of the irregularities to form a film, thereby forming the light reflector / electrode 10.
Further, the leveling film 9 is formed in the concave portion of the light reflection plate and electrode 10.
Is formed to make the thickness of the liquid crystal layer 7 uniform. In this configuration, the light incident from the first polarizing plate 1 is
1 and enters the liquid crystal layer 7 via the first transparent substrate 2 and the first transparent electrode 3. After that, the light reflected by the reflector / electrode 10 exits the polarizing plate 1 to the outside through a path reverse to that at the time of incidence. And even in this case, the first transparent electrode 3
The gap between the electrode and the light reflector / electrode 10 is partially different, whereby the thickness of the liquid crystal layer 7 is partially changed, thereby giving a change to the electric field intensity applied to the liquid crystal layer 7. This makes it possible to improve the display of halftones as described above. On the other hand, since the thickness of the liquid crystal layer 7 itself is constant, the liquid crystal alignment does not cause unevenness, and it is possible to eliminate the influence on the display due to the disorder of the liquid crystal alignment. is there.

In the present embodiment, the second transparent substrate 5 does not need to be particularly transparent, and there is no problem even if an opaque substrate such as a metal, polymer plate, or ceramic is used. In addition, in this embodiment, since it is configured as a reflection type that does not require a backlight, there is an effect that a low power consumption type liquid crystal display can be manufactured. In the configuration shown in FIG. 6, a guest-host type liquid crystal obtained by mixing a dichroic dye with a nematic liquid crystal for the liquid crystal layer 7 can also be used.
In this case, it is possible to omit the first polarizing plate 1 and the phase difference compensating plate 11 as well, and to obtain a brighter display as compared with a method requiring a polarizing plate, while further simplifying the configuration. Yes, and no additional backlight is required.

[Fifth Embodiment] FIG. 7 is a schematic sectional structural view showing the structure of a fifth embodiment of the present invention. This liquid crystal display device includes a first polarizing plate 1, a first transparent substrate 2, a first transparent electrode 3, a first alignment film 12, a liquid crystal layer 7, a second alignment film 13, a second transparent electrode 4, a second transparent substrate. 5, the second polarizing plate 6 is superposed in this order. In this structure, the first polarizing plate 1, the first transparent substrate 2, the first transparent electrode 3, the first alignment film 12, and the second polarizing plate 6 have the same structure as the conventional example. The liquid crystal layer 7 has a twist angle of 270 degrees or more and less than 450 degrees between the first transparent electrode 3 and the second transparent electrode 4. The second transparent substrate 5 has a structure in which at least a side surface facing the liquid crystal layer 7 is roughened.
For example, the second transparent substrate 5 is processed by a method such as direct etching, or the second transparent substrate 5 that has been polished in advance is dissolved with hydrofluoric acid or the like to achieve a target roughened surface. The second transparent electrode 4 is obtained by forming a transparent electrode such as ITO on the roughened surface by sputtering or coating or vapor deposition. Thereafter, a second alignment film 13 is formed on the surface of the second transparent electrode 4 for the purpose of giving initial alignment to liquid crystal molecules. The first alignment film 12 and the second alignment film 13 are subjected to an alignment treatment by a method such as a rubbing method.
And the first alignment direction of the first alignment film 12 and the initial alignment direction of the second alignment film are substantially equal to the twist angle calculated from the specific pitch of the liquid crystal layer 7 and the gap d1. A liquid crystal display device is configured by combining the liquid crystal display device with the alignment film 12 so as to face each other and forming a configuration in which the liquid crystal layer 7 is interposed therebetween. In this structure, since the first alignment film 12 and the second alignment film 13 can give the initial alignment control force to the liquid crystal layer 7 by a method such as rubbing, the first alignment film 12 and the second alignment film 13 When the liquid crystal is injected into the gap between the second transparent substrates 5 to form the liquid crystal layer 7, it is possible to suppress the flow alignment generated by the liquid crystal flowing on the alignment film.

When light is incident on the liquid crystal element formed as described above from the outside, for example, light incident from the first polarizing plate 1 side has all polarization planes when transmitted through the first polarizing plate 1. The light is converted from natural light into linearly polarized light, passes through the first transparent electrode 3 and the first alignment film 12, and enters the liquid crystal layer 7. The light incident on the liquid crystal layer 7 rotates the plane of polarization due to the refractive index anisotropy of the liquid crystal molecules constituting the liquid crystal layer 7. Thereafter, the light passes through the second alignment film 13, the second transparent electrode 4, and the second transparent substrate 5 and reaches the second polarizing plate 6. Then, in the second polarizing plate 6, display can be performed by cutting the plane of polarization rotated in the liquid crystal layer 7 at an arbitrary angle. At this time, when an electric field is applied between the first transparent electrode 3 and the second transparent electrode 4, the refractive index anisotropy of the liquid crystal layer 7 changes. As a result, the first transparent electrode 3 and the second transparent electrode 4
Since the liquid crystal layer 7 has a different refractive index anisotropy between the portion where the voltage is applied and the portion where the voltage is not applied, a display difference occurs between the portion where the voltage is applied and the portion where the voltage is not applied, resulting in ON.
State and OFF state.

Here, the liquid crystal molecules constituting the liquid crystal layer 7 on the surface of the second transparent substrate 5 are arranged in parallel with the surface of the second transparent substrate 5, so that the liquid crystal molecules have irregularities such as θ1 and θ2 in FIG. It is divided into a region 1 and a region 2 having a dependent pretilt angle (however, θ1 and θ2 are for convenience of explanation, and do not need to be at the same angle everywhere). When no voltage is applied to the liquid crystal, the liquid crystal layer 7 keeps a uniform alignment state because the inside of the liquid crystal layer 7 is in a stable state, but an electric field is applied between the first transparent electrode 3 and the second transparent electrode 4. When the voltage is applied, the rising direction of the liquid crystal molecules is different because the pretilt angle is different between the region 1 and the region 2, and as a result, a region boundary line which is a discontinuous portion in the tilt angle of the liquid crystal molecule is generated between the region 1 and the region 2. . Since this region boundary line is generated between the region 1 and the region 2, the size of each region is substantially equal to the pitch of the unevenness formed on the second transparent substrate 5 (the region existing next to the region 1 is In the case of the region 1, the apparent size of the region may be large because the two are fused.) As a result, the change (ON state to OFF state or OFF state to ON state) generated in the portion (domain) surrounded by the region boundary line as shown in FIG. In the microscopic view, each domain has the same hysteresis as in the past, but in the macroscopic view, the changing region increases and decreases depending on the voltage applied from the outside. It is possible to obtain an optical response free of hysteresis as shown in FIG. Therefore, even in a liquid crystal having a twist angle exceeding 270 degrees, which cannot be avoided by the method of using the entire liquid crystal element as a single region conventionally used,
The state is uniquely determined by the voltage applied from the outside, and a stable halftone can be obtained.

[Sixth Embodiment] FIG. 9 is a diagram showing a sixth embodiment according to the present invention. In the fifth embodiment, the unevenness provided on the second substrate in order to give the pretilt to the liquid crystal layer 7 is formed by processing the second substrate 5 itself using a method such as polishing or etching. As shown in FIG. 9, an inorganic or organic film is formed as necessary on the flat surface of the second transparent substrate 5, and the film is subjected to surface unevenness processing, or an inorganic or organic film is formed. The film is transferred by means of a printing method or the like so as to form required irregularities to form a roughened film 8, and there is no problem if the second transparent electrode 4 is formed on the surface of the roughened film 8. There is no. Also in this configuration, unevenness is formed on the surface of the second transparent electrode 4, and a pretilt angle depending on the uneven shape can be given to the liquid crystal layer 7 via the second alignment film 13. Therefore, in the configuration shown in FIG.
The same effect as that of the embodiment can be obtained.

[Seventh Embodiment] FIG. 10 is a schematic sectional view showing a seventh embodiment of the present invention. In this embodiment, in the fifth embodiment, the unevenness provided on the second substrate in order to give the pretilt to the liquid crystal layer 7 is formed by processing the second substrate 5 itself using a method such as polishing or etching. While the unevenness is formed and a different pretilt is partially applied to the liquid crystal layer 7, in the present embodiment, the direction of the pretilt angle in the pixel is obtained by rubbing the second alignment film 13 in a different direction. Is changed to separate the region 1 from the region 2. In order to obtain such a structure, the surface of the second alignment film 13 is rubbed in a certain direction, and an alignment film having a pretilt angle with the direction θ1 in FIG. 10 is created. After that, a metal mask or a resist film having a hole in the region 2 is overlaid on the second alignment film 13 and a rubbing process is performed again. By doing so, the area 2 becomes θ in the second rubbing direction.
It becomes possible to provide an alignment film capable of giving the liquid crystal a pretilt angle of 2. A liquid crystal element having a liquid crystal layer 7 can be produced by superposing the second transparent substrate 5 and the first etc. marking plate 2 having been subjected to such an alignment treatment and injecting liquid crystal into the gap.

In the structure of the present embodiment, when an electric field is applied between the first transparent electrode 3 and the second transparent electrode 4, the pretilt angles in the regions 1 and 2 are θ1 and θ2. The rising directions of the liquid crystal molecules are different from each other, and a discontinuous portion is generated between the region 1 and the region 2, which becomes the boundary boundary 14. According to the present invention, since the twist angle of the liquid crystal layer 7 is 270 degrees or more, each portion of the region 1 and the region 2 has a hysteresis characteristic as shown in the conventional example of FIG. When a certain voltage is exceeded, O
The N state and the OFF state are switched. However, when one pixel is divided into the region 1 and the region 2 as in the present invention, the influence of the region boundary 14 generated between the ON state and the OFF state in a certain region does not affect the region boundary 1.
4 does not affect adjacent areas. Therefore,
In this embodiment, as in the fifth embodiment, the effect of the hysteresis is substantially eliminated in one pixel as a whole, and the halftone display can be improved. Also in the present embodiment, since the first alignment film 12 and the second alignment film 13 are rubbed, unnecessary alignment defects such as flow alignment can be suppressed even during liquid crystal injection.

[Eighth Embodiment] FIG. 11 is a schematic sectional view showing an eighth embodiment of the present invention. In the fifth to seventh embodiments of the present invention, by processing the surface of the second transparent substrate 5 or the alignment film 13, the pretilt angle on the substrate surface is made different in a portion within a pixel, and the region 1 In the present embodiment, the polymer component is dispersed in the liquid crystal layer to change the direction in which the liquid crystal molecules rise when an electric field is applied to the bulk portion in the liquid crystal layer. A method of dividing 1 and area 2 is adopted. Specifically, the first alignment film 12 and the second alignment film 13 formed on the surfaces of the first transparent electrode 3 and the second transparent electrode 4 are each made of an alignment film having a pretilt of almost 0 degree, and a rubbing treatment is performed. I do. After that, the first transparent substrate 2 and the second transparent substrate 5 are overlapped so as to take a predetermined twist angle. The liquid crystal layer 7 slightly contains a monomer that becomes a polymer by applying ultraviolet light or heat to the nematic liquid crystal and an oligomer that is a polymerization initiator (by a weight ratio of 0.1 w
(t% to 5 wt%), and the mixture is injected into a gap between the first alignment film 12 and the second alignment film 13. After the injection, the liquid crystal element is heated until the liquid crystal layer 7 becomes a liquid phase, and cooled while applying a voltage or a magnetic field, and an external stimulus such as ultraviolet rays is applied to the liquid crystal element at a specific temperature depending on the liquid crystal. As a result, the monomer mixed in the liquid crystal layer 7 reacts to form a network of the polymer 16.
When the liquid crystal molecules are formed in this manner, the monomers are polymerized while an electric field is applied to the liquid crystal molecules, so that the polymers are arranged according to the tilt angle of the liquid crystal. Therefore, the polymer 16 also forms a network with an angle that gives tilt to the liquid crystal. Therefore, the liquid crystal layer 7
Even when the electric field applied to the liquid crystal layer 7 is zero, the liquid crystal molecules in the central portion of the liquid crystal layer 7 have different tilt angles in the regions 1 and 2 respectively. In this case, the rising direction of the liquid crystal molecules differs, and a region boundary 14 occurs. As a result, the fifth embodiment to the seventh
Hysteresis occurs in each region for the same reason as in the embodiment of FIG.
It is possible to obtain an optical response characteristic having no hysteresis as described above. Also in this embodiment, since the first alignment film 12 and the second alignment film 13 are rubbed, unnecessary alignment defects such as flow alignment can be suppressed even during liquid crystal injection.

In the fifth to eighth embodiments, the case where light is incident from the first polarizing plate 1 has been described. Even if light is incident, it is possible to obtain exactly the same operation and effect. In each embodiment, a liquid crystal having a twisted nematic structure is used as the liquid crystal layer 7. However, a guest-host type liquid crystal obtained by mixing a dichroic dye with the nematic liquid crystal may be used.
When a guest-host type liquid crystal is used as the liquid crystal layer 7, the first polarizing plate 1 and the second polarizing plate 6 in each of the above embodiments can be omitted. In this case, it is possible to simplify the structure of the liquid crystal element and to obtain a bright display because there is no loss of light due to the polarizing plate as compared with a method requiring a polarizing plate. Furthermore, in the fifth to eighth embodiments, by using one of the first polarizing plate and the second polarizing plate as a deflecting reflector, it is possible to reflect light incident from the other, and it is possible to use a reflection type. A liquid crystal element can be formed.

[Ninth Embodiment] FIG. 12 is a diagram showing a ninth embodiment according to the present invention. In this embodiment, the second transparent electrode 4 in the fifth to eighth embodiments is formed of a metal such as aluminum or a dielectric multilayer film structure to be changed to a light reflector / electrode 10. This is an embodiment applied to an integrated reflective liquid crystal display. In the present embodiment, the guest-host type liquid crystal is used as the liquid crystal layer 7 so that the second polarizing plate 6 can be used.
In addition, the first polarizing plate 1 can be omitted.
Here, the light reflecting plate / electrode 10 is formed by forming fine irregularities on the surface of the second transparent substrate 5 and forming a film on the surface by evaporating aluminum, silver, or the like. By forming the second alignment film 13 on the plate / electrode 10, it is possible to divide the inside of the pixel into the minute regions 1 and 2 and obtain an optical response characteristic without hysteresis as shown in FIG. .

[Tenth Embodiment] FIG. 13 is a diagram showing a tenth embodiment according to the present invention. In the present embodiment, as in the ninth embodiment, the second transparent electrode 4 is made of a metal such as aluminum or a dielectric multilayer film structure to serve as a light reflector / electrode 10, and the liquid crystal layer 7 is made of a fifth transparent electrode. This is a case where a twisted nematic structure is employed as in the embodiments to the eighth embodiment. In the case of the present embodiment, since there is only one polarizing plate, it is possible to perform monochrome display by combining a phase difference compensating plate that performs optical compensation.

In the ninth and tenth embodiments, it is not necessary to use a transparent substrate as the second transparent substrate 5 on which the light reflecting plate 10 is formed.
Even if an opaque substrate such as a ceramic is used, there is no problem in its operation.

[Eleventh Embodiment] FIGS. 14 to 1
6 is a diagram showing an eleventh embodiment according to the present invention,
FIG. 3 is a diagram illustrating a surface shape of a roughened electrode that can be used in each of the embodiments. First, in the example shown in FIG. 14, the surface of the second transparent substrate 5 is # 100
After polishing with 0 abrasive, 3% with hydrofluoric acid of 25% concentration
Then, a transparent electrode made of ITO or the like was formed by a sputtering method after forming wavy irregularities to form a second transparent electrode 6. In the surface shape in the example shown in the figure, as a whole, it has wavy random irregularities, and each concave portion is separated by a ridge-like convex portion, and therefore, a valley line that can be traced long. I do not have.

Next, in the example shown in FIG.
As shown in FIG. 15A, a plurality of columnar base structures 81 are formed at random on the second transparent substrate 5, and subsequently, FIG.
As shown in (b), a roughened film 8 is formed by forming an interlayer film 82 so as to cover the base structure 81,
Thereafter, a transparent electrode such as ITO was formed by a sputtering method to form a second transparent electrode 6. The surface shape in the example shown in FIG. 3 has random mountain-like irregularities as a whole, and has valley lines so as to trace between the individual convex portions.

In the example shown in FIG.
As shown in FIG. 16A, a base structure 81 characterized by a plurality of random holes is formed on the second transparent substrate 5, and then, as shown in FIG. By forming an interlayer film 82 so as to cover the surface, the roughened film 8 is formed.
After that, a transparent electrode such as ITO was formed into a film by a sputtering method to form the second transparent electrode 6. The surface shape in the example shown in the figure is characterized by random concave portions, and each concave portion is separated by a ridge-like convex portion, and thus does not have a valley line that can be traced long.

As described above, when a liquid crystal display device was manufactured using the electrodes having the surface shapes shown in FIGS. 14 to 16, the hysteresis was reduced in each case, and the gradation display characteristics were improved. In particular, in the case of the surface shape shown in FIG. 14 or FIG. 16, the generation of alignment defects called finger texture was completely suppressed, and very good gradation display characteristics were obtained. On the other hand, in the case of the surface shape shown in FIG. 15, an alignment defect occurs so as to follow the valley line in the uneven shape, and the effect of reducing the hysteresis is not so significant as in the case of the surface shape of FIG. 14 or FIG. Did not.

FIG. 17 is a photograph showing the appearance of halftone display in the case of the surface shape shown in FIG. 14, and FIG. 18 is a view showing the appearance of halftone display in the case of the surface shape shown in FIG. A photograph is shown. However, in FIG. 17 and FIG.
Instead of the transparent electrode 6 in FIG. 4 and FIG. 15, a light reflector / electrode is formed using aluminum as a material, and a guest-host type liquid crystal obtained by mixing a dichroic dye with a nematic liquid crystal is formed in the liquid crystal layer. Used. FIG.
In, the occurrence of alignment defects is not observed, and the ON state region and the OFF state region are mixed. Very good multi-tone display was possible by changing the area ratio of these regions according to the applied voltage.

In each of the above embodiments, the liquid crystal display device has been described as a method of driving the liquid crystal layer 7 by performing static driving or simple matrix driving without using an active element. Even when the liquid crystal driving element is divided into small pixel units and at least one two-terminal or three-terminal active element is provided for each element, the effect of the present invention is not changed even if active matrix driving is adopted. . In particular, in this method, each pixel can be driven independently, so that the applied voltage can be finely controlled, and a clearer halftone display can be obtained. Further, in each of the above embodiments, a monocolor liquid crystal display element having no color filter has been described, but a color filter is added to the monocolor liquid crystal display element as shown in each of the above embodiments. It is needless to say that color display can be performed by performing the above.

[0040]

As described above, the present invention is configured so that the electric field strength applied to the liquid crystal layer having a twist angle of 270 degrees or more partially differs, so that hysteresis would normally occur and an intermediate Even when key display is not possible,
It is possible to eliminate the hysteresis when the liquid crystal display device is viewed as a whole, to enable a smooth halftone display, and to obtain a liquid crystal display device capable of full color display.

[Brief description of the drawings]

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

FIG. 2 is a diagram illustrating hysteresis characteristics according to the first embodiment.

FIG. 3 is a schematic sectional view of a second embodiment of the present invention.

FIG. 4 is a schematic sectional view of a third embodiment of the present invention.

FIG. 5 is a schematic sectional view of another embodiment of the third embodiment of the present invention.

FIG. 6 is a schematic sectional view of a fourth embodiment of the present invention.

FIG. 7 is a schematic sectional view of a fifth embodiment of the present invention.

FIG. 8 is a schematic sectional view of another embodiment of the fifth embodiment of the present invention.

FIG. 9 is a schematic sectional view of a sixth embodiment of the present invention.

FIG. 10 is a schematic sectional view of a seventh embodiment of the present invention.

FIG. 11 is a schematic sectional view of an eighth embodiment of the present invention.

FIG. 12 is a schematic sectional view of a ninth embodiment of the present invention.

FIG. 13 is a schematic sectional view of a tenth embodiment of the present invention.

FIG. 14 is a schematic perspective view of an eleventh embodiment of the present invention.

FIG. 15 is a schematic perspective view of another embodiment of the eleventh embodiment of the present invention.

FIG. 16 is a schematic perspective view of still another embodiment of the eleventh embodiment of the present invention.

FIG. 17 is a photograph showing a state during halftone display in the liquid crystal display device according to the eleventh embodiment of the present invention.

FIG. 18 is a photograph showing a state during halftone display in another liquid crystal display device according to the eleventh embodiment of the present invention.

FIG. 19 is a schematic sectional view of a conventional liquid crystal display device.

FIG. 20 is a photograph showing a state of an alignment defect in a conventional liquid crystal display device.

FIG. 21 is a diagram showing hysteresis characteristics in a conventional liquid crystal display device.

[Description of Signs] 1 First polarizing plate 2 First transparent substrate 3 First transparent electrode 4 Second transparent electrode 5 Second transparent substrate 6 Second polarizing plate 7 Liquid crystal layer 8 Roughening film 9 Leveling film 10 Light reflecting plate Common electrode 11 Phase difference compensator 12 First alignment film 13 Second alignment film 14 Area boundary 15 Liquid crystal molecule 81 Base structure 82 Interlayer film

Claims (15)

[Claims] 1. A liquid crystal display device in which a liquid crystal layer having a layer structure twisted by 270 degrees or more is interposed between a first electrode and a second electrode at least one of which is formed transparent. A liquid crystal display device characterized in that the electric field intensity generated in the liquid crystal layer by the voltage applied between the electrode and the electrode partially differs. 2. The liquid crystal display device according to claim 1, wherein one of the first electrode and the second electrode has irregularities formed on the surface thereof, and the thickness of the liquid crystal layer is partially different due to the irregularities. 3. One of the first electrode and the second electrode has irregularities formed on its surface, and an organic or inorganic substance having a dielectric constant equal to or lower than that of the liquid crystal layer is embedded in the concave part. 2. The liquid crystal display device according to claim 1, wherein the liquid crystal layer has a uniform thickness. 4. The liquid crystal display device according to claim 2, wherein the electrode having the uneven surface is formed on the surface of the substrate having the uneven surface. 5. An electrode having unevenness on its surface has an inorganic or organic film on a substrate having a flat surface, and is formed on an uneven surface of the surface formed by changing the thickness of this film. The liquid crystal display device according to claim 2, wherein the liquid crystal display device is configured. 6. The liquid crystal display device according to claim 2, wherein the generation of alignment defects called finger texture is suppressed by the features of the irregularities formed on the surface of the first electrode or the second electrode. . 7. The first electrode or the second electrode does not have a long valley line in the surface shape of the unevenness formed on the surface thereof, and each of the concave portions and the convex portions, in particular, the concave portions are ridge-like with each other. 7. The liquid crystal display device according to claim 2, wherein the liquid crystal display device is separated by a convex portion. 8. The first electrode or the second electrode has a randomly wide distribution with respect to the depth of each concave portion included in a region corresponding to one pixel in the surface shape of the unevenness formed on the surface. The liquid crystal display device according to any one of claims 2 to 7, which is configured as described above. 9. A liquid crystal display device in which a liquid crystal layer having a layer structure twisted by 270 degrees or more is interposed between a first electrode and a second electrode, at least one of which is formed transparent. A liquid crystal display device comprising a plurality of regions having different rising directions. 10. The rising direction of liquid crystal molecules in adjacent regions is made different by changing the direction in which the pretilt angle of the liquid crystal molecules appears on the electrode surface of the liquid crystal molecules on at least one of the first electrode and the second electrode. Item 10. A liquid crystal display device according to item 9. 11. A method according to claim 1, wherein at least one of the first electrode and the second electrode is subjected to a first alignment process in a specific direction with respect to an alignment film formed on the electrode, and includes a plurality of windows in one pixel. The direction of the pretilt angle is different for each region by performing an orientation process different from the direction in which the first orientation process is performed through a mask made of an inorganic or organic film having
11. The liquid crystal display device according to claim 9, wherein rising directions of liquid crystal molecules in the liquid crystal layer are different. 12. At least one of the first electrode and the second electrode has fine irregularities formed on the surface thereof, alignment treatment is performed on the irregularities, and the liquid crystal molecules arranged on the irregularities have tilt angles with respect to the substrate plane. 11. The liquid crystal display device according to claim 9, wherein the rising direction of the liquid crystal molecules in the liquid crystal layer is changed in one pixel by changing the direction of the pretilt angle in one pixel. 13. A mixture of a monomer and a polymerization initiator in a liquid crystal, and in a state of a liquid crystal element filled between a first electrode and a second electrode which has been subjected to an alignment treatment in a single direction, the monomer is stimulated by an external stimulus. By polymerizing, a polymer network is formed in the liquid crystal, and the liquid crystal molecules are arranged along the polymer network, so that an electric field is applied between the first electrode and the second electrode in the liquid crystal layer. A liquid crystal display device wherein the rising directions of liquid crystal molecules are different. 14. The liquid crystal display device according to claim 1, wherein the first electrode and the second electrode are formed as transparent electrodes, respectively formed on opposing surfaces of the first transparent substrate and the second transparent substrate. 13. The liquid crystal display device according to any one of items 13 to 13. 15. One of the first electrode and the second electrode is configured as a transparent electrode, the other is configured as a reflective electrode,
14. The liquid crystal display device according to claim 1, which is configured as a reflection type liquid crystal display device.