JPH0772485A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal display element having a large gradation number by rubbing the element parallel to the longitudinal direction of a stripe pattern formed on the surface of an electrode, and specifying the range of angle made by the longitudinal direction of the stripe pattern and the normal direction of chirale smectic phase of the liquid crystal. CONSTITUTION:A rugged pattern in stripes are formed on the surface of upper and lower electrodes, an oriented film is formed on the electrode. Then the electrode is rubbed in the longitudinal direction of the stripe pattern. By specifying the angle range made by the longitudinal direction of the stripe pattern 12 and the normal direction of layers of chirale smectic phase in the liquid crystal cell to 90 deg.+ or -20 deg., the shape and position of reversed domains can be severely controlled. Thus, stable domains can be obtd. and variation of medium display characteristics among picture elements can be decreased. The orienting material is preferably a polyamide material, pendant polymer or the like.

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 used in televisions and the like, and more particularly to a liquid crystal display device using a ferroelectric liquid crystal and having gradation.

[0002]

2. Description of the Related Art In a liquid crystal television panel using a conventional active matrix driving system, thin film transistors (hereinafter referred to as "TFTs") are arranged in a matrix for each pixel, and an ON pulse is applied to the gate of the TFT to form a source. A conductive state is established between the drains, at this time, an image signal is applied from the source and accumulated in a capacitor, and a liquid crystal (for example, TN liquid crystal) is driven corresponding to the accumulated image signal, and at the same time, the voltage of the image signal is modulated As a result, gradation display is performed.

However, in such an active matrix drive type television panel using a TN liquid crystal, since the TFT used has a complicated structure, the number of manufacturing steps is large and the high manufacturing cost is a bottleneck. In addition to
It is difficult to form a thin film semiconductor (for example, polysilicon or amorphous silicon) forming a TFT over a wide area.

On the other hand, T can be manufactured at low cost.
A passive matrix drive type display panel using N liquid crystal is known. In this display panel, one selection point is provided while scanning one pixel (one frame) as the number of scanning lines (N) increases. The time (duty ratio) during which an effective electric field can be applied to is reduced at a rate of 1 / N, which causes crosstalk and has a problem that the contrast of the image is low, and the duty ratio is When it becomes smaller, it becomes difficult to control the gradation of each pixel by voltage modulation. For this reason, it is not suitable for a display panel with a high-density wiring number, particularly for a liquid crystal television panel.

As a solution to such a fundamental problem of the conventional TN liquid crystal, a ferroelectric liquid crystal having a bistable state (hereinafter referred to as "FLC") is disclosed in US Pat. No. 4,367,924 to Clark and Ragawall et al. Note) devices have been proposed. It has been considered that this FLC element is not suitable for gradation expression because it ideally tries to stabilize in one of two bistable states and does not take an intermediate molecular position. On the other hand, gradation display is performed by a digital method represented by the dither method.

[0006]

However, the above-mentioned F
The gradation display method using LC is not suitable for high-resolution display such as HDTV compatible because the resolution is lowered. Further, it is difficult to increase the number of luminance gradations without increasing the number of pixel divisions. Further, a large number of drive electrodes are required for one-pixel gradation display, a complicated arithmetic processing circuit is required, and the yield is reduced.

In view of the above problems, it is an object of the present invention to provide an FLC element having a simple structure and a large number of gradations.

[0008]

According to the present invention, in a liquid crystal display device having a pair of counter electrodes and an FLC sandwiched between the counter electrodes, a stripe-shaped concavo-convex pattern is formed on the surface of at least one of the electrodes. Then, the rubbing treatment is performed in parallel with the longitudinal direction of the stripe pattern, and the angle between the layer normal direction in the chiral smectic phase of the liquid crystal and the longitudinal direction of the stripe pattern is 90.
The liquid crystal display device is characterized in that it is within a range of ± 20 °.

The present invention will be described in detail below.

In the present invention, as FLC, chiral smectic C phase (SmC ^* ), H phase (SmH)
^* ), A liquid crystal having an I phase (SmI ^* ) or the like is used. Hereinafter, the chiral smectic C phase will be described.

The layer normal direction L of the smectic phase in the liquid crystal cell is, for example, two extinction direction directions when observing a polarizing plate and an analyzer plate crossed Nicol while applying a bipolar rectangular pulse having an amplitude of 20 V and a frequency of 10 Hz. It is the direction of the bisector. Usually, the liquid crystal molecules tend to be aligned along the rubbing direction of the alignment film, and therefore the rubbing direction and the layer normal direction L of the smectic phase are substantially parallel. However, depending on the proper combination of the alignment film material and the rubbing conditions, the molecules are oriented in a direction perpendicular to the rubbing direction, and as a result, the layer normal direction L of the smectic phase can be made substantially perpendicular to the rubbing direction. . In the present invention, a polyamide material, a pendant polymer and the like are preferably used as the alignment film material, but the alignment film material is not limited thereto.

FIG. 1 shows a pixel of a cell in which a stripe-shaped concavo-convex pattern is provided on the upper and lower electrode surfaces, an alignment film as described above is formed thereon, and then rubbing is performed in the longitudinal direction of the stripe pattern. It is the figure which represented typically the result observed from the direction perpendicular | vertical to a surface. In the figure, 11 is a pixel region, 12 is a stripe-shaped convex portion, and 13 is an inversion domain. The layer normal direction is the direction indicated by L and is substantially perpendicular to the rubbing direction, that is, the longitudinal direction of the stripe pattern.

The inversion domain 13 extends in a straight line perpendicular to the layer normal direction L, which means that the domain grows in the in-layer direction. As the voltage rises, the inversion domain first appears on the edge portion of the stripe-shaped convex portion and its extension (V = V ₁ ), and then the stripe-shaped convex portion and its extension portion are inverted (V = V ₂ ), After that, the concave portion is inverted from the side closer to the convex portion (V = V ₃ ). In this case, since the direction of the stripe pattern in which the threshold voltage decreases due to the decrease in the cell thickness and the effective increase in the electric field coincides with the in-layer direction in which the domain easily extends, the stripe pattern is aligned in the longitudinal direction of the stripe pattern. It is considered that domains that extend in the vertical direction do not appear much and that one-dimensional domains are formed. Further, in the concave portion, the closer to the convex portion, the larger the disorder of the layer structure and the lower the threshold value. Therefore, it is considered that inversion occurs from the portion closer to the convex portion.

The controlled domain having such a shape is excellent in stability, and the dispersion of the transmittance between pixels can be made very small.

In the present invention, since the layer normal direction is substantially perpendicular to the longitudinal direction of the stripe pattern, the layer structure is largely disturbed by the convex portions, and this can be effectively utilized. That is, by changing the pitch or height of the convex portions, it is possible to change the degree of disorder of the layer.
By providing regions having different pitches or heights in the pixel, it is possible to create regions having different inversion thresholds in the pixel. At this time, depending on the rubbing condition, the layer normal direction changes in the region where the unevenness modification is different, and the angle formed by the alignment control direction and the layer normal direction can be distributed in one pixel, and thus the inversion can be achieved. It is also possible to increase the difference between the thresholds.

FIG. 2 is a diagram schematically showing a comparison of inversion domain regions when cells in which stripe-shaped convex portions having a constant height are provided on one side of a transparent thin film electrode at different pitches are driven at the same voltage. is there. The pitch size is (a) <(b)
It becomes larger in the order of <(c). In the figure, 21 is a convex portion, and the cell is all black 22 in the initial state. . Inversion domain 2 after applying an equal voltage to the cells of (a) to (c)
The area of 3 was (a)>(b)> (c).

FIG. 3 shows applied voltage-transmittance characteristics. Dotted lines A to C show the characteristics of the cells (a) to (c) in FIG. Here, if the arrangement density of the stripe pattern is distributed within one pixel as shown in FIG. 4, it is possible to control the domain position by creating a portion having a different inversion threshold within the pixel. Further, as a result, the value γ = saturation voltage / threshold voltage value indicating the gradation display characteristic can be set to a desired value as shown by the solid line in FIG.

By using an alignment film such as polyimide or PVA,
Even when rubbing is performed perpendicularly to the longitudinal direction of the stripe pattern, the layer normal direction is perpendicular to the longitudinal direction of the stripe pattern, but in this case, the unevenness of rubbing in the vicinity of the stripe-shaped unevenness is large. However, this causes a problem such as a shift in the threshold value.

Further, the angle formed by the layer normal direction in the chiral smectic phase and the longitudinal direction of the stripe pattern is 9
If it is outside the range of 0 ° ± 20 °, the domains grow in directions other than the longitudinal direction of the stripe pattern, and the one-dimensional domain as described above cannot be obtained.

[0020]

EXAMPLES The present invention will be specifically described below with reference to examples.

(Embodiment 1) FIG. 5 shows a pixel pattern of this embodiment. A square 51 in the figure indicates one pixel. 52
Is a modified portion (stripe-shaped convex portion) provided on the transparent thin film electrode. The pixel size is 200 μm square, the width of the stripe-shaped convex portion is 5 μm, and the interval of the stripe pattern is 15.
A pattern is formed on both the upper and lower substrates in μm.

FIG. 6 shows a cell sectional view taken along the line AA 'in FIG. ITO 63, 64 (15
00Å) is formed, and a pixel pattern and a stripe pattern are formed by two photolithography steps. About 10 steps in stripe pattern
It is 00Å. About 200 Å of albumin is further formed on this film, and the indentation is 0.35 mm and the roller rotation speed is 100.
The stripe pattern is rubbed parallel to the longitudinal direction under the conditions of 0 rotation and a stage speed of 40 mm / s, and then bonded with a cell gap of 1.2 μm. FLC (product name: blended with CS1014 as a base) is injected therein. The cell bonding method is a parallel cell shown in FIG.

The cell of this example shows a good orientation, and the angle formed by the layer normal direction L of the smectic phase and the longitudinal direction of the stripe pattern measured by applying a bipolar rectangular pulse having an amplitude of 20 V and a frequency of 10 Hz. It was about 88 °. A pulse voltage as shown in FIG. 10 was applied between the upper and lower electrodes of the cell thus manufactured, and the optical response was measured. In this example, Δt = 50 μs. As a result of observing the inverted domain shape in this case, a one-dimensional domain extending in the longitudinal direction of the stripe pattern was formed, as schematically shown in FIG. This domain had a uniform shape and excellent stability.

(Embodiment 2) FIG. 7 shows a pixel pattern of this embodiment. The square 71 indicates one pixel. 72 is a modified portion (stripe-shaped convex portion) provided on the transparent thin film electrode
Is. The pixel size is 200 μm square, and the pitch of the stripes is changed within the pixel. The stripe-shaped convex portions have a width of 2 μm, the densest portion of the stripe-shaped pattern has an interval of 2 μm, and the sparsest portion has an interval of 16 μm, and patterns are formed on both upper and lower substrates.

FIG. 8 is a sectional view of the cell taken along the line BB 'in FIG. ITO 83, 84 (15
00Å) is formed, and a pixel pattern and a stripe pattern are formed by two photolithography steps. About 10 steps in stripe pattern
It is 00Å. Further, about 200 Å of albumin was formed on this, and after rubbing treatment under the same conditions as in Example 1, they were bonded together with a cell gap of 1.2 μm.
The FLC used is the same as in Example 1. The cell bonding method is a parallel cell shown in FIG.

This cell exhibits a good orientation and an amplitude of 20.
The angle between the layer normal direction L of the smectic phase and the longitudinal direction of the stripe pattern measured by applying a bipolar rectangular pulse of V and a frequency of 10 Hz was about 88 °. A pulse voltage as shown in FIG. 10 was applied between the upper and lower electrodes of the cell thus manufactured, and the optical response was measured. In this example, Δt = 50 μs and V _ap = 12 to 30 V. As a result of observing the inversion domain shape in this case, as schematically shown in FIG. 2, the inversion threshold voltage was low in the region with a small pitch, and the inversion threshold voltage was high in the region with a large pitch. That is, in the pixel, a domain inversion rate differs between regions having different modification pitches, and a threshold distribution can be created in the pixel. In addition, the variation in transmittance between pixels for each voltage value was very small. The applied voltage-transmittance characteristic measured in this cell is shown in FIG. As described above, the γ value was increased by forming the stripe-shaped concavo-convex pattern, and the controllability of gradation display was improved.

(Example 3) A liquid crystal cell in which the cell bonding direction was an antiparallel cell shown in FIG. 9 was prepared by using the same stripe-patterned substrate and albumin alignment film as in Example 2. The rubbing conditions, FLC, and cell gap are the same as in Examples 1 and 2. This cell exhibited a good orientation, and the angle formed by the layer normal direction in the chiral smectic phase and the longitudinal direction of the stripe pattern was about 88 °. As a result of measuring the same optical response characteristics as in Examples 1 and 2 with respect to this cell, it is possible to obtain a display device similar to that in Example 2 in which the variation in transmittance between pixels is small and the controllability of gradation display is high. Was obtained. A larger γ value could be obtained in the antiparallel cell than in the parallel cell.

(Embodiment 4) FIG. 12 shows a pixel pattern of this embodiment. A square 1201 indicates one pixel. 1
Reference numeral 202 denotes a modified portion (here, a stripe-shaped convex portion) provided on the transparent thin film electrode. Four regions having different heights of convex portions are provided in the pixel. The size of 1201 is 2
00 μm square, the width of the stripe-shaped convex portion is 2 μm, the interval between the convex portions is 10 μm, and the height of the convex portion is 2000 Å, 150
0Å, 1000Å, 500Å.

FIG. 13 is a sectional view of a cell taken along the line CC 'in FIG. ITO13 on the glass substrates 1301 and 1302
03, 1304 (1500Å) are formed, and a pixel pattern and a stripe pattern are formed by a photolithography process. The stripe pattern is formed on the upper and lower electrode surfaces. A film of polystyrene 200Å is formed on this, and rubbing treatment (pushing 0.4
0 mm, roller rotation speed 1000 rotations, stage speed 5
0 mm / s) and then bonded with a cell gap of 1.2 μm. The rubbing direction is parallel to the longitudinal direction of the stripe pattern, and the cell bonding direction is the parallel direction shown in FIG. The FLC used is the same as that used in Example 1.

The cell of this example showed good orientation, and the angle formed by the layer normal direction in the chiral smectic phase and the longitudinal direction of the stripe pattern was about 85 °.

A pulse voltage as shown in FIG. 10 was applied between the upper and lower electrodes of the cell thus manufactured, and the optical response was measured. In this embodiment, Δt = 50 μs and V _ap = 10.
It was 30V. As a result of observing the shape of the inversion domain in this case, the inversion threshold voltage is generally low in the region where the height of the protrusion is modified, and the inversion threshold voltage is generally high in the region where the height of the protrusion is low. Was becoming. That is, in the pixel, the domain inversion rate differs between the regions having different heights of the convex portions, and the threshold distribution can be created in the pixel. Also,
Also in this case, the variation in the transmittance between pixels for each voltage value is very small, and the γ value is large, so that the controllability of gradation display is improved.

[0032]

As described above, in the liquid crystal display device of the present invention, since the shape and position of the inversion domain can be highly controlled, a stable domain can be obtained, and the dispersion of the intermediate display characteristics between pixels. Can be kept very small. Further, since the value of γ can be increased, the halftone display characteristic is good. Moreover, since high-speed driving is possible and it is not necessary to increase the size of one pixel, a display with high gradation and high definition can be manufactured.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing an inversion domain in a liquid crystal cell in which a stripe-shaped concavo-convex pattern is formed.

FIG. 2 is a diagram showing comparison of inversion domains when the pitch of the stripe-shaped concavo-convex pattern is changed.

FIG. 3 is a diagram showing an applied voltage-transmittance characteristic in the liquid crystal display element of the present invention.

FIG. 4 is a diagram showing a stripe-shaped concavo-convex pattern having a distribution of arrangement density within one pixel.

FIG. 5 is a diagram showing a stripe pattern according to the first embodiment of the present invention.

6 is a cross-sectional view taken along the line A-A ′ of FIG.

FIG. 7 is a diagram showing a stripe pattern according to a second embodiment of the present invention.

8 is a cross-sectional view taken along the line B-B ′ of FIG. 7.

FIG. 9 is an explanatory diagram of a bonding direction of liquid crystal cells.

FIG. 10 is a diagram showing drive applied voltage of a liquid crystal cell.

FIG. 11 is a diagram showing an applied voltage-transmittance characteristic of the second embodiment of the present invention.

FIG. 12 is a diagram showing a stripe pattern according to a fourth embodiment of the present invention.

13 is a cross-sectional view taken along the line C-C ′ of FIG.

[Explanation of symbols]

 11 Pixel Region 12 Striped Convex 13 Inversion Domain (White) 14 Initial Domain (Black) 21 Convex 22 Initial Domain (Black) 23 Inversion Domain (White) 41 Pixel Region 42 Striped Convex 51 Pixel Region 52 Stripe Pattern 61 , 62 glass substrate 63, 64 ITO 65, 66 albumin 71 pixel region 72 stripe pattern 81, 82 glass substrate 83, 84 ITO 85, 86 albumin 1201 pixel region 1202 stripe pattern 1301, 1302 glass substrate 1303, 1304 ITO 1305 1306 polystyrene

Claims (5)

[Claims] 1. A liquid crystal display device having a pair of counter electrodes and a ferroelectric liquid crystal sandwiched between the counter electrodes, wherein a stripe-shaped concavo-convex pattern is formed on the surface of at least one of the electrodes, and the length of the stripe pattern is long. Liquid crystal which is rubbed parallel to the direction, and the angle between the layer normal direction in the chiral smectic phase of the liquid crystal and the longitudinal direction of the stripe pattern is within the range of 90 ° ± 20 °. Display element. 2. The liquid crystal display device according to claim 1, wherein the rubbing directions are substantially parallel to each other on the upper and lower substrates. 3. The liquid crystal display device according to claim 1, wherein the rubbing directions are substantially antiparallel to each other on the upper and lower substrates. 4. The liquid crystal display device according to claim 1, wherein one pixel has a plurality of regions having different pitches of the stripe-shaped concave-convex pattern. 5. The liquid crystal display device according to claim 1, wherein a plurality of regions having different stripe-shaped concavo-convex patterns having different heights are provided in one pixel.