JPH06308501A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To provide the liquid crystal element having nearly symmetrical switching characteristics and a large number of gradations by forming striped projecting parts on one of a pair of electrodes and subjecting these parts to an orienting treatment. CONSTITUTION:The films of ITO 1203, 1204 are formed on upper and lower glass substrates 1201, 1202 and further, pixel patterns and stripe patterns 1205 are formed on the upper glass substrate 1202 by a photolithography stage. Only the pixel patterns are formed on the lower glass substrate 1201. Further, polysiloxane 1207 is spin coated on the electrodes on the upper substrate 1202. On the other hand, the film of polyimide 1206 is formed on the electrodes on the lower substrate 1201 and is subjected to the rubbing treatment. Two sheets of the substrates 1201, 1202 are thereafter stuck to each other at a prescribed cell gap and a ferroelectric liquid crystal is injected into this gap.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal element used in televisions and the like, and more particularly to a liquid crystal element using a strongly inductive liquid crystal.

[0002]

2. Description of the Related Art In a conventional liquid crystal television panel using an active matrix drive system, thin film transistors (hereinafter referred to as "TFTs") are arranged in a matrix for each pixel, and a TFT gate on pulse is applied between the source and the drain. Is made conductive, and at this time, the image signal is applied from the source, accumulated in the capacitor, and the 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. 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 during which an effective electric field is applied (duty ratio) decreases at a rate of 1 / N, which causes crosstalk, and has the problem that the contrast of the image is low. Is difficult to control the gradation of each pixel by voltage modulation, and therefore it is not suitable for a display panel having a high number of wirings, particularly a liquid crystal television panel.

As a solution to such a fundamental problem of the conventional TN liquid crystal, a ferroelectric liquid crystal device having a bistable state has been proposed in US Pat. No. 4,367,924 to Clark and Lagavar et al. . It has been considered that this ferroelectric liquid crystal device 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. Therefore, in order to perform gradation display using the ferroelectric liquid crystal element, it was necessary to rely on gradation display by a digital method typified by a pixel division method.

[0006]

However, in the gradation display method by the digital method described above, one frame is divided into subclaims composed of a plurality of pixels, and when drawing one frame, The pixels are driven by applying electric fields having different duty ratios. In this case, in order to obtain high gradation characteristics,
As the number of pixels that make up one subclaim increases,
As the display screen becomes larger, the duty ratio per pixel becomes considerably smaller. Therefore, in order to obtain high contrast, high-speed response of the liquid crystal material is required. Further, a large number of drive electrodes are required for gradation display of one pixel. Further, there are too many technical problems to be solved for use in a high gradation display device such as a high definition television (HDTV) which has been attracting attention in recent years because it requires a complicated arithmetic processing circuit.

On the other hand, the present inventors firstly proposed a method of applying gray scale display by applying pulse voltages having different peak values corresponding to gray scale display to a liquid crystal for a single frame. I found it. However, in this method, since the threshold characteristic of the ferroelectric liquid crystal is steep, the applied voltage must be controlled with extremely high accuracy. Moreover, the position of the domain-inverted region (domain) that locally develops in the display pixel with respect to the applied voltage and the growth direction thereof are likely to be random,
As a result, it was difficult to easily obtain a linear applied voltage-transmittance characteristic.

[0008]

The present invention has been made in view of the above problems, and an object thereof is to provide a liquid crystal element having a large number of gradations with a simple structure.

Another object of the present invention is to provide a liquid crystal element having substantially symmetrical switching characteristics even in a cell in which a pair of substrates or electrodes have asymmetrical shapes.

The present invention, which solves the above problems and achieves the above objects, provides a liquid crystal device having a ferroelectric liquid crystal between a pair of electrodes, wherein a stripe-shaped convex portion is formed on one of the pair of electrodes. The liquid crystal element is formed and is subjected to alignment treatment so as to compensate for the asymmetry of the switching characteristics due to the convex portions.

Alternatively, in a liquid crystal element having a ferroelectric liquid crystal between a pair of electrodes, a stripe-shaped convex portion is formed on one electrode of the pair of electrodes, and the longitudinal direction of the convex portion is The layer normal direction of the smectic layer of the liquid crystal in the device is different, and the acute angle between the longitudinal direction of the convex portion and the two molecular orientation directions of the liquid crystal in the device in the bistable state The liquid crystal element is characterized in that the size of the angle having the smallest absolute value is equal to or smaller than the cone angle in the chiral smectic layer, and an alignment treatment is performed so that the switching characteristics are substantially symmetrical.

[0012]

According to the present invention, the final switching characteristic as an element is made substantially symmetrical by performing the alignment treatment for producing the asymmetrical component of the switching characteristic that cancels the asymmetrical component in the switching characteristic by the stripe-shaped convex portion. Can be Therefore, light (white) to dark (black)
Since the switching to and the switching to the opposite are symmetrical, the degree of freedom in selecting the drive system is widened.

[0013]

【Example】

(Description of Preferred Embodiment) First, the point of exerting asymmetry on the switching characteristic will be described.

When the alignment control layer is vertically asymmetric, since the interaction between the alignment film and the liquid crystal molecules is different at the upper and lower interfaces, the switching between the two bistable states of the liquid crystal molecules is asymmetric. For example, as shown in FIG. 1, asymmetry occurs in the applied voltage-transmittance characteristic when switching from state U1 to U2 and when switching from state U2 to U1. When such an element is driven, the applied voltage-transmittance characteristics differ for writing in both directions, and therefore the driving is not simple as compared with the case where switching is symmetrical.

FIG. 2 shows a bistable potential diagram in the case of FIG.
Shown in. In this case, which of the state U1 and the state U2 is stable and the difference in stability between the two states are determined by the liquid crystal material used and the combination of the upper and lower alignment films. It is possible to change it to some extent by making an appropriate selection.

On the other hand, when the stripe-shaped convex portions are formed and the stripe-shaped domains are to be expressed, the effect of shape alignment is produced by the stripe-shaped convex portions. And as shown in Figure 3,
When the layer normal direction L in the chiral smectic phase is not parallel to the longitudinal direction of the stripe-shaped convex portion, the molecule is in the state U1 of the bistable states and in the state U2. The bistable states are asymmetric because of the different magnitude of the effect. A bistable potential diagram at this time is shown in FIG. The stable state shown by A in FIG. 4 corresponds to the one in which the angle between the long axis of the molecule and the direction of the stripe convex portion is small, that is, the state of U1 shown in FIG.
The stable state indicated by corresponds to the one in which the angle formed by the molecular long axis direction and the direction of the stripe convex portion is large, that is, the state of U2 shown in FIG.

For this reason, the switching characteristics between the two bistable states are asymmetrical, and as shown in FIG.
Asymmetry occurs in the transmittance characteristic. In this asymmetry, which of the two states is stable is determined depending on which side the layer normal direction is inclined with respect to the longitudinal direction of the stripe.

The magnitude of the asymmetry, that is, the difference between the two stable states, changes depending on the distance between the stripe-shaped protrusions. In general, within a certain range, the smaller the distance between the stripe-shaped protrusions, the greater the degree of asymmetry. Become. It is considered that this is because the smaller the distance between the stripe-shaped convex portions is, the greater the effect of the shape orientation that causes the asymmetry becomes. In FIG. 4, the curve indicated by the broken line is the potential curve of the element with a small stripe spacing, and the curve indicated by the solid line is the potential curve of the element with a large stripe spacing. In addition to this, the degree of asymmetry can be changed also by the width and height of the stripe-shaped convex portion. Since this asymmetry changes depending on the angle formed by the layer normal direction and the stripe-shaped convex portion, the degree of asymmetry can be changed by changing the rubbing direction. However, of the acute angles formed by the longitudinal direction of the stripe-shaped convex portions and the two molecular orientation directions of the liquid crystal in the device in the bistable state, the angle having the smallest absolute value is the magnitude of the chiral smectic of the ferroelectric liquid crystal. Above a cone angle in the layer, the effect of asymmetry is not significant.

As described above, the directionality and size of the asymmetric switching asymmetry formed when the stripe-shaped protrusions are formed are as follows: angle in the layer normal direction with respect to the stripe direction, stripe interval, stripe convex portion. It can be freely controlled by changing the width and height of the convex portion.

The switching asymmetry appears in a different manner depending on the driving pulse width and the like, and in particular, a difference in stripe interval dependency is recognized. When the width of the applied pulse is large, the dependency on the stripe spacing is observed to be large, but when the width of the applied pulse is small, the difference in asymmetry due to the stripe spacing is small.

Therefore, in the liquid crystal device according to the present invention, the above-mentioned asymmetry of switching due to the difference in the upper and lower alignment control layers and the asymmetry due to the effect of the shape alignment of the stripe-shaped convex portions are canceled to each other. , The bidirectional switching characteristics are symmetrical. In the device of the present invention, the applied voltage-transmittance characteristic can be represented by almost one curve for both bidirectional switching.
It is possible to simplify the drive.

Specifically, the positive / negative of the spontaneous polarization of the ferroelectric liquid crystal material used and the positive / negative of the angle of the layer normal direction with respect to the stripe direction in a direction in which the asymmetry is canceled by the combination of the upper and lower alignment films. To decide. It is preferable to form an alignment film on the electrode on which the stripe-shaped convex portions are not formed and perform the uniaxial alignment treatment. Then, for the driving conditions used, the height, width, and
Adjust the spacing to make switching symmetrical.

At least one of the pair of electrodes forming the liquid crystal cell used in the present invention, that is, the pixel is preferably formed of a transparent conductor. Examples of such a material include tin oxide, indium oxide, and oxide. Indium tin (I
(TO) and the like are preferably used.

The alignment film used is preferably an organic substance such as polyimide or polyvinyl alcohol, and the vertical alignment treatment is preferably polysiloxane coating or silane coupling treatment, but is not limited thereto.

In the present invention, the stripe-shaped convex portions may be formed in one pixel in a uniform shape or in a non-uniform shape. Alternatively, one pixel may be divided into a plurality of sub-pixels, and the sub-pixels may be uniform and different sub-pixels may not be uniform. Such a stripe-shaped convex portion may be formed by using a part of the electrode or the alignment film thereon, or a special member for the stripe-shaped convex portion may be provided. In any case, the stripe-shaped convex portion can be easily formed by film formation and patterning.

It is necessary to select an optimum value for the pitch of the stripe convex portions depending on the liquid crystal material used and the cell thickness, but it is generally preferable to be 3 μm to 50 μm. In addition, the smaller the width of the concave portion and the convex portion is about the cell thickness or more, generally 1 μm.
The above is preferable. Further, the length of the stripe is preferably about a chiral pitch or more, and generally, it is necessary to be 3 times or more, and preferably 10 times or more, to the smaller width of the concave portion and the convex portion. It is sufficient that the unevenness has a level difference that maintains a uniform alignment state, and is about half the cell thickness or less,
Generally, the range of 100 nm to 500 nm is preferable.

The liquid crystal element of the present invention is preferably used as an element for performing the following switching.

FIG. 6 is a diagram schematically showing the inversion domain observed in the device of the present invention. The region (black region) 12 in the initial state in which the liquid crystal molecule is one of the bistable states is shown. In the figure, a state in which a domain (white region) 13 in which the polarization is inverted to the other of the bistable states is expressed in a plurality of stripes in the pixel 11 is shown.

The expression of the striped inversion domain is formed by connecting the inversion domains in the direction crossing the stripe by forming a striped projection on at least one electrode. In the absence of parts, the inversion domains are randomly formed as shown in FIG.

When the inversion domains are randomly formed, even when signals of the same waveform are applied, the shape and size of the domains appearing each time are often different, resulting in poor reproducibility of transmittance. The transmittance does not completely correspond to the crest value and / or the pulse width of the signal. Therefore, the variation in transmittance between pixels also increases.

On the other hand, when the domains are expressed in a striped pattern, the probability that the same domain appears when the signals having the same waveform are applied becomes very large, and moreover, depending on the peak value and / or pulse width of the signal. Since the length and density of the striped domains change linearly, the controllability of the transmittance becomes good, and the display becomes suitable for gradation display. Furthermore, after application of the signal, the instability of expanding or contracting the domain further after the domain wall is formed is extremely small, and there is almost no variation in transmittance between pixels.

Basically, by forming a concavo-convex stripe on the surface of the electrode, the shape of the inversion domain of the liquid crystal molecules can be controlled so as to form a stripe, and the stability of the domain and the gradation controllability can be improved. You can

The halftone signals used in the present invention include:
It may be either a signal in which only the peak value is modulated, a signal in which only the pulse width is modulated, or a signal in which both the peak value and the pulse width are modulated. The halftone signal generating means for generating such a halftone signal is manufactured by a semiconductor integrated circuit or the like. More preferably, it is desirable to apply an independent signal to each of the pair of electrodes and combine them to obtain a halftone signal.

In the element of the present invention, when the interval between the stripe convex portions in one pixel is changed, more excellent gradation controllability can be obtained.

Under a driving condition such that the dependency of asymmetry on the stripe spacing is small, the switching asymmetry is canceled in any stripe spacing region. Therefore, for switching in both directions, the area of the inversion domain after application of an equal voltage. Becomes larger because the domains are connected more easily in the region where the stripe interval is smaller, and therefore it is possible to form the distribution of the inversion threshold within the pixel. The state of domain inversion at this time is schematically shown in FIG. In each pixel in FIG. 8, the stripe interval is smaller on the left side, and the threshold gradient is formed in one direction.

Further, FIG. 9 schematically shows a state of the inversion domain observed under a driving condition in which the asymmetry has a large stripe spacing dependency. In this case, the polarity of the applied voltage is changed so that white writing is performed in both switching directions. For the switching from U2 to U1 shown in FIG. 1, the inversion threshold is lower in the region of stripe spacing smaller than the region of stripe spacing in which the above two asymmetry effects are just cancelled, while the asymmetry is The inversion threshold is higher in the region of the stripe interval larger than the region of the stripe interval to be canceled. Also, for switching from U1 to U2,
On the contrary, the inversion threshold is higher in the region with a smaller stripe spacing than in the asymmetrical cancellation region, while it is lower in the region with a larger stripe spacing than the asymmetrical cancellation region. Again, it is possible to form a threshold gradient. Also in this case, as in FIG. 8, the stripe interval becomes smaller toward the left side of the pixel.

However, when a threshold gradient is created by utilizing this asymmetry of the stripe spacing dependence, FIG.
As shown in, the same part of the applied voltage-transmittance curve corresponds to different regions in the pixel by both switching, and therefore, in order to make the switching characteristics symmetrical in both directions, as a device, parts with different stripe intervals are used. It is necessary to design the area of each.

Also in this case, the formation of the above-mentioned striped domains due to the formation of the above-mentioned stripe protrusions is not affected at all, so that the present invention achieves good orientation and controllability of transmittance. It is possible to eliminate the asymmetry of switching while keeping the advantages of good, excellent gradation display, and small variation between pixels.

Specific examples will be described in more detail below. In the embodiments described below, the rubbing direction of one of the pair of substrates or electrodes is shifted counterclockwise with respect to the stripe, and the other is vertically aligned.

(Embodiment 1) FIG. 11 shows a pixel pattern of the liquid crystal display element of this embodiment. A square portion 1101 indicates each pixel, and 1102 is a stripe convex portion provided on the transparent thin film electrode on the substrate. The size of the pixel 1101 is 200 μm on each side, and the width of the stripe convex portion is 5 μm.
The space is 5 μm. FIG. 12 shows aa ′ in FIG.
The cross section of the cell by the line is shown. Upper and lower glass substrates 120
1,1202, ITO 1203,1204 on the thickness of 15
The film is formed to a thickness of about 0 nm, and a pixel pattern,
And a stripe pattern 1205 are formed, and only the pixel pattern is formed on the lower glass substrate. The step of the stripe pattern is about 70 nm. Polysiloxane 1207 is further formed on the electrode of the upper substrate on which the convex portion is formed.
On the other hand, polyimide 1206 is applied on the electrode of the lower substrate on which the stripe-shaped convex portions are not formed by about 20 times.
A film having a thickness of nm is formed and a rubbing process is performed. The rubbing direction is 7 degrees counterclockwise with respect to the longitudinal direction of the stripe when viewed from the upper substrate side. After that, the two substrates are bonded together with a cell gap of 1.2 μm. Ferroelectric liquid crystal is injected into the gap. As a ferroelectric liquid crystal,

[0041]

[Outer 1] A liquid crystal molecule having a phase sequence of, a negative Ps, and a large tilt angle of 28.8 ° of liquid crystal molecules at 30 ° C. was used.

A liquid crystal cell was prepared as described above. This cell shows a good orientation, and the angle formed by the two extinction positions is 45.0 ° at 30 ° C., which is 2 ° of the tilt angle of liquid crystal molecules.
It was a value close to twice, and high contrast could be achieved. The layer normal direction in the smectic C phase was 5 degrees counterclockwise from the longitudinal direction of the stripe pattern.

A pulse voltage as shown in FIG. 13 was applied between the upper and lower electrodes of this cell, and the optical response characteristics were measured. In this embodiment, Δt = 20 μsec and V _ap = 15 to 30 V. The optical response characteristics were evaluated in two switching directions, and the polarity of the applied voltage was determined so that white writing was always performed.

When the inversion domain shape was observed by applying different pulse voltages V _ap in the initial black state in a 4 × 4 matrix, a striped domain as schematically shown in FIG. 6 was observed and the applied voltage was It was observed that the width of the stripes widened with the increase of.

The applied voltage-transmittance characteristic of this element was very stable and excellent in reproducibility, and the variation in the transmittance of each pixel was very small.

Further, γ = which is an index showing the gradation controllability
The value of (saturation inversion voltage) / (inversion threshold voltage) was increased from γ = 1.03 in the element in which the stripe-shaped convex portion was not formed to γ = 1.10 to improve the gradation controllability. I was able to.

Further, the optical response characteristics to switching in two directions, which were measured with the crossed Nicols at the two extinction positions, were as follows. Difference of 1.
What was 5 V is now represented by substantially equal curves as shown in FIG. 14, and switching can be made almost symmetrical. This switching symmetry can be further improved by changing the pulse width, the width of the stripe convex portions, the interval between the stripe convex portions, the rubbing direction, the alignment film material, the liquid crystal material, and the like.

(Embodiment 2) FIG. 15 shows a pixel pattern of the liquid crystal display element of this embodiment. The square portion of 1501 indicates each pixel, and 1502 is the stripe convex portion provided on the transparent thin film electrode on the substrate. The size of the pixel 1501 is 200 μm on each side, and the width of the stripe convex portion is 5 μm. The densest part of the stripe-shaped convex part is a 5 μm space, the sparsest part is a 15 μm space, and the step is 7
It is 0 nm. The rubbing direction is the same as in Example 1 and is 7 degrees counterclockwise with respect to the longitudinal direction of the stripe when viewed from the upper substrate side. Fabrication method, liquid crystal material, alignment film material,
The vertical alignment treatment, cell gap, etc. are the same as in the first embodiment.

A liquid crystal cell was prepared as described above. This cell shows a good orientation, and the angle formed by the two extinction positions is 45.2 ° at 30 ° C., which is 2 times the tilt angle of the liquid crystal molecules.
It was a value close to twice, and high contrast could be achieved. The layer normal direction in the smectic C phase was about 5 degrees counterclockwise from the longitudinal direction of the stripe pattern.

A pulse voltage as shown in FIG. 13 was applied between the upper and lower electrodes of this cell, and the optical response characteristics were measured. The measurement was performed under the same conditions as in Example 1 with Δt = 20 μsec and V _ap = 15 to 30 V. The optical response characteristics were evaluated in two switching directions, and the polarity of the applied voltage was determined so that white writing was always performed.

When a different pulse voltage V _ap was applied in the initial black state in a 4 × 4 matrix and the inversion domain shape was observed, as shown in FIG. When the voltage was low, it was observed that stripe-shaped inversion domains appeared only on the side with a small stripe interval and extended to the side with a wide stripe interval as the applied voltage increased. This is because the stripe spacing dependency of the shape orientation effect by the stripe-shaped convex portions is small under the driving condition where the pulse width is small as in the present embodiment,
It is considered that the switching asymmetry due to the asymmetry of the upper and lower alignment films could be canceled in all the stripe spacing regions in the present embodiment.

The applied voltage-transmittance characteristic of this element was very stable and excellent in reproducibility, and the variation of the transmittance among the pixels was very small.

The applied voltage-transmittance characteristic of this element is shown in FIG.
Shown in. As described above, the two applied voltage-transmittance curves showing switching in both directions are substantially the same, which shows that symmetrical switching is achieved. The symmetry of this switching is pulse width, stripe convex width,
It can be further improved by changing the distribution of the stripe-shaped convex portions within the pixel, the rubbing direction, the alignment film material, the liquid crystal material, and the like.

Further, γ = which is an index showing gradation controllability
The value of (saturation inversion voltage) / (inversion threshold voltage) was γ = 1.30 in the element in which the stripe-shaped convex portion was not formed, and was increased to γ = 1.30. By changing it, the gradation controllability could be improved very effectively in this way.

(Embodiment 3) FIG. 17 shows a pixel pattern of the liquid crystal display element of this embodiment. A square portion of 1701 indicates each pixel, and 1702 is a stripe convex portion provided on the transparent thin film electrode on the substrate. The size of the pixel 1701 is 200 μm on a side, and the width of the stripe convex portion is 3 μm. The densest stripe-shaped convex portion has a 1 μm space and the sparsest portion has a 15 μm space, and the arrangement is as shown in FIG. The step difference of the convex portion is 70 nm. The rubbing direction is 9 degrees counterclockwise with respect to the longitudinal direction of the stripe when viewed from the upper substrate side. The manufacturing method, liquid crystal material, alignment film, vertical alignment treatment, cell gap, etc. are the same as in Example 1.

A liquid crystal cell was prepared as described above. This cell shows a good orientation, and the angle formed by the two extinction positions is 45.2 ° at 30 ° C., which is 2 times the tilt angle of the liquid crystal molecules.
It was a value close to twice, and high contrast could be achieved. The layer normal direction in the smectic C phase was approximately 7 degrees counterclockwise from the longitudinal direction of the stripe pattern.

A pulse voltage as shown in FIG. 13 was applied between the upper and lower electrodes of this cell, and the optical response characteristics were measured. Δt
= 100 μsec, V _ap = 5-9V. The optical response characteristics were evaluated in two switching directions, and the polarity of the applied voltage was determined so that white writing was always performed.

When a different pulse voltage V _ap was applied in the 4 × 4 matrix in the initial black state and the shape of the inverted domain was observed, the result schematically shown in FIG. 9 was obtained. That is, for switching when the extinction position is adjusted to the side of the two extinction positions where the angle formed by the stripe convex portion with the longitudinal direction is large, the inversion threshold value becomes low in the region with a small stripe interval, while the stripe The reversal threshold was high in the region with a large interval. On the contrary, for switching when the extinction position is adjusted to the side where the angle formed by the stripe convex portion with the longitudinal direction is small, the inversion threshold becomes low in the region with a large stripe interval while the inversion threshold becomes low in the region with a large stripe interval. In, the inversion threshold is higher. Then, in the portion of the intermediate spacing in the stripe spacing used in this embodiment, for either switching,
They showed almost the same inversion voltage value. This is because under a driving condition with a long pulse width, the asymmetry of switching due to the shape effect greatly depends on the stripe spacing,
It is considered that this is because the two asymmetries can be canceled only in the region of the intermediate stripe range, and the almost symmetric switching behavior is exhibited.

As shown above, although there is a difference in the inversion region depending on the switching direction, it is possible to create regions having different inversion thresholds in one pixel.

When the threshold gradient is created by utilizing this asymmetry of stripe spacing dependence, as shown in FIG. 10, the same portion of the applied voltage-transmittance curve is different in the pixel due to both switching. Since it corresponds to the region, the areas of the portions having different stripe intervals are designed as elements in order to make the switching characteristics in both directions symmetrical.

The applied voltage-transmittance characteristic of this element was very stable and excellent in reproducibility, and the variation in the transmittance of each pixel was very small.

The applied voltage-transmittance characteristic of this element is shown in FIG.
Shown in. The solid line shows the switching when the extinction position is adjusted to the side with a larger angle with the longitudinal direction of the stripe protrusions, and the broken line shows the extinction position with the smaller angle to the longitudinal direction of the stripe protrusions. The case of switching is shown. As described above, the two applied voltage-transmittance curves showing the switching in both directions are substantially in agreement with each other, indicating that substantially symmetrical switching is achieved. This switching symmetry can be further improved by changing the pulse width, stripe convex width, stripe convex distribution within a pixel, rubbing direction, alignment film material, liquid crystal material, and the like. .

Further, γ = which is an index showing the gradation controllability
The value of (saturation inversion voltage) / (inversion threshold voltage) was as large as γ = 1.38 from γ = 1.03 in the element in which the stripe-shaped convex portion was not formed, and the interval between the stripes within the pixel was increased. By changing it, the gradation controllability could be improved very effectively in this way.

[0064]

As described above, according to the present invention, the contrast is high, the reproducibility of halftone display is excellent, the gradation controllability can be improved, and the bidirectional switching behavior is improved. It is possible to provide a ferroelectric liquid crystal device which is substantially symmetrical and can be driven more simply.

[Brief description of drawings]

FIG. 1 is a diagram showing bidirectional applied voltage-transmittance characteristics of cells having different upper and lower alignment control layers.

FIG. 2 is a diagram illustrating an asymmetric bistability potential when the upper and lower alignment control layers are different.

FIG. 3 is a diagram illustrating bistability when a stripe-shaped convex portion is provided.

FIG. 4 is a diagram illustrating an asymmetric bistability potential when a stripe-shaped convex portion is provided.

FIG. 5 is a diagram showing bidirectional applied voltage-transmittance characteristics of a cell provided with a stripe-shaped convex portion.

FIG. 6 is a plan view illustrating a striped domain.

FIG. 7 is a plan view illustrating a random domain.

FIG. 8 is a schematic diagram of domain inversion under a driving condition in which asymmetry of stripe spacing dependency is small.

FIG. 9 is a schematic diagram of domain inversion under a driving condition in which asymmetry has a large dependency on stripe spacing.

FIG. 10 is a diagram illustrating a correspondence between a transmittance-applied voltage curve and an inversion domain position under a driving condition in which asymmetry has a large stripe spacing dependency.

FIG. 11 is a diagram showing a stripe pattern according to the first embodiment of the present invention.

FIG. 12 is a sectional view taken along the line aa ′ of the device of Example 1 of the present invention.

FIG. 13 is a diagram showing a cell drive applied voltage.

14 is a diagram showing applied voltage-transmittance characteristics of the device of Example 1. FIG.

FIG. 15 is a diagram showing a stripe pattern according to a second embodiment of the present invention.

16 is a diagram showing an applied voltage-transmittance characteristic of the device of Example 2. FIG.

FIG. 17 is a diagram showing a stripe pattern according to the third embodiment of the present invention.

FIG. 18 is a diagram showing applied voltage-transmittance characteristics of the device of Example 3;

[Explanation of symbols]

 11 Pixel Area 12 Initial Domain 13 Inversion Domain 21 Pixel Area 22 Inversion Domain 81 Pixel Area 82 Inversion Domain 91 Pixel Area 92 Inversion Domain 1101 Pixel Area 1102 Striped Convex 1201 1202 Glass Substrate 1203, 1204 ITO 1205 Striped Convex 1206 Polyimide 1207 Polysiloxane 1501 Pixel area 1502 Striped convex portion 1701 Pixel area 1702 Striped convex portion

Claims (3)

[Claims] 1. A liquid crystal device having a ferroelectric liquid crystal between a pair of electrodes, wherein a stripe-shaped convex portion is formed on one electrode of the pair of electrodes, and a switching characteristic of the convex portion is formed. A liquid crystal element characterized by being subjected to an alignment treatment to compensate for asymmetry. 2. A liquid crystal device having a ferroelectric liquid crystal between a pair of electrodes, wherein a stripe-shaped convex portion is formed on one electrode of the pair of electrodes, and a longitudinal direction of the convex portion is formed. The layer normal direction of the smectic layer of the liquid crystal in the device is different, and the acute angle between the longitudinal direction of the convex portion and the two molecular orientation directions of the liquid crystal in the device in the bistable state A liquid crystal element characterized in that the angle having the smallest absolute value is equal to or less than the cone angle in the chiral smectic layer, and an alignment treatment is performed so that the switching characteristics are substantially symmetrical. 3. The alignment treatment is a vertical alignment treatment on the convex side and a uniaxial alignment treatment on the other side.
2. The liquid crystal device according to items 2 and 3.