JPH11167113A - Liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure a wide driving margin by preventing crosstalk due to the growth of an inverted domain from a pixel gap part as to a liquid crystal element which uses chiral smectic liquid crystal. SOLUTION: When liquid crystal which is easy to move in a liquid crystal layer is used, a rubbing processing is performed in a direction 3 crossing the rubbing direction 2 of the majority in a pixel part 1 at right angles outwardly from nearby a pixel end part 12 parallel to the rubbing direction 2 to form an orientation defect 4 parallel to the end part 12 nearby the end part 12 in the pixel part 1, and the liquid crystal is oriented so that the normal direction of a smectic layer cross the end part at right angles at any end part forming the pixel part 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device used for a display device for displaying characters and images.

[0002]

2. Description of the Related Art Conventionally, in a liquid crystal element having a liquid crystal sandwiched between a pair of substrates, a matrix arrangement is made up of matrix electrodes composed of a scanning electrode group formed on one substrate and an information electrode group formed on the other substrate. There is a well-known simple matrix type liquid crystal element which constitutes a pixel and displays image information.

Further, research and development of a liquid crystal device using a ferroelectric liquid crystal having a characteristic that the liquid crystal itself has spontaneous polarization, responds rapidly to an electric field, and can stably realize two liquid crystal molecular alignment states. Has been popular since the 1980's, and has been proposed in, for example, Japanese Patent Application Laid-Open No. 56-107216.

Usually, in such a liquid crystal element, a rubbing treatment with a flocked cloth is performed as a method of aligning liquid crystal molecules. The rubbing treatment is performed by rubbing the film surface in contact with the liquid crystal with a cylindrical drum around which a flocked cloth is wound. Usually, the entire film surface is rubbed uniformly in one direction.

[0005]

FIG. 10 shows a liquid crystal alignment state of an arbitrary pixel of a liquid crystal element using a conventional chiral smectic liquid crystal. In the figure, reference numeral 1 denotes a pixel portion which is a region where a scanning electrode and an information electrode face each other, and reference numeral 5 denotes a gap between the pixel portion 1 and an adjacent pixel portion. In this figure, for convenience, the pixel portion 1 is shown only in the pixel gap portion adjacent to the end of two sides, but usually the pixel gap portion 5 is present on all sides.
Reference numerals 101 and 102 denote rubbing directions of the pixel portion 1 and the pixel gap portion 5, and reference numerals 103 to 104 denote smectic layer structures of the respective regions (the pixel portion 1 and the pixel gap portion 5).

As shown in FIG. 10, since the rubbing process is usually performed only in one direction, the layer structure of the liquid crystal is the same in the pixel portion 1 and the pixel gap portion 5. Therefore, the end of the pixel unit 1 is connected to the end 111 perpendicular to the layer normal direction of the layer structure 103.
And a parallel end 112. Crosstalk may occur when such a liquid crystal element is driven in a matrix. Crosstalk is likely to occur due to inversion domain growth from the end 111 depending on the type of liquid crystal used, and crosstalk may occur from the end 112 depending on the type of liquid crystal used. In some cases, this is likely to occur due to inversion domain growth.

The above phenomenon is considered to be related to the ease of movement of the domain wall. In the case of a ferroelectric liquid crystal device having bistability, the domain wall is a portion where the molecular arrangement changes continuously at the boundary between different molecular alignment states (different display states). In this case, the domain wall itself is easily moved with low energy in the in-layer direction. Therefore, as the liquid crystal extends in the layer direction in the state of partial inversion of molecules in the pixel and easily takes a long and thin domain shape, the pixel end perpendicular to the layer structure 103 (FIG. 1)
At 0, crosstalk is likely to occur due to the growth of the inversion domain from 112). When molecules move easily between layers, the domain wall easily moves in a direction parallel to the layer normal direction. Therefore, in a liquid crystal that easily takes a wide domain shape, the liquid crystal is perpendicular to the layer normal direction of the layer structure 103. Crosstalk is likely to occur due to the growth of the inversion domain from the end of the pixel (111 in FIG. 10).

The driving margin for maintaining appropriate display characteristics (for example, contrast, fluctuation, etc.) as a display element is greatly reduced by the growth of the inversion domain from the end of the pixel, which is a serious problem in practical use. .

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems and prevent crosstalk from occurring by preventing the growth of an inversion domain from a pixel end, thereby securing a wide driving margin.

[0010]

The present invention provides a liquid crystal device having a plurality of pixels, in which a chiral smectic liquid crystal is sandwiched between a pair of electrode substrates.
A liquid crystal element having a plurality of regions having different normal directions of a smectic liquid crystal layer, and having an alignment defect at a boundary between the different regions.

In the case of a conventional pixel having a uniform layer structure in one direction in the entire surface, one of two sets of opposite ends constituting the pixel portion has a layer structure in which an inversion domain is easily grown. Had become. According to the present invention, by adopting the above structure, a layer structure in which an inversion domain is unlikely to grow at each pixel end can be present, and crosstalk due to the growth of the inversion domain from the pixel end can be prevented.

As shown in FIG. 10, in the conventional liquid crystal element, the layer structures 103 to 1 of the pixel portion 1 and the pixel gap portion 5 are provided.
05 are equal. In such a configuration, when the liquid crystal easily moves in parallel in the layer, crosstalk is likely to occur due to the movement of the domain wall at the pixel end 112 parallel to the layer normal direction of the layer structure 103 of the pixel unit 1. On the other hand, end 11
Crosstalk due to movement of the domain wall from 1 is unlikely to occur. When the liquid crystal easily moves between the layers, the pixel end 11 perpendicular to the layer normal direction of the layer structure 103 is formed.
In the case of 1, the crosstalk due to the movement of the domain wall easily occurs.

The principle of preventing crosstalk according to the present invention will be described with reference to FIG. 11 by taking as an example a case where liquid crystal easily moves in a layer. Crosstalk from the pixel gap 5 occurs due to the movement of the domain wall. That is, when the orientation state (direction of spontaneous polarization) of the pixel unit 1 and the pixel gap unit 5 is different (when the display state is different), the domain of the pixel gap unit 5 is expanded in the pixel unit 1. At this time, when the layer structure of the pixel portion 1 and the pixel gap portion 5 is the same and continuous, the domain wall easily moves (FIG. 11C), and the orientation of the pixel gap portion 5 is different from that of the pixel portion 1. When the layer structure is continuous, the domain wall is likely to move (FIG. 11A). However, it was found that if the layer structure was discontinuous and an alignment defect was present at the boundary, the domain wall would hardly move from that portion (FIG. 11B). The present invention is configured using this phenomenon.

[0014]

FIG. 1 is a schematic view of an arbitrary pixel according to an embodiment of the present invention. In the figure, 1 is a pixel portion, 5 is a pixel gap portion, and 2 and 3 are rubbing directions, respectively.
Note that, also in this figure, 2 for forming the pixel gap 5 for convenience.
Although the configuration of the present invention will be described by showing only a portion of the side adjacent to the pixel ends 12 and 13, a similar configuration is provided at the ends opposite to the ends 12 and 13.

As shown in FIG. 1A, the rubbing process is performed in the direction of arrow 2 on the left side of the dotted line in the figure and in the direction of arrow 3 on the right side, so that the dotted line is As a result, an alignment defect 4 can be formed at the boundary. As a result, a smectic layer structure 14 orthogonal to the rubbing direction 2 is formed in a large part (left side in the drawing) of the pixel portion 1, and an end portion orthogonal to the layer normal direction (= rubbing direction 2) of the layer structure 14. Pixel gap 5 adjacent to 13
In the G1 region, a smectic layer structure 15 having the same layer normal direction as the layer structure 14 is formed, and a small area in the pixel portion 1 is sandwiched between the end portions 12 of the layer structure 14 parallel to the layer normal direction. In the G3 region of the pixel gap 5, a smectic layer structure 16 parallel to the end 12 (that is, the layer normal direction is orthogonal to the end 12) is formed. However, G is larger than alignment defect 4.
In the G2 region of the end portion 13 located on the three region side, since the layer normal direction of the layer structure 16 is at a position parallel to the end portion 13, crosstalk is likely to occur, but the end portion corresponding to the G2 region. Since the length of 13 is short, the effect is substantially small.

With the above configuration, the liquid crystal is oriented so that the normal direction of the smectic layer is perpendicular to the corresponding end at each end of the pixel portion 1, and even if the pixel is displayed in white. Even when black display is performed, no crosstalk occurs as shown in FIG.

Next, how the left and right display states of the alignment defect 4 will be described when regions in different rubbing directions are formed in the pixel portion 1 will be described. In FIG. 1B, reference numeral 6 denotes an analyzer, 7 denotes a polarizer, which are arranged in an orthogonal state to be in a crossed Nicol state. The rubbing direction of the left region in the pixel portion 1 is 2, and the average molecular axes of the liquid crystal molecules in the two stable states of the chiral smectic liquid crystal at this time are indicated by 8 and 9. According to this arrangement, the liquid crystal molecules enter a black state when the average molecular axis is 8, and enter a white state when the average molecular axis is 9. On the other hand, the average molecular axes in the pixel portion 1 on the right side of the alignment defect 4 are represented by 10 and 11. Since the rubbing directions are rotated by 90 ° on the left and right sides of the alignment defect 4, 8 and 10 are also rotated by 90 °, and 9 and 11 are also rotated by 90 °.
° is rotating. Therefore, a black state is obtained when the average molecular axes are 8 and 10, and it can be formed in the same electric field direction.
Similarly, a white state is obtained at the time of the average molecular axes 9 and 11, and they can be formed in the same electric field direction.

As described above, by rotating the other rubbing direction 3 by 90 ° with respect to the one rubbing direction 2 in the pixel section 1, (1) crosstalk from the pixel gap is avoided, and (2) ) The contrast in the pixel portion can be maintained.

In the present embodiment, the liquid crystal easily moves in the layer. Such a liquid crystal has a fluorocarbon terminal portion and a hydrocarbon terminal portion, and both terminal portions are bonded by a central nucleus. Examples of the liquid crystal composition include a fluorine-containing liquid crystal compound having a smectic mesophase or a latent smectic mesophase. In particular, when the tilt angle is 19
It is preferably applied to a liquid crystal having an angle of from 26 ° to 26 °.

In the above embodiment, the case where the liquid crystal easily moves in the layer has been described as an example. However, in the case where the liquid crystal easily moves between the layers, the alignment defect is reversed in the rubbing direction in the above embodiment. 2 are formed in the vicinity of the orthogonal end 13,
The liquid crystal may be oriented so that the normal direction of the smectic layer is parallel to the corresponding end at all ends of the pixel portion 1. Any pixel of the embodiment using such a liquid crystal is schematically shown in FIG. In the figure, reference numerals 91 and 93 denote rubbing directions, 94 denotes an alignment defect, and 95 to 96 denote a smectic layer structure. Also in this figure, for convenience, the pixel gap portion 5 shows only a region adjacent to two sides of the pixel portion 1.

As shown in FIG. 9, in the present embodiment, a small area of the pixel section 1 and the rubbing of the pixel gap section 5 are sandwiched across an end perpendicular to the rubbing direction 92 occupying most of the pixel section 1. The direction 93 was rotated 90 °. as a result,
As shown in FIG. 9, at any pixel end,
The liquid crystal is oriented so that the normal direction of the smectic layer and the end are parallel to each other, and the direction in which the inversion domain easily grows is parallel to the end, so that the growth of the inversion domain in the pixel portion 1 is prevented. .

As means for forming regions in different rubbing directions in the pixel, first, rubbing is performed in one direction on the entire surface of the alignment film, and then rubbing is performed in different directions while protecting a predetermined region with a resist or the like. By removing the resist, a rubbing treatment in a desired direction can be performed on a desired region.

In the present invention, as described above, except for forming a region having a different layer structure by changing the rubbing direction at the pixel end where the crosstalk is liable to occur, the structure of each member (material, shape, manufacturing method) For ()), a general liquid crystal element technology can be applied.

[0024]

[Embodiment 1] As a first embodiment of the present invention, a liquid crystal element having an alignment treatment configuration shown in FIG. 1 was formed. FIG. 2 is a schematic cross-sectional view of the cell of the liquid crystal element of this embodiment. In the figure,
21 and 31 are glass substrates, 22 is a black matrix made of MoTa, and 23 is a pigment-based color filter layer formed to a thickness of 1.5 μm. 24 is a flattening layer ("PA-1000C" manufactured by Ube Industries, Ltd., polymer content = 10%, solvent = N-methyl-2-pyrrolidone (NMP)) of 1.5
It was formed to a thickness of μm. 25 and 33 are 8 μm wide Al-
Metal wires 26 and 33 made of Si-Cu were formed by sputtering using ITO electrodes formed at a low temperature without heating the substrate. Each was formed in a stripe shape with a width of 60 μm and an interval of 8 μm. 27 is a polyimide-based liquid crystal alignment film, and 34 is tin oxide conductive particles doped with antimony (having a diameter of 5 to 1).
0 nm) was dispersed and the surface energy in the state of a coating film was adjusted to 27 to 35 dyne / cm. The upper and lower substrates were bonded together with a sealing material (epoxy adhesive) (not shown) via spacer beads 35 (SiO ₂ particles, diameter 2.4 μm), and a liquid crystal composition 36 was injected.

The liquid crystal composition used in this example is shown below. This liquid crystal has a bookshelf type layer structure, and liquid crystal molecules tend to move easily in the layer.

[0026]

Embedded image

The tilt angle and spontaneous polarization are values measured by the following measuring methods.

[Measurement of tilt angle Θ] ± 30 to 50 V, 1
While applying an AC (alternating current) of 100 Hz to between the upper and lower substrates of the liquid crystal element through electrodes, the liquid crystal element disposed therebetween is rotated in parallel with the polarizing plate under crossed Nicols, and at the same time, photomultiplier (Hamamatsu) The first extinction position (the position at which the transmittance is lowest) and the second extinction position are determined while detecting the optical response with a photonics company. Then, a half of the angle from the first extinction position to the second extinction position at this time is defined as a tilt angle Θ.

[Measurement of spontaneous polarization Ps]
Miyasato et al. "Direct Measurement of Spontaneous Polarization of Ferroelectric Liquid Crystal Using Triangular Waves" (Journal of the Japan Society of Applied Physics 22, 10 (66)
1) 1983, "DirectMethod with
Triangular Waves for Mea
surviving Spontaneous Polari
Zation in Ferroelectric Li
quid Crystal ”, as describe
d by K. Miyasato et al. (Ja
p. J. Appl. Phys. 22. No. 10, L6
61 (1983))).

FIG. 3 shows an alignment treatment method according to this embodiment. First, as shown in FIG. 3A, a rubbing process is performed in a direction 38 orthogonal to the stripes of the ITO electrode 26, and then, as shown in FIG. A pixel portion (60 μm × 60 μ
m) to a region having a depth of 10 μm.
And rubbed in a direction perpendicular to the paper surface.
For comparison, the pixel gap was not covered with the resist, and the pixel portion and the pixel gap portion were also rubbed in one direction in the same device as in the prior art. The resist used here was photosensitive PVA (manufactured by Toyo Gosei Co., Ltd.) and had a thickness of 1 μm.
m, prebaked at 70 ° C. for 10 minutes,
Exposure was performed with UV light of 5 mJ / cm ² . Development at 25 ° C
For 1 minute, and peeling after rubbing was performed with a mixed solution of water and NMP.

The rubbing was performed using a rubbing roller having a diameter of 80 mm to which a cotton flocking cloth was stuck. The rubbing strength was doubled.

The liquid crystal device of this embodiment was driven at 30 ° C. The driving waveform is shown in FIG. In FIG. 4, V ₁ = 3
_{0.0V, V 2 = -30.0V, V} 3 = 12.0V, V
_{When 4} = -12.0 V, V ₅ = 12.0 V, and the drivable one-line scanning time is A to B, the M2 margin was defined as follows.

M2 = (BA) / (B + A) It is desirable that the M2 margin is large because a display independent of variations in various panels can be performed.

FIG. 5 shows the drive margin of this embodiment. In the figure, the ordinate represents the M2 margin, and the abscissa represents the offset voltage of the drive circuit and the fluctuation of the output voltage of the drive circuit. In the figure, for comparison, the M2 margin of the region where the pixel gap portion and the pixel portion are rubbed in one direction is shown, and it can be seen that the M2 margin becomes almost zero due to the generated crosstalk. In the figure, the M2 margin in the configuration of the present invention is the M2 margin in consideration of the crosstalk in G2, and both can be increased to 0.2 or more. Due to the crosstalk of G2, M2
Since the margin is slightly reduced, it is preferable that the alignment defect be as close to the pixel edge as possible.

FIG. 6 shows a display state in this embodiment.
In order to confirm the display state of the pixel gap, no black matrix was formed on the pixel gap adjacent to the two sides of the pixel end to be observed. In the drawing, the left side shows a configuration in which the pixel portion 1 and the adjacent pixel gap portion 5 are rubbed in one direction as usual, and the right side has the configuration of the present invention and the alignment defect 4 is formed. FIG. 6B shows a state in which white display is performed, but no crosstalk occurs from the alignment defect 4.
On the other hand, it can be seen that crosstalk occurs in the pixel subjected to the conventional rubbing process from the pixel gap portion, and the black domain wall grows from the pixel end portion in the white display pixel portion. FIG. 6C shows a state of black display.
It can be seen that black display is favorably performed on both sides of the alignment defect 4, and that there is no growth of a white domain wall from the edge of the pixel.

Therefore, according to the present invention, it is possible to prevent the crosstalk generated from the pixel gap without lowering the contrast.

Embodiment 2 As a second embodiment of the present invention,
A liquid crystal element having the electrode configuration shown in FIG. 7 was manufactured. The electrode configuration is such that the substrates shown in FIG. 8 are overlapped with each other. In the figure, 71 and 81 are glass substrates, 72 and 82 are ITO electrodes, and 73 and 83 are metal wirings. Example 1 on this substrate
A rubbing process was performed by forming an alignment film similar to that described above, and the rubbing direction was as shown in FIG. Other members are the same as in the first embodiment.

When the distance in the rubbing direction is as short as about 10 μm, the orientation of the area may be deteriorated. However, as shown in the present embodiment, the length of the rubbed area is increased to make the area smaller. Can be improved.
Further, by changing the rubbing direction within the plane, the viewing angle characteristics can be improved, and the flow of liquid crystal molecules can be suppressed.

[Embodiment 3] The low resistance opposed film 34 of the embodiment 1
And the rubbing treatment was performed on the substrates on both sides. The rubbing direction is shown in FIG. In the figure, reference numerals 91 and 93 denote rubbing directions, 94 denotes an alignment defect, and 95 to 96 denote a smectic layer structure.

As shown in FIG. 9, in the present embodiment, a small area of the pixel section 1 and the rubbing of the pixel gap section 5 are sandwiched across an end perpendicular to the rubbing direction 92 which occupies most of the pixel section 1. The direction 93 was rotated 90 °.

Thereafter, both substrates were adhered in the same manner as in Example 1 except that 1.1 μm spacer beads were used, a cell was prepared, and a liquid crystal composition was injected. In this example, a liquid crystal composition having the following characteristics was used. The liquid crystal composition has a chevron-type smectic layer structure, and liquid crystal molecules tend to move easily between layers.

(Characteristics of Liquid Crystal Composition)

[0043]

Embedded image

When the liquid crystal element of the present embodiment was driven in the same manner as in the first embodiment, the width between the pixel gap and the adjacent pixel gap was wider than that in the conventional case where the rubbing process was performed in the same direction in the pixel and in the adjacent pixel gap. Domain did not grow and the margin could be improved.

[0045]

As described above, in a liquid crystal device using a chiral smectic liquid crystal, a crosstalk due to the growth of an inversion domain from a pixel gap is prevented, so that a driving margin can be widened without lowering contrast. And a highly reliable liquid crystal element is provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a configuration of the present invention.

FIG. 2 is a schematic cross-sectional view of the liquid crystal element according to the first embodiment of the present invention.

FIG. 3 is an explanatory diagram of a rubbing process according to the first embodiment of the present invention.

FIG. 4 is a driving waveform diagram of the liquid crystal element according to the first embodiment of the present invention.

FIG. 5 is a diagram illustrating a driving margin of the liquid crystal element according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating a display state of the liquid crystal element according to the first embodiment of the present invention.

FIG. 7 is a schematic diagram illustrating an electrode structure and a rubbing direction of a liquid crystal element according to a second embodiment of the present invention.

FIG. 8 is a schematic diagram illustrating an electrode structure of each substrate of a liquid crystal element according to a second embodiment of the present invention.

FIG. 9 is a schematic diagram illustrating a rubbing direction of a liquid crystal element according to a third embodiment of the present invention.

FIG. 10 is a schematic diagram showing a rubbing direction and a smectic layer structure of a conventional liquid crystal element.

FIG. 11 is a schematic diagram for explaining the principle of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pixel part 2, 3 Rubbing direction 4 Alignment defect 5 Pixel gap 6 Analyzer 7 Polarizer 8-11 Average molecular axis 12, 13 Pixel end 14-16 Smectic layer structure 21, 31 Glass substrate 22 Black matrix 23 Color filter 24 Flat Layer 25, 33 metal wiring 26, 32 ITO electrode 27 alignment film 34 low resistance facing film 35 spacer bead 36 liquid crystal composition 38 rubbing direction 39 resist 71, 81 glass substrate 72, 82 ITO electrode 73, 83 metal wiring 75, 76 Rubbing direction 92,93 Rubbing direction 94 Alignment defect 95-97 Smectic layer structure 101,102 Rubbing direction 103-105 Smectic layer structure 111,112 Pixel edge

Claims (7)

[Claims] 1. A liquid crystal element having a plurality of pixels with a chiral smectic liquid crystal sandwiched between a pair of electrode substrates, wherein each pixel has a plurality of regions in which the normal direction of the smectic liquid crystal layer is different. And a liquid crystal element having an alignment defect at a boundary between the different regions. 2. The method according to claim 1, wherein the plurality of regions having different layer normal directions are:
2. The liquid crystal device according to claim 1, comprising two types of regions whose layer normal directions are orthogonal to each other. 3. The method according to claim 2, wherein said layer normal directions are orthogonal to each other.
3. The liquid crystal device according to claim 2, wherein the boundary between the types of regions is substantially parallel to the vicinity of each of a pair of pixel ends facing each other. 4. The liquid crystal device according to claim 3, wherein the direction of the layer normal of the liquid crystal in the pixel gap adjacent to the pixel end substantially parallel to the boundary is substantially parallel to the boundary. 5. The liquid crystal device according to claim 3, wherein the direction of the liquid crystal layer normal in a pixel gap adjacent to a pixel end substantially parallel to the boundary is orthogonal to the boundary. 6. The liquid crystal has a fluorine-containing liquid crystal compound having a fluorocarbon terminal portion and a hydrocarbon terminal portion, both terminal portions of which are linked by a central nucleus, and having a smectic intermediate phase or a potential smectic intermediate phase. The liquid crystal device according to claim 1, which is a liquid crystal composition. 7. The liquid crystal composition has a tilt angle of 19 ° to 2 °.
The liquid crystal device according to claim 1, wherein the angle is 6 °.