JP2001281666A - Liquid crystal display element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain satisfactory and stable display performance. SOLUTION: The liquid crystal display element is provided with a first electrode substrate, having a transparent first substrate, a first electrode formed on the first substrate and a first alignment layer formed on the first substrate so as to cover the first electrode, a second electrode substrate having a transparent second substrate, a second electrode formed on the second substrate and a second alignment layer formed on the second substrate, so as to cover the second electrode and a light control layer comprising an antiferroelectric liquid crystal material, with no threshold type voltage-transmittance characteristic being held between the first and the second electrode substrates. The combination of the first and the second alignment layers and the liquid crystal material is characterized, so that a pre-tilt angle &alpha; in the SA phase in the light control layer satisfies 0 deg.<=&alpha;<=1 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a liquid crystal display device.

[0002]

2. Description of the Related Art Smectic liquid crystal materials having spontaneous polarization, such as ferroelectric liquid crystals and antiferroelectric liquid crystals, have characteristics such as high-speed response and a wide viewing angle in a surface stabilized display mode. It is expected as a material for liquid crystal display devices. Particularly in recent years, many attempts have been made to display moving images in combination with an active matrix driving method. As a material without hysteresis suitable for this application, a thresholdless antiferroelectric liquid crystal (Thresholdless Anti-
-ferroelectric Liquid Crystal (hereinafter also referred to as TLAF liquid crystal)) and polymer stabilized ferroelectric liquid crystal (Polymer Stab)
ilized Ferroelectric Liquid Crystal (PS-
(Also referred to as FLC liquid crystal)).

However, a characteristic of a liquid crystal display device using a liquid crystal material having spontaneous polarization is difficulty in controlling the alignment. The TLAF liquid crystal is obtained from Iso in order from the high temperature side.
It has a phase sequence of phase → SA phase → SC ^* phase (TLAF phase). At the time of the phase transition from the Iso phase to the SA phase, a layer structure is formed, and at the time of the phase transition from the SA phase to the SC ^* phase, a chevron structure in which the layer is bent due to a change in the distance between the smectic layers is generated (FIG. 8 ( a), (b)). Because of the relationship between the bending direction and the pretilt angle,
There are two types, one orientation and C2 orientation (see FIG. 8B).
Preferably the display characteristics on the C2 orientation in the case of the liquid crystal display device using the TLAF LCD, select a rib structure or a rubbing method (e.g., see Japanese Patent Application No. 10-184903 by the present applicant), SC ^* phase from Iso phase By applying an AC electric field when gradually cooling to C2, uniform C2 orientation can be selectively obtained. However, it became clear that even with the same C2 orientation, there is a difference in the orientation depending on the type of the orientation film.

In an ideal TLAF liquid crystal, the average optical axis (hereinafter referred to as the extinction direction) when a voltage of 0 V is applied coincides with the normal direction of the smectic layer. When used as a display element, two polarizing plates (crossed Nicols arrangement) whose polarization axes are orthogonal to each other are arranged in front of and behind the liquid crystal panel, and the normal direction of the smectic layer coincides with one of the polarization axes. In this case, a voltage-transmittance characteristic as shown in FIG. 9, which displays black when a voltage of 0 V is applied and displays halftone to white when a positive or negative voltage is applied, is obtained.

However, depending on the type of the alignment film used, a domain in which the extinction direction of a stripe shape parallel to the smectic layer direction is shifted is generated. In addition, the size of the domain increases with the passage of time, and the shift in the domain extinction direction increases. FIG.
(A), (b), and (c) are schematic views showing examples of observation of alignment degradation. FIG. 10A is a diagram of a substrate constituting a cell as viewed from the outside of the cell. The alignment films provided on both substrates holding the liquid crystal are rubbed at a predetermined angle, and T
By introducing the LAF liquid crystal material, a smectic layer structure as shown is formed. The rubbing angle is uniquely determined by the liquid crystal material and alignment film material used. The initial alignment state of the liquid crystal display element thus formed and the alignment in which a domain in which the extinction direction was partially shifted occurred were observed with a crossed Nicol microscope, respectively.
(B) and FIG. 10 (c). The deviation of the domain extinction direction from the layer normal direction (± θ ′ degrees, θ ′> 0)
It is smaller than the cone angle (θ> 0) (θ ′ ≦ θ). To make it easier to observe the extinction direction of the domain,
The polarization direction of the polarizer or analyzer is x degrees (0 <x ≦ θ ′) from the normal direction of the smectic layer as shown in FIG.
It is good to stagger. When the orientation state is good, the extinction direction is uniformly parallel to the layer normal direction as shown in FIG. 10B, so that the angle x between the polarization direction of the polarizer or the analyzer and the extinction direction is set. Accordingly, light appears to be transmitted uniformly. However,
When the orientation state is bad, domains in which the ± θ ′ extinction direction is shifted are generated. Therefore, as shown in FIG. 10C, the polarization direction of the polarizer or the analyzer is uniform in a uniform orientation. The domain where the angle formed by the extinction direction is | θ'-x | is black, and the angle formed by the polarization direction of the polarizer or analyzer and the extinction direction is |
The domain of θ ′ + x | is observed brightly. Note that FIG.
The shaded portions shown in (b) and (c) indicate regions observed at a brightness intermediate between the brightly observed portion and the blackly observed portion. In the case where there is a domain in which the extinction direction is shifted, a uniform black display cannot be obtained even if the arrangement of the polarizer and the analyzer is devised. Therefore, when used for a display element, it is necessary to completely suppress the deviation of the extinction direction from the layer normal direction.

As a control measure, Japanese Patent Laid-Open No. 10-319377
In Japanese Patent Application Laid-Open Publication No. H11-264, a method is proposed in which a polymer precursor is introduced into a TLAF liquid crystal material, injected between substrates, and then photopolymerized in an SA phase to stabilize the structure when a 0 V voltage is applied.

[0007]

However, according to our study, in the method of introducing a polymer precursor as disclosed in JP-A-10-319377, the alignment itself of the TLAF liquid crystal is disturbed by foreign molecules other than the liquid crystal material. Regardless of the polymerization method, it was confirmed that light leakage at the time of black display increased and the contrast decreased.

The present invention has been made in view of the above circumstances, and has as its object to provide a liquid crystal display device having good and stable display performance.

[0009]

A liquid crystal display device according to the present invention comprises a transparent first substrate, a first electrode formed on the first substrate, and a first electrode formed on the first substrate so as to cover the first electrode. First
A first electrode substrate having a first alignment film formed on the first substrate, a transparent second substrate, a second electrode formed on the second substrate, and a second electrode formed on the second substrate. A second electrode substrate having a second alignment film formed on the second substrate so as to cover the electrodes; and a thresholdless voltage sandwiched between the first and second electrode substrates. A dimming layer composed of an antiferroelectric liquid crystal material having a transmittance characteristic, wherein the first and second alignment films and the liquid crystal material are pretilt in the SA phase of the dimming layer. The combination is such that the angle α satisfies 0 ° ≦ α ≦ 1 °.

It is preferable that the first and second alignment films are made of soluble polyimide.

The first electrode substrate is provided at a plurality of scanning lines and a plurality of signal lines arranged in a matrix on the first substrate, and at an intersection of the scanning lines and the signal lines. A switching element that is formed and has one end connected to a corresponding signal line, and that opens and closes based on a signal of a corresponding scanning line, a pixel electrode connected to the other end of the switching element, and covers the pixel electrode An array substrate having the first alignment film formed on the first substrate, wherein the second electrode substrate includes a counter electrode formed on the transparent substrate, and a counter electrode formed on the transparent substrate. And a second alignment film formed on the second substrate so as to cover the second alignment film.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Prior to the description of the embodiments of the present invention, the circumstances leading to the present invention will be described.

As described in the prior art, in a liquid crystal display device using a thresholdless antiferroelectric liquid crystal (hereinafter also referred to as a TLAF liquid crystal), the C2 orientation is preferable in view of display characteristics. However, it is clear that there is a difference in the orientation depending on the type of the orientation film even in the same C2 orientation.

Therefore, the present inventors have developed an alignment film material and TL
Considering that there is an optimum combination with the AF liquid crystal material, the pretilt angle (measured by the crystal rotation method) in the SA phase of a plurality of TLAF liquid crystal materials and alignment film materials was examined.

The pretilt angle of the laser (He-N
Crystal rotation method using e-laser: 632.8 nm (F. Nakano et. al., Jpn. J. Appl. Ph.
ys., 19 (10), 2013 (1980)). As described in detail in the patent application (Japanese Patent Application No. 11-369363) filed by the present applicant, a layer structure induced from the upper substrate and a layer structure induced from the lower substrate are used as the measurement sample. (= 2θBD), and observed with a cell for measurement in which anti-parallel rubbing (cross rubbing) was performed (see FIG. 5). Unlike a surface-stabilized cell used as a display element (gap is set to about 2 μm), a cell for measurement with a gap of 20 μm has an alignment control force that does not reach the bulk portion. Therefore, I
If the liquid crystal is injected in the so phase and then rapidly cooled, the direction of the uniform smectic layer is formed without being determined in one direction (see FIG. 6D). For this reason,-
The substrate was gradually cooled at 1 ° C./min, and an SA phase was slowly formed from the substrate surface that was not in contact with the hot plate (air-cooled) (see FIG. 6D). As a result, a uniform smectic layer was successfully formed (see FIG. 6E). The formation of the smectic layer can be easily confirmed by observing the texture. It is known that, even when a layer structure is formed, when the gap is as thick as 20 μm, the antiferroelectric liquid crystal takes a twist arrangement in the temperature range of the SC ^* phase (see FIG. 6F). Therefore, in order to measure the pretilt angle, it is necessary to heat up to the SA phase so that the liquid crystal molecules are parallel to the layer normal direction. The purpose of making the rubbing directions antiparallel is to make the arrangement inside the cells uniform in the SA layer (see FIG. 6E). For this experiment, a new structure that can measure while heating the dummy cell with a rubber heater was introduced.

As described in detail in the above-mentioned patent application (Japanese Patent Application No. 11-369363), substantially parallel rubbing is shifted in a direction to offset the deviation (θBD) between the rubbing direction and the extinction direction. (Cross-rubbing) was observed on the panel (see FIG. 7). By this cross rubbing, it is possible to make the layer normal directions induced from both alignment film surfaces coincide. On the other hand, if the rubbing direction is set to the antiparallel direction, two kinds of bending directions of the chevron structure occur (C1, C2), and the boundary portion of the domain becomes an alignment defect, which causes light leakage. I know it.

Alignment film material A composed of six kinds of polyimides
-F, the pretilt angle in the nematic liquid crystal measured by the manufacturer of these alignment film materials, and the spontaneous polarization P
FIG. 3 shows the results obtained by preliminarily measuring the pretilt angle and the initial alignment measured by the inventor for combinations of three types of TLAF liquid crystal materials a, b, and c having different s values.

The alignment film materials A and B and the alignment film materials C to F have the same main chain structure. That is, alignment film material B is obtained by introducing a side chain into the main chain of alignment film material A,
Alignment film materials D to F have side chains introduced into the main chain of alignment film material C. Also, D, E, F in the order of increasing side chain ratio
There is a relationship. In the alignment film material, it is common to reduce the surface free energy by introducing a hydrophobic side chain, that is, to increase the pretilt angle.

Regarding the arrangement of the TLAF inside the cell,
In recent years, multiple proposals have been made by academic societies and the like. A representative array model is a collective model by Takezoe et al. Shown in FIG.
Model (B. Park et al., Phys. Rev. E, 59 (4), R3815
(1999)) and the random model by A. Fukuda et al.
ukuda et al., IDW97, 355 (1997)), and the twist model by Clark et al. (P. Rudqist et al., J. Matr.
Chem., 9, 1257 (1999)). It is currently unclear which of these models is correct. One of the reasons is that the initial alignment of TLAF greatly depends on the alignment method and the material. Although average data on bulk has been obtained, data on molecular arrangement near the interface of the alignment film has not been presented due to technical difficulty.

FIG. 11A is a diagram viewed from a direction parallel to the normal direction of the smectic layer, FIG. 11B is a diagram viewed from a direction parallel to the layer direction of the smectic layer, and FIG.
(C) is a diagram showing the positions of liquid crystal molecules on the alignment film surface assuming that the bulk structure is maintained near the alignment film surface. In FIG. 11A, a circle indicates a trajectory (cone) on which liquid crystal molecules move, and an arrow indicates a director. FIG.
In FIG. 1 (b), a triangle indicates a state in which the cone is viewed from the side, and a thick line indicates a liquid crystal molecule. Arrows indicate the upper and lower alignment films and the rubbing direction. The smectic layer is bent at an angle of δ from the direction normal to the substrate surface. FIG.
In 1 (c), θ indicates the angle of the cone. The liquid crystal molecules can be located on the cone, but need to be located above the surface of the alignment film only. Inevitably, the pretilt angle is not less than zero degrees and not more than θ-δ.

In our experiments, many results have been obtained that support the collective model shown in FIG. As described above, in the present proposal, for the purpose of improving the orientation near the interface, attention was paid to the regulation of the orientation of molecules near the orientation film. Although the molecular arrangement in the vicinity of the alignment film is unknown as described above, assuming that the molecular arrangement in the bulk is maintained in the vicinity of the alignment film, the alignment film having a lower pretilt angle is more likely to have a higher TL of the molecules in the bulk.
It is expected to stabilize the AF sequence. However, it is known that the pretilt angle is not uniquely determined by the alignment film material alone, but changes depending on the combination with the liquid crystal material. Further, in general, a catalog value indicated by an alignment film material maker often uses a pretilt angle measured in combination with a nematic material.

For this reason, we newly tried to actually measure the pretilt angle in the SA phase of the TLAF material. As a result, the pretilt angle measured in the nematic material is significantly different from the pretilt angle measured in the SA phase of the smectic liquid crystal.
It became clear that there is a correlation between the orientations of LAF. That is, it was found that the alignment film having a low pretilt angle of 0 to 1 degree improved the alignment of TLAF, whereas the alignment film having a pretilt angle of minus or higher than 1 degree had poor alignment.

From the above results, it is correct that the pretilt angle was selected as a criterion for selecting an alignment film for improving the alignment of TLAF, and the alignment of TLAF was optimized by the combination of the alignment film material and the TLAF material satisfying the following relationship. Is newly found. That is, the pretilt angle α measured in the SA phase is 0 ° ≦ α ≦ 1 °.

By forming a panel using a liquid crystal material and an alignment film satisfying the above conditions, a thresholdless antiferroelectric liquid crystal display device having excellent alignment properties can be realized. In this case, since impurities other than the liquid crystal material are not mixed into the liquid crystal material, the orientation is not disturbed by the impurities.

Next, an embodiment of the liquid crystal display device according to the present invention will be described with reference to FIGS.

The liquid crystal display element of this embodiment is an active matrix drive type liquid crystal display element using an antiferroelectric liquid crystal material as a light control layer, as shown in FIG.
The pretilt angle α in the phase is configured to be 0 ° ≦ α ≦ 1 °. FIG. 1 is a diagram schematically showing a cross section of the liquid crystal display element of the present embodiment. This cross-sectional view is a cross-section along the rubbing direction of the alignment film formed on the upper substrate.

In this embodiment, the light modulating layer uses the antiferroelectric liquid crystal material b shown in FIG. 3 and the alignment film uses the alignment film material A shown in FIG. This combination is such that the pretilt angle α in the SA phase is 0 ° ≦ α ≦ 1
In order to confirm that the condition of ° was satisfied, a dummy cell shown in FIG. 5 was created for the combination of the antiferroelectric liquid crystal material b and the alignment film A, and the temperature was set to 70 ° C. (SA phase).
The pretilt angle was measured by the crystal rotation method while maintaining the above condition. Since the transmitted light showed a symmetric dependence on the incident light around + 1.0 °, the pretilt angle was +
It was confirmed that the angle was 1.0 °.

The phase sequence of the antiferroelectric liquid crystal material b is Iso (82 ° C.) → SA (62 ° C.) → SC ^* .
The compound name of the alignment film material A is AL105I, and the molecular structure is shown in FIG.

The configuration of the active matrix drive type liquid crystal display device of the present embodiment will be described with reference to FIGS. 2 (a) and 2 (b).

FIG. 2A is a plan view of the active matrix drive type liquid crystal display device of the present embodiment.
FIG. 2B is a cross-sectional view taken along a cutting line AA ′ shown in FIG.

The liquid crystal display device of this embodiment is shown in FIG.
As shown in (a) and (b), the threshold-less voltage-transmittance characteristic sandwiched between the array substrate 10, the opposing substrate 30, and these substrates by a predetermined gap by spacer balls 45 is obtained. Dimming layer 4 made of antiferroelectric liquid crystal material having
0 is provided.

The array substrate 10 includes a transparent insulating substrate 11
A plurality of scanning lines 12 and auxiliary capacitance lines 13 extending in the negative direction are formed on the main surface of the substrate 11, and are formed on the main surface of the substrate 11 so as to cover the scanning lines 12 and the auxiliary capacitance lines 13. The structure is such that a transparent insulating layer 14 is formed (see FIG. 2B). Then, on this insulating layer 14, the IT
A plurality of pixel electrodes 15 made of O are formed,
A plurality of signal lines 16 are formed so as to be substantially orthogonal to the scanning lines 12 (see FIGS. 2A and 2B). This signal line 16 is covered with an insulating film 17 (FIG. 2).
(B)). A switching element 18 made of a TFT is formed on the main surface of the substrate 11 near the intersection of the scanning line 12 and the signal line 16. This switching element 1
Reference numeral 8 denotes a gate connected to a corresponding scanning line 12, one terminal of a source or a drain connected to a corresponding signal line 16 via a contact (not shown) provided in an insulating film 17, and the other terminal. Are connected to the pixel electrodes 15 via contacts (not shown) provided in the insulating film 17.

Then, an alignment film 19 is formed on the main surface of the substrate 11 so as to cover the pixel electrodes 15 and the switching elements 18. On the back surface of the substrate 11, a polarizing plate 28 is formed.

On the other hand, the opposite substrate 30 includes a color portion 32a formed in a pixel region on the main surface of the transparent insulating substrate 31 and transmitting a light of a specific wavelength, and a black matrix 32b formed in a non-pixel region. Are provided. A counter electrode 34 made of ITO is formed on the display area of the color filter portion 32, and an alignment film 36 is formed on the counter electrode 34 via an inorganic insulating film 35.
Is formed. The inorganic insulating film 35
Is preferably provided to maintain insulation. A polarizing plate 38 is formed on the back surface of the substrate 31.

The optical axis of the polarized light 28 of the array substrate 10 and the optical axis of the polarizing plate 38 of the counter substrate 30 are arranged in a crossed Nicols arrangement.

In this embodiment, the alignment film 1
Reference numerals 9 and 36 designate a film having a film thickness of 43 using the alignment film material A shown in FIG.
nm. And the alignment film 1
Reference numerals 9 and 36 respectively denote 5 counterclockwise from the normal direction of the smectic layer constituting the light control layer 40 toward the alignment film surface.
The rubbing is performed almost in parallel to the direction of the angle, and the array substrate 10 and the opposing substrate 30 are rubbed as shown in FIG.
Cross rubbing is performed so as to be different in degree (= 2θ _BD ).

The array substrate 10 and the counter substrate 30 are made of alignment films 19 and 36 except for an injection port (not shown) and an exhaust port (not shown) by a sealing material applied on a non-display area.
Are bonded so as to face each other.

This liquid crystal material is introduced through an injection process in which the liquid crystal material is introduced from an injection port while being degassed from an exhaust port. The injection port and the exhaust port are completely sealed by a sealing material (not shown) after the liquid crystal material is injected, and are shut off from the outside air. The panel into which the liquid crystal material b has been injected is
After heating to 85 ° C, which is the so phase, -2 ° C / min.
In was slowly cooled to 30 ° C., substantially coincides with the intermediate, layer normal direction in the SC ^* phase in the extinction direction the rubbing direction of batonnet deposited from both the alignment film surface in Iso-SA point transition near (SA phase) Formed a uniform smectic layer structure corresponding to the extinction direction. The polarizing plates 28 and 38 in the crossed Nicols arrangement are arranged such that the polarization direction of one of them coincides with the layer normal direction.

Observation of the alignment state of this liquid crystal display element revealed that the alignment defect was C2 alignment except for the alignment defect part, and the extinction direction was the layer normal direction, based on the shape and rubbing direction of the minute alignment defects generated near the spacer balls. Turned out to match. The contrast of the liquid crystal display element, that is, the ratio between the maximum transmitted light amount and the minimum transmitted light amount (maximum transmitted light amount / minimum transmitted light amount) is approximately 180, and a sufficient contrast is achieved. It was also confirmed that this contrast was maintained for 500 hours.

Next, in order to confirm the performance of the liquid crystal display device of the present embodiment, the following liquid crystal display devices of Comparative Examples 1, 2 and 3 were prepared, and the performance was examined. The result will be described below.

(Comparative Example 1) A dummy cell (see FIG. 5) was prepared for the combination of the antiferroelectric liquid crystal material b and the alignment film C, and was pretilted by the crystal rotation method while being kept at 70 ° C. (SA phase). The corner was measured. The transmitted light exhibited incident light dependence symmetric around -1.0 [deg.], Confirming that the pretilt angle was -1.0 [deg.]. Using this combination, a liquid crystal display device having the same configuration as shown in FIG. 2 was produced.

Next, the alignment films 19 and 36 are formed using the alignment film material C shown in FIG.
The liquid crystal is the same as in the present embodiment except that cross-rubbing is performed in the direction opposite to the clock toward the alignment film surface in the direction opposite to the clock by 7 degrees, and in the parallel direction by ± 7 degrees (2θ _BD = 14 degrees) between the array substrate and the counter substrate. A cell of a display element was manufactured, and a liquid crystal display element into which the antiferroelectric liquid crystal material b shown in FIG. 3 was injected was prepared.

The liquid crystal display device of Comparative Example 1 was once heated to 85 ° C., which is the Iso phase, and then heated to -2 ° C./mi.
n. When the quenching direction was deviated from the rubbing direction, the extinction direction of the vine was almost the same as that of the rubbing direction. At room temperature, the layer normal in the SC ^* phase was observed. A smectic layer structure in which the direction and the extinction direction were almost halfway between the rubbing directions was obtained. Further, it was found from the shape and the rubbing direction of a small amount of alignment defects generated in the vicinity of the spacer balls that the alignment defects were present, except for the alignment defect portions. However, when the alignment state of the cell was observed one hour later, it was found that a domain in which the extinction direction deviated ± 14 degrees from the layer normal direction occurred. Although the contrast of this liquid crystal display element was approximately 180 at the initial value, the black level floated due to the occurrence of a domain in which the extinction direction deviated from the transmission axis of the polarizing plate, and the contrast after 24 hours was 50 or less. Down to

(Comparative Example 2) A dummy cell (see FIG. 5) was prepared for the combination of the antiferroelectric liquid crystal material b and the alignment film E, and pretilt was performed by the crystal rotation method while maintaining at 70 ° C. (SA phase). After measuring the angle,
Transmitted light did not show incident light dependency, suggesting that the molecular arrangement inside the cell was not uniform.

Next, the alignment films 19 and 36 are formed using the alignment film material E shown in FIG.
The liquid crystal is the same as in the present embodiment except that cross-rubbing is performed in the direction opposite to the clock toward the alignment film surface in the direction opposite to the clock by 7 degrees, and in the parallel direction by ± 7 degrees (2θ _BD = 14 degrees) between the array substrate and the counter substrate. A cell of a display element was manufactured, and a liquid crystal display element into which the antiferroelectric liquid crystal material b shown in FIG. 3 was injected was prepared.

When the alignment state of this liquid crystal display element was examined, it was found that, although the alignment defect portion was in C2 alignment except for the alignment defect portion, the extinction direction was entirely observed. Was a ferri orientation composed of two types of domains shifted by ± 15 ° from the layer normal direction. This orientation was not improved by applying an AC voltage.

In the liquid crystal display device of Comparative Example 2, the black level did not decrease because the extinction directions were not aligned, and the contrast was almost 30.

(Comparative Example 3) A dummy cell (see FIG. 5) was prepared for the combination of the antiferroelectric liquid crystal material b and the alignment film F, and was pretilted by the crystal rotation method while being kept at 70 ° C. (SA phase). After measuring the angle,
Transmitted light did not show incident light dependency, suggesting that the molecular arrangement inside the cell was not uniform.

Next, a single-sided rubbing liquid crystal display element for determining the extinction direction of the tone was prepared by using the orientation film material F shown in FIG. 3 for the orientation films 19 and 36. The extinction position of the tone was one direction. I did not decide. Although the antiferroelectric liquid crystal material b shown in FIG. 3 was used as the liquid crystal material, the antiferroelectric liquid crystal material was not oriented at all, and a fan-shaped structure generated when the smectic layer structure was not clearly defined. Was observed.

As described above, according to the present embodiment, good and stable display performance can be obtained without being affected by a change with time or a voltage history in contrast.

In the above embodiment, the material for the alignment film is AL1051, but a soluble polyimide may be used.

[0052]

As described above, according to the present invention, good and stable display performance can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating features of an embodiment of a liquid crystal display device according to the present invention.

FIG. 2 is a diagram showing a configuration of an active matrix drive type liquid crystal display element.

FIG. 3 is a view showing the results of an experiment performed to obtain a liquid crystal display device according to the present invention.

FIG. 4 is a diagram showing a molecular structure of an alignment film used in an embodiment of a liquid crystal display device according to the present invention.

FIG. 5 is a diagram showing a configuration of a dummy cell used for measuring a pretilt angle in an SA phase.

FIG. 6 is a schematic diagram illustrating the relationship between the liquid crystal phase and the arrangement inside the cell depending on the difference in cooling rate of the antiferroelectric liquid crystal material.

FIG. 7 is a diagram showing a rubbing direction and a smectic layer structure formed.

FIG. 8 is a diagram showing a phase transition and a layer structure change of an antiferroelectric liquid crystal material.

FIG. 9 is a diagram showing a relationship between voltage and transmittance of an antiferroelectric liquid crystal material.

FIG. 10 is a diagram illustrating a conventional problem.

FIG. 11 is a diagram showing a collective model relating to the arrangement of TLAF inside a cell.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Array substrate 11 Transparent substrate 12 Scanning line 13 Auxiliary capacitance line 14 Insulating layer 15 Pixel electrode 16 Signal line 17 Insulating film 18 Switching element (TFT) 19 Alignment film 28 Polarizing plate 30 Opposite substrate 31 Transparent substrate 32 Color filter 32a Color part 32b Black matrix 34 Counter electrode 35 Insulating film 36 Alignment film 38 Polarizing plate 40 Dimming layer 50 Alignment defect

Continuing on the front page (72) Inventor Tomo Hasegawa 1 Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Toshiba R & D Center (72) Inventor Tatsuo Sugami 1 Komukai Toshiba-cho, Sai-ku, Kawasaki-shi, Kanagawa Inside Toshiba R & D Center (72) Inventor Takatake Takato 1 Komukai Toshiba-cho, Koyuki-ku, Kawasaki-shi, Kanagawa Prefecture F-term (reference) 2H090 HB08Y KA15 LA04 MA05 MA07 MB02 MB03

Claims (3)

[Claims] A transparent first substrate; a first electrode formed on the first substrate; and a first electrode formed on the first substrate so as to cover the first electrode. A first electrode substrate having an alignment film; a transparent second substrate; a second electrode formed on the second substrate; and a second substrate covering the second electrode. A second electrode substrate having a second alignment film formed thereon; and an antiferroelectric material having a threshold-less voltage-transmittance characteristic sandwiched between the first and second electrode substrates. A dimming layer composed of a liquid crystal material, wherein the first and second alignment films and the liquid crystal material have a pretilt angle α in the SA phase of the dimming layer of 0 ° ≦ α ≦ 1
A liquid crystal display element characterized by a combination of degrees. 2. The liquid crystal display device according to claim 1, wherein said first and second alignment films are made of soluble polyimide. 3. The first electrode substrate includes: a plurality of scanning lines and a plurality of signal lines arranged in a matrix on the first substrate; and an intersection between the scanning lines and the signal lines. A switching element that is formed and has one end connected to a corresponding signal line, and that opens and closes based on a signal of a corresponding scanning line, a pixel electrode connected to the other end of the switching element, and covers the pixel electrode An array substrate having the first alignment film formed on the first substrate, wherein the second electrode substrate has a counter electrode formed on the second substrate, and the counter electrode 3. The liquid crystal display device according to claim 1, wherein the counter substrate has a second alignment film formed on the second substrate so as to cover the second substrate. 4.