JPH11183911A - Liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent orientation defect of a liquid crystal caused by a 1st oriented film exposed on a uniaxial orientation-processed surface due to the surface ruggedness of the 1st oriented film by being controlling asymmetry of switching, in a liquid crystal element of an asymmetrical structure wherein the 1st oriented films with a specific volume resistivity are provided on both substrates and an oriented film processed with uniaxial orientation is provided on the oriented film on one of the substrates. SOLUTION: Electrodes 12, 22 and 1st oriented films 13, 23 having volume resistivities of 1×10<4> -1×10<10> Ωcm are formed on substrates 11, 21, respectively, and on the 1st oriented film 23 on the substrate 21, a 2nd oriented film 24 having a 1×10<10> Ωcm or smaller volume resistivity and a 100 Å or thinner film thickness is provided for flattening the surface ruggedness of the 1st oriented film 23, and further, a 3rd oriented film 25 is formed thereon, which is formed out of polyamide, polyimide, etc., with a 100 Å or thinner film thickness and processed with uniaxial orientation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a liquid crystal device used for a flat panel display, a projection display, a printer, and the like.

[0002]

2. Description of the Related Art In recent years, as a liquid crystal element which has been widely used, a panel having a TFT for each pixel is representative. Insufficient points in this TFT type include narrow viewing angle characteristics, difficulty in large-area processing, and high driving power. As a means for solving these problems, a liquid crystal device having bistability proposed by Clark and Lagerwall et al. (JP-A-56-107)
No. 216, U.S. Pat. No. 4,367,924).

As the liquid crystal having the bistability, a ferroelectric liquid crystal exhibiting a chiral smectic C phase (SmC ^* ) or a chiral smectic H phase (SmH ^* ) is generally used. Since the ferroelectric liquid crystal performs inversion switching by spontaneous polarization, bistability with memory properties can be realized. For this reason, pulse driving with a small duty ratio is possible in a simple matrix configuration, and low-power driving can be performed as compared with the TFT type. Further, since the matrix configuration can be easily operated, a large area can be easily realized. Furthermore, the wide viewing angle, which is a major feature of ferroelectric liquid crystals, makes it possible to compensate for the weak points of the TFT type.

In such a chiral smectic liquid crystal element, for example, as described in “Structure and Physical Properties of Ferroelectric Liquid Crystal” (Corona Co., Atsuo Fukuda, Hideo Takezoe, eds., 1990), a zigzag shape is used. However, there is a problem that the alignment defects are generated and the contrast is remarkably reduced.
This defect is attributable to the fact that the layered structure of the chiral smectic liquid crystal carried between the upper and lower substrates forms two types of chevron structures. Recently, there has been a movement to improve the chevron structure having such disadvantages and to realize a layered structure called a bookshelf or a structure similar thereto, thereby realizing a high-contrast and good liquid crystal element (for example, “Next-generation liquid crystal”). Display and Liquid Crystal Materials ", edited by CMC Co., Atsuo Fukuda, 1992).

A liquid crystal compound having a perfluoroether side chain as a liquid crystal material exhibiting a bookshelf or a structure similar thereto (US Pat. No. 5,262,082, International Patent Publication WO 93/22396, 4th International Ferroelectric Liquid Crystal 1993) Conference P-46, Mark D. Radcli
ffe etc.) are disclosed. This liquid crystal can exhibit a bookshelf or a structure with a small layer tilt angle close to the bookshelf without using an external field such as an electric field, and is suitable for high-speed, high-definition, large-area liquid crystal elements and display devices. .

On the other hand, as an element configuration for satisfactorily aligning the liquid crystal material, there is a configuration in which an asymmetric alignment film is provided as described in, for example, JP-A-61-20930. In this configuration, by performing uniaxial alignment processing on one alignment film and not performing uniaxial alignment processing on the other, the alignment of the liquid crystal can be controlled in a high order from the uniaxially aligned side, It becomes easy to obtain a good liquid crystal alignment state.

In the configuration having the asymmetric alignment film, although the uniaxiality of the alignment state is improved, an asymmetrical characteristic may occur in switching, and the bistability of the ferroelectric liquid crystal may be hindered. Thus, there is a problem that the so-called switching memory property is reduced. In order to solve such a problem, those in which the polarities of both substrates are adjusted are disclosed in JP-A-62-235928 and JP-A-63-228.
No. 130 is disclosed.

Further, in the vertically asymmetric configuration, considering the operating temperature of the device, even if the above-mentioned switching symmetry is obtained at a certain temperature, the temperature dependence of the electrical physical properties differs between the materials in contact with the liquid crystal molecules. However, there has been a problem that switching symmetry cannot be obtained when the temperature changes. In order to solve this problem, by providing an alignment film having a volume resistance value of 1 × 10 ⁴ to 1 × 10 ¹⁰ Ωcm on both substrates, the temperature dependence can be reduced. This configuration is shown in FIG. In the figure, 11 and 21 are substrates, 12, 22
Is an electrode made of ITO, 13 and 23 are alignment films having the above-mentioned specific volume resistance value, 15 is a chiral smectic liquid crystal, and 25 is an alignment film subjected to uniaxial alignment processing.

Further, in order to suppress the so-called anti-electric field problem that the presence of spontaneous polarization of the liquid crystal induces the uneven distribution of charges in the liquid crystal element and cause switching failure, the impedance of the alignment film is reduced. JP-A-63-12
No. 1020 and Japanese Patent Application Laid-Open No. 64-49023. In order to apply this to the structure shown in FIG. 2, when the liquid crystal 15 having a spontaneous polarization of 20 nC / cm ² or more and the polyimide or polyamide are used for the alignment film 25, the thickness of the alignment film 25 is set to 100 ° or less. Is desirable.

[0010]

In the vertically asymmetrical configuration shown in FIG. 2, the alignment film 13, which suppresses the problem of the anti-electric field,
23 is desirably formed of a film in which conductive fine particles are dispersed in an organic or inorganic binder. However, unevenness having a height difference of about several hundreds of degrees due to the aggregated fine particles is densely present on the surfaces of the alignment films 13 and 23, and when the thickness of the alignment film 25 is set to 100 ° as described above, the covering state is reduced. A part of the alignment film 23 is exposed, the uniaxiality is weakened at that part, and the liquid crystal molecules in contact with the part are randomly aligned, which causes a problem that a good image display cannot be obtained.

An object of the present invention is to provide an alignment film having the above-mentioned specific volume resistance on both of a pair of substrates, and to provide an alignment film subjected to a uniaxial alignment treatment on at least one of the substrates. It is another object of the present invention to provide a liquid crystal device having a liquid crystal alignment state free of the above-mentioned alignment defect and realizing good image display.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a liquid crystal element comprising a pair of substrates each having an electrode and a liquid crystal interposed between the pair of substrates, wherein 1 × 10 ⁴ to 1 × 10 ¹⁰ Ω
Provide a first alignment film having a volume resistance value of cm, on at least one substrate, on the first alignment film, a second alignment film that is a planarization film of the first alignment film, a film Thickness 10
A third alignment film whose surface is uniaxially oriented at 0 ° or less is provided.

According to the present invention, by adding the second alignment film and flattening the surface of the first alignment film, the coverage of the thin third alignment film having a thickness of 100 ° or less can be reduced to 100%. The liquid crystal molecules in contact with the alignment film of (1) are favorably uniaxially oriented to obtain good image display.

Therefore, in the present invention, even when the alignment film formed by dispersing the conductive fine particles in the film is used as the first alignment film, the influence of the surface unevenness is prevented by the second alignment film. Can be. Also, particularly in the present invention,
By setting the volume resistance value of the second alignment film to 1 × 10 ¹⁰ Ωcm or less, it is possible to suppress an extreme increase in the counter electric field due to the introduction of the second alignment film. Even in comparison, the switching characteristics can be kept equal.

[0015]

FIG. 1 is a schematic partial sectional view of an embodiment of the liquid crystal device of the present invention. In the figure, 11 and 21 are substrates, 12 and 22 are electrodes, 13 and 23 are first alignment films,
5 is a liquid crystal compound, 24 is a second alignment film, and 25 is a third alignment film.

Substrates 11, 21 used in the present invention
Is usually a glass substrate, but a plastic substrate or the like can be used as long as it has the necessary strength and transparency. In the case of a reflection type liquid crystal element, the substrates 11, 2
An opaque substrate such as a silicon substrate may be used for one of the substrates.

The electrodes 12 and 22 are usually made of a transparent conductive material such as ITO. However, in the case of a reflection type liquid crystal element, the reflection side substrate may be made of a metal which also serves as a reflection member. Further, in the present embodiment, the electrode 12 constitutes a simple matrix electrode formed in a stripe shape parallel to the paper surface and the electrode 22 in a stripe shape perpendicular to the paper surface.

In the present invention, the first alignment films 13 and 23
Has a volume resistance value of 1 × 10 ⁴ to 1 × 10 ¹⁰ Ωcm. Specifically, the alignment film having such a volume resistance value can be suitably obtained by forming a film in which conductive fine particles are dispersed in an organic or inorganic binder. As the organic binder used here, polyimide and polycarbonate are preferably used, and as the inorganic binder, a polymer of SiO _x or Al ₂ O ₃ is preferably used. As the conductive fine particles, SnO _x and TiO _x having an average particle diameter of preferably 100 to 1000 ° are preferably used.

The surface irregularities of the first alignment film 23 are flattened by the second alignment film 24. It is preferable that the second alignment film 24 has a thickness of 100 ° or more and a volume resistivity of 1 × 10 ¹⁰ Ωcm or less in order to suppress an increase in the counter electric field. As a material for such a second alignment film, SnO ₂ , polyaniline, TiO ₂ , and polypyrrole are preferably used.

In the present invention, the third alignment film 25 can be made of a conventional polyimide or polyamide, and its thickness is set to 100 ° or less in order to suppress an increase in the counter electric field. Has been given.

In the liquid crystal element of the present invention, necessary members are formed on the pair of substrates 11 and 21 as described above, and the substrates are arranged to face each other with spacers (not shown) facing each other. The cells are adhered and fixed with a sealant to form a cell, and liquid crystal is injected into the cell to seal the liquid crystal injection port.

As the liquid crystal used in the present invention, a chiral smectic liquid crystal which uses the action of spontaneous polarization for driving, such as a ferroelectric liquid crystal and an antiferroelectric liquid crystal, is preferably used. As a ferroelectric liquid crystal, for example, from the high temperature side to the low temperature side, isotropic phase → SmA (smectic A phase) → Sm
A liquid crystal having a phase transition series of C ^* → crystal phase is used. Examples of the liquid crystal suitably used in the present invention include, for example, Japanese Patent Application Laid-Open No. 2-127553 and US Pat.
No. 2587, International Patent Application Publication No. WO 93/22396, and the like, have a fluorocarbon terminal portion and a hydrocarbon terminal portion, and the both terminal portions are bound by a central nucleus to form a smectic intermediate or a potential smectic intermediate. And a fluorine-containing liquid crystal compound having a phase. Here, the central nucleus is selected from at least two of an aromatic ring, a heteroaromatic ring, an aliphatic ring, or a substituted aromatic ring, a substituted heteroaromatic ring, or a substituted aliphatic ring, and these rings are -COO-, -COS-, -HC =
It may be bonded by a functional group selected from N- and -COSe-. Also, even if these rings are fused,
You don't have to. The heteroatom in the heteroaromatic ring is N,
It contains at least one atom selected from O or S.
Non-adjacent methylene groups in the aliphatic ring may be replaced by O.

The ferroelectric liquid crystal used in the present invention preferably has a spontaneous polarization of 20 nC / cm ² or more. In the present invention, the term “spontaneous polarization” refers to K.K. Miyasato et al. "Direct measurement method of spontaneous polarization of ferroelectric liquid crystal by triangular wave" (Journal of the Japan Society of Applied Physics, 22, 10, No. (661) 1)
983, "Direct Method with T
rangular Waves for Measu
ring Spontaneous Polariza
Tion in FerroelectricLiqu
id Crystal ”, as desscribed
by K. Miyasato et al. (Jap.
J. appl. Phys. 22. No. 10, L661
(1983))).

In the liquid crystal device, a polarizing plate is usually bonded to the outside of each substrate, and a backlight in which a fluorescent lamp and a scattering plate are combined is generally used. The liquid crystal compound changes the light transmittance of the backlight. The display is performed by functioning as an optical shutter (transmission type).

Although the above embodiment has been described with respect to the vertically asymmetric configuration, the present invention can also be applied to a vertically symmetric configuration. That is, in FIG. 1, even when the third alignment film subjected to the same uniaxial alignment treatment as the alignment film 25 is provided also on the first alignment film 13, the second alignment film 24 is provided between them. In addition, the unevenness on the surface of the first alignment film 13 can be flattened to suppress the influence on the liquid crystal alignment. In the above embodiment, the case of the simple matrix type has been described. However, the present invention can be applied to a TFT type liquid crystal element.

[0026]

[Example 1] As an example of the present invention, a liquid crystal device having the structure shown in FIG. 1 was manufactured. In this embodiment, an alignment film is formed on one of the substrates by using a ferroelectric liquid crystal and uniaxially aligning the liquid crystal, which has a structure close to a bookshelf in the cell, in order to uniaxially align the liquid crystal.

First, glass was used for the substrates 11 and 21, using a general DC sputtering apparatus, an ITO target, a power of 1 W / cm ² , and Ar: 90 SCCM and O ₂ = 10 SCCM flowing as a sputtering gas.
An ITO film having a thickness of 700 ° was deposited by discharging for 2.5 minutes. Thereafter, the electrodes 12 and 22 were formed by patterning the ITO film into stripes by ordinary wet etching.

Subsequently, the substrates 11 and 21 on which the electrodes are formed
A solution obtained by dispersing SnO _x oxide ultrafine particles in a matrix made of a polymer of SiO _x was applied at 1000 rpm, 1 rpm.
Coating was performed under a spin condition of 0 sec to form a film having a thickness of 1500 °. This was baked at 200 ° C. for 60 minutes to provide first alignment films 13 and 23.

Subsequently, the first alignment film 2 is formed on the substrate 21.
3, SnO ₂ as a second alignment film 24 is formed by ion plating to form a gas (O ₂ , Ar) pressure ratio of 80%.
The thickness was changed in a range of 30 ° to 1000 ° under O ₂ .

Further, on the substrate 21, a second alignment film 24 is formed.
On top, polyamic acid (“LP-64” 0.5, manufactured by Toray Industries, Inc.)
Wt%) at 500 rpm, 15 sec and 1500 rpm
Spin coating under conditions of m and 30 sec.
It was baked at 60 ° C. for 60 minutes to form a 50 ° thick polyimide film. Thereafter, the number of rotations is 1000 rpm and the pushing amount is 0.4.
rubbing treatment is performed on the polyimide film twice in one direction at a feed speed of 50 mm / sec.
5 was formed.

On the third alignment film 25 of the substrate 21,
A solution containing 2.4 μm-diameter SiO ₂ fine particles was spin-coated, heated to be dispersed and fixed, and then a solution containing adhesive particles (manufactured by Toray, particle size: 5 μm) was spin-coated and heated to be dispersed and fixed.

On the other hand, a sealing material was applied to a desired position on the substrate 11 using a printing machine, and prebaked at 90 ° C. for 5 minutes. The obtained substrates 11 and 21 are arranged to face each other such that the first alignment film 13 and the third alignment film 25 face each other, and 30 g
While applying a pressure of f / cm ² with an air cushion, heating was performed at 150 ° C. for 90 minutes to cure the sealing material and bond the upper and lower substrates together.

The obtained cell is placed in an ordinary load lock type vacuum chamber, evacuated to 1.3 × 10 ⁻³ Pa, and then poured into a liquid crystal storage tank heated to 105 ° C. in a vacuum of 1.3 Pa. It was immersed so as to have an inlet, and the liquid crystal compound 15 was injected into the cell, and the inlet was sealed. In this embodiment, a ferroelectric liquid crystal having a spontaneous polarization of 31 nC / cm ² (30 ° C.) was used.

Further, a liquid crystal element without the second alignment film 24 on the substrate 21 side was manufactured in the same manner as in the above steps, and was used as a comparative sample.

After the liquid crystal element produced above was realigned at 105 ° C., the number of defective pixels per unit area (defective pixel density) was examined. On display, about 0.5 / cm ² is an allowable range. In addition, surface irregularities after polyimide film formation are
M (atomic force microscope) was used to measure Ra (center line average roughness).

FIG. 3 is a graph showing the density of defective pixels with respect to the thickness of the second alignment film 24. FIG. 4 is a graph showing Ra of the polyimide film surface with respect to the thickness of the second alignment film 24.

As can be seen from FIGS. 3 and 4, when the second alignment film is too thin, Ra is large and the density of defective pixels is 0.5 / cm ² or more. The film thickness is 1
From around 00 °, the Ra gradient becomes gentle and the density of defective pixels becomes less than 0.5 / cm ² . That is, although the defective pixel density is reduced by providing the second alignment film, the alignment defect due to the surface exposure of the first alignment film is surely suppressed by forming the thickness to 100 ° or more. I understood.

Example 2 A liquid crystal element was formed in the same manner as in Example 1 except that films having a thickness of 100 ° and various volume resistances were formed as the second alignment film 24. For a film having a volume resistance of 1 × 10 ² to 1 × 10 ⁸ Ωcm, SnO ₂ was formed by ion plating, and the volume resistance was controlled by a gas (O ₂ , Ar) pressure ratio. In addition, Ta ₂ O ₅
Is formed by DC sputtering to form a film of 1 × 10 ¹⁰ Ωcm
Films of 5 × 10 ¹¹ Ωcm were formed by F sputtering. Further, as a film having a higher volume resistance value, 1 × 10 ¹³ Ω is used by using polyimide (the same material as the third alignment film).
cm film was formed.

With respect to the obtained liquid crystal device, the relationship (VT characteristic) between the applied voltage and the light transmission amount of the device was examined. FIG. 5 shows the VT characteristics of the liquid crystal element of the present invention. The solid line and the broken line show the switching characteristics corresponding to the polarity of the drive voltage. Although it is desirable that the switching characteristics match each other, a slight shift is actually observed. The amount of the deviation is called asymmetry of the VT characteristic. If the asymmetry is large, the memory property of switching is reduced.

On the other hand, for each of the solid line and the broken line, there is a forward and backward direction (corresponding to the upper and lower directions of the arrow) in a voltage range where the transmittance greatly changes, and this rising voltage difference is called hysteresis. The anti-electric field is considered to be the main cause of hysteresis. That is, the greater the anti-electric field at the time of switching, the greater the hysteresis. The asymmetry and hysteresis have different allowable ranges depending on the drive waveform. For example, when driving a high-resolution panel of about 15 inches, a pulse voltage of about 10 μm is used, the asymmetry is ± 0.8 V or less, and the hysteresis is 1.2 V. If it is less than or equal to 1, the change over time such as defective writing or burn-in is suppressed without extremely disturbing the bistable potential.

FIG. 6 shows the results of evaluation of the liquid crystal element manufactured in the above steps, and FIG. 7 shows the hysteresis. As to asymmetry, all samples had no problem of 0.8 V or less, whereas hysteresis showed 1.2 V or more at 1 × 10 ¹¹ Ωcm or more. That is, the volume resistivity of the second alignment film is 1 × 10 ¹⁰
It can be seen that the use of one having a resistance of Ωcm or less can suppress the extreme influence on the switching characteristics due to the increase of the anti-electric field.

[0042]

As described above, according to the present invention,
Preventing the influence on the liquid crystal alignment due to the unevenness of the surface of the first alignment film having a volume resistance of 1 × 10 ⁴ to 1 × 10 ¹⁰ Ωcm,
The uniaxial orientation of the third orientation film in contact with the liquid crystal can be sufficiently exhibited to obtain a good image display. In particular, by applying the present invention to a liquid crystal element having an asymmetric configuration in which only one of them is provided with the above-described uniaxially-aligned alignment film,
The effect can be obtained after suppressing the asymmetry of the switching characteristics, and a good image display can be obtained.

In the present invention, by forming the second alignment film to have a thickness of 100 ° or more, it is possible to reliably prevent the surface of the first alignment film from being exposed and prevent the occurrence of alignment defects in the liquid crystal. . Further, the volume resistance value of the second alignment film is 1 ×
By setting the resistivity to 10 ¹⁰ Ωcm or less, it is possible to suppress an extreme increase in the reversal electric field due to the introduction of the second alignment film, and it is possible to obtain a good image display without alignment defects and writing failure.

[Brief description of the drawings]

FIG. 1 is a schematic partial cross-sectional view of one embodiment of a liquid crystal element of the present invention.

FIG. 2 is a schematic partial cross-sectional view of an example of a conventional liquid crystal element.

FIG. 3 shows a second alignment film (Sn) according to the first embodiment of the present invention.
6 is a graph showing the density of defective pixels with respect to the film thickness of O ₂ ).

FIG. 4 shows a second alignment film (Sn) according to the first embodiment of the present invention.
4 is a graph showing Ra on the surface of a polyimide film with respect to the film thickness of O ₂ ).

FIG. 5 is a diagram showing VT characteristics of the liquid crystal element of the present invention.

FIG. 6 is a graph showing asymmetry with respect to a volume resistance value of a second alignment film in Example 2 of the present invention.

FIG. 7 is a graph showing a hysteresis with respect to a volume resistance value of a second alignment film in Example 2 of the present invention.

[Explanation of symbols]

 11, 21 substrate 12, 22 electrode 13, 23 first alignment film 15 liquid crystal compound 24 second alignment film 25 third alignment film

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Seishi Miura 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (10)

[Claims] 1. A liquid crystal element having a liquid crystal sandwiched between a pair of substrates each having an electrode, the liquid crystal element having a volume resistance of 1 × 10 ⁴ to 1 × 10 ¹⁰ Ωcm on the electrode of each substrate. Providing one alignment film, at least one substrate,
On the first alignment film, a second alignment film which is a planarization film of the first alignment film, and a third alignment film having a thickness of 100 ° or less and having a surface subjected to a uniaxial alignment treatment are provided. A liquid crystal element characterized by the above-mentioned. 2. The liquid crystal device according to claim 1, wherein the thickness of the second alignment film is 100 ° or more. 3. A volume resistivity of the second alignment film is 1 × 1.
The liquid crystal element according to claim 1, wherein the liquid crystal element has a value of 0 ¹⁰ Ωcm or less. 4. The liquid crystal device according to claim 1, wherein the first alignment film is a film in which conductive particles are dispersed in an organic or inorganic binder. 5. The liquid crystal device according to claim 1, wherein the third alignment film is made of polyimide or polyamide. 6. The liquid crystal device according to claim 1, wherein the uniaxial alignment treatment of the third alignment film is a rubbing treatment. 7. The liquid crystal device according to claim 1, wherein the liquid crystal is a chiral smectic liquid crystal. 8. A fluorine-containing liquid crystal compound having a smectic intermediate phase or a latent smectic intermediate phase, wherein the chiral smectic liquid crystal has a fluorocarbon terminal chain and a hydrocarbon terminal chain, and both terminal chains are linked by a central nucleus. The liquid crystal device according to claim 7, which is a chiral smectic liquid crystal composition containing: 9. The liquid crystal device according to claim 7, wherein the chiral smectic liquid crystal is a ferroelectric liquid crystal. 10. The spontaneous polarization of the ferroelectric liquid crystal is 20n.
The liquid crystal device according to claim 9, wherein C / cm ² or more.