JPH06138441A - Bistable liquid crystal display device - Google Patents

Abstract

(57) [Summary] [Purpose] A large-area liquid crystal display device. [Structure] After an electrode is selectively formed on the surface and an insulating film and an alignment film are formed on the electrode, a pair of substrates subjected to an alignment treatment are arranged so as to be substantially parallel to each other, and a pretilt angle is set. Is approximately 0 degrees in one alignment film and 5 to 45 degrees in the other alignment film, a liquid crystal is interposed between substrates to form a liquid crystal cell, and a voltage is selectively applied to the electrodes. In a liquid crystal display device having a switching means for switching the optical axis of the liquid crystal, the directions of the alignment treatment are different between the two substrates, the liquid crystal is a nematic liquid crystal to which a chiral agent is added, and the switching is near the upper substrate surface. The unit vector of the liquid crystal molecule's molecular long axis from the substrate surface to the rising direction and the unit vector of the liquid crystal molecule's molecular long axis near the lower substrate surface from the substrate surface to the rising direction are projected on each substrate surface. The angle formed by each projection vector is 90
A bistable liquid crystal display device characterized in that the angle is up to 180 °.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of a display device for bistable switching of a nematic liquid crystal.

[0002]

2. Description of the Related Art Up to now, display systems using liquid crystals include a DS (dynamic scattering) system and a TN system which convert an electric signal applied to the liquid crystal into optical information.
(Twisted nematic) method, ECB (electrically contro
lled birefringence) method, PC (phase change) method, memory method, GH (guest-host) method, SSF (su
rfacestabirized ferro-electric) method is considered.

Among them, the systems currently used as display devices in products such as watches, calculators, word processors, personal computers, and televisions are mainly the TN system using nematic liquid crystal and its improved STN system. However, since its operating principle is a field effect type that utilizes the dielectric anisotropy of liquid crystal molecules, the response speed is only on the order of msec, and for applications such as CAD terminals that require a faster response speed, The combination with the current nematic liquid crystal is insufficient in response speed. In addition, since the electro-optical effect is caused by the switching between two states, that is, a twisted homogeneous alignment state of liquid crystal molecules and a state in which the liquid crystal molecules are raised on the substrate surface, the visual dependence on the twist direction of the liquid crystal molecules Can not be avoided in principle.

On the other hand, as a liquid crystal element having a high response speed, Clark (NAClark) and Lagabal (La
surface stabilized ferroelectric liquid crystal device (Surface Stabilized Ferro-electric Liquid Crystal)
Display, SSFLCD) (Appl.Phy.Lett., 36,899 (19
80); JP-A-56-107216; US Pat. No. 4,366,924)
There is. SSFLC is an element that performs switching on the cone where liquid crystal molecules can move by utilizing the electrical interaction between the polarity of spontaneous polarization and the polarity of electric field that smectic liquid crystals have, so switching is much faster than nematic liquid crystals. Has the advantage that there is no visual dependence. On the other hand, since smectic liquid crystals have a layered structure, it is difficult to control the alignment, and it is difficult to recover the alignment once broken due to impact or the like.

For the above method, Georges. Duran has proposed two types of bistable liquid crystal display devices using nematic liquid crystals. One uses chiral ions for driving torque (International Publication No. WO 91/11747).
No.), right-handed and left-handed chiral ions are mixed with the liquid crystal, and a bias is created in the ion distribution by the voltage.
This is the drive torque. This method is SSF
By applying a pulsed electric field, it is possible to switch the liquid crystal molecules in parallel with the substrate surface as in the LCD.
However, since this method uses ions as impurities for driving, an inherently large problem remains in terms of reliability.

The other one is a method in which flexopolarization due to orientation distortion is used as a driving torque, and high reliability is expected without causing problems such as impurities. Similar to SSFLCD, this method also makes it possible to switch liquid crystal molecules parallel to the substrate surface by applying a pulsed electric field, and the response speed is 1
At about 00 μsec, the liquid crystal molecules switch in parallel to the substrate surface, so there is no visual dependency. Further, since the nematic liquid crystal is used, there is no problem such as weakness in alignment control and impact unlike SSFLCD, and the operating temperature range can be sufficiently wide.

Georges. Previously reported by Duran (91 SID Proceedings PP606-607, Appl.Ph
ys.Lett.60 (9), 2 March 1992 pp1085-1086) The structure of the nematic bistable display element by flexo polarization is as shown in FIG. 1 is a glass substrate,
Is a liquid crystal layer, is a transparent electrode, a SiO alignment film, and is a spacer. The deposition angle of the SiO alignment film is 74 from the substrate radiation.
The film thickness is 30Å and the spacer diameter is about 1 to 3 μm. Under such conditions, the alignment direction of liquid crystal molecules is shown in FIG.
As shown in FIG. 3, the direction tilted by θ ° from the substrate surface and the direction projected on the substrate surface is α ° from the SiO vapor deposition direction and −
It becomes bistable in the directions A and B inclined by α °. In addition, when the cell thickness is sufficiently thin as 1 to 3 μm, the liquid crystal molecules also have stable orientation in a direction C perpendicular to the SiO vapor deposition direction and parallel to the substrate surface.

FIG. 3 shows the SiO vapor deposition direction and the direction in which the alignment of liquid crystal molecules can be stabilized. The orientation of the upper and lower substrates is anti-parallel with the direction of SiO vapor deposition on the upper and lower substrates.
It is constructed by twisting 45 degrees from. As the liquid crystal material, a liquid crystal alone is used to which a chiral material is added so that the upper and lower substrates can be twisted by 22.5 °. The twisting direction is opposite to the twisting direction of the SiO vapor deposition between the upper and lower substrates shown in FIG.

In the figure, the broken line arrows indicate the SiO vapor deposition direction, and the symbols "~" indicate the stable directions of molecules on the surface of each substrate. When the structure in which the direction of SiO vapor deposition is rotated by 45 ° from anti-parallel (anti-para) is adopted and the liquid crystal material under the above conditions is injected, the orientation that can stably exist is limited by the effect of the chiral material, and the liquid crystal molecules are -',
Two combinations of −'are stable.

FIG. 4 shows a cross-sectional view of the cell, and a is shown in FIG.
-'And b in correspond to the -'orientation. If the molecular shape of the liquid crystal used here is wedge-shaped, flexo polarization occurs due to the alignment strain of the spray. The arrow in the figure indicates the direction of flexo polarization. Where a and b
In, the vertical component of flexo polarization points in the opposite direction.
Therefore, by applying a pulsed electric field to invert the vertical component of flexo polarization, it is possible to perform bistable switching between the two states a and b.

[0011]

However, in the actual alignment of the liquid crystal molecules in the above-mentioned constitution, the alignment of ~ 'in FIG. 3 becomes more stable, and there is a tendency that a twisted alignment is easily formed between the upper and lower substrates. It is difficult to obtain flexopolarization due to the orientation distortion of the spray, and to obtain the switching process uniformly over a large area. The currently reported experimental example is Georges. Made by Duran (Appl.Phys.Lett.60 (9), 2 March 1992 pp1085-108.
6) Due to this, only an area of about 1 mm 2 is switched. The present invention has been made to solve the above problems and to form a splayed orientation between upper and lower substrates, and realizes a uniform orientation state over a large area and enables stable bistable switching. The purpose was to do.

[0012]

Thus, according to the present invention, a pair of substrates on which electrodes are selectively formed and on which an insulating film and an alignment film are formed are opposed to each other so as to be substantially parallel to each other. And the pretilt angle is approximately 0 degree in one alignment film and 5 to 45 degrees in the other alignment film, and a liquid crystal cell is formed by interposing a liquid crystal between the substrates, and is selectively applied to the electrodes. In a liquid crystal display device having a switching means for switching the optical axis of the liquid crystal when a voltage is applied to (1), the respective alignment films of both substrates are:
The alignment directions are different from each other, (2) the liquid crystal is a nematic liquid crystal to which a chiral agent is added, and (3) when the switching means is operated, the substrate cross-sectional direction and the liquid crystal molecule long axis are in the upper substrate. At a constant tilt angle, in the lower substrate, the cross-sectional direction of the substrate is parallel to the long axes of the liquid crystal molecules, and the molecular axes of the liquid crystal molecules projected on the respective substrate surfaces are parallel to each other. In, the substrate cross-section direction and the liquid crystal molecule long axis are parallel, in the lower substrate, the substrate cross-section direction and the liquid crystal molecule long axis have a constant tilt angle, and each molecular long axis of the liquid crystal molecule projected on each substrate surface is (4) showing the bistable state with the state 2 in which they are parallel to each other, and in the state 1 on the upper substrate and the lower substrate, the rising direction from the substrate surface of the molecular long axis of the liquid crystal molecules near the upper substrate surface. Unit vector to In the state 2, when the unit vector of the molecular long axis of the liquid crystal molecule near the lower substrate surface is projected from the substrate surface to the rising direction, the angle formed by each projection vector in each state is 90 to 180 °. A bistable liquid crystal display device is provided.

A transparent insulating substrate is used as the substrate of the present invention, and a glass substrate is usually used. This insulating substrate has InO _3, SnO _{2 and} ITO (Indium Tin Ox), respectively.
A transparent electrode having a predetermined pattern made of a conductive thin film such as ide) is formed. An insulating film is formed on it. As the insulating film, for example, an inorganic thin film such as SiO _2, SiNx, Al ₂ O ₃ or the like, an organic thin film such as polyimide, photoresist resin or polymer liquid crystal can be used. When the insulating film is an inorganic thin film, vapor deposition, sputtering, CVD
It can be formed by a (Chemical Vapor Deposition) method or a solution coating method. When the insulating film is an organic thin film, a solution in which an organic substance is dissolved or a precursor solution thereof is used and applied by a spinner coating method, a dip coating method, a screen printing method, a roll coating method, or the like. It is formed by curing under curing conditions (heating, light irradiation, etc.), or by vapor deposition, sputtering, CVD, etc.
It can also be formed by an LB (Langumuir-Blodgett) method or the like.

An alignment film is formed on the insulating film. The alignment film may be an inorganic layer or an organic layer. When an inorganic alignment film is used, oblique deposition of silicon oxide is good. Alternatively, a method such as rotary evaporation can be used. When an organic alignment film is used, nylon, polyvinyl alcohol, polyimide or the like can be used, and the alignment treatment is usually performed by rubbing the top. In addition, using polymer liquid crystal and LB film for alignment,
Alignment by a magnetic field and alignment treatment by a spacer edge method are also possible. In addition, vapor deposition of SiO _2, SiNx, etc.
A method of rubbing the surface and performing an alignment treatment is also possible.

The pretilt angle is defined as the angle of inclination of liquid crystal molecules from the vertical direction with respect to the substrate. After rubbing an alignment film of polyimide or the like or obliquely depositing silicon oxide, the pretilt angle is applied to the vertical alignment agent N, N-octadecyl-3-aminopropyl trimesooxylyl chloride (N, N-
octadedecyl-3-aminopropytrr
imoxixysil chloride: DM
It can be changed by processing by OAP). Under the rubbing treatment conditions, the pretilt angle can be changed by changing the type of cloth, the length of the fur and the number of rotations of the roller during the rubbing treatment. Further, under the vapor deposition processing conditions, it can be controlled by the vapor deposition angle of silicon oxide and the thick film.

In the invention of the present application, the pretilt angle is set to approximately 0 degree in the alignment film on one substrate and 5 to 45 degrees in the alignment film on the other substrate. In the present invention, it is preferable that the alignment film on one substrate and the alignment film on the other substrate have different alignment directions from each other.
It is preferable to arrange so as to be 0 degree. Furthermore, this angle is preferably 15 to 60 degrees.

Specifically, the oblique SiO vapor deposition film is used as an alignment film, and the SiO vapor deposition directions on the upper and lower substrates are set within 90 ° twist direction from parallel, preferably about 45 °. FIG. 5 shows the SiO vapor deposition direction and the direction in which the liquid crystal molecule alignment can be stabilized in this case. The liquid crystal material used is a mixture of chiral materials, and the twist direction is Si between the upper and lower substrates.
The direction is opposite to the twist in the O vapor deposition direction. Under the above conditions, liquid crystal molecules are stable only when two combinations of -'and-'are complete. As a result, an ideal orientation is uniformly obtained over a large area, and stable layer stability switching can be realized.

The nematic liquid crystal of the present invention includes Schiff base type, azo type, azoxy type, benzoic acid ester type, biphenyl type, terphenyl type, cyclohexylcarboxylic acid type, phenylcyclohexane type, pyrimidine type and dioxane type liquid crystals. A multi-component liquid crystal which is a mixture thereof can be mentioned. As a concrete commercially available mixed liquid crystal,
Merck Z series (Z-1625, Z-156
5, Z-1780, Z-1800, Z1840, Z-1
825), E-series manufactured by BDH (E-7, E-3
7, E-31LV, E-80, E-44), R series manufactured by Roche (R-200, R-623, R-701,
R-619, R-627C), Chisso L series (L-GR46, L-9106, L-EN24, LP)
23NN23) and D series (D-601T, D-X01A, D-800) manufactured by Dainippon Ink and Co., and the like. Further, these liquid crystals may be appropriately mixed and used.

Then, a chiral agent (optically active compound) is added to the above liquid crystal. Thereby, the helical pitch of the liquid crystal phase is adjusted. The type of chiral agent is such that the twist direction of the liquid crystal molecules is calculated from the unit vector of the long axis of the liquid crystal molecules near the upper substrate surface in the state 1 to the rising direction from the substrate surface to the liquid crystal molecule near the lower substrate surface in the state 2. The twisting direction of the molecular long axis from the substrate surface to the rising direction to the unit vector is selected to be the opposite direction. Specific chiral agents are cholesteryl bromide, cholesteryl-
n-hexyl ether, cholesteryl benzoate, cholesteryl-n-hexyl heptanoate, cholesteryl nananoate, 4- [4- (2-methylbutyl) phenyl] benzene acid 4'-cyanophenyl ester, t-
4- (2-Methylbutyl) cyclohexylcarboxylic acid cyanobiphenyl ester, 4-n-hexyloxybenzenic acid 4 ′-(2-butoxycarbonyl) phenyl ester, 4- (4-methylbutyl) -4 ″ -cyano-
p-terphenyl, N- (4-ethoxybenzylidene)
-4- (2-methylbutyl) aniline, 4- (2-methylbutyl) benzene acid 4'-n-hexyloxyphenyl ester, 4-n-heptoxy-4 '-(2-methylbutyloxycarbonyl) biphenyl, 4- (2-methylbutyl) -4'-carbonylphenyl, 4- [4-
(2-methylbutyl) phenyl] benzene acid 4′-butylphenyl ester and the like.

The amount of the chiral agent added varies depending on the types of the liquid crystal and the chiral agent, but the following formula 0.05 <d / p <0.1 is satisfied for the liquid crystal cell (d) and the chiral pitch (p) of the liquid crystal. It is preferable that the relationship is satisfied, and d
Most preferably, / p is about 0.0625.

Compounds other than the above nematic liquid crystal compounds may be appropriately mixed. This compound does not necessarily have to exhibit a liquid crystal phase, and (a) a compound for adjusting the temperature range of the liquid crystal phase of the composition to be prepared, (b) exhibiting a large spontaneous polarization in the ferroelectric liquid crystal phase or inducing it. And the like.

After the injection, the injection port is sealed with a UV curable resin such as acrylic resin to obtain a liquid crystal cell. Further, polarizing plates with polarization axes substantially orthogonal to each other are arranged above and below the liquid crystal cell, and one polarization axis of the polarizing plate is made to substantially coincide with one of the optical axes of the liquid crystals of the cell to form a liquid crystal display device. You can

[0023]

【Example】

Example 1 Hereinafter, the present invention will be described in more detail. The bistable nematic liquid crystal cell portion was prepared by the following procedure. Figure 7
[FIG. 3] is a cross-sectional view of a liquid crystal device display unit driven by multiplex.

1. On each of the glass substrates 1a and 1b, a plurality of transparent electrodes (2a and 2b) having a thickness of 1000 angstroms are formed by arranging the electrode patterns in stripes so as to be parallel to each other. The thickness of the transparent electrode is 300 to 5000 angstrom, preferably 100.
It can be set in the range of 0 to 3000 angstroms (1000 angstroms in this example). 1. Insulating films 3a and 3b for protecting electrodes are formed on the substrate of 2.1.
It is formed with a film thickness of 000 angstroms. The thickness of the insulating film is 300 to 5000 angstrom, preferably 5
It can be set in the range of 00 to 2000 angstrom (1000 angstrom in this embodiment). For the insulating film, SiO ₂ or O produced by Tokyo Ohka
CD (OCD P-59310) was used. In the case of SiO ₂ , the insulating film was formed by sputtering, and in the case of OCD, it was formed by coating the substrate with a spinner and then firing (800 Å in this example). SiO (4a, 4b) is formed as an alignment film on the substrate of 3.3 by using the oblique deposition method. The vapor deposition angle can be set in the range of 70 ° to 76 °, preferably 73 ° to 75 ° from the substrate radiation (the angle is 74 in this embodiment).
°). The film thickness can be set in the range of 50 to 300 angstroms, preferably 50 to 100 angstroms (70 angstroms in this example). 4. The vapor deposition direction of SiO on the upper and lower substrates was set such that the direction projected on the substrate was shifted by about 45 ° from the same direction. A diameter of 1.5μ between the upper and lower substrates that have undergone the steps of 5.1 to 3
m silica beads are dispersed and bonded with an epoxy resin sealing member. The diameter of the silica beads can be set in the range of 1 to 3 μm, preferably 1.2 to 1.8 μm (about 1.2 to 1.5 μm in this example). A nematic liquid crystal (host liquid crystal 5CB with a chiral agent S-811 added to a panel manufactured through the steps of 6.1 to 4).
A mixture of 36 w% was injected by a vacuum injection method. After the injection, the injection port was sealed with an acrylic UV curable resin. 7. FIG. 6 shows the response characteristics when a pulsed electric field is applied to the panel prepared by the above procedure. The angle of the projection vector of the device thus manufactured was about 45 degrees. In this way, a response on the order of 100 μsec was possible. Further, it showed stable bistability in the region of 1 cm ² , and the contrast was 20: 1.

Comparative Example 1. Substrates that have been subjected to the same processing as in the above-mentioned Example items 1 to 3 are set so that the SiO directions of the upper and lower substrates are at 135 ° from the same direction, and then similar panels are created along with Example items 5 to 6. did. 2. In this case, the orientation of the panel could not be in an ideal state and no switching state was stated.

[0026]

According to the present invention, a liquid crystal element device which operates at high speed and has a large area can be manufactured. This is because the liquid crystal exhibits a uniform alignment state over a large area as compared with a conventional liquid crystal device and performs stable bistable switching.

[Brief description of drawings]

FIG. 1 is a schematic view of a liquid crystal display device of the present invention.

FIG. 2 is a schematic diagram showing bistable liquid crystal.

FIG. 3 is a schematic diagram showing a relationship between a vapor deposition direction and liquid crystal molecule alignment.

FIG. 4 is a schematic diagram showing alignment of liquid crystals in a cross section of a liquid crystal cell.

FIG. 5 is a schematic view showing the SiO vapor deposition direction and liquid crystal molecule alignment of the present invention.

FIG. 6 is a diagram showing a relationship between an applied pulse width and an applied voltage in the liquid crystal display device of the present invention.

FIG. 7 is a schematic sectional view of a liquid crystal display device of the present invention.

[Explanation of symbols]

 1,1 'Direction of stable liquid crystal molecule on substrate surface 2,2' Direction of stable liquid crystal molecule on substrate surface 3,3 'Direction of stable liquid crystal molecule on substrate surface 1a, 1b Glass substrate 2a, 2b Transparent electrode 3a , 3b Electrode protection film 4a, 4b SiO alignment film 11 Glass substrate 12 Glass substrate 13 Liquid crystal layer 14 Transparent electrode 15 SiO alignment film 16 Spacer A Long axis of liquid crystal molecule showing bistability B Long length of liquid crystal molecule showing bistability Axis C long axis of liquid crystal molecules showing bistability

Claims (6)

[Claims] 1. A pair of substrates, each having an electrode selectively formed on the surface thereof, on which an insulating film and an alignment film are formed, are arranged so as to face each other so as to be substantially parallel to each other, and the alignment film has one pretilt angle. Is about 0 degree, and the other alignment film is 5 to 45 degrees.
In a liquid crystal display device having a switching means for switching the optical axis of the liquid crystal by forming a liquid crystal cell with a liquid crystal interposed between substrates and selectively applying a voltage to the electrodes, ) Alignment directions of the respective substrates are different from each other, (2) the liquid crystal is a nematic liquid crystal to which a chiral agent is added, and (3) when the switching means is operated, the upper substrate is Shows that the substrate cross-section direction and the liquid crystal molecule long axis have a constant tilt angle, and in the lower substrate, the substrate cross-section direction and the liquid crystal molecule long axis are parallel, and the molecular axes of the liquid crystal molecules projected on the respective substrate surfaces are mutually In the parallel state 1, in the upper substrate, the substrate cross-sectional direction and the liquid crystal molecule long axis are parallel, and in the lower substrate, the substrate cross-sectional direction and the liquid crystal molecule long axis have a constant tilt angle, and It shows a bistable state with a state 2 in which the long axes of the liquid crystal molecules projected on the plate surface are parallel to each other. (4) In the state 1 on the upper substrate and the lower substrate, the upper substrate surface In state 2, the unit vector of the molecular long axis of the nearby liquid crystal molecule from the substrate surface to the rising direction is
Bistability characterized in that when a unit vector of the molecular long axis of liquid crystal molecules near the lower substrate surface is projected from the substrate surface to the rising direction, the angle formed by the projected vectors of each state is 90 to 180 °. Type liquid crystal display device. 2. The chiral agent is added so that the twist direction of the liquid crystal molecules is opposite to the twist direction from the unit vector in the state 1 to the unit vector in the state 2. Bistable liquid crystal display device. 3. The liquid crystal cell (d), wherein the amount of chiral agent added is
3. The bistable liquid crystal display device according to claim 1 or 2, wherein the following equation 0.05 <d / p <0.1 is satisfied between and the chiral pitch (p) of the liquid crystal. 4. The chiral agent is cholesteryl bromide,
Cholesteryl-n-hexyl ether, cholesteryl benzoate, cholesteryl-n-hexyl heptanoate, cholesteryl nananoate, 4- [4- (2-methylbutyl) phenyl] benzene acid 4'cyanophenyl ester, t-4- (2- Methylbutyl) cyclohexylcarboxylic acid cyanobiphenyl ester, 4-n-hexyloxybenzene acid 4 '-(2-butoxycarbonyl) phenyl ester, 4- (4-methylbutyl)-
4 ''-cyano-p-terphenyl, N- (4-ethoxybenzylidene) -4- (2-methylbutyl) aniline,
4- (2-methylbutyl) benzene acid 4'-n-hexyloxyphenyl ester, 4-n-heptoxy-4 '
-(2-methylbutyloxycarbonyl) biphenyl,
The compound selected from the group consisting of 4- (2-methylbutyl) -4'-carbonylphenyl and 4- [4- (2-methylbutyl) phenyl] benzene acid 4'butylphenyl ester, according to claim 1. Bistable liquid crystal display device. 5. The bistable liquid crystal display device according to claim 1, wherein an alignment treatment direction angle between the alignment film on the upper substrate and the alignment film on the lower substrate is 0 to 90 degrees, respectively. 6. The bistable liquid crystal display device according to claim 1, wherein the alignment treatment method for the alignment film is oblique vapor deposition of silicon oxide.