JP2000241817A - Liquid crystal element and driving method thereof - Google Patents

Abstract

(57) [Problem] To provide an active matrix type chiral smectic liquid crystal element with improved afterimage, deterioration of alignment with time, burn-in, and the like. SOLUTION: An asymmetric cell is configured so as to generate a difference of 100 mV or more in a switching threshold voltage between bistable and different stable states, and after resetting to a more stable state, to an unstable state. The non-hold type display is performed by providing a non-display period before or after the period in which the display is performed, and applying a voltage whose polarity is inverted to the voltage applied in the display period before or after the period in which the display is performed. I do.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a liquid crystal element used for a flat panel display, a projection display, a printer, and the like, and a driving method thereof.

[0002]

2. Description of the Related Art As a display which has been most widely used, a CRT is widely known as a moving image output such as a television or a VTR or a monitor of a personal computer. However, due to the characteristics of the CRT, flicker and scanning fringes due to insufficient resolution lower the visibility of a still image, and the phosphor deteriorates due to burn-in. Also, recently, it has been found that the electromagnetic waves generated by the CRT have an adverse effect on the human body, and there is a concern that the health of a VDT worker may be impaired. Since the CRT is required to have a large volume behind the screen due to its structure, the convenience of information devices is significantly impaired, and the space saving of offices and homes is impeded.

As a solution to such a drawback of the CRT, there is a liquid crystal element. For example, M. Shut (M. Sc
hadt) and W.W. Helfrich (W. Helfric)
h), Applied Physics Letters (App
led Physics Letters) No. 18
Vol. 4, No. 4 (issued February 15, 1971), p. 127-
The twisted nematic (T
A liquid crystal using a liquid crystal (ie, a switched nematic) is known. In recent years, using this type of liquid crystal, TFT (T
2. Description of the Related Art An active matrix type liquid crystal element called a TFT type, which is configured using a thin film transistor (thin film transistor) as an active element, has been developed and commercialized. In this type, a transistor is manufactured for each pixel, there is no problem of crosstalk, and 10 to 12 inch class displays are being manufactured with good productivity due to rapid progress in production technology in recent years. is there. However, if the frame frequency is set to 60 Hz or higher in order to reproduce a larger size or a moving image without any problem, there are still problems in productivity, response speed of liquid crystal, and viewing angle.

On the other hand, a liquid crystal device using spontaneous polarization as a switching torque has been proposed by Clark and Lagerwall (JP-A-56-107216, US Pat. No. 4,368,924).
Specification) There is a chiral smectic liquid crystal element. In this device, a ferroelectric liquid crystal (FLC) generally comprising a chiral smectic C phase or a chiral smectic H phase is used as a liquid crystal. Since this ferroelectric liquid crystal performs inversion switching by spontaneous polarization, it has a very fast response speed and also has an excellent viewing angle characteristic, so that it has a high-speed, high-definition, large-area simple matrix display element or light. It is considered suitable as a valve.

Recently, a chiral smectic antiferroelectric liquid crystal device has also been proposed by Chandani, Takezoe et al. [Japanese Journal of Applied Physics].
of Applied Physics), Volume 27,
1988, L729]. Recently, among the antiferroelectric liquid crystal materials, a V-shaped response characteristic having a thresholdless value, a small hysteresis, and a characteristic advantageous for gradation display has been discovered (for example, Japanese Journal of Physics).
Applied Physics, Vol. 36, 1997, 35
86).

Further, as a V-shaped switching liquid crystal using spontaneous polarization as a switching torque, monostable surface stabilized FLC (for example, Journal of Applied Physics, Vol. 61, 1987, p. 2400), Deformed Helix FLC (for example, Ferroelectronics, Vol. 85, p. 173, 1988), Twisted smectic FLC (for example, Applied Physics Letter, Vol. 60, p. 280, 1992), thresholdless antiferroelectric liquid crystal, Molecular liquid crystal stabilized FLC (for example, S
ID '96 digest, 1996, p. 699).

[0007] There is an active movement to realize a high-speed display by using these liquid crystals as an active matrix type liquid crystal element (for example, Japanese Patent Application Laid-Open No. 9-50049).

[0008]

However, an active matrix type device using a chiral smectic liquid crystal having the above-mentioned ferroelectricity has a problem in terms of reliability such as afterimages due to hysteresis, deterioration of alignment over time, and image sticking. There are still problems, and there is a strong demand for solutions to these problems.

An object of the present invention is to solve the above-mentioned problems and to realize a liquid crystal device with high speed response, high image quality and high reliability.

[0010]

A liquid crystal device according to the present invention is an active device in which a chiral smectic liquid crystal is sandwiched between a pair of substrates, has a plurality of pixels, and the liquid crystal of each pixel is arranged for each pixel. Active matrix type liquid crystal element driven in a matrix by the following method, wherein the liquid crystal has at least two stable states in an electric field-free state, and a difference in switching threshold voltage between different stable states is 100 mV.
As described above, a halftone state corresponding to an applied voltage is obtained between the two different stable states.

Further, the method for driving a liquid crystal element according to the present invention is the method for driving a liquid crystal element according to the present invention, wherein after resetting the entire surface of the pixel to a more stable state, a voltage corresponding to the display state is applied to the pixel. Writing is performed by applying to a liquid crystal.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the structure of the liquid crystal device of the present invention will be described.

FIGS. 1 and 2 schematically show the structure of an embodiment of the liquid crystal device of the present invention. FIG. 1 is a schematic plan view, FIG.
Is a schematic sectional view. In the figure, 11 is a column driver, 12 is a row driver, 13 is a pixel electrode, 14 is a TFT, 15 is a scanning signal line, 16 is an end of a scanning signal line, 17 is an information signal line, and 18 is an end of an information signal line. Parts, 21 and 22 are substrates, 24
Is a common electrode, 22 and 25 are alignment films, 27 is a liquid crystal layer, 26
Is a spacer, and 28 is a sealing material.

In the present invention, as the substrates 21 and 22, transparent substrates such as glass and plastic are used. The electrodes 13 and 24 are usually formed of a transparent conductive material of ITO.

In the liquid crystal device of the present invention, the difference in switching threshold voltage of the liquid crystal between different stable states is 100 mV or more. Such asymmetry is specifically, for example, the alignment film 23 of the upper and lower substrates. , 25 are different from each other, or in a ferroelectric liquid crystal, when a burn-in occurs in any stable state. In the present invention, in order to realize this asymmetry without causing image sticking, it is preferable that the alignment films 23 and 25 of the upper and lower substrates are different from each other. More specifically, one is desirably a uniaxial orientation control layer.

As a method of forming the uniaxial orientation control layer that can be used in the present invention, for example, silicon monoxide, silicon dioxide,
Aluminum oxide, zirconia, magnesium fluoride,
Inorganic substances such as cerium oxide, cerium fluoride, silicon nitride, silicon carbide, and boron nitride, and polyvinyl alcohol, polyimide, polyimide amide, polyester, polyamide, polyester imide, polyparaxylene, polycarbonate, polyvinyl acetal, polyvinyl chloride, and polystyrene After forming a film using an organic substance such as polysiloxane, cellulose resin, melamine resin, urea resin, and acrylic resin, the surface is rubbed with a fibrous material such as velvet, cloth or paper. . Also, an oblique vapor deposition method or the like in which an oxide or a nitride such as SiO is vapor-deposited from the oblique direction of the substrate is used.

In particular, in order to obtain better uniaxial orientation, a polyimide orientation film having a repeating unit represented by the following general formula (1) is preferably used. Usually, polyimide is obtained by coating a film in the form of a polyamic acid and baking it. Polyamic acid is excellent in productivity because it is easily soluble in a solvent. Recently, polyimides soluble in solvents have also been produced, and even with the advancement of such technology, polyimides are preferably used because they can obtain better uniaxial orientation and have high productivity. It is preferable that the thickness of the polyimide film is thin in order to suppress the adverse effect due to the anti-electric field, and specifically, it is preferably 200 ° or less.

[0018]

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The orientation film on the side other than the uniaxial orientation control layer may be a material used for the uniaxial orientation control layer, which has not been subjected to the uniaxial orientation control treatment, various polymer materials, or a material which suppresses the influence of an anti-electric field. And a film having conductivity. Examples of the conductive film include a film in which conductive fine particles are dispersed in a binder material, and are preferably used in that a charge characteristic can be differentiated from a polyimide film preferably used as a uniaxial alignment control layer. Further, the asymmetricity of the upper and lower alignment films can be changed by changing the coating solvent. Although the upper and lower substrates 21 and 22 are opposed to each other via the spacer 26, the average molecular axis of the liquid crystal molecules is made substantially the same as the average direction of the alignment processing axis with uniform uniaxial orientation and without electric field. The cell gap is preferably set to 0.3 to 10 μm in order to develop an alignment state.

On the substrates 21 and 22, alignment films 13 and 25 are provided.
Besides, an insulating layer for preventing short circuit can be provided.

As the liquid crystal layer 27 of the liquid crystal element of the present invention,
A chiral smectic liquid crystal such as a ferroelectric liquid crystal and an antiferroelectric liquid crystal is used. Preferably, a surface stabilized ferroelectric liquid crystal is used. Since these liquid crystals use the spontaneous polarization as a switching torque, a high-speed liquid crystal element can be realized. Specifically, although depending on the drive voltage, the switching speed is 1 msec or less or 50 msec.
It can be set to 0 μsec or less, and further to 100 μsec or less.

The liquid crystal element of the present invention has at least two stable states in the absence of an electric field, despite the asymmetry of the switching threshold voltage from one to the other between two different stable states of 100 mV or more. Is a major feature. Normally, if such a threshold voltage has a large asymmetry, it becomes monostable even in a non-electric field state. The liquid crystal preferably used in the present invention is a ferroelectric liquid crystal having bistability. In order to realize bistability even under such asymmetric conditions, the activation energy of the transition between two stable states is required. It needs to be large and can be implemented in various ways.

For example, a liquid crystal having a large tilt angle is preferable. Typically, a tilt angle of 15 ° or more is preferable. Also, a bistable liquid crystal having two states of a uniform without having a twisted state is preferably used. In this case, in order to suppress the twisted state, it is preferable that the presence of ions in the liquid crystal is as small as possible. Furthermore, a chiral smectic liquid crystal whose spontaneous polarization is not so large has a tendency that the threshold voltage between two states tends to be large, and is preferably used.
Specifically, the spontaneous polarization is preferably 10 nC / cm ² or less. In addition, it is preferable that the spontaneous polarization is small from the viewpoint of suppressing the hysteresis.

The method for measuring the tilt angle and the spontaneous polarization in the present invention will be described below.

[Tilt angle] ± 30 to ± 50 V, 1 to 10
While applying 0 Hz AC (alternating current) between the upper and lower substrates of the liquid crystal element through electrodes, the liquid crystal element disposed therebetween is rotated in parallel as a polarizing plate under crossed Nicols, and at the same time, the photomultiplier (Hamamatsu Photonics) The first extinction position (the position at which the transmittance becomes lowest) and the second extinction position are determined while detecting the optical response using the method described above. And the first at this time
A half of the angle from the extinction position to the second extinction position is defined as a tilt angle.

[Spontaneous polarization] 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, (661) 1983, "Di
rect Method with Triangul
ar Waves for Measuring Sp
ontaneous Polarization in
Ferroelectric Liquid Cry
stal ", as described by KM
iyasato et al. (Jap. J. App
l. Phys. 22. No. 10, L661 (198
3) Measure according to).

The chiral smectic liquid crystal used in the present invention is preferably a liquid crystal composition containing the following fluorine-containing liquid crystal compound. That is, a fluorochemical terminal portion having at least one chiral or achiral methylene group and optionally having one or more ether oxygens in the chain, and a chiral or achiral saturated hydrocarbon terminal portion are formed into a central core portion. And a fluorine-containing liquid crystal compound having a smectic phase or a potential smectic phase. In the present invention, it is desirable to use a liquid crystal composition composed of only the above-mentioned fluorine-containing liquid crystal compound group. The liquid crystal composition containing the fluorine-containing liquid crystal compound, by increasing the degree of purification, can reduce the ion content, having a good uniform orientation, bookshelf or a structure with a small layer tilt angle that can avoid zigzag defects. Because it can appear, it can be preferably used.

Specific examples of the fluorine-containing liquid crystal compound include the following general formulas (I), (II) and (III)
Is mentioned.

[0029]

Embedded image Represents

Ga, ha and ia each independently represent an integer of 0 to 3 (provided that ga + ha + ia is at least 2).

Each of L ¹ and L ² is independently a single bond, —CO
-O-, -O-CO-, -COS-, -S-CO-,-
CO-Se-, -Se-CO-, -CO-Te-, -T
_{e-CO -, - CH 2} CH 2 -, - CH = CH -, - C≡
C -, - CH = N - , - N = CH -, - CH 2 -O-,
-O-CH ₂ -, - CO- or represent -O-.

Each of X ¹ , Y ¹ , and Z ¹ is a substituent of A ¹ , A ² , and A ³ and independently represents —H, —Cl, —F, —Br, —
_{I, -OH, -OCH 3, -CH} 3, -CN, or -NO
₂ and each of ja, ma and na independently represents an integer of 0-4.

J ¹ is —CO—O— (CH ₂ ) _ra —, —O
_{- (CH 2) ra -,} - (CH 2) ra -, - O-SO 2 -,
_{-SO 2 -, - SO 2 -} (CH 2) ra -, - O- (CH 2)
_{ra -O- (CH 2) rb -} , - (CH 2) ra -N (C pa H
_2pa + 1) -SO ₂ -, or _{- (CH 2) ra -N (} C pa H
_{2pa + 1} ) represents -CO-. ra and rb are independently 1
-20 and pa is 0-4.

R ¹ is _{-OC qa} H _{2qa -OC qb} H
_{2qb + 1, -C qa H 2qa} -O-C qb H 2qb + 1, -C qa H 2qa -
_{^{R 3, -O-C qa H}} 2qa -R 3, -CO-O-C qa H 2qa -
R ³ or —O—CO—C _qa H _2qa —R ³ , which may be linear or branched (where R ³ _{is-
O-CO-C qb H 2qb} + 1, -CO-O-C qb H 2qb + 1, -
_{H, -Cl, -F, -CF 3} , -NO 2, represents a -CN, qa and qb are 20 independently).

R ² represents C _xa F _2xa -X (X represents -H or -F, and xa is an integer of 1 to 20).

[0036]

Embedded image Represents

Gb, hb and ib are each independently 0 to 3
(Where gb + hb + ib is at least 2).

Each of L ³ and L ⁴ is independently a single bond, -CO
-O-, -O-CO-, -CO-S-, -S-CO-,
-CO-Se-, -Se-CO-, -CO-Te-,-
Te-CO -, - (CH 2 CH 2) ka - (ka is 1
4), -CH = CH-, -C≡C-, -CH = N-,-
_{N = CH -, - CH 2} -O -, - O-CH 2 -, - CO-
Or -O-.

Each of X ² , Y ² , and Z ² is a substituent of A ⁴ , A ⁵ , and A ⁶ and independently represents —H, —Cl, —F, —Br, —
_{I, -OH, -OCH 3, -CH} 3, -CF 3, -O-C
F ₃ , —CN, or —NO ₂ , and each jb, m
b and nb each independently represent an integer of 0 to 4;

J ² is —CO—O—C _rc H _2rc —, —O—
_{C rc H 2rc -, - C} rc H 2rc -, - O- (C sa H 2sa -
O) _ta -C _rd H _2rd- , _-O -SO _2- , -SO ₂ -,-
_{SO 2 -C rc H 2rc -,} - C rc H 2rc -N (C pb H 2pb + 1)
_{-SO 2 -, - C rc H} 2rc -N (C pb H 2pb + 1) -CO-
_Where rc and rd are independently 1-20, sa is independently 1-10 for each (C _sa H _2sa -O), ta is 1-6, pb is 0-4. is there.

R ⁴ is -O- (C _qc H _2qc -O) _wa- C _{qd
H 2qd + 1, - (C} qc H 2qc -O) wa -C qd H 2qd + 1, -C
_qc H _2qc -R ⁶ , _{-OC qc} H _2qc -R ⁶ , -CO- _OC
qc H _2qc -R ^6, or represents _{-O-CO-C qc H 2qc} -R 6, linear, may be either branched (Here, R
⁶ is _{-O-CO-C qd H 2qd} + 1, -CO-O-C qd H
_{2qd + 1, -Cl, -F,} -CF 3, -NO 2, represents -CN, or -H, qc and qd are independently an integer of 1 to 20, the wa is an integer of 1 to 10).

R ⁵ is (C _xb F _2xb -O) _za -C _ya F
_{2ya + 1} is represented by (wherein, the formula xb is 1 to 10 independently of each _{(C xb F 2xb -O),} ya is 1
And za is 1-10).

The compound represented by the above general formula (I) is
JP-A-2-142755, U.S. Pat.
2,587.
Specific examples of such compounds are listed below.

[0044]

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[0045]

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[0046]

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[0047]

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[0048]

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[0049]

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[0050]

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[0051]

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[0052]

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[0053]

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[0054]

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[0055]

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The compound represented by the above general formula (II) is described in WO 93/22396, JP-T-Hei 7-506.
368 can be obtained.
Specific examples of such compounds are listed below.

[0057]

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[0058]

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[0059]

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[0060]

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[0061]

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[0062]

Embedded image Represents

A, b and c each independently represent an integer of 0 or 1 to 3 (where a + b + c is at least 1).

A and B are each independently selected from the following groups containing covalent bonds (regardless of direction) (k is an integer of 1 to 4).

-CO-O-, -CO-S-, -CO-S
e -, - CO-Te - , - (CH 2 CH 2) k -, - CH
= CH -, - C≡C -, - CH = N -, - CH 2 -O
-, -CO-, -O-

X, Y and Z are each independently -H, -Cl,
-F, -Br, -I, -OH, -OCH 3, -CH 3, -
CF _3, -CN, selected from -NO _2.

L, m and n each independently represent an integer of 0 or 1-3.

D is selected from the following group containing a covalent bond (in any direction).

[0069] _{-CO-O-C r H 2r} -, - O-C r H
_{2r -, - O-OC-} C r H 2r -, - C≡C -, - CH =
CH -, - CO -, - O- (C s H 2s O) t -C r 'H 2r'
_{-, - C r H 2r -} , - (C s H 2s O) t -C r 'H 2r' -, -
O -, - S -, - OSO 2 -, - SO 2 -, - SO 2 -C r
_{H 2r -, - C r H} 2r -N (C p H 2p + 1) -SO 2 -, - N
_{(C p H 2p + 1)} -, - C r H 2r -N (C p H 2p + 1) -CO
-, -CH = N-, and combinations thereof. here,
r and r ′ are each independently an integer of 0 to 20, and s is each (C _s H _2s
O) is independently an integer of 1 to 10, t is an integer of 1 to 6, and p is an integer of 0 to 4.

[0070] R _{is, -O - ((C q '} H 2q'-v' - (R ')
_{v ') -O) w -C q} H 2q + 1-v - (R') v, - ((C q 'H
_{2q-v - (R ')} v') -O) w -C q H 2q + 1-v -
_{(R ') v, -CO-} O-C q H 2q + 1-v - (R') v, -
_{O-OC-C q H 2q} + 1-v - (R ') v,

[0071]

Embedded image _{-CR'H- (D) g -CR'H-C} q H 2q + 1-v -
(R ′) _v , where R ′ is independently —Cl, —F,
_{-CF 3, -NO 2, -CN,} -H, -C q H 2q + 1, -O
_{-OC-C q H 2q + 1} , -CO-O-C q H 2q + 1, -Br,
-OH, it represents a -OC _q H _{2q + 1.} q ′ is (C _{q ′} H _{2q ′} −
O) is independently an integer of 1 to 20, q is an integer of 1 to 20, w is an integer of 0 to 10, v is an integer of 0 to 6, each v 'is independently an integer of 0 to 6, g is 1 -3. Each D is independently a group in which the D is selected (in any direction)
(Provided that the ring containing D is composed of 3 to 10 atoms). Each W is independently N, CR ', SiR
Is selected from R is chiral or achiral.

R _f ′ is -R ^* -D- (O) _x -CH ₂ -D '
—R _f , where R ^* is a cyclic or chain-like chiral moiety. D and D 'are each independently selected from the group in which D is selected (regardless of direction). x is 0
Or an integer of 1, and R _f represents a fluoroalkyl group, a perfluoroalkyl group, a fluoroether group, or a perfluoroether group.

Examples of the method for synthesizing the compound represented by the above general formula (III), and specific examples thereof include those described in WO 96/33251. Further, specific examples of the compound are shown below.

[0074]

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[0075]

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[0076]

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[0077]

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The liquid crystal element of the present invention is usually sandwiched between a pair of polarizing plates (not shown), irradiates light from the substrate 21 side, and changes the voltage applied to the liquid crystal layer 27 for each pixel to thereby increase the transmittance. Is changed, and the transmission amount of the emitted light is changed to perform display. Note that this configuration is an example of a transmission type liquid crystal element,
By using the substrate 21 or the pixel electrode 13 as a reflection member, or by providing a separate reflection member on the substrate 21,
A reflection type liquid crystal element that reflects light incident from the substrate 22 side can also be configured.

Further, the pixel electrode 1 is provided on the lower substrate 21.
3 and active elements 14 connected to each pixel electrode 13 are formed in a matrix. A TFT is preferably used as the 14 active elements, and is formed using a semiconductor such as amorphous silicon, polysilicon, microcrystal silicon, or single crystal silicon.
This example shows an element configured using a TFT. TF
T is usually a gate electrode formed on the substrate 21, a gate insulating film covering the gate electrode, a semiconductor layer formed on the gate insulating film, a source electrode and a drain electrode formed on the semiconductor layer. Consists of

Further, on the substrate 21, scanning signal lines (gate lines) 15 are arranged between rows of the pixel electrodes 13, and information signal lines (source lines) 17 are arranged between columns of the pixel electrodes 13. The gate electrode of each TFT 14 is connected to the corresponding scanning signal line 15, and the source electrode is connected to the corresponding information signal line 17. The scanning signal line 15 is connected to the row driver 12 via the end 16, and the information signal line 17 is connected to the column driver 11 via the end 18. The row driver 12 sequentially selects the scanning signal lines 12 and applies a gate signal, and the column driver 11 applies an information signal corresponding to display data to each information signal line 17 in synchronization with the gate signal.

The scanning signal line 15 is a TFT except for the end 16.
The information signal line 17 is formed on the gate insulating film. The pixel electrode 13 is formed on the same gate insulating film, and has one end connected to the drain electrode of the TFT 14.

The common electrode 14 facing each pixel electrode 13 on the lower substrate 21 is formed on the upper substrate 22 in FIG. The common electrode 14 is formed of one electrode having an area covering the entire display area, and a reference voltage is applied. Further, a capacitor serving as an auxiliary capacitance may be arranged for each pixel.

In the active matrix type liquid crystal element configured as described above, charge is injected into the liquid crystal cell which is a pixel when the gate is turned on, the gate is turned off in a short time, and information is transferred to the pixel on the next scanning line. Written. Since the liquid crystal used in the present invention has spontaneous polarization, the voltage drops when the gate is turned off with the reversal of the spontaneous polarization except when switching is completed within the gate-on time. Therefore, it is preferable that the spontaneous polarization is not too large for such a reason, and as described above, the spontaneous polarization of the liquid crystal used in the present invention is preferably 10 nC / cm ² or less. This is also preferable in order to suppress alignment degradation due to the incorporation of polar impurities and the like.

The liquid crystal element of the present invention exhibits at least two stable states in the absence of an electric field, shows a halftone state between these states, that is, shows a coexistence state of a plurality of domains, and shows one of the stable states. By arranging a polarizing plate so that black display and white display are performed on the other side, gradation display between these two stable states is possible. Still further, the intermediate state can be stored.

Next, a method for driving the liquid crystal element of the present invention will be described. The driving method of the present invention is characterized in that, for each pixel of the liquid crystal element of the present invention, writing is performed by resetting to a more stable state and then applying a voltage according to the display state. Here, the meaning of resetting to a more stable state is because it has the effect of suppressing the previous state history and increasing the reproducibility of the gradation expression ability as compared to the case of resetting to a more unstable state. is there. For this reason, in the liquid crystal element of the present invention, application development such as partial pixel rewriting in which a part of the display area is in a memory state and the other is in a driving state, a still image mode in which the entire area is used in a memory state, or a low power consumption mode is developed. it can.

Further, in the method of driving a liquid crystal element of the present invention, when attention is paid to one pixel, it is preferable that a voltage signal whose polarity is alternately inverted is input from the information signal line. In the present invention, when such polarity inversion driving is performed, the method described below is preferably used.

First, a voltage signal having a sign that switches from an initial state (reset state to a more stable state) to a more unstable direction is applied, and the liquid crystal is switched to be converted into a light modulation signal. This, of course, enables gradation display. Next, when signals having different polarities are given, switching is performed in a more stable direction. The state of switching in the stable direction is such that when one of the optical axes of the orthogonal polarizing plate is used as a normally black element used in accordance with the optical axis in the stable state, a black state or an extremely black state occurs during the original display. Will be displayed. In this case, when this element is viewed as a display element, it becomes a non-hold type display in which a display period and a non-display period are provided in one frame, and since the liquid crystal element of the present invention performs high-speed switching, the image quality of moving image display is excellent. Is very preferred. The time ratio between the non-display period when switching to a stable state and the display period when switching to a more unstable state is not particularly limited, but in the sense of minimizing the bias of the DC component and suppressing image sticking. , Preferably in the range of 1: 9 to 9: 1, more preferably in the range of 3: 7 to 7: 3. Regarding the information signal voltage value that switches in a more stable direction,
It is also a preferable embodiment to minimize the bias of the DC component in total in accordance with this time ratio. Specifically, there is a method in which the time ratio is set to 1: 1 and a reset signal having the same absolute value as the write signal applied in the display period and having a different polarity is provided to a non-display period provided immediately before or immediately after the display period. Can be

The liquid crystal element of the present invention can be applied to a direct view type and a projection type, and can also be used as a light valve of a printer or the like.

A liquid crystal device having various functions can be constituted by using the liquid crystal element of the present invention. One example of such a liquid crystal device is shown in FIGS. The liquid crystal display device is realized by using a data synchronizing means using a data format including image information having gate line address information and a SYN signal. In the figure, 101 is a liquid crystal display device, 102 is a graphic controller, 103 is a display panel, 104 is a gate line drive circuit, 105 is an information line drive circuit, 106 is a decoder, 107 is a gate line signal generation circuit, 108 is a shift register, 109 is a line memory, 110 is an information signal generation circuit, 111 is a drive control circuit, 112 is a GCPU,
Reference numeral 113 denotes a host CPU, and 114 denotes a VRAM.

The image information is generated by the graphic controller 102 of the main unit, and is transferred to the display panel 103 in accordance with the signal transmission means shown in FIGS. The graphic controller 102 is a GCPU
(Central processing unit) and a VRAM (memory for storing image information) 114 serving as a core, a host CPU 113 and a liquid crystal display 1
It is responsible for management and communication of image information during 01. Note that a light source is disposed on the back surface of the display panel.

In the liquid crystal display device constituted by using the liquid crystal element of the present invention, since the liquid crystal element has good switching characteristics, it exhibits excellent driving characteristics and reliability, and can display a high-speed, large-area display image. Obtainable.

[0092]

EXAMPLES (Example 1) A / B / C / D =
The liquid crystal composition α was adjusted by mixing at a ratio of 15/55/25/5 (% by weight). As for the phase transition temperature of this liquid crystal composition, T _iso was 87 ° C., and the SmA → SmC ^* transition temperature was 52 ° C.
The tilt angle was 26 ° and the spontaneous polarization was 6.0 nC / cm ² (all at 30 ° C.).

[0093]

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An ITO film having a thickness of about 70 nm was formed as a transparent electrode on each of two glass substrates having a thickness of 1.1 mm. Thereafter, for both substrates, 0.7% of the polyamic acid of the polyimide precursor having the following repeating unit
The first solution was spin-coated at 500 rpm for 5 seconds and the second at 1500 rpm for 30 seconds.

[0095]

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Thereafter, pre-drying was carried out at 80 ° C. for 5 minutes, followed by baking at 220 ° C. for 1 hour. The thickness of the obtained polyimide film was 60 °, and the polyimide film was subjected to a rubbing treatment with a nylon cloth as a uniaxial orientation treatment.

Next, on one substrate, a ladder-type polysiloxane base material and antimony-doped SnO _x oxide ultrafine particles (particle diameter: about 100 °) were dispersed to a solid concentration of 10%.
Wt% ethanol / methanol / isopropanol =
44/43/13 (wt%) solution at 1500 rpm
It was applied by spin coating under the condition of 0 second. 80
After pre-drying at 5 ° C. for 5 minutes, it was dried by heating at 200 ° C. for 1 hour. An IPA (isopropanol) solution in which silica beads having an average particle size of 2.4 μm are dispersed at 0.01% by weight is spin-coated on the surface of the substrate under the conditions of 1500 rpm and 10 sec, and a bead spacer having a dispersion density of about 100 / mm ^2. Was sprayed. On this substrate, a thermosetting liquid adhesive was applied by a printing method. On this substrate, a substrate on which only the polyimide film is formed is opposed and bonded to each other.
The composition was cured by heating in an oven at 50 ° C. for 90 minutes to obtain a cell.

Activated alumina fine particles 1 were added to the liquid crystal composition α.
Weight%, and injected into the above cell, 5 Hz, ± 7
When a triangular wave of V was applied and a voltage-transmittance curve was measured by the optical response measurement method described above, a hysteresis curve of a typical bistable ferroelectric liquid crystal was obtained, and a threshold voltage of 50% inversion was obtained. The difference was 180 mV.

Next, using a single crystal silicon transistor (on resistance 50 Ω), the liquid crystal cell (having an area of 0.9
The active matrix type liquid crystal element having the configuration shown in FIG. 6 was manufactured by connecting a ceramic capacitor of ² cm and ² nF. In FIG. 6, reference numeral 61 denotes an information signal line;
2 is a scanning signal line, 63 is a single crystal silicon transistor,
64 is a liquid crystal cell, and 65 is a capacitor.

A gate signal is applied to the element so that the selection period is 30 μsec.
A pulse signal having a width of 30 μsec as shown in FIG.
In the waveform of FIG. 5, a positive pulse having a width of 30 μsec is a write signal, and a negative pulse having a width of 30 μsec is a reset pulse forming a non-display period. Also, 1
The frame is 16 msec, the display period is 8 msec after the application of the positive pulse, and a negative pulse is applied immediately thereafter, and the non-display period is 8 msec after the application of the negative pulse.

Next, the electro-optical response of the obtained device was measured. The measurement was performed using a polarizing microscope equipped with a photomultiplier tube.
The change in transmittance was measured under crossed Nicols. At this time, the cell was set so that the cell was darkest in the state where no electric field was applied.

The transmittance for each frame when the transmittance for white 1 is 100% is shown below. White 2 = 99% White 3 = 99% White 4 = 100% Gray 1 = 35% Gray 2 = 39% Gray 3 = 39% Gray 4 = 41% Black 1 <1% Black 2 <1% Black 3 <1% Black 4 <1%

As described above, regardless of the previous state,
Light modulation was performed with good reproducibility, and there was almost no hysteresis. The switching speed to the white state (90
% Switching time) was measured to be 290
μsec.

Example 2 For the active matrix type liquid crystal element of Example 1, the waveform represented by the white waveform in FIG. 5 was continuously applied for 100 hours. Thereafter, using the waveforms shown in FIG. 5, the transmittance of each of the white, gray, and black waveforms was measured in the same manner as described above. The transmittance almost equivalent to that of Example 1 was measured in each frame. It was found that in the liquid crystal element, the sticking of the liquid crystal was suppressed.

Example 3 An active matrix type having the same structure as in Example 1 except that the composition of the liquid crystal compound used in Example 1 was changed to A / B / D = 37/55/8 (% by weight). Was prepared, and the electro-optical response characteristics were measured. The results are shown below. Incidentally, the spontaneous polarization at 30 ° C. of the liquid crystal composition used in the present invention was 9.6 nC / cm ² . White 2 = 98% White 3 = 100% White 4 = 100% Gray 1 = 45% Gray 2 = 50% Gray 3 = 49% Gray 4 = 51% Black 1 <1% Black 2 <1% Black 3 <1% Black 4 <1%

As described above, light modulation was performed with good reproducibility, and there was almost no hysteresis. Further, when the burn-in durability measurement was performed on this device in the same manner as in Example 2,
The same transmittance as described above was obtained.

(Example 4) In the active matrix type liquid crystal element of Example 1, the voltage was applied until before the reset signal of Gray 3 in FIG. In this state, halftones based on the domain gradation were displayed. Thereafter, this state was maintained over time. Similarly, when a similar display was performed using the device of Example 3, the memory state of the domain gradation could be similarly maintained. From the above, it was found that the partial moving image display and the partial still image display were possible, and the full-screen still image display or the low power consumption mode was possible.

(Example 5) In Example 1, a cell was prepared in which the thickness of the polyimide film was 100 °, and the liquid crystal composition α used in Example 1 was injected. The difference in threshold voltage between the two stable states in this liquid crystal cell was 200 mV. Using this cell, an active matrix element similar to that of Example 1 was formed, and the optical response characteristics were measured.
Light modulation was performed with good gradation reproducibility. When the memory function was observed using this device in the same manner as in Example 4, the same memory properties as in Example 4 were observed.

(Comparative Example) A ferroelectric liquid crystal (“CS1014” manufactured by Chisso Corporation) was injected into the cell manufactured in Example 1.
A DC of 10 V was applied for 100 hours to obtain a monostable liquid crystal.
The difference in threshold voltage was 100 mV or more. However, when the memory function was observed in the same manner as in Example 4, no memory property was confirmed.

[0110]

According to the present invention, in an active matrix type liquid crystal device using a chiral smectic liquid crystal, problems in terms of reliability such as hysteresis, deterioration of alignment over time, and image sticking which cause an afterimage are improved. Further, a high-performance, high-speed response, high-quality liquid crystal element having a memory property is provided.

[Brief description of the drawings]

FIG. 1 is a schematic plan view of one embodiment of a liquid crystal element of the present invention.

FIG. 2 is a schematic sectional view of one embodiment of the liquid crystal element of the present invention.

FIG. 3 is a block diagram showing a liquid crystal display device including a liquid crystal element of the present invention and a graphic controller.

4 is a diagram showing a timing chart of image information communication between the liquid crystal display device of FIG. 3 and a graphic controller.

FIG. 5 is a voltage waveform used in an example of the present invention.

FIG. 6 is an equivalent circuit diagram of an active matrix type liquid crystal element manufactured in an example of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Column driver 12 Row driver 13 Pixel electrode 14 TFT 15 Scan signal line (gate line) 16 Scan signal line end 17 Information signal line (Source line) 18 Information signal line end 21,22 Substrate 23,25 Alignment film 24 Common Electrode 26 Spacer 27 Liquid crystal layer 28 Sealant 61 Information signal line 62 Scanning signal line 63 Single crystal silicon transistor 64 Liquid crystal cell 65 Auxiliary capacitance 101 Liquid crystal display device 102 Graphic controller 103 Display panel 104 Gate line drive circuit 105 Information line drive circuit 106 Decoder 107 Gate line signal generation circuit 108 Shift register 109 Line memory 110 Information signal generation circuit 111 Drive control circuit 112 GCPU 113 Host CPU 114 VRAM

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Koji Noguchi, Inventor 3--30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. Within Non Corporation (72) Inventor Minato Yagyu 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Masahiro Terada 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. F term (reference) 2H088 EA03 EA12 EA40 GA04 GA17 HA08 HA18 JA17 JA19 KA14 KA28 MA12 MA13 MA18 MA20 2H090 HA11 HB02Y HB03Y HB04Y HB07Y HB08Y HC05 JB02 JB03 KA14 KA15 MA02 MA11 MB03 NC22 NC11 NC03 NG12 5C006 AA02 AA16 AC26 BA12 BB16 FA11 FA34 FA47 GA03 5C080 AA10 BB05 DD29 EE29 FF11 JJ02 JJ04 JJ06

Claims (12)

[Claims] 1. An active matrix type liquid crystal element comprising a plurality of pixels, wherein a chiral smectic liquid crystal is sandwiched between a pair of substrates, and a matrix is driven by an active element in which the liquid crystal of each pixel is arranged for each pixel. So,
The liquid crystal has at least two stable states in the absence of an electric field, a difference in switching threshold voltage between different stable states is 100 mV or more, and an intermediate voltage corresponding to an applied voltage between the two different stable states. A liquid crystal element characterized in that the liquid crystal element is in a toned state. 2. The liquid crystal device according to claim 1, wherein different alignment films are provided for the upper and lower substrates on a surface of the substrate in contact with the liquid crystal. 3. The liquid crystal device according to claim 2, wherein one of the alignment films is a uniaxial alignment control layer. 4. The liquid crystal device according to claim 1, wherein the halftone state is formed by a domain. 5. The liquid crystal device according to claim 1, wherein the chiral smectic liquid crystal is a bistable ferroelectric liquid crystal. 6. The above-mentioned chiral smectic liquid crystal is a liquid crystal composition, having at least one chiral or achiral methylene group and having at least one ether oxygen in the chain, a fluorochemical terminal portion, The liquid crystal device according to any one of claims 1 to 5, comprising a fluorine-containing liquid crystal compound having a smectic phase or a potential smectic phase, wherein a chiral or achiral saturated hydrocarbon terminal portion is bonded at a central core portion. . 7. The liquid crystal device according to claim 7, wherein the chiral smectic liquid crystal is a liquid crystal composition composed of only the fluorine-containing liquid crystal compound group. 8. The liquid crystal device according to claim 1, wherein the chiral smectic liquid crystal has a spontaneous polarization of 10 nC / cm ² or less. 9. The liquid crystal device according to claim 1, wherein said active element is a transistor. 10. The method for driving a liquid crystal element according to claim 1, wherein after resetting the entire surface of the pixel to a more stable state, a voltage corresponding to a display state is applied to the liquid crystal of the pixel. A method for driving a liquid crystal element, wherein writing is performed. 11. A display period and a non-display period are provided in each frame for liquid crystal of each pixel, and a signal voltage having a polarity inverted from that of a signal voltage applied in the display period is applied in the non-display period. 11. The method for driving a liquid crystal element according to item 10. 12. The method of driving a liquid crystal element according to claim 10, wherein at least some of the pixels perform display in a non-drive state by removing an applied voltage after writing.