JPS62223729A - Method for driving ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To prevent the display surface of an element from flickering at the time of writing and to enhance the display quality by converting a ferroelectric liq. crystal in a spray oriented state into that in a uniform oriented state simultaneously with the beginning of writing. CONSTITUTION:When a ferroelectric liq. crystal is in a spray oriented state, liq. crystal molecules adjacent to a substrate 41a are oriented on the right of the normal line of the central axis of a vertical layer and liq. crystal molecules adjacent to a substrate 41b are oriented on the left of the normal line. The ferroelectric liq. crystal in the spray oriented state can be converted into that in a uniform oriented state by applying AC voltage before or during driving. At the time of writing in a liq. crystal device provided with a matrix electrode having scanning lines and data lines by line sequential system, AC voltage Vac satisfying a formula Vthac<=Vac<Vth is applied to elements on the unselected scanning lines. In the formula, Vth is the switching threshold value at the time of driving of the ferroelectric liq. crystal between two kinds of stable state, and Vthac is the effective value of AC voltage converting a dual- or multi-stable state in the spray oriented state into that in the uniform oriented state.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for driving a ferroelectric liquid crystal element, and more particularly to a method for driving a ferroelectric liquid crystal element with improved display and driving characteristics.

[Conventional technology]

Examples of conventional liquid crystal elements include M-Shut (M,
5chadt) and double urn Helfrich (W, He
1frich) “Applied Physics Letters°1”
etters”) Volume 18, No. 4 (February 1, 1971
"Voltage Dependent Optical and Activities of a Twisted Nematic Liquid Crystal"
ptical Activity of aTw
isted Nematic LiquidC
Twisted Nematic shown in rystal”
One that uses liquid crystal is known. This TN liquid crystal has a problem in that crosstalk occurs during time-division driving using a matrix electrode structure with a high pixel density, so the number of pixels is limited.

A display element is known in which a switching element such as an FJ or a film transistor is connected to each pixel, and each pixel is switched. However, the process of forming the thin film transistor on the substrate is extremely complicated. There is a problem that it is difficult to create a display element.

Clark (C1
ark) and Lagauer (Lage rwa l 1)
) (#Open and Close Publication No. 56-107216, U.S. Patent No. 43-67924, etc.), liquid crystals having bistability are generally chiral smectic C phase (AmC) k) or H phase. (SmH)k) is used. This liquid crystal has a bistable state with respect to an electric field, and therefore, unlike the optical modulation element used in the above-mentioned TN type liquid crystal, the liquid crystal is oriented in one optically stable state for one electric field vector. However, the liquid crystal is oriented in the other optically stable state with respect to the other electric field vector. Furthermore, this type of liquid crystal has the property of very quickly taking one of the above two stable states in response to an applied electric field, and maintaining that state when no electric field is applied. By utilizing such properties, many of the problems of the conventional TN type device described above can be significantly improved.

[Problem that the invention seeks to solve]

The biggest problem in forming devices using liquid crystals with such ferroelectric properties is that the layer having the SmC* phase is aligned perpendicularly to the substrate surface, and the liquid crystal molecules are aligned approximately parallel to the substrate surface. It is difficult to form highly oriented monodomain cells.

That is, when forming the 5rnC* heptadomain, an alignment method has been adopted in which the vertical layer of SmC)H is aligned along the normal direction by a uniaxial alignment treatment applied to the substrate. SmC)k whose orientation was controlled by such an orientation method had a tendency to be oriented in the above-mentioned spray orientation state, so it was in a bistable state or a multistable state with a tilt angle θ considerably smaller than the maximum tilt angle 0.

A ferroelectric liquid crystal in a bistable or multistable state with a small tilt angle θ has a maximum tilt angle of 0 during switching, but returns to the tilt angle Q in the memory state after switching, so the optical properties also change accordingly. It exhibits maximum transmittance during switching, but the transmittance gradually decreases under subsequent memory conditions. Therefore, when a ferroelectric liquid crystal in a splay alignment state is applied to a line-sequential writing method, the screen becomes bright for a moment before writing, which causes flickering on the display screen, and the low transmittance under the memory state causes a dark display screen. It is the cause of

[Means for solving the problem] and [effect] Therefore,
An object of the present invention is to provide a method for driving a ferroelectric liquid crystal element that solves the above-mentioned problems, and more specifically, for driving a ferroelectric liquid crystal element in which ferroelectric liquid crystal is driven in a unifold alignment state. It is about providing law.

That is, the present invention provides a ferroelectric liquid crystal that has a matrix electrode forming a pixel at the intersection of a scanning line and a data line, and a ferroelectric liquid crystal that exhibits a bistable state or a multistable state when no electric field is applied. In the driving method of a dielectric liquid crystal element, the voltage required to switch the ferroelectric liquid crystal from one stable state to the other stable state is defined as a switching threshold Vth, and the bistable state of the ferroelectric liquid crystal when no electric field is applied is set as the switching threshold Vth. Necessary alternating current voltage to convert one state or multistable state to another bistable state or multistable state: When Vth is the alternating voltage applied to the pixels on the scanning line that is not selected among the scanning lines. It is characterized by a method for driving a ferroelectric liquid crystal element. In a preferred embodiment of the present invention, a, when no electric field is applied, the orientation is in one of a bistable or multistable orientation state having at least a first stable state and a second stable state; A liquid crystal cell in which a ferroelectric liquid crystal is arranged between a pair of substrates; b) a ferroelectric liquid crystal arranged in a first stable state in a third cell;
and means for applying an alternating current electric field to orient the ferroelectric liquid crystal in a fourth stable state when the ferroelectric liquid crystal is oriented in a second stable state.

C. matrix electrode means; d. means for applying a scan selection signal to the matrix electrode means; and means for applying an information signal having a voltage peak value greater than the effective value of the AC electric field in synchronization with the scan selection signal. .

e. means for detecting an optical difference between a light beam passing through a ferroelectric liquid crystal oriented in a third stable orientation and a light beam passing through a ferroelectric liquid crystal oriented in a fourth stable orientation; This is achieved by

(Example) The present invention will be described in further detail below with reference to the drawings as necessary.

A particularly suitable liquid crystal material for use in the present invention is a chiral smectic liquid crystal having ferroelectricity. Specifically, chiral smectic C phase (Sm
c*), chiral smectic C phase (SmG) k), chiral smectic F phase (SmF) k), chiral smectic I phase (SmI*) or chiral smectic H
(SmH*) liquid crystal can be used.

For more information on ferroelectric liquid crystals, see, for example, "Les Journals de Fijic L'Etre°"("LE
JOtTRNAL DE PHYSIQUE
LETTRE") 36 (L-69) 1975 "Ferroelectric Liquid Crystal J (F
erroelectricLiquid Cryst
als;”Applied Physics Letters (”
Applied Physics Letters
”) 36 (11) 1980 “Submicro Φ 2nd Bi-stipple Electro-optic Switching in Liquid Meeting Ristals J (rsub
microSecondBistable
eElectrooptic Switching
in L Iq u i dCyst
als”);”Solid Objects Volume 6 (141) 1981 r
"LCD" etc.

Specific examples of liquid crystal compounds that can be used in the present invention include p-decyloxybenzylidene-p'-amino-2-methylbrucinname (DOBAMBC), p-hexyloxybenzylidene-p'-amino-2-chloro Propyl cinnamate (HOBACPC), P-decyloxybenzylidene-p'-amino-2-methylbutyl-α-cyanosine-j-)-1 (DOBAMBCC), p-tetradecyloxybenzylidene-p'-amino-2-methylbutyl -α-cyanosinname) (TDOBAM BCC)
, P-cutyloxybenzylidene-p'-7 minnow 2
-Methylbutyl-α-chlorocinnamate (OOBAM
BCC), P-octyloxybenzylidene-p'-amino-2-methylbutyl-α-methylcinnamate, 4
．． 4'-7 Soxycinnamic acid bis(2-methylbutyl) ester 4-0-(2-methyl)-butylresorsilitin-4'-octylaniline (MBRA
8), 4-(2'-methylbutyl)phenyl-4
'-Octyloxyphenyl-4-carboxylate, 4-hexyloxyphenyl-4-(2'-methylbutyl)biphenyl-4'-rupoxylate, 4-octyloxyphenyl-4-(2'-methylbutyl)biphenyl- 4'-carboxylate, 4-hebutylphenyl-4-(4-methylhexyl)biphenyl-4'-
Rupoxylate, 4-(2'-methylbutyl)phenyl-4-(47-methylhexyl)biphenyl-4'-
Examples include hydroxylupoxylate and others used in the examples below. Particularly preferred ferroelectric liquid crystals include those exhibiting a cholesteric phase at high temperatures; for example, phenyl ester liquid crystals exhibiting a phase transition temperature listed in the Examples below may be used.

When constructing an element using these materials, the element can be supported by a copper block or the like in which a heater is embedded, if necessary, in order to maintain the temperature at which the liquid crystal compound becomes a desired phase.

FIG. 4 schematically depicts an example of a cell for explaining the operation of a ferroelectric liquid crystal. Hereinafter, S as the desired phase
This will be explained using mC)k as an example.

41a and 1b are I n203 or ITO (Ind
It is a substrate (glass plate) coated with a transparent electrode made of a thin film such as ium-Tin oxide), between which a liquid crystal molecular layer 42 is oriented perpendicularly to the glass surface.
mC) IC phase liquid crystal is sealed. A thick line 43 represents a liquid crystal molecule, and the liquid crystal molecule 43 continuously forms a helical structure in the plane direction of the substrate. The angle formed between the central axis 45 of this helical structure and the axial direction of the liquid crystal molecules 43 is expressed as ■. This liquid crystal molecule 43 has a dipole moment (on P) 44 in a direction perpendicular to the molecule.

When a voltage equal to or higher than a certain threshold is applied between the electrodes on the substrates 41a and 41b, the helical structure of the liquid crystal molecules 43 is unraveled, and the liquid crystal molecules 43 are aligned so that all dipole moments (P) 44 are oriented in the direction of the electric field. You can change direction.

The liquid crystal molecules 43 have an elongated shape and exhibit refractive index anisotropy in the long axis direction and the short axis direction. Therefore, for example, if crossed nicol polarizers are placed above and below the glass surface, the polarizer will change depending on the voltage applied polarity. It is easily understood that this results in a liquid crystal optical element whose optical properties change.

The liquid crystal cell preferably used in the liquid crystal optical element of the present invention can have a size of, for example, 10 l or less. As the liquid crystal layer becomes thinner, the helical structure of the liquid crystal molecules unwinds even when no electric field is applied, as shown in Figure 5.
It has a non-helical structure, and its dipole moment (Pa or Pb) is either upward (54a) or downward (54b). The molecular axis of this liquid crystal molecular axis 53a and 53
The angle that is 1/2 of the angle formed by b is called the tilt angle (■),
This tilt angle (0) is equal to 1/2 of the apex angle formed by the cone when it takes a spiral structure, and corresponds to the maximum tilt angle that can be lowered. Voltage applying means 51a and 51b apply electric fields Ea or Eb of different polarity above a certain threshold to such cells.
When given by Orient in one direction.

As mentioned earlier, there are two advantages to using such ferroelectricity as a liquid crystal optical element.

The first is that the response speed is extremely fast, and the second is that the alignment of liquid crystal molecules has bistability or multistability. To further explain the second point, for example, with reference to FIG.
3a, and this state is stable even when the electric field is turned off. Furthermore, when an electric field Eb in the opposite direction is applied, the liquid crystal molecules are aligned to another stable orientation 53b and the orientation of the molecules is changed, but they remain in this state even after the electric field is turned off.

In order to effectively realize such fast response speed and bistability or multistability, it is preferable that the cell thickness be as thin as possible.

By the way, in manufacturing a liquid crystal cell with a larger area than before,
A method is known in which a substrate surface is subjected to uniaxial alignment treatment. Examples of the uniaxial alignment treatment include a method of rubbing the substrate surface in one direction with velvet, cloth, or paper, and a method of obliquely depositing SiO or SiO2 on the substrate surface.

However, it has been found that when the above-mentioned rubbing method or oblique evaporation method is applied as a method for controlling the orientation of ferroelectric liquid crystal, bistable or multistable orientation is formed in the spray orientation state shown in FIG. FIG. 8 is a cross-sectional view of the vertical layer 42 in FIG.
4b onto the vertical layer (C-director), and 8
2 represents the tip of the liquid crystal molecule 54a or 54b, and 83
represents spontaneous polarization. That is, according to FIG. 8, the liquid crystal molecules adjacent to the substrate 41a are oriented to the right with respect to the normal to the central axis of the vertical layer (in the direction perpendicular to the plane of the paper), but the liquid crystal molecules adjacent to the substrate 4Lb are oriented in the vertical layer. It is oriented to the left with respect to the normal to the central axis of. When an electric field higher than the threshold voltage is applied to the ferroelectric liquid crystal in the splay alignment state, the liquid crystal molecules align at the maximum tilt angle ■, but after the electric field is removed, the tilt angle gradually decreases and the ferroelectric liquid crystal in the splay alignment state becomes oriented. The tilt angle θ returns to .

FIG. 7 schematically shows the alignment state of the liquid crystal molecules described above, and is a view seen from above the substrate surface 41a.

In the figure, 70 corresponds to the direction of uniaxial alignment treatment, that is, the rubbing direction in this example. In the SmA phase, liquid crystal molecules are oriented with the average molecular axis direction 71 of the liquid crystal coinciding with the rubbing direction 70. In the SmC* phase, the average molecular axis direction of liquid crystal molecules is inclined in the direction 72a, and the rubbing direction 70 and the average molecular axis direction 72a of SmC)k are as follows.
The angle θ is formed and the first stable orientation state is achieved. When a voltage is applied to the upper and lower substrates in this state, the average molecular axis direction of the liquid crystal molecules of SmC* changes to an angle larger than the angle θ,
A third stable orientation state saturated at an angle of 0 is assumed. This゛
The average molecular axis direction at the time is 73a.

Next, when the voltage is returned to zero, the liquid crystal molecules return to the original state in the first molecular axis direction 72a.

Therefore, in the state of the first molecular axis direction 72a, the liquid crystal molecules have memory properties. Moreover, the molecular axis direction 72a
When a voltage in the opposite direction is applied in the state of 73b. Then, when the voltage is returned to zero again, the liquid crystal molecules settle into a second stable alignment state forming an angle θ in the average molecular axis direction 72b.

Therefore, the present inventors have discovered that by applying an alternating current voltage to the ferroelectric liquid crystal in the spray alignment state as described above beforehand or during driving, the uniform alignment state shown in FIG. 9 can be achieved. . In particular, in a preferred embodiment of the present invention, when a liquid crystal device having a matrix electrode formed of scanning lines and data lines is written in a line-sequential writing method, the ferroelectric liquid crystal is changed from a first stable state to a second stable state. Vt is the voltage required to reverse the state or from the second stable state to the first stable state, that is, the switching threshold during driving.
h, and the AC voltage required to convert the bistable state or multistable state under the splay orientation state shown in FIG. 8 to the bistable state or multistable state under the uniform orientation state shown in FIG. 9. When the effective value (hereinafter referred to as rms value) is applied, a certain AC voltage Vac is applied to unselected sections in the matrix electrode.

FIG. 9 is a cross-sectional view schematically showing the uniform orientation state used in the present invention. According to FIG. 9, the substrate 41a
The liquid crystal molecules 54a or 54b adjacent to the substrate 41b are oriented to the left or right, respectively, with respect to the normal to the central axis of the vertical layer, and similarly, the liquid crystal molecules 54a or 54b adjacent to the substrate 41b are also oriented to the normal to the central axis of the vertical layer. On the other hand, the projection axes of the respective liquid crystal molecular axes adjacent to both substrates, which are oriented on the left or right side and are adjacent to both substrates, are parallel to each other.

FIGS. 6A and 6B show an embodiment of a liquid crystal element used in the present invention. FIG. 6(A) is a plan view of the liquid crystal element of the present invention, and FIG. 6(B) is a sectional view taken along the line AN.

In the cell structure 60 shown in FIG. 6, a pair of substrates 61a and 61b made of glass plates, plastic plates, etc. are held at a predetermined distance by a spacer 64, and are bonded with an adhesive 66 to seal the pair of substrates. Furthermore, a plurality of transparent electrodes 62 are provided on the substrate 61a.
A group of electrodes (for example, a group of electrodes for applying a scanning voltage in a matrix electrode structure) is formed in a predetermined pattern such as a strip pattern.

On the substrate 61b, an electrode group (for example, a signal voltage application electrode group in a matrix electrode structure) is formed, which is made up of a plurality of transparent electrodes 62b intersecting with the transparent electrode 62 described above.

The substrate 61b provided with such a transparent electrode 62b may be made of, for example, silicon oxide, silicon dioxide, aluminum oxide, zirconia, magnesium fluoride, cerium oxide, cerium fluoride, silicon nitride, silicon carbide, boron nitride, etc. inorganic insulating materials and organic materials such as polyvinyl alcohol, polyimide, polyamideimide, polyesterimide, polyparaxylylene, polyester, polycarbonate, polyvinyl acetal, polyvinyl chloride, polyamide, polystyrene, cellulose resin, melamine resin, urea resin and acrylic resin. Although the alignment control film 65 may be formed using an insulating material, the alignment control film 65 formed from polyvinyl alcohol is particularly preferable.

This orientation control film 65 is formed by coating the above-mentioned inorganic insulating material or organic insulating material, and then coating the surface with velvet.
Obtained by rubbing in one direction with cloth or paper.

In another preferred embodiment of the invention, SiO or S i 0
The alignment control film 65 can be obtained by forming a film of an inorganic insulating material such as No. 2 on the substrate 61b by oblique vapor deposition.

The above-mentioned alignment control film 65 preferably functions as an insulating film at the same time, and for this reason, the thickness of the alignment control film 65 is generally 50 to 1K, preferably 100 to 100K.
It can be set to a range of 0 people. This insulating film also has the advantage of being able to prevent the generation of current caused by trace amounts of impurities contained in the liquid crystal layer 63, and therefore does not deteriorate the liquid crystal compound even if the operation is repeated.

Further, in the liquid crystal element of the present invention, the above-mentioned alignment control lN5i6
5 can be provided on the other substrate 61a.

The liquid crystal layer 63 in the cell structure 60 shown in FIG.
It can be a C-tree. Further, the thickness of the liquid crystal layer 63 is sufficiently thin, and the liquid crystal molecules do not have a helical structure.

In such a cell structure 60, polarizers 67 and 68 in a crossed Nicol state are arranged on both sides of the substrates 61a and stb, respectively, and the polarizers 67 and 68 polarize the electrode 62.
Optical modulation when a voltage is applied between a and 62b can be detected.

Next, regarding the method for producing the liquid crystal element of the present invention, rcslo, an ester liquid crystal manufactured by Chisso Corporation, will be used as a liquid crystal material.
This will be explained using l (product name) J as an example.

This liquid crystal material exhibits the following phase transition during the cooling process.

I so-+ Ch-+ S mA-+ SmC-
+ Crysta191℃ 78℃ 58℃
0°C (Iso: Tokichi phase, Ch: cholesteric phase.

SmA (smectic A phase) First, the cell structure 60 in which the above-mentioned ester-based liquid crystal is sealed is set in a heating case (not shown) so that the entire cell 60 is uniformly heated.

Next, the temperature at which the compound in the cell 60 becomes the tokiyoshi phase (approximately 95
Heat to 10°F (°C). Thereafter, the temperature of the heating case is lowered, and the compound in the isokyoshi phase in the cell 60 is transferred to the temperature lowering process. During this temperature raising process, the compound in the isotokyoshi phase undergoes a phase transition to the cholesteric phase with a Grandshuan structure at approximately 91"C, and when the temperature continues to decrease roughly, the phase transitions from the cholesteric phase to SmA, which is a uniaxial hethoptic phase, at approximately 78°C. At this time, the liquid crystal molecular axes of SmA are aligned in the rubbing direction.

Thereafter, this SmA undergoes a phase transition to SmC* in the process of cooling, thereby obtaining monodomen SmC* having a non-helical structure with a cell thickness of about 6 gm or less, for example.

The angle between the uniaxial processing direction and the average molecular axis direction in the SmC* phase of the above-mentioned ester compound liquid crystal, that is, the tilt angle 0, is approximately 8° at room temperature.
The average molecular axis direction (f8
The value of 1), that is, the maximum tilt angle (2), was approximately 18'', although it differed slightly depending on the thickness of the liquid crystal layer.

Now, as described above, by applying an alternating current electric field parallel to the liquid crystal molecular layer 12 in the smectic phase to the liquid crystal cell having the spray alignment state, the first and second stable alignment states can be changed to the third and fourth stable alignment states, respectively. It has become possible to "convert" to a stable orientation state. This phenomenon occurs by applying a predetermined alternating current electric field to untwist the liquid crystal molecules in the thickness direction of the liquid crystal cell shown in FIGS. It is believed that a "conversion" between two types of bistable states, splayed orientation and uniform orientation, occurred to result in a bistable or multistable state.

Therefore, the angle (θ') of the average molecular axis direction in the absence of an electric field after application of an alternating electric field was approximately equal to e, and was approximately 18''.

At this time, the polarization axis of one of the crossed Nicol polarizers is in the average molecular axis direction 63a of the third stable orientation state or the average molecular axis direction 63b of the fourth stable orientation state shown in FIG. Matched.

Next, the alternating current electric field that causes the "conversion" between these two types of bistable states will be explained.

The present inventors investigated the relationship between the frequency and voltage value of the applied alternating current electric field and changes in the orientation state, and found that the above-mentioned "conversion" (
The alternating current electric field that causes the transition from bistability or multistability in the splayed orientation state to bistability or multistability in the uniform orientation state does not depend much on frequency, and ranges from several Hz to several Hz. It was found that in the KHz frequency region, it strongly depends on the effective voltage value Vac of the AC electric field, and that the above-mentioned "conversion" occurs by applying an AC' electric field with an effective voltage Vac above the uniformization threshold. .

In this example, when a rectangular wave alternating current electric field with a frequency of IKHz, a voltage value of ±3V, and a duty of -1/2 (therefore, the effective value is 3V) was applied for about 1 minute, "conversion" occurred, and at lower voltage values, Since no conversion occurred, the aforementioned effective voltage threshold (threshold) was approximately 3 ■. Of course, conversion occurred even at effective values higher than this.

Furthermore, it has been found that even if this uniform orientation state is achieved, the original splayed orientation state is returned again if the material is heated once again to the isoyoshi phase and then slowly cooled again from the ch phase to the SmA phase to the SmC* phase. Therefore, the uniform orientation state is considered to be a bistable state with higher energy than the splay orientation state, although the energy of the entire system is a minimum value, but not the minimum value. Therefore, the uniform orientation state is not a permanently maintained bistable state;
It can be said that the state will eventually return to the spray state. The time to return from the uniform orientation to the spray orientation was several hours to several weeks when left unattended.

On the other hand, the switching threshold between the bistable states in each bistable state is determined by the pulse width and voltage value of the applied pulse required for switching between the bistable states before conversion, that is, in the spray state.
' was about 3V at 1m5eC.

On the other hand, in the bistable state in the uniform orientation state, the switching threshold Vth is somewhat higher than that in the splayed orientation state, and in this example was about 10 V at 1 m5ec.

Therefore, in a preferred embodiment of the present invention, the uniformization threshold Vth is preferably set to a value smaller than the switching threshold Vth in the uniform orientation state, and particularly preferably to a value equal to or less than the value of the write pulse 3v1 applied to the pixel.

In the effective values described herein, the voltage is defined as v (t) effective value? = [+f'roV2 (t) d t'2] (where t represents time.

) In a preferred embodiment of the invention, the alternating current voltage Vac is
The repair duty square wave shown in the figure can be used. The effective value of Vac at this time is the effective value? = [(v2 T+
v2 T)]' = vT o”T
.

becomes.

FIG. 2 is a matrix circuit diagram of scanning electrodes (scanning lines) and display electrodes (data lines), and FIG. 3 is a diagram showing an example of display of pixels corresponding to each intersection in FIG. 2. Incidentally, FIG. 2 shows the matrix electrodes in the case of actual multiplex driving, and in the figure, 81 to S5 indicate scanning lines, and 1 to 5 indicate data lines. In addition, the pixels in the shaded area in Figure 3 are "black",
Pixels shown in white correspond to each writing state of "white".

FIG. 1 shows a timing chart when the matrix circuit shown in FIG. 2 writes the pixels shown in FIG. In Figure 1, ΔT
indicates the write pulse width, and when writing, it is assumed that white is written with an electric field in ten directions, and black is written with an electric field in one direction. Further, the write pulse (pulse exceeding the switching threshold) has a pulse width ΔT and a peak value ±3v1. Furthermore, let A represent the voltage waveform applied to pixel A in FIG.

When writing the pixels shown in FIG. 3 by first clearing the pixels on the scanning line to white and then applying a black write signal to the selected pixels on the data line (line clear line writing), such data By applying the "black" signal to the line, it is possible to apply an alternating current voltage Vac having a voltage peak value v1 to the pixels on the unselected scanning line.

Therefore, in the driving method of the present invention, pixels in the writing screen excluding the writing line always have an effective value equal to or higher than the uniformization threshold, and a value Ω smaller than the switching threshold.
Since an alternating current voltage is applied, the ferroelectric liquid crystal can switch to a uniform alignment state at the same time as writing starts, so there is no flickering on the screen that occurs during writing, and it has a high transmittance. A "white" display state can be achieved.

Further, in the driving method of the present invention, in synchronization with the scanning selection signal,
The “black” signal applied to the data line is +V as shown in Figure 1.
The "white" signal can be an alternating waveform signal of -■ and +V.

〔Effect of the invention〕

According to the present invention, the ferroelectric liquid crystal in the Sovrei alignment state can be converted to the ferroelectric liquid crystal in the uniform alignment state at the same time as writing starts, thereby eliminating screen flickering during writing and providing high transmittance. A clear "white" display state can be formed, and the display quality can be significantly improved.

[Brief explanation of drawings]

FIG. 1 is a timing chart of driving waveforms used in the driving method of the present invention. FIG. 2 is a schematic diagram showing the matrix electrode used in the present invention. FIG. 3 is an explanatory diagram showing a display example of pixels written by the method of the present invention. FIG. 4 is a perspective view of an element using ferroelectric smectic liquid crystal that forms a helical structure when no electric field is applied. FIG. 5 is a perspective view of an element using a ferroelectric smectic liquid crystal that forms a non-helical structure when an electric field is applied, which is used in the present invention. - Fig. 6(A) is a plan view of the ferroelectric liquid crystal element used in the present invention, and Fig. 6(CB) is a cross-sectional view thereof. 7th
The figure is a plan view schematically showing the direction of stable alignment of liquid crystal molecules and the direction of uniaxial alignment treatment. FIG. 8 is a cross-sectional view schematically showing the spray orientation state. FIG. 9 is a cross-sectional view schematically showing the uniform orientation state. FIG. 10 is a waveform diagram of AC voltage Vac used in the method of the present invention.

Claims (8)

[Claims] (1) A ferroelectric liquid crystal that has a matrix electrode that forms a pixel at the intersection of a scanning line and a data line, and a ferroelectric liquid crystal that produces a bistable or multistable state when no electric field is applied. In the device driving method, the voltage required to switch the ferroelectric liquid crystal from one stable state to the other stable state is set as a switching threshold Vth, and the ferroelectric liquid crystal is in a bistable state or multistable state when no electric field is applied. When the effective value of the alternating current voltage required to convert from a stable state to another bistable state or multistable state is ＾a＾cth, the alternating current voltage applied to the pixels on the scanning line that is not selected among the scanning lines. A method for driving a ferroelectric liquid crystal element, characterized in that the effective value Vac of is set to ■^a^cth≦Vac<Vth. (2) The driving method according to claim 1, wherein the AC voltage is a voltage applied from a data line. (3) The ■^a^ct is applied to the data line in synchronization with the scanning signal applied to the selected scanning line among the scanning lines.
2. The driving method according to claim 1, wherein an alternating waveform voltage signal of h or more is applied. (4) The driving method according to claim 3, wherein the alternating waveform voltage is an alternating current voltage. (5) The angle formed between one stable state of the ferroelectric liquid crystal and the other stable state that occurs when or after the application of the AC voltage is the same as the angle between one stable state and the other stable state of the ferroelectric liquid crystal that occur when no electric field is applied. The driving method according to claim 1, wherein the angle is larger than the angle formed with the state. (6) The driving method according to claim 1, wherein the ferroelectric liquid crystal is a liquid crystal in which a bistable state or a multistable state is formed in the presence of a substrate subjected to a uniaxial alignment treatment. (7) The driving method according to claim 6, wherein the uniaxial alignment treatment is a rubbing treatment. (8) The driving method according to claim 1, wherein the ferroelectric liquid crystal is a chiral smectic liquid crystal.