DE69133146T2 - liquid crystal device - Google Patents

Abstract

Disclosed is a liquid crystal element comprising a liquid crystal exhibiting spontaneous polarization, a pair of electrode substrates for sandwiching said liquid crystal therebetween, characterized in that insulating layers are formed between said electrode substrates and said liquid crystal, wherein a spontaneous polarization Ps value of said liquid crystal, an interelectrode composite capacitance Ci of said insulation layers, and a voltage threshold value Vth of optical response of said liquid crystal in said liquid crystal element satisfy the following condition: <MATH> <IMAGE>

Description

GENERAL BACKGROUND ART Field of the Invention

The present invention relates rely on a liquid crystal device, which shows spontaneous polarization, and in particular on one Liquid crystal device, which is a ferroelectric liquid crystal (FLC) used.

The status of technology

A ferroelectric liquid crystal (FLC) as a liquid crystal, that shows the spontaneous polarization has because of the advantages like for example high-speed reaction and good storage properties, size Attracted attention, and has been developed forcefully, around optical devices and the like. Goals using the above advantages are optical shutter arrangements, a high resolution Display unit with simple matrix control, an optical device for high-resolution recording in connection with a photoconductive body. In addition, the ferroelectric liquid crystal expects a moving picture through an active matrix control using thin film transistors (TFT).

The European patent application EP 294 852 A2 discloses a liquid crystal device of the type indicated in the preamble of claim 1. In the prior art device, bistability was evaluated by applying a single polarity to an alternating polarity.

When driving an FLC one finds Generally the following problems are the result of research which were carried out by the local inventors.

One of the problems is the rise the response speed of the liquid crystal when a DC component (DC component) is continuously applied to the FLC over a long period, and for the following reason. It is believed that the establishment of internal ions in liquid crystal is induced to form an electric field.

To solve this problem, the local strikes Applicant for eliminating a DC component an additional Impulse. Because about it In addition, an FLC shows spontaneous polarization, becomes an electrical one Field formed by internal ions that correspond to this spontaneous Polarization are localized, and a desired image gradation becomes unstable. It has been found that hysteresis with an optical response to an external voltage value occurs (applied voltage value).

The phenomenon occurring after the application of a reset pulse and a write pulse which is continuously applied to the FLC with a drive frequency of approximately a television frequency (60 Hz) is shown in FIG 20 to 22 described.

In terms of the problems that were identified in the above investigations, the local ones Inventors conducted additional extensive detailed studies to in a stable way a gradation (graded display) at a To achieve television frequency of optical response in the FLC.

SUMMARY THE INVENTION

It is a task of the present Invention, a liquid crystal device to create that is suitable for graded display.

Another task of the present Invention is a liquid crystal device to create that using an improved tiered display both an active matrix control using TFT as well as a liquid crystal has spontaneous polarization, such as a ferroelectric liquid crystal.

This object is achieved with the characterizing features of claim 1 solved.

SHORT DESCRIPTION THE DRAWING

1 (a) to 1 (e) are waveform tables of drive signals used in accordance with the present invention;

2A Fig. 4 is a cross-sectional view of a cell used in the present invention;

2 B is an equivalent circuit diagram of the cell;

3 to 5C are diagrams showing polarization states of the cell according to the present invention;

6A to 6C are waveform charts of drive signals used in the present invention;

7 Fig. 4 is an equivalent circuit diagram showing a polarization state of the cell used in the present invention;

8th Fig. 14 is a waveform chart showing drive signals used in the cell according to the present invention;

9 Fig. 4 is an equivalent circuit diagram showing a polarization state of the cell used in the present invention;

10 and 11 FIG. 14 are views showing changes in response time after continuously applying a DC component of about 0.3 V as V _SX at a 44 Hz period;

12 and 13 are waveform charts showing drive signals used in the present invention;

14 is a perspective view of the FLC;

15 is a block diagram of an apparatus according to the present invention;

16 (a) to 16 (d) are waveform charts of drive signals used in the present invention;

17 is a top view of a flat panel display;

18A and 18B and 19A and 19B are views showing polarization states of the cell according to the present invention;

20 Fig. 11 is a graph for explaining a VT curve and hysteresis instability obtained after a sustained voltage application at a 60 Hz period;

20 Fig. 11 is a graph for explaining the instability that occurs after a constant voltage application at a 44 Hz period;

22 Fig. 11 is a graph for explaining a change in response deterioration over time after continuously applying a DC component of 0.9 V _a in the 44 Hz period; and

23 Figure 3 is a cross-sectional view of a cell according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A liquid crystal display used in the present invention is a liquid crystal flat panel display with an active matrix driving scheme as shown in FIG 17 shown. The liquid crystal device includes switching elements (TFT using thin film semiconductors such as non-crystalline silicon or polycrystalline silicon) arranged along a plurality of rows (scan lines) and a plurality of columns (data lines), first wiring lines (gate lines) that jointly connect the first terminals (gates) of the switching elements in units of rows, second wiring lines (source lines) that connect the second terminals (source) of the switching elements in units of columns, a plurality of pixel electrodes (transparent electrodes) that in units of third terminals (drains) connecting the switching elements, counter electrodes (transparent electrodes) which are arranged opposite the pixel electrodes, and a liquid crystal (chiral smectic C, H, I, G, F liquid crystal which has ferroelectric properties), which have the spontaneous polarization and are placed between the plurality of pixel electrodes and the counter electrodes.

The distance between each Pixel electrode and the associated Counter electrode is set to a minimum distance (about 5 μm or less), about oppression the formation of a helical Structure of the chiral smectic liquid crystal is sufficient prevention. In the present invention, the formation of the helical However, structure is not suppressed to become.

The thermal control can be activated during the control of the liquid crystal done to the liquid crystal within a desired one Keep temperature range.

As in the 1 (a) to 1 (e) is shown, after a reset voltage signal V _R and a recording voltage signal V _W , both of which are applied to a pixel for a predetermined period of time required to effect the optical change of the pixel, an additional voltage signal V _SX with a height corresponding to that of the recording voltage signal V _W , thereby controlling an internal electric field as described below.

For a more detailed description of the additional Voltage signal becomes the internal electric field caused by ionic Definition is generated, due to the spontaneous polarization by the DC component described below.

spontaner Polarisation (P_S) des Flüssigkristalls anzeigt, daß der Flüssigkristall dem Schwarzzustand entspricht, wird ein elektrisches Feld so erzeugt, daß die Flüssigkristallmoleküle dazu neigen, durch diese Ionenfestlegung in Schwarz anzuzeigen. 2A and 2 B show a model of a pseudo equivalent circuit of an FLC element. 3 FIG. 3 shows an ion localization diagram obtained when an external DC component is continuously applied for a longer period of time. When a positive external DC voltage is applied, it is assumed that the ion fixation that occurs through (+) and (-) in the liquid crystal layer. If at that time the direction is up

Spontaneous polarization (P _S ) of the liquid crystal indicates that the liquid crystal corresponds to the black state, an electric field is generated so that the liquid crystal molecules tend to display black by this ion fixation.

-Zustand beibehalten wird, wird die Ionenlokalsation in 4A erzielt. Wenn jedoch die Richtung der spontanen Polarisation (P_S) im "Weiß"-

-Zustand beibehalten wird, wird die Ionenortsfestlegung in 4B erzielt. Im Ergebnis erzeugen die Ionen ein elektrisches Feld. Wenn eine neue äußere Spannung V_W gleich der vorherigen Spannung angelegt wird, abhängig davon, ob der Flüssigkristallzustand im "Schwarz"- oder "Weiß"-Zustand für eine längere Zeitdauer beibehalten wird, variiert der Grad der Leichtigkeit der Änderung der Ionenortsfestlegung in den "Weiß"-Zustand, wodurch die Hysterese beim optischen Ansprechen verursacht wird. Darüber hinaus tritt Instabilität auf, wenn der gleiche Anzeigezustand wiederholt herbeigeführt wird. 4A and 4B show the ion determination by spontaneous polarization (P _S ) itself. If the direction of the spontaneous polarization (P _S ) in the "black" -

-State is maintained, the ion location in 4A achieved. However, if the direction of spontaneous polarization (P _S ) in the "white" -

-State is maintained, the ion location in 4B achieved. As a result, the ions create an electric field. When a new external voltage V _W equals the previous voltage depending on whether the liquid crystal state is maintained in the "black" or "white" state for a long period of time, the degree of ease of changing the ion location to the "white" state varies, thereby causing hysteresis in optical response is caused. In addition, instability occurs when the same display state is brought about repeatedly.

The function of the present invention will be explained in more detail with reference to the waveform of the drive signals in FIGS 1 (a) to 1 (e) described.

Although the number of ions induced by spontaneous polarization is difficult to control, the DC component can be controlled by an external voltage applied to the liquid crystal. According to the present invention, the additional voltage V _S serves as a DC component and the ion location is kept "constant" regardless of the state of spontaneous polarization P _S. The term "constant" means a total amount of ion location setting. The "constant" value can have a predetermined value or be 0. However, the "constant" value does not always have to be 0.

A method for setting the ion location as "constant" is shown in the 5A to 5C described. For example, a total amount of ion location is obviously maintained as the amount by which the in 4A shown "black" state remains set.

The ion location state of the "black" state shown in 5A , is assumed as the initial state. In this case, a control signal with an in 1 (a) shown waveform applied to the liquid crystal in advance. In order to indicate the "black" state from this state, a drive signal with an in 6A shown waveform applied to bring about the "black" state. At this time, the superimposed amount of the DC voltage by the additional voltage V _{SX may be} zero. To indicate a graded state as in 5B is shown, the ion locating state of the display to be achieved looks as in FIG 18A shown. In order to keep the entire ionization location setting amount constant in the "black" display state, one in 6a _Shown additional voltage + V _SX1 to add the ion location of 18B created. In order to bring about a "white" state, one in 6C _Shown additional _voltage + V _SX2 ( 6C ) at the total amount won in the case of the "black" display to the state of 19A (ie, the ion location determined by this display).

(wobei Δa die Abstufung am Ende des Anlegens der Spannung V_W ist und der Bedingung 0 > Δa > 1 genügt, und Ci ist die Kapazität der Isolationsschicht).The numerical control of the additional voltages V _SX1 and V _SX2 is carried out approximately according to the size of the spontaneous polarization P _S and the ambient temperature. It is advantageous if the size of the spontaneous polarization P _{S is} not set too high (ie, 10 nC / cm ² or less, and preferably 5 nC / cm ² or less) in the liquid crystal used in the present invention, since then the excessive Rise in the amplitude of the additional voltage signal V _SX can be suppressed. The numerical value for the amplitude of the _VSX1 signal _preferably falls within the range below:

(where Δa is the gradation at the end of the application of the voltage V _W and the condition 0>Δa> 1 satisfies and Ci is the capacitance of the insulation layer).

Da eine die Bewegung von Ionen in diesem abgestuften Zustand bewirkende Spannung durch die obige Beziehung angegeben ist, wenn eine externe, umgekehrte, die Ionenbewegung verursachende Spannung V_SX der Spannung angelegt wird und die geteilte Spannung

des Flüssigkristalls durch die Spannung V_SX gleich

gesetzt, wird angenommen, daß die Ionenbewegung nicht auftritt. Folglich wird die nachstehende Gleichung erfüllt:

und die Lösung kann folgendermaßen gewonnen werden:

The numerical value criterion is shown below 7 described. 7 Fig. 14 shows a measurement of a divided voltage applied to a liquid crystal layer when a terminal voltage of a liquid crystal pixel is applied to 0 V immediately after a gradation _recording voltage V _W. At this time, the liquid crystal molecules will partially return in the "black" direction and will be put in the graded state. When the ratio of the "white" state is set as Δa, the divided voltage of the liquid crystal layer is as follows:

Since a voltage causing the movement of ions in this graded state is given by the above relationship when an external, reverse voltage V _SX causing the ion movement is applied to the voltage and the divided voltage

of the liquid crystal by the voltage V _SX equal

is set, it is assumed that the ion movement does not occur. As a result, the following equation is satisfied:

and the solution can be obtained as follows:

For example, if P _S and Ci are 5 nC / cm ² and 20 nF / cm ² , respectively, the voltage V _SX can be obtained approximately equal to 0.5 V, even in the completely "white" state.

If the voltage V _{SX is} within a range of 0 V to 0.5 V with the in 8th shown waveform is applied according to the graded state, the original ion location state can be kept constant.

If the voltage V _SX is kept applied as a DC component corresponding to the graded state of each image until the next image is repeated, the ion location can be kept constant. As a result, the instability that may be caused by the ion location can be eliminated.

Second, the DC component also as a "white" preservation voltage of the liquid crystal serves, a high response speed of the liquid crystal can be achieved and come to terms with moving images.

10 and 11 show an optical response test that was improved by the above driving method.

der zusätzlichen Spannung vorzugsweise stabilisiert, wie zuvor beschrieben. Nach diesem Ansteuerverfahren wird der Maximalwert der Spannung V_SX vorzugsweise folgendermaßen eingestellt:

Die vorliegende Erfindung schlägt eine Flüssigkristallvorrichtung auf der Grundlage des Herausfindens vor, daß der obige Zustand zum Ionenausgleich im wesentlichen erfüllt sein muß.In order to stabilize the ion location setting condition due to the display condition, the peak value is

the additional voltage is preferably stabilized as previously described. According to this control method, the maximum value of the voltage V _{SX is} preferably set as follows:

The present invention proposes a liquid crystal device based on the finding that the above condition for ion balance must be substantially satisfied.

As a condition for an in 23 The liquid crystal element structure shown must the effective strength of the spontaneous polarization P _{S of} the liquid crystal used and the composite capacitance Ci of the alignment layer as important components forming the element, or an insulation layer portion including an additional insulation layer in the element satisfy the above permanent relationship, whereby an im substantially stable gradation control is executed.

From the qualitative point of view, the composite capacitance Ci is preferably set high, and the spontaneous polarization value P _{S of} the liquid crystal used is preferably set to a small value.

In an experiment carried out by the inventors, the insulation layers formed on the top and bottom electrodes of each cell to avoid electrical short circuits are such that an oxide mixture (Ti-SiO _X ) of Ti (titanium) and Si (silicon) as Layer is placed on the electrodes and baked to form thin films about 1000 Å thick. A 200 Å thick polyimide alignment layer is formed on this insulating film and baked. The resulting structure is rubbed to maximize the composite capacitance Ci. In this case the capacitance Ci can have approximately several 10 nF / cm ² . To further increase the capacitance Ci, the physical film thickness must be reduced and a layer with a high dielectric constant must be selected.

The strength of the spontaneous polarization P _{S of} the liquid crystal is at most 10 nC / cm ² when it is evaluated by a reverse polarization current. This thickness is preferably 5 nC / cm ² or less. As a result, the value 2 P _S / Ci is set to about 0.5 V or lower. In order to increase the value Vth, the viscosity of the liquid crystal is adjusted. However, increasing the drive voltage is generally disadvantageous.

In this case the tension Vth is set as a voltage application limit, which is an optical change essentially not within a period of the tiered display is determined when the element is actuated.

A control method of the element will be described below.

The above control method can not every gradation level when building an image by one control simple matrix. In principle, however, this control method to an arrangement for driving pixels independently of one another are used, such as when driving an optical single-bit shutter or a 7-segment display or as with the active matrix control of TFT (thin film transistors).

Current drive waveforms at the active TFT matrix control are described in detail below.

12 is a time table with activated control waveforms.

A reset signal V _R for setting a pixel in the "black" state is applied and a time voltage for sufficiently setting the pixel in the "black" state using the non-conducting properties of the TFT is also used (V _R in 12 ). A recording voltage V _W is applied, and this gradation level voltage V _W is applied for a predetermined period of time corresponding to the same open characteristics. A ground signal V _E is then applied to the pixels placed. During the application of the ground voltage V _E , the gradation permeability changes, but can be stabilized by the following additional signal.

The additional voltage signal V _SX is then applied to the pixel. This signal can be selected from V _SX1 and V _SX2 according to a desired graded display state. As with the voltages V _SX1 and V _SX2 in the display _{image serving} as the vertical _{scanning period} in the gradation transfer state, the additional voltage signal is applied as a voltage _{value having} an appropriate DC voltage. It should be noted that, with a sufficiently high applied voltage as the reset voltage, the voltages V _SX1 and V _SX2 can be _applied as values which _correspond to voltages for effecting the DC voltage components for the gradation level according to the voltage difference between the voltages V _R and V _W during the image period be compensated.

The target DC voltage value of this additional voltage signal V _SX is selected according to the strength of the spontaneous polarization P _{S of} the liquid crystal used. The target value of the DC component value is specified with V _DC = 2P _S Δa / Ci according to the ratio Δa of the "white" state if the maximum permeability is fixed at "1". For example, if P _S is 5 nC / cm ² and the capacitance of the insulation layers forming the liquid crystal cell is about 20 nF / cm ² , the voltage V _W for recording the entire "white" state is set to about 0.5 V. , In the graded display state, a DC voltage component of approximately 0.5 V or less is superimposed on the additional voltage signal.

The recording voltage V _W or the recording voltage signal V _W is a signal for determining the optical state of each pixel and represents a voltage signal (gradation voltage signal) corresponding to the display brightness of the pixel. The additional voltage V _SX or the additional voltage signal V _SX is assumed as a voltage which essentially stabilizes the graded display state. This voltage signal is well stabilized with a DC voltage equal to or less than the optical threshold Vth. In this case, the optical threshold Vth is set as a value at which an optical change is substantially not detectable even if the threshold Vth is applied over an entire image.

The absolute value of the additional voltage signal V _SX is preferably set to about 1/50 to 1/5 of that of the gradation voltage signal.

In 12 the application interval of the ground voltage V _e between the voltages V _W and V _SX is given to stabilize a reaction component as response of the liquid crystal molecules after the gradation voltage signal V _W is applied. However, even if this application interval is not provided in this element, the drive effect is not impaired in this exemplary embodiment. In this case, the V _SX value must be controlled exactly according to a drive waveform.

If a change in the state of the liquid crystal is assumed to occur due to the application interval of the reset voltage signal Vr, the application intervals of the voltage signals V _W and V _E can be equated with that of the reset voltage Vr.

In order to effectively carry out the above driving method, a recording period of each line is made at least four intervals (if the V _E application interval is not provided, only three intervals are required; and the description below illustrates a case where the V _E application interval is provided ) assigned. In 12 the lower time table represents a case in which the recording period A of the nth line is divided into four intervals. That is, the recording period A is divided into a subinterval a for activating a gate corresponding to a subsequent line a few lines after the current line for resetting the pixels of the following line, and a subinterval b for activating a gate of the nth line for execution the recording of the nth line, in a sub-interval c for activating a gate corresponding to the preceding line of a few lines before the current line for applying the ground voltage to the recorded pixels of the previous line, and in a sub-interval d for activating a gate accordingly another previous line a few lines before the previous line for applying an additional voltage signal to the recorded pixels of the other previous line. It should be noted that the subintervals a , b , c and d in the recording period A of the nth line have any of the following orders: a bcd, abdc, acdb, acbd, bacd, badc, bcad, bc da, bdac, bdca, cabd, ....

12 shows optical states 101 to 104 of a liquid crystal pixel of the nth line. These states are in 13 shown enlarged.

14 11 is a view showing an FLC sandwiched between an upper electrode substrate 11 having an active TFT matrix and a lower substrate with its entire surface serving as an electrode.

If the direction of the spontaneous polarization P _{S is} directed upwards 201, the principal axis of each FLC molecule is in principle given as the direction by a solid line 1 is designated; and when the direction of spontaneous polarization P _{S is} down 202, the major axis of each FLC molecule is by a dotted line 2 given direction. If in the 20 shown reset voltage Vr is applied to keep the upper electrode in a negative state, the spontaneous polarization is ideally directed upwards in this interval 201. If one of the polarizing plates 301 and 302 as crossed polarizers with the solid line 1 indicated main axis direction is arranged, the pixel is set to the "black" state. Complete "black" states 101 and 103 in 12 be achieved.

When the gradation voltage signal as the recording voltage signal V _{W has} a magnitude that exceeds the reverse threshold voltage Vth of the liquid crystal, a "white" domain is formed. However, if V _{W is} less than Vth, a reset "black" state is maintained. When the ground voltage signal V _{E is} activated to be applied to the ground voltage V _E , some molecules that are not cached in the "white" state will tend to react, but the state will change to the graded display state ( 103 in 12 ) according to the gradation voltage V _W. Thereafter, when the additional voltage signal V _{SX is applied in} accordance with the voltage V _W , the graded state is maintained and variations in the ion location setting described above can be avoided. As a result, since the variations in ion polarization in each image are eliminated, there is no undesirable change in transmittance. As a result, a stable image display operation can be performed.

In a so-called compatible high-vision television display, in which 1000 scanning lines are scanned at 30 or 60 Hz, each picture is driven for every 33 msec. For this reason, a recording period for each line is about 33 microseconds per picture. The recording period of 33 µsec for applying a recording voltage in every nth line is divided into four intervals (ie, each interval takes about 8 µsec or less). These four intervals consist, for example, of an interval for applying the VR pulse for resetting a line pixel to which the recording voltage (V _W ) is applied six lines after the current line (= S ₃ ), and a recording pulse interval for applying the voltage V _W the pixel of the nth line, a ground signal interval for applying the ground voltage V _E to a line pixel to which the voltage VW has been applied six lines before the current line (= S ₂ ), and an interval for applying the additional voltage signal V _SX to a line pixel to which the V _{W has been} applied twelve lines before the current line (= S ₁ ). A total time for applying the respective voltages will be approximately 198 μsec (= approximately 33 μsec × 6). A satisfactory image display could be achieved by a material used by the present inventors with a maximum V _R and V _W voltage of about 7 V. In addition, the DC component with the additional voltage V _{SX was} superimposed by a voltage that was equal to or less than the threshold Vth according to the gradation level for stabilizing the graded display state.

This in 12 control method shown is based on 13 described in more detail.

The peak voltage value of the additional voltage signal V _SX can be set as follows.

It is assumed that the peak value V _{R of} the reset voltage Vr is in the ideal voltage waveform during the reset signal interval aV ₀ and that during the recording signal interval b the voltage value V _{W is} equal to the recording voltage V _W + V ₀ . If the frequency of application of these voltages to one another is the same, a peak value V _{S0 of} the additional voltage signal V _SX is set to approximately 0.5 V during the additional voltage signal interval d when Ps is at 5 nC / cm ² and Ci is at 20 nF / cm ² is set according to the calculation 2PS (Δa = 1) / Ci (interval 401).

Wenn die Gleichspannungskomponenten durch die Spannungen Vr und V_W auf 0 gesetzt werden, und wenn ein Spannungswert gemäß

jedem 0-Gleichspannungwert hinzugefügt wird, so daß die Spitzenwerte der zusätzlichen Spannungssignale in Hinsicht auf die Abstufungswerte Δa₁, Δa₂ und Δ_a3 festgelegt werden (basierend auf den Durchlässigkeiten und dem Ende der Massenspannungs-Anlegeperiode), gilt:

(0 < Δa₁, Δa₂ , Δa₃ < 1).On the other hand, if gradation levels are designated for the recording signal, as by the intervals 402 . 403 and 404 are displayed, peak values V _S1 , V _S2 and V _{S3 are set as} follows, when the reset voltage is sufficiently high, the number of scanning lines 1000 is and a 24-line period is provided as a picture interval (blanking period) as follows. When the reset interval, the recording interval and the mass interval are set as S ₂ , S ₃ or. (S ₄ - S ₃ ), and if the condition S ₂ = S ₃ (= S ₄ - S ₃ ) = S is established, the following equations can be approximated:

When the DC components are set to 0 by the voltages Vr and V _W , and when a voltage value according to

is added to each 0-DC voltage value so that the peak values of the additional voltage signals are set with respect to the gradation values Δa ₁ , Δa ₂ and Δ _a3 (based on the permeability and the end of the mass voltage application period):

(0 <Δa ₁ , Δa ₂ , Δa ₃ <1).

If the intervals S ₂ , S ₃ and (S ₄ - S ₃ ) are different from each other, the voltage V _S1 'can be rewritten as follows:

For example, it is assumed that the spontaneous polarization P _{S of} the FLC used = 5 nm / cm ² , the capacitance Ci = 20 nF / cm ² , the voltage V _W = -7 V and a permeability of 60% at V1 = 5.5 V is achieved. If S ₂ = S ₃ = (S ₄ - S ₃ ) = 6, the following equation is obtained:
V S1 '= (7 × 6 - 5.5 × 6) / (1024 - 19) = 9/1005 ≅ 9 mV , and therefore is
V S1 = 9 (mV) + 0.5 (V) × 0.6 = 0.309 (V) ,

The additional voltage signal V _SX can be calculated according to the analog recording signal voltage V _W at the point or can be automatically output from a previously stored table T (V _W and V _SX ) if the recording signal V _{W is} a digital signal.

The control method described above can in principle be implemented in a simple manner by arranging an image memory or a line memory of at least S ₄ lines.

That is, since there is a delay time of S ₄ = 12 lines between the generation of the recording signal and the generation of the additional signal, the information of S ₄ = 12 lines must be generated for the generation of the recording signals for each line during this period.

15 shows a simple block diagram of a control circuit. All signal tuning operations are performed dependent on a clock (shown in 15 ). The gate signal output timing of the rows, reset signals for the source electrodes, and recording and additional signal output timing are controlled by this clock.

It's easy to understand that a good effect can be achieved by a combination of a liquid crystal with spontaneous polarization and an active matrix element in order to additional tension to apply.

In the above description, the Ion locating state stabilizes when the FCL state in total "black" condition. however this location can also be stabilized when FCL state is an entirely "white" state.

In this case, the location the original "white" state when it occurred of the start of the operation. According to this procedure a waveform in

und diese Komponente wird als Zusatzsignal angelegt. Wenn das "Weiß"-Domänenverhältnis mit Δa angegeben ist, um den Ionenortsfestlegungsbetrag im "Weiß"-Zustand in Hinsicht auf das verbleibende Schwarz-Domänenverhältnis (1 – Δa) beizubehalten, wird eine Zusatzspannung mit folgendem Gleichspannungs- Komponentenüberlagerungsbetrag angelegt (16(a) bis 16(d)):

Das heißt, wenn die vorliegende Erfindung auf die aktive Matrixansteuerung angewandt wird, können die zusätzlichen Spannungssignale folgendermaßen angegeben werden, wie auch in 21 dargestellt ist:
V_S0 = 0

In diesem Falle unterscheidet sich die Entsprechung zwischen den Auzeichnungsspannungswerten V₁, V₂ und V₃ (13) und den Abstufungswerten Δa₁, Δa₂ und Δa₃, wenn die Ionenortsfestlegung im "Schwarz"-Zustand stabilisiert wird. Eine niedrige Spannung wird als Spannung V_W ausgewählt, um eine gute abgestufte Anzeige wie im obigen Beispiel zu erzielen. 16 (d) created continuously. The DC component source for maintaining the ion location is in the "black" state

and this component is created as an additional signal. If the "white" domain ratio is given by Δa to maintain the ion location amount in the "white" state with respect to the remaining black domain ratio (1 - Δa), an additional voltage is applied with the following DC component overlay amount ( 16 (a) to 16 (d) ):

That is, when the present invention is applied to the active matrix drive, the additional voltage signals can be given as follows, as in FIG 21 is shown:
V _S0 = 0

In this case, the correspondence between the recording voltage values V ₁ , V ₂ and V ₃ differs ( 13 ) and the gradation values Δa ₁ , Δa ₂ and Δa ₃ when the ion location determination is stabilized in the “black” state. A low voltage is selected as the voltage V _W to achieve a good graded display as in the example above.

immer kleiner als Vth sein.When the stabilized graded display is reached, the DC component value becomes

always be smaller than Vth.

With the optical described above A good liquid crystal device is provided for the modulation element. A highly precise, directly viewable flat display or projection display can be set up become. By providing a color filter on each pixel or by Using a variety of liquid crystal elements the control method can according to the present invention execution a color light projection of a high definition flat color television of permeability or the reflection type or projection color television become.

Claims (8)

A liquid crystal device having a liquid crystal element having a liquid crystal showing spontaneous polarization, a pair of electrode substrates for enclosing the liquid crystal, insulating layers are formed between the electrode substrates and the liquid crystal, and wherein the P _S value of the spontaneous polarization of the liquid crystal, the composite electrode capacity Ci of Insulation layers and the voltage threshold Vth optical response of the liquid crystal in the liquid crystal elements satisfy the relationship:

characterized by a first means for applying a gradation voltage signal in accordance with the gradation information for the pair of electrodes, and a second means for applying a direct current component which serves as a reverse bias of an internal electric field which arises after application of the gradation voltage signal to the liquid crystal during a vertical scanning period. Device according to claim 1, characterized in that the liquid crystal consists essentially of a ferroelectric liquid crystal. Device according to one of the preceding claims, thereby characterized in that the Vertical scan period is one frame scan period. Device according to one of the preceding claims, thereby characterized in that the DC component value within a range of 1/50 is up to 1/5 of the gradation voltage signal. Device according to one of the preceding claims, characterized in that the liquid crystal element is equipped with: a plurality of pairs of electrodes, each pair consisting of a pixel electrode and a counter electrode, switching elements arranged along a plurality of rows and a plurality of columns, first Wiring lines commonly connected to first terminals of the switching elements in units of rows, second wiring lines commonly connected to second terminals of the switching elements in units of columns, a plurality of pixel electrodes connected in units of third terminals of the switching elements, counter electrodes which are arranged opposite the pixel electrodes, an insulation member which is formed on at least one of the pixel and counter electrodes, and with a scanning means for scanning scanning pulses for the first wiring lines; wherein the first means applies the gradation voltage signal (V _W signal) to the electrodes by applying a signal according to the gradation information to the second wiring lines, and wherein the second means applies the direct current component (V _SX ) to the liquid crystal by applying an additional voltage signal to the second wiring lines , Device according to claim 5, characterized in that the the first means is set up to apply the signal according to the gradation information to the second wiring lines after a reset voltage signal is created. Apparatus according to claim 6, marked by on Means for applying a voltage signal before applying a reset voltage signal, wherein the voltage signal is designed so that a voltage difference between an absolute value of the reset voltage signal and an absolute value of the gradation voltage signal becomes zero. Apparatus according to claim 6, marked by on Means for applying a zero voltage during a period between the additional voltage signal and the gradation voltage signal.