JPH1062753A - Driving method for liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten memory time and to eliminate hysteresis by making a frame rate by selection electrodes faster than the intrinsic value in such a manner that the driving of the next line is started before the memory characteristic of liquid crystals falls to a prescribed value. SOLUTION: Data pulses are impressed on the liquid crystal display element by changing the time when the memorization in the intrinsic driving waveforms (A) of an NTSC system is executed under crossed nicols, i.e., the frame rate (corresponding to one field component as an interlace system in this case) from, for example, 16.7msec to 8.4msec (B) and 4.2msec (C) respectively. The hysteresis is affected by the frame rate time. The hysteresis is decreased if the frame rate time is made shorter than the intrinsic value and is set particularly at <=12msec and further, <=10msec. Namely, the frame rate is made faster by making the frame rate at the time of driving the element faster than the intrinsic value in such a manner that the next line comes before the memory characteristic to generate the hysteresis degrades.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a first base having data electrodes (column electrodes) arranged in one direction, and a select electrode (row electrode) arranged in a direction intersecting the data electrodes. The present invention relates to a method for driving a liquid crystal element (for example, a liquid crystal display element or a liquid crystal display) in which a liquid crystal is arranged between a second substrate and the liquid crystal element.

[0002]

2. Description of the Related Art A liquid crystal display (LCD) using a liquid crystal as a display has features of low power consumption, thinness and light weight, and taking advantage of this, from a clock and a calculator to a computer display and a television receiver. (T
Application to V) is progressing.

Research and development for using a ferroelectric liquid crystal (FLC) as a liquid crystal in such an LCD has been actively pursued. Regarding FLC, a ferroelectric liquid crystal was first synthesized by Meyer in 1975, and a surface-stabilized ferroelectric liquid crystal capable of domain inversion by an electric field was invented in 1980 by Clark and Lagaard. F
LC is a liquid crystal that has a permanent dipole moment in the molecule itself perpendicular to the long axis of the molecule, has spontaneous polarization, and can be switched by an electric field.
The display is an excellent display mainly having the following features (1) to (3).

(1) The switching speed is on the order of microseconds, the response is 1000 times faster than that of the TN liquid crystal display, and the high-speed response is excellent. (2) There is basically no twist structure in the molecular arrangement, and there is little viewing angle dependence. (3) Even if the power is turned off, the image is retained, the image has memory properties, and simple matrix driving is possible even for 1000 or more scanning lines that can support high definition.

Accordingly, the FLC display has a high definition,
It is a display that can pursue the performance of low cost and large screen.

Such an FLC display (ferroelectric liquid crystal display element) has a structure as schematically shown in FIGS. 8 and 9, for example. First, a transparent electrode (100Ω / □ ITO: Indium tin oxide) 2 was placed on a transparent glass substrate (Corning 7059, 0.7 mm thick) 1a, 1b.
a, 2b are provided. These transparent electrodes are patterned into stripes by etching, and intersect each other in a matrix in a data electrode (column electrode) 2a.
And the scanning electrodes (row electrodes) 2b.

On the transparent electrodes 2a, 2b, obliquely deposited SiO films 3a, 3b are formed as liquid crystal alignment films. In forming an obliquely deposited SiO film, a substrate is disposed vertically from a SiO deposition source in a vacuum deposition apparatus, and an angle between a vertical line and a substrate normal is set to 85 degrees. Si
After vacuum deposition of O at a substrate temperature of 170 ° C., baking is performed at 300 ° C. for 1 hour.

In the pair of substrates 1a and 1b provided with the alignment film thus manufactured, the alignment directions of the data electrode 2a and the scanning electrode 2b are antiparallel on opposite surfaces, and the data electrode 2a and the scanning electrode 2b are arranged so that the electrode arrangement is orthogonal. As the spacer, glass beads (straightening sphere: 0.8 to 3.0 μm in diameter (manufactured by Catalyst Chemical Industry Co., Ltd.)) 4 corresponding to the target gap length are used. Here, the alignment processing directions are set antiparallel, but they may be set parallel.

Depending on the size of the transparent substrates 1a and 1b, the spacer 4 has a sealing material (UV-curable adhesive (Photorec: manufactured by Sekisui Chemical Co., Ltd.)) 6 that adheres to the periphery when the area is small. By dispersing about 0.3 wt%, the gap between the substrates is controlled. When the substrate area is large, the above-mentioned straightening spheres have an average density of 100 pieces / ball on the substrate.
After spraying mm ² , a gap was formed, a liquid crystal injection hole was secured, and the periphery of the cell was bonded with a sealant 6.

A liquid crystal composition in which, for example, a ferroelectric liquid crystal (YS-C152 manufactured by Chisso Corporation) 5 is uniformly dispersed at an isotropic phase temperature using an ultrasonic homogenizer between a pair of substrates 1a-1b. Has been injected. This ferroelectric liquid crystal composition is injected under reduced pressure in a state showing fluidity such as an isotropic phase temperature or a chiral nematic phase temperature. After injecting the liquid crystal, the liquid crystal is slowly cooled, and the liquid crystal on the glass substrate around the injection hole is removed, and then sealed with an epoxy-based adhesive.
The display 11 is manufactured.

As a driving method of the FLC display 11, an XY matrix method is used. When the NTSC system is selected, 1H (one horizontal scanning time or one line selection time) is 63.5 μs, and the voltage is applied in bipolar in consideration of the electrical neutral condition. .5 / 2 μs width. Row side (electrode 2b)
, A select pulse as a threshold is applied, and a data pulse is applied from the column side (electrode 2a).

A ferroelectric liquid crystal element (for example, a surface-stabilized ferroelectric liquid crystal element) has an externally applied electric field E (Ps is spontaneous polarization).
As shown in FIG.
And state 2 are switched. This change in molecular orientation appears as a change in transmittance when the liquid crystal element is placed between orthogonal polarizing plates. As shown in FIG. 11, the transmittance changes from 0% at a threshold voltage _Vth with respect to an applied electric field. It changes sharply to 100%. The voltage width at which the transmittance changes is generally 1 V or less.

As described above, since the conventional ferroelectric liquid crystal display using the bistable mode is stable only in two states, it is difficult to provide a stable voltage range in the transmittance-applied voltage curve. In addition, gradation display by voltage control is difficult or impossible.

Therefore, the threshold voltage width for switching between the bistable states of the liquid crystal in one pixel is extended by giving a distribution to the effective electric field applied to the liquid crystal in one pixel. Can achieve analog gray scale display by the present applicant.
(This is hereinafter referred to as a prior invention).

According to the invention of the prior application, a method of adding and dispersing ultrafine particles such as titanium oxide in a ferroelectric liquid crystal in order to "extend the threshold voltage width" is employed.

By the addition of the ultrafine particles, fine regions (micro domains) having different threshold voltages (V _th ) are developed in one pixel, and the transmittance of the micro domains is changed according to the magnitude of the applied voltage. Is changed, the transmittance does not change sharply, but shows a relatively gradual change, and analog gray scale display becomes possible. And
In one domain, if the liquid crystal molecules are bistable, they have a memory function, and one pixel is formed from domains having a different threshold voltage on the order of μm, so that continuous gradation display is possible.

Therefore, as shown in FIG. 12, in the liquid crystal element obtained by the prior application, the transmittance does not change sharply as shown in FIG. 11 but changes relatively slowly according to the applied voltage. It is. This is, as mentioned above,
In particular, in one pixel, a fine region (micro domain) having a different threshold voltage (V _th ) _appears ,
This is because the number of microdomains changes according to the magnitude of the applied voltage, and thus the transmittance as a sum of one pixel changes. Then, in one domain, the liquid crystal molecules have a memory function of being bistable, and have different threshold voltages.
Since one pixel is formed from an m-order domain,
Continuous tone display becomes possible.

[0018]

The present inventors have concluded that the ferroelectric liquid crystal display element has the above-described excellent characteristics, but the dipole moment of the ferroelectric liquid crystal molecule itself, the dielectric constant, and the inside of the panel. The phenomenon that the transmittance cannot be determined to one value by the voltage applied in the previous frame due to impurity ions or the like (applied voltage-transmittance hysteresis),
It has been found that a phenomenon (burn-in phenomenon) that leaves the display color selected in the previous frame may occur.

This is because, in a normal black-and-white binary ferroelectric liquid crystal display, if the same image is continuously displayed for a long time, the next image cannot be displayed, or if the power consumption is increased, the driving method becomes complicated. And so on. In particular, in the above-mentioned ultrafine particle-containing ferroelectric liquid crystal display capable of analog gradation display, in addition to the above-described problems (hysteresis and burn-in phenomenon), instability of the number of gradation displays occurs, and The advantage of the tone display cannot be fully utilized.

It has been found that one of the causes of the above-mentioned hysteresis involves the degree of memory stability, which is a characteristic of ferroelectric liquid crystals. Hereinafter, the phenomenon will be described in detail.

As a method of evaluating the hysteresis, a transmittance curve in which the applied voltage is gradually increased and a transmittance curve in which the applied voltage is gradually decreased are measured, and a comparison can be made based on the voltage width of the deviation. For example, it corresponds to HΔV in FIG.
The value of the transmittance by random voltage application corresponding to the normal image quality display is between the curves, and the magnitude of the hysteresis (HΔV) causes the instability of the display color.

Therefore, this voltage width is set to zero (HΔV = 0)
By doing so, the effect of the applied voltage of the previous frame can be eliminated, that is, the transmittance can be selected to one value by the applied voltage value.

It has been said that the main cause of the hysteresis is the influence of impurity ions in the liquid crystal panel. However, the present inventor has found that the hysteresis of the stability of the memory during the measurement of the applied voltage-transmittance is measured. It was found by experiment. That is, the time that is actually integrated and reflected by the human eye (for example, in the case of the NTSC system, about 15 msec corresponding to 16.7 msec as one frame rate).
In addition, there is an instability in transmittance due to a difference in memory characteristics as shown in FIGS. 14 (A), (B) and (C). In addition, as shown in FIG. 15, there are several types of applied voltages indicating one transmittance.

[0024]

SUMMARY OF THE INVENTION An object of the present invention is to eliminate the instability of the memory property, which is considered to be the largest cause of the hysteresis in driving a liquid crystal element, to improve the image quality and smoothly display moving images. Is to make it happen.

[0025]

That is, the present invention provides a first substrate having data electrodes arranged in one direction and a second substrate having select electrodes arranged in a direction intersecting the data electrodes. When driving a liquid crystal element in which a ferroelectric liquid crystal exhibiting hysteresis of applied voltage-transmittance is arranged, before the memory property of the ferroelectric liquid crystal causing the hysteresis is reduced to a predetermined value. The present invention relates to a method for driving a liquid crystal element, in which the frame rate by the select electrode is increased so that the next line is started to be driven.

In the evaluation of the hysteresis described above, the present inventor has found that the longer the time, the more the memory instability increases.
In the case of the SC system, if the driving method is faster than 16.7 msec for one field, and the frame rate is increased so that the next line comes before the memory property causing hysteresis is reduced, the memory time can be reduced. Decrease
The inventors have found that only the transmittance of a portion having high stability can be used, and have reached the present invention.

In this way, the hysteresis due to the memory property can be eliminated, and in the ordinary ferroelectric liquid crystal display, the data voltage value input from the column electrodes of the simple matrix can be reduced and a smooth moving image can be obtained. become. In the ultrafine particle-containing element as in the above-mentioned prior invention, a complete analog gradation can be realized.

In the driving method according to the present invention, the liquid crystal is composed of a ferroelectric liquid crystal exhibiting a hysteresis of applied voltage-transmittance, and before the memory property of the ferroelectric liquid crystal causing the hysteresis decreases to a predetermined value, It is desirable to increase the frame rate so that driving of the next line is started.

In particular, for a pixel which is most affected by the memory property in the previous frame, the frame rate is set so that the driving of the next line is started before the decrease in the memory property exceeds a predetermined value, especially 12.5%. Is desirable in order to obtain sufficient gradation.

Further, in terms of gradation, it is desirable that regions having different threshold voltages for switching the ferroelectric liquid crystal are finely distributed, as in the above-mentioned prior application. In order to form such fine regions having different threshold voltages, fine particles are preferably added to the ferroelectric liquid crystal.

Here, the above-mentioned "regions having different threshold voltages are finely distributed" means that the transmissivity due to the inversion domain (for example, the black domain in white or the opposite) is 2%.
When it is 5%, there are 300 or more (preferably 600 or more) domains (microdomains) having a size of 2 μmφ or more in a visual field of 1 mm ² , and a threshold voltage width within the domain. Means 1 V or more, preferably 2 V or more in a transmittance range of 10 to 90%.

Therefore, as shown in FIG. 12, in this liquid crystal element, the transmittance does not change sharply as shown in FIG. 11, but shows a relatively gradual change depending on the applied voltage. This is because, as described above, in particular, in one pixel, micro-domains having different threshold voltages (V _th ) are developed, and the transmittance of the micro-domains is changed according to the magnitude of the applied voltage. Is changed. Then, within one domain, the liquid crystal molecules have a memory function when they are bistable, and have different threshold voltages.
Since one pixel is formed from an m-order domain,
Continuous tone display becomes possible.

In FIG. 12, among the threshold voltages at which the transmittance changes, when the transmittance is 10%, V _th1 and the transmittance are 90%.
In the case where V _th2 is the time of (3), the variation width of the threshold voltage (△
(V _th = V _th2 −V _th1 ) is 1 V or more.

As for the micro domain, FIG.
As shown in the figure, when the transmittance is 25%, domains MD having a size of 2 μmφ or more are present at a rate of 300 domains / mm ² or more. Such a fine light-transmitting portion of the microdomain can realize a halftone screen (transmittance) as a whole, but since the structure of such a microdomain has a so-called starry sky,
Hereinafter, it is referred to as “starlight texture”.

According to the starlight texture, the light transmitting portion MD of the micro domain is enlarged (increased in transmittance) or reduced as shown by a dashed line in FIG. 5A according to the magnitude of the applied voltage. (Decrease in transmittance), and the transmittance can be arbitrarily changed by the applied voltage. On the other hand, in the devices of FIGS. 8 and 9, as shown in FIG. 5B, the threshold voltage width is extremely small, so that the light transmitting portion D due to the applied voltage sharply increases or disappears. And gray scale display is difficult.

In this method of manufacturing a liquid crystal element, fine particles (or ultrafine particles) can be dispersed in the liquid crystal 5 in a liquid crystal cell as a means for forming the microdomain.

Here, the change of the threshold voltage due to the ultrafine particles will be described in principle with reference to FIG. When the particle diameter of the ultrafine particles 10 is d ₂ , the dielectric constant is ε ₂ , the thickness of the liquid crystal 5 excluding the ultrafine particles 10 is d ₁ , and the dielectric constant is ε ₁ , the electric field Eeff applied to the ultrafine particles is expressed by the following equation (1). ). Eeff = (ε ₂ / (ε ₁ d ₂ + ε ₂ d ₁ )) × Vgap (1)

Therefore, when ultrafine particles having a dielectric constant smaller than that of the liquid crystal are added (ε ₂ <ε ₁ ), the total thickness dga of the liquid crystal layer is increased.
By introducing fine particles (d ₂ ) smaller than p (= d ₁ + d ₂ ), Eeff <Egap, and a small electric field Eeff acts on the liquid crystal as compared with the case where no fine particles are inserted (Egap).

On the contrary, by adding fine particles having a dielectric constant larger than that of the liquid crystal (ε ₂ > ε ₁ ), Eeff>
Egap, and liquid crystal without fine particles (Ega
A large electric field Eeff acts as compared to p).

The above is summarized as follows. When ε ₁ > ε ₂ → Eeff <{Vgap / (d ₁ + d ₂ )}
_{= Vgap / dgap = Egap ε 1} = ε 2 when → Eeff = Egap ε ₁ <when ε ₂ → Eeff> Egap

In any case, the addition of the ultrafine particles changes the effective electric field Eeff applied to the liquid crystal itself, and the effective electric field applied to the liquid crystal differs between a region where the ultrafine particles exist and a region where the ultrafine particles do not exist. . As a result, even when the same electric field Egap is applied, there is a region where an inversion domain is generated and a region where no inversion domain is generated between these regions.
The starlight texture structure as shown in (A) can be expressed.

From this, the starlight texture structure is suitable for realizing continuous gradation, and the applied voltage (magnitude, pulse width, etc.) is controlled with the addition of ultrafine particles (ie, two or more types). , A variety of transmittances (that is, two or more types of gradation levels) can be obtained. Contrary to this, only the presence of fine particles gives only the one shown in FIG. 5 (B). In particular, even if fine particles of 0.3 to 2 μm are present in a minute gap (about 2 μm), It is apparent that the display performance cannot be obtained, and even if the gap is not very small, color unevenness occurs due to the fine particle portion. In the starlight texture structure, the desired performance can be obtained without such a phenomenon.

In the liquid crystal device of the present invention, the fine particles added to the liquid crystal are distributed in the effective electric field intensity applied to the liquid crystal 5 existing between the opposed transparent electrode layers 2a and 2b shown in FIGS. Any fine particles can be used as long as the particles can have the following. For example, fine particles of a plurality of materials having different dielectric constants can be mixed and used. The presence of the fine particles having different dielectric constants as described above forms a distribution of the dielectric constant in each pixel.

As a result, as described above, even when an external electric field is uniformly applied between the transparent electrode layers 2a and 2b of the pixel, the effective electric field applied to the liquid crystal in the pixel has a distribution, and The distribution width of the threshold voltage for switching between bistable states (especially ferroelectric liquid crystal) can be widened, and analog gray scale display can be performed within one pixel.

When fine particles having the same dielectric constant are used as the fine particles to be used, the fine particles may have a distribution in size. As described above, the presence of fine particles having different dielectric constants but different sizes allows distribution of the thickness of the liquid crystal layer. As a result, even when an external electric field is applied uniformly between the transparent electrode layers 2a and 2b of one pixel, the effective electric field intensity applied to the liquid crystal in that pixel is distributed, and analog gradation display is performed in one pixel. Becomes possible. Regarding the distribution of the size of the fine particles, it is preferable that the spread of the distribution be large to some extent because excellent analog gradation display can be performed.

In the liquid crystal device of the present invention, it is desirable that the fine particles added to the liquid crystal have a surface of pH = 2.0 or more. This is because it is easily deteriorated.

The amount of the fine particles is not particularly limited and can be appropriately determined in consideration of a desired analog gradation, etc., but is not more than 50% by weight and not less than 0.1% by weight. Desirably, it is added to the liquid crystal. If the added amount is too large, it is difficult to develop a starlite texture structure due to aggregation, and it is difficult to inject liquid crystal.

The usable fine particles may be composed of carbon black and / or titanium oxide. The carbon black is preferably carbon black produced by a furnace method, and the titanium oxide is preferably amorphous titanium oxide. Pyrolytic carbon black produced by the furnace method has a relatively wide particle size distribution of fine particles, and amorphous titanium oxide has good surface properties and excellent durability.

The usable fine particles, in the state of non-aggregated primary fine particles, preferably have a size of not more than half (0.4 μm or less, particularly 0.1 μm or less) of the liquid crystal cell gap.
The shape is preferably spherical for ease of control. Although the gradation display characteristics can be controlled by the particle size distribution, it is desirable that the standard deviation of the particle size distribution be 9.0 nm or more in that the change in transmittance (transmittance) can be moderated. The specific gravity of the fine particles is 0.1
It is preferably from 10 to 10 times from the viewpoint of preventing sedimentation when dispersed in the liquid crystal, and it is preferable that the fine particles are surface-treated with a silane coupling agent or the like so as to exhibit good dispersibility.

As described above, since the size of the fine particles is extremely small, the fine particles may be referred to as ultrafine particles.

In the present invention, the fine particles are desirably present in the liquid crystal between the electrodes facing each other. In addition, they may be present in the liquid crystal alignment film or on the liquid crystal alignment film. Except that the fine particles are present between the corresponding electrodes, the configuration can be the same as that of the liquid crystal display device (particularly, the ferroelectric liquid crystal display device) of FIGS.

For example, a transparent glass plate is used as a substrate, ITO (indium tin oxide) or the like is used as an electrode layer, and a rubbed polyimide film or SiO 2 is used as a liquid crystal alignment film.
An obliquely deposited film can be used. Although the driving method is performed based on the present invention, the gray level in the above-mentioned micro domain starlight texture is obtained by changing the voltage of the data pulse. Is in a state where a data pulse is applied.

The gradation can also be obtained by giving a distribution to the tilt angle of the liquid crystal layer. In other words, the existence of the ultrafine particles described above allows the distribution of the layer tilt angle of the liquid crystal represented by δ in FIG. 7 to be formed without being related to the characteristics thereof, that is, the effective spontaneous polarization Ps _eff (the value of the ferroelectric liquid crystal). The distribution of the characteristic values that determine the threshold values) results in a large number of domains having various threshold values within one pixel. Regarding the size of the domain, it has been found that ultrafine particles of the order of nanometers have a small particle size, break the continuity of the layer in the vicinity thereof, and have an effect of stopping domain expansion (pinning effect). In the case of large fine particles on the order of submicrons, this pinning effect is scarcely observed, and even when it is observed, it becomes a large defect and greatly affects the transmittance.

In practice, the ferroelectric liquid crystal usable in the present invention is preferably a mixture of a chiral smectic C (SmC ^* ) liquid crystal and a non-chiral smectic C (SmC) liquid crystal. Each of these liquid crystals may be composed of only one kind, or may be a mixture of plural kinds.

Here, chiral smectic C (SmC
^* ) As the liquid crystal (ferroelectric liquid crystal), known pyrimidine-based, biphenyl-based, phenylbenzoate-based, etc. (however,
These ferroelectric liquid crystals may show a chiral nematic phase, a smectic phase or the like depending on a change in temperature. ) Is a chiral smectic C liquid crystal (ferroelectric liquid crystal).

The usable non-chiral liquid crystal is a non-chiral nematic C (SmC) liquid crystal ZLI-2008-000 manufactured by Merck (melting point -6 ° C., nematic phase temperature range -20 to 64 ° C.). Is mentioned. In addition to this liquid crystal, a known non-chiral smectic liquid crystal can be used. For example, biphenyl type, terphenyl type,
Tricyclic cyclohexyl, cyclohexylphenyl, biphenylcyclohexane, cyclohexylethane,
Ester, pyrimidine, pyridazine, ethane,
Dioxane type and the like.

[0057]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples.

A 40 nm thick transparent ITO film is formed by sputtering.
A tantalum boat (manufactured by Nippon Bax Metal Co., Ltd.) containing SiO powder (purity: 99.99%, manufactured by Furuuchi Chemical Co., Ltd.) was heated (resistance heating) on a glass substrate provided with a film (sheet resistance: 100 Ω / cm ² ). ), A 50 nm-thick SiO oblique deposition film was vacuum-deposited at a substrate temperature of 100 ° C. as a liquid crystal alignment film. At this time, the vapor deposition was performed so that the angle between the substrate normal and the vertical line of the vapor deposition source was 85 °. After vapor deposition, firing was performed at 200 ° C. for 1 hour in the air in order to obtain good orientation.

The two glass substrates thus treated are
The deposition directions of the obliquely deposited SiO film are antiparallel to each other using a 1.6 μm-diameter spacer (warping sphere: manufactured by Sekisui Chemical Co., Ltd.) and an ultraviolet curable adhesive (Photorec: manufactured by Sekisui Fine Chemical Co., Ltd.). And assembled an empty liquid crystal cell. A ferroelectric liquid crystal (YS-C152: manufactured by Chisso Corporation) in which titanium oxide (IT-S: manufactured by Idemitsu Kosan Co., Ltd.) was uniformly dispersed at a ratio of 2% by weight was injected into the cell gap, and FIG. A liquid crystal display device (FLC display) similar to the liquid crystal device of FIG. 9 was obtained. Since this device is configured in the same manner as the above-described prior invention, description other than the above is omitted.

The relationship between the applied voltage and the transmittance of this liquid crystal display device was examined. Under orthogonal Nicols, the memory time, that is, the frame rate (corresponding to one field as an interlace method) with respect to the original driving waveform of the NTSC method shown in FIG.
The data pulse was applied to the liquid crystal display element from 8.4 msec to 8.4 msec and 4.2 msec as shown in FIGS. 1B and 1C, respectively, and the light transmission intensity was monitored.

As a result, it was found that the relationship between the frame rate time and the hysteresis was as shown in FIG. The hysteresis is influenced by the frame rate time, and the frame rate time is made shorter than the original value (16.7 msec), particularly, 12 msec or less, and furthermore, 10 m or less.
It can be seen that setting the time to less than sec is effective for reducing the hysteresis.

That is, the frame rate at the time of driving the element is made faster than the original value (16.7 msec in the NTSC system), and the frame rate is increased so that the next line comes before the memory property causing hysteresis is reduced. With this driving method, the memory time can be reduced, and only the transmittance of the portion with high stability can be used.

Next, the relationship between the reduction of hysteresis and the gradation will be schematically described with reference to FIG.

In the above-described driving method, when a voltage (V) is applied to a pixel which is most affected by the memory property in the previous frame (for example, a pixel having a black level in the previous frame) so as to have a white level, 12. A decrease in memory performance.
Before 5%, for example, 5% or more (when the decrease is 12.5% or less, for example, 5% or less), increasing the frame rate so that driving of the next line is started can sufficiently improve gradation. It was found to be desirable to put it out.

That is, FIG. 3 is a simplified view of the hysteresis as shown in FIG. 13. When the magnitude of the hysteresis when the memory performance is reduced is HΔV, the minimum value of the number of gradations that can be displayed is And the number of gradations = (V / HΔV) +2.

Further, when the calculation is performed again in consideration of the reduction amount of the memory property, the following result is obtained. Degradation amount of memory property Number of gradations 12.5% 16 gradations 5% 40 gradations 3% 64 gradations 0% 256 gradations

Normally, gradation display requires 16 or more gradations for OA (office automation) applications and 64 or more gradations for television applications. Starting the next line before the reduction amount becomes a predetermined value, especially a value exceeding 12.5% (that is, 12.5% or less) is required to realize gradation of 16 gradations or more. Is desirable. Similarly, when the decrease of the memory property is 3% or less, when the next line is started,
64 gradations or more can be realized.

FIG. 4 shows the change in the transmittance (vertical axis) at each frame rate described above in the previous field (1/2 of the previous frame).
This is shown according to the relationship between the level of the screen portion) and the level of the current field (current frame).

In FIG. 4, the transmittance change from Ta to Tb due to memory development when the previous field is at the black level and the current field is displayed at the white level, and the current field is black when the previous field is at the white level Regarding a change in transmittance from Td to Tc due to memory development when displaying at a level, an example based on the present invention (B) as compared with the conventional example (A)
In (C) and (C), the change in transmittance is (Ta′−Tb ′) / T
a ′ ≦ (3 to 12.5)%, (Td ″ −Tc ″) / Td ″
The frame rates are respectively increased so that the driving of the next line is started when ≦ (3 to 12.5)%.

Although the embodiment of the present invention has been described above, the above-described embodiment can be further modified based on the technical idea of the present invention.

For example, the frame rate at which the next line starts and its timing may be variously changed within a range in which the object of the present invention can be achieved, and the driving method may be any of a simple matrix method, an active matrix method and the like. . Further, the driving start timing of the next line described above may be appropriately changed according to the required gradation.

Further, the type and combination of the above-mentioned liquid crystals, the material and physical properties of the fine particles, and the like may be changed. In addition, as the above-mentioned transparent electrode, in addition to the above-mentioned ITO, a known transparent electrode such as tin oxide and indium oxide can be used.
Conventionally known materials can be used as constituent materials of the liquid crystal element such as a spacer and a sealing material.

Further, the above-mentioned element can be used not only for a display but also for an optical shutter, an optical switch, an optical blind and the like. Further, when combined with an electro-optical element or the like, a liquid crystal prism, a liquid crystal lens, an optical path switching switch, It can also be used for optical modulators, phase diffraction gratings, A / D converters, optical logic circuits and the like.

[0074]

As described above, the present invention provides a first base having data electrodes arranged in one direction and a second base having select electrodes arranged in a direction intersecting the data electrodes. When driving a liquid crystal element (especially an FLC display) in which a liquid crystal (especially a ferroelectric liquid crystal exhibiting a hysteresis of applied voltage-transmittance) is disposed between the liquid crystal elements, the liquid crystal element is driven before the memory property of the liquid crystal decreases to a predetermined value. Since the frame rate by the select electrode is made faster than the original value so that the line starts to be driven, the memory time can be reduced, and only the transmittance of the portion with high stability can be used, and the hysteresis due to the memory property can be used. Can be eliminated.

Therefore, in the ordinary ferroelectric liquid crystal display, the data voltage value input from the column electrodes of the simple matrix can be reduced and a smooth moving image can be obtained. In the ultrafine particle-containing device as in the above-mentioned prior invention, a complete analog gradation can be realized. However, the driving method of the present invention can improve image quality, obtain good reproducibility, and perform smooth moving image display irrespective of a liquid crystal material or fine particles to be added.

[Brief description of the drawings]

FIG. 1 is a driving waveform diagram applied to a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a graph showing a relationship between a frame time and a hysteresis in the liquid crystal display device.

FIG. 3 is a graph showing a simplified relationship between applied voltage and transmittance in the liquid crystal display device.

FIG. 4 is a graph showing a relationship between transmittance and time in the liquid crystal display element for each frame rate.

FIG. 5 is a schematic diagram for explaining a state of domain generation at the time of driving a liquid crystal display element in comparison with a conventional example.

FIG. 6 is a principle diagram for explaining a change in threshold voltage of the liquid crystal display element.

FIG. 7 is a schematic diagram showing a relationship between a layer tilt angle of a ferroelectric liquid crystal of a liquid crystal display element and an effective spontaneous polarization.

FIG. 8 is a schematic plan view of a conventionally used liquid crystal display element as viewed from a select electrode side.

FIG. 9 is a sectional view taken along line IX-IX in FIG. 8;

FIG. 10 is a model diagram of a ferroelectric liquid crystal.

FIG. 11 is a transmittance-applied voltage characteristic diagram showing a threshold voltage characteristic of a conventionally used liquid crystal display element.

FIG. 12 is a transmittance-applied voltage characteristic diagram showing a threshold voltage characteristic of the liquid crystal display element according to the prior application.

FIG. 13 is a general characteristic diagram (particularly, an explanatory diagram of hysteresis) showing a relationship between an applied voltage and transmittance in a liquid crystal display element.

FIG. 14 is a graph showing a comparison between transmittance and time for the same applied waveform in a liquid crystal display element.

FIG. 15 is a graph showing the relationship between transmittance and time at different applied voltages in the liquid crystal display device in comparison.

[Explanation of symbols]

1a, 1b: substrate, 2a, 2b: transparent electrode layer, 3a, 3
b: SiO oblique deposition layer, 5: liquid crystal (FLC), 10: fine particles, 11: FLC element

Continued on the front page (72) Inventor Hiroshi Murayama 6-7-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Inside Sony Corporation (72) Inventor Akio Yasuda 6-35-35 Kita-Shinagawa, Shinagawa-ku, Tokyo Sony Stock In company

Claims (5)

[Claims] An applied voltage-transmittance between a first base having data electrodes arranged in one direction and a second base having select electrodes arranged in a direction intersecting the data electrodes; When driving the liquid crystal element in which the ferroelectric liquid crystal exhibiting the hysteresis is arranged, the driving of the next line is started before the memory property of the ferroelectric liquid crystal causing the hysteresis is reduced to a predetermined value. 2. The driving method according to claim 1, wherein a frame rate by the select electrode is increased. 2. For a pixel which is most affected by the memory property in the previous frame, the decrease in the memory property is 12.5%.
The driving method according to claim 1, wherein the frame rate is increased so that the driving of the next line is started before the driving time exceeds the threshold value. 3. A frame rate is increased so that the next line is started to be driven before the deterioration of the memory property of the pixel which is most affected by the memory property in the previous frame exceeds 3%. 2. The driving method described in 2. 4. The driving method according to claim 1, wherein regions having different threshold voltages for switching the ferroelectric liquid crystal are finely distributed. 5. The driving method according to claim 4, wherein fine particles are added to the ferroelectric liquid crystal to form fine regions having different threshold voltages.