JP2001013529A - Liquid crystal element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce influence of preceding display states and to ensure excellent display quality even when a gray scale is displayed. SOLUTION: A pair of substrates 1a, 1b is arranged in a state with a specified gap in between. A bistable ferroelectric liquid crystal 2 is placed between the substrates 1a and 1b. Also a pair of electrodes 3a, 3b is arranged so as to sandwich the bistable ferroelectric liquid crystal 2 in between. Furthermore, ion quantity in the element is kept <=10 nC/cm2. In the case the liquid crystal panel P is driven by applying voltage to the pair of electrodes 3a, 3b, influence of preceding display states is reduced and excellent display quality is ensured.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device using a liquid crystal.

[0002]

2. Description of the Related Art Conventionally, a CRT has been known as a display for displaying various information.
It is widely used in TVs and VTRs that output moving images, or in monitors of personal computers.

[0003] However, this CRT has various problems, that is, * due to its characteristics, a still image suffers from deterioration of visibility due to flicker and scanning stripes due to insufficient resolution, and deterioration of a fluorescent lamp due to burn-in. Or the electromagnetic waves generated by the CRT have a bad effect on the human body,
There is a problem that the health of DT workers may be harmed, and a problem that the structure requires a space behind the screen, which hinders space saving in offices and homes. Various types of liquid crystal devices have been developed to solve the problem of the CRT. * For example, twisted nematic (twiste
d nematic (TN) liquid crystal is known, which is disclosed by M. Schadt.
And W. Helfrich
"Applied Physics Letters (Appl
ied PhysicsLetters), Volume 18,
No. 4 (issued February 15, 1971), pages 127-1
Page 28 ".

In recent years, as a liquid crystal element using such a liquid crystal, an active matrix type liquid crystal element has been developed, and a display of 10 to 12 inch class has been manufactured with a high yield due to rapid progress in production technology. Such a liquid crystal element includes a transistor (TF) in each pixel.
T), which solves the problem of crosstalk and the like, but has the problem that the response speed of the liquid crystal is slow, the image quality of moving images is inferior, and the viewing angle is narrow. * On the other hand, a display element of a type that controls transmitted light in combination with a polarizing element using the refractive index anisotropy of ferroelectric liquid crystal molecules (liquid crystal molecules exhibiting ferroelectricity) is known as Clark. ) And Lagerw
all) (JP-A-56-1072).
No. 16, US Pat. No. 4,367,924).
This ferroelectric liquid crystal generally has a chiral smectic C phase (SmC *) or H phase (SmC *) in a specific temperature range.
H *), and in this state, takes one of the first optical stable state and the second optical stable state in response to the applied electric field, and changes the state when no electric field is applied. It has the property of maintaining (i.e., bistable memory property), and also exhibits a very fast response speed because it performs inversion switching by spontaneous polarization. Furthermore, since the visual characteristics are also excellent, it is considered that they are particularly suitable as high-speed, high-definition, large-screen display elements or light valves. * Recently, Chandan, Takezoe et al. Have proposed a liquid crystal element using a liquid crystal exhibiting antiferroelectricity (hereinafter referred to as “antiferroelectric liquid crystal”) (Japan).
ese Journal of Applied Ph
ysics 27, 1988, L729). This antiferroelectric liquid crystal forms a display element by utilizing the refractive index anisotropy and spontaneous polarization of liquid crystal molecules, like the ferroelectric liquid crystal. In addition, this antiferroelectric liquid crystal generally has a chiral smectic CA phase (Sm
CA *), and in this state, when no electric field is applied, the average optical stable state is in the normal direction of the smectic layer, but the average optical stable state is tilted away from the normal direction of the layer by the application of an electric field. It has a state. Since the liquid crystal element using the antiferroelectric liquid crystal performs switching using spontaneous polarization as described above, it exhibits a very fast response speed and a high-speed display element or light valve. It is expected as. * With regard to this antiferroelectric liquid crystal material, a material having a small hysteresis and a V-shaped response characteristic having characteristics advantageous for gradation display was recently discovered (for example, Japanese Journal of Applied Physics).
ied Physics) Vol. 36, 1997, 35
86). Also, it has been proposed to use this type of liquid crystal for an active matrix type liquid crystal element to realize a high-speed display (Japanese Patent Laid-Open No. 9-50049).
No.).

[0005]

When gradation display is performed using the above-described liquid crystal panel, the relationship between the writing voltage and the transmittance differs depending on the display state of the previous frame (that is, the relationship between the write voltage and the transmittance). Even if a constant write voltage is applied to perform a predetermined gradation display, the gradation will be affected by the display state of the previous frame), and the display quality will be degraded.

The present inventor has found that ionic impurities greatly contribute to such a phenomenon (phenomenon of deteriorating display quality).

[0007] The liquid crystal contains ionic impurities, and the ions move with the application of a voltage to the liquid crystal. 6
At a driving frequency of about 0 Hz, one frame period is about 16.
Since it is a short time of about 7 msec, the movement of ions does not end in one frame period (very slow with respect to the reversal of spontaneous polarization). Therefore, when the polarity of the applied voltage is switched in the next frame period, such as when displaying a moving image, there is no particular effect of ions.

[0008] However, some pixels display the same information for several seconds or more. In such a pixel, the movement of ions is completed and ionic uneven distribution occurs. Therefore, in order to switch the liquid crystal in such a pixel, an electric field for inverting ionic polarization in addition to spontaneous polarization is required.

By the way, an actual liquid crystal panel is driven by applying a voltage that takes into account only spontaneous polarization without taking into account such ions. For this reason, information (gradation) different from the information (gradation) to be displayed is displayed in the pixel in which the movement of the ions has been completed as described above.

[0010] Such uneven distribution of ions is considered to change with time, and it is very difficult to reduce such unevenness by a driving method even if spots are considered.

Therefore, an object of the present invention is to provide a liquid crystal device having good display quality.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has a pair of substrates arranged with a predetermined gap therebetween, and a pair of substrates arranged between the pair of substrates. A stable ferroelectric liquid crystal, and a first electrode and a second electrode which constitute a plurality of pixels and are arranged so as to sandwich the bistable ferroelectric liquid crystal, and apply a voltage to these electrodes. In a liquid crystal device in which the bistable ferroelectric liquid crystal is driven based on the application, the amount of ions in the device is 10 nC / cm ² or less.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS.
An embodiment of the present invention will be described.

Liquid crystal element P driven in the present embodiment
As shown in FIGS. 1 and 2, a pair of substrates 1a and 1b arranged with a predetermined gap therebetween, and a bistable ferroelectric liquid crystal arranged between the pair of substrates 1a and 1b. 2
And a first electrode 3a and a second electrode 3a which constitute a plurality of pixels and are arranged so as to sandwich the bistable ferroelectric liquid crystal 2.
And an electrode 3b for driving the bistable ferroelectric liquid crystal 2 based on application of a voltage to these electrodes 3a and 3b.

The amount of ions in the device is 10 nC / c.
m ² or less, and is preferably as small as possible.
C / cm ² or less, more 2nC / cm ² or less, or even 1 nC / cm ² or less.

In order to control the amount of ions in the device as described above, * a method of including fine particles for adsorbing ions (for example, fine alumina particles) in the bistable ferroelectric liquid crystal 2; The alignment control films 6a and 6b for controlling the alignment state of the bistable ferroelectric liquid crystal 2
Is disposed at a position in contact with the substrate, and water molecules are adsorbed on the orientation control films 6a and 6b.

The bistable ferroelectric liquid crystal 2 includes:
What is necessary is just to use what has a distribution rather than a fixed threshold value in each pixel. By using such a bistable ferroelectric liquid crystal 2, the switching area changes according to the applied writing voltage, and the relationship between the transmittance and the writing voltage becomes a smooth curve as shown in FIG. 3, for example. As a result, gray scale display by domain gray scale becomes possible.

Further, the alignment control films 6a and 6b may be made of an inorganic material (such as silicon monoxide, silicon dioxide, aluminum oxide, zirconia, magnesium fluoride, cesium oxide, silicon nitride, silicon carbide, boron nitride, etc.) or an organic material. (Polyvinyl alcohol, polyimide, polyamide,
Polyester, polyimide amide, polyester imide, polyparaxylene, polycarbonate, polyvinyl acetal, polyvinyl chloride, polystyrene, polysiloxane, cellulose resin, melanin resin, urea resin, and acrylic resin may be used. Among them, polyimide is preferable in order to obtain better uniaxial orientation. In such a case, a polyamic acid that is soluble in a solvent may be applied and baked to form the resist. In order to perform patterning, resist application, etching and cleaning may be performed. The surfaces of the alignment control films 6a and 6b have
A rubbing treatment is preferably performed with a fibrous material such as velvet, cloth, or paper.

On the other hand, the liquid crystal element P may be of a transmission type or a reflection type. In the case of a transmissive type, it is preferable to make both substrates 1a and 1b transparent and to arrange a backlight device for illumination. In the case of a reflective type, a function of reflecting light to one of the substrates 1a and 1b is provided. Should be given. Here, as a method of imparting the function of reflecting light, a method of providing a reflection plate separately from the substrate, a method of forming the substrate itself with a reflection member, and a method of forming a reflection film on the substrate Method, and the like. The liquid crystal element P may be applied to a direct-view type or a transmissive type.

On the other hand, on the surface of each of the electrodes 3a and 3b,
An insulating film (only one insulating film 5b is shown in FIG. 2) for preventing a short circuit between these electrodes may be formed.
The insulating film 5b is made of SiO ₂ , TiO ₂ , Ta ₂ O ₅
And the like.

A spacer (not shown) may be arranged in the gap between the substrates 1a and 1b, and the dimension of the gap may be defined by the spacer. For this spacer, silica beads or the like may be used. The gap size may be adjusted according to the liquid crystal material.However, a uniform uniaxial orientation can be achieved, or the average molecular axis of the liquid crystal molecules in the state where no voltage is applied is set in the average direction of the alignment processing axis. In order to make the axis substantially coincide with the axis, it is preferable to set the range of 0.3 to 10 μm. When a chiral smectic liquid crystal is used, the thickness is preferably 5 μm or less in order to realize the stability of the ferroelectric phase.

Furthermore, adhesive particles (not shown) made of epoxy resin or the like are dispersed and arranged in the gap between the substrates 1a and 1b to improve the adhesiveness between the substrates 1a and 1b and the impact resistance of the liquid crystal element P. good.

Further, for example, a color filter (not shown) may be arranged on at least one of the substrates 1a and 1b so that color display can be performed.

The substrates 1a and 1b may be made of glass, plastic, or the like.

Further, In ₂ O ₃ is applied to the electrodes 3a and 3b.
Or a material such as ITO (Indium Tin Oxide), and these electrodes 3a and 3b are preferably formed on the respective substrates 1a and 1b.

Further, as the liquid crystal 2, a liquid crystal having a switching torque of spontaneous polarization is preferably used, and a chiral smectic liquid crystal which is a ferroelectric liquid crystal having bistability is preferably used.

On the other hand, the liquid crystal element P may be of a simple matrix type or an active matrix type (see FIG. 2).
In the case of using the active matrix system, an active element 4 is connected to the second electrode 3b in each pixel, and the bistable ferroelectric liquid crystal 2 is driven by turning on / off the active element 4. You can do it. In such a case, a thin film transistor such as a TFT can be used as the active element 4. Specifically, an amorphous silicon-based one, a polysilicon type one, a microcrystal-based one, a single crystal silicon or the like can be used. A semiconductor may be used. Further, the second electrode 3b to which the active element 4 is connected is preferably arranged in a dot shape, and the other first electrode 3a is preferably formed on the entire other substrate 1a or in a predetermined pattern.

Next, the active matrix type liquid crystal element P
An example of the configuration will be described with reference to FIGS.

The liquid crystal element P shown in FIG. 2 includes a pair of glass substrates 1a and 1b arranged with a predetermined gap therebetween, and a common electrode having a uniform thickness is provided on the entire surface of one glass substrate 1a. (First electrode) 3a is formed, and the common electrode 3a
Is formed with an orientation control film 6a.

On the other glass substrate 1b side, as shown in FIG. 4, a number of gate lines G ₁ , G ₂ ,... Are arranged in the x direction in the figure, and the gate lines G ₁ , G ₂ ,. , A large number of insulated source lines S ₁ , S ₂ ,... Are arranged in the y direction in the figure. Then, these gate lines G ₁ , G ₂ ,
And the pixel at each intersection of the source lines S ₁ , S ₂ ,..., A thin film transistor (amorphous SiTFT) 4 as an active element, a pixel electrode (second electrode) 3 b made of a transparent conductive film such as an ITO film, The capacitance electrode 7 and the like are arranged.

Of these, the amorphous Si TFT 4 is
As shown in FIG. 2, a gate electrode 10, an insulating film 5b made of silicon nitride (SiNx), and a semiconductor layer a
It is composed of a -Si layer 11, n + a-Si layers 12, 13, a source electrode 14, a drain electrode 15, and a channel protection film 16 for protecting a channel. That is, the gate electrode 10 is formed for each pixel on the glass substrate 1b, the surface of the gate electrode 10 is covered with the insulating film 5b, and the surface of the insulating film 5b is located at the position where the gate electrode 10 is formed. An a-Si layer 11 is formed. The surface of the a-Si layer 11 has n
+ A-Si layers 12 and 13 are formed, and each n + a-
The source and drain electrodes 14 and 1 are formed on the Si layers 12 and 13.
5 are formed apart from each other. Further, a channel protective film 16 is formed so as to cover the a-Si layer 11 and the electrodes 14 and 15.

The gate electrode 10 of the TFT 4 is connected to the scanning signal driver 20 via the gate lines G ₁ , G ₂ ,..., And the source electrode 14 of the TFT 4 is connected via the source lines S ₁ , S ₂ ,. In each pixel, the drain electrode 15 of the TFT 4 is connected to the pixel electrode 3b.

Incidentally, the above-mentioned storage capacitor electrode 7 is formed on the surface of the glass substrate 1b, and the above-mentioned insulating film 5 is formed.
b is formed to a position that covers the storage capacitor electrode 7 and the glass substrate 1b, and the source electrode 14 and the pixel electrode 3 described above are formed.
b is formed on the surface of the insulating film 5b. As a result, the storage capacitor electrode 7 and the pixel electrode 3b are arranged with the insulating film 5b interposed therebetween, and the storage capacitor Cs is configured by these (see FIG. 5). Note that this storage capacitor electrode 7 is preferably formed of transparent ITO in order to prevent a decrease in aperture ratio when the area is increased.

Further, as shown in FIG.
An alignment control film 6b is formed on the surface of the pixel electrode 3 or the pixel electrode 3b, and a uniaxial alignment process (rubbing process) is performed on the surface.

Further, a bistable ferroelectric liquid crystal 2 is disposed between the pixel electrode 3b and the common electrode 3a in a gap between the glass substrates 1a and 1b, and a liquid crystal capacitor C
_lc is configured (see FIG. 5).

On both sides of such a liquid crystal element P,
A pair of polarizing plates (not shown) whose polarization axes are orthogonal to each other are arranged.

In the liquid crystal element P shown in FIG. 2, an amorphous silicon (a-Si) TF
Although T is used, of course, the present invention is not limited to this, and other types of TFTs such as polysilicon (p-Si) may be used, and MIM (Metal-Insulator-
Metal-type (DRA) may be used, and a type (DRA) using a MOS-FET formed on a silicon wafer as a liquid crystal driving substrate (backplane) may be used.
M use / Normal reflection type, SOI (Silicon On)
(Insulator) system / normal transmission type).

Next, a method for driving the liquid crystal element P according to the present embodiment will be described.

In driving the liquid crystal element P, a voltage is applied between the pair of electrodes 3a and 3b to drive the bistable ferroelectric liquid crystal 2. Note that gradation display may be performed by applying a write voltage having a magnitude corresponding to the display gradation.

In this case, the switching of the bistable ferroelectric liquid crystal 2 may be performed by a swing process or a latch process. Here, whether to perform the swing process or the latch process may be controlled by the substrate gap between the pair of substrates 1a and 1b, the material of the liquid crystal 2 (particularly, spontaneous polarization Ps), the application time of the write voltage, and the like. In addition,
When the switching of the liquid crystal 2 is performed by the latch process, an image can be displayed by utilizing the memory property of the bistable ferroelectric liquid crystal 2.

Further, a moving image is displayed by switching the liquid crystal 2 by a swing process in a part of the liquid crystal element P, and switching of the liquid crystal 2 by a latch process is performed in another part of the liquid crystal element P. By doing so, a still image may be displayed. In such a case, a still image can be displayed using the memory property of the bistable ferroelectric liquid crystal 2.

Further, a reset voltage may be applied to the pair of electrodes 3a and 3b before the writing voltage is applied to reset the bistable ferroelectric liquid crystal 2.

Hereinafter, the active matrix type liquid crystal element P
An example of the driving method will be specifically described with reference to FIG. Here, FIG. 6 is a timing chart showing an example of a method for driving a liquid crystal element according to the present invention, and FIG.
Is, TFT diagram showing a timing of the gate voltage V _g applied to the gate electrode 10 of the (active element) 4, (b)
Is a diagram showing the voltage applied to the source electrode 14 and its timing, (c) is a diagram showing the potential of the common electrode (first electrode) 3a, (d) is a diagram showing the voltage applied to the liquid crystal 2, (e) is a diagram showing the optical response of the liquid crystal 2.

In the driving method shown in the figure, * a reset voltage V _R is applied to the liquid crystal 2 to reset the liquid crystal 2, and * a write voltage V _D is applied to the liquid crystal 2 to write an image. ing.

Note that the write voltage V _D and the reset voltage V
It is preferable that _R and _R have opposite polarities and that a DC component hardly occurs.

[0046] Also, application of the applied and the write voltage V _D of the reset voltage V _R described above, the gate lines G _1, G _2, the source lines S ₁ by turning on the TFT4 by applying a gate voltage V _g ... to , S ₂ ,... And the pixel electrode 3b may be set at the same potential. The method is to set the source lines S ₁ , S ₂ ,... To a predetermined potential (ie, a potential equal to the reset voltage or the writing voltage). And turning on the TFT 4 with the potential of the common electrode 3a as a reference potential (the image writing in FIG. 6 is performed by this method), or setting the source lines S ₁ , S ₂ ,. At the same time, with the common electrode 3a kept at a predetermined potential (that is, a potential equal to a reset voltage or a writing voltage), the TFT 4
(The reset in FIG. 6 is performed by this method), the source lines S ₁ , S ₂ ,... And the common electrode 3a.
There is a method in which the TFT 4 is turned on in a state where each of the potentials is set to a predetermined potential.

[0047] Here, the voltage width of the gate voltage V _g at the time of applying the reset voltage, the source lines S _1, S _2, ...
And said common applied to the electrode 3a is made larger than the width of the voltage, the liquid crystal 2 before terminating the application of the gate voltage V _g
Is preferably set to 0V.

[0048] Further, the voltage range of the gate voltage V _g at the time of applying the write voltage, for example, may be shortened to about 10 .mu.sec.

In this specification, the writing voltage V _D means a voltage applied to the liquid crystal 2 for displaying an image (that is, a voltage applied between the common electrode 3a and the pixel electrode 3b). and, the reset voltage V _R, the voltage applied to the liquid crystal 2 for resetting the image (i.e.,
Voltage applied between common electrode 3a and pixel electrode 3b)
Means

By the way, the present inventor has found that the amount of ions in the element described above has a large correlation with the difference in the previous state history. It has been found that the influence of the previous history difference can be reduced by setting the range to.

The present inventor has confirmed that the previous state history difference has a large correlation with the number of times of image writing, and the previous state history difference becomes smaller as the same image is written more times.
FIG. 7 is a timing chart showing another example of the driving method of the liquid crystal element (the driving method for examining the relationship between the amount of ions and the number of times of image writing, etc.), wherein (a) to (d) show the previous state. Diagram showing a driving method for creating an all-white state, (e)
(H) is a diagram showing a driving method for creating an all black state as a previous state. Further, (a) and (e) the TFT diagram showing a timing of the gate voltage V _g applied to the gate electrode 10 of the (active element) 4, (b) and (f) is applied to the source electrode 14 Diagram showing voltage and its timing,
(c) and (g) are diagrams showing the potential of the common electrode (first electrode) 3a, and (d) and (h) are diagrams showing the optical response of the liquid crystal 2. During the period Δt ₁ , the gate voltage _Vg is applied to the gate lines G ₁ , G ₂ ,.
Perform a reset liquid crystal 2 by applying _R, a period Delta] t _2, the source lines S ₁ in a state of applying a gate voltage V _g, S _2, before a predetermined voltage is applied ... to the state (all white State), and the state is maintained for 1 second (refer to the symbol Δt ₃ ). In the period Δt ₄ , the same voltage is applied to reset the liquid crystal 2, and in the period Δt ₅ , the gate voltage _Vg is applied. source lines S _1, S ₂ in the remains, the image writing was performed by applying a predetermined voltage V _D ... to.

And * the previous state history difference when the above voltage application is performed only once, and * the voltage application number when the above voltage application is repeatedly performed until the previous state history difference disappears. (Image writing frequency). This experiment was conducted not only for an active matrix type liquid crystal element but also for a simple matrix type liquid crystal element. The experimental results are as shown in the following table (regardless of active matrix type / simple matrix type). It has been found that the number of times the previous state history difference disappears and the ion amount have a large correlation, and the number of times the previous state history difference disappears decreases as the ion amount decreases. When the amount of ions was reduced to ² nC / cm ² or less, it was found that the number of times of voltage application can be reduced and power consumption can be reduced.

[0053]

[Table 1] (1) In case of active matrix type liquid crystal device (2) Simple matrix type liquid crystal element The strictest condition of the previous state history is that a pair of orthogonal deflecting plates are arranged on the liquid crystal element P, the previous state is completely displayed white, and the optical response corresponding to the information voltage change of the pixel left for a sufficient time is determined. This is considered to be the difference between the change in the optical response corresponding to the change in the information voltage of the pixel left completely for a sufficient amount of time after the change and the previous state are completely displayed black.

From the viewpoint of utilizing the memory property, the previous history difference due to the number of times of writing can be considered as follows. First, consider a display medium mainly composed of a moving image in which information is constantly rewritten. In such a medium, slightly different data is constantly rewritten at a considerably high speed. That is, the difference between the previous histories is not a serious problem as long as the histories are lost after writing five times. By the way, when a so-called partial rewriting mode of a partial moving image and a partial still image is used for this, the previous state history of the still image portion (the portion not scanned) is 1
The state where writing is not performed once is the best, and the state where it is not complete partial rewriting but becomes less than about twice is required.

Next, effects of the present embodiment will be described.

According to the present embodiment, since the amount of ions in the element is 10 nC / cm ² or less, the influence of the display state of the previous frame can be reduced, and even when gray scale display is performed, gray scale display is performed. The display quality can be improved by reducing spots.

The effect of the previous state history difference becomes smaller as the same image is written more than once, but the ion amount in the element is reduced by two.
In the case of nC / cm ² or less, power consumption can be reduced by reducing the number of times of writing (the number of times of voltage application).

Further, by using the memory state of the domain gradation, the occurrence of flicker and the power consumption can be reduced.

[0059]

The present invention will be described below in more detail with reference to examples.

Example 1 In this example, an active matrix type liquid crystal panel (liquid crystal element) P shown in FIGS. 2 and 4 was produced.

The substrates 1a and 1b have a thickness of 1.1.
mm glass substrate was used.

The common electrode (first electrode) 3a and the pixel electrode (second electrode) 3b are made of ITO having a thickness of about 1000 °.
Films were formed on the surfaces of the glass substrates 1a and 1b.

Further, the alignment control films 6a and 6b are formed at 400 ° so as to cover the common electrode 3a and the pixel electrode 3b, respectively.
Formed with a thickness of Note that the orientation control films 6a and 6b are L
Q1802 (manufactured by Hitachi Chemical) with N-methylpyrrolidone /
2.5% by weight solution of n-butyl cellosolve = 1/1
The coating was performed at a rotation speed of 3000 rpm, and a heat treatment was performed at 250 ° C. for about 1 hour, and the surface was rubbed with a nylon flocking cloth. As a result, the surface energy after the rubbing treatment was 43.9 dyne / cm, which was larger than the surface energy before the rubbing of 11.6 dyne / cm, and the difference between the values of the dispersion terms was 11.2 dyne / cm.
/ Cm.

On the other hand, as the bistable ferroelectric liquid crystal 2, a liquid crystal composition 1 prepared by mixing the following liquid crystal compositions at the weight ratios shown on the right side was used. The composition 1 was prepared using a compound obtained by purifying each single component of the liquid crystal composition 1 with an alumina column and a silica gel column, and was injected into the gap between the substrates under reduced pressure.

[0065]

Embedded image The phase transition temperature of the prepared liquid crystal 2 is as follows, and the spontaneous polarization at a temperature of 30 ° C. is 10.2 nC / cm ^2.
Met.

[0066]

Embedded image Further, the ion amount Qt of the liquid crystal 2 was 10 nC / cm ² .

Here, a method of measuring the ion amount Qt in the element will be described.

When measuring the ion amount Qt, as shown in FIG. 8, a liquid crystal panel P and a resistor R are connected in series, and ±
A triangular wave voltage V _ex of 20 V and 5 Hz (see FIG. 9A) was applied to the liquid crystal panel P, and the amount of current I flowing through the liquid crystal was measured by monitoring the voltage across the resistor R. When such a voltage is applied, as shown in FIG.
A current peak (Ps) associated with the spontaneous polarization and a current peak (Qt) associated with the ion amount appear. The ion amount Qt was obtained by integrating the observed current peaks other than the current peak associated with the spontaneous polarization. . The measurement was performed at a temperature of 30 ° C. The previous state history was evaluated as numerical values as shown in FIG.

The liquid crystal panel according to the present embodiment does not need to write information constantly and has a memory property because of domain gradation control as shown in FIG.

One glass substrate 1a has an average particle size of 1.
Alumina beads of 5 μm are sprayed, and the two rubbing directions of the two substrates are the same, and the rubbing direction of the lower glass substrate 1b is shifted to the left by 6 ° with respect to the rubbing direction of the upper glass substrate 1a. Glass substrates 1a and 1b were bonded together.

Thereafter, the liquid crystal 2 described above was injected into the gap between the substrates in an isotropic phase, and cooled at a cooling rate of 20 ° C./h.

When the liquid crystal panel P was driven by the method shown in FIG. 7, when the writing was performed only once, the previous state history difference remained about 10%, and the writing was 4%.
The previous state history difference has disappeared when it has been performed twice.

Comparative Example 1 A liquid crystal composition 1 was injected into a gap between substrates under reduced pressure.

The other configurations were the same as in the first embodiment.

The ion amount Qt was 20 nC / cm ² .

When the liquid crystal panel P was driven by the method shown in FIG. 7, when the writing was performed only once, the previous state history difference remained about 10% and the writing was 5%.
The previous state history difference did not disappear even if it went round.

(Example 2) A composition obtained by adding 1% of alumina fine particles to the liquid crystal composition used in Example 1 was injected under reduced pressure into a gap between substrates.

Other configurations were the same as those of the first embodiment.

The ion amount Qt was 5 nC / cm ² .

When the liquid crystal panel P was driven by the method shown in FIG. 7, the previous state history difference remained about 7% when writing was performed only once, and when the writing was performed three times. The previous state history difference has disappeared.

(Example 3) Using the liquid crystal composition used in Example 2, LQ1802 (manufactured by Hitachi Chemical Co., Ltd.) purified using an alumina column was used.

Other configurations were the same as those in the first embodiment.

The ion amount Qt was ² nC / cm ² .

When the liquid crystal panel P was driven by the method shown in FIG. 7, the difference between the previous state histories remains about 5% when writing is performed only once, and when the writing is performed twice. The previous state history difference has disappeared.

Example 4 The liquid crystal was injected at a humidity of about 80%.
Was performed by capillary injection (non-vacuum injection) in a humid atmosphere.

The other configuration was the same as that of the third embodiment.

The ion amount Qt was 1 nC / cm ² .

Then, when the liquid crystal panel P was driven by the method shown in FIG. 7, the difference between the previous state histories became 2% or less by writing only once, and the effect was hardly observed.

[0089]

As described above, according to the present invention,
Since the amount of ions in the device is 10 nC / cm ² or less,
The influence of the display state of the previous frame can be reduced, and even when gradation display is performed, gradation display unevenness can be reduced and display quality can be improved.

The effect of the previous state history difference becomes smaller as the same image is written more than once.
In the case of nC / cm ² or less, power consumption can be reduced by reducing the number of times of writing (the number of times of voltage application).

Further, by using the memory state of the domain gradation, the occurrence of flicker and the power consumption can be reduced.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of the structure of a liquid crystal element according to the present invention.

FIG. 2 is a sectional view showing another example of the structure of the liquid crystal element according to the present invention.

FIG. 3 is a diagram showing an applied voltage-transmitted light amount characteristic of a liquid crystal.

FIG. 4 is a circuit diagram showing a circuit configuration of a liquid crystal element driven by the present invention.

FIG. 5 is a circuit diagram showing a circuit configuration of a liquid crystal element driven by the present invention.

FIG. 6 is a timing chart illustrating an example of a method for driving a liquid crystal element according to the present invention.

FIG. 7 is a timing chart showing another example of a method for driving a liquid crystal element according to the present invention.

FIG. 8 is a circuit diagram illustrating a method for measuring the amount of ions.

FIG. 9 is a diagram for explaining a method for measuring the amount of ions.

FIG. 10 is a diagram for explaining a method of evaluating a previous state history.

[Explanation of symbols]

1a, 1b Glass substrate (substrate) 2 Bistable ferroelectric liquid crystal 3a Common electrode (first electrode) 3b Pixel electrode (second electrode) 4 TFT (active element) 10 Gate electrode (gate) 14 Source electrode (source) G ₁ … Gate line P Liquid crystal panel (liquid crystal element) S ₁ … Source line

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takao Takiguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Koichi Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Within Non Corporation (72) Inventor Shinichi Nakamura 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Corporation (72) Inventor Yasushi Shimizu 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Corporation (72) Inventor Minato Yagyu 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Tsuneki Nobushin 3-30-2 Shimomaruko 3-chome, Ota-ku, Tokyo F-term in Canon Inc. (Reference) 2H088 GA04 GA17 HA03 HA08 JA19 MA01 MA13 MA20 5C094 AA01 AA22 BA03 BA49 CA19 CA25 HA08 JA20

Claims (8)

[Claims] 1. A pair of substrates disposed with a predetermined gap therebetween, a bistable ferroelectric liquid crystal disposed between the pair of substrates, a plurality of pixels, and a plurality of pixels. A first electrode and a second electrode disposed so as to sandwich the ferroelectric liquid crystal, and wherein the bistable ferroelectric liquid crystal is driven based on application of a voltage to these electrodes 3. The liquid crystal device according to claim 1, wherein the amount of ions in the device is 10 nC / cm ² or less. 2. The liquid crystal device according to claim 1, wherein the amount of ions in the device is 5 nC / cm ² or less. 3. The liquid crystal device according to claim 2, wherein the amount of ions in the device is ² nC / cm ² or less. 4. The liquid crystal device according to claim 3, wherein the amount of ions in the device is 1 nC / cm ² or less. 5. The liquid crystal device according to claim 1, wherein the bistable ferroelectric liquid crystal contains fine particles for adsorbing ions. 6. The liquid crystal device according to claim 5, wherein the bistable ferroelectric liquid crystal contains alumina fine particles. 7. An alignment control film for controlling an alignment state of said liquid crystal at a position in contact with said bistable ferroelectric liquid crystal,
7. The liquid crystal device according to claim 1, wherein water molecules are adsorbed on the alignment control film. 8. The device according to claim 1, wherein an active element is connected to the second electrode in each of the pixels, and the bistable ferroelectric liquid crystal is driven by turning on / off the active element. 8. The liquid crystal device according to any one of items 7.