JP2001215534A - Liquid crystal device, and drive method for liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent occurrence of the display gradation changes, luminance unevenness, etc., which accompany temperature change. SOLUTION: In a liquid crystal panel P1 shown in drawing, since a chiral smectic liquid crystal 2 in which a threshold voltage for switching differs for each domain is used, when a certain write voltage is applied only a domain where the threshold voltage is smaller than the writing voltage is switched, and the domain where the threshold voltage is larger than the write voltage is not switched. Therefore, the area switched by controlling the write voltage changes, and the gradation display can be performed by it. In addition, a liquid crystal material with a small (for example, change per 10 deg.C is 10% or less) temperature change of the threshold voltage is used for the chiral smectic liquid crystal 2, the display gradation change, etc., accompanying the temperature change can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a liquid crystal element for performing gradation display and a method for driving the liquid crystal element.

[0002]

2. Description of the Related Art Conventionally, a CRT has been known as a display for displaying various kinds of information.
It is widely used for V and VTRs, and for 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.

[0005] As a device for widening the viewing angle, a device utilizing an in-plane mode or an MVA alignment technique has recently been developed. * 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.).

Meanwhile, there has been proposed a method of performing gradation display using the above-mentioned chiral smectic liquid crystal. This method uses a chiral smectic liquid crystal whose threshold voltage (DC threshold voltage) for switching differs for each domain, and when a certain write voltage is applied to the chiral smectic liquid crystal, the threshold voltage is higher than the write voltage. Taking advantage of the fact that only the small domains are inverted and the domains whose threshold voltage is higher than the write voltage are not inverted, the area to be switched is changed by controlling the write voltage, whereby the gradation display (domain level) is performed. Tone display).

[0007]

However, in the conventional chiral smectic liquid crystal, since the threshold voltage greatly changes depending on the temperature, the display gradation fluctuates depending on the temperature, and accordingly, uneven brightness and undisplayed portions occur. There was a problem that the image quality deteriorated.

As a method of solving such a problem, there is a method of controlling an applied voltage according to a temperature. However, there is a problem that a driving circuit becomes complicated and a cost is increased.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal element for preventing a change in display gradation due to a temperature change and a method for driving the liquid crystal element.

Another object of the present invention is to provide a liquid crystal element for preventing the occurrence of luminance unevenness and an undisplayed portion due to a temperature change, and a method of driving the liquid crystal element.

Another object of the present invention is to provide a liquid crystal element having a simple structure.

[0012]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a pair of substrates arranged with a predetermined gap therebetween and a threshold voltage for switching are different for each domain. Together with a chiral smectic liquid crystal arranged between the pair of substrates, and a pair of electrodes sandwiching the chiral smectic liquid crystal and arranged to constitute a plurality of pixels, and comprising these pair of electrodes In a liquid crystal device that performs gradation display by changing a switching area by controlling a voltage applied to the chiral smectic liquid crystal through the chiral smectic liquid crystal, the chiral smectic liquid crystal has a temperature change of the threshold voltage of 10% per 10 ° C. The following liquid crystal is characterized.

Further, according to the present invention, a chiral smectic liquid crystal is swing-inverted by applying a write voltage exceeding a threshold voltage for swing, or a chiral smectic liquid crystal is applied by applying a write voltage exceeding a threshold voltage for latch. A method for driving a liquid crystal element for latch inversion is provided.

[0014]

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

The liquid crystal element according to the present embodiment comprises a pair of substrates 1a and 1b arranged with a predetermined gap therebetween, as shown by reference numerals P ₁ and P ₂ in FIGS. And a pair of electrodes 3a and 3b sandwiching the chiral smectic liquid crystal 2 and forming a plurality of pixels.

Among these, the chiral smectic liquid crystal 2 has a threshold voltage for switching (DC threshold voltage) different for each domain, and a temperature change of the threshold voltage is 10% or less per 10 ° C. Used. The chiral smectic liquid crystal 2 preferably has a temperature change of the threshold voltage of 5% or less per 10 ° C., and more preferably 3% or less per 10 ° C. In order to make the temperature change of the threshold voltage 10% or less per 10 ° C. as described above, a liquid crystal material in which the upper limit temperature of the chiral smectic phase where switching occurs is 70 ° C. or more may be used. In order to reduce the threshold voltage change to 3% or less, a liquid crystal material having an upper limit temperature of the chiral smectic phase of 80 ° C. or more may be used.

In the liquid crystal elements P ₁ and P ₂ as described above, the area to be switched is changed by controlling the write voltage applied to the chiral smectic liquid crystal 2 through the pair of electrodes 3a and 3b. Thereby, gradation display (domain gradation display) can be performed.
That is, when a certain write voltage is applied, only the domain whose threshold voltage is lower than the write voltage is inverted, and the domain whose threshold voltage is higher than the write voltage is not inverted, whereby the gradation display is not performed. It becomes possible.

As the threshold voltage, a threshold voltage for a swing and a threshold voltage for a latch are considered. * A write voltage exceeding the threshold voltage for a swing is applied to swing the chiral smectic liquid crystal 2 so as to reverse the swing. * A chiral smectic liquid crystal 2 may be latch-inverted by applying a write voltage exceeding a threshold voltage for latching.

When the switching of the liquid crystal 2 is performed by the latch process, the chiral smectic liquid crystal 2
The image display can be performed by utilizing the memory property of the device, and the power consumption can be reduced. In addition, both the switching by the swing process and the switching by the latch process can perform gradation display, but the former is suitable for moving image display,
The latter is suitable for displaying still images.

[0020] In this case, the part of the liquid crystal element P _1, P _2, and displays a moving image by performing switching of the liquid crystal 2 by the swing processes, and the liquid crystal element P _1,
In other parts of P _2, the still image is displayed by performing switching of the liquid crystal 2 by the latch process, it may be.

Further, before applying the write voltage, a reset voltage may be applied to the pair of electrodes 3a and 3b to reset the chiral smectic liquid crystal 2.

The chiral smectic liquid crystal 2 may be a ferroelectric liquid crystal or an antiferroelectric liquid crystal. Specifically, liquid crystal compounds of the following general formulas (1) to (5) may be used.

[0023]

Embedded image

(Wherein R ₂₁ and R _{22 each} have 1 to 18 carbon atoms)
And one or more methylene groups in the alkyl group may be -O-, -S-, -CO-, -C
HW -, - CH = CH - , - C≡C- may be replaced by, W is a halogen, CN, a CF _3.

R ₂₁ and R ₂₂ may be optically active. Y ₁ represents a hydrogen atom or a fluorine atom. p, q
Is 0, 1, 2 and p + q is 1 or 2. )

[0026]

Embedded image (Where B ₁ is

[0027]

Embedded image And Y ₁ represents a hydrogen atom or a fluorine atom.

R ₂₃ represents a linear or branched alkyl group having 1 to 18 carbon atoms, and R ₂₄ represents a hydrogen atom, a halogen, a CN group or a linear or branched alkyl group having 1 to 18 carbon atoms. an alkyl group, one or two or more methylene groups in the alkyl group represented by R _23, R ₂₄ are, -O under the condition that heteroatoms are not adjacent -, - S -, - CO -, - C
HW -, - CH = CH - , - C≡C- may also be replaced by, W is a halogen, CN or CF _3. R ₂₃ and R ₂₄ may be optically active. )

[0029]

Embedded image (Where B ₂ is

[0030]

Embedded image Represents

R ₂₅ and R _{26 each} represent a linear or branched alkyl group having 1 to 18 carbon atoms.
One or more methylene groups may be -O-, -S-, -CO-, -CHW
—, —CH ＝ CH—, —C≡C— may be replaced, and W represents halogen, CN or CF ₃ .

Further, R ₂₅ and R ₂₆ may be optically active. )

[0033]

Embedded image (Where B ₃ is

[0034]

Embedded image And Z represents -O- or -S-.

R ₂₇ and R _{28 each} represent a linear or branched alkyl group having 1 to 18 carbon atoms.
One or more methylene groups may be -O-, -S-, -CO-, -CHW-,
—CH ＝ CH—, may be replaced by —C 置 き 換 え C—, and W represents halogen, CN or CF ₃ .

R ₂₇ and R ₂₈ may be optically active. )

[0037]

Embedded image

(Wherein R ₂₉ and R _{30 each} have 1 to 18 carbon atoms)
And one or more methylene groups in the alkyl group may be -O-, -S-, -CO-, -C
HW -, - CH = CH - , - C≡C- may be replaced by, W is a halogen, CN or CF _3.

R ₂₉ and R ₃₀ may be optically active. In addition, examples of the liquid crystal compound represented by the general formula (1) include compounds represented by the following general formulas (1-1) to (1-7).

[0040]

Embedded image Further, examples of the liquid crystal compound represented by the general formula (2) include compounds represented by the following general formulas (2-1) to (2-5).

[0041]

Embedded image Furthermore, examples of the liquid crystal compound represented by the general formula (3) include compounds represented by the following general formulas (3-1) to (3-9).

[0042]

Embedded image Further, examples of the liquid crystal compound represented by the general formula (4) include compounds represented by the following general formulas (4-1) to (4-6).

[0043]

Embedded image

The above general formulas (1-1) to (4-)
In 6), R in the formula is a linear, branched or cyclic alkyl group having 1 to 18 carbon atoms, and one or more methylene groups in the alkyl group are adjacent to a hetero atom. -O-, -S-, -CO-, -C
HW -, - CH = CH - , - may also be rewritten by C≡C-, W represents a halogen, CN or CF _3. R may be optically active.

Here, in order to make the threshold voltage different for each domain as described above, the alignment state of the liquid crystal 2 may be made different for each domain.

On the other hand, various structures can be cited as the structure of the liquid crystal element.

For example, the liquid crystal element may be of a simple matrix type or an active matrix type. In the case of using the active matrix method, as shown in FIG. 2, the active element 4 is connected to one electrode 3b in each pixel.
Just connect to it.

The liquid crystal elements P ₁ and P ₂ may be of a transmission type or a reflection type. In the case of the transmission type, it is preferable to make both substrates 1a and 1b transparent and to arrange a pair of polarizing plates on both sides of the liquid crystal elements P ₁ and P ₂ such that their polarization axes are orthogonal to each other (FIG. 1). Symbols 9a and 9b of
In the case of the reflection type, the polarizing plate is connected to the liquid crystal elements P ₁ and P ₁ .
₂ and at least one of the substrates 1a, 1
It is preferable to add a function of reflecting light to one of b.

Further, a color filter (not shown) may be arranged on at least one of the substrates 1a and 1b to enable color display. By irradiating each color light sequentially without disposing such a color filter, a color filter can be obtained. Display may be performed.

By the way, the above-mentioned substrates 1a and 1b include:
A highly transparent material such as glass or plastic may be used.

The electrodes 3a and 3b may be made of a material such as In ₂ O ₃ or ITO (indium tin oxide), and these electrodes 3a and 3b may be formed on the respective substrates 1a and 1b. . In the case where the liquid crystal element is of an active matrix type, the electrode 3b to which the active element 4 is connected is arranged in a dot shape, and the other electrode 3a is formed on the entire other substrate 1a or in a predetermined pattern. good.

Further, alignment control films 6a and 6b for controlling the alignment state of the liquid crystal 2 may be disposed at positions in contact with the liquid crystal 2. The alignment control films 6a and 6b may be made of an inorganic material (silicon monoxide, silicon dioxide, oxidized oxide). Aluminum, zirconia, magnesium fluoride, cesium oxide, silicon nitride, silicon carbide, boron nitride, etc., and organic substances (polyvinyl alcohol, polyimide, polyamide, polyester, polyimide amide, polyester imide, polyparaxylene, polycarbonate, polyvinyl) Acetal,
Polyvinyl chloride, polystyrene, polysiloxy acid,
Cellulose resin, melanin resin, urea resin, acrylic resin) may be used, and may be formed by solution coating, vapor deposition, or sputtering. Further, the orientation control films 6a,
The surface of 6b may be rubbed with a fibrous material such as velvet, cloth or paper. Further, an oblique evaporation method in which an oxide or a nitride such as SiO is evaporated from an oblique direction of the substrate may be used.

Of these, polyimide is preferable in order to obtain better uniaxial orientation. In such a case, a polyamic acid or polyimide that is soluble in a solvent may be applied and baked.

Further, it is preferable to form a green film on the surface of each of the electrodes 3a and 3b to prevent a short circuit between these electrodes (only one insulating film 5b is shown in FIG. 2). The film may be formed of SiO ₂ , TiO ₂ , Ta ₂ O ₅ or the like.

Further, a spacer (see reference numeral 8 in FIG. 1) may be arranged in the gap between the substrates 1a and 1b, and the size of the gap may be defined by the spacer 8.
For this spacer 8, 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. 0.3-10 to substantially match the axis
It is preferable to set it in the range of μm. For example, the gap between the substrates 1a and 1b when the chiral smectic liquid crystal 2 is arranged is preferably 5 μm or less in order to realize the stability of the ferroelectric phase.

Further, adhesive particles (not shown) made of epoxy resin or the like are dispersed and arranged in the gap between the substrates 1a and 1b, and the adhesiveness between the two substrates 1a and 1b and the liquid crystal elements P ₁ and P _2.
It is good to improve the impact resistance of the dies.

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

[0058] The liquid crystal element P ₂ shown in FIG. 2, a pair of glass substrates 1a arranged with a predetermined spacing, 1b, comprises a, the entire surface of one glass substrate 1a, a common uniform thickness An electrode 3a is formed, and an alignment control film 6a is formed on the surface of the common electrode 3a.

Further, on the other glass substrate 1b side,
As shown in FIG.₁, G _Two, ... are shown in x direction
And the gate line G₁, G_Two, ... is insulated from
Source line S₁, S_Two, ... are arranged in the y direction in the figure.
Is placed. And these gate lines G₁, G_Two,
… And source line S₁, S_TwoThe pixel at each intersection of
Thin film transistor (amorphous
(SiTFT) 4 or an image made of a transparent conductive film such as an ITO film
The elementary electrode 3b, the storage capacitor 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 (gate insulating film) 5b made of silicon nitride (SiNx),
A-Si layer 11 or n + a-Si layer 12, which is a semiconductor layer,
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. On the surface of the a-Si layer 11, n + a-Si layers 12, 13 are formed so as to be separated from each other, and the source electrode 14 is formed on each of the n + a-Si layers 12, 13.
And the drain electrode 15 are formed to be separated from each other. Further, the a-Si layer 11 and the electrodes 14, 1
Channel protection film 16 is formed so as to cover 5.

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 ,. And 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.
The storage capacitor Cs provided in parallel with the liquid crystal 2 is configured (see FIG. 4). 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 chiral smectic 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 capacitance Clc is formed. (See FIG. 4).

[0065] On both sides of the liquid crystal element P _2, are a pair of polarizing plates (of FIG. 1 reference numeral 9a, reference 9b) is arranged in relation to the polarization axis are orthogonal to each other.

In the liquid crystal element P ₂ shown in FIG. 2, an amorphous silicon (a-Si) T
Although FT is used, of course, it is not necessary to limit to this,
Other types of TFTs such as polysilicon (p-Si) may be used, and MIM (Metal-Insulator)
-Metal) or the like (DR-type) in which a MOS-FET formed on a silicon wafer is used as a liquid crystal drive substrate (backplane).
AM use / Normal reflection type, SOI (Silicon O
n Insulator method / normal transmission type).

Next, describes a method of driving the liquid crystal device P ₂ described above.

First, the active element 4 is turned on to apply a reset voltage to the pair of electrodes 3a and 3b to reset the chiral smectic liquid crystal 2 to a bright state or a dark state.

Next, when the active element 4 is turned on and a write voltage (a write voltage corresponding to a display gradation) is applied to the pair of electrodes 3a and 3b, only the domain whose threshold voltage is smaller than the write voltage is applied. Are inverted, and the domain whose threshold voltage is higher than the write voltage is not inverted, whereby a gray scale display is performed.

FIG. 5 shows the liquid crystal element P ₂ shown in FIG. 2 and FIG.
FIGS. 3A and 3B are diagrams illustrating an example of the driving method of FIG. 1A, and FIG. 2A illustrates a state in which a gate voltage _Vg is applied to a certain gate line G _i , and FIG. FIG. 3C shows a state in which a source voltage (write voltage V _w ) is applied to the source line _Sj , FIG. 3C shows the potential of the common electrode 3a, and FIG. pixels intersection of G _i and the source line S _j (i.e., the liquid crystal 2) shows a state of holding the voltage change of the drawing (e) is a diagram showing changes in transmitted light quantity in the pixel.

Now, a gate voltage V _g1 is applied to a certain gate line G _i for a certain period (see FIG. 7A), and a certain source line _Sj is held at a reference potential (see FIG. Figure (b) refer), the reset voltage V _R is applied to the common electrode 3a reference (FIG. (c)). Then, the TF of the pixel is
T4 is turned on by the application of the gate voltage V _g1, the pixel electrode 3b and the source line S _j is the same potential, the liquid crystal 2 negative reset voltage -V _R is applied (see FIG. (D)), As a result, the liquid crystal 2 is reset to a first state (for example, a black state). The reset voltage V _R of the common electrode 3a, it is preferable to off before turning off the gate voltage V _g1.

Next, the write voltage V _w of the positive polarity to the source line S _j is applied (see FIG. (B)), by applying a gate voltage V _g2 to the gate line G _i (FIG. (A) see) , Liquid crystal 2
Switching of the liquid crystal 2 is performed write voltage V _w is applied to. Note that the liquid crystal capacitance Clc is used to turn off the gate voltage V _g2 before the potential of the source line _Sj returns to the reference potential.
While the write voltage V _w is held in the liquid crystal 2 (the voltage held in the liquid crystal capacitor Clc) holding voltage by the rotation of the dipole accompanying the liquid crystal response because it has a spontaneous polarization decreases (details described next). In this case, gray state of the pixel is, until the next reset voltage V _R is applied is held in a very stable condition.

Then, such driving is repeated every fixed period (frame period) to rewrite an image.

Next, the present inventors set the write voltage _Vw to 1
When the voltage was set to 0 V, 7 V, or 4 V, a change in holding voltage and a change in optical response were measured. When measuring,
A voltage follower amplifier (not shown) was connected to the point indicated by the symbol A in FIG. 4, and a polarizing microscope set in a crossed Nicols was used. The evaluation area under a microscope was 10 micronsφ. FIG. 6A shows various write voltages V _w (10 V,
FIG. 7B is a diagram illustrating a measurement result of a change in a holding voltage when 7V, 4V) is applied, and FIG. 7B is a diagram illustrating a measurement result of a change in an optical response. In these figures, the symbol V
₁₀ shows the holding voltage change when the write voltage V _w is 10V, the code V ₇ write voltage V _w represents the holding voltage change when the 7V, reference numeral V ₄ is held when the write voltage V _w is 4V 3 shows a voltage change. Further, reference numeral B ₁₀ write voltage V _w represents the optical response changes when the 10V, code B
₇ write voltage V _w represents the optical response changes when the 7V, code B ₄ shows the optical response changes when the write voltage V _w is 4V.

For example, at the timing of the symbol T ₀ shown in FIG.
The application of a write voltage V _w, after a predetermined time has elapsed (in the figure the time T ₁₎ liquid crystal response begins (FIG. 6
(B) reference numeral B ₇ of). In such a case, between T _{0 and} T ₁ , since the TFT 4 is turned on, a new charge is supplied to the pixel electrode 3 b and the holding voltage V ₇ does not decrease (see FIG. 6A). T ₁ in the following, TF
Since T4 is turned off and supply of electric charge to the pixel electrode 3b is not performed, the holding voltage decreases as the dipole rotates. Note that the decrease ΔV of the holding voltage is

[0076]

Equation 1 ΔV = ΣPs · S / (Clc + Cs) where Ps; spontaneous polarization S; area of inverted domain Clc; liquid crystal capacitance Cs;

When the present inventor observed the response of the liquid crystal using a microscope and a strobe light source, at time T ₁ , first, domain 1 was inverted in white, domain 2 was inverted in white, and domain 3 was completely inverted. It turned out that white inversion did not occur.

By the way, the present inventor has determined that the operation of each domain
In order to know the details in more detail, a rectangular wave as shown in FIG.
Pulse write voltage V_wIs the magnitude and pulse width t
_wIs applied to the liquid crystal element as shown in FIG. 8 so that the * domain has a pulse width t_wNeeded to invert white within
Write voltage V_w(That is, flipping during the swing process
The relationship between the magnitude of the threshold voltage for the
* White is determined 16 msec after the pulse is turned off.
Voltage V required for_w(Ie latch
Threshold voltage for inversion in the process) and pulse width t
_wRelationship with, sought. The result was as shown in FIG. In addition,
Code C₁, C_Two, C_ThreeCurve has a domain whose pulse width t
_wThreshold voltage V required for white inversion within_wThe size of
Pulse width t_wAnd the symbol C₁Is in domain 1
About the symbol C_TwoIs for domain 2,
Code C_ThreeIs for domain 3. Also,
No. D₁, D_Two, D_ThreeThe curve of the domain cuts the pulse
Required since white is determined 16 msec after
Threshold voltage V_wSize and pulse width t _wShows the relationship with
Sign D₁Is for domain 1, reference D_TwoIs Dome
For in 2, symbol D_ThreeIs about domain 3
belongs to.

Next, the present inventor: * Changes in the integral value (= ∫V _m dt) of the applied voltage necessary to invert each domain in the swing process, and * Inverts each domain in the latch process. The change in the integral value (= 印 加 V _m dt) of the applied voltage required for the measurement was examined, and the result was as shown in FIG. In this figure, symbols E ₁ , E ₂ , and E ₃ indicate the former (that is, changes in the integral value of the applied voltage necessary to invert each domain in the swing process), and symbol E ₁ indicates the domain. The symbol E ₂ is for domain 2 and the symbol E ₃ is for domain 3.
Further, reference numeral F _1, F _2, F _3, the latter (i.e., change in the integrated value of the applied voltage required to invert each domain in the latch process) shows the reference numeral F ₁ for domain 1 ones, the code F ₂ are those for domain 2, reference numeral F ₃ are for domain 3.

Now, when a voltage whose integral value changes as shown by the symbol H is applied, the domain 1 swings and inverts at time T ₁ when the integral value of the curve H exceeds the integral value of the curve E ₁ ,
Integrated value of the curve H domain 2 when T ₂ exceeds the integrated value of the curve E ₂ swings reversed. The threshold voltage (integral value) of each domain is different as shown in the figure, and the threshold voltage (integral value) of the domain 1 is lowest in the domain 1 and increases in the order of the domain 2 and the domain 3. Therefore, white inversion is performed in order from domain 1 having a lower threshold voltage.

The reason why the domain 3 is not white-inverted is that the liquid crystal potential decreases due to the white inversion of the domain 1 and the domain 2 (rotation of the dipole of the domain), and the rising degree of the curve H gradually becomes gentle, and the curve E ₃ Not to be larger than Then, since the domain 3 does not invert white, the gradation change stops.

On the other hand, whether or not the gradation obtained by the white inversion in the swing process is maintained as it is depends on the threshold voltage of the latch (that is, the curve of the signs F ₁ , F ₂ , F ₃ ). It was revealed.

[0083] Figure 11 is a diagram showing a state of the voltage change and the optical response change when the applied voltage was 0V after all the domains by applying a write voltage of 10V is swung inverted code K ₁ is , A change in optical response when the voltage is set to 0 V at time T ₁ , a code K ₂ indicates a change in optical response when the voltage is set to 0 V at time T ₂ , and a code K ₃ shows an optical response change when the voltage to 0V at time T _3.

When the voltage is set to 0 V at time T ₁ , 5
0% domain is not latched, if 30% of the domains when a voltage to 0V at time T _2, which is not latched, the voltage at time T ₃ to 0V 10
0% of the domains were latched. From this,
It can be understood that a threshold voltage for the latch exists for each domain separately from the swing. By applying a voltage exceeding the "threshold voltage for latching", the domain gradation is maintained even after the application of the voltage is stopped, and the memory property of the image can be realized. Liquid crystal has a resistance component,
The internal potential goes to 0V with the RC time constant. At this time, the threshold voltage must be exceeded to maintain the gradation state.

Next, effects of the present embodiment will be described.

According to the present embodiment, since the chiral smectic liquid crystal 2 having a threshold voltage change of 10% or less per 10 ° C. is used, the display gradation change due to the temperature change is small, and uneven brightness and undisplay The occurrence of portions can be avoided, and good image quality can be obtained.

Further, it is not necessary to use a drive circuit for controlling the applied voltage according to the panel temperature as described in the conventional example, so that the apparatus can be simplified and the cost can be avoided.

[0088]

The present invention will be described below in more detail with reference to examples. EXAMPLE 1 In this Example, was prepared a liquid crystal panel (liquid crystal device) P ₂ shown in FIGS.

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

The common electrode 3a and the pixel electrode 3b are
The glass substrates 1a and 1 are made of an ITO film having a thickness of about 1000 mm.
b.

Further, the alignment control films 6a and 6b are formed so as to cover the common electrode 3a and the pixel electrode 3b by 400.degree.
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, the liquid crystal 2 was prepared by mixing the following liquid crystal compositions at the weight ratios shown on the right side.

[0093]

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.

Below room temperature 81 ° C. 86 ° C. 103 ° C. Cry-SmC ^* -SmA-Ch-Iso

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.

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

The inventor of the present invention has prepared the liquid crystal panel P ₂
Under crossed Nicols, set to a polarizing microscope with a photomultiplier and at various temperatures (30 ° C, 40 ° C,
(50 ° C.) at the driving method shown in FIG. 5 to determine the relationship between the writing voltage _Vw and the transmittance. The reset voltage V _R was 30 V · 100 μsec, the pulse width of the gate voltage V _g2 during image writing was 10 μsec, and the writing voltage V _w was 0 to +10 V. The evaluation area is 1
The transmittance was measured 16 msec after turning off the gate voltage V _g2 during image writing. As a result, as shown in FIG. 12, a very smooth gradation curve was obtained, and an extremely good and stable display was obtained regardless of the display history before reset. Observation with the naked eye showed no roughness. Further, the gradation state was held extremely stably until the next reset voltage was applied.

In the liquid crystal 2 used in this example, the maximum temperature of the chiral smectic phase is 80 ° C. or more, and the temperature change of the threshold voltage is 3% or less per 10 ° C.

[0099]

[Formula 2] DC threshold voltage at 30 ° C./DC threshold voltage at 40 ° C. = 1.025 DC threshold voltage at 40 ° C./DC threshold voltage at 50 ° C. = 1.0
20.

According to the present embodiment, a change in display gradation due to a change in temperature was small, and it was possible to avoid the occurrence of luminance unevenness and undisplayed portions, and to obtain good image quality. (Example 2) In this example, the following liquid crystal composition was mixed at the weight ratio shown on the right side to prepare liquid crystal 2.

[0101]

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.

-6.degree ^. C. 71.degree ^. C. 85.degree. C. 97.degree ^. C. Cry-SmC ^* -SmA-Ch-Iso The tilt angles at each temperature are as shown in the table below.

[0103]

[Table 1] Other configurations and manufacturing conditions were the same as in Example 1.

Then, the relationship between the write voltage _Vw and the transmittance was obtained by the same method as in the first embodiment.
As a result, the same effect as in Example 1 was obtained.

In the liquid crystal 2 used in this example, the maximum temperature of the chiral smectic phase is 70 ° C. or more, and the temperature change of the threshold voltage is about 10% or less per 10 ° C., specifically,

[0106]

Equation 3 DC threshold voltage at 30 ° C./DC threshold voltage at 40 ° C. = 1.103 DC threshold voltage at 40 ° C./DC threshold voltage at 50 ° C. = 1.0
97, and an effect almost the same as that of Example 1 was obtained. (Embodiment 3) In this embodiment, * the maximum temperature of the chiral smectic C phase is 76 ° C, and * the temperature change of the threshold voltage is 5% or less per 10 ° C (specifically, the DC threshold voltage at 30 ° C / 40 (DC threshold voltage at 100 ° C. = 1.042, DC threshold voltage at 40 ° C./DC threshold voltage at 50 ° C. = 1.054), and the other configuration was the same as that of Example 1.

According to the present embodiment, almost the same effects as in the first embodiment were obtained. (Example 4) In this example, * the maximum temperature of the chiral smectic C phase is 83 ° C, and * the temperature change of the threshold voltage is 3% or less per 10 ° C (specifically, the DC threshold voltage at 30 ° C / 40 (DC threshold voltage at 100 ° C. = 1.024, DC threshold voltage at 40 ° C./DC threshold voltage at 50 ° C. = 1.023), and the other configuration was the same as that of Example 1.

According to the present embodiment, substantially the same effects as in the first embodiment were obtained. (Comparative Example) In this comparative example, * the maximum temperature of the chiral smectic C phase is 53 ° C, and * the temperature change of the threshold voltage is 20% or more per 10 ° C (specifically, the DC threshold voltage at 30 ° C / 40 ° C). DC threshold voltage = 1.234, DC threshold voltage at 40 ° C./DC at 50 ° C.
Threshold voltage = 1.344), and the other configurations were the same as in the first embodiment.

Then, the relationship between the write voltage _Vw and the transmittance was determined by the same method as in the first embodiment.
As shown in FIG.

According to this comparative example, a change in display gradation with a change in temperature was large, and luminance unevenness and a non-display portion occurred depending on the temperature.

[0111]

As described above, according to the present invention,
Since a chiral smectic liquid crystal having a threshold voltage temperature change of 10% or less per 10 ° C. is used, a change in display gradation due to a temperature change is small, and the occurrence of luminance unevenness and a non-display portion can be avoided, and good image quality can be obtained. be able to.

Further, it is not necessary to use a drive circuit for controlling the applied voltage according to the panel temperature as described in the conventional example, so that the apparatus can be simplified and the cost can be avoided.

[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 circuit diagram showing another example of the structure of the liquid crystal element according to the present invention.

FIG. 4 is an equivalent circuit diagram illustrating an example of a structure of a liquid crystal element according to the present invention.

FIG. 5 is a timing chart illustrating an example of a method for driving a liquid crystal element according to the present invention.

FIG. 6 is a diagram showing a change in holding voltage and a change in optical response.

FIG. 7 is a waveform chart showing a waveform of a write voltage.

FIG. 8 is a diagram for explaining how a write voltage is applied.

9 is a diagram showing a threshold voltage of each domain (the relationship between the voltage value V _w and the pulse width t _w).

FIG. 10 is a diagram showing a change in an integrated value of an applied voltage and the like.

FIG. 11 is a diagram showing a change in holding voltage and a change in optical response.

FIG. 12 is a diagram showing a relationship between a writing voltage and transmittance.

FIG. 13 is a diagram showing a relationship between a writing voltage and transmittance.

FIG. 14 is a diagram showing a relationship between a writing voltage and transmittance.

[Explanation of symbols]

1a, 1b Glass substrate (substrate) 2 Chiral smectic liquid crystal 3a Common electrode (electrode) 3b Pixel electrode (electrode) P ₁ liquid crystal panel (liquid crystal element) P ₂ liquid crystal panel (liquid crystal element)

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Yukio Hanyu 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Takao Takiguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Shinichi Nakamura 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Koji Noguchi 3-30-2, Shimomaruko 3-chome, Ota-ku, Tokyo Canon Inc. ( 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 ( Reference) 2H088 GA04 GA17 HA03 HA06 HA08 JA17 MA01 MA04 2H093 NA16 NA54 NC34 NC38 ND06 ND44 NE04 NF17 5C006 AA12 AC02 AC26 AF64 BA12 BB16 BC03 BC06 BC13 FA19 FA22 FA56

Claims (9)

[Claims] 1. A pair of substrates arranged with a predetermined gap therebetween, a chiral smectic liquid crystal having a switching threshold voltage different for each domain and arranged between the pair of substrates, and a chiral smectic liquid crystal arranged between the pair of substrates. A pair of electrodes arranged to sandwich the smectic liquid crystal and constitute a plurality of pixels, and an area switched by controlling a voltage applied to the chiral smectic liquid crystal through the pair of electrodes. Wherein the chiral smectic liquid crystal is a liquid crystal having a threshold voltage change of 10% or less per 10 ° C. in the liquid crystal element. 2. The liquid crystal device according to claim 1, wherein the chiral smectic liquid crystal is a liquid crystal having a threshold voltage change of 5% or less per 10 ° C. 3. The liquid crystal device according to claim 1, wherein the chiral smectic liquid crystal is a liquid crystal having a threshold voltage change in temperature of 3% or less per 10 ° C. 4. The liquid crystal device according to claim 1, wherein the chiral smectic liquid crystal has a maximum temperature of a chiral smectic phase of 70 ° C. or higher. 5. The liquid crystal device according to claim 4, wherein the chiral smectic liquid crystal has a maximum temperature of a chiral smectic phase of 80 ° C. or higher. 6. The liquid crystal device according to claim 1, wherein the chiral smectic liquid crystal is a bistable ferroelectric liquid crystal. 7. The method of driving a liquid crystal element according to claim 1, wherein a write voltage exceeding a threshold voltage for swing is applied to swing the chiral smectic liquid crystal. A method for driving a liquid crystal element. 8. The method for driving a liquid crystal element according to claim 1, wherein a writing voltage exceeding a threshold voltage for latching is applied to invert the chiral smectic liquid crystal. A method for driving a liquid crystal element. 9. A moving picture is displayed by performing switching of a liquid crystal by a swing process in a part of the liquid crystal element, and by performing a switching of a liquid crystal by a latch process in another part of the liquid crystal element. The method for driving a liquid crystal element according to claim 7, wherein a still image is displayed.