JP2000250073A - Liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the lowering of gray scale reproducibility and the occurrence of uneven brightness in a liquid crystal device surface or the like due to veriation of panel temperature. SOLUTION: As for this liquid crystal device, in a liquid crystal panel P in which a pair of electrodes 3a, 3b are arranged so as to hold a liquid crystal 2 and one of the electrode 3b is connected to an active element 4, the temperature dependence of the voltage holding capacity between the pair of electrodes 3a, 3b is regulated to be <=10%/10 deg.C. Thus, even if the temperature of the liquid crystal panel P is locally varied by about 10 deg.C, the voltage effectively applied to the liquid crystal 2 is hardly changed, so that the lowering of gray scale reproducibility and the occurrence of uneven brightness in the liquid crystal device surface or the like are prevented.

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 used for a flat panel display, a projection display, a printer, and the like.

[0002]

2. Description of the Related Art Various types of liquid crystal panels (liquid crystal elements) for switching light using liquid crystals have been proposed.

[0003] Such a liquid crystal panel includes an active matrix type liquid crystal panel using a nematic liquid crystal and arranging a thin film transistor (active element) such as a TFT in each pixel. * Twisted nematic.
atic) mode and * In-plane switching (In-Plane S)
switching mode, * Super Twisted Nematic (Super T)
In the case of a switched nematic mode, there has been a problem that the response speed of the liquid crystal is slow and a response takes several tens of msec or more in any of the modes.

The details of the above-mentioned twisted nematic mode are described in “M.
adt) and W. Helfrich
ich), “Applied Physics Le
ters ", Vol. 18, No. 4, February 15, 1971
Published on pages 127-128).

[0005] The in-plane switching mode, which has recently been announced, improves the viewing angle characteristics, which is a drawback of the twisted nematic mode liquid crystal panel, by using a lateral voltage.

On the other hand, unlike such a nematic liquid crystal, a smectic liquid crystal, particularly a liquid crystal using a chiral smectic liquid crystal such as a ferroelectric liquid crystal or an antiferroelectric liquid crystal, performs the above-described inversion switching by spontaneous polarization. The problem of a quick response speed can be improved.

[0007] A liquid crystal panel using a ferroelectric liquid crystal is provided by Clark and Lagawell.
erwall) (Japanese Unexamined Patent Publication No.
No. 6-107216, U.S. Pat. No. 4,367,924). In this ferroelectric liquid crystal, the reversal switching of the liquid crystal molecules is performed by applying a voltage to the spontaneous polarization of the liquid crystal molecules when a voltage is applied, so that a very fast response speed can be obtained. Further, the ferroelectric liquid crystal is considered to be suitable for a high-speed, high-definition, large-area display element or light valve because it has memory properties and excellent viewing angle characteristics.

Further, as an antiferroelectric liquid crystal, recently, an antiferroelectric liquid crystal exhibiting a three-stable state has been attracting attention. In this antiferroelectric liquid crystal, as in the case of the above-mentioned ferroelectric liquid crystal, the switching of the molecules is performed by the effect on the spontaneous polarization of the liquid crystal molecules, so that a very fast response speed can be obtained. Further, the antiferroelectric liquid crystal is characterized in that, when no voltage is applied, the liquid crystal molecules have a molecular alignment structure such that the liquid crystal molecules cancel each other's spontaneous polarization.

In particular, recently, by driving the above-mentioned smectic liquid crystal with an active matrix type liquid crystal panel, sufficient gradation reproducibility is obtained, and at the same time, high quality and high speed having high speed capable of coping with moving images are realized. There is a movement to provide a liquid crystal display device having a large capacity.

[0010]

In the case where a smectic liquid crystal having spontaneous polarization as described above is driven by an active matrix using a TFT, electric charges injected from the TFT in a selected pixel are as shown in FIG. First, the liquid crystal molecules suddenly drop due to the switching of the liquid crystal molecules, that is, the reversal of the spontaneous polarization (see the symbol ΔV ₁ ). Thereafter, the liquid crystal drops gradually due to the flow of a non-ohmic leak current caused by mobile ions. (See sign ΔV ₂ ), (Japanese Journal of Applied Physics, Vol. 36, 1997, 720-200)
Pp. 729).

Therefore, the voltage holding ratio during one frame is determined by these voltage drop factors (spontaneous polarization of liquid crystal molecules and mobile ion density), but these voltage drop factors themselves have temperature dependence. The ambient temperature of the liquid crystal panel (or heating by a backlight device, etc.)
Accordingly, the spontaneous polarization of liquid crystal molecules and the mobile ion density change, and the degree of voltage drop (in other words, the voltage holding ratio during active driving) also changes. For this reason, there is a problem that the voltage effectively applied to the liquid crystal is changed, and the gradation reproducibility is reduced and the luminance unevenness in the panel surface is generated.

Although it is conceivable to introduce a temperature compensation program into the drive circuit in consideration of these temperature dependencies, it is not preferable because the device becomes complicated and expensive.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid crystal element which prevents a decrease in gradation reproducibility and the occurrence of luminance unevenness in a panel surface.

[0014]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and comprises a pair of substrates disposed with a predetermined gap therebetween, and a chiral substrate disposed between the pair of substrates. A smectic liquid crystal, comprising a pair of electrodes constituting a plurality of pixels and arranged to sandwich the chiral smectic liquid crystal, and a plurality of active elements connected to one electrode and arranged for each pixel, In a liquid crystal element driven by applying a voltage to the chiral smectic liquid crystal through the pair of electrodes, the temperature dependency of the voltage holding ratio of the pair of electrodes is 10% or less per 10 ° C. It is characterized by.

[0015]

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

As shown in FIGS. 1 and 2, a liquid crystal element P according to the present embodiment has a pair of substrates 1a and 1b arranged with a predetermined gap therebetween, and a pair of substrates 1a and 1b.
b, and a pair of electrodes 3a and 3b which constitute a plurality of pixels and are arranged so as to sandwich the chiral smectic liquid crystal 2 therebetween.
And a plurality of active elements 4 connected to one electrode 3b and arranged for each pixel, and applying a voltage to the chiral smectic liquid crystal 2 via the pair of electrodes 3a and 3b. Driven by the The temperature dependency of the voltage holding ratio of the pair of electrodes 3a and 3b is 10% or less per 10 ° C.

Here, a method for controlling the temperature dependency of the voltage holding ratio of the pair of electrodes 3a and 3b within the above-described range will be described.

The liquid crystal composition used for the chiral smectic liquid crystal 2 is roughly classified into a trace amount of chiral component for imparting spontaneous polarization and a non-chiral component as a base material. The temperature dependence of spontaneous polarization was determined by the composition of the chiral component, and the temperature dependence of the mobile ion density was determined by the composition of the non-chiral component. Therefore, the pair of electrodes 3a, 3
In order to set the temperature dependency of the voltage holding ratio in b in the above range, the composition of the chiral component and the composition of the non-chiral component may be adjusted.

It should be noted that "temperature change of 10 ° C."
It varies from 10C to 20C, from 20C to 30C and from 30C to 40C. Ideally, in any of these cases, it is desirable that the change in the voltage holding ratio be 10% or less, but at least a temperature change of 10 ° C. near room temperature (that is, 35 ° C. to 45 ° C.) The above condition (ie,
It is desirable that the change in the voltage holding ratio is 10% or less).

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. . The electrodes 3b to which the active elements 4 are connected are preferably arranged in a matrix in the form of dots, and the other electrode 3a is preferably formed on the entire other substrate 1a or in a predetermined pattern.

Further, on the surface of each of the electrodes 3a, 3b, a green-green film 5a, 5b for preventing a short circuit between these electrodes.
5b is preferably formed (only the insulating film 5b is shown in FIG. 1,
FIG. 3 shows both the green-colored films 5a and 5b), and the green-colored film 5b may be formed of SiO ₂ , TiO ₂ , Ta ₂ O ₅ or the like.

Further, at positions in contact with the chiral smectic liquid crystal 2, alignment control films 6a and 6a for controlling the alignment state are provided.
6b may be arranged. The orientation control films 6a and 6b may be subjected to a uniaxial orientation treatment. For example, * a film made of an organic material such as polyimide, polyimide amide, polyamide or polyvinyl alcohol is applied to form a film. And a method of forming an obliquely deposited film by obliquely depositing an inorganic material made of an oxide or a nitride such as * SiO on the substrates 1a and 1b. The alignment control films 6a, 6a
The pretilt angle of the liquid crystal molecules (that is, the angle formed by the liquid crystal molecules with respect to the alignment control films 6a and 6b near the interface between the alignment control films 6a and 6b) is adjusted by the material b and the conditions of the uniaxial alignment treatment. When the alignment control films 6a and 6b subjected to the uniaxial alignment treatment are arranged on both sides of the chiral smectic liquid crystal 2, the relationship between the uniaxial alignment treatment directions (particularly the rubbing direction) is determined in consideration of the liquid crystal material used. Parallel, * anti-parallel, * crossing in a range of 45 ° or less may be set.

Further, a spacer (see reference numeral 8 in FIG. 3) 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 substrate 1a on which the chiral smectic liquid crystal 2 is arranged,
The gap size of 1b is preferably set to be equal to or less than half the helical pitch of the chiral smectic liquid crystal 2 in the bulk state.

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 adhesion between the substrates 1a and 1b and the shock resistance of the liquid crystal element P. And 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.

Further, the liquid crystal element P may be of a transmission type or a reflection type. In the case of the transmission type, the substrates 1a and 1b may be made transparent and a pair of polarizing plates may be arranged on both sides of the liquid crystal element P such that their polarization axes are orthogonal to each other. , A polarizing plate is disposed on at least one side of the liquid crystal element P, and the substrates 1a, 1
It is preferable to add a function of reflecting light to one of b. 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.

On the other hand, gradation control may be performed by using the method described in Japanese Patent Application No. 10-177145. That is, when no voltage is applied, the chiral smectic liquid crystal 2 shows an alignment state in which the average molecular axis of the liquid crystal molecules is monostable, and is driven by applying a voltage of one polarity. in case of,
The average molecular axis of the chiral smectic liquid crystal 2 is tilted to one side from the mono-stabilized position, and a voltage of another polarity (the opposite polarity to the one polarity; hereinafter the same) is applied. When driven, the average molecular axis of the chiral smectic liquid crystal 2 is opposite to the other side (that is, the side that tilts when the voltage of one polarity is applied) from the monostabilized position. Tilt to the side).

When the voltage of one polarity or the voltage of the other polarity is applied, the tilt angle (hereinafter referred to as “tilt angle”) with respect to the position where the average molecular axis is monostable is referred to. Is continuously changed according to the magnitude of the voltage. Accordingly, the amount of light emitted from the liquid crystal element P changes continuously according to the magnitude of the voltage applied to the chiral smectic liquid crystal 2, thereby enabling gradation control. Note that in order to perform such gradation control, a driving circuit for supplying a gradation signal is preferably connected to the liquid crystal element P.

In this case, it is preferable that the maximum value of the tilt angle when the voltage of one polarity is applied is different from the maximum value of the tilt angle when the voltage of the other polarity is applied. In such a case, the maximum value of the amount of light emitted from the liquid crystal element P in a state where the voltage of the one polarity is applied (hereinafter referred to as “first amount of light”), and the voltage of the other polarity is applied. In this state, the maximum value of the amount of light emitted from the liquid crystal element P (hereinafter, referred to as “second amount of light”) is different.

It is preferable that the maximum value of the tilt angle when the voltage of one polarity is applied is larger than the maximum value of the tilt angle when the voltage of another polarity is applied.
In such a case, the first light amount becomes larger than the second light amount.

Specifically, when the maximum value of the tilt angle when the voltage of one polarity is applied is five times or more the maximum value of the tilt angle when the voltage of the other polarity is applied, good.

Further, it is preferable that the tilt angle when the voltage of the other polarity is applied is substantially 0 °.

Further, by appropriately disposing the polarizing plate, the light quantity (third light quantity) emitted from the liquid crystal element in the state where no voltage is applied may be substantially zero. FIG. 4 shows a voltage-transmitted light amount characteristic of the chiral smectic liquid crystal 2 in such a manner.

In order to make the chiral smectic liquid crystal 2 exhibit the above-mentioned characteristics, the liquid crystal 2 is required to have * an isotropic liquid phase (Iso) -cholesteric phase (Ch) -chiral smectic C A phase transition series of a phase (SmC ^* ) and a phase transition series of an * isotropic liquid phase (Iso) -chiral smectic phase (SmC ^* ), and the normal direction of the smectic layer of the liquid crystal 2 is substantially changed. It is only necessary to use a unidirectional one and to form a state where the memory property is lost in the SmC ^* phase by any of the following methods. Ch-SmC ^{* During} phase transition or Iso-SmC
^* A method of applying a positive or negative DC voltage to the liquid crystal 2 between a pair of substrates during a phase transition. A method of arranging an alignment control film made of a different material so as to sandwich the liquid crystal 2. For the alignment control film, the treatment method (film formation conditions, rubbing strength, UV
A method of differentiating treatment conditions such as light irradiation) A pair of alignment control films are arranged so as to sandwich the liquid crystal 2 and an underlayer is arranged on the back side (substrate side) of each alignment control film, respectively. On the other hand, as the active element 4 described above, TFT or M
IM (Metal-Insulator-Metal)
Etc. may be used.

Here, an example of the configuration of an active matrix type liquid crystal element P using a TFT will be described with reference to FIGS.

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

Further, on the side of the other glass substrate 1b, as shown in FIG. 2, the gate lines G _1, G _2, ... are arranged in large numbers in the illustrated x-direction, the gate lines G _1, G _2, ... and , 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 source lines S ₁ , S ₂ ,..., A pixel at each intersection, a thin-film transistor (amorphous SiTFT) 4 as an active element, a pixel electrode 3 b made of a transparent conductive film such as an ITO film, a storage capacitor electrode 7, and the like. Are located.

Of these, the amorphous Si TFT 4 is
As shown in FIG. 1, 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. 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 chiral smectic liquid crystal 2 having spontaneous polarization is arranged in the gap between the glass substrates 1a and 1b and between the pixel electrode 3b and the common electrode 3a, thereby forming a liquid crystal capacitor Clc. (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.

Although the amorphous Si TFT 4 is used in the liquid crystal element P shown in FIG. 1, the present invention is not limited to this, and a polycrystalline Si (p-Si) TFT may be used.

Next, an example of a method for driving the above-described liquid crystal element P will be described.

In the above-described liquid crystal element P, a gate voltage is applied to each of the gate lines G ₁ , G ₂ ,... From the scanning signal driver 20 in a line-sequential manner, and the TFT 4 is turned on by the application of the gate voltage. Become.

On the other hand, in synchronization with the application of the gate voltage, a source voltage (an information signal voltage corresponding to information to be written in each pixel) is applied from the information signal driver 21 to the source lines S ₁ , S ₂ ,.
Is applied. Therefore, in a pixel in which the TFT 4 is in the ON state, the source voltage is applied to the liquid crystal 2 via the TFT 4 and the pixel electrode 3b, and the switching of the liquid crystal 2 is performed in pixel units.

Such driving is repeated at regular intervals (frame periods) to rewrite an image.

As shown in FIG. 6, one frame period is divided into a plurality of field periods F ₁ , F ₂ ,.
The image rewriting may be performed in each of the field periods F ₁ , F ₂ ,. Hereinafter, the driving method will be described.

FIG. 6 shows that each frame period F ₀ is 2
FIG. 4A is a diagram showing an example in which the field is divided into _two field periods F ₁ and F ₂ , and FIG. 4A shows a state in which a gate voltage Vg is applied to one certain gate line Gi _; ) Is a certain 1
FIG. 4C shows a state in which a source voltage Vs is applied to a source line _Sj . FIG. 4C shows a state in which a pixel (ie, liquid crystal 2) at the intersection of the gate line G _i and the source line _Sj is supplied with a voltage Vpi.
FIG. 4D is a diagram showing a state in which x is applied, and FIG. 4D is a diagram showing a change in the amount of transmitted light in the pixel.

Now, a gate voltage Vg is applied to a certain gate line G _i for a certain period (selection period Ton) (see FIG. 3A), and a gate voltage is applied to a certain source line _Sj. During the selection period Ton synchronized with the application of Vg, the common electrode 3
source voltage Vs (= V
x) is applied. Then, the TFT 4 of the pixel is turned on by the application of the gate voltage Vg, the source voltage Vx is applied via the TFT 4 and the pixel electrode 3b, and the liquid crystal capacitance Clc and the storage capacitance Cs are charged.

During the non-selection period Toff other than the selection period Ton, the gate voltage Vg is not applied to the other gate lines G ₁ ,
G ₂ ,... Are applied to the gate lines G _i shown in FIG.
, And the TFT 4 of the pixel is turned off. Therefore, the liquid crystal capacitor Clc and the storage capacitor Cs hold the charged charges during this period (see FIG. 3C). Thereby, it becomes possible throughout the field period F ₁ on the liquid crystal 2 voltage Vpix (= Vx) is continuously applied, 1 almost the same amount of transmitted light will be maintained throughout the field period F ₁ (see the (d) of FIG ).

[0054] Other gate lines G _1, G _2, ... of the scan is completed (i.e., when the field period F ₁ is completed), is applied again the gate voltage Vg to the gate line G _i as described above (FIG. ( a)), in synchronization with this, the source line S
_{To j} , a source voltage -Vx having a polarity opposite to that of the previous one is applied (see FIG. 3B). As a result, the source voltage −
Vx is charged to the liquid crystal capacitance Clc and the storage capacitance Cs, and the charge is held during the non-selection period Toff (see FIG. 3C).

Here, since the polarity of the source voltage Vs is inverted for each of the field periods F ₁ and F ₂ , the liquid crystal 2 is shown in FIG.
Is used, the transmitted light amount T _{1 in the first} field period F ₁ to which the positive source voltage Vx is applied increases, and the negative source voltage − in the second field period F ₂ where Vx is being applied, the amount of transmitted light T ₂ regardless of the magnitude of the absolute value of Vx is substantially 0 level (provided that, since not completely zero, the human eye Luminance enough to feel is secured). Then, the transmitted light amount obtained by averaging T ₁ and T ₂ can be obtained in the entire one frame period, but in the field period unit, bright and dark display is alternately performed. Therefore, when displaying a moving image, the image quality is good. In addition, since the positive voltage Vx and the negative voltage −Vx are alternately applied to the liquid crystal 2, the liquid crystal 2
Is prevented from deteriorating.

Here, the voltage value of the source voltage Vx of the positive polarity depends on the voltage-transmitted light amount characteristic of the liquid crystal 2 and the information to be written in the pixel (that is, the optical state or display information to be obtained in the pixel). It should just be determined based on. However,
As described above, the amount of transmitted light during the entire one frame period is T ₁ and T
Since the ₂ that average, for example, in the case of using the liquid crystal 2 of considerably smaller characteristic T ₂ as shown in FIG. 4, T ₁ value (i.e., voltage value Vx which defines the value of T ₁ ) Should be set large considering that amount.

Next, effects of the present embodiment will be described.

According to the present embodiment, a pair of electrodes 3a,
The temperature dependency of the voltage holding ratio in 3b is 1 per 10 ° C.
Since it is set to 0% or less, even if the temperature of the liquid crystal element P locally fluctuates by about 10 ° C., the voltage effectively applied to the liquid crystal 2 does not change much, and the gradation reproducibility decreases. And the occurrence of uneven brightness in the liquid crystal element surface can be prevented.

Further, according to the present embodiment, since the switching by the spontaneous polarization is performed using the chiral smectic liquid crystal 2, the response speed at the time of the switching can be increased.

[0060]

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

Example 1 In this example, a liquid crystal panel (liquid crystal element) P shown in FIGS. 1 and 2 was prepared.

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
It was formed on the surfaces of the glass substrates 1a and 1b with a 700 ° ITO film.

Further, the alignment control films 6a and 6b were formed of a polyimide film having a thickness of 50 ° so as to cover the common electrode 3a and the pixel electrode 3b, respectively. The alignment control films 6a and 6b are coated with SE-7992 manufactured by Nissan Chemical Industries, Ltd. by spin coating, pre-dried at a temperature of 80 ° C. for 5 minutes, and heated and baked at a temperature of 200 ° C. for 1 hour. And formed. Rubbing treatment was performed on these alignment control films 6a and 6b. This rubbing treatment has a diameter of 1
Nylon cloth (NF-77, manufactured by Teijin Limited) on a roll of 0 cm
Using a rubbing roll with affixed thereon, the roll pushing amount was set to 0.3 mm, the feed rate was set to 10 cm / sec,
The rotation speed is 1000 rpm and the number of rubbing treatments is 4
Times.

On the other hand, the bonding of the pair of glass substrates 1a and 1b involves dispersing silica beads (average particle size: 1.4 μm) as spacers 8 on one of the glass substrates 1a, and the rubbing directions of both substrates are substantially parallel. It went so that it might become.

In this example, the method and composition for adjusting the chiral smectic liquid crystal 2 were as follows. That is, first, the following liquid crystal compositions 1 to 8 are
The base material Base-
1 was created.

[0067]

Embedded image The base material Base-1 thus prepared was mixed with the following chiral material at a concentration of 2% by weight to prepare a chiral smectic liquid crystal 2.

[0068]

Embedded image The physical parameters of the prepared chiral smectic liquid crystal 2 were as follows.

[0069]

[Table 1] The injection of the liquid crystal 2 into the liquid crystal cell was performed in an isotropic phase, and after the liquid crystal was injected, the liquid crystal 2 was cooled to a temperature at which a chiral smectic liquid crystal phase was exhibited. In addition, Ch-SmC at the time of the cooling
^* Offset voltage (DC voltage) of -5 V was applied at the time of phase transition.

Then, for the liquid crystal panel P created,
As described below, (1) observation of the alignment state of the liquid crystal, (2) observation of the optical response, and (3) measurement of the voltage holding ratio were performed. (1) Observation of alignment state of liquid crystal With respect to the liquid crystal panel P prepared in this example, room temperature (30
(° C.), no voltage was applied, and the alignment state of the liquid crystal 2 was observed with a polarizing microscope. As a result, the darkest axis was slightly deviated from the rubbing direction, and the normal direction of the layer was substantially the entire panel. In only one direction, a substantially uniform alignment state was observed. (2) Observation of Optical Response Further, the liquid crystal panel P was set on a polarizing microscope equipped with a photomultiplier under crossed Nicols, and the polarization axis was adjusted so that the liquid crystal panel P had a dark field with no voltage applied. Then, at room temperature, the positive and negative voltages (±
A triangular wave voltage of 5 V and 0.2 Hz) was applied to the liquid crystal panel P, and the optical response was observed.

As a result, when the positive or negative voltage is applied, the amount of light transmitted through the liquid crystal panel P continuously changes according to the magnitude of the applied voltage. In this case, the maximum value of the transmitted light amount was about 10 times the maximum value of the transmitted light amount when the voltage of the negative polarity was applied. (3) Measurement of voltage holding ratio For the measurement of the voltage holding ratio, a liquid crystal voltage holding ratio measurement system VHR-1A manufactured by Toyo Technica Co., Ltd. was used.

Here, the driving conditions of the liquid crystal panel P were such that the gate voltage application time (gate on time) was 8 μsec, one field period was 8.33 msec, and the applied voltage was 7V. In addition, the liquid crystal 2
The switching time was sufficiently long, and spontaneous polarization inversion within the gate-on time was set to be negligible. Note that the voltage holding ratio in the present invention is based on the product Vs * t1 of the applied voltage Vs and the one-field time t1, and the liquid crystal cell potential V
The area ratio was obtained from the profile of (t) as follows.

VHR (%) = 100 * ∫ | V (t) | d
t / (Vs * t1) In this manner, the voltage holding ratio was set to 10 ° C., 30 ° C., and 45 ° C.
It was as follows when determined at each temperature of 10 ° C.
It was found that the temperature dependency of the voltage holding ratio was 10% or less per 10 ° C. in the temperature range of from 45 ° C. to 45 ° C.

[0074]

[Table 2] When the temperature dependence of the spontaneous polarization of the chiral smectic liquid crystal 2 was examined, the result was as follows.

[0075]

[Table 3] In this embodiment, by selecting and mixing an appropriate chiral component with the base liquid crystal Base-1 as described above,
The temperature dependency of the spontaneous polarization of the liquid crystal 2 and the temperature dependency of the mobile ion density were balanced, and the voltage holding ratio was improved.

The inventor of the present invention has made the above-mentioned base material Base
A liquid crystal panel was prepared by using -1 (without adding a chiral material) as the liquid crystal, and the voltage holding ratio of the liquid crystal panel was measured in the same manner. The liquid crystal was injected into the liquid crystal cell in an isotropic state, and after the liquid crystal was injected, the liquid crystal was cooled to a temperature at which a chiral smectic liquid crystal phase was exhibited. In addition, no offset voltage (DC voltage) was applied during the cooling. Further, no storage capacitor was formed on the liquid crystal panel.

The voltage holding ratio monotonously decreased with the rise in temperature as shown in the following table. This is because the voltage drop due to mobile ions is determined by the non-chiral component, and the voltage of mobile ions contained in the liquid crystal is reduced. It is considered that the influence of the temperature dependency of the mobility is reflected. In other words, it is considered that the higher the temperature, the more easily the ions move in the liquid crystal, so that a larger amount of leak current flows and lowers the voltage holding ratio.

[0078]

[Table 4] (Comparative Example 1) In this comparative example, the base material Base-
1 was mixed with the following chiral material at a concentration of 8% by weight to prepare a chiral smectic liquid crystal.

[0079]

Embedded image The physical parameter of the prepared chiral smectic liquid crystal was as follows.

[0080]

[Table 5] The injection of the liquid crystal into the liquid crystal cell is performed in an isotropic state,
After injecting the liquid crystal, the mixture was cooled to a temperature at which a chiral smectic liquid crystal phase was exhibited. Note that an offset voltage (DC voltage) of -5 V was applied during the Ch-SmC ^* phase transition during cooling.

Then, for the liquid crystal panel P created,
As in Example 1, (1) observation of the alignment state of the liquid crystal, (2) observation of the optical response, and (3) measurement of the voltage holding ratio were performed. (1) Observation of alignment state of liquid crystal When observation was performed in the same manner as in Example 1, an almost uniform alignment state was observed. (2) Observation of Optical Response When the observation was performed in the same manner as in Example 1, the amount of transmitted light through the liquid crystal panel P was reduced by the magnitude of the applied voltage regardless of whether a positive or negative voltage was applied. The maximum value of the amount of transmitted light when a positive voltage is applied is about 10 times the maximum value of the transmitted light when a negative voltage is applied. (3) Measurement of voltage holding ratio The measurement was performed in the same manner as in Example 1. As a result, the temperature dependency of the voltage holding ratio was 1 in the temperature range of 10 ° C to 45 ° C.
It was found to be 10% or more per 0 ° C. The voltage holding ratio at each temperature was as follows.

[0082]

[Table 6] When the temperature dependence of the spontaneous polarization of the chiral smectic liquid crystal was examined, the result was as follows.

[0083]

[Table 7] As described above, it was found that when the temperature dependence of the spontaneous polarization of the chiral component added to the base liquid crystal was large, the temperature dependence of the voltage holding ratio became significant.

[0084]

As described above, according to the present invention,
Since the temperature dependency of the voltage holding ratio of the pair of electrodes is set to 10% or less per 10 ° C., the voltage is effectively applied to the liquid crystal even if the temperature of the liquid crystal element fluctuates about 10 ° C. locally. The voltage does not change much, and it is possible to prevent a decrease in gradation reproducibility and the occurrence of luminance unevenness in the surface of the liquid crystal element.

Further, according to the present invention, since the switching by the spontaneous polarization is performed by using the chiral smectic liquid crystal, the response speed at the time of the switching can be increased.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an example of the structure of a liquid crystal panel according to the present invention.

FIG. 2 is a plan view showing an example of the structure of the liquid crystal panel according to the present invention.

FIG. 3 is a cross-sectional view illustrating an example of a structure of a liquid crystal panel according to the present invention.

FIG. 4 is a diagram showing an example of a voltage-transmitted light amount characteristic of a liquid crystal.

FIG. 5 is a diagram showing a transmission circuit of the liquid crystal panel according to the present invention.

FIG. 6 is a timing chart illustrating an example of a method for driving a liquid crystal panel.

FIG. 7 is a diagram for explaining a conventional problem.

[Explanation of symbols]

 1a, 1b Glass substrate (substrate) 2 Chiral smectic liquid crystal 3a Common electrode (electrode) 3b Pixel electrode (electrode) 4 TFT (active element) P Liquid crystal panel (liquid crystal element)

Continuing on the front page (72) Inventor: Makoto Mori 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Takeshi Kadoba 3- 30-2 Shimomaruko, Ota-ku, Tokyo Canon stock Inside the company (72) Inventor Masahiro Terada 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inventor Shinichi Nakamura 3-30-2, Shimomaruko 3-chome, Ota-ku, Tokyo F-term in Canon Inc. (Reference) 2H088 EA02 EA12 EA40 FA10 GA02 GA04 GA17 HA08 HA12 HA18 HA21 KA30 LA06 LA07 LA09 MA04 MA10 2H092 GA05 HA04 JA03 JA26 KA05 KA12 NA05 PA08 PA11 RA05

Claims (15)

[Claims] 1. A pair of substrates disposed with a predetermined gap therebetween, a chiral smectic liquid crystal disposed between the pair of substrates, and a plurality of pixels configured to sandwich the chiral smectic liquid crystal. Comprising a pair of electrodes arranged and a plurality of active elements connected to one electrode and arranged for each pixel, and applying a voltage to the chiral smectic liquid crystal through the pair of electrodes. In the liquid crystal device driven by the above, the temperature dependency of the voltage holding ratio of the pair of electrodes is 1
The liquid crystal element is 10% or less per 0 ° C. 2. The chiral smectic liquid crystal, when no voltage is applied, exhibits an alignment state in which the average molecular axis of liquid crystal molecules is monostable, and is driven by applying a voltage of one polarity. In this case, the average molecular axis of the chiral smectic liquid crystal is tilted to one side from the mono-stabilized position, and when driven by applying a voltage of another polarity, the chiral smectic liquid crystal is driven. The liquid crystal device according to claim 1, wherein the average molecular axis of the liquid crystal tilts from the mono-stabilized position to the other side. 3. When the voltage of the one polarity or the other polarity is applied, a tilt angle with respect to a position where the average molecular axis is mono-stabilized depends on the magnitude of the voltage. The liquid crystal element according to claim 2, wherein the liquid crystal element changes continuously in response to the change. 4. The method according to claim 1, wherein the maximum value of the angle tilted by applying the voltage of one polarity is different from the maximum value of the angle tilted by applying the voltage of the other polarity. The liquid crystal device according to claim 3, wherein: 5. The maximum value of the angle that is tilted when the voltage of one polarity is applied is larger than the maximum value of the angle that is tilted when the voltage of another polarity is applied. The liquid crystal device according to claim 4, wherein: 6. The maximum value of the angle that is tilted when the voltage of one polarity is applied is five times or more the maximum value of the angle that is tilted when the voltage of another polarity is applied. The liquid crystal device according to claim 5, wherein: 7. The liquid crystal device according to claim 4, wherein an angle of tilt when the voltage of the other polarity is applied is substantially 0 °. 8. The liquid crystal device according to claim 3, wherein the amount of light emitted from the liquid crystal device changes continuously according to the magnitude of a voltage applied to the chiral smectic liquid crystal. 9. A maximum value of a light amount emitted from the liquid crystal element in a state where the voltage of one polarity is applied, and a maximum value of the light amount emitted from the liquid crystal element in a state in which the voltage of the other polarity is applied. The liquid crystal device according to claim 4, wherein the first light amount and the second light amount are different from each other when the maximum value of the emitted light amount is the second light amount. 10. The liquid crystal device according to claim 9, wherein the first light amount is larger than the second light amount. 11. The liquid crystal device according to claim 10, wherein the first light amount is at least five times the second light amount. 12. A polarizing plate is arranged such that, when a light amount emitted from the liquid crystal element in a state where no voltage is applied is a third light amount, the third light amount is substantially zero. The liquid crystal device according to claim 8, wherein: 13. The chiral smectic liquid crystal comprises an isotropic liquid phase (Iso) -cholesteric phase (C
h) a phase transition series of a chiral smectic C phase (SmC ^* ) or a phase transition series of an isotropic liquid phase (Iso) -chiral smectic phase (SmC ^* ), wherein the smectic of the chiral smectic liquid crystal is shown. The liquid crystal element according to claim 7, wherein the normal direction of the layer is substantially one direction. 14. The liquid crystal device according to claim 13, wherein a gap dimension of the substrate on which the chiral smectic liquid crystal is arranged is equal to or less than half a helical pitch of the chiral smectic liquid crystal in a bulk state. 15. The liquid crystal element according to claim 13, wherein a driving circuit for supplying a gradation signal is connected.