JPH06186532A - Liquid crytal electrooptical device - Google Patents

Abstract

PURPOSE:To improve screen display of a large driving frequency and to effectively utilize high-speed responsiveness, high contrast ratio and high visual field angle characteristic by adopting the constitution that image electrodes have the voltage above the voltage necessary for maintaining first and second states within a display period. CONSTITUTION:Spacers which are silica particles are sprayed on a TFT substrate 180 side. A counter electrode side is subjected to screen printing of a sealing material, an epoxy resin in such a case. Both substrates 180, 183 are stuck to each other and a ferroelectric liquid crystal 190 of a phenyl pyrimidine system is injected into the cell. Either the positive or negative voltage is supplied to the liquid crystal via the TFT. Which state of the first state and the second state adopted by the liquid crystal is to be adopted is determined by the electrolytic direction generated in the pixel electrodes. Simultaneously, the potential of the pixel electrodes has the voltage exceeding the voltage capable of maintaining the potential in either of the first or second state within the display period. The liquid crystal having >=0.1V and <=4V voltage mentioned above is utilized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal electro-optical device which realizes a high speed and high gradation liquid crystal display.

[0002]

2. Description of the Related Art Electronic devices using liquid crystals are expected to be applied not only to clocks and thermometers, but also to a wide range of video equipment such as word processors, laptop computers and television receivers.

The appeal of ferroelectric liquid crystals having spontaneous polarization in the liquid crystal itself has been widely known by Clark and Lagerval. The antiferroelectric liquid crystal, which is the opposite of this, was widely introduced by Chandani et al. These have characteristics different from those of nematic liquid crystals such as a twisted nematic (abbreviated as TN) liquid crystal display and a super twisted nematic (abbreviated as STN) liquid crystal display which have been widely used until now.

In the schematic diagram shown in FIG. 1, the ferroelectric liquid crystal is composed of liquid crystal molecules 10 according to the orientation control of the surface of the substrate 100.
2 are arranged in a fixed direction. A layered structure 101 is formed between the liquid crystal molecules, and they are highly ordered in the three-dimensional direction. Under a thin cell thickness, the orientation of the liquid crystal molecule long axis takes two states, a first state 102 and a second state 103.

Ferroelectric liquid crystals have a spontaneous polarization Ps (C /
m ² ), which is indicated by the arrow in FIG. The direction of the spontaneous polarization is antiparallel to the direction of the electric field due to the torque Ps · E which is the product of the spontaneous polarization and the electric field intensity E (V / m) generated in the direction perpendicular to the substrate surface generated by applying a voltage to the liquid crystal cell. To move. In accordance with the movement, the liquid crystal molecule long axis switches between the two states of the first state 102 and the second state 103. In other words, which of the two states is taken can be controlled by the direction of the electric field applied thereto.

Switching between the two states can be performed at high speed by switching using spontaneous polarization, that state can be stably maintained even after application of an electric field, and a wide field of view when observed through a polarizing plate. Since it has excellent properties such as being able to distinguish between the two states over the corners, it is greatly expected as a liquid crystal material that can realize a high-speed and large-capacity screen.

Actually, as shown in FIG. 1, not only does the spontaneous polarization show a uniform orientation indicating either of the substrates, but also when no electric field is applied, the direction of the spontaneous polarization is on the inside of both substrates. In some cases, the direction of the major axis of the liquid crystal molecule is twisted between the substrates and the twisted orientation is given. Those having such a twist orientation cannot take an extinction position and have a low contrast ratio, but if the above-described torque of Ps · E is applied by application of an electric field, spontaneous polarization as shown in FIG. The orientation is such that the orientation uniformly points to either substrate surface.

On the other hand, the antiferroelectric liquid crystal can take the third state 122 in addition to the first state 120 and the second state 121 as shown in FIG. When the voltage is not applied, it is in the third state, when the negative voltage is applied, for example, it is in the first state, and when the positive voltage is applied, it is in the second state.

At this time, a clear threshold voltage exists between the third state and the first state and between the third state and the second state. Due to the existence of this threshold value, driving characteristics are greatly different from the characteristics of the ferroelectric liquid crystal.

Utilizing the characteristics of the ferroelectric liquid crystal and the anti-ferroelectric liquid crystal as described above, a simple matrix display has been developed in which the liquid crystal is sandwiched and driven by electrodes whose drive electrodes are processed into strips.

However, because it is difficult to develop a high-performance display in which a liquid crystal material having spontaneous polarization is driven by a simple matrix, it is difficult to develop a more stable display and a high-performance panel. A) and metal-insulating film-metal (abbreviated as MIM) non-linear elements are being studied for display.

By utilizing such a switching element, many problems which have been difficult so far have been solved. Ferroelectric liquid crystals and anti-ferroelectric liquid crystals have two or three states that are uniquely determined by the direction of the applied electric field. Therefore, like TN liquid crystals, the whiteness depends on the applied voltage. It was difficult to change the degree of color tone of the sheath and black, and it was difficult to obtain gradation.

As a result, it has not been used for a display that requires high gradation such as a television image while having characteristics of high speed switching and a wide viewing angle. Therefore, there has been an urgent need to develop a technique for realizing high gradation in a display using a ferroelectric liquid crystal and an antiferroelectric liquid crystal.

To solve this, three kinds of methods can be used.

One is to divide one pixel into n, and perform gradation display of 2 to the n-th power in one pixel. However, in this method, the number of pixels is required to be substantially n times, so that there are problems such as a decrease in yield and an increase in cost.

The second is due to analog gradation using a TFT. The peak value of the voltage applied to the ferroelectric liquid crystal is changed to adjust the area ratio of the liquid crystal in the first state and the second state. When driving a ferroelectric liquid crystal with a simple matrix, it was impossible because the electric charge flowing in and out of the capacitance of the pixel electrode was changed at any time.

However, when a TFT is used, when the gate is turned off after charge injection, the amount of charge that goes in and out of the pixel electrode through the TFT disappears, so that the liquid crystal can maintain a constant state. Therefore, gradation display is possible by changing the area ratio in the pixel in the first state and the second state in which the liquid crystal can be taken at that time.

The other method is based on digital gradation using TFTs. This is because the ferroelectric liquid crystal takes only binary values of white and black and is capable of high-speed response. The gradation is created by changing the time taken by the white and black states. For example, white is displayed for 0.2 ms, black is displayed for 0.8 ms, and if this is repeatedly displayed, 100% of all white and all black are displayed to the eyes of the observer. 2 for 0% transmission
A transmittance of 0% will be obtained. If the operating frequency at this time exceeds 60 Hz, it does not appear as flicker to the human eye. Since a ferroelectric liquid crystal has a high-speed switching in the first place, a multi-gradation display can be realized by using digital gradation.

Digital gradation is a technology that can be realized only by taking advantage of the characteristic that the ferroelectric liquid crystal is 3 to 4 digits faster than the response speed of TN or STN. This is a method that can maximize the high-speed characteristics of ferroelectric liquid crystals. Switching elements such as TFTs are needed there.

[0020]

When a liquid crystal material having spontaneous polarization is driven by a TFT, a nematic liquid crystal is used as a T
A problem different from the case of driving with FT occurs. This is undeniably because the switching modes differ depending on the liquid crystal material.

The magnitude of spontaneous polarization of a liquid crystal material which is usually used is 1 to 100 nC / cm ² . In the case of antiferroelectric liquid crystal, a material of several 100 nC / cm ² is rarely used. This charge amount is the charge amount that flows when the liquid crystal is inverted, and at the same time, the liquid crystal is not inverted unless this charge amount is supplied from the outside at least. This charge amount is much larger than the charge amount required for driving the nematic liquid crystal.

Therefore, when driving a nematic liquid crystal, a liquid crystal material having a large voltage holding ratio should be used, but it cannot be applied to a ferroelectric liquid crystal driven by a TFT.

The measurement of the voltage holding ratio, which is used as an evaluation method when using the nematic liquid crystal, will be described with reference to FIG. The liquid crystal pixel 134 has a source 130 and a drain 13.
1 and the gate 132 are connected to the TFT. The data signal sent from the supply terminal 138 to the source part is sent to the drain side by the voltage applied to the gate. The signal is supplied to the pixel electrode. Since the resistance between the source and the drain is high when the gate is off, the electric charge supplied to the pixel does not flow in and out through the TFT.

The signals at that time are described in FIG. A data signal of, for example, a square wave 143 is applied between the source and the drain, and the voltage 144 is supplied to the drain part only when the gate electrode 140 is turned on. As a result, the voltage 141 accumulated in the ideal pixel capacitance maintains a constant voltage without being attenuated. On the other hand, the voltage 142 accumulated in a normal liquid crystal pixel is attenuated over time. The ideal voltage and the voltage of the evaluation liquid crystal are measured as effective values, and the ratio is called the voltage holding ratio. Naturally, the closer the voltage holding ratio is to 100%, the more desirable the characteristics.

When the voltage holding ratio is small, the voltage of the pixel capacitance changes with time. When the nematic liquid crystal has a low holding ratio because the transmittance changes depending on the applied voltage, the amount of light passing through the pixel changes with time and a highly reproducible gradation cannot be realized.

On the other hand, a liquid crystal material having spontaneous polarization is used as a TFT.
State when driven by. The measurement system is as shown in FIG. 3, and the liquid crystal cell 134 part is a ferroelectric liquid crystal which is a liquid crystal material having spontaneous polarization, or is changed to an antiferroelectric liquid crystal. An example of measurement will be described with reference to FIG. The change in the optical response of the liquid crystal was measured simultaneously with the potential of the pixel electrode.

Charge is injected into the pixel electrode with the gate turned on, and a constant voltage V ₀ 152 is supplied to the pixel electrode in FIG. 5- (1). After that, the pixel potential is attenuated and becomes constant. The optical change 155 of the liquid crystal at that time changes from bright to dark or from dark to bright. Since the optical change at this time coincides with the decrease of the pixel potential,
This means that the pixel charge was consumed for the inversion of the ferroelectric liquid crystal. At this time, spontaneous polarization and twice the charge of the electrode area are consumed. As a result, the potential remaining in the pixel becomes V _rem 153. After that, the pixel voltage and the optical response become constant. The ferroelectric liquid crystal responds well in the TFT.

In this state, the voltage is, for example, 1/2 V _0.
The state when changed to 156 is shown in FIG. V
_{The rem} 157 is further lowered, the optical response 158 of the liquid crystal is not sufficiently performed, and the optical position up to the middle is continued.

Such a phenomenon occurs not only when the voltage is lowered but also when the time during which a pixel is selected is shortened. That is, the amount of charge injected into the pixel is insufficient to invert the liquid crystal.

Considering that the ferroelectric liquid crystal is driven by the TFT from such a phenomenon, it is necessary to newly construct an evaluation method specific to the ferroelectric liquid crystal, which is different from the conventional voltage holding ratio.

It should be evaluated that the liquid crystal potential naturally decreases because the ferroelectric liquid crystal accompanies the inversion of spontaneous polarization during switching, and there is a clear threshold value for the inversion. It must be understood that the two points of how to understand what is said not to do are fundamentally different from nematic liquid crystals.

[0032]

Means for Solving the Problems The present inventors have paid attention to the generation mechanism of spontaneous polarization of a ferroelectric liquid crystal when the ferroelectric liquid crystal is driven by a TFT, and what is the optical response of the liquid crystal depending on the drive waveform. , And investigated in detail what happens to the voltage remaining in the liquid crystal. As a result, they have found that the voltage required for the ferroelectric liquid crystal to perform switching is extremely important.

It has been generally considered that the ferroelectric liquid crystal is switched by the change of the electric field direction as described above, and that the voltage applied at that time has no threshold value.

However, when the ferroelectric liquid crystal is actually driven by the TFT, the threshold voltage for changing the state is small, but the first state or the second state as shown in FIG. It turns out that a certain voltage is necessary for stable display. Threshold voltage has become a very important issue. The threshold voltage (V _th ) here means that the liquid crystal is the first
The voltage required when changing from the state to the second state is shown. This threshold is not actually zero, but a certain voltage is required.

More strictly speaking, the liquid crystal is the first
When switching from the state 2 to the second state, when a predetermined voltage is applied, as shown in FIG. 1, how much appropriate voltage remains in the pixel electrode due to the reversal of spontaneous polarization and the movement of other charges. As shown, it is necessary to consider the state-maintaining voltage (V _SM ) that can maintain the state in which the spontaneous polarization in the second state is uniformly arranged.

Such a voltage is different from the threshold value in the strict sense such as the Freedericksz transition in the nematic liquid crystal. Originally, it is something like a bias in the electrical characteristics of the liquid crystal cell affected by the material properties or the alignment treatment method, or it is caused by the interaction between spontaneous polarization and the alignment film.

First, a method of evaluating the threshold value of the ferroelectric liquid crystal cell will be described. As the structure of the cell used, a liquid crystal material having spontaneous polarization is sandwiched between transparent substrates on which lead electrodes and pixel electrodes are arranged. On the surface of the substrate that is in contact with the liquid crystal, there is provided a means for aligning the liquid crystal material in the uniaxial orientation direction at least in the initial stage. 20 here
An optical change was investigated when a slow square wave was applied up to 0.1 V and the optical response fully responded to each electric field direction. When the applied voltage becomes small, the optical response of the liquid crystal becomes very slow, sometimes exceeding 1 second to several seconds. The cell transmissivity responded sufficiently from the first state to the second state at a voltage of 5 V or higher, but at a voltage lower than 5 V, it responded only in a range of a smaller transmissivity. The smaller the applied voltage, the smaller the range of response.

This voltage of 5 V is the threshold voltage required to invert the liquid crystal. At the same time, the state maintaining voltage V _SM becomes necessary to show a constant state. It is extremely important for the switching of the ferroelectric liquid crystal to compare this with the parameter of the voltage V _rem remaining in the pixel when the ferroelectric liquid crystal is driven by the TFT.

The difference between whether the ferroelectric liquid crystal responds sufficiently in the TFT or only halfway is that the magnitude of the pixel potential V _rem after liquid crystal inversion exceeds the liquid crystal state maintaining voltage sufficiently. Depends on what you do.

It is not necessary to distinguish between the threshold voltage and the state-maintaining voltage, but in the case of TFT driving, a voltage much higher than this voltage is applied in the initial stage, but this voltage is particularly important for switching. It is not a critical condition, but the magnitude of the voltage remaining in the pixel at the end becomes a problem.
Therefore, when the liquid crystal having spontaneous polarization is driven by the TFT, the state maintaining voltage is more appropriate than the threshold voltage.

Therefore, the inventors of the present invention pay attention again to the state maintaining voltage of the ferroelectric liquid crystal, measure the threshold voltage of the ferroelectric liquid crystal in various liquid crystal cells, and find out the TFT of the liquid crystal material having spontaneous polarization. It was found that there are optimum conditions for driving in.

The configuration of the present invention will be described. A liquid crystal material having spontaneous polarization is sandwiched between transparent substrates on which lead electrodes and pixel electrodes are arranged. On the surface of the substrate in contact with the liquid crystal, there is provided a means for aligning the liquid crystal material in the uniaxial orientation direction at least in the initial stage. This is in a liquid crystal electro-optical device in which a thin film transistor is arranged on the pixel electrode. In the liquid crystal, the first state or the second state is selected by voltages having different polarities supplied from the thin film transistor, and a voltage higher than a voltage required to maintain the state is applied to the pixel electrode within a display period. The present invention relates to a liquid crystal electro-optical device characterized by having.

Further, a liquid crystal material having spontaneous polarization is sandwiched between transparent substrates on which lead electrodes and pixel electrodes are arranged. On the surface of the substrate that is in contact with the liquid crystal, there is provided a means for aligning the liquid crystal material in the uniaxial orientation direction at least in the initial stage. This is in a liquid crystal electro-optical device in which a thin film transistor is arranged on the pixel electrode. For the liquid crystal, the first state or the second state is selected by the voltages having different polarities supplied from the thin film transistor, and the voltage required to maintain the state is 0.1 V or more and 4 V or less. The present invention relates to a liquid crystal electro-optical device characterized by the following.

Further, a liquid crystal material having spontaneous polarization is sandwiched between transparent substrates on which lead electrodes and pixel electrodes are arranged. On the surface of the substrate that is in contact with the liquid crystal, there is provided a means for aligning the liquid crystal material in the uniaxial orientation direction at least in the initial stage. This is in a liquid crystal electro-optical device in which a thin film transistor is arranged on the pixel electrode. At this time, the present invention relates to a liquid crystal electro-optical device characterized in that the liquid crystal exhibits an orientation in which the direction of the spontaneous polarization in the substrate spacing direction when no voltage is applied indicates any substrate direction.

Further, the present invention relates to a liquid crystal electro-optical device characterized in that the liquid crystal used at that time exhibits multi-microdomain alignment.

The use of the present invention as described above is extremely effective in driving a liquid crystal material having spontaneous polarization by a TFT.

[0047]

When the ferroelectric liquid crystal is injected into the cell in which the TFT is arranged and is driven, the pixel voltage is lowered due to the reversal of the spontaneous polarization. If it is lowered too much, either one of the ferroelectric liquid crystals cannot be displayed.

However, as shown in the present invention, the liquid crystal has TF.
Either a positive voltage or a negative voltage is supplied via T, and it is determined whether the liquid crystal is in the first state or the second state depending on the direction of the electric field generated in the pixel electrode. At the same time, the potential of the pixel electrode changes to the first potential during the display period.
Since the liquid crystal molecule has a voltage exceeding the voltage V _SM for maintaining either the state 1 or the second state, the liquid crystal molecules can stably maintain either state.

When a liquid crystal having spontaneous polarization is driven by a TFT, this must be obeyed.

For example, when the voltage is not applied, the direction of spontaneous polarization of the liquid crystal is inward or outward between the substrates, and the molecular long axis direction is twisted. The present invention is necessary when the twisted orientation is exhibited.

The state maintaining voltage V _SM of the liquid crystal exhibiting the twisted orientation is as large as 5 V or more. When the above invention is used, the twisted state is deformed to form the first state or the second state, and the ferroelectric liquid crystal can be sufficiently driven by the TFT.

The present invention is necessary when the antiferroelectric liquid crystal having a threshold value in the liquid crystal itself is driven by the TFT. Even after the voltage of the spontaneous polarization is consumed and the pixel voltage is reduced, the threshold value of the antiferroelectric liquid crystal, which represents the state-maintaining voltage V _SM as it is, is changed to the third state if it exceeds the threshold value. The stable display of the first or second state is possible without the need.

Further, the present inventors considered that it is disadvantageous to drive a liquid crystal having spontaneous polarization with a TFT if the voltage required for maintaining the liquid crystal in any state is large. Therefore, the state maintenance voltage V _{SM has been} improved by developing materials and improving the orientation technology.
Was found to be 0.1 to 4V. The state maintaining voltage V _SM
Is very small, the drive of the liquid crystal with spontaneous polarization is
This was easily possible with FT.

One of them is such that the direction of spontaneous polarization has an orientation indicating either direction of the sandwiched substrate. As shown in FIG. 1, the uniform orientation is obtained. In this case, the spontaneous polarization does not interact with the alignment film, and the state selected in the direction of the electric field is stably maintained even after the electric field is applied. Naturally, the state maintaining voltage V _SM is low and is 1 V or less. Therefore, it is possible to perform stable display by driving with the TFT even if the residual voltage is small. Even if the liquid crystal potential V _rem after the liquid crystal is inverted is, for example, 1.5 V, a sufficient optical response is possible, and the ferroelectric liquid crystal can be driven by the TFT.

Further, as the liquid crystal alignment at that time, a liquid crystal exhibiting multi-microdomain alignment which is an assembly of a large number of clusters 170 having a long axis in the rubbing direction as shown in FIG. 6 was also effective. The threshold value was about 0.8 V, and it was possible to sufficiently drive the TFT. At that time, the liquid crystal potential V _rem after the liquid crystal is inverted is, for example, 1.
A sufficient optical response was possible even at 3 V, and the ferroelectric liquid crystal could be driven by the TFT. Hereinafter, details will be described in examples.

[0056]

【Example】

[Example 1] The results of evaluating the state-maintaining voltage V _SM characteristics of a liquid crystal cell having spontaneous polarization will be described with reference to FIG. 7. Indium-tin-oxide (abbreviated as ITO) 195 was formed on the blue plate glass 190 by a sputtering method or a vapor deposition method to a film thickness of 500 to 2000 Å, and patterned by a normal photolithography process. Two of these substrates were prepared, polyimide 191 was applied to one of the substrates 190 by a spin coating method, and baked at 280 ° C. As the polyimide, Hitachi Chemical LQ5200 or Toray LP-64 was used.
The thickness was 100 to 300Å. This substrate was subjected to rubbing treatment to obtain uniaxial orientation treatment. This was opposed to the other glass substrate 192 not provided with an alignment film. On the alignment film side substrate, a spacer (not shown in the drawing) of silica gel particles made by Catalysts and Chemicals Co., Ltd. made of catalyst chemical, 1.5 μm, is sprinkled, and an epoxy resin sealant 193 is formed by screen printing on the counter electrode side. did. Both substrates were attached to each other to a thickness of 1.5 μm according to the diameter of the spacer. Phenylpyrimidine-based ferroelectric liquid crystal 194 was injected into the cell.
The phase sequence of this liquid crystal was isotropic phase-smectic A phase-smectic C ^* phase-crystal phase. The magnitude of spontaneous polarization is 6
nC / cm ² , relative permittivity 4.4, 14V in cell
The response speed when applied was 100 μsec. The transition temperature to the isotropic phase was about 90 ° C., the liquid crystal material was heated to 110 ° C., and vacuum injection was performed while the liquid crystal was in the isotropic phase.
As the orientation state, multi-microdomain orientation was shown as shown in FIG.

A square wave was applied to this from 20 to 0.1 V, and the optical response at that time was measured. The transmittance of the liquid crystal cell changes rapidly when a high voltage is applied, and it takes 1 second or more to saturate when a low voltage is applied. The transmittance at that time was examined. In addition, the position of the extinction position obtained by aligning the long axis of the liquid crystal molecule with that of the polarizing plate is
The measurement was performed both in the case of adjusting to the state of 1 and in the case of adjusting to the second state. The results are shown in Fig. 8. Good brightness was obtained from 20 to 0.8 V at any extinction position. No change in state occurred at voltages below that. It can be said that the threshold voltage when the liquid crystal switches is 0.8V.

The characteristics when the above liquid crystal is injected into the cell in which the TFT is arranged will be described with reference to FIG. Corning 7
A self-aligned n-channel polysilicon TFT 181 was formed on a 059 substrate 180 by an ordinary low temperature process.
The source side 192 is connected to the lead electrode 187, and the drain side 188 is provided with the pixel electrode 182 made of ITO. Similarly, the Corning 7059 substrate 18 is used as the opposite substrate.
3, the pixel common electrode 186 is formed on the substrate with ITO, and then polyimide 189 is applied by spin coating to 280
Baked at ° C. As a polyimide, Hitachi Chemical LQ15
00 or Toray LP-64 was used. Thickness is 100
It was ~ 300Å. This substrate was subjected to rubbing treatment to obtain uniaxial orientation treatment. At this time, when rubbing the TFT substrate side, each lead electrode was dropped to the ground, and sufficient consideration was given so that the device would not be destroyed by static electricity.

Next, a spacer of 1.5 μm in diameter, which is a silica particle made of catalyst chemical and made of catalyst, was sprayed on the TFT substrate side, and a sealant, in this case, an epoxy resin was screen-printed on the counter electrode side. Both substrates were attached to each other to a thickness of 1.5 μm according to the diameter of the spacer. Phenylpyrimidine-based ferroelectric liquid crystal 190 was injected into the cell. The phase sequence was isotropic phase-smectic A phase-smectic C ^* phase-crystalline phase. The transition temperature to the isotropic phase was about 80 ° C., the liquid crystal material was heated to 100 ° C., and vacuum injection was performed while the liquid crystal was in the isotropic phase. In the drawing, the direction 191 of spontaneous polarization between the substrates shows a uniform direction, which is a uniform orientation. The drive circuit after sealing was subjected to a test after connection.

FIG. 10 shows the gate-drain characteristics of a typical TFT. An on / off ratio of about 7 digits was obtained. The voltage applied to the pixel was kept constant at 14 V, the gate was turned on, and the time applied to the pixel was changed from 100 to 1 μsec. The direction of the electric field was changed every 5 ms, and the liquid crystal was switched in the direction of the electric field. As shown in FIG. 11, even if the pixel selection time (actually, the time when a signal was input to the gate) was shortened from 100 μsec to 1 μsec, the position of the inverted transmissivity was almost constant. In addition, the pixel residual voltage at that time decreases as the time is shortened to V
_rem was 1.5V. This is the liquid crystal threshold of 0.8
It is sufficiently larger than V and is capable of a sufficient optical response.

Example 2 The same material as in Example 1 was used to examine the characteristics when an alignment film was formed on both sides of one of the two substrates this time. Further, the threshold characteristics when the alignment films are provided on both surfaces of the two glass substrates are as shown in FIG. 12, and the transmittance is attenuated on the low voltage side, but the state maintaining voltage V _SM is It was 0.8V.

When the TFT was used for driving, a sufficient response was obtained with a residual voltage of 1.5 V despite the selection time width of 1 μsec.

Comparative Example 1 The same cell configuration as in Example 1, that is, a cell with one-sided orientation was used, and measurement was performed using ZLI3654 manufactured by Merck as a liquid crystal material. This cell exhibits a twist orientation. The state maintaining voltage V _SM at this time is
As shown in FIG. 13, only one side had a voltage of 5 V, and the other had a stable state. Although it is a twist, it is monostable in terms of electrical characteristics.

When the same liquid crystal was driven using the TFT, V _rem fell below 5 V when the drive selection time width was 20 μsec or less, and the optical response was not sufficiently performed.

"Comparative Example 2" The experiment of Comparative Example 2 was carried out when the alignment films were provided on both sides of the glass substrate. The state maintaining voltage V _SM was 5 V on both sides as shown in FIG. Below this voltage, the transmission state gradually narrowed on both sides. In this state, the cell exhibits twist orientation.

When the same liquid crystal was driven using the TFT, V _rem fell below 5 V when the drive selection time width became 20 μsec or less, and the optical response was not sufficiently performed.

Example 3 An antiferroelectric liquid crystal was injected into the measuring cell used in Example 1 and the state-maintaining voltage V _SM was measured. The state maintaining voltage V _SM was 8V. TFT
When the liquid crystal cell was measured with the following, the residual voltage V
_{The rem} became 10 V and a sufficient response was obtained. The contrast ratio at that time was 170. Using this cell, a digital gradation test was performed by driving the cell while changing the on (bright) state and the off (dark) state with time. As shown in FIG. 15, the gradation number is 1
Achieved 00.

[0068]

When a liquid crystal material having spontaneous polarization is driven by a cell having a TFT, the threshold voltage for switching the liquid crystal material from the first state to the second state is 0.1 to 4V. Small materials, those with uniform orientation, and those with multi-microdomain orientation are very effective.

When such a liquid crystal is used, the inversion when driven through the TFT becomes very good, and the time when the charge is injected into the pixel, that is, the time when the gate is in the ON state, is the response speed of the liquid crystal. Within a much shorter time than, for example, 1μ
It can be driven sufficiently in seconds. As a result, it is possible to satisfactorily display images with a large driving frequency such as digital gradation, and to use a high-performance liquid crystal display that utilizes the high-speed response, high contrast ratio, and wide viewing angle of ferroelectric liquid crystals. It is effective in creating an LCD TV that can be realized and can be displayed with a video signal.

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of a ferroelectric liquid crystal.

FIG. 2 is a diagram showing an outline of an antiferroelectric liquid crystal.

FIG. 3 is a circuit diagram for measuring voltage holding ratio.

[Fig. 4] Measurement example of nematic liquid crystal

FIG. 5: Driving example of a ferroelectric liquid crystal TFT

FIG. 6 is a diagram showing multi-microdomain orientation.

FIG. 7: Structure of cell in which threshold voltage of ferroelectric liquid crystal is measured

FIG. 8: Example of measurement of threshold voltage of ferroelectric liquid crystal used in the present invention

FIG. 9 is a diagram showing an outline of an apparatus of the present invention.

FIG. 10: Characteristics of TFT used in the present invention

FIG. 11 is a diagram showing the characteristics and effects of the present invention.

FIG. 12: Example of measurement of threshold voltage of ferroelectric liquid crystal used in the present invention

FIG. 13 is a comparative example showing the threshold voltage of a ferroelectric liquid crystal.

FIG. 14 is a comparative example showing the threshold voltage of a ferroelectric liquid crystal.

FIG. 15 is a diagram showing a result of performing digital gradation.

Claims (4)

[Claims] 1. A liquid crystal material having spontaneous polarization is sandwiched between transmissive substrates on which lead electrodes and pixel electrodes are arranged, and liquid crystal materials are arranged in a uniaxial orientation direction at least at an initial stage on the substrate surface in contact with the liquid crystal. Have means for doing
In a liquid crystal electro-optical device in which a thin film transistor is disposed between the lead electrode and the pixel electrode, the liquid crystal is selected from a first state or a second state with voltages of different polarities supplied from the thin film transistor, 2. The liquid crystal electro-optical device, wherein the pixel electrode has a voltage higher than a voltage required to maintain the pixel electrode during a display period. 2. A liquid crystal material having spontaneous polarization is sandwiched between transmissive substrates on which lead electrodes and pixel electrodes are arranged, and liquid crystal materials are arranged in a uniaxial orientation direction at least in an initial stage on the substrate surface in contact with the liquid crystal. Have means for doing
In a liquid crystal electro-optical device in which a thin film transistor is arranged between the lead electrode and the pixel electrode, the liquid crystal is selected from a first state or a second state by voltages of different polarities supplied from the thin film transistor, The voltage required to maintain the state of is 0.1V or more, 4V
A liquid crystal electro-optical device characterized by using the following liquid crystal. 3. A liquid crystal material having spontaneous polarization is sandwiched between transmissive substrates provided with lead electrodes and pixel electrodes, and the liquid crystal material is arranged in a uniaxial orientation direction at least in an initial stage on the substrate surface in contact with the liquid crystal. Have means for doing
In a liquid crystal electro-optical device in which a thin film transistor is arranged between the lead electrode and the pixel electrode, the liquid crystal exhibits an orientation in which the direction of the spontaneous polarization in the substrate spacing direction when no voltage is applied indicates any substrate direction. Characteristic liquid crystal electro-optical device. 4. The liquid crystal electro-optical device according to claim 3, wherein the liquid crystal exhibits multi-microdomain alignment.