JP3135724B2 - Liquid crystal electro-optical device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION arranged element supplying <br/> constant charge amount in the liquid crystal material having spontaneous polarization on the substrate, helps the switching of the ferroelectric liquid crystal or anti-ferroelectric liquid crystal, high gradation The present invention relates to a liquid crystal electro-optical device that realizes a transparent 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.

There are various types of liquid crystal,
Particularly popular is the nematic liquid crystal,
The operation mode is used in many fields such as a twisted nematic liquid crystal or a super twisted nematic liquid crystal. They are sandwiched between substrates having individually patterned electrodes, and are used as inexpensive panels with relatively short manufacturing steps as simple matrix panels. However, when the number of pixel electrodes increases, crosstalk occurs and the display quality deteriorates.

In order to solve the above problem, thin film transistors and non-linear elements made of metal-insulating film-metal are manufactured on a substrate even if the manufacturing process becomes complicated.

[0005] These aid switching of the liquid crystal. As a result, high-performance display quality is realized, and clear television images can be displayed on the liquid crystal panel. However, in the case of the nematic liquid crystal, the response speed is 1 to 500 msec, and there has been a problem that the rewriting speed is low.

[0006] Attention has been paid to ferroelectric liquid crystals. The same applies to antiferroelectric liquid crystals.

A ferroelectric liquid crystal is applied to a substrate 10 as shown in FIG.
The liquid crystal molecules 102 are oriented in a certain direction according to the zero plane alignment control. A layer structure 101 is formed between the liquid crystal molecules and is arranged in a three-dimensional direction with high order. Under a large cell thickness, the liquid crystal molecules may exist on any position where the cone is formed, and are arranged so as to form a spiral.

Under the thin cell thickness shown in FIG. 1, the directions of the long axes of the liquid crystal molecules are the first state 102 and the second state 103.
Take two states. In that state, the spontaneous polarization of the liquid crystal molecules can be controlled by the direction of the electric field applied thereto.

The direction of the spontaneous polarization in the first state is downward,
The spontaneous polarization in the second state points upward. High-speed rewriting between the two states is possible, the state can be stably maintained even after the application of the electric field is completed, and the two states can be identified over a wide viewing angle when observed through a polarizing plate. Since it has excellent characteristics such as being able to be used, it is expected to be a liquid crystal material capable of realizing a high-speed and large-capacity screen.

On the other hand, the antiferroelectric liquid crystal can take a third state 122 in addition to the first state 120 and the second state 121 as shown in FIG. When no voltage is applied, the third state is established. When a negative voltage is applied, the first state is established. When a positive voltage is applied, the second state is established.

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. The existence of this threshold value is extremely superior to the ferroelectric liquid crystal in terms of driving.

The switching from the third state to the first state and the switching from the third state to the second state have a high speed corresponding to the applied voltage. However, from the first and second states to the third
The switching speed to the state of (1) tends to be somewhat slower. This is because the effects of the clay and the interface of the liquid crystal are relatively large, and the driving force for changing the direction of spontaneous polarization from a uniform state to an alternately existing state is lacking.

All of the characteristics of such an antiferroelectric liquid crystal are similar to those of a nematic liquid crystal rather than a ferroelectric liquid crystal.

The ferroelectric liquid crystal and the antiferroelectric liquid crystal are
A layer structure is formed. This layer is not perpendicular to the surface of the substrate, but rather bends and has a U-shaped structure. The one that is perpendicular to the substrate surface is called a bookshelf structure, and the one that is bent is called a chevron structure. There are two bending directions when forming this U-shape. Defects occur where the bending directions differ.

This allows the liquid crystal cell to be easily observed with a polarizing microscope. This defect causes a decrease in memory performance and contrast ratio, and hinders display quality. As a solution to this, a high pretilt alignment film is used to make the bending direction uniform in one direction, a liquid crystal material that keeps the layer perpendicular to the substrate surface, or a chevron structure by applying an electric field. There is a method such as forcibly changing to a bookshelf structure. Both are very difficult techniques and it is difficult to suppress the occurrence of defects.

However, in the case of the antiferroelectric liquid crystal, the layer structure which is easily bent so that the layer is easily deformed by an electric field changes perpendicularly to the substrate surface, and realizes good defect-free alignment. Can be done. The antiferroelectric liquid crystal is easier to handle than the ferroelectric liquid crystal in that not only the antiferroelectric liquid crystal itself has a threshold value but also good alignment.

[0017]

As described above, the ferroelectric liquid crystal and the antiferroelectric liquid crystal have similar characteristics and different characteristics, but in any case, two states are uniquely determined. In addition, it is difficult to change the degree of whiteness or blackness with an applied voltage like a TN liquid crystal, and it is difficult to obtain a 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 high viewing angle. Therefore, there is an urgent need to develop a technique for realizing high gradation in a display using a ferroelectric liquid crystal and an antiferroelectric liquid crystal.

The waveform and the response of the liquid crystal when driving the actual ferroelectric liquid crystal will be described with reference to FIG. This is a standard waveform when the ferroelectric liquid crystal is driven by a simple matrix having a plurality of electrodes. The waveform when driving the ferroelectric liquid crystal includes a selection pulse 131 of a large voltage for selecting the state of the liquid crystal and １ ／ or 1 of the voltage of the selection pulse.
It is composed of small pulses of the non-selection section 132 having a size of / 4.

The optical response is a bright state 13 according to the selection pulse.
3 (for example, the first state) to the dark state 134 (the second state). In the next state, it responds to the non-selected pulse and does not return from the second state to the first state, but optical fluctuations occur, which is a major factor in lowering the contrast ratio.

In such a state, an intermediate state between the first state and the second state cannot be maintained even if the peak value of the selection pulse is changed. This is because a positive voltage and a negative voltage are alternately applied to the pixel electrode, so that the charge does not become constant and constantly changes, so that the optical response becomes unstable.

In such a simple matrix driving situation, it is rather a problem whether the first state and the second state of the liquid crystal molecules can be stably obtained and a state having a high contrast ratio can be obtained. Was not the situation to achieve.

Therefore, when the ferroelectric liquid crystal is driven by a simple matrix to perform gradation display, a plurality of (n) pixels are considered as one display picture element, and a pixel in an ON state and a pixel in an OFF state are displayed. In most cases, halftones were produced based on the area ratio. With this area gradation, the number of gradations of 2 n can be realized. However, in order to achieve a certain display capacity, n times the number of display pixels is required, and a high-definition display cannot be realized because a display image is coarsely described.

Then, it is necessary to realize a gray scale within one electrode pixel in order to realize a higher definition display. The present invention relates to a method for solving the problem.

[0025]

The present inventors have paid attention to the mechanism of spontaneous polarization of a ferroelectric liquid crystal, and have detailed the optical response of the liquid crystal depending on the driving waveform, and the correspondence with the spontaneous polarization at that time. I checked. As a result, it has been found that the transfer of charges into and out of the liquid crystal is extremely important for the gradation property of the ferroelectric liquid crystal.

According to the present invention, it is intended to drive a ferroelectric liquid crystal or an antiferroelectric liquid crystal to perform gradation display using an element capable of supplying a constant charge. First, a liquid crystal material having spontaneous polarization is sandwiched between a transparent substrate on which a lead electrode and a pixel electrode are arranged. Means are provided on the substrate surface in contact with the liquid crystal for arranging the liquid crystal material in a uniaxial alignment direction at least at an initial stage. A means for supplying a charge to the pixel electrode is provided, and a charge amount more than twice a product of a spontaneous polarization of a liquid crystal and a pixel area in the pixel electrode is supplied to the pixel electrode, and a period until the next charge is supplied. This is a liquid crystal electro-optical device capable of controlling a first state and a second state that can be taken by liquid crystal by holding the charge amount so as not to change.

Further, a liquid crystal material having spontaneous polarization is sandwiched between a transparent substrate on which a lead electrode and a pixel electrode are arranged, and the liquid crystal material is arranged at least in an initial stage in a uniaxial alignment direction on a substrate surface in contact with the liquid crystal. . A means for supplying electric charge to the pixel electrode is provided, and an arbitrary electric charge of not more than twice the product of the spontaneous polarization of the liquid crystal and the pixel area of the liquid crystal is supplied to the pixel electrode. The liquid crystal is characterized in that by maintaining the amount of charge so as not to change until the charge is supplied, the ratio of the area of the liquid crystal between the first state and the second state can be varied to perform gradation control. The present invention relates to an electro-optical device.

A liquid crystal material having spontaneous polarization is sandwiched between transparent substrates on which lead electrodes and pixel electrodes are arranged, and the liquid crystal material is arranged in a uniaxial alignment direction at least at an initial stage on a substrate surface in contact with the liquid crystal. Means for supplying electric charges to the pixel electrode.

An arbitrary charge of less than twice the product of the spontaneous polarization of the liquid crystal and the pixel area in the pixel electrode is supplied to the pixel electrode, and the amount of charge is changed until the next charge is supplied. The first state in which the liquid crystal can be obtained by inverting the spontaneous polarization corresponding to the supplied charge and maintaining the supplied charge and the spontaneously polarized charge in the pixel electrode in a quasi-equilibrium state by keeping the charge unchanged. And controlling the gradation by changing the ratio of the area in the second state to the second state.

In these cases, it is necessary to supply a reverse charge before supplying a fixed amount of charge so that the direction taken by the liquid crystal material is aligned in one state in advance. It is necessary to keep the constant.

A thin film transistor is used as a part of the means for supplying electric charges. One feature is to add capacitance in parallel to the pixel electrode connected to the thin film transistor.
The effect is great for driving a liquid crystal material having spontaneous polarization as in the present invention.

As a part of the charge supply means, a two-terminal diode element or a ferroelectric thin film can be used.

The invention having such a structure is necessary for the present inventors to realize the gradation of a liquid crystal material accompanied by spontaneous polarization. The element that can supply the electric charge is an element such as a thin film transistor or a ferroelectric thin film that can supply a predetermined electric charge to the pixel when the pixel is selected for a predetermined time.

As a matter of course, the charge supplied as a liquid crystal cell must not be consumed inside the cell. For this purpose, the volume resistance of the liquid crystal is 10 ¹¹ Ω · cm.
As described above, the cell needs to be high, and a cell in which a current flows in addition to the occurrence of spontaneous polarization due to the electric field of the liquid crystal is undesirable.

[0035]

First, the charge when switching a liquid crystal material having spontaneous polarization will be described. Electric charges are supplied to the pixel electrode by various means, and a constant voltage is applied to the pixel electrode in relation to the pixel capacitance.

When the TN liquid crystal is operated, the liquid crystal itself has a clear threshold voltage value. Therefore, if a voltage smaller than the threshold value is supplied, no response is made, but if a voltage larger than that is supplied, the state gradually changes. The color tone changes. That is, by adjusting the applied voltage, it is possible to change the non-transmission state from the transmission state.

In the same sense, the ferroelectric liquid crystal has no threshold. When a large voltage is applied, the liquid crystal changes from the first state to the second state at a high speed. When a small voltage is applied, the state changes while taking time. Therefore, it does not mean that the liquid crystal responds or does not respond simply by applying a voltage of several volts to the ferroelectric liquid crystal.

In the case of a ferroelectric liquid crystal, since the liquid crystal itself has a spontaneous polarization, how to invert the spontaneous polarization by the amount of charge supplied from the outside becomes a problem. In this case, what is important is not the applied voltage but the amount of charge to be supplied.
If twice the product of the pixel area and the spontaneous polarization (the amount of charge per unit area) of the liquid crystal material is supplied, the liquid crystal theoretically changes from the first state to the second state. Change. However, in practice, it is necessary to supply charges several times (1 to 5 times) as large as this.

This is because even though the liquid crystal is a ferroelectric liquid crystal, the threshold voltage for changing the state exists unclearly. When the amount of electric charge supplied from the outside is equal to or less than the above-mentioned amount of electric charge, it is not enough to invert all spontaneous polarizations in the pixel electrode. , That is, gradation display is realized.

As described above, the operation of applying a voltage to the liquid crystal is the same as the operation of supplying a charge, but here, how to supply the charge for inverting the spontaneous polarization of the liquid crystal is a problem. This is more appropriate than using a voltage expression.

First, a case where a thin film transistor (TFT) is used as a charge supply means will be described with reference to FIG. The TFT includes a source section 140 on the signal providing side, a drain section 141 connected to the liquid crystal pixel 143, and a gate section 142 for controlling a potential difference between the source and the drain. The other end of the pixel electrode is normally grounded 144. During operation, a constant voltage is supplied to the source section.

In this state, a voltage is applied to the gate and the gate is turned on, the resistance between the source and the drain is reduced, and a predetermined charge is supplied to the pixel electrode connected to the drain. After the charge is supplied, the gate is turned off, and the resistance between the source and the drain is increased by four to eight orders of magnitude of that of the on state. The pixel electrode is substantially in an open state, and the potential is kept as it is.

The state when the ferroelectric liquid crystal is driven via the TFT will be described with reference to FIG. Gate is O
The time in the N state was 60 μsec. Charge is supplied to the liquid crystal only during this time.

The relationship between the current flowing through the system and the optical response was examined. When a voltage of 10 V is applied, the optical response of the liquid crystal becomes 20.
0s are all inverted from the first state to the second state. Looking at the current at this time, the initial charge injection 20 into the pixel capacitance
A large current 202 flows corresponding to 1 and the optical change. The latter large current 202 is a current accompanying the reversal of spontaneous polarization of the ferroelectric liquid crystal.

On the other hand, when the applied voltage is 4 V, the injection of electric charge ends before the optical response 203 of the liquid crystal shows a sufficient change, and the optical response 204 ends accordingly, and thereafter the optical response becomes constant. State. Looking at the change in the current, the current accompanying the reversal of the spontaneous polarization stops at an intermediate stage.
In other words, the inversion of the liquid crystal was not completed during the period between the voltage and the time, and the operation was terminated halfway.

Further, the state of the optical response is such that the supply of electric charge is stopped even after the gate is turned off. In other words, the amount of charge injected at this time is not enough to invert the entire liquid crystal, but only a few inversions are performed. This is extremely important in the present invention.

As for the optical response of the liquid crystal, an OFF state and an ON state can be obtained when the applied voltage is large. The cone angle obtained from the state at this time is the same as that at the time of applying the DC voltage, and it can be seen that the liquid crystal responds sufficiently. On the other hand, in the low voltage region, the optical response changes while the gate is in the ON state, but a sufficient response cannot be made within that time, so that the optical position does not reach a sufficient optical position as described above, and the state is an intermediate state. . Further, the state is maintained after the gate is turned off, and a stable intermediate state is obtained.

FIG. 6 shows a change in the optical response when the voltage applied to the pixel electrode is changed when the gate is turned on. When the applied voltage is changed, the amount of light transmitted through the pixel changes continuously. This is in a region where there is almost no problem with gradation display by ferroelectric liquid crystal.

When the liquid crystal is observed with an optical microscope while applying a voltage of 5 V or less in FIG. 6, a domain in which the first state and the second state are mixed (the two states are mixed in the sense of the region). Is observed). On the other hand, when a voltage of 5 V or more is applied, no domain is observed, and the blackness and whiteness of the entire pixel are changed. Probably at this stage, the cone angle has changed.

As described above, halftone with a domain and halftone without a domain are realized at a certain voltage.
As can be seen from FIG. 6, it is possible to greatly change the gradation with respect to the applied voltage when the domain having the domain of 5 V or less is applied. The change in transmittance in the region of 5 V or more is actually gentle. Therefore, performing gray scale display by changing the area in the first state and the second state is a main method in practice in comparison with performing gray scale display by changing whiteness and blackness.

Further, when a gray scale display of ferroelectric liquid crystal is performed by using a TFT, there is a method in which the time during which the gate is turned on is fixed and the voltage peak value to be applied is changed, In the sense of how much response is made, even if the applied voltage is kept constant and the time during which the gate is turned on is changed, there is no problem in realizing the gradation. Naturally, if the application time is long, the liquid crystal responds sufficiently from the first state to the second state, and if the application time is short, the degree of spontaneous polarization is reversed optically. Can only give an inadequate response.

Further, it is possible to perform gradation by changing both the applied voltage and the application time for keeping the gate on. At that time, it is more convenient for actual driving to change the factor that can be easily handled in multiple stages and to change the factor with no margin in small stages. In this case, if the time is changed, the driving frequency also changes, and it is more practical to control the voltage peak value.

It is said that ferroelectric liquid crystals do not themselves have a definite threshold voltage. Certainly, the optical response when a DC voltage is applied to the ferroelectric liquid crystal cell gradually changes while taking time.

In the pulse driving, the response of the ferroelectric liquid crystal can have a threshold value, but the halftone cannot be stably maintained. That is, when a voltage is simply applied to the pixel electrode, charge is consumed to compensate for the inversion of liquid crystal molecules in the pixel electrode, so that the supplemented charge is replenished, and although a low voltage is applied, there is no threshold for the liquid crystal. All liquid crystal molecules are inverted. In the pulse application state, the potential of the pixel electrode becomes the same level after the pulse application, and the potential difference disappears.

Therefore, in this case, the state of the liquid crystal is further changed after the voltage is applied under the influence of the anti-electric field generated inside the cell. On the other hand, when only a certain amount of electric charge is supplied from the TFT within a certain time, only the amount of spontaneous polarization corresponding to the amount of electric charge responds. Holding.
That is, the supplied charge amount and the spontaneous polarization are in an equilibrium state in a metastable state.

Further, when electric charge is consumed in the pixel electrode, or when the spontaneous polarization is so large as in the case of an antiferroelectric liquid crystal, a charge amount sufficient to invert the liquid crystal cannot be injected within a certain period. In such a case, it is necessary to replenish the charge to make up for it. In such a case, it is a good technique not only to connect the TFT and the liquid crystal in series but also to connect an appropriate amount of capacitance (referred to as an additional capacitance) in parallel with the pixel. It is sufficient that the capacitance is equivalent to the pixel capacitance or several times the pixel capacitance. If the capacitance is large, it will be enough to replenish the pixel charge,
There is a problem that it takes too much time to accumulate charges in the additional capacitance. Then, the magnitude of the capacity as described above becomes appropriate.

As described above, a device for supplying a fixed amount of electric charge to the pixel electrode is not limited to the TFT, but may be some other device. 2
Such a phenomenon can be captured even when a metal-insulating film-metal (MIM) or a ferroelectric thin film is used as a terminal element. Ferroelectric thin films include organic polymers such as polyvinylidene fluoride, copolymers of viridene fluoride and trifluoroethylene, copolymers of viridene fluoride and tetrafluoroethylene, and inorganic materials such as barium titanate and titanium oxide. Or a composite inorganic film.

Such a ferroelectric thin film is provided in the pixel electrode. Like a ferroelectric liquid crystal, a ferroelectric thin film generates spontaneous polarization when a voltage is applied to the thin film. This will be described with reference to FIG. The ferroelectric thin film 151 and the liquid crystal 152 are connected in series, and a signal voltage is supplied from one terminal 153. The other terminal 154 of the pixel electrode is grounded. Terminal 153
When a signal voltage pulse is supplied from the device, a voltage is applied to the ferroelectric thin film and the liquid crystal, and the dipoles of the ferroelectric thin film and the liquid crystal are arranged in a certain direction. The magnitude of the spontaneous polarization of the above-described ferroelectric thin film is 1000 to 100000 nC / cm 2, which is about 3 to 5 digits larger than that of the spontaneous polarization of the ferroelectric liquid crystal.

Accordingly, the behavior of spontaneous polarization of the ferroelectric thin film may be regarded as a main component of this system. When the potential after applying the pulse is grounded, the spontaneous polarization generated from the ferroelectric thin film is applied to the liquid crystal. That is, the spontaneous polarization generated in the ferroelectric thin film is divided by the capacitance of both, and the electric charge at that time is supplied to the liquid crystal.

The magnitude of the spontaneous polarization generated when a voltage is applied to the ferroelectric thin film hardly occurs when the applied voltage is small. When the applied voltage exceeds a certain voltage (coercive electric field), the spontaneous polarization is proportional to the applied voltage. growing. Therefore, the magnitude of the spontaneous polarization generated by the applied voltage can be controlled, which can control the amount of charge provided to the ferroelectric liquid crystal of the pixel electrode.
Thereby, the ratio of the liquid crystal of the pixel electrode in the first state and the second state can be controlled.

That is, gradation display of ferroelectric liquid crystal becomes possible. One method is to change the voltage applied to the ferroelectric thin film as in the case of the TFT, but it is also possible to change the voltage application time while keeping the voltage constant. Is also one means to change both.
In any case, it is better to select a method with a margin.

As described above, the ratio between the first state and the second state taken by the liquid crystal can be controlled by the amount of charge supplied to the ferroelectric liquid crystal. Since the liquid crystal itself does not have a definite threshold value, the gradation control based on this is determined only by the two conditions of the initial position and the amount of charge supplied thereto. .

Therefore, in order to realize a reproducible gradation, the initial state of the liquid crystal must be determined. Therefore, before applying the pulse to supply the charge,
This means that a pulse in the opposite direction to that pulse is applied to initialize the state of the liquid crystal. As a result, a target state can be realized in the next state regardless of the state before the pixel state to be displayed.
Hereinafter, an embodiment will be described.

[0064]

【Example】

Example 1 An n-channel polysilicon TFT was formed on a Corning 7059 substrate by a normal low-temperature process. A pixel electrode was arranged on the drain side. Polyimide was applied on the substrate by spin coating and baked at 200 ° C.
The thickness was 100-300 °. The counter substrate is a substrate in which pixels are not divided, and polyimide is directly applied by spin coating. Both substrates were subjected to a rubbing treatment to obtain a uniaxial orientation treatment. The rubbing direction was set so that the rubbing direction was orthogonal when the cells were assembled.

At this time, when performing rubbing on the TFT substrate side, each lead electrode was dropped to the ground, and sufficient care was taken so that the element was not destroyed by static electricity. Next, spacers were 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 bonded to 1.5 μm according to the diameter of the spacer. Into the cell, ZLI3654 ferroelectric liquid crystal manufactured by Merck was injected. The liquid crystal material was heated to 100 ° C., and vacuum injection was performed in a state where the liquid crystal was in an isotropic phase. After the sealing, the driving circuit was subjected to a test after connection.

A voltage of 15 V was applied to the gate so that the gate was turned on for 50 μsec. FIG. 6 shows the state of the optical response of ON and OFF when the source voltage was changed. The transmission state on the light side when a positive voltage was applied as the source voltage increased as the applied voltage increased. On the other hand, the dark state decreased as the applied voltage increased. Clear gradation is obtained.

Further, in order to make the ON state more clearly with the plus voltage, it is necessary to apply a minus voltage before applying the plus voltage. By applying a voltage of -8 V in advance, a clear gradation can always be realized.

Example 2 A display using an organic ferroelectric thin film as a charge supply means will be described with reference to FIG. An ITO pixel electrode was formed on the glass substrate 160 by a DC sputtering method at a thickness of 1000 、, and was etched into a predetermined pixel pattern 161 by an ordinary photolithography method.

Next, a copolymer of trifluoroethylene and vinylidene fluoride was dissolved in dimethylformamide to prepare a 1 to 5% solution. This was applied on the substrate by spin coating, heated at 170 ° C. for 2 hours and gradually cooled to room temperature to increase the crystallinity of the ferroelectric thin film 162.

Next, 1500 ° of chromium was deposited by sputtering. This was patterned to form a lead electrode 163. FIG. 8 shows a ferroelectric thin film of the same size as a chromium electrode. If the entire ferroelectric thin film is etched when the resist is ashed after the patterning of chromium, the result is as shown in FIG. If left in the middle, a ferroelectric thin film will remain on the entire surface. In an experiment, any may be sufficient. After processing the electrodes on the opposing glass substrate 166 into a predetermined pattern 164, polyimide 165 was applied thereon by spin coating to form a film by heating. After rubbing treatment, the ferroelectric thin film side substrate 160 and 2 μm
The substrate was bonded to the opposing substrate at a distance of m and fixed with the sealant 167. To this, a phenylpyrimidine-based ferroelectric liquid crystal having a phase sequence of isotropic phase-smectic A phase-smectic C * phase was injected under heating, connected to a circuit, and subjected to measurement.

FIG. 9 shows the result of measuring the potential between the liquid crystal and the ferroelectric thin film when a pulse was applied to the liquid crystal cell with the ferroelectric thin film as the liquid crystal potential. The liquid crystal potential increases when a pulse is applied, but remains constant after the end of the pulse. That is, a certain amount of spontaneous polarization generated in the pulse application state is provided to the liquid crystal pixel after the end of the pulse, and the liquid crystal potential is generated.

This liquid crystal potential is actually applied to the liquid crystal, and the liquid crystal responds. FIG. 10 shows changes in the liquid crystal potential when the applied voltage and the pulse width are changed. Pulse width 1000μ
When set to seconds, the liquid crystal potential is generated at 40 Vpp and 100 V
pp is 10 Vpp. Here is a clear threshold. Even when the applied voltage is changed only by the ferroelectric thin film and the value of the spontaneous polarization generated there is measured, as the applied voltage decreases, the value of the spontaneous polarization also decreases. The same tendency was confirmed when the liquid crystal was connected in series.

When the pulse width is further changed to 100 μs, a large voltage is required to obtain the same liquid crystal potential. This liquid crystal potential means the same as the voltage on the horizontal axis in FIG. 6 showing the response of the liquid crystal when the TFT is used. Therefore, if such a liquid crystal potential is measured using a ferroelectric thin film, it goes without saying that the gradation of the optical response of the liquid crystal can be sufficiently obtained. In the present invention using a ferroelectric thin film, as in the case of using a TFT, 20 to 40 V
A sufficient gradation could be realized by changing the voltage value between.

[0074]

According to the present invention, a liquid crystal material having spontaneous polarization is driven by a TFT or a cell having a ferroelectric thin film, and a predetermined amount of charge is applied to the liquid crystal material. When it was possible to do so, it was possible to change the area ratio of the liquid crystal in the first state and the liquid crystal in the second state depending on the amount of charge supplied. By utilizing the high speed and high field of view of the ferroelectric liquid crystal or the antiferroelectric liquid crystal, a high-performance liquid crystal display can be realized in combination with the high gradation performance of the present invention, and a liquid crystal television capable of displaying a video signal can be realized. It became an effective means to create.

[Brief description of the drawings]

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

FIG. 2 is a diagram schematically showing an antiferroelectric liquid crystal.

FIG. 3 is a diagram in which a ferroelectric liquid crystal is driven by a conventional method.

FIG. 4 is a diagram illustrating the present invention.

FIG. 5 is a diagram showing the operation of the present invention.

FIG. 6 is a diagram showing the operation of the invention.

FIG. 7 is a sectional view when a ferroelectric thin film is used in the present invention.

FIG. 8 is a diagram showing an operation when a ferroelectric thin film is used.

FIG. 9 is a diagram showing an operation when a ferroelectric thin film is used.

FIG. 10 is a diagram showing an operation when a ferroelectric thin film is used.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/133 G09G 3/36

Claims (10)

(57) [Claims] 1. A pair of opposing substrates, a pixel electrode provided above at least one of the substrates, and a liquid crystal comprising an antiferroelectric liquid crystal having spontaneous polarization sandwiched between the pair of substrates. A liquid crystal electro-optical device, comprising: a material; a unit for arranging the liquid crystal material in a uniaxial alignment direction; a unit for supplying a charge to the pixel electrode; and a unit for holding the supplied charge. The amount of charge supplied to the liquid crystal material is equal to or less than the amount of charge for inverting all of the spontaneous polarization, and gradation control is performed by changing the ratio of the area of the liquid crystal material between the first state and the second state. Electro-optical device. 2. A pair of opposing substrates, a pixel electrode provided above at least one of the substrates, and a liquid crystal comprising antiferroelectric liquid crystal having spontaneous polarization sandwiched between the pair of substrates. A liquid crystal electro-optical device, comprising: a material; a unit for arranging the liquid crystal material in a uniaxial orientation direction; a unit for supplying a charge to the pixel electrode; and a unit for holding the charge. A charge equal to or less than the amount of charge to be supplied is supplied to the pixel electrode, and the spontaneous polarization of the liquid crystal material in the pixel electrode is inverted by inverting the spontaneous polarization corresponding to the charge supplied to the pixel electrode. A liquid crystal electro-optical device characterized in that gradation is controlled by changing the ratio of the area between the first state and the second state of the liquid crystal material by keeping the charge and the quasi-equilibrium state. 3. A pair of substrates facing each other, a pixel electrode provided above at least one of the substrates, and a liquid crystal comprising an antiferroelectric liquid crystal having spontaneous polarization sandwiched between the pair of substrates. A liquid crystal electro-optical device comprising: a material; a unit for arranging the liquid crystal material in a uniaxial orientation direction; a unit for supplying a charge to the pixel electrode; and a unit for holding the charge. Supply to the pixel electrode by supplying a charge amount of not more than twice the product of the spontaneous polarization and the pixel area, and keeping the charge amount unchanged until the next charge supply. The first state of the liquid crystal material is maintained by inverting the spontaneous polarization corresponding to the charge and maintaining the supplied charge and the spontaneous polarization charge of the liquid crystal material in the pixel electrode in a quasi-equilibrium state. Of the second state Liquid crystal electro-optical device, which comprises gradation control by varying the proportion of the product. 4. The method according to claim 1, wherein
A liquid crystal electro-optical device, wherein the liquid crystal material has a volume resistance of 10 ¹¹ Ω · cm or more. 5. The method according to claim 1, wherein
The liquid crystal electro-optical device according to claim 1, wherein the amount of charge for inverting all of the spontaneous polarization is a charge amount of 2 to 10 times the product of the spontaneous polarization and the area of the pixel electrode. 6. The method according to claim 1, wherein
A liquid crystal electro-optical device, wherein a charge in a direction opposite to a charge supplied to the pixel electrode is supplied to supply the liquid crystal material to the first state or the second state before supplying the charge to the pixel electrode. 7. The method according to claim 1, wherein
The pixel electrode is a liquid crystal electro-optical device characterized in that it is connected to the thin film transistor. 8. The method of claim 7, prior to the liquid crystal electro-optical device, characterized in that capacity in parallel outs pixel electrode is added. 9. A any one of claims 1 to 5,
A liquid crystal electro-optical device comprising a diode element as a part of the means for supplying electric charges. 10. In any one of claims 1 to 5, the liquid crystal electro-optical device which comprises a ferroelectric thin film as a means for supplying the charge.