JPH06160809A - Liquid crystal electrooptical device - Google Patents

Abstract

PURPOSE:To perform liquid crystal display with high gradation by supplying specific charge quantity that is the product of spontaneous polarization and a picture element area in liquid crystal to a picture element electrode, and holding it so as not to change until next charge supply. CONSTITUTION:A thin film transistor TET consists of a source part 140 on a signal supply side, a drain part 141 connected to a liquid crystal picture element, and a gate part 142 which controls potential difference between a source and a drain. The terminal on the other side of the picture element electrode is grounded 144 ordinarily. When an operation is performed, a constant voltage is supplied to the source part 140. The gate is turned on by applying the voltage in such state, and resistance between the source and the drain is decreased, and prescribed charge is supplied to the picture element electrode connected to the drain part 141. After the charge is supplied, the gate is turned off, and a resistance value between the source and the drain is increased by four to eight times that in an on-state. The picture element electrode is set in an open state essentially, and the potential of the electrode can be held as it is.

Description

Detailed Description of the Invention

[0001]

[Industrial application] A high gradation liquid crystal display in which a device for supplying a certain amount of charge of a liquid crystal material having spontaneous polarization is arranged on a substrate to assist switching of ferroelectric liquid crystal or antiferroelectric liquid crystal. The present invention relates to a liquid crystal electro-optical device that realizes the above.

[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 crystals,
Especially popular are nematic liquid crystals,
As the operation mode, it is used in many fields such as twisted nematic liquid crystal or super twisted nematic liquid crystal. They are sandwiched between substrates having electrodes which are individually patterned, and are used as a simple matrix panel, which has a relatively short manufacturing process and is an inexpensive panel. However, when the number of pixel electrodes increases, crosstalk occurs and the display quality deteriorates.

In order to solve the problem, thin film transistors, non-linear elements made of metal-insulating film-metal, etc. are formed on a substrate, even though it is prepared that the manufacturing process becomes complicated.

These assist the switching of the liquid crystal. As a result, high-performance display quality is realized, and clear TV images can be displayed on the LCD panel. However, in the case of the nematic liquid crystal, the response speed is 1 to 500 msec, and the problem that the rewriting speed is slow occurs.

Therefore, the ferroelectric liquid crystal is attracting attention. The same applies to antiferroelectric liquid crystals.

Ferroelectric liquid crystal is used for the substrate 10 as shown in FIG.
The liquid crystal molecules 102 are oriented in a fixed direction according to the orientation control of the 0 plane. A layered structure 101 is formed between the liquid crystal molecules, and they are highly ordered in the three-dimensional direction. It is said that the liquid crystal molecules may exist at any position where a cone is formed under a large cell thickness, and they 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.
There are two states. In that state, the spontaneous polarization of liquid crystal molecules can be controlled by the direction of the electric field applied thereto.

In the first state, the direction of spontaneous polarization is downward,
The spontaneous polarization in the second state is upward. High-speed rewriting between the two states, stable maintenance of the state even after application of the electric field, and distinction between the two states over a wide viewing angle when observed through a polarizing plate Since it has excellent properties such as being possible, it is highly expected as a liquid crystal material that can realize a high-speed and large-capacity screen.

On the other hand, with respect to the antiferroelectric liquid crystal, as shown in FIG. 2, the ferroelectric liquid crystal can take the third state 122 in addition to the first state 120 and the second state 121. It is in the third state when no voltage is applied, in the first state when a negative voltage is applied, and in the second state when a positive voltage is applied.

At this time, there is a clear threshold voltage 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, it became extremely superior to the ferroelectric liquid crystal in terms of driving.

The speed of switching from the third state to the first state and from the third state to the second state becomes high in accordance with the applied voltage. However, from the first and second states to the third
The switching speed to the state of (4) tends to be somewhat slower. The reason for this is that the effect of clay and the interface of the liquid crystal is relatively large, and the lack of a driving force for changing the direction of spontaneous polarization from a uniform state to a state in which they are present alternately.

There is a point that all the characteristics of the antiferroelectric liquid crystal are similar to those of the nematic liquid crystal rather than the ferroelectric liquid crystal.

Further, the ferroelectric liquid crystal and the antiferroelectric liquid crystal are
It forms a layered structure. This layer is not perpendicular to the substrate surface, but is somewhat curved and has a doglegged structure. The structure that is perpendicular to the substrate surface is called the bookshelf structure, and the bent structure is called the chevron structure. There are two bending directions when forming the V-shape. Defects occur where the bending directions differ.

This allows the liquid crystal cell to be easily observed with a polarization microscope. This defect causes a deterioration in the memory property and the contrast ratio, and becomes a cause of impairing the 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 whose layer is kept perpendicular to the substrate surface, or an electric field is applied to form a chevron structure. There are methods such as forcibly changing to a bookshelf structure. Both are very difficult technologies and it is difficult to suppress the occurrence of defects.

However, in the case of the antiferroelectric liquid crystal, the layer structure in which the layer deformation easily occurs due to the electric field changes perpendicularly to the substrate surface, and good defect-free orientation can be realized. Can be done. The antiferroelectric liquid crystal is easier to handle than the ferroelectric liquid crystal in that it has not only a threshold value but also good alignment.

[0017]

As described above, the ferroelectric liquid crystal and the antiferroelectric liquid crystal have similar and different characteristics, but in both cases, the two states are uniquely determined. In addition, it is difficult to change the degree of whiteness or blackness of the color tone by the applied voltage like TN liquid crystal, and it is 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 the 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.

The waveform and the response of the liquid crystal when actually driving the ferroelectric liquid crystal will be described with reference to FIG. This is a standard waveform when driving a ferroelectric liquid crystal with a simple matrix having a plurality of electrodes. The waveform when driving the ferroelectric liquid crystal has a large voltage selection pulse 131 for selecting the state of the liquid crystal and 1/3 or 1 of the voltage of the selection pulse.
It is composed of a small pulse of the non-selection unit 132 having a size of / 4.

The optical response is in the bright state 13 according to the selection pulse.
3 (for example, the first state) is switched 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 of the decrease in contrast ratio.

In such a state, it is impossible to maintain the intermediate state between the first state and the second state even if the crest value of the selection pulse is changed. This is because the positive voltage and the 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.

Under such a simple matrix driving condition, it is rather a problem whether the first state and the second state of the liquid crystal molecules can be stably obtained and a high contrast ratio state can be obtained. The situation did not reach.

Therefore, when the ferroelectric liquid crystal is driven by a simple matrix for gradation display, a plurality (n) of pixels are considered as one display picture element, and pixels of ON state and pixels of OFF state are considered. Most of them were said to produce a halftone in terms of area ratio. With this area gradation, a gradation number of 2 to the n-th power can be realized. However, in order to achieve a certain display capacity, n times the number of display pixels is required, and since the displayed image is a rough depiction, it is not possible to realize a high-definition display.

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

[0025]

Means for Solving the Problems The inventors of the present invention have focused on the mechanism of generation of spontaneous polarization of a ferroelectric liquid crystal, and have a detailed description of what happens to the optical response of the liquid crystal depending on the drive waveform and the correspondence with the spontaneous polarization at that time. I checked. As a result, it was found that charge and discharge of the liquid crystal are extremely important for the gradation of the ferroelectric liquid crystal.

The present invention intends to perform gradation display by driving an ferroelectric liquid crystal or an anti-ferroelectric liquid crystal by using an element capable of supplying a constant electric charge. First, a liquid crystal material having spontaneous polarization is sandwiched between transmissive substrates provided with lead electrodes and pixel electrodes. Means for arranging the liquid crystal material in the uniaxial orientation direction at least in the initial stage is provided on the surface of the substrate in contact with the liquid crystal. A means for supplying charges to the pixel electrode is arranged, and a charge amount exceeding twice the product of the spontaneous polarization of the liquid crystal and the pixel area of the pixel electrode is supplied to the pixel electrode, and until the next charge is supplied. The liquid crystal electro-optical device is capable of controlling the first state and the second state that the liquid crystal can have by holding the charge amount so that it does not change.

Further, a liquid crystal material having spontaneous polarization is sandwiched between transparent 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 surface of the substrate in contact with the liquid crystal. . Means for supplying an electric charge to the pixel electrode is arranged, and an arbitrary amount of charge equal to or less than twice the product of the spontaneous polarization of the liquid crystal and the pixel area of the pixel electrode is supplied to the pixel electrode. The liquid crystal is characterized in that the ratio of the area of the first state and the second state of the liquid crystal that can be taken is changed and gradation control is performed by holding the amount of charge so that it does not change until the charge is supplied. The invention relates to an electro-optical device.

In addition, a liquid crystal material having spontaneous polarization is sandwiched between transmissive substrates on which lead electrodes and pixel electrodes are arranged, and the liquid crystal material is arranged in a uniaxial orientation direction at least in an initial stage on a substrate surface in contact with the liquid crystal. Therefore, a means for supplying charges to the pixel electrode is provided.

An arbitrary charge amount not more than twice the product of the spontaneous polarization of the liquid crystal in the pixel electrode and the pixel area is supplied to the pixel electrode, and the charge amount is changed until the next charge supply. By holding the charge so as not to change, the spontaneous polarization corresponding to the supplied charge is inverted to maintain the supplied charge and the spontaneously polarized charge in the pixel electrode in a quasi-equilibrium state, which is the first state that the liquid crystal can assume. And the gradation control is performed by changing the ratio of the area in the second state.

Before supplying a fixed amount of electric charges to these liquids, it is necessary to preliminarily align the direction taken by the liquid crystal material to one state so that the optical change amount of the liquid crystal becomes constant. It is necessary to keep constant.

A thin film transistor is used as part of the means for supplying charges. It is also one of the features 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.

Further, a diode element which is a two-terminal element or a ferroelectric thin film can be used as a part of the charge supplying means.

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

Further, as a matter of course, the charge supplied as the liquid crystal cell must not be consumed inside the cell. For that purpose, the volume resistance value of the liquid crystal is 10 ¹¹ Ω · cm.
It is necessary to have a high value as described above, and a cell in which a current flows in addition to the occurrence of spontaneous polarization due to the electric field of 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, so that if a voltage smaller than the threshold value is supplied, no response occurs, but if a larger voltage is supplied, the state gradually changes. It changes and the color tone changes. That is, by adjusting the applied voltage, it is possible to change the transparent state to the non-transparent state.

In the same sense, the ferroelectric liquid crystal has no threshold value. When a large voltage is applied, the liquid crystal changes from the first state to the second state at high speed, and 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 it has spontaneous polarization itself, there is a problem how to invert the spontaneous polarization by the amount of charge supplied from the outside. In that case, what is important is not the applied voltage, but the amount of charges supplied.
If the product of the product of the spontaneous polarization (unit is the amount of charge per unit area) of the liquid crystal material and the pixel area is doubled, theoretically the liquid crystal will change from the first state to the second state. Change. However, in actuality, it is necessary to supply the electric charge several times (1 to 5 times) this amount.

This is because the threshold voltage for changing the state of a ferroelectric liquid crystal exists, though it is unclear. When the amount of charge supplied from the outside is less than or equal to the above-mentioned amount of charge, inversion of all the spontaneous polarization in the pixel electrode occurs, and inversion corresponding to the supplied charge occurs, and the optical response corresponds to that amount. Partial inversion, that is, gradation display is realized.

The operation of applying a voltage to the liquid crystal and the operation of supplying an electric charge are the same as described above, but the problem here is how to supply an electric charge that reverses the spontaneous polarization of the liquid crystal. It is more appropriate than using the expression using voltage.

First, the 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 part 140 on the signal providing side, a drain part 141 connected to the liquid crystal pixel 143, and a gate part 142 for controlling a potential difference between the source and the drain. The other end of the pixel electrode is normally grounded 144. When operating, a constant voltage is supplied to the source section.

In this state, a voltage is applied to the gate to turn it on, the resistance between the source and the drain decreases, and a predetermined charge is supplied to the pixel electrode connected to the drain portion. After supplying the electric charge, the gate is turned off, and the resistance value between the source and the drain is increased by 4 to 8 digits of that in the on state. The pixel electrode is substantially in an open state, and the electric potential is retained as it is.

The state in which the ferroelectric liquid crystal is driven through the TFT will be described with reference to FIG. The gate is O
The time in the N state was 60 μsec. Electric charges are supplied to the liquid crystal only during this time.

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

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

Further, as for the state of the optical response, the state in which the supply of electric charges is stopped even after the gate is turned off is maintained. In other words, the amount of charges injected at this time is not enough to invert all liquid crystals, and only some percentage of inversion is performed. This is extremely important in the present invention.

Regarding 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 the response cannot be sufficiently made within that time, so that the optical position as described above cannot be reached and the state is in the intermediate state. . Further, after the gate is turned off, that state is maintained and a stable intermediate state can be obtained.

FIG. 6 shows the change in 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 passing through the pixel changes continuously. As a result, there is almost no problem in gradation display with the ferroelectric liquid crystal.

Further, when observing the liquid crystal 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 (two states are mixed in the sense of a region) Are 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 changes. The cone angle is probably changing at this stage.

In this way, halftones with domains and halftones without domains are realized with a certain voltage as a boundary.
As can be seen from FIG. 6, it is possible to make a large gradation change with respect to the applied voltage when the domain with 5 V or less is included. The change in transmittance in the region of 5 V or higher is actually moderate. Therefore, performing the gradation display by changing the areas of the first state and the second state is the main method in actuality as compared with the case of changing the whiteness and blackness.

Further, when performing gradation display of the ferroelectric liquid crystal using the TFT, there is a method in which the time during which the gate is on is made constant and the applied voltage peak value is changed, and within a certain time. In terms of how much response is made to, 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. As a matter of course, when the application time is long, the liquid crystal responds sufficiently from the first state to the second state, and when the application time is short, the spontaneous polarization is optically reversed by a problem. However, they can only respond poorly.

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 steps and change the factor that has no margin in small steps. In this case, if the time is changed, the drive frequency also changes, and it is more practical to control the voltage peak value.

Ferroelectric liquid crystals are said to have no well-defined threshold voltage. Certainly, the optical response in the state where a DC voltage is applied to the ferroelectric liquid crystal cell gradually changes over time.

Further, in the pulse drive, the response of the ferroelectric liquid crystal can have a threshold value, but the halftone cannot be stably maintained. When a voltage is simply applied to the pixel electrode, the charge is replenished because the charge is consumed due to the inversion of liquid crystal molecules in the pixel electrode, and there is no threshold of liquid crystal although low voltage is applied. All liquid crystal molecules are inverted. Further, in the pulse applied state, the potential of the pixel electrode becomes the same level after the pulse is applied, and the potential difference disappears.

Therefore, in this case, the state of the liquid crystal is further changed after the voltage is applied due to the influence of the anti-electric field generated inside the cell. On the other hand, when only a certain amount of charge is supplied from the TFT within a certain period of time, only the amount of spontaneous polarization commensurate with the amount of charge responds, and in the later open state, the liquid crystal can be in the state that the liquid crystal can take. Holding
In other words, the amount of charge supplied and the spontaneous polarization are in equilibrium in a metastable state.

Further, when the charge is consumed in the pixel electrode, or in particular, as in the case of the antiferroelectric liquid crystal, the spontaneous polarization is large and the charge amount for inverting the liquid crystal cannot be injected within a certain period. In some cases, it is necessary to replenish the charge to make up for it. In that 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 additional capacitance) in parallel with the pixel. As for the size of the capacitance, it is sufficient that it is equivalent to the pixel capacitance or several times larger than 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 the charge in the additional capacitance. Then, the size of the capacity as described above becomes appropriate.

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

Such a ferroelectric thin film is arranged 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 ferroelectric thin film and the liquid crystal, 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-mentioned ferroelectric thin film is 1000 to 100000 nC / cm2, which is about 3 to 5 digits larger than that of the spontaneous polarization of the ferroelectric liquid crystal.

Therefore, the behavior of spontaneous polarization of the ferroelectric thin film can be regarded as the main component of this system. When the potential after the pulse application is grounded, the spontaneous polarization generated from the ferroelectric thin film is also applied to the liquid crystal. That is, the spontaneous polarization generated in the ferroelectric thin film is divided by the two capacitors, and the electric charge at that time is supplied to the liquid crystal.

The magnitude of spontaneous polarization generated when a voltage is applied to the ferroelectric thin film is almost non-existent when the applied voltage is small, and the spontaneous polarization is proportional to the applied voltage when a certain voltage (coercive electric field) is exceeded. 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 the ferroelectric liquid crystal becomes possible. Further, one method is to change the voltage applied to the ferroelectric thin film as in the case of the TFT, but the voltage application time may be changed while the voltage is kept constant. Is also one way to change.
In any case, it is better to select a method with a margin.

As described above, the ratio of 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. Gradation control by this is decided for the first time by the two conditions of what position the initial state is, and how much charge is supplied to it, because the liquid crystal itself does not have a clear threshold value. .

Therefore, in order to realize a reproducible gradation, the initial state of the liquid crystal must be determined. Therefore, before applying the pulse for supplying the electric charge,
It means that it is sufficient to apply a pulse in the opposite direction to that pulse to initialize the state of the liquid crystal. This makes it possible to realize a target state in the next state, regardless of the state before the pixel state to be displayed.
An example will be described below.

[0064]

【Example】

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

At this time, when rubbing the TFT substrate side, each lead electrode was dropped to the ground to give sufficient consideration so that the device would not be destroyed by static electricity. Next, spacers were scattered 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. ZLI3654 ferroelectric liquid crystal manufactured by Merck was injected into the inside of the cell. The liquid crystal material was heated to 100 ° C., and vacuum injection was performed while the liquid crystal was in the isotropic phase. The drive circuit after sealing 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 optical response states of ON and OFF when the source voltage was changed. When a positive voltage was applied as the source voltage, the transmission state on the bright side 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 clearer with the positive voltage, it is necessary to apply the negative voltage before applying the positive voltage. If a voltage of -8 V was applied in advance, clear gradation could 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. A 1000 Å film of an ITO pixel electrode was formed on the glass substrate 160 by a DC sputtering method, and a predetermined pixel pattern 161 was etched by a normal photolithography method.

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

Next, 1500 Å of chromium was deposited by the sputtering method. This was patterned to form a lead electrode 163. In FIG. 8, the ferroelectric thin film is shown in the same size as the chromium electrode. When the ferroelectric thin film is completely etched when the resist is ashed after the chromium patterning, the result is as shown in this figure. If left in the middle, the ferroelectric thin film will remain on the entire surface. Either may be used in the experiment. An electrode was processed into a predetermined pattern 164 on the opposite glass substrate 166, and then polyimide 165 was applied thereon by spin coating to form a film by heating. After rubbing treatment, ferroelectric thin film side substrate 160 and 2μ
It was fixed to the opposite substrate at a distance of m with a sealant 167. A phenylpyrimidine-based ferroelectric liquid crystal having a phase sequence of isotropic phase-smectic A phase-smectic C * phase was heated and injected into this, and after the circuit was connected, it was subjected to the measurement.

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

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 is 1000μ
In seconds, the liquid crystal potential is 40Vpp and 100V.
It is 10 Vpp in pp. A clear threshold appears here. Even when the applied voltage is changed only by the ferroelectric thin film and the value of the spontaneous polarization generated therein is measured, the value of the spontaneous polarization also decreases as the applied voltage decreases. A similar tendency was confirmed even when the liquid crystal was connected in series.

Further, when the pulse width is changed to 100 μsec, a large voltage is required to obtain the same liquid crystal potential. This liquid crystal potential means the same thing as the voltage on the horizontal axis of FIG. 6, which shows the response of the liquid crystal when a TFT is used. Therefore, it goes without saying that if such a liquid crystal potential is measured using a ferroelectric thin film, the gradation of the optical response of the liquid crystal can be sufficiently obtained according to this. Also in the present invention using a ferroelectric thin film as in the case of using a TFT, 20 to 40 V
It was possible to realize a sufficient gradation by changing the voltage value between.

[0074]

EFFECTS OF THE INVENTION A liquid crystal material having spontaneous polarization is driven by a TFT or a cell having a ferroelectric thin film, a predetermined amount of charge is applied to the liquid crystal material, and a high resistance state is set in the next state to maintain the amount of charge. When it is possible to do so, the area ratio of the liquid crystal in the first state and the second state can be changed by the amount of electric charge supplied. This makes it possible to realize a high-performance liquid crystal display in combination with the high gradation performance of the present invention by utilizing the high speed and high field of view of the ferroelectric liquid crystal or the anti-ferroelectric liquid crystal, and to provide a liquid crystal television capable of displaying a video signal. It became an effective way to create it.

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

FIG. 4 is a diagram showing the present invention.

FIG. 5 is a diagram showing the operation of the 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 the action when a ferroelectric thin film is used.

FIG. 9 is a diagram showing the action when a ferroelectric thin film is used.

FIG. 10 is a diagram showing the action when a ferroelectric thin film is used.

Claims (8)

[Claims] 1. 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 a substrate surface in contact with the liquid crystal. Means for supplying charges to the pixel electrode, and supplying to the pixel electrode a charge amount exceeding twice the product of the spontaneous polarization of the liquid crystal and the pixel area. The liquid crystal electro-optical device capable of controlling the first state and the second state that the liquid crystal can have by holding the amount of charge so as not to change before the charge is supplied. 2. 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 a substrate surface in contact with the liquid crystal. Means for supplying electric charges to the pixel electrode, and the pixel electrode is provided with an arbitrary charge amount less than twice the product of spontaneous polarization of the liquid crystal and the pixel area. And hold the charge so that the amount of charge does not change until the next charge is supplied, whereby the ratio of the area of the first state and the second state that the liquid crystal can take is varied to control the gradation. Liquid crystal electro-optical device characterized. 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 a substrate surface in contact with the liquid crystal. Means for supplying electric charges to the pixel electrode, and the pixel electrode is provided with an arbitrary charge amount less than twice the product of spontaneous polarization of the liquid crystal and the pixel area. And the amount of charge is maintained so that the amount of charge does not change until the next charge is supplied, so that the spontaneous polarization corresponding to the supplied charge is inverted to provide the supplied charge and the spontaneous polarization charge in the pixel electrode. Is maintained in a quasi-equilibrium state to change the ratio of the areas of the first state and the second state that the liquid crystal can assume to control the gray scale. 4. The liquid crystal electro-optical device according to claim 1, wherein the direction in which the liquid crystal material takes is preliminarily aligned to one state by supplying a reverse charge before supplying a fixed amount of charge. apparatus. 5. A liquid crystal electro-optical device characterized in that a thin film transistor is used as a part of the means for supplying electric charge according to any one of claims 1 to 3. 6. The liquid crystal electro-optical device according to claim 5, wherein a capacitance is added in parallel to the pixel electrode connected to the thin film transistor. 7. A liquid crystal electro-optical device characterized in that a diode element is used as a part of the charge supply means according to any one of claims 1 to 3. 8. A liquid crystal electro-optical device using a ferroelectric thin film as the charge supply means according to claim 1.