JPH11174413A - Device and method for driving liquid crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To drive a liquid crystal without requiring of an ineffective signal complicated in waveform or cancelling the DC component by controlling the device by the use of a state selection period and a state holding period. SOLUTION: Two substrates 1a, 1b forming data electrodes 2a and orientation films 3a, 3b on respective surfaces are arranged with a prescribed interval and the gap is filled with ferroelectric liquid crystal 5 and either one of two states that light is to be transmitted and not transmitted can be selected in accordance with an electric signal impressed between the two electrodes. A period for impressing a pulse group consisting of a reset pulse and a selection pulse for selecting a pixel from the row side and impressing an electric signal for state selection from the column side and a period for holding a selected state by the memory property of liquid crystal without impressing the state to the electric signal are prepared. An electric signal for selecting one state consists of a reset pulse and a pulse signal exceeding a threshold and an electric signal for selecting the other state consists of a reset pulse and a pulse group signal of selection pulses.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal driving apparatus and method for driving a liquid crystal display using a ferroelectric liquid crystal material.

[0002]

2. Description of the Related Art A liquid crystal display (LCD) using a liquid crystal as a display has features of low power consumption, thinness and light weight. Applications to television receivers (TVs) are in progress.

Research and development for using a ferroelectric liquid crystal (FLC) as a liquid crystal in such an LCD has been actively advanced. F
As for LC, a ferroelectric liquid crystal was first synthesized by Meyer in 1975, and a surface-stabilized ferroelectric liquid crystal capable of domain reversal by an electric field was developed by Clark and Lagawar in 1980. FLC is
A liquid crystal that has a permanent dipole moment in the molecule itself, perpendicular to the long axis of the molecule, has spontaneous polarization, and can be switched by an electric field. FLC displays using this are mainly as follows. It has features.

[0004] First, the switching speed is on the order of microseconds, which is one time smaller than that of a TN (twisted nematic) liquid crystal display.
It responds 000 times faster and is excellent in high-speed response. Second, there is basically no twist structure in the molecular arrangement, and there is little viewing angle dependence. Third, even when the power is turned off, the image is retained, the image has memory properties, and simple matrix driving can be performed on 1000 or more scanning lines that can support high definition.

Therefore, the FLC display is a display that can pursue the performance of high definition, low cost, and large screen.

[0006]

By the way, it has been found that in all liquid crystal display devices, display deterioration is caused by ions in the panel. The ions in the panel may be mixed during the liquid crystal synthesis, during the preparation of the alignment film, and during the injection of the liquid crystal. At present, it is difficult or impossible to control the amount of ions after deviceization.

Here, when DC asymmetry occurs in the drive waveform of the liquid crystal display device, ions are considered to be unevenly distributed and deteriorate the liquid crystal material. Therefore, an electrically neutral condition is indispensable for the drive waveform. The common sense that there was has been present in the LCD industry.

That is, as a method of driving the liquid crystal display device, in order to prevent a DC component from being generated in a signal, FIG.
As shown in FIG. 9, a plurality of pulse signals of a pulse signal which is a write signal for selecting one state and a pulse signal of an opposite polarity which cancels this are combined. Alternatively, as shown in FIG. 30, after a predetermined write signal is applied for a certain period, a DC component of the signal is canceled by applying an electric signal having the same voltage and time and the opposite polarity. . Here, “W” in the figure is white that transmits light, and “B” is black that does not transmit light.
Respectively.

However, when the former signal waveform is used, the driving circuit becomes complicated due to the complicated signal waveform, and the signal is invalid while the signal for canceling the DC component is applied. The period in which the predetermined selection state is taken becomes short. Furthermore, when the period of signal application is limited, a part of the period must be assigned to an invalid pulse for canceling the DC component, so that the pulse width of the write signal becomes short and a liquid crystal material with a high response speed is required. .

[0010] When the latter signal waveform is used,
DC for the same period as the period during which the write signal is applied
Since an invalid signal for canceling the component is applied,
The period during which a predetermined selection state can be taken is halved,
That is, it becomes dark.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and a liquid crystal driving device for driving a liquid crystal so as not to apply a complicated signal waveform or an invalid signal for canceling a DC component. And a method.

[0012]

In order to solve the above-mentioned problems, a liquid crystal driving device according to the present invention is provided so as to face a main surface at a predetermined interval, and a transparent surface is provided on the opposing main surface. First and second transparent substrates each having an electrode, a first stable state having a spontaneous polarization in a direction substantially perpendicular to the long axis of the molecule, and aligning the spontaneous polarization in parallel with a predetermined direction; A bistable ferroelectric liquid crystal material having a second stable state in which polarization is aligned antiparallel to the predetermined direction, wherein the ferroelectric liquid crystal material is filled in a gap between the first and second transparent substrates; A first ferroelectric liquid crystal material capable of switching between the first and second stable states in accordance with a voltage applied between transparent electrodes provided on the second transparent substrate, and a first and second ferroelectric liquid crystal material, respectively. Optically distinguishes the stable state of 2 as transmission or non-transmission of light An optical member, a first voltage for selecting the first stable state including a pulse voltage for reset and a pulse voltage exceeding a predetermined threshold, a pulse voltage for reset, and the predetermined threshold A state selection period in which either one of the second voltage for selecting the second stable state, which is composed of pulses not exceeding, is applied between the transparent electrodes of the first and second transparent substrates, Liquid crystal drive control means for controlling using a state holding period for holding one of the selected stable states by the self-holding property of the ferroelectric liquid crystal material without applying a voltage between the transparent electrodes It is. Here, the first and second
The pulse voltage for resetting at the voltage of the first voltage is opposite in polarity to the pulse voltage of the first voltage exceeding a predetermined threshold and the pulse voltage of the second voltage not exceeding the predetermined threshold.

Further, during the state selection period and the state holding period of the liquid crystal driving means, the charge accumulated by the ions in the ferroelectric liquid crystal material filled in the gap between the first and second transparent substrates is reduced by the ferroelectric liquid crystal. The liquid crystal driving means is set so as to be neutralized by spontaneous polarization of the dielectric liquid crystal material, and the state selection period and the state holding period of the liquid crystal driving means are set so that the selected stable state does not stick to the one of the stable states. Is done.

In order to solve the above-mentioned problems, a liquid crystal driving method according to the present invention includes a first liquid crystal driving method which is disposed opposite to a main surface at a predetermined interval, and has a transparent electrode on the opposing main surface. And a second transparent substrate, having a spontaneous polarization in a direction substantially perpendicular to the long axis of the molecule, a first stable state in which the spontaneous polarization is aligned in parallel with a predetermined direction, and the spontaneous polarization in the predetermined direction. A bi-stable ferroelectric liquid crystal material having a second stable state aligned antiparallel, filled in a gap between the first and second transparent substrates, and provided in the first and second transparent substrates, respectively. A ferroelectric liquid crystal material capable of switching between the first and second stable states according to a voltage applied between the provided transparent electrodes; Optical member that is optically distinguished as transmission or non-transmission of A first voltage for selecting the first stable state, comprising a pulse voltage for resetting and a pulse voltage exceeding a predetermined threshold, a pulse voltage for resetting, and a pulse voltage for resetting. A second voltage for selecting the second stable state consisting of a pulse that does not exceed the threshold value of the first and second transparent substrates is applied between the transparent electrodes of the first and second transparent substrates. And a liquid crystal drive control step of controlling using the state holding period for holding the one of the selected stable states by the self-holding property of the ferroelectric liquid crystal material without applying a voltage between the transparent electrodes. Have

Here, the pulse voltage for resetting at the first and second voltages is a pulse voltage exceeding a predetermined threshold value at the first voltage and a pulse voltage exceeding the predetermined threshold value at the second voltage. There is no pulse voltage and opposite polarity.

Further, during the period of the state selection step and the state holding step, the charge accumulated by the ions in the ferroelectric liquid crystal material filled in the gap between the first and second transparent substrates is replaced by the ferroelectric liquid crystal. It is set so as to be neutralized by spontaneous polarization of the material, and the respective periods of the above-mentioned state selection step and the above-mentioned state holding step are set so that the seizure of the selected stable state to the one side does not occur.

The liquid crystal display device and the method according to the present invention include:
This utilizes the properties of a ferroelectric liquid crystal material. That is, in the ferroelectric liquid crystal, the DC asymmetry does not cause deterioration of the liquid crystal but reduces burn-in and hysteresis.

This DC asymmetric waveform has a period during which an electric signal for selecting one state is applied, and a period following the period.
A period in which the selected state is held by the memory property of the liquid crystal without applying an electric signal is provided, and the electric signal for selecting one state is substantially changed from one pulse signal of either positive or negative polarity. The electric signal for selecting the other state is an electric signal composed of one pulse signal of substantially the opposite polarity.

More specifically, ions moving and unevenly distributed due to application of an asymmetric monopolar pulse and ions moving and unevenly distributed due to a reverse electric field in the direction opposite to the applied pulse due to spontaneous polarization generated after switching of the ferroelectric liquid crystal are respectively It is considered that there is a condition that can be neutralized by making the pulse width time and the memory time, which is the time when the anti-electric field is generated, asymmetric.

That is, a comparison was made between a drive waveform in consideration of DC symmetry and a drive waveform in which DC was asymmetric.
The liquid crystal element using the drive waveform whose DC is asymmetric has the lowest electro-optical deterioration.

The characteristic of this waveform is that the ratio of the length of the period during which the electric signal is applied to the length of the period during which the selected state is maintained without applying the electric signal is set so that the burn-in to one state is eliminated. Alternatively, the voltage of the applied electric signal is set so that the burn-in to one state is eliminated.

Generally, the cause of uneven distribution of ions in a liquid crystal panel during driving of a liquid crystal element is due to an applied waveform. The parameters of the ion movement include the polarity of the applied waveform, the high voltage, and the time.

However, in a type in which liquid crystal molecules themselves have spontaneous polarization and respond to an applied electric field, such as a ferroelectric liquid crystal or an antiferroelectric liquid crystal, it is considered that the spontaneous polarization itself induces ions in the liquid crystal panel. .

Here, the electric field generated by the spontaneous polarization, which is reversed in response to the applied electric field, is always opposite in polarity to the applied electric field and is known as an anti-electric field. Naturally, the magnitude of the anti-electric field depends on the spontaneous polarization value, the film pressure / conductivity of the high-level film, and the liquid crystal layer pressure.

It is recognized that there is a condition that balances the movement of ions with respect to DC asymmetry and the movement of ions with respect to the anti-electric field due to spontaneous polarization of the ferroelectric liquid crystal. Therefore, according to the anti-electric field generated by this spontaneous polarization,
What is necessary is just to set a memory time.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a liquid crystal display device and a method according to the present invention will be described with reference to the drawings.

As an embodiment for realizing the liquid crystal driving device according to the present invention, as shown in FIG.
A ferroelectric liquid crystal display device using an oelectric liquid crystal (FLC), a so-called FLC display, will be described.

In this liquid crystal display device, transparent data electrodes 2a and scan electrodes 2 are formed on transparent glass substrates 1a and 1b.
b is provided. Specifically, the glass substrates 1a, 1
b is 0.7 mm thick, and data electrode 2a and scan electrode 2
b is 100Ω / cm ² of indium tin oxide (Indium tin oxide).
Use tin oxide (ITO).

These transparent data electrodes 2a and scanning electrodes 2b are arranged in columns (co.
The data electrode 2a of the (lumn) electrode and the scanning electrode 2b of the row (row) electrode are formed by patterning in a stripe shape by etching.

On the data electrode 2a and the scanning electrode 2b,
SiO obliquely deposited films 3a and 3b are formed as liquid crystal alignment films. In forming the SiO oblique deposition films 3a and 3b, a substrate is placed vertically from a SiO deposition source in a vacuum deposition apparatus, and an angle between a vertical line and a substrate normal is set to 85 degrees. After vacuum deposition of SiO at a substrate temperature of 100 ° C., baking is performed at 200 ° C. for 2 hours.

In the pair of glass substrates 1a and 1b provided with the alignment film thus manufactured, the alignment directions of the data electrode 2a and the scanning electrode 2b are antiparallel to each other at the opposing surfaces.
In addition, the electrode arrangement of the data electrodes 2a and the scanning electrodes 2b is set so as to be orthogonal. As the spacer 4, glass beads according to the target gap length are used. Specifically, a sphere having a diameter of 0.8 to 3.0 μm is used. In addition, although the orientation processing directions are set antiparallel, they may be set parallel.

Depending on the size of the glass substrates 1a and 1b, the spacers 4 are dispersed in a sealing material 6 which adheres to the periphery in the case of a small area to disperse about 0.3 wt% to control the gap between the substrates. Specifically, an ultraviolet (UV) curable adhesive can be used as the sealant. When the substrate area is large, the above-mentioned spheres are scattered on the substrate at an average density of 100 pieces / mm ² , a gap is formed, a liquid crystal injection hole is secured, and the periphery is adhered with a sealant 6.

A liquid crystal composition in which the ferroelectric liquid crystal 5 is uniformly dispersed at an isotropic phase temperature using an ultrasonic homogenizer is injected between the pair of glass substrates 1a and 1b. The ferroelectric liquid crystal composition is injected under reduced pressure in a state showing fluidity such as an isotropic phase temperature or a chiral nematic phase temperature. After the injection of the liquid crystal, the liquid crystal is cooled, the liquid crystal on the glass substrate around the injection hole is removed, and the liquid crystal is sealed with an epoxy-based adhesive, whereby the FLC display 11 is manufactured.

Pixels include a data electrode 2a and a scanning electrode 2b.
Are generated in the crossing range and are selected by the scanning line and the data line. Since the incident light 102 is transmitted through the FLC, the amount of light transmitted through the FLC is changed by an electric field applied by the data electrode 102a and the scanning electrode 102b, that is, the transmitted light is modulated.

Here, in the case of a ferroelectric liquid crystal such as a surface-stabilized ferroelectric liquid crystal, the orientation direction of the molecule M with respect to the externally applied electric field E changes to state 1 as shown in FIG. Switching between the two states of state 2. That is, the direction of the spontaneous polarization Ps is parallel or anti-parallel to the externally applied electric field.

The change in the orientation of the liquid crystal molecules M appears as a change in the transmittance when the liquid crystal element is disposed between the orthogonal polarizing plates. As shown in FIG. The threshold voltage Vth sharply changes from 0% to 100%.

As described above, since the ferroelectric liquid crystal display using the bistable mode is stable only in two states, TN (tw
isted nematic) It is difficult to display gradation by voltage control like liquid crystal.

The liquid crystal display has a drive control circuit 20 for driving the liquid crystal 5 by applying a voltage having a predetermined waveform between the data electrode 2a and the scanning electrode 2b. The liquid crystal control circuit 20 drives and controls the liquid crystal with a voltage having a predetermined waveform described later.

Next, a method of driving the FLC display 11 will be described with reference to FIG. The FLC display 11 receives the data electrode 2a from the drive control circuit 20.
And the driving signal supplied to the scanning electrode 2b.

As a driving method of the FLC display 11, an XY simple matrix method in which the data electrodes 2a are column electrodes and the scanning electrodes 2b are data electrodes is used. A select pulse, which is a threshold, is applied from the row-side scan electrode 2b as indicated by A in the figure, and a data pulse is applied from the column-side data electrode 2a as indicated by B in the figure.

When the NTSC system is selected, 1H which is one horizontal scanning time or one line selection time is 63.5 μm.
s, and considering the electrical neutralization condition where no DC voltage is applied, since the voltage is applied in bipolar, each selection pulse has a width of 63.5 / 2 μs.

Next, a specific example of a method of driving a liquid crystal display device using simple matrix driving will be described with reference to FIG.

With respect to the data electrode 2a and the scanning electrode 2b constituting the matrix, the data D is applied to the n-th data electrode.
n, the pixels Pn (m−1), Pnm, Pn from the (m−1) th to the (m + 1) th lines when scanning the scanning electrodes
This will be described by taking (m + 1) as an example.

The scanning electrode is enabled during the scanning line selection period,
If a signal is applied to the data line during that time, a voltage is applied to the pixel and the FLC is driven. In the non-selection period, a signal is input to the data line, so that a voltage is applied to the FLC. However, as shown in FIG. 3, since the FLC is not driven unless a value larger than the threshold voltage Vth is applied to the FLC, the FLC does not operate during the non-selection period.

Here, the application time of the pulse is represented by A in FIG.
This is a waveform in which the ratio of the application time and the memory time sufficient to reverse the spontaneous polarization, that is, the ratio of the neutralization period is smaller than 1: 1. Further, a conceptually monopolar pulse waveform may be used. As shown by B to D in the figure, a trapezoidal pulse, a cubic pulse, an exponential It may be a pulse. In addition, a short-time pulse having the same sign as the selection signal, a different sign, or a combination thereof may be added.

That is, assuming that the voltage value of the selection pulse is Vs and the generated reverse electric field is -Vr, when the selection pulse width is Tw, the memory time during which no signal is applied is Vs ·
If Tw / Vr is set, it seems that ions in the liquid crystal panel satisfy the electrical neutrality condition. A reset + select pulse is applied from the outside, that is, a DC voltage is added by + (Vs × Vr) / (Vs + Vr) per unit time.

Hereinafter, specific examples of the above embodiment and comparative examples of the examples will be described.

Example 1 A 40 nm thick sheet resistance of 100 Ω / cm ² was formed by sputtering.
99.9 purity on a glass substrate provided with a transparent ITO film of
By heating a tantalum boat containing 9% SiO powder by resistance heating, a 50 nm thick S as a liquid crystal alignment film is formed.
The iO obliquely deposited film was vacuum deposited at a substrate temperature of 80 ° C. At this time, the vapor deposition was performed so that each of the normals of the substrate and the vertical line of the vapor deposition source was 85 °. After evaporation, to obtain good orientation,
The firing was performed at 200 ° C. for 1 hour in the air.

The two glass substrates thus treated are
An empty liquid crystal cell was assembled using spacers of 1.6 μm diameter straight spheres and an ultraviolet curing adhesive so that the deposition directions of the obliquely deposited SiO films were parallel and antiparallel to each other. A ferroelectric liquid crystal was injected into the cell gap to obtain an FLC display as a liquid crystal display device including one pixel.

The relationship between the applied voltage and the transmittance of this liquid crystal display device, that is, the liquid crystal panel, was examined. Specifically, under orthogonal Nicols, a driving waveform as shown in FIG. 6 is applied to the liquid crystal display device to increase the number of white display times and increase the number of black display times. The transmission intensity was monitored. As a result, as shown in FIGS. 7 and 8, the change amount was about 5% for both the white level and the black level. In the figure, a white circle “○” indicates a white level / mV, and a black circle “●” indicates a black level / mV.

Comparative Example 1 A comparative example of Example 1 described above is shown. In this comparative example, a similar experiment was performed using a liquid crystal cell manufactured in the same manner as in Example 1 and using a DC-symmetric drive waveform as shown in FIGS.

FIG. 1 shows the results of the dependence on the number of white / black times.
1 and FIG. 12, FIG. 13 and FIG. FIG.
The degree of change in the white level when the drive waveforms of FIG. 10 and FIG. 10 are used indicates that burn-in has clearly occurred. That is, when the number of white displays is large, the white level increases, and when the number of black displays is large, the white level decreases. In the figure, a white circle “○” indicates a white level / mV, and a black circle “●” indicates a black level / mV.

Compared with the first embodiment, the change amount of the white level was 4 times and the change amount of the black level was 6 times or more. A drive waveform which is DC asymmetric as shown in FIG. 6, has high ion movement and accumulated charge, and is likely to cause image sticking does not cause image sticking as a result.

According to these results, it is considered that the ion movement due to the pulse and the ion movement due to the anti-electric field due to the spontaneous polarization after switching of the ferroelectric liquid crystal are balanced to reach an equilibrium state. Generally, it is said that the anti-electric field due to spontaneous polarization is less than half the applied electric field. Since the transfer time is considered as a parameter for the charge accumulated by the ions, it was concluded that the amount of ion accumulation by the pulse application and the amount of ion accumulation by the anti-electric field were balanced in one display.

Example 2 A liquid crystal display device was continuously driven with a DC asymmetric waveform, and the deterioration of the liquid crystal was examined. Specifically, white count 35: black count 1 time,
The time change of the transmittance of white was measured. As a result, as shown in FIG. 15, it was found that the transmittance change was stabilized in the first hour or so even after continuous driving for one week, and there was no deterioration of the liquid crystal composition due to the accumulation of ions. Here, a black circle “●” in the figure indicates a white level / mV, and a white square “□” indicates a black level / mV.
V is shown.

Example 3 A liquid crystal device manufactured in the same manner as in Example 1 described above was replaced with Example 1
The first ferroelectric liquid crystal material used in the above and the second and third ferroelectric liquid crystal materials different from the first ferroelectric liquid crystal material were respectively injected, and the hysteresis was measured. In the measurement of the hysteresis, as shown in FIG. 16, for 72 combinations in which the number of times of white + the number of times of black is 36, the white level at a predetermined position of two types of black or white was monitored immediately before. As the driving waveform, as shown in FIG.
An asymmetric waveform was used for the DC level. As a result, hysteresis as shown in FIGS. 17 to 19 was obtained for each ferroelectric liquid crystal material.

As the transmittance, for example, as shown in FIG. 20, hysteresis is a state in which the white level following black becomes lower. This transmittance was measured for the third ferroelectric liquid crystal material.

This hysteresis was thought to have two causes. One is that if the number of white displays is large and the previous display is black, the amount of ions accumulated in the de-electric field due to black display reduces the current white display voltage.
The spontaneous polarization of the first ferroelectric liquid crystal material is 35 nCcm ^-2.
And the dielectric constant of the second and third ferroelectric liquid crystal materials is 9 nCcm ⁻² , but considering that the reversal electric field depends on the spontaneous polarization value,
It is possible to change the memory level.

Therefore, as a proof that the pulse voltage for white display next to black display, which is considered to be the first cause, was reduced, the hysteresis was measured by changing the pulse voltage for white display. FIG. 21 shows the combinations of white 35: black 1 and white 34: black 2 with the maximum hysteresis.
The voltage dependence of the hysteresis in the latter case is shown. W in the figure
Represents white and B represents black. The same applies to the following.

In FIG. 21, a is 5 V / μ.
m and b correspond to 5.6 V / μm, c corresponds to 6.1 V / μm, d corresponds to 6.7 V / μm, and e corresponds to 7.2 V / μm.

As a result, the threshold voltage was 1.7 V / μm higher than the threshold voltage.
It was confirmed that hysteresis was eliminated by using the pulse voltage added by m. However, although the memory level was stable, the value was lower than the original transmittance.

Example 4 It was confirmed whether ions in the liquid crystal panel could neutralize a reversal electric field due to spontaneous polarization. That is, since the time required for ion movement is a large parameter, the hysteresis is measured by variously changing the time during which the anti-electric field is generated, that is, the memory time. FIG. 22, FIG. 23 and FIG. 24 show that the first, second and third ferroelectric liquid crystal materials are white 34: black 2
Shows the memory time dependence of the hysteresis in the combination of.

In FIG. 22, a is 50 μs,
b is 100 μs, c is 150 μs, d is 200 μs
Respectively. 23 and 24, a is 100 μs, b is 200 μs, and c is 3 μs.
00 μs, d to 400 μs, e to 500 μs, f
Corresponds to 600 μs, respectively.

As a result, for the first ferroelectric liquid crystal material, the time during which the demagnetizing field was generated was 200 μs or more, and for the second ferroelectric liquid crystal material, it was 100 μs.
As described above, it was confirmed that the hysteresis disappeared in the third ferroelectric liquid crystal material in 500 μs or more.

Since these ferroelectric liquid crystal materials have completely different constituent compounds, the types and amounts of ions contained therein are completely different. A similar tendency was obtained for such separate materials, that is, the fact that they were in equilibrium over a certain period of time.

It should be noted that the time when the ion and the reversal electric field are balanced does not reach a certain point at a certain time, but saturates at a certain time or more. This tendency indicates that a margin can be given to the device.

As described above, the memory time is determined with a certain width depending on the false contour problem and the transfer rate. At that time, the final time may be determined from the result of the present embodiment, or, if the time is not within the time from the device side, optimization can be achieved by changing the liquid crystal material.

Embodiment 5 Using the liquid crystal panel shown in Embodiment 1 above,
The dependence of the electro-optical characteristics on the slew rate was measured.

The driving waveform was based on a monopolar waveform as shown in FIG. However, considering the slew rate of each pulse so as not to change the electric field intensity area of the pulse, as shown in FIG.
, Or in a trapezoidal manner as indicated by B in the figure.

FIG. 26 and FIG. 27 show the relationship between the rounding time and the pulse height which is a threshold at which the memory appears in the liquid crystal panel as the liquid crystal display device.

In the case of a pulse having a cubic function round waveform, there was no difference in the threshold value of memory expression, as shown in FIG. 26, even if the round time was the entire width of the pulse. In the case of a trapezoidal round waveform, as shown in FIG. 27, the round time had no effect up to 15 μs. If it becomes longer, the applied electric field must be increased, but there is no effect on the switching dynamics.

That is, the slew rate affects only at the beginning of switching. This is because in the case of the 3 o'clock function, only the rise of the pulse was very fast, and it is considered that there was no effect. Thus, no matter what the pulse shape is,
Although there is a change in the threshold value, it is not related to the original switching.

Next, a series of steps relating to the liquid crystal driving method will be described with reference to a flowchart shown in FIG.

This liquid crystal driving method includes, for example, a first and a second transparent substrate which are disposed opposite to the main surface at a predetermined interval and each of which has a transparent electrode on the opposing main surface;
A first stable state having a spontaneous polarization in a direction substantially perpendicular to the long axis of the molecule and aligning the spontaneous polarization parallel to a predetermined direction, and a second stable state aligning the spontaneous polarization antiparallel to the predetermined direction. A bistable ferroelectric liquid crystal material having a stable state,
The first and second stable states are filled in the gap between the first and second transparent substrates according to a voltage applied between transparent electrodes provided on the first and second transparent substrates, respectively. A liquid crystal display device is used that has a switchable ferroelectric liquid crystal material and an optical member that optically distinguishes the first and second stable states of the ferroelectric liquid crystal material as light transmission or non-transmission.

The first step S1 comprises a first voltage for selecting the first stable state, which comprises a pulse voltage for resetting and a pulse voltage exceeding a predetermined threshold, a pulse voltage for resetting, and a pulse voltage for resetting. A state in which one of the second voltage for selecting the second stable state, which is composed of a pulse not exceeding the predetermined threshold, is applied between the transparent electrodes of the first and second transparent substrates. This is a selection step.

The following step S2 uses a state holding period in which one of the selected stable states is held by the self-holding property of the ferroelectric liquid crystal material without applying a voltage between the transparent electrodes. This is a liquid crystal drive control step for controlling.

Here, in the state selecting step of the step S1, the pulse voltage for resetting the first and second voltages is a pulse voltage exceeding a predetermined threshold value in the first voltage and the second pulse voltage. Has a polarity opposite to that of the pulse voltage that does not exceed the predetermined threshold value.

During the period of the state selection step of step S1 and the state holding step of step S2, the charge accumulated by the ions in the ferroelectric liquid crystal material filled in the gap between the first and second transparent substrates is reduced. The ferroelectric liquid crystal material is set to be neutralized by spontaneous polarization.

The respective periods of the state selecting step of step S1 and the state holding step of step S2 are set so that the selected stable state is not burned to the one.

The above-described embodiments of the liquid crystal driving device and method can be further modified.

For example, a transparent glass substrate is used as a substrate, ITO or aluminum is used as an electrode layer, and a rubbed polyimide film or Si is used as a liquid crystal alignment film.
An O obliquely deposited film can be used. The driving method may be the same as that described above.

In practice, the usable ferroelectric liquid crystal is preferably a liquid crystal obtained by mixing a chiral compound and an achiral compound. Each of these liquid crystals is composed of only one kind. Or a mixture of a plurality of types.

Here, examples of the chiral compound include known pyrimidine compounds, biphenyl compounds, phenylbenzoate compounds and the like. However, these ferroelectric liquid crystals may show a chiral nematic phase, a smectic phase or the like depending on a change in temperature.

Examples of usable non-chiral compounds include known biphenyl compounds, terphenyl compounds, tricyclic cyclohexyl compounds, ester compounds, pyrimidine compounds, pyridazine compounds, ethane compounds and dioxane compounds.

Further, the above-mentioned driving waveform may be variously changed within a range in which the object of the present invention can be achieved, and the driving method may be any of a segment method, a simple matrix method, an active matrix method, and the like. In particular, the drive waveform finally applied to the liquid crystal by the composite of the matrix electrode and the auxiliary capacitor may be as described above.

The types and combinations of the above-mentioned liquid crystals may be variously changed. In addition, as the above-mentioned transparent electrode, in addition to the above-mentioned ITO, a known transparent electrode such as tin oxide and indium oxide can be used. A high material can be used, and a conventionally known material can be used as a constituent material of the liquid crystal element such as a transparent substrate, a spacer, and a sealant.

Further, the liquid crystal driving device and the method described in the above embodiment can be used for an optical modulator, an optical shutter, an optical switch, an optical brand and the like in addition to the liquid crystal display device. If elements are combined, it can be used for a liquid crystal prism, a liquid crystal lens, an optical path switch, a display phase diffraction grating, an A / D converter, an optical logic circuit, and the like.

As described above, the liquid crystal driving device and the liquid crystal driving method according to the present invention can be used in a simple matrix driving.
The DC neutral condition is not required by balancing the anti-electric field due to spontaneous polarization of the ferroelectric liquid crystal and the anti-electric field due to accumulated charge of ions in the liquid crystal panel induced by the spontaneous polarization of the ferroelectric liquid crystal. .

That is, in the liquid crystal driving device and method according to the present invention, two substrates on which electrodes and an alignment film are formed are arranged at a predetermined interval, and a ferroelectric liquid crystal is arranged in the gap.
A liquid crystal display device in which two states of transmitting (or reflecting) and not transmitting (or reflecting) light can be selected by an electric signal applied between two electrodes, and a reset pulse and a pixel are supplied from a low side. A pulse group consisting of select pulses for selection is applied from the column side to a period in which an electric signal for selecting one of the states is applied, and a subsequent state in which the electric signal is not applied to the selected state, or In order to deselect, a period is provided in which the electric signal is not applied and the liquid crystal is held by the memory property, and an electron transfer signal for selecting one of the states is substantially a reset pulse and a pulse signal exceeding a threshold. And the electric signal for selecting the other state is an electric signal composed of a pulse group signal composed of only a reset pulse and a select pulse.

The presence of hysteresis development was confirmed in the ferroelectric liquid crystal light valve used in the present invention.
That is, the display of the currently displayed color is affected by the previously displayed white and black. More specifically, even if the previous color is black, the display color currently displayed cannot be determined to be white or black depending on whether the previous line is white or black.

[0091]

According to the liquid crystal driving device of the present invention, the driving of the liquid crystal display device becomes very simple, and various device designs are possible.

Further, according to the liquid crystal driving method of the present invention,
Driving the liquid crystal display device becomes very simple, and various device designs are possible.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a simple matrix type liquid crystal display device.

FIG. 2 is a conceptual diagram of a bistability model of a ferroelectric liquid crystal.

FIG. 3 is a diagram showing a threshold characteristic (VT curve) of a general ferroelectric liquid crystal.

FIG. 4 is a time chart showing driving waveforms of a general simple matrix panel.

FIG. 5 is a diagram illustrating an example of a driving waveform of a simple matrix type liquid crystal display device.

FIG. 6 is a time chart showing a DC asymmetric drive waveform of the liquid crystal display device.

FIG. 7 is a diagram illustrating a relationship between the number of white display times and a change in transmittance when a DC asymmetric drive waveform is used.

FIG. 8 is a diagram showing the relationship between the number of black displays and the change in transmittance when using a DC asymmetric drive waveform.

FIG. 9 is a time chart showing a DC symmetric bipolar pulse driving waveform.

FIG. 10 is a time chart showing a DC symmetric waveform bipolar pulse driving waveform.

FIG. 11 is a diagram showing a relationship between the number of white display times and a change in transmittance when a DC symmetric drive waveform is used.

FIG. 12 is a diagram showing the relationship between the number of black displays and the change in transmittance when using a DC symmetric drive waveform.

FIG. 13 is a diagram showing a relationship between the number of white display times and a change in transmittance when using a DC symmetric deformation driving waveform.

FIG. 14 is a diagram showing a relationship between the number of black display times and a change in transmittance when using a DC symmetric deformation driving waveform.

FIG. 15 is a diagram showing a change over time in white level when driven by a DC asymmetrical monopolar pulse driving waveform for one week continuously.

FIG. 16 is a diagram illustrating a method for measuring hysteresis.

FIG. 17 is a diagram showing hysteresis of the first ferroelectric material.

FIG. 18 is a diagram showing hysteresis of a second ferroelectric material.

FIG. 19 is a diagram showing hysteresis of a third ferroelectric material.

FIG. 20 is a photograph showing hysteresis of a third ferroelectric liquid crystal.

FIG. 21 is a diagram showing the applied pulse voltage dependence of the hysteresis of the third ferroelectric liquid crystal.

FIG. 22 is a diagram showing the memory time dependence of the hysteresis of the first strongly inducing electro-liquid crystal.

FIG. 23 is a diagram showing the memory time dependence of the hysteresis of the second ferroelectric liquid crystal.

FIG. 24 is a diagram showing the dependence of the hysteresis of the third ferroelectric liquid crystal on the memory time.

FIG. 25 is a diagram showing a rounded shape of an applied pulse.

FIG. 26 is a diagram illustrating a relationship between a rounding time and a threshold when a cubic function rounding waveform is used.

FIG. 27 is a diagram illustrating a relationship between a rounding time and a threshold when a trapezoidal rounding waveform is used.

FIG. 28 is a flowchart showing a series of steps of a liquid crystal driving method.

FIG. 29 is a diagram illustrating an example of a driving waveform in which a write signal and a plurality of pulse signals of opposite polarity pulse signals that cancel each other out are combined;

FIG. 30 is a diagram showing an example of a driving waveform in which a predetermined write signal is applied for a certain period, and then an electric signal having the same voltage and time and the same polarity as that of the write signal is applied to cancel the DC component of the signal. .

[Explanation of symbols]

1a, 1b glass substrate, 2a data electrode, 2b scanning electrode, 5 liquid crystal, 20 drive control circuit

Claims (8)

[Claims] 1. A first and a second transparent substrate disposed opposite to a main surface at a predetermined interval and provided with a transparent electrode on the opposing main surface, respectively, substantially perpendicular to a major axis of a molecule. Bistability having a first stable state in which the spontaneous polarization is aligned parallel to a predetermined direction and a second stable state in which the spontaneous polarization is aligned antiparallel to the predetermined direction. A ferroelectric liquid crystal material,
The first and second stable states are filled in the gap between the first and second transparent substrates according to a voltage applied between transparent electrodes provided on the first and second transparent substrates, respectively. A ferroelectric liquid crystal material to be switched; an optical member for optically distinguishing the first and second stable states of the ferroelectric liquid crystal material as light transmission or non-transmission; a pulse voltage for resetting and a predetermined voltage; A first voltage for selecting the first stable state consisting of a pulse voltage exceeding a threshold, and a second voltage consisting of a pulse voltage for resetting and a pulse not exceeding the predetermined threshold; And a second voltage for applying a voltage between the transparent electrodes provided on the first and second transparent substrates, and a state selection period without applying a voltage between the transparent electrodes. The stable state The liquid crystal drive apparatus, comprising a liquid crystal drive control means for controlling with a state holding period for holding the self-holding of the ferroelectric liquid crystal material. 2. A pulse voltage for resetting in the first and second voltages does not exceed a pulse voltage exceeding a predetermined threshold value in the first voltage and does not exceed a predetermined threshold value in the second voltage. 2. The liquid crystal driving device according to claim 1, wherein the polarity is opposite to the pulse voltage. 3. A state selection period and a state holding period of the liquid crystal driving means, wherein the charge accumulated by ions in the ferroelectric liquid crystal material filled in the gap between the first and second transparent substrates is reduced by the ferroelectric liquid crystal material. 2. The liquid crystal material is set to be neutralized by spontaneous polarization of a dielectric liquid crystal material.
The liquid crystal driving device according to the above. 4. The liquid crystal according to claim 1, wherein the state selection period and the state holding period of the liquid crystal driving unit are set so that the selected stable state does not burn into the one of the stable states. Drive. 5. A first and a second transparent substrate, which are disposed opposite to the main surface at a predetermined interval and each have a transparent electrode on the opposing main surface, substantially perpendicular to the major axis of the molecule. Bistability having a first stable state in which the spontaneous polarization is aligned parallel to a predetermined direction and a second stable state in which the spontaneous polarization is aligned antiparallel to the predetermined direction. A ferroelectric liquid crystal material,
The first and second stable states are filled in the gap between the first and second transparent substrates according to a voltage applied between transparent electrodes provided on the first and second transparent substrates, respectively. A liquid crystal driving device having a switchable ferroelectric liquid crystal material and an optical member that optically distinguishes between the first and second stable states of the ferroelectric liquid crystal material as light transmission and non-transmission, And a first voltage for selecting the first stable state, comprising a pulse voltage for exceeding the predetermined threshold and a pulse voltage for exceeding the predetermined threshold. A state selecting step of applying one of a second voltage for selecting a second stable state between the transparent electrodes of the first and second transparent substrates, and a voltage between the transparent electrodes. Without applying Liquid crystal driving method characterized by comprising a liquid crystal drive control step for controlling the one of the selected stable states using the state holding period for holding the self-holding of the ferroelectric liquid crystal material. 6. A pulse voltage for resetting in the first and second voltages does not exceed a pulse voltage exceeding a predetermined threshold value in the first voltage and does not exceed a predetermined threshold value in the second voltage. 6. The liquid crystal driving method according to claim 5, wherein the polarity is opposite to the pulse voltage. 7. During the period of the state selection step and the state holding step, charges accumulated by ions in the ferroelectric liquid crystal material filled in the gap between the first and second transparent substrates are transferred to the ferroelectric liquid crystal. 6. The liquid crystal driving method according to claim 5, wherein the liquid crystal is driven so as to be neutralized by spontaneous polarization of the material. 8. The liquid crystal according to claim 5, wherein each of the periods of the state selection step and the state holding step is set so as not to cause burn-in to the one of the selected stable states. Drive method.