JPH08234174A - Liquid crystal display device - Google Patents

Abstract

PURPOSE: To simplify driving circuits and to retain display in a small impressed voltage by constituting a liquid crystal display device so that molecular orientations become first stable states at the time of a no electric field, the orientation becomes second stable states at the time of impressing the electric field of the electric field direction of one side and the orientation becomes third stable state at the time of impressing the electric field of the electric field direction of other side. CONSTITUTION: When an ample electric field with which liquid crystal molecules are rotated is impressed from the front side of the plane of the figure, the spontaneous polarization directions 30 of the liquid crystal molecules line up in an electric field direction 40. The liquid crystal molecules are re-orientated like the figure (b) in accordance with this to form a tilt angle θ with respect to a layer normal direction. Next, when an electric field is impressed from the back side of the plane of the figure, the spontaneous polarization directions 30 line up in the electric field direction 40. The liquid crystal molecules are re-oriented like the figure (c) in accordance with this to form the tilt angle of -θ from the layer normal direction. In such a manner, the optical axis of the liquid crystal is changed in three states by the polarities and the magnitudes of impressed electric fields. The device can be used as an electric optical device by holding the liquid crystal in between one pair of polarizing plates.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal electro-optical device and can be used for a surface display device such as an optical shutter and a wall-mounted television.

[0002]

2. Description of the Related Art As an electro-optical device using a liquid crystal, D
Electro-optical devices using nematic liquid crystals such as SM type, TN type, G / H type and STN type have been developed and put into practical use. However, all of those using such a nematic liquid crystal have a drawback that the response speed is extremely slow from several msec to several tens msec.

Against this background, a ferroelectric liquid crystal having a high-speed response has been developed, and some high-speed electro-optical devices using the ferroelectric liquid crystal have already been proposed. For example,
As shown in JP-A-56-107216, a twist structure is unraveled by the force of a wall surface and two molecular orientations parallel to the wall surface are changed by the polarity of an applied electric field, or JP-A-60-195521. As shown in, there is a method utilizing a transient molecular scattering state that occurs when the polarity of the applied electric field is reversed.

[0004]

However, in the conventional ferroelectric liquid crystal, there are problems in that a stable molecular orientation with a clear contrast of light and dark in the absence of an electric field is realized and a clear threshold characteristic appears. is there. The present inventors, as a result of earnest research on such problems,
We have developed a ferroelectric liquid crystal with a structural formula as described below. In this ferroelectric liquid crystal, the molecular orientation exhibits a first stable state when there is no electric field, and the second molecular orientation shows a second stable state which is different from the first stable state when an electric field is applied in one electric field direction, When an electric field is applied in the other electric field direction, the molecular orientation shows a third stable state different from the first and second stable states.

Further, such a ferroelectric liquid crystal has hysteresis characteristics on the positive polarity side and the negative polarity side, as shown in FIG. It is an object of the present invention to perform liquid crystal display by novel driving using such a hysteresis characteristic of a ferroelectric liquid crystal.

[0006]

In order to achieve the above object, in the invention described in claims 1 and 2, as the ferroelectric liquid crystal, the applied voltage is the first on the one polarity side of the applied voltage.
When the applied voltage drops below the second threshold, the first stable state changes to the second stable state when the voltage exceeds the second threshold.
Has a first hysteresis characteristic that returns from the stable state to the first stable state, and when the applied voltage exceeds the third threshold value on the other polarity side of the applied voltage, the first stable state is changed to the third stable state. It has a second hysteresis characteristic that changes to a stable state and returns from the third stable state to the first stable state when the applied voltage drops below the fourth threshold value, and the second threshold value is the second threshold value. The threshold voltage is smaller than the first threshold value, and the fourth threshold value is smaller than the third threshold value. The applied voltage is displayed as a voltage exceeding the first threshold value, and the applied voltage is displayed as It is characterized in that the display is held by using the ferroelectric liquid crystal as the voltage for maintaining the second stable state by the hysteresis characteristic of 1.

Therefore, since the display can be held by using the above-mentioned hysteresis characteristic, the drive circuit for displaying can be simplified. In addition, since the liquid crystal having the second threshold value smaller than the first threshold value is used as the liquid crystal, the display can be held without increasing the applied voltage during the display holding.

[0008]

FIG. 1 shows the structure of a liquid crystal electro-optical device which is an embodiment of the present invention. For example, 2μ
A spontaneous polarization of at least 50 nC / is provided between two electrode substrates 1 and 2 which are spaced apart by m and are arranged in parallel with each other.
The ferroelectric liquid crystal material 6 of cm ² or more is sealed. As the ferroelectric liquid crystal material, a liquid crystal material (TFH) having a structural formula shown in Chemical formula 1 is used.
POBC) can be mentioned.

[0009]

Embedded image

[0010] [4- (1- t ri f luoro m ethyl h epty
oxycarbonyl) p henyl 4'- o ctyloxy b iphenyl -
4- c arboxylate] As shown in FIG. 1, the electrode substrate 1 has an electrode 1a made of a transparent conductive film such as indium oxide or tin oxide along the inner surface of the transparent substrate 1c made of transparent glass or resin. . The other electrode substrate 2 has the same configuration.

On the inner surfaces of the transparent electrodes 1a and 2a of the conductive film, alignment films 1b and 2b of a polymer film, which have been subjected to an alignment treatment for aligning liquid crystal molecules in parallel with the substrate, are arranged. In addition to this, rubbing treatment on the electrode substrate, oblique vapor deposition of silicon oxide or the like on the surface, or
In general, a method of aligning liquid crystal such as a treatment with a surfactant can be applied.

The electrode substrates 1 and 2 are assembled in parallel so that liquid crystals are aligned in one direction. After that, the ferroelectric liquid crystal material of Formula 1 is heated to be an isotropic liquid, which is injected between the electrode substrates 1 and 2 by utilizing a capillary phenomenon, and then the entire liquid crystal cell is supplied at 0.1 to 1. It is cooled at 0 ° C. and cooled to the chiral smectic C phase. As a result of such cooling, the ferroelectric liquid crystal molecules 20 that have become the chiral smectic C phase are
Due to the large polarization of the liquid crystal molecule itself and the order of the liquid crystal, Fig. 2
Orient as shown in (a).

The polarizing plates 4 outside the electrode substrates 1 and 2,
5 are arranged orthogonally. Furthermore, the polarizer (P) of this polarizing plate is oriented such that the long axis direction of the liquid crystal molecules in the absence of an electric field forms an angle of 0 ° (180 °). Transparent electrode 1a,
An external power supply 3 including a drive circuit is connected to 2a,
A voltage waveform described below is applied to the liquid crystal.

Next, the operation of the above apparatus will be described with reference to FIG.
This will be described with reference to (b) and (c). Here, each left figure is a plan view of the apparatus, and each right figure is a side view. When no electric field is applied, the liquid crystal molecules 20 between the substrates 1 and 2 are aligned in the normal direction of the smectic layer 10 and have the alignment state shown in FIG. At this time, the spontaneous polarization of liquid crystal molecules is determined by this device (cell).
In the upper half, the left direction (or right direction) is directed, and in the lower half, the right direction (or left direction), that is, on the cone where the ferroelectric liquid crystal molecules move (Fig. 2 (a) right diagram), In the upper half of the cell, the molecule is located above (or below) the cone, and in the lower half below (or above) the cone, and the cumulative value of spontaneous polarization in the cell thickness direction becomes zero.

Next, when an electric field sufficient to rotate the liquid crystal molecules from the front side to the back side of the paper surface is applied, the spontaneous polarization direction 30 of the liquid crystal molecules is aligned with the electric field direction 40. Along with this, the liquid crystal molecules are realigned as shown in FIG. At this time, the liquid crystal molecules form a tilt angle θ with respect to the layer normal direction. By the way, 1
Angle of the ferroelectric liquid crystal material of the formula is 70 ° C to 110 ° C
10 ° C to 31 ° C in the temperature range of.

Next, when an electric field sufficient to rotate the liquid crystal molecules from the back side of the paper to the front side is applied, the spontaneous polarization 30 is aligned with the electric field direction 40. Accordingly, the liquid crystal molecules are
Reorient as in (c). At this time, the liquid crystal molecules form a tilt angle of −θ from the layer normal direction. Thus, the optical axis of the liquid crystal can be changed to three states depending on the polarity and magnitude of the applied electric field.

By sandwiching the liquid crystal having such three states between a pair of polarizing plates 4 and 5, it can be used as an electro-optical device. For example, as shown in FIG. 2 (a), the polarizer (P) of the polarizing plate and the liquid crystal molecule major axis direction are installed so as to form an angle of 0 °. The linearly polarized light that has passed through the polarizer (P) in this state passes through the liquid crystal, but is blocked by the analyzer (A), resulting in a dark state.

In the case of FIG. 2 (b) in which an electric field is applied from the front side to the back side of the paper surface, the light passing through the polarizer (P) is generally elliptically polarized light due to the birefringence effect of the liquid crystal. Since this light component passes through the analyzer (A), it is in a bright state. In addition, an electric field is applied from the back side of the paper to the front side of FIG.
In the case of (c), the light passing through the polarizer (P) is generally elliptically polarized light due to the birefringence effect of the liquid crystal. The component of this light also passes through the analyzer (A), and thus becomes a bright state.

Next, the voltage-transmittance curve of this device will be described. The polarizer (P) is installed so that the direction of the long axis of the molecule with respect to the polarization axis of the polarizer (P) is 0 °, and the threshold is a voltage at which the luminance changes by 10%. Figure 3 shows the voltage waveform used for the measurement, the applied pulse width is 1 msec,
It is repeatedly applied at a constant cycle. The optical response at this time is shown in FIG. It can be seen that it is in a dark state when there is no electric field, but is in a bright state while a voltage is applied.

FIG. 5 shows a plot of light transmittance with respect to voltage when this electric field is applied. 0 voltage
As it increases from (V), it passes the threshold value 1 and suddenly changes from the dark state to the bright state, but thereafter becomes constant. next,
When the voltage is decreased, the threshold value 1 at the time of increasing the voltage is passed and then the threshold value 2 changes from the bright state to the dark state.

When the voltage is further decreased, the threshold value 3 is exceeded again and the dark state changes to the bright state, but thereafter it becomes constant. Next, when the voltage is increased, it can be seen that after the threshold value 3 at the time of the voltage decrease, the threshold value 4 changes from the bright state to the dark state. Thus, there is a clear threshold and a large hysteresis. Next, the temperature dependence of the response speed of this device was measured using the ferroelectric liquid crystal material represented by Chemical formula 1. The definition of response speed is that after applying voltage,
The time required for the light transmittance to change to 90% was set.
The measured voltage waveform is a square wave of 10Hz and a voltage of 30.
(V). FIG. 6 shows the temperature dependence of the response speed. μ
It shows a fast response in the sec range.

Regarding the orientation of the liquid crystal molecules, the twisted state observed in the conventional ferroelectric liquid crystal when no electric field was applied was not observed, but only one stable orientation state was observed.
The orientation of the previous chiral smectic C phase can be reproduced by increasing the temperature after cooling once to bring it into a crystalline state and then changing the temperature to a chiral smectic C phase. In the above-described embodiment, the polarizer (P) of the polarizing plate and the molecular long axis direction in the absence of an electric field form an angle of 0 ° (180 °), but for example, 22.5 °, 45. The angle may be 90 ° or 90 °. For example, in the case of 22.5 °, when an electric field is applied, one electric field direction shows a dark state and the other electric field direction shows a bright state. At the time of electric field, it will show the intermediate state.

With this configuration (22.5 °), the molecular orientations of the three states were confirmed by the transmittance to the triangular wave voltage and the polarization reversal current. The voltage waveform used for measurement is ± 30 (V), 1
It is a triangular wave voltage of 0 (Hz). The transmittance and polarization reversal current at two temperatures when this waveform is applied are shown in FIGS. 7 and 8. In the figure, (a) shows the applied voltage waveform, (b) shows the transmittance, and (c) shows the polarization reversal current waveform. The transmittance (b) clearly shows a dark state in the negative range, an intermediate bright state in the 0 volt range, and a bright state in the positive range. Regarding the polarization reversal current (c), it can be seen that peaks of the polarization reversal current waveform appear corresponding to the above-mentioned state changes.

Further, as shown in FIG. 9, on the electrode substrates 1 and 2, a plurality of transparent electrodes 1a and 2a each having a stripe shape are formed in parallel so that the electrodes of the substrate 1 and the substrate 2 are orthogonal to each other. A matrix type display device is formed by arranging the electrodes and connecting an external power supply including a circuit that can be dynamically driven to the electrodes to perform the driving using the hysteresis characteristic shown by the voltage-transmittance curve. You can also

Now, the line sequential method of the dynamic driving method will be described. As an example, the 1/3 bias method will be described with reference to FIG. X indicates an electrode (scan electrode) that is line-sequentially scanned, and Y indicates an electrode (signal electrode) to which a signal voltage is applied. The points marked with ○ indicate points to be displayed (selected points), and the points without marks indicate points to retain the display (non-selected points). + 2V is applied to the electrodes selected in the scan electrodes, and 0V is applied to the non-selected electrodes. On the signal electrode side, -1V is applied to the selected electrode and + 1V is applied to the non-selected electrode.
Is applied. In this way, the voltage of 3V is applied to the selected points, and -1V or + 1V is applied to the other non-selected points.
Will be applied.

When dynamic driving is performed in this way,
Since the bias voltage is also applied to the non-selected points, the voltage applied to the non-selected points needs to be below the threshold range. In addition, the voltage applied to the non-selected point is set to the threshold 1 and the threshold 2 in FIG.
In the meantime, if the voltage between the thresholds 2 and 3 is applied to the dark display point and the voltage applied to the bright display point is higher than the threshold 1, the contrast ratio is high and the display can be maintained. Dynamic drive is easy. Note that not only the display drive in the positive polarity to which a positive voltage is applied but also the display in the negative polarity to which a negative voltage is applied can be performed in the same manner as described above, and the positive and negative voltages are alternately applied. It is also possible to drive the display and drive the liquid crystal by alternating current.

Further, in the above-mentioned liquid crystal, as shown in FIG. 5, the threshold value 2 is smaller than the threshold value 1 and the threshold value 4 is smaller than the threshold value 3. However, the relationship may be reversed depending on the liquid crystal material. In that case, the voltage for holding the display needs to be increased. Therefore, by using the liquid crystal having the relationship of threshold 2 <threshold 1 and threshold 4 <threshold 3 shown in FIG. Can be set to a low voltage.

The present invention is not limited to the transmissive type in which display is performed by illumination from the back surface, but can be applied to the reflective type in which light from the entire surface is reflected. By the way, as the liquid crystal material having a large spontaneous polarization used in the device of the present invention, the following structural formula (TFMNPOBC) can also be used.

[0029]

Embedded image

[0030] [4- (1- t ri f luoro m ethyl n onyl
oxy carbonyl) p henyl 4'- o ctyloxy b iphenyl -
4- c arboxylate] FIG. 11 shows transmittance characteristics and polarization reversal current characteristics when a triangular wave voltage (± 30 V, 10 Hz) is applied to this liquid crystal material, and shows the same three states as those of the above-mentioned liquid crystal material.

Further, as another liquid crystal material having a large spontaneous polarization, one having the following structural formula (MHPOBC) can be used.

[0032]

Embedded image

[0033] [4- (1- m ethyl h eptyloxy carbony
l) p henyl 4'- o ctyloxy b iphenyl -4- c arbox
ylate] FIG. 12 shows transmittance characteristics and polarization reversal current characteristics when the above-mentioned triangular wave voltage is applied to this liquid crystal material, and the above-mentioned three states are obtained.

Next, with respect to the above three liquid crystal materials, FIG. 13 shows the values of the spontaneous polarization Ps at which the three states of the transmittance appear. 50 types (nC / c
It shows three states when it has a large spontaneous polarization of m ² ) or more. A general triangular wave method was used for measuring the spontaneous polarization. In addition to the above three liquid crystal materials, other liquid crystal materials have the following structural formula (TFMHB2FD
B) can be used.

[0035]

[Chemical 4]

[0036] [4- (1- t ri f luoro m ethyl h epty
loxy carbonyl) -4'- b iphenyl2- f luoro -4
- d ecyloxy b enzoate] became a phase transition of the compound differential heat content folding (DSC) results as measured by texture observation under a polarizing microscope in the following manner.

[0037] Here, Cry: crystal phase, SmC ^* : chiral smectic C phase (ferroelectric liquid crystal phase), SmA: smectic A
Phase, I: indicates an isotropic liquid phase.

The spontaneous polarization of this compound in the ferroelectric smectic phase was measured using a general triangular wave method.
The characteristics shown in FIG. 14 were obtained. Further, the appearance of the above-mentioned three states spreads over the entire area of the ferroelectric smectic phase, that is, the magnitude of spontaneous polarization is from about 4 [nC / cm ² ] to 80 [nC].
/ Cm ² ]. Note that FIG. 15 shows 5
The transmittance characteristics (b) and the polarization inversion characteristics (c) when a triangular wave voltage (a) is applied at 5 ° C. are shown, and it can be seen that the three states described above are shown.

In order to bring the temperature range of the ferroelectric smectic phase to room temperature and to expand it, among the above four kinds of compounds,
TFMHPOBC, MHPOBC, TFMHB2FDB
TFMHPOBC ...... 20% MHPOBC ...... 46% TFMHB2FDB ...... 34% The phase transition was measured by differential thermal analysis (DSC) and a polarization microscope, and the following results were obtained. It was

[0040] The mixture was sealed in a liquid crystal cell, the transmittance characteristics and the polarization reversal current when a triangular wave voltage was applied were measured, and the appearance of the three states was examined. Was observed.

FIG. 16 shows the structure of a liquid crystal electro-optical device which is another embodiment of the present invention. In the present embodiment, for example, a ferroelectric liquid crystal material having a spontaneous polarization of at least 50 nC / cm ² or more is dichroic between two electrode substrates 1 and 2 which are spaced apart by 2 μm and arranged in parallel with each other. 6'in which the sex dye is dissolved is sealed. As the ferroelectric liquid crystal material, for example, the above-mentioned four liquid crystal materials (TFMHPOBC, TFMNPOBC, MHPOB) are used.
C, TFMHB2FDB). As the dichroic dye, for example, S-33 manufactured by Mitsui Toatsu Co., Ltd.
4 (azo black dichroic dye) is used, and the ferroelectric liquid crystal is heated to an isotropic liquid phase, and 2 wt% of the dichroic dye is added and dissolved. After that, after injecting between the electrode substrates 1 and 2 by utilizing the capillary reduction, the entire liquid crystal cell is gradually cooled at 0.1 to 1.0 ° C. per minute and cooled to a chiral smectic C phase. As a result of such cooling, the ferroelectric liquid crystal molecules 20 that have become the chiral smectic C phase are
Due to the large polarization of the liquid crystal molecules themselves and the order of the liquid crystals, Fig. 1
7 (a).

In the present embodiment, the electrode substrate 2
The polarizing plate 5 is arranged only on the outer side of. Furthermore, the polarizer (P) of this polarizing plate and the liquid crystal molecule long-axis direction at the time of no electric field make an angle of 0 ° (180 °). Transparent electrode 1
An external power supply 3 including a drive circuit is connected to a and 2a, and the voltage waveform as described above is applied to the liquid crystal.

Next, the operation of the apparatus having the above-described structure will be described with reference to FIG.
A description will be given using (a), (b), and (c). Here, each left figure is a plan view of the apparatus, and each right figure is a side view. When no electric field is applied, the liquid crystal molecules 20 between the substrates 1 and 2 are aligned in the normal direction of the smectic layer 10 and have the alignment state shown in FIG. At this time, the spontaneous polarization of the liquid crystal molecules is directed to the left (or right) in the upper half of the device (cell) and to the right (or left) in the lower half, that is, on the cone where the ferroelectric liquid crystal molecules move. In the upper half of the cell, the molecule is located above (or below) the cone, and in the lower half below (or above) the cone, and spontaneously in the cell thickness direction. The integrated value of polarization becomes zero. At this time, the dichroic dye 21 is dispersed in the liquid crystal molecules 20, and faces the same direction as the major axis direction of the liquid crystal molecules 20.

Next, when an electric field sufficient to rotate the liquid crystal molecules from the front side to the back side of the paper surface is applied, the spontaneous polarization direction 30 of the liquid crystal molecules is aligned with the electric field direction 40. Along with this, the liquid crystal molecules are realigned as shown in FIG. At this time, the liquid crystal molecules form a tilt angle θ with respect to the layer normal direction. By the way, the tilt angle of the dichroic dye dissolved in the ferroelectric liquid crystal material of Formula 1 is 10 ° to 31 ° within the temperature range of 70 ° C to 110 ° C. Also in this case, the dichroic dye 21 moves according to the movement of the liquid crystal molecules 20.

Next, when an electric field sufficient to rotate the liquid crystal molecules from the back side of the paper to the front side is applied, the spontaneous polarization 30 is aligned with the electric field direction 40. Accordingly, the liquid crystal molecules are
Reorient as in (c). At this time, the liquid crystal molecules form a tilt angle of −θ from the layer normal direction. Also in this case, the dichroic dye 21 moves according to the movement of the liquid crystal molecules 20. Thus, the optical axis of the liquid crystal can be changed to three states depending on the polarity and magnitude of the applied electric field.

A polarizing plate 5 is formed on the liquid crystal having such three states.
Can be used as an electro-optical device. For example, as shown in FIG. 17A, the polarizer (P) of the polarizing plate and the liquid crystal molecule long axis direction are arranged so as to form an angle of 0 °. In this state, the linearly polarized light passing through the polarizer (P) has a polarization direction that coincides with the absorption axis of the dichroic dye and is absorbed, so that it becomes a dark state.

In the case of FIG. 17 (b) in which an electric field is applied from the front side to the back side of the paper and in the case of FIG. 17 (c) in which an electric field is applied from the back side of the paper to the front side, linearly polarized light passing through the polarizer (P) is Since the polarization direction and the absorption axis of the dichroic dye do not coincide with each other, light is transmitted and a bright state is obtained. The polarizing plate 5 may be provided outside the electrode substrate 1. The optical response, the light transmittance, the temperature dependence of the response speed, the orientation of the liquid crystal molecules, and the like in this embodiment are substantially the same as those in the above embodiments.

In the present embodiment, the polarizer (P) of the polarizing plate and the molecular long-axis direction (dichroic dye molecule long-axis direction) in the absence of an electric field form an angle of 0 ° (180 °). However, the configuration may be such that an angle of 45 ° or 90 °, for example, in the case of 90 °, when an electric field is applied, one electric field direction indicates a dark state and the other electric field direction indicates a bright state. Shows the state and shows the intermediate state when there is no electric field. 2
It is possible to display gradation in stages.

The dichroic dye is not limited to an azo type dichroic dye, but an anthraquinone type dichroic dye having good light resistance can be used.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a liquid crystal electro-optical device showing an embodiment of the present invention.

2 (a), (b) and (C) are diagrams showing alignment states of liquid crystal molecules in the device shown in FIG.

FIG. 3 is a voltage waveform diagram used for measuring the relationship between the liquid crystal voltage and the transmittance.

FIG. 4 is a diagram showing changes in transmittance when the voltage of FIG. 3 is applied to liquid crystal.

FIG. 5 is a diagram showing a relationship between a voltage of liquid crystal and a transmittance.

FIG. 6 is a characteristic diagram showing the relationship between the response speed of liquid crystal and temperature.

FIG. 7 is a diagram showing a transmittance and a polarization reversal current with respect to a triangular wave voltage.

FIG. 8 is a diagram showing the transmittance and polarization reversal current for a triangular wave voltage at a temperature different from that shown in FIG. 7.

FIG. 9 is a diagram showing another configuration of the liquid crystal electro-optical device of the present invention.

FIG. 10 is an explanatory diagram for explaining a dynamic driving method.

FIG. 11 is a diagram showing transmittance and polarization inversion current with respect to a triangular wave voltage in another liquid crystal material.

FIG. 12 is a diagram showing transmittance and polarization inversion current with respect to a triangular wave voltage in still another liquid crystal material.

FIG. 13 is a diagram showing the values of spontaneous polarization at which three states of transmittance with respect to three liquid crystal materials appear.

FIG. 14 is a diagram showing temperature dependence of spontaneous polarization in still another liquid crystal material.

15 is a diagram showing transmittance and polarization inversion current with respect to a triangular wave voltage in the liquid crystal shown in FIG.

FIG. 16 is a configuration diagram of a liquid crystal electro-optical device showing another embodiment of the present invention.

17 is a diagram showing an alignment state of liquid crystal molecules in the device shown in FIG.

[Explanation of reference numerals] 1, 2 ... Electrode substrates 1a, 2a ... Transparent electrodes 1b, 2b
... Alignment film, 1c, 2c ... Transparent substrate, 4, 5 ... Polarizing plate,
6, 6 '... Ferroelectric liquid crystal, 10 ... Smectic layer, 20
... liquid crystal molecule, 21 ... dichroic dye, 30 ... spontaneous polarization direction,
40 ... electric field direction, 50 ... polarization direction.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norio Yamamoto 1-1, Showa-cho, Kariya city, Aichi Nihon Denso Co., Ltd. (72) Inventor Ichiro Kawamura 2-3-7 Marunouchi, Chiyoda-ku, Tokyo Showa Inside Shell Oil Co., Ltd.

Claims (2)

[Claims] 1. A ferroelectric liquid crystal (6) is sandwiched between a first electrode substrate (1) and a second electrode substrate (2) which is arranged at a predetermined interval. First and second
In the liquid crystal display device in which a voltage is applied between the electrodes of the display, the ferroelectric liquid crystal has a first stable state when the applied voltage exceeds a first threshold value on the one polarity side of the applied voltage. The first hysteresis characteristic is such that the state changes from the second stable state to the second stable state, and the second stable state returns to the first stable state when the applied voltage falls below the second threshold value. On the other polarity side, the first stable state changes to the third stable state when the applied voltage exceeds the third threshold value, and the third stable state when the applied voltage falls below the fourth threshold value. Has a second hysteresis characteristic such that the state returns to the first stable state, the second threshold value is smaller than the first threshold value, and the fourth threshold value is smaller than the third threshold value. The applied voltage exceeds the first threshold The display is performed as a voltage, and the applied voltage is held as the voltage for maintaining the ferroelectric liquid crystal in the second stable state by the first hysteresis characteristic. Display device. 2. The liquid crystal display device according to claim 1, wherein an applied voltage when holding the display is set to a voltage between the first and second threshold values.