JP2001235727A - Antiferroelectric liquid crystal device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an antiferroelectric liquid crystal device which can sufficiently decrease the luminance of black color and can realize display with high contrast. SOLUTION: An AC electric field of a high voltage at a low frequency not to decompose an antiferroelectric liquid crystal layer 15 is preliminarily applied for a specified time between a signal electrode 12a and a selective electrode 12b. The liquid crystal molecules respond and move by the spontaneous polarization induced by the AC field, and the movement of the molecules forms a bookshelf-like structure in the antiferroelectric liquid crystal layer 15. Thus, zigzag defects or parabolic focal conic defects in the antiferroelectric liquid crystal layer 15 are eliminated and a good alignment state can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an antiferroelectric liquid crystal device used for an optical shutter or a display device.

[0002]

2. Description of the Related Art An antiferroelectric liquid crystal has been discovered by Chandani et al. (Japan Journal Applied Physics, 1989, 28, L1256 (Jpn.
J. Appl. Phys. , No. 28, p. L125
6, 1989)).

An example of the prior art of an antiferroelectric liquid crystal device is as follows.
This will be described below with reference to the drawings. FIG. 2 is a schematic diagram of an antiferroelectric liquid crystal. In FIG. 2, 21 is a cone, 22 is a layer normal, 23 is a liquid crystal molecule, 24 is an absorption axis of a polarizing plate, and 25 is a half of a helical pitch.

FIG. 3 is a schematic diagram showing the display principle of an antiferroelectric liquid crystal element, and is a view of an opposing substrate in which liquid crystal is sealed, as viewed from above the substrate. In FIG. 3, 31 is a liquid crystal molecule, 3
2 is the layer normal, 33 is the spontaneous polarization Ps, 34 is the absorption axis of the polarizing plate, 35 is the direction of the applied electric field, and in FIG. Show, FIG.
In the case of (c), (x mark) indicates the electric field in the forward direction with respect to the drawing.

The operation of the conventional antiferroelectric liquid crystal device having the above components will be described below.
The antiferroelectric liquid crystal sealed between the aligned substrates subjected to the alignment treatment and layered in a direction perpendicular to the substrate is shown in FIGS. 2 and 3 (b) when no voltage is applied (no electric field). As shown in ()), the spontaneous polarizations Ps33 are alternately in opposite directions, and thus are canceled as a whole.

When a voltage equal to or higher than a predetermined threshold value is applied between the opposing substrates, the anti-ferroelectric liquid crystal in FIG.
As shown in FIG. 3A and FIG. 3C, a ferroelectric phase is induced according to the direction of the electric field.

Therefore, for example, as shown in FIG. 3, a counter substrate filled with liquid crystal is placed between a pair of crossed Nicol polarizing plates arranged so that one of the absorption axes 34 coincides with the direction of the layer normal 32. For example, a dark state is obtained in the anti-ferroelectric phase state when an electric field below the threshold voltage shown in FIG.
In the ferroelectric phase state when an electric field equal to or higher than the threshold voltage shown in (a) or FIG. 3 (c), a bright state due to the birefringence effect can be obtained.

[0008]

However, in the conventional antiferroelectric liquid crystal device as described above, FIG. 2 and FIG.
In the state of the antiferroelectric phase shown in FIG. 4, especially in the initial state of the antiferroelectric phase immediately after the liquid crystal is sealed and before the voltage is applied, a schematic diagram of the layer structure in the initial orientation state of the antiferroelectric liquid crystal shown in FIG. As described above, the layer 41 has a chevron structure, and 41 is a layer, which has a problem that alignment defects such as a hairpin defect 42 and a lightning defect 43 are likely to occur.

Here, the chevron structure will be briefly described. As a main method of enclosing and orienting the smectic liquid crystal, there is a method of encapsulating the liquid crystal in an isotropic phase and then lowering the temperature to room temperature by slow cooling. According to this method, a layer structure is generated in a smectic phase due to a phase change according to a temperature drop, and further a phase transition to a chiral smectic layer occurs. At this time, liquid crystal molecules are tilted, a helical structure is generated, and a layer interval is narrowed. A chevron structure is created to alleviate this volume change.

In the ferroelectric liquid crystal, the interaction between the layers is weak, and zigzag defects such as the hairpin defect 42 and the lightning defect 43 due to the reversal of the direction of the chevron are generated, thereby reinforcing the volume relaxation. On the other hand, antiferroelectric liquid crystals need to cancel the spontaneous polarization as a whole, so the interaction between the layers is strong, so that zigzag defects are less likely to occur, and parabolic focal conic defects are generated, resulting in volume change. It is thought to be reinforcing mitigation.

Therefore, in the antiferroelectric liquid crystal device,
This parabolic focal conic defect appears as a defect on a white bright line in a dark state, causing a problem that black luminance increases and contrast is reduced.

In addition, since spontaneous polarization of an antiferroelectric liquid crystal is induced by an electric field, the ferroelectric phase is maintained even after the power is turned off due to an electric field generated by charges remaining on the electrodes after the power of the antiferroelectric liquid crystal element is turned off. Is still induced, and since this residual electric field is a direct current, there is also a problem that the alignment of the liquid crystal is significantly adversely affected.

The present invention solves the above-mentioned conventional problems, and provides an antiferroelectric liquid crystal element capable of sufficiently reducing black luminance and realizing high contrast display.

[0014]

In order to solve the above-mentioned problems, an antiferroelectric liquid crystal device according to the present invention comprises a transparent substrate in which signal electrodes and selection electrodes are arranged in a matrix on a surface of an opposing substrate. An electrode is formed, having a substrate pair subjected to an alignment treatment on at least one surface of the opposed substrate, sandwiching an antiferroelectric liquid crystal between the substrates of the substrate pair, and detecting power-on. It is characterized in that a means for applying an alternating electric field is provided between the signal electrode and the selection electrode for a certain period.

As described above, even if the pseudo ferroelectric liquid crystal returns to the chevron structure in the antiferroelectric liquid crystal due to a temperature change while the antiferroelectric liquid crystal element is left unused, By applying an alternating electric field for a certain period immediately after turning on the power to the antiferroelectric liquid crystal element, a favorable pseudo bookshelf alignment state can be realized in the antiferroelectric liquid crystal at any time during use.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The antiferroelectric liquid crystal device according to claim 1 of the present invention has a structure in which a transparent electrode in which signal electrodes and selection electrodes are arranged in a matrix on a surface of an opposing substrate, An antiferroelectric liquid crystal is sandwiched between the substrates of the pair of substrates on at least one surface of the opposing substrate, and a power-on is detected for a certain period of time. A means for applying an alternating electric field is provided between the electrode and the selection electrode.

According to this structure, when the antiferroelectric liquid crystal element returns to the chevron structure in the antiferroelectric liquid crystal due to a temperature change while the antiferroelectric liquid crystal element is left unused. However, by applying an alternating electric field for a certain period immediately after turning on the power to the antiferroelectric liquid crystal element, a favorable pseudo bookshelf alignment state can be realized in the antiferroelectric liquid crystal at any time during use.

The antiferroelectric liquid crystal device according to the second aspect is the antiferroelectric liquid crystal device according to the first aspect, having a backlight or a sidelight light source. It is configured to include a unit for turning off the light source.

According to this structure, when the alternating electric field is applied for a certain period immediately after the power supply to the antiferroelectric liquid crystal element is turned on, the light source is turned off, whereby the external
It is not necessary to show the state when the alternating electric field is applied.

The antiferroelectric liquid crystal device according to claim 3 is the antiferroelectric liquid crystal device according to claim 1 or 2, wherein a signal electrode and a selection electrode are connected for a certain period after power-off is detected. It is configured to include a means for short-circuiting all.

The antiferroelectric liquid crystal device according to a fourth aspect is the antiferroelectric liquid crystal device according to the third aspect, wherein when a signal electrode and a selection electrode are short-circuited, the potentials of all the electrodes are grounded. Level configuration.

According to these configurations, all the signal electrodes and all the selection electrodes are short-circuited for a certain period immediately after the power supply of the antiferroelectric liquid crystal element is cut off, thereby removing the DC electric field due to the residual charges of the electrodes. In addition, the alignment state of the antiferroelectric liquid crystal is maintained in a good state.

Hereinafter, an antiferroelectric liquid crystal device according to an embodiment of the present invention will be specifically described with reference to the drawings. FIG. 1 is a sectional view of the antiferroelectric liquid crystal device of the present embodiment. In FIG. 1, 11a is an upper substrate forming a substrate pair, 11b is disposed opposite to the upper substrate 11a, and a lower substrate forming a substrate pair together with the upper substrate 11a, 12a is a signal electrode, 12b is a selection electrode, 13b Is an insulating thin film, 14
Is an alignment film, 15 is an antiferroelectric liquid crystal layer, 16 is a light source, 17
Is a polarizing plate.

In this embodiment, glass substrates are used as the upper substrate 11a and the lower substrate 11b, and the signal electrodes 1
Indium tin oxide (ITO) is formed as 2a and the selection electrode 12b, and further, an insulating thin film 13 (for example, RTZ-1, manufactured by Catalyst Chemical Industry Co., Ltd.) containing metal oxide as a main component is 1000 Angstrom thickness was formed. Polyimide (for example, LX-5400, manufactured by Hitachi Chemical Co., Ltd.) was applied thereon as an alignment film 14 and formed to a thickness of 500 Å by firing. Then, the alignment film 14 was rubbed by a rotational rubbing method using rayon so that the rubbing direction was parallel to the upper and lower substrates, and an alignment treatment was performed. The antiferroelectric liquid crystal layer 15 is made of an antiferroelectric liquid crystal material which is a mixture of ester liquid crystals using MHPOBC as a chiral material. The thickness of the antiferroelectric liquid crystal layer 15 is 1.5 μm.
And As the light source 16, a surface light source unit using a side light was used.

The first embodiment of the present invention will be described with reference to FIG. In the first embodiment, after the injection of the antiferroelectric liquid crystal, an alternating electric field of a rectangular wave having a different amplitude voltage and a different frequency is applied between the signal electrode 12a and the selection electrode 12b.
After the application for 2 seconds, the relative transmittance of the liquid crystal element (transmittance with the maximum transmittance when an electric field was applied to the liquid crystal element as 100%) was measured microscopically in the pixel portion in the state where no electric field was applied.
The result is shown in FIG. At a frequency of 1 Hz, the voltage was 55 volts, and at a frequency of 5 Hz, the voltage was 60 volts.

From the above results, in order to make the relative transmittance sufficiently small and not to destroy the liquid crystal, the amplitude voltage of the alternating electric field should be 10 to 50 volts.
Desirably, it is required to be 20 volts or more and 40 volts or less, and the frequency is required to be an alternating electric field of 1 Hz or more and 100 Hz or less, and preferably 5 Hz or more and 50 Hz or less.

Further, by the alternating electric field satisfying this condition,
In the space where there is no electrode on at least one substrate,
It was also confirmed that an electric field capable of sufficiently reducing black luminance was applied, and a good alignment state was realized.

A second embodiment of the present invention will be described with reference to FIG. In the second embodiment, after injecting the antiferroelectric liquid crystal, a rectangular wave of 25 volts and 10 Hz is applied between the signal electrode 12a and the selection electrode 12b for a different application time, and the first embodiment is applied. The relative transmittance when no electric field was applied was measured in the same manner as described above. FIG. 6 shows the result.

From the above, in order to make the black luminance sufficiently small for practical use, the lower limit of the application time is 0.5 seconds or more.
Desirably, one second or more is required, and it is understood that the upper limit should be 60 seconds or less, and desirably 30 seconds or less from the limitation of the length allowed for the application time.

The third embodiment of the present invention will be described with reference to FIG. In the third embodiment, after injecting the antiferroelectric liquid crystal, the three-phase waveform of the rectangular wave, the sine wave, and the triangular wave is applied between the signal electrode 12a and the selection electrode 12b while changing the amplitude voltage to 10 Hz. For 10 seconds. Then, the relative transmittance when no electric field was applied was measured in the same manner as in the above embodiment. FIG. 7 shows the result.

From this, it can be seen that the black luminance can be reduced most efficiently in the case of a rectangular wave. But it also turns out to be effective.

A fourth embodiment of the present invention will be described with reference to FIG. In the fourth embodiment, after the injection of the antiferroelectric liquid crystal, the temperature of the antiferroelectric liquid crystal element is changed,
A rectangular wave of 10 Hz was applied between the signal electrode 12a and the selection electrode 12b for 10 seconds, and then the relative transmittance was measured in the same manner as in the above embodiment. Then, at each temperature, the minimum amplitude voltage required for the relative transmittance to decrease and saturate was obtained. FIG. 8 shows the result. The numerical values in the graph indicate the values of the saturated relative transmittance.

From this result, it is understood that the lower the temperature, the larger the amplitude voltage must be. From this, it can be seen that the black luminance can be sufficiently reduced by adjusting the temperature of the liquid crystal element.

A fifth embodiment of the present invention will be described with reference to FIG. In the fifth embodiment, the anti-ferroelectric liquid crystal element is provided with a mechanism for performing control as shown in the flowchart of FIG. 9, so that the anti-ferroelectric liquid crystal element is turned on by turning on the power. For a certain period of time, an alternating electric field is applied between the signal electrode 12a and the selection electrode 12b.

As a result, it was confirmed that, after the power was turned on, good orientation in which the black luminance was sufficiently reduced could be realized. Further, while the alternating electric field is being applied, the light source 16 is turned off, so that the state is shut off from the outside.

A sixth embodiment of the present invention will be described with reference to FIG. In the sixth embodiment, the antiferroelectric liquid crystal element is provided with a mechanism for performing control as shown in the flowchart of FIG. 10 so that the liquid crystal element is turned off by turning off the power supply for a certain period of time. All signal electrodes 12a and all selection electrodes 12b are short-circuited to the ground level.

As a result, it was confirmed that the orientation was not disturbed by the residual DC electric field after the power was turned off. By the operation of each of the above embodiments, the black luminance can be sufficiently reduced and the contrast can be increased.

Needless to say, the transparent electrode, insulating thin film, alignment film, antiferroelectric liquid crystal material, light source, etc. are not limited to those used in the embodiment of the present invention. It should be added that the effects of the present invention are guaranteed if the above requirements are satisfied.

[0039]

As described above, according to the present invention, a mechanism for applying an alternating electric field for a certain period immediately after the power supply of the liquid crystal element is turned on is provided.
A good orientation state can be realized at any time.

Further, by providing a mechanism for turning off the light source of the backlight or the side light during the period in which the alternating electric field is applied, the state is shut off from the outside. In addition, for a certain period immediately after the liquid crystal element is turned off,
By providing a mechanism that short-circuits all signal electrodes and all selection electrodes, the potential at the time of short-circuiting is set to the ground level, thereby preventing a residual DC electric field from being generated in the liquid crystal element and ensuring a good alignment state. Can be maintained.

As described above, the black luminance can be sufficiently reduced, and a high-contrast display can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an antiferroelectric liquid crystal device according to an embodiment of the present invention.

FIG. 2 is a schematic view of an antiferroelectric liquid crystal.

FIG. 3 is a schematic view showing a display principle of an antiferroelectric liquid crystal element.

FIG. 4 is a schematic diagram showing a layer structure of an antiferroelectric liquid crystal in an initial alignment state.

FIG. 5 is a diagram showing the relationship between the amplitude voltage and frequency of an applied electric field of an antiferroelectric liquid crystal element and the relative transmittance of the antiferroelectric liquid crystal element when no electric field is applied.

FIG. 6 is a diagram showing the relationship between the application time of a rectangular wave applied to the antiferroelectric liquid crystal device and the relative transmittance of the antiferroelectric liquid crystal device when no electric field is applied.

FIG. 7 is a diagram showing the relationship between the difference in the waveform of the alternating electric field applied to the antiferroelectric liquid crystal element and the amplitude voltage, and the relative transmittance of the antiferroelectric liquid crystal element when no electric field is applied.

FIG. 8 is a diagram showing the relationship between the temperature of the antiferroelectric liquid crystal element and the minimum amplitude voltage of the alternating electric field required for the relative transmittance of the antiferroelectric liquid crystal element to be saturated when no electric field is applied.

FIG. 9 is a flowchart when the power of the antiferroelectric liquid crystal element is turned on.

FIG. 10 is a flow chart when the power supply of the antiferroelectric liquid crystal element is turned off.

[Description of Signs] 11a Upper substrate 11b Lower substrate 15 Antiferroelectric liquid crystal layer 16 Light source

Claims (4)

[Claims] 1. A substrate in which signal electrodes and selection electrodes are arranged in a matrix on a surface of an opposing substrate, and a transparent electrode is formed on at least one surface of the opposing substrate. Anti-ferroelectric liquid crystal is sandwiched between the substrates of the pair of substrates, and means for applying an alternating electric field between the signal electrode and the selection electrode for a certain period after power-on is detected. Ferroelectric liquid crystal device. 2. The antiferroelectric liquid crystal device according to claim 1, further comprising a light source of a backlight or a sidelight, and a means for turning off the light source during an application of an alternating electric field. 3. The anti-ferroelectric liquid crystal device according to claim 1, further comprising means for short-circuiting all of the signal electrode and the selection electrode for a certain period of time after detecting power-off. 4. The anti-ferroelectric liquid crystal device according to claim 3, wherein when the signal electrode and the selection electrode are short-circuited, the potentials of all the electrodes are set to the ground level.