JP3048886B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display having a wide viewing angle.

[0002]

2. Description of the Related Art A liquid crystal display device has very advantageous characteristics for a flat display device, such as a thin, lightweight, low power consumption and low driving voltage. Therefore, a laptop personal computer, a word processor, a portable terminal, a portable terminal, and the like. It has become indispensable for these information devices as displays for televisions and the like. Current,
Two display modes, an STN mode and a TN mode using a TFT (thin film transistor), are actively used, and ferroelectric liquid crystals are also being actively studied.

FIG. 8A is a schematic sectional view showing an example of the structure of a liquid crystal cell in a conventional liquid crystal display device.

In FIG. 1, reference numeral 1 denotes a liquid crystal cell having a pair of opposing substrates 10 and 11 arranged opposite to each other. Indium tin oxide (hereinafter referred to as “indium tin oxide”) is formed on the surface of a glass substrate 2 a constituting one of the opposing substrates 10. A plurality of transparent signal electrodes 3a made of ITO or the like are arranged in parallel with each other;
A transparent insulating film 4a made of SiO ₂ or the like is formed thereon. A plurality of transparent scanning electrodes 3b made of ITO or the like are arranged on the surface of the glass substrate 2b constituting the other counter substrate 11 in parallel with each other so as to be orthogonal to the signal electrodes 3a. The surface of
It is covered with a transparent insulating film 4b made of O ₂ or the like. On the insulating films 4a and 4b, alignment films 5a and 5b that have been subjected to a uniaxial alignment process such as a rubbing process are formed. The alignment film includes a polyimide film, a nylon film,
An organic polymer such as a polyvinyl alcohol film or a SiO oblique deposition film is used.

Here, the two glass substrates 2a, 2b
Are bonded together with a sealant 6 leaving a part of the liquid crystal injection port, and the liquid crystal is injected from the injection port into a space sandwiched between the alignment films 5a and 5b, and is supported. It is sealed with a stopper 8. On the outer surfaces of the two glass substrates 2a, 2b thus bonded, the polarizing plates 12a, 12 positioned so that their respective polarization axes are orthogonal to each other.
b is arranged.

In a liquid crystal panel having a large display area, as shown in FIG. 8A, a spacer is provided between two glass substrates 2a and 2b so as to face each other in parallel with a constant cell thickness. 9 are arranged.

By the way, the nematic liquid crystal used in the above STN mode or TN mode is a uniaxial molecule in view of optical and electrical characteristics, and its refractive index and dielectric constant are different from those in the direction parallel to the molecular long axis. It has anisotropy in the direction perpendicular to the long axis of the molecule (the short axis of the molecule).

For this reason, as shown in FIG. 8B, when an electric field is applied to the nematic liquid crystal by the electrode 22 sandwiching the nematic liquid crystal, the molecules 21 of the nematic liquid crystal are aligned horizontally and vertically as indicated by arrows. And the alignment state is changed.

Therefore, the light that has passed through the liquid crystal cell 1 changes its polarization state in accordance with this change in alignment. That is, the liquid crystal cell can be used as a display device.

Here, the change in the alignment is largely determined by the dielectric anisotropy of the liquid crystal and the initial alignment state, and is properly used depending on the purpose. In general, liquid crystal is aligned (horizontal alignment) so that its molecular long axis is parallel to the electrode film if its dielectric anisotropy is positive, and its molecular anisotropy if its dielectric anisotropy is negative. The alignment treatment is performed so that the major axis is perpendicular to the electrode film (vertical alignment).

[0011]

However, a display device using these nematic liquid crystals performs display in a horizontal alignment, a vertical alignment, or an intermediate state between them, so that the birefringence and the polarization state depend on the observation direction. There is a problem that the viewing angle characteristic is fundamentally poor, and the display cannot be recognized clearly from a deep oblique direction even if the display can be recognized from the front direction of the device.

In order to solve the problem that the viewing angle is narrow, a direction in which a pretilt angle (an angle at which liquid crystal molecules rise from the substrate surface in a state where no electric field is applied) faces one pixel (hereinafter, the pretilt angle is referred to as a pretilt angle). A solution such as a multi-domain method in which a plurality of portions having different directions are provided has been tried, but this solution does not completely solve the problem of the viewing angle.

By the way, ferroelectric liquid crystal [NAClark and ST Lag
erwall: Appl. Phys. Lett. 36 (1980) 899.)
This is expected as a liquid crystal of a next-generation liquid crystal display device, and has a feature that a viewing angle is wide.

FIG. 2 is a conceptual diagram for explaining the principle of the molecular orientation of the ferroelectric liquid crystal. The ferroelectric liquid crystal molecules 13 are oriented at an angle inclined by θ with respect to the smectic layer normal 17 and have spontaneous polarization 23 in a direction perpendicular to the molecular long axis. Such a liquid crystal phase is referred to as a chiral smectic C phase, and a liquid crystal phase in which liquid crystal molecules are non-chiral, that is, a non-ferroelectric liquid crystal is simply referred to as a smectic C phase.

The smectic layer normal 17 is often
This is the same as the uniaxial orientation processing direction such as rubbing.
Driving such a ferroelectric liquid crystal, as shown in FIG.
This is performed by applying an electric field substantially parallel to the y direction. That is, one end of the liquid crystal molecule 13 rotates on the conical trajectory 14 due to the interaction between the electric field applied substantially parallel to the y direction and the spontaneous polarization. That is, the liquid crystal molecules 13 switch between two states in which one end thereof is located at two points a and b on the conical trajectory 14 by the pulse electric fields having different polarities.

Here, 15 is a projection (C-direct) of the liquid crystal molecules 13 projected onto the bottom of the cone. This switching is a switching in which the molecular major axis is parallel to the cell substrate surface in both states of the liquid crystal molecules. Therefore, in the image display using the ferroelectric liquid crystal, the angle dependence of birefringence is small, Even when viewed from a deep angle with respect to the front of the screen, it is possible to recognize a display that is the same as the front of the screen.

As described above, the ferroelectric liquid crystal has advantageous characteristics for a flat display device, but the molecular alignment is complicated, uniform alignment control is not easy, and the internal reversal electric field generated when the spontaneous polarization is inverted is reduced. There is a problem that the switching is adversely affected, and the liquid crystal material and device configuration need to be devised more than nematic liquid crystal.

FIGS. 3A to 3E are diagrams for explaining the actual molecular orientation of the ferroelectric liquid crystal. In the layer structure of the chiral smectic C-phase liquid crystal, actually, each smectic layer is not completely perpendicular to the substrate surface, but has a chevron structure bent in a “<” shape as shown in FIG. . The same applies to a smectic C-phase liquid crystal which is not a ferroelectric liquid crystal. The chevron structure is
Depending on the relationship between the bending direction of the smectic layer and the direction of the pretilt angle, the smectic layer is classified into two types, C1 orientation and C2 orientation, in which the bending directions are different.

Further, in the chiral smectic C phase and the smectic C phase, there are two types, a uniform orientation in which liquid crystal molecules are oriented substantially parallel to the direction from the lower substrate to the upper substrate, and a twist orientation in which the liquid crystal molecules are twisted. There are four types of orientation states, for a total of four types of C1U, C1T,
It is known that U and C2T orientations appear. This is discussed in our paper [N. Itoh et al .: LIQUID CRY
STALS, 15 (1993) 699.]. Note that FIG.
3 (a), 3 (b), 3 (c) and 3 (d) show the C1U, C1T, C2U and C2T orientations, respectively, and FIG. 3 (e) shows the high pretilt. The C2U orientation of the state is shown.

In an actual display device, if a plurality of alignment states coexist, an uneven display is obtained.
It must be aligned to different types of orientation. Cl and C2 orientations having different bending angles of the smectic layer can be aligned by geometric control between the layer bending angle and the pretilt angle defined by the alignment film [J. Kanbe et al .: Ferroelectrics, 114 (199
1) 3., A. Tagawa etal.:JAPAN DISPLAY '92 DIGEST,
519.] However, it is not easy to control two types of orientations, that is, the uniform orientation and the twist orientation, to make them one of the orientations.

Since the ferroelectric liquid crystal molecules have a chiral property, adjacent molecules have the property of being spontaneously twisted and arranged, and an electric polar force acts between the alignment film and the spontaneous polarization. Since the direction of spontaneous polarization is regulated at the interface between the alignment film and the liquid crystal, the twist alignment state is often stabilized when the same alignment treatment is performed on the upper and lower substrates.

Further, in order to make the memory property appear stably, it is necessary to make the liquid crystal molecules bistable at positions indicated by the line segments oa and ob in the conical locus described in FIG. It is desirable to perform the same alignment treatment on the substrate. Optically, the uniform alignment state has a dark state and is suitable for a display device, and the twist alignment state does not have a dark state and is not suitable for a display device. Although measures such as optimizing the alignment film and cross-rubbing have been reported in order to make the uniform alignment state appear stably, the problem of obtaining a stable uniform alignment has not been completely solved.

Although the memory property cannot be utilized, the ferroelectric liquid crystal is combined with an active element such as a TFT, and then the liquid crystal molecules are unidirectionally aligned, that is, the line in the conical locus described in FIG. Min oa and line segment ob
Although a method of obtaining a gray scale display by orienting to any of the positions indicated by, has been reported, due to the spontaneous twisting property of the ferroelectric liquid crystal molecules, uniform alignment even when the liquid crystal molecules are unidirectionally aligned. The state is not always stable.

In addition, the switching failure due to the internal reversal electric field is a problem that is very difficult to solve for ferroelectric liquid crystal because it is caused by spontaneous polarization.

The present invention has been made to solve such a problem, and can realize a stable uniform alignment state in which the optical axis of liquid crystal molecules changes in a plane parallel to the substrate surface. It is an object of the present invention to provide a liquid crystal display device capable of avoiding a switching failure due to an internal anti-electric field and thereby realizing a display with a high contrast and a wide viewing angle.

[0026]

A liquid crystal display device according to the present invention comprises a pair of light-transmitting substrates which are disposed to face each other and have at least an electrode film and an alignment film, and a liquid-crystal display device between the pair of light-transmitting substrates. Driving means for selectively applying a voltage to the intervening smectic C-phase liquid crystal and the electrode film to switch the direction of the optical axis of the liquid crystal molecules in the smectic C-phase liquid crystal; Identification means for optically identifying an axis change. The smectic C phase liquid crystal is one in which the liquid crystal molecules are semi-stablely aligned such that the major axis of the liquid crystal molecules is parallel to the electrode film. Thereby, the above object is achieved.

According to the present invention, in the above liquid crystal display device, an insulating film having a different material from that of the one substrate and the other substrate is formed on each of the pair of light transmitting substrates so as to cover the electrode film. It was done.

According to the present invention, in the above-mentioned liquid crystal display device, an alignment film having different constituent materials is formed on each of the pair of translucent substrates on the one substrate and the other substrate.

According to the present invention, in the above liquid crystal display device, an alignment film formed on one of the pair of translucent substrates and an alignment film formed on the other side are subjected to rubbing treatment under different conditions. is there.

[0030]

In the present invention, since a smectic C-phase liquid crystal is used as a liquid crystal for displaying an image, the optical axis of the liquid crystal molecule changes in a plane parallel to the substrate surface. Is less dependent on the angle of birefringence, and the display can be recognized as from the front even at a deep angle with respect to the display surface.

Further, since the smectic C phase liquid crystal does not have spontaneous polarization, it is possible to prevent the internal reversal electric field generated when the spontaneous polarization is reversed from adversely affecting the switching, and there is no twist of the liquid crystal molecules due to the spontaneous polarization. Therefore, uniform orientation can be easily realized.

Further, in the smectic C phase liquid crystal, since the structure of the smectic layer is a chevron structure, the liquid crystal molecules are not completely parallel to the substrate surface in the initial stable state.
Applying an electric field to the phase liquid crystal, the liquid crystal molecules are displaced between the initial stable position on the conical locus of the optical axis change and other positions by the action of the biaxial dielectric anisotropy of the liquid crystal molecules. Can be. Therefore, an image can be displayed by extracting the change in the liquid crystal molecules as a change in brightness using a polarizing plate or the like.

Further, since the smectic C-phase liquid crystal does not have spontaneous polarization, the phenomenon that the alignment directions are aligned by the electric field response of the spontaneous polarization does not occur. The liquid crystal molecules can be unidirectionally aligned to achieve a uniform uniform alignment state, thereby preventing the display by the smectic C-phase liquid crystal from being non-uniform.

Here, by making the constituent material of the alignment film or the constituent material of the insulating film covering the electrode film different between the upper substrate side and the lower substrate side, the molecules of the smectic C-phase liquid crystal are uni-stablely aligned. Uniform uniform alignment state can be obtained.

By subjecting the alignment film on the upper substrate side and the alignment film on the lower substrate side to rubbing treatment under different conditions,
The molecules of the smectic C-phase liquid crystal can be half-stably aligned to obtain a uniform uniform alignment state.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the basic principle of the present invention will be described.

In the present invention, a smectic C-phase liquid crystal which is half-stable and oriented so that the optical axis of the liquid crystal molecule is parallel to the electrode film is provided between a pair of opposed substrates, and an electric field is applied to the liquid crystal. By changing the optical axis of the liquid crystal molecules on a conical trajectory by the interaction between the axial dielectric anisotropy and the electric field, and detecting the movement of the optical axis using a polarizing plate or the like, the conventional nematic liquid crystal can be used. The problem of the viewing angle characteristics in the display device used can be solved.

That is, the chiral smectic C-phase liquid crystal (ferroelectric liquid crystal) and the smectic C-phase liquid crystal are biaxial in optical and electrical characteristics, and have a refractive index and a dielectric constant in a direction parallel to the molecular long axis. Have different values in the two orthogonal molecular short axis directions.

Regarding the refractive index, the biaxial anisotropy is very small and is not particularly useful in practical use, but the biaxial anisotropy of the dielectric constant (biaxial dielectric anisotropy) is useful.

The biaxial dielectric anisotropy will be described with reference to FIG. The three different dielectric constant values ε1, ε2, and ε3 are components in which ε1 is parallel to the molecular minor axis direction and also parallel to the plane (tilt plane) that includes the pretilt angle of the liquid crystal molecule.
ε2 is a component parallel to the minor axis of the molecule and perpendicular to the tilt plane, and ε3 is a component parallel to the major axis of the molecule.

The smectic C phase liquid crystal has a spontaneous polarization of 23.
Does not exist, but the component ε2 of the dielectric constant coincides with the component parallel to the spontaneous polarization of the ferroelectric liquid crystal. In a uniaxial nematic liquid crystal, the permittivity ε1 and the permittivity ε2 are equal, and only the permittivity ε3 is different from the others. The values are different.

In general, Δε = ε3-ε1, δε = ε2-ε1, and δε is called biaxial dielectric anisotropy.

The smectic C-phase liquid crystal does not have spontaneous polarization and does not spontaneously twist, so that uniform alignment is easy. However, the smectic layer has a chevron structure like the ferroelectric liquid crystal. Therefore, C1 shown in FIG.
The state of U orientation or C2U orientation tends to appear. In these alignment states, the liquid crystal molecules are not completely horizontally aligned as shown in FIG. 2, and the liquid crystal molecules exist at positions between the line segment oa or the line segment ob and the line segment oc on the conical locus. ing.

When an electric field is applied to the smectic C-phase liquid crystal, the liquid crystal molecule changes its optical axis by the action of biaxial dielectric anisotropy as reported by Jones et al. [JC Jone
s etal .: Mol. Cryst. Liq. Cryst. Letter, vol. 7
(3), pp.91]. If the biaxial dielectric anisotropy is positive, the liquid crystal molecules move from the place where the biaxial dielectric anisotropy is stably present on the conical locus 14 onto the line segment oa or the line segment ob, and the biaxial dielectric anisotropy becomes negative. If there is, the molecule moves toward the line segment co.

FIG. 5 shows the change of the optical axis at this time. 17 is a smectic layer normal line. 18, 18 '
Are optical axis positions in the C2U alignment state, and 19 and 19 ′ are optical axis positions in the C1U alignment state. Generally layer normal 17
Is larger in the C1U orientation than in the C2U orientation. For example, the biaxial dielectric anisotropy of the liquid crystal is positive,
In the case of a display device in which the liquid crystal is C2U-oriented, the initial optical axis is located at the optical axis position 18 or 18 ', and when an electric field is applied, the optical axis is moved from the optical axis position 18 to 20 or from the optical axis position 18'.
Move to 0 '. The polarization axis 12a of one polarizing plate is parallel to the initial optical axis position 18 '
If b is perpendicular to the optical axis 12a of the one polarizing plate, the initial optical axis position 18 'and the optical axis position 2 when an electric field is applied can be obtained.
By changing the optical axis of the liquid crystal molecules between 0 ', bright and dark display can be obtained.

At this time, a problem occurs in a portion where the optical axis changes between the optical axis positions 18 and 20 which are shifted from the polarization axis 12a of the polarizing plate. When a bistable orientation is obtained in a normal cell configuration, as shown by Ouchi et al., Two orientation states UP and DOWN shown by a straight line and a broken line in FIG. 3 appear at random [Y. Ouchi et al .: Jap. J. Appl. Phy
s., vol.26, 1987, pp.1].

In the ferroelectric liquid crystal, the entire display portion can be aligned in one of the two alignment states UP and DOWN by the electric field response of spontaneous polarization, but in the smectic C phase liquid crystal without spontaneous polarization, It is not possible to align the orientations.

According to the report of Jones et al., The alignment layer is a SiO film with a deposition angle of 30 °, and the two alignment states U
It indicates that P and DOWN are mixed. Since the alignment portion where the optical axis of the liquid crystal molecules is located at the optical axis position 18 and the optical axis position 20 leads to non-uniform display, in the display device of the smectic C-phase liquid crystal, the optical axis of the liquid crystal molecule is initially adjusted to the optical axis position 18. Only the alignment part at 'must be kept. For this purpose, it is necessary to perform one-sided stable alignment by means such as separate alignment treatment between the upper and lower substrates.

In FIG. 2, points a, b and c on the cone locus are shown.
Is drawn in a three-dimensional arrangement, but this is a story on the molecular level only, and in practice, the movement of the optical axis in the substrate plane as shown in FIG. Then, as with the ferroelectric liquid crystal, a wider viewing angle than the nematic liquid crystal can be obtained.

Hereinafter, embodiments of the present invention will be described.

Embodiment 1 FIG. 1 is a sectional view showing the structure of a liquid crystal cell of a liquid crystal display according to a first embodiment of the present invention. In the figure, reference numeral 100 denotes a liquid crystal cell of this embodiment.
In the liquid crystal cell 100, OCD TYPE2 (product name of a silicon film manufactured by Tokyo Ohka Co., Ltd.) is formed on the surfaces of the upper and lower glass substrates 2a and 2b as insulating films 104a and 104b.
PVA is used as an alignment film 105b on the upper glass substrate 2b.
(Polyvinyl alcohol), nylon is applied to the lower glass substrate 2a as an alignment film 105a. The alignment films 105a and 105b of both substrates 2a and 2b are subjected to uniaxial alignment processing by parallel rubbing under the same conditions. The two glass substrates 2a and 2b are bonded together so that the cell thickness becomes 1.5 μm.

SCE13R (manufactured by Merck) is injected between the two glass substrates as a liquid crystal 107 exhibiting a smectic C phase. In addition, as the alignment state of the liquid crystal, the liquid crystal is cooled from the isotropic phase, and two alignment states UP
And DOWN are realized, and a half-stability uniform C2U orientation is realized. SCE13R is a liquid crystal having positive biaxial dielectric anisotropy.

Further, regarding the polarizing plates 12a and 12b,
One of the polarizing plates is oriented such that its polarization axis is parallel to the optical axis of the liquid crystal, and the other polarizing plate is oriented such that a dark state is obtained in a direction whose polarization axis is orthogonal to that of the one polarizing plate. Installed in Here, the angle formed by the optical axis of the liquid crystal with respect to the smectic layer normal was 6.3 °.

The other structure of the liquid crystal cell of this embodiment is the same as that of the conventional liquid crystal cell shown in FIG.

In this embodiment having such a configuration, the frequency of 60 Hz
Was applied to the liquid crystal while changing the voltage, and the change in the optical axis of the liquid crystal was examined. The result shown in FIG. 6 was obtained.
As the voltage increases, the angle (θm) between the optical axis of the liquid crystal and the normal to the smectic layer increases. FIG. 7 shows the change of the transmitted light due to the change of the optical axis at this time. There is a threshold value near 2 V, and the voltage-transmitted light characteristic as usually seen in a nematic liquid crystal is obtained. . Also, by applying a waveform determined by a voltage averaging method used in a normal nematic liquid crystal display device,
When the display device of this example was driven, information could be selectively displayed.

This display device is compatible with a ferroelectric liquid crystal.
Since the transmitted light changes continuously as shown in FIG. 7 instead of the value display, an arbitrary gradation display can be performed.

When the viewing angle characteristics were measured, the front direction was set to 0 ° and the substrate surface was set to 90 °, and the contrast and the number of gradations were not different from the front up to ± 80 ° in the vertical direction and ± 75 ° in the horizontal direction. A display with high visibility was obtained.

(Embodiment 2) FIG. 4A is a sectional view showing the structure of a liquid crystal cell of a liquid crystal display according to a second embodiment of the present invention. In the figure, reference numeral 200 denotes a liquid crystal cell of this embodiment. In this liquid crystal cell 200, the insulating films 204a, 20
As 4b, OCD TYPE2 (manufactured by Tokyo Ohka Co., Ltd.) is formed on the upper and lower glass substrates 2b and 2a, respectively, as alignment films 205a and 205b. The upper and lower substrates 2a and 2b are subjected to rubbing treatments with different pushing amounts, and these substrates are bonded to each other so that the cell thickness becomes 1.5 μm. Here, the rubbing direction is based on parallel processing.

A smectic C is provided between the two glass substrates.
SCE13R (manufactured by Merck) is injected as a liquid crystal 207 indicating a phase. Further, as the alignment state of the liquid crystal, the liquid crystal is cooled from the isotropic phase to realize a monostable and uniform C2U alignment in which the two alignment states UP and DOWN are not mixed. As described above, by performing rubbing treatments having different intensities between one and the other of the pair of substrates, it was possible to obtain a half-stable orientation in the smectic C-phase liquid crystal.

Further, regarding the polarizing plates 12a and 12b,
A dark state can be obtained by setting one polarizing plate so that its polarization axis is parallel to the optical axis of the liquid crystal, and setting the other polarizing plate so that its polarization axis is orthogonal to that of the one polarizing plate. It is installed as follows.

The other structure of the liquid crystal cell of this embodiment is the same as that of the conventional liquid crystal cell shown in FIG.

In this embodiment, when a rectangular wave was applied to the liquid crystal cell having the above configuration, the liquid crystal cell exhibited a voltage-transmitted light characteristic having a threshold value as in the first embodiment. Also,
When the waveform determined by the voltage averaging method was applied to the liquid crystal to drive the liquid crystal cell, information could be selectively displayed. As a result, a gradation display with a wide viewing angle characteristic was obtained by the display device of the present embodiment as in the first embodiment.

(Embodiment 3) FIG. 4B is a sectional view showing the structure of a liquid crystal cell of a liquid crystal display according to a third embodiment of the present invention. In the figure, reference numeral 300 denotes a liquid crystal cell of this embodiment. In this liquid crystal cell 300, the insulating films 304b, 30
4a, OCDTYPE2 (manufactured by Tokyo Ohka Co., Ltd.) is formed on the upper glass substrate 2b, ZQ-3 (manufactured by Catalyst Chemicals Co., Ltd.) is formed on the lower glass substrate 2a, and nylon is used as the alignment films 305a, 305b. And both substrates are subjected to parallel rubbing under the same conditions. The two substrates 2a and 2b are bonded together so that the cell thickness becomes 1.5 μm.

Further, SCE13R (manufactured by Merck) is injected as a liquid crystal 307 exhibiting a smectic C phase between the two glass substrates. In addition, as the alignment state of the liquid crystal, the liquid crystal is cooled from the isotropic phase, and two alignment states UP
And DOWN are realized, and a half-stability uniform C2U orientation is realized. As described above, by forming different insulating films on the upper and lower substrates, it was possible to obtain a half-stable orientation in the smectic C-phase liquid crystal.

Further, regarding the polarizing plates 12a and 12b,
A dark state can be obtained by setting one polarizing plate so that its polarization axis is parallel to the optical axis of the liquid crystal, and setting the other polarizing plate so that its polarization axis is orthogonal to that of the one polarizing plate. It is installed as follows.

The other structure of the liquid crystal cell of this embodiment is the same as that of the conventional liquid crystal cell shown in FIG.

In this embodiment, when a rectangular wave was applied to the liquid crystal cell having the above configuration, the liquid crystal cell exhibited a voltage-transmitted light characteristic having a threshold value as in the first and second embodiments. In addition, when the waveform determined by the voltage averaging method was applied to the liquid crystal cell and driven, information could be selectively displayed. With this display device, a gradation display with a wide viewing angle characteristic was obtained as in the first and second embodiments.

(Embodiment 4) FIG. 4C is a sectional view showing the structure of a liquid crystal cell of a liquid crystal display according to a fourth embodiment of the present invention. In the figure, reference numeral 400 denotes a liquid crystal cell of this embodiment. In this liquid crystal cell 400, the upper glass substrate 2b
OCD TYPE2 (manufactured by Tokyo Ohka Co., Ltd.) is formed as an insulating film 404b, and no insulating film is formed on the lower glass substrate 2a. As the alignment films 405b and 405a, nylon is formed on the upper and lower glass substrates 2b and 2a, and both substrates are subjected to parallel rubbing under the same conditions. The two substrates are bonded so that the cell thickness becomes 1.5 μm.

Further, SCE13R (manufactured by Merck) is injected as a liquid crystal 407 exhibiting a smectic C phase between the two glass substrates. In addition, as the alignment state of the liquid crystal, the liquid crystal is cooled from the isotropic phase, and two alignment states UP
And DOWN are realized, and a half-stability uniform C2U orientation is realized. As described above, even with the cell structure in which the insulating film was formed only on one side of the substrate, it was possible to obtain a half-stable orientation in the smectic C-phase liquid crystal.

Further, regarding the polarizing plates 12a and 12b,
A dark state can be obtained by setting one polarizing plate so that its polarization axis is parallel to the optical axis of the liquid crystal, and setting the other polarizing plate so that its polarization axis is orthogonal to that of the one polarizing plate. It is installed as follows.

The other structure of the liquid crystal cell of this embodiment is the same as that of the conventional liquid crystal cell shown in FIG.

In this embodiment, when a rectangular wave was applied to the liquid crystal cell having the above-described structure, the liquid crystal cell exhibited a voltage-transmitted light characteristic having a threshold value similarly to the first, second, and third embodiments. Indicated. When the liquid crystal cell was driven by applying the waveform determined by the voltage averaging method to the liquid crystal, information could be selectively displayed. With the display device of this embodiment, a gradation display with a wide viewing angle characteristic was obtained as in the first, second, and third embodiments.

In the above embodiment, the structure of the liquid crystal cell is the same as that of the conventional liquid crystal cell shown in FIG. 8, but the structure of the liquid crystal cell is not limited to this. May be provided with a substrate on which is formed.

Therefore, as a modified example of the above-described first to fourth embodiments, the liquid crystal cell of each of the embodiments was manufactured such that one of a pair of opposed substrates had a structure having a TFT.

In any of the modifications of the first to fourth embodiments, the alignment state of the liquid crystal is such that the two alignment states UP and DOWN are uniform and half-stable.
2U orientation could be realized.

Here, each of the above-described modifications is different from the above-mentioned respective embodiments only in that a TFT is formed as a switching element on a substrate, and the other configuration is the same. For example, as for a pair of polarizing plates, one polarizing plate has a polarizing axis in a direction parallel to the optical axis of the liquid crystal, and the other polarizing plate has a polarizing axis of the one polarizing plate. It is installed so that a dark state can be obtained in the direction perpendicular to the direction.

In the modification of the first to fourth embodiments, a liquid crystal cell is driven by a TFT driving voltage used for a nematic liquid crystal, thereby selectively displaying information in a liquid crystal constituting a pixel. Was able to do.
As a result, in each of the above-described modified examples, the above-described first to fourth embodiments are performed.
A gray scale display having a wide viewing angle characteristic was obtained in the same manner as in the above.

The present invention is not limited to the above-described embodiment and its modified examples. As the alignment state of the liquid crystal in the smectic phase, a uniform half-stable alignment can be obtained, and the switching of the optical axis direction of the liquid crystal can be performed. Any means may be used as long as it has means for applying a voltage and means for optically discriminating the change in the optical axis.

[0079]

As described above, according to the liquid crystal display device of the present invention, there is provided a smectic C-phase liquid crystal in which the liquid crystal molecules are unidirectionally aligned in parallel with the electrode film, and a voltage is selectively applied to the electrode film. By doing so, the direction of the optical axis of the liquid crystal is switched, and the change in the optical axis of the liquid crystal is optically identified. Therefore, there is an effect that a display with a high contrast and a wide viewing angle can be realized.

[Brief description of the drawings]

FIG. 1 is a diagram showing a cross-sectional structure of a liquid crystal cell of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining in principle the molecular orientation of a smectic C-phase liquid crystal and a ferroelectric liquid crystal.

FIG. 3 is a diagram illustrating the molecular orientation of a smectic C-phase liquid crystal and a ferroelectric liquid crystal assuming the state of liquid crystal molecules in an actual liquid crystal cell.

4A and 4B are views for explaining a liquid crystal display device according to another embodiment of the present invention. FIG. 4A is a cross-sectional structure of a liquid crystal cell according to a second embodiment, and FIG. FIG. 4C is a diagram showing a cross-sectional structure of the liquid crystal cell according to the fourth embodiment.

FIG. 5 is a diagram for explaining a change in the optical axis of the liquid crystal in the liquid crystal display device according to the first to fourth embodiments of the present invention.

FIG. 6 is a diagram showing a voltage-optical axis change characteristic in the liquid crystal display device of each of the above embodiments.

FIG. 7 is a diagram showing voltage-transmitted light characteristics in the liquid crystal display devices of the above embodiments.

8A and 8B are views for explaining a conventional liquid crystal display device, FIG. 8A is a view showing a cross-sectional structure of the liquid crystal cell, and FIG. 8B is a view for explaining the movement of molecules of a conventional nematic liquid crystal. FIG.

[Explanation of symbols]

2a Lower glass substrate 2b Upper glass substrate 3a Signal electrode 3b Scanning electrode 6,8 Sealant 9 Spacer 10,11 Counter substrate 100,200,300,400 Liquid crystal display device (liquid crystal cell) 104a, 104b, 204a, 204b, 304a ,
304b, 404b insulating films 105a, 105b, 205a, 205b, 305a,
305b, 405a, 405b Alignment film 107, 207, 307, 407 Smectic C phase liquid crystal

Claims (4)

(57) [Claims] 1. A pair of translucent substrates each having at least an electrode film and an alignment film disposed opposite to each other; a smectic C-phase liquid crystal interposed between the pair of translucent substrates; A driving means for applying a voltage to switch the direction of the optical axis of the liquid crystal molecules in the smectic C-phase liquid crystal; and an identification means for optically identifying a change in the optical axis of the liquid crystal molecules in the smectic C-phase liquid crystal. A liquid crystal display device in which the smectic C-phase liquid crystal is one in which liquid crystal molecules are semi-stablely aligned such that the major axis of the liquid crystal molecules is parallel to the electrode film. 2. The substrate according to claim 1, wherein each of the pair of translucent substrates is formed with an insulating film having a different material from that of the one substrate and the other substrate so as to cover the electrode film. Liquid crystal display. 3. The liquid crystal display device according to claim 1, wherein each of the pair of light-transmitting substrates is formed with an alignment film whose constituent material is different between one substrate and the other substrate. 4. The liquid crystal display according to claim 1, wherein the alignment film formed on one of the pair of translucent substrates and the alignment film formed on the other side are subjected to rubbing treatment under different conditions. apparatus.