JPH09281526A - Liquid crystal electro-optic device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an liquid crystal electro-optic device which has a high contrast and a wide visual field angle without utilizing polarizing plates. SOLUTION: Electric fields parallel with substrates are formed between a pair of electrodes 110 and 112 arranged on the TFT substrate 101 side. The liquid crystal molecules of a light controllable layer are electro-optically responded by these electric fields. The light controllable layer is composed by a liquid crystal material, an optically active material and dichromatic dyestuff. The device is so formed that the spiral pitch p of the liquid crystal material attains 1<=p<=15(μm), the cell thickness d attains 2<=d<=25(μm), the twist angle θ of the liquid crystal molecules attains θ<=300 deg. and the spacing L between the electrodes 110 and 112 attains L<25(μm).

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD [0001] The invention disclosed in the present specification is:
The present invention relates to a liquid crystal electro-optical device which has good electric characteristics and good contrast and can obtain a bright and uniform display on the entire screen.

[0002]

2. Description of the Related Art A liquid crystal electro-optical device has a structure in which a liquid crystal material, which is generally an organic material, is sandwiched between a pair of substrates. Then, the intensity of the electric field emitted from the electrodes formed on the pair of substrates is changed to modulate the light traveling through the liquid crystal material. The result of this optical modulation is displayed.

Therefore, if a specific electric signal is applied to the electrodes, the electric signal can be displayed in a visually recognizable state. Further, a desired image can be formed by combining a plurality of the electrodes and applying image data.

In this conventional liquid crystal electro-optical device,
Light modulation is performed by applying the electric field perpendicularly to the substrate and changing the electric field strength so that the alignment direction of the liquid crystal molecules, which are generally rod-shaped, is parallel to the substrate or perpendicular to the substrate. It was realized by changing.

Generally, in this case, light is modulated by utilizing optical anisotropy, which is one of the characteristics of the liquid crystal material.
Therefore, a polarizing plate is arranged in the device so that the incident light is linearly polarized.

However, the liquid crystal electro-optical device adopting such an operation method has a normal display state when viewed from a direction perpendicular to the display surface, but when viewed obliquely, the display is dark and unclear. The phenomenon of discoloration was seen in the case of color display.

This phenomenon is explained as follows from the relationship between the output light from the liquid crystal electro-optical device and the alignment direction of the liquid crystal molecules.

When the structure in which the liquid crystal molecules are arranged in a direction perpendicular to the substrate is adopted, an alignment state in which the major axis directions of the liquid crystal molecules are aligned is realized at the time of predetermined display. In this state, the output light is observed from the vertical plane of the liquid crystal molecules.

In this state, when viewed from a direction slightly deviated from the direction perpendicular to the substrate, the line of sight is slightly inclined with respect to the long axis of the liquid crystal molecules. This means that the observed area of the output light varies greatly depending on the viewing direction.

Therefore, the viewing angle characteristic for the observer is
The more it deviates from the vertical direction, the greater the deterioration.

As a method for solving the above problem, a method different from the operation mode of the conventional liquid crystal electro-optical device has been proposed. This is an operation mode in which liquid crystal molecules rotate only in a direction parallel to the substrate to change optical characteristics. The details are disclosed in Japanese Examined Patent Publication No. 63-21907. Hereinafter, this operation mode is referred to as an IPS mode.

In the IPS mode, an electric field is formed between a pair of electrodes formed on one substrate. This electric field has its main component in the direction parallel to the substrate and the liquid crystal layer. The electric field causes liquid crystal molecules to rotate in a plane parallel to the substrate.

Therefore, it is possible to solve the above-mentioned problem of the viewing angle caused by the liquid crystal molecules being vertically aligned during the operation.

However, since the IPS mode uses the birefringence due to the optical anisotropy of the liquid crystal material to display bright and dark, a polarizing plate is indispensable. However, the absorption of light by the polarizing plate is large, which causes a decrease in light transmittance.

Various liquid crystal electro-optical devices have been proposed in which the reduction of the light transmittance due to the polarizing plate as described above is improved.

Among them, the guest-host mode which does not require a polarizing plate is known as a method in which the conventional technique for manufacturing a liquid crystal electro-optical device can be used as it is. Especially White and Tayl
The one invented by or is known as a typical one. Hereinafter, this operation mode is referred to as WT type.

In general, the guest-host mode is an operation mode in which a liquid crystal material added with a dichroic dye is used. The reason why it is called the guest-host mode is that the liquid crystal molecule is regarded as the host and the dichroic dye is regarded as the guest.

Among them, in the WT type, the cholesteric liquid crystal undergoes a phase transition to a nematic phase by switching between no voltage application and voltage application. Thereby, absorption or transmission of light is selected.

The guest-host mode in which the polarizing plate is unnecessary is described in "Liquid Crystal Display", edited by The Television Society, supervised by Takanori Ogoshi, pp. 84-94.
In addition, it is described in "Basics of Liquid Crystal and Display Applications", Corona Publishing Co., Masami Yoshino, Masanori Ozaki, pp. 143-147.

However, in the conventional guest-host type liquid crystal electro-optical device, when the light is transmitted, the optical axes of the liquid crystal molecules are aligned in the direction perpendicular to the substrate surface. As a result, the above-mentioned problem of the viewing angle also occurs in the guest-host type liquid crystal electro-optical device.

For example, even when an electric field is applied to bring the device into a non-colored state, it may appear colored depending on the viewing angle.

[0022]

As described above, I
The liquid crystal electro-optical device that operates in the PS mode is characterized by a wide viewing angle. However, the use of the polarizing plate has a drawback that the screen becomes dark.

On the other hand, the guest-host mode which does not require a polarizing plate is characterized in that the incident light can be output as it is without the need for a polarizing plate and the light can be effectively used. However, it has a drawback that the viewing angle dependency is large as seen in the conventional liquid crystal electro-optical device.

The invention disclosed in the present specification eliminates the above-mentioned drawbacks, and has the above-mentioned significance, that is, the high viewing angle characteristic of the IPS mode, and the effective utilization of light in the guest-host mode. A liquid crystal electro-optical device having both functions is provided.

[0025]

The invention disclosed in the present specification is characterized in that in a liquid crystal electro-optical device driven by a lateral electric field, light is transmitted and absorbed by a light control layer formed by liquid crystal. The feature is that display is possible without using a polarizing plate.

That is, one of the inventions disclosed in this specification is to provide a pair of substrates, at least one of which has a light-transmitting property, a dimming layer sandwiched between the substrates, and a direction parallel to the substrates. Means for applying an electric field, and the light control layer is composed of at least a liquid crystal, an optically active substance, and a dichroic dye.

Another aspect of the present invention is to provide a pair of substrates, at least one of which has a light-transmitting property, a dimming layer made of a liquid crystal material containing a dichroic dye sandwiched between the substrates, and the dimming layer. And a means for applying an electric field in a direction parallel to the substrate, wherein the light control layer is at least a liquid crystal,
It is characterized in that it is composed of an optically active substance and a dichroic dye.

As a specific example of the liquid crystal electro-optical device utilizing the invention disclosed in this specification, there is a configuration shown in FIG.

In FIG. 2, the first and second substrates (1
01) and (201) are made of a material having a light-transmitting property and having a certain strength against an external force. As a material forming the first and second substrates (101, 201), for example, an inorganic material such as glass or quartz can be used.

A liquid crystal material is provided between the substrates to control the light control layer (20).
It is clamped as 4). As the liquid crystal material, a dichroic dye and an optically active substance were added to the liquid crystal.

As a means for applying an electric field, a metal material such as copper, aluminum, tantalum, titanium or chromium, or a silicide material is used. Alternatively, a light-transmitting conductive material such as ITO (indium tin oxide), tin oxide, or indium oxide can be used.

Further, the pair of substrates (101, 201)
A sealant (202) is formed in a desired pattern as an adhesive in order to fix the.

Further, the pair of substrates (101, 20)
A spacer (203) is arranged to keep the distance of 1) constant throughout the cell.

In the liquid crystal electro-optical device disclosed in this specification, the cell parameters are set as follows in order to obtain a good display.

(1) Wavelength λ of incident light (generally 380 nm
˜780 nm), refractive index anisotropy Δn, and spiral pitch p
The relationship is λ ≧ Δn · p. (2) The spiral pitch p is set within the range of 1 ≦ p ≦ 15 (unit: μm). (3) The cell thickness d is set within the range of 1 ≦ d ≦ 10 (unit: μm). (4) The orientation twist angle θ of the liquid crystal molecules on the upper and lower substrates is θ ≦
The range is 300 °. (5) The distance L between the electrodes is in the range of L <25 μm.
(The lower limit is about 1 μm)

As a driving method, an active matrix method, a multiplex method or the like can be used.

In the multiplex system, the first substrate (1
01) Only two kinds of electrodes, a display electrode and a reference electrode, need to be formed on top, but in the case of the active matrix system, a non-linear element such as a thin film transistor (TFT) or a diode is formed as a switching element in addition to this in each pixel. To do.

As the TFT, one using a-Si (amorphous silicon) or P-Si (polycrystalline) silicon for the active layer can be used. In the case of the active matrix system, the structure of the drive element may be a known structure such as a stagger type or an inverted stagger type.

The electrode cross section is not limited to a rectangle or trapezoid,
You may make it a gently curved surface. If the electrode cross section is gentle, a continuous transverse electric field can be formed with a gentle change in strength.

On the other hand, for the counter substrate (201), TF
It is possible to use the same material as the substrate on which T is formed. Further, although it is not necessary to form an electrode on the counter substrate, an electrode may be formed on a part or the whole surface of the substrate in some cases. As the electrode material at this time, in addition to the above metals, a material having a light-transmitting property, such as ITO, can be used.

On the counter substrate (201) or TF
It is effective to dispose means (black matrix) for shielding the portion not related to display for improving the contrast on the T substrate (101) or both substrates. The light shielding means can be made of a metal such as Cr or a polymer material in which a black pigment is dispersed.

As the liquid crystal, nematic liquid crystal or the like can be used. Further, an optically active substance is added to the liquid crystal material so as to exhibit a cholesteric phase. Further, the concentration of the dichroic dye with respect to the liquid crystal is preferably around 1% by weight. Note that the liquid crystal is not limited to the nematic type, and may be any liquid crystal that exhibits a cholesteric phase in a used state.

Here, a nematic liquid crystal containing an optically active substance and a dichroic dye (positive type) are used in combination.

Further, as a display form, there are a reflection type and a transmission type. In the reflection type, a reflection plate made of metal or the like is formed on one of the pair of substrates. Further, the metallic reflector can also serve as the pixel electrode.

The switching principle of the liquid crystal electro-optical device of the invention disclosed in this specification will be described.

In the light control layer when no electric field is applied, the liquid crystal / dichroic dye molecules are oriented in a spiral shape as shown in FIG.

In this state, the molecular long axis of the dichroic dye contained in the liquid crystal is aligned in any direction with the direction parallel to the substrate and perpendicular to the substrate as the axis. . Therefore, incident natural light absorbs any polarized component. As a result, a dark state is realized.

On the other hand, when an electric field is applied, the molecular long axis of the liquid crystal / dichroic dye is oriented in the direction of the electric field. Here, since the electric field is applied in the direction parallel to the substrate, the molecular long axis of the dichroic dye contained in the liquid crystal molecules and the liquid crystal material is parallel to the substrate and aligned in a predetermined direction. To do.

At this time, if a positive dye is used, the light in the long axis direction of the dichroic dye is absorbed. However, the absorption of light in a direction deviated from the major axis direction is not so great.
Therefore, the incident light passes through the light control layer.

Although the light transmission amount is slightly absorbed by the dichroic dye, it is much larger than that of the liquid crystal electro-optical device driven by the IPS mode using the conventional polarizing plate. This provides a bright display.

In driving the liquid crystal, switching of liquid crystal molecules is performed by an electric field parallel to the substrate,
It is possible to reduce the viewing angle dependence that is seen in conventional liquid crystal displays.

Further, since the step of forming the polarizing plate is eliminated, the liquid crystal electro-optical device can be manufactured in a smaller number of steps as compared with the conventional IPS mode.

Next, the reasons for limiting various parameters will be described. The characteristics of the liquid crystal electro-optical device disclosed in this specification depend on (1) cell thickness d (2) interelectrode distance L (3) liquid crystal refractive index anisotropy Δn (4) spiral pitch p, and other cell parameters. To do.

In order to allow natural light to be absorbed by the light control layer, the relationship between the refractive index anisotropy Δn and the spiral pitch p is λ ≧.
Set so as to satisfy Δn · p.

The pitch p has a helical structure of liquid crystal molecules of 3
It is defined as the distance to make a 60 ° turn.

By satisfying the above relational expression, each polarization component of incident light can be effectively absorbed in the light control layer.

If each parameter does not satisfy the above relational expression, a component that is not absorbed in the dimming layer remains in the polarized component of the incident light to the dimming layer. In this case, light is transmitted even in the dark state. This causes a decrease in display contrast.

In the invention disclosed in this specification, by reducing the spiral pitch p, the light control layer can more effectively absorb light. Therefore, the display contrast can be further increased.

However, if the spiral pitch p is made too small, the threshold value becomes high and the drive voltage becomes high. Therefore, the power consumption becomes large, and the low power consumption characteristics of the liquid crystal display cannot be fully utilized. This is a problem common to both the multiplex type and the active matrix type liquid crystal displays.

Further, if the driving voltage is high, the load on the thin film transistor is heavy, and the durability of the display is low.

As another problem, as the spiral pitch p becomes smaller, the phenomenon that the steepness of the threshold of the liquid crystal material becomes lower occurs. Therefore, when the spiral pitch p becomes small, switching cannot be performed at high speed.

In this case, when switching from the no-voltage-applied state to the voltage-applied state, the light absorption state continues for a while, and the light transmission state is not quickly realized.

On the contrary, if the voltage is switched from the voltage-applied state to the voltage-unapplied state, the light absorption state is not promptly realized, and the light passes through the light control layer for a while. Therefore, it is difficult to realize a high-speed display.

As described above, the relationship between the contrast and the threshold characteristic has a trade-off relationship. And the relationship depends on the spiral pitch.

In the invention disclosed in this specification, the spiral pitch p is set within the range of 1 ≦ p ≦ 15 (μm). In this way, both the contrast and threshold characteristics can be satisfied. Then, the display state of the display can be maintained.

The display characteristics also depend on the cell thickness d.
Further, the display state is influenced not only by the cell thickness but also by the viscosity of the optically active substance to be added and the helical pitch p of the liquid crystal.

Therefore, in order to reduce these effects, a dichroic dye, which is said to have relatively little thickening effect on the liquid crystal layer by addition, is used.

The results of examining the influence of the cell thickness d when an azo dye is used as the dichroic dye are shown below.

Here, the helical pitch p of the liquid crystal is kept constant by adjusting the amount of the optically active substance added.

The threshold characteristics, contrast, rise time, and display uniformity in the cell thickness direction depend on the cell thickness of the entire dimming layer having a certain spiral pitch p.

As the cell thickness d decreases, the threshold increases,
The drive voltage will increase. Therefore, it is difficult to realize low power consumption. Further, a voltage exceeding the voltage setting range of the conventional drive circuit is required. Therefore, a new circuit design is needed.

However, when the cell thickness d increases, the electric field strength becomes uneven. As a result, in the rise time of the liquid crystal material when the electric field is applied (the time when the orientation of the liquid crystal material changes in the substrate parallel direction and in a predetermined direction),
Variations occur. For this reason, when the hue changes due to the dichroic dye, the display of the color fluctuates.

Further, the contrast decreases as the cell thickness d increases. Therefore, it is desirable to reduce the cell thickness in order to improve the contrast.

Particularly in the invention disclosed in this specification,
The cell thickness d is set in the range of 1 ≦ d ≦ 10 (μm). This makes it possible to obtain a relatively good display in terms of threshold, contrast, rise time, and display uniformity in the cell thickness direction.

It has been confirmed that the contrast is increased by increasing the orientation twist angle θ of the liquid crystal molecules.

On the other hand, if the twist angle θ is too large, the rising characteristics when the electric field is turned on and the falling characteristics when the electric field is turned off do not match, which is not preferable for a display device.

The range in which the two characteristics of the contrast and the threshold value are good is preferably θ ≦ 300 °.

The point where the distance L between the electrodes is 25 μm or less will be described below.

First, the alignment state of the dichroic dye molecules by the electric field will be described. The dichroic dye is aligned in the same direction as the liquid crystal molecules. That is, when a lateral electric field is applied, the liquid crystal molecules are oriented in a predetermined direction with the major axis direction parallel to the substrate. Following this, the dichroic dye molecules also have the major axis parallel to the substrate and are arranged in a predetermined direction.

In the invention disclosed in this specification, the positive type dichroic dye is switched by the lateral electric field. Therefore, even when an electric field is applied, light is absorbed in the long axis direction of the dichroic dye, so that some light absorption occurs.

During conventional vertical electric field driving, the dichroic dye is vertically aligned. Therefore, light absorption by the positive type dichroic dye does not occur. That is, the method using the lateral electric field drive is theoretically inevitable to reduce the contrast, as compared with the method using the vertical electric field drive.

Therefore, the lateral electric field formed affects the light transmission state of the light control layer. As described above, the dichroic dye has the major axis direction parallel to the substrate surface. However, the electric field near the electrodes is perpendicular to the substrate. That is, the long axis of the dichroic dye molecule near the electrode is oriented perpendicular to the substrate.

The positive type dichroic dye has a large absorption coefficient in the major axis direction. Further, there is almost no light absorption in the minor axis direction of the dye. That is, the vertically-oriented dichroic dye near the electrodes hardly absorbs light.

Therefore, when the distance L between the electrodes is relatively short, the total light absorption by the dichroic dye is small. This is because the shorter the distance between the electrodes is, the steeper the rising of the electric field formed near the electrodes is.

In the invention disclosed in this specification, a light transmission state is realized when a lateral electric field is applied. Therefore, the overall contrast can be increased by increasing the light transmission amount when an electric field is applied. That is, it is desirable that the distance L between the electrodes is small in terms of contrast.

Also in the threshold characteristic, the inter-electrode distance L
Influences. When the inter-electrode distance L is increased, the threshold value is increased and the drive voltage is increased. Therefore, it is difficult to realize low voltage driving.

According to the experiment by the present inventor, when the change in contrast was measured by changing the distance L between the electrodes, L <
It was found that when the thickness is 25 μm (adjustment is about 1 μm), a relatively good contrast can be obtained.

[0088]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described with reference to FIG. FIG. 3 is a schematic diagram when the dimming layer is in a state in which incident light is not transmitted, that is, in a dark state.

In this case, as shown in FIG. 3, the alignment state of the light control layer is such that the alignment vector of the liquid crystal molecule (301) is aligned with the minor axis direction of the liquid crystal molecule (301) as an axis.
Each time the layer formed in 1) changes, the spiral state is gradually changed.

In the state shown in FIG. 3, the major axes of the liquid crystal molecules (301) and the dichroic dye (302) are the substrate (101).
This is an example of a case in which there is an orientation state in which the substrate is rotated from the substrate to the substrate (201) by 180 ° about the direction perpendicular to the substrate.

When no electric field is applied in the direction parallel to the substrate, the dichroic dye added to the liquid crystal is oriented in all directions with the direction perpendicular to the substrate as an axis, as shown in FIG.

Therefore, no matter which component of natural light is incident, it has a component in the long axis direction of the dichroic dye molecule. In this case, most of the incident light is absorbed by the dichroic dye molecules, so that the incident light does not pass through the light control layer. That is, a dark state can be obtained.

On the other hand, when an electric field is applied, as shown in FIG. 4, the molecules constituting the light control layer (204) have their major axes oriented in the electric field direction parallel to the substrate.

Therefore, of the incident natural light, the polarized component parallel to the molecular long axis direction is absorbed, but the other components are not absorbed and are transmitted through the light control layer. Therefore, a transparent state is visually obtained. That is, a bright state is obtained.

Then, the black state and the transparent state can be displayed by switching the state in which the electric field is not applied and the state in which the electric field is applied.

[0096]

EXAMPLE In this example, a manufacturing process of the liquid crystal electro-optical device shown in FIG. 2 will be described. FIG. 2 is a schematic sectional view of the liquid crystal electro-optical device of this embodiment. The liquid crystal electro-optical device in FIG. 2 uses the substrate on which the TFT, the wiring, and the like as shown in FIG. 1 are formed as one substrate.

In FIG. 1, FIG. 1A is a schematic top view of the pixel portion. FIG. 1B is a line A in FIG.
It is a schematic diagram of a section in -A '.

First, a silicon oxide film is formed as a base film (102) on a glass substrate (101) by a plasma CVD method or a thermal CVD method to a thickness of 2000 Å.

At this time, the substrate (hereinafter referred to as a TFT substrate) 10
For No. 1, it is desirable to use non-alkali glass such as Corning # 1737 or quartz glass.

For the purpose of reducing the weight of the liquid crystal electro-optical device, a film having a small birefringence, such as PES, is used.
(Polyethylene sulfate) or the like can also be used.

Next, an amorphous silicon film is formed to a thickness of 300 to 2000 Å, for example, 500 Å by plasma CVD.

Next, 600 ° C. or lower, preferably 550 ° C.
Crystallization was performed by performing thermal annealing at the following temperatures. After thermal annealing, crystallinity may be enhanced by annealing with laser light or strong light equivalent thereto.

Particularly, in the case of thermal crystallization, by adding a trace amount of a catalyst element such as nickel that promotes crystallization to the amorphous silicon film, crystallization is promoted and high crystallinity is achieved on an inexpensive glass substrate. A polysilicon film can be formed. Details are disclosed in Japanese Patent Laid-Open No. 6-244103.

The silicon film thus obtained is etched to obtain an island-shaped silicon film (103). Next, a silicon oxide film as the gate insulating film (104) is formed by a plasma CVD method using TEOS to a thickness of 500 to 1200Å,
For example, a film is formed to a thickness of 1000Å.

Thereafter, aluminum is formed to a thickness of 2000 to 6000Å by a sputtering method, and this is patterned to obtain a gate line (105). Gate line (10
The width of 5) is 8 μm.

The gate line (105) is anodized on its surface by anodizing using a weak acid solution as a chemical conversion solution.
6) is formed. This anodic oxide film (106) has a dense film quality. The thickness of the anodic oxide film (106) is 700 Å.

The anodic oxide film (106) has a function of mechanically and electrically protecting the gate electrode.

Next, by ion doping, impurity ions are implanted into the island-shaped silicon region (103) in a self-aligned manner using the gate line (105) as a mask, and n
Type or p-type conductivity is imparted to form a conductive region (107). One of the conductive layers (107) serves as a source region and the other serves as a drain region.

It is effective to use a so-called monolithic type in which a peripheral driving circuit (not shown) is provided by forming a thin film transistor made of polysilicon around the outer periphery of the active matrix region. At that time, p-channel type and n-channel type thin film transistor complementary types are manufactured.

A silicon nitride film having a thickness of 3000 to 6000Å, for example 4000Å, is formed thereon by plasma CVD to form a first interlayer insulating film (108). This may be a silicon oxide film or a multilayer film of a silicon oxide film and a silicon nitride film.

Next, a first interlayer insulating film (108) on the source region and drain region (107) of the thin film transistor.
Then, a contact hole is formed by etching. On top of that, the thickness is 2000-6000Å by the sputtering method,
For example, 3000 Å aluminum or a multilayer film of titanium and aluminum is formed and patterned to form a source line (109) and a drain electrode (110). The width of the source line (109) is 6 μm, and the drain electrode (1
The width of 10) is 8 μm.

On top of this, a polyimide or acrylic translucent organic resin film is placed in the range of 4000 to 10000Å, for example 5000.
Å Then, the second interlayer insulating film (111) is formed. It is needless to say that an inorganic material such as silicon oxide, silicon nitride, or silicon oxynitride can be used for this interlayer insulating film, but if the above-mentioned polyimide or acrylic organic material is used, unevenness due to electrodes, elements, etc. can be formed. It can be flattened.

Then, a conductive film of aluminum, copper, chromium, titanium, ITO or the like is formed and patterned by a known method such as a sputtering method to form the common line (112). The width of the common line (112) is 8 μm. Also,
As shown in FIG. 1, the common line (112) has a portion parallel to the drain electrode (110), and the distance between the common line (112) and the drain electrode (110) in this portion is 12 μm.
m.

Here, in FIG. 1B, the sectional shape of the electrode is shown as a rectangular shape, but it may be a trapezoidal shape having an inclined surface or a curved surface. In this case, after forming a photoresist, isotropic plasma etching or wet etching is performed.

Furthermore, silicon oxide of 5000 to 10000 Å, for example 5000 Å, is further formed on this as a protective film (not shown).
Formed.

Next, as shown in FIG. 2, one substrate (2
01) around the sealing material with epoxy resin (202)
And the substrates (101) and (201) are bonded together,
Form a cell.

In the present embodiment, the pair of substrates are arranged such that spherical spacers (203) having a diameter of 4 μm are sandwiched between the substrates so that the substrates are uniformly spaced over the entire panel surface. In addition,
FIG. 2 does not show the TFT element, wiring, etc. shown in FIG.

Further, the sealing material (202) is not limited to the epoxy resin, and there is no problem even if another resin such as a urethane acrylate resin is used. Further, the material of the spherical spacer may be any of inorganic and organic materials.

In this embodiment, the cell thickness is 4 μm.

Then, a liquid crystal or the like is injected between the pair of substrates (101) and (201) by a vacuum injection method or the like to form a light control layer (204).

As the material forming the light control layer (204), a material in which a dichroic dye and an optically active substance are mixed with a liquid crystal material is used.

In this embodiment, as the liquid crystal material, ZLI-3200 (manufactured by Merck) in which an azo dye is added to nematic liquid crystal is used. Its dielectric anisotropy is -4.8 and its refractive index anisotropy is +0.0437. The dye is added at 3.46%.

The nematic liquid crystal material is not limited to the above materials, and any material exhibiting nematic property at room temperature can be used.

As the dichroic dye, those having high solubility in liquid crystal and stable photochemically are desirable. Specifically, azo dyes, anthraquinone dyes, naphthoquinone dyes, perylene dyes, quinophthalone dyes,
It is possible to use a tetrazine dye, a coumarin dye, or the like.

The viscosity of the liquid crystal (light control layer 204) is changed by the addition of the dichroic dye. The change in viscosity depends on the dichroic dye added, and the azo dye has a smaller thickening effect than the anthraquinone type and other dyes.

Further, S-811 (manufactured by Merck) was added as an optically active substance to the liquid crystal material. When the optically active substance is mixed with the liquid crystal material, it exhibits a cholesteric phase at room temperature.

FIG. 3 is a schematic diagram when the light control layer is in a state in which incident light is not transmitted, that is, in a dark state.

In this case, as shown in FIG. 3, the alignment state of the light control layer (204) is such that the alignment vector of the liquid crystal molecule (301) is aligned with the minor axis direction of the liquid crystal molecule (301) as an axis. Each time the layer formed by the molecule (301) changes, the angle is gradually changed into a spiral state.

Note that FIG. 3 schematically shows the liquid crystal molecules (301) and the dichroic dye molecules (302), and their scales are not the same as those of the substrates (101, 102). Also, FIG.
The TFT element, the wiring, etc. as shown in FIG. 3, the spacer and the sealing material as shown in FIG. 2 are not shown in FIG. In reality, the molecules are innumerable between the substrates (101) and (201). Furthermore, an optically active substance (not shown)
Is not limited to the above materials, and any material may be used as long as it is soluble in the liquid crystal material.

In this example, the amount of the optically active substance added was adjusted so that the spiral pitch p was p = 8 μm. With such a structure, liquid crystal molecules (30
1) and the molecular long axis of the dichroic dye (302) are
From (01) to the substrate (201), the alignment state is obtained by rotating 180 ° about the direction perpendicular to the substrate as an axis.

In the liquid crystal electro-optical device shown in this embodiment, the dichroic property added to the liquid crystal material is set in the state where the electric field is not applied between the drain electrode (110) and the common electrode (112) whose interval is L. The dye (302) is oriented in all directions with the axis perpendicular to the substrate as an axis.

Here, no matter which component of natural light is incident, it has a component in the major axis direction of the dichroic dye molecule (302). Therefore, the incident light is absorbed by the dye molecules to display black. That is, a state in which incident light does not pass through the light control layer (204) is realized.

On the other hand, when an electric field is applied, as shown in FIG. 4, the molecules constituting the light control layer (204) are in a state in which their major axes are oriented in the electric field direction parallel to the substrate (101).

Therefore, of the incident natural light, the polarized component parallel to the molecular long axis direction is absorbed, but the other components are not absorbed and are transmitted through the light control layer. Therefore, a transparent state is visually obtained. That is, a bright state is obtained.

Black and transparent states can be displayed by switching the state in which the electric field is not applied and the state in which the electric field is applied.

In this embodiment, an alignment film may be provided on at least one of the substrates (101) and (201) to exert an alignment regulating force on the liquid crystal or the like. When the alignment film is formed, a uniform liquid crystal alignment is realized by the alignment regulating force, and a display with less color unevenness is realized. In addition, the occurrence of orientation defects such as disclination can be reduced.

[0137]

By utilizing the invention disclosed in the present invention, it is possible to provide an excellent liquid crystal electro-optical device which does not require a polarizing plate, is bright, has a high contrast ratio, and has little viewing angle dependency.

[Brief description of drawings]

FIG. 1 is a schematic view of a TFT substrate of a liquid crystal electro-optical device according to an embodiment.

FIG. 2 is a schematic cross-sectional view of a liquid crystal electro-optical device according to an example.

FIG. 3 is a diagram showing a light absorption state of the liquid crystal electro-optical device of the present embodiment.

FIG. 4 is a diagram showing a light transmission state of a liquid crystal electro-optical device of an example.

FIG. 5 is a diagram showing a light transmission state of a conventional liquid crystal electro-optical device.

[Explanation of symbols]

 101, 201, 501, 502 Substrate 102 Base film 103 Silicon film 104 Gate insulating film 105 Gate line 106 Anodized film 107 Conductive area 108 First interlayer insulating film 109 Source line 110 Drain electrode 111 Second interlayer insulating film 112 Common line 202 Sealing material 203 Spacer 204 Light control layer 301, 503 Liquid crystal molecule 302, 504 Dichroic dye

Claims (10)

[Claims] 1. A pair of substrates, at least one of which has translucency, a light control layer sandwiched between the substrates, and a means for applying an electric field in a direction parallel to the substrates, A liquid crystal electro-optical device, wherein the light control layer is composed of at least a liquid crystal, an optically active substance, and a dichroic dye. 2. The liquid crystal electro-optical device according to claim 1, wherein the dichroic dye is a positive type. 3. The liquid crystal electro-optical device according to claim 1, wherein the light control layer contains liquid crystal molecules having positive dielectric anisotropy. 4. The liquid crystal electro-optical device according to claim 1, wherein the helical pitch p of the liquid crystal is in the range of 1 ≦ p ≦ 15 (unit: μm). 5. The cell thickness d according to claim 1, wherein 1 ≦ d
A liquid crystal electro-optical device having a range of ≦ 10 (unit: μm). 6. The liquid crystal electro-optical device according to claim 1, wherein the orientation twist angle θ of the liquid crystal molecules is in the range of θ ≦ 300 °. 7. The device according to claim 1, wherein the means for applying an electric field in a direction parallel to the substrate has a pair of electrodes, and the distance L between the pair of electrodes is in the range of L <25 (unit: μm). A liquid crystal electro-optical device characterized by the above. 8. A pair of substrates, at least one of which has translucency, a light control layer made of a liquid crystal material containing a dichroic dye and sandwiched between the substrates, and an electric field in a direction parallel to the substrates. And a means for orienting the light control layer, the orienting means being provided on at least one of the substrates. 9. The liquid crystal electro-optical device according to claim 8, wherein the dichroic dye is a positive type. 10. The liquid crystal electro-optical device according to claim 8, wherein the dielectric constant anisotropy of the light control layer is positive.