JPS6398632A - Liquid crystal electrooptical device - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal electrooptical device having good and uniform orientation characteristics by aligning major axes of chiral smectic liquid crystal molecules to a direction which is approximately parallel to the slant faces provided in plural numbers on one surface of a substrate being perpendicular to the direction of the edge of the slant faces. CONSTITUTION:Coating liquid for forming silicon oxide film is coated to ca. 0.5mum thickness on a glass substrate 1 provided with transparent electroconductive film 2. Then, a mold prepd. to have a slant face having 10 deg.(theta) slant angle and 1mum pitch (W) of the slant faces is allowed to contact with the coated film interposing a parting material to transfer thus the unevenness of the surface. Two substrates having thus transferred unevenness are superposed on each other arranging both surfaces having the transferred unevenness to the inside, edges of the slant faces parallel to each other, and both slant surface being parallel to each other. The outside periphery of the superposed substrates are sealed and chiral smectic liquid crystals are injected while preserving the isotropic state. By this method, it has been able to realize the orientation state of uniform and defectless liquid crystals in a large area using smectic C phase in a display device utilizing liquid crystal electrooptical effect using chiral smectic liquid crystals.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a liquid crystal electro-optical device that utilizes the electro-optic properties of a liquid crystal material to exhibit two states, particularly one using an optically active chiral smectic liquid crystal. .

[Prior art]

Liquid crystals have traditionally been used in a variety of electro-optical applications, especially as thin displays in portable electronic products.
It is widely used because of its extremely low power consumption. The liquid crystal materials used in these applications are those exhibiting a nematic or cholesterin smectic phase, and displays are performed based on the dielectric alignment effect of the material.

In this case, due to the dielectric anisotropy of the liquid crystal material itself,
Displays are performed using the phenomenon that the long axes of liquid crystal molecules are aligned in one direction on average due to an externally applied electric field. However, in this case, due to the externally applied electric field, the time for the long molecular axes of the liquid crystal material to align in one direction, that is, the electro-optical response speed, is quite slow, ranging from several tens to several hundreds of milliseconds.
The order was

This can be a very big drawback, especially when constructing a display element. In other words, in the case of a large-area matrix structure, if the number of pixels to be displayed becomes very large, the response speed will be slow, and many improvements will need to be made to the liquid crystal display driving method. This caused many problems, such as the inability to display video and the occurrence of crosstalk between pixels.

One solution to these problems is Clark (
USP4367924) proposes a new display method using smectic phase liquid crystal.

This will be briefly explained below.

This smectic liquid crystal has a layered structure of rod-shaped liquid crystal molecules as shown in Figure 2, and each molecule is perpendicular to the plane of this layer or tilted at a certain angle ψ. is doing.

In either case, the constituent liquid crystal molecules are arranged parallel to each other.

This liquid crystal exhibits optically positive birefringence, in which the speed of light in the direction perpendicular to the molecular layer is faster than the speed of light in the direction parallel to it, that is, the speed of light in the so-called molecular axis direction is faster.

Among these smectic liquid crystals, Clark et al. discovered the C phase among the optically active chiral smectic liquid crystals.

We are proposing a new display method using liquid crystals that exhibit ferroelectric properties such as H-phase.

For example, a ferroelectric liquid crystal exhibiting a chiral smectic C phase as shown in Figure 2 generally has an electric dipole density, P, and the direction of this P is perpendicular to the direction N of the long axis of the liquid crystal molecules. The direction is parallel to the layer plane of the smectic layer, and this is true not only for the C phase but also for other phases. Due to the presence of electric dipoles in these ferroelectric liquid crystals,
These liquid crystals change the direction in which their molecules tilt depending on the direction of an externally applied electric field.

In other words, if an electric field of 10 E is applied from the outside to the liquid crystal from the front to the back of the paper shown in Figure 2, and the slope is ψ, if an electric field of -E is applied, -ψ
Display is performed using these two states, ψ and -ψ, which are tilted at an angle of Due to the anisotropy, the response time was much faster, on the order of several to several hundred microseconds, compared to the case where the response was based on the presence or absence of an external electric field.

In order to display using two states due to such spontaneous polarization, it is necessary to uniformly align liquid crystal molecules in the uniaxial direction in the entire liquid crystal element.

In addition, since this chiral smectic liquid crystal has strong interactions between molecules, when an alignment treatment is applied to the substrate surface to give an alignment control force to the liquid crystal molecules, molecules not only near the substrate surface but also far away can be In other words, it can be said that the alignment of liquid crystal is greatly influenced by the alignment treatment on the substrate surface.

Conventionally, a shearing method, a temperature gradient method, a magnetic field orientation method, a rubbing method, etc. have been used as a surface orientation treatment for a substrate to give a liquid crystal a uniaxial orientation parallel to the substrate.

Among these, the rubbing method is widely used industrially because orientation over a large area can be easily obtained.

However, there is a limit to the amount of liquid crystal that can be uniformly aligned over a large area by this rubbing method.

In other words, as a series of phase transitions of the liquid crystal phase, the equal phase -5mA-
A liquid crystal having a region exhibiting a smectic A phase on the higher temperature side than a temperature region exhibiting a chiral smectic C phase and a 3sC* or isolaboratory phase -N+SmA-SmC* can be uniformly and favorably uniaxially aligned over a large area.

However, for smectic liquid crystals with phase series other than this series, sufficient alignment cannot be obtained by this rubbing method.
It could not be used in liquid crystal electro-optical devices because a uniform, large-area, uniaxially aligned state could not be obtained. On the other hand, even if a liquid crystal with good alignment is obtained by the rubbing method, the rubbing process exerts a very strong uniaxial alignment regulating force on the liquid crystal from the substrate surface, so it is difficult to actually apply an electric field from the outside. When a ferroelectric liquid crystal is inverted, a difference appears in the inversion process due to the regulating force of this -axis orientation.

In other words, there is a difference in response speed between the case of reversing from +ψ to one ψ and the case of reversing from -ψ to +ψ. Furthermore, the liquid crystal molecules are tilted smaller than the original tilt angle ψ of the liquid crystal.

Various problems have arisen, and many problems have been desired to be solved before they can be applied to liquid crystal electro-optical devices.

[Purpose of the invention]

The present invention solves the problems seen in these conventional rubbing methods and provides a liquid crystal electro-optical device with good and uniform alignment.

[Structure of the invention]

Therefore, in the present invention, as described in the claims, ``an optically active chiral smectic liquid crystal is used, and a liquid crystal electric In the optical device, at least one surface of the two substrates constituting the liquid crystal container of the liquid crystal electro-optical device is provided with a plurality of slopes forming an angle of θ with respect to the surface, substantially parallel to the slopes, and a ridge line of the slope. A liquid crystal electro-optical device characterized by aligning the long axes of chiral smectic liquid crystal molecules in any one of the phase series of the liquid crystal in a direction that makes an angle perpendicular to the direction. It is something to do.

That is, regularly arranged slopes are formed on the surface of at least one of the two substrates of a liquid crystal container used in a liquid crystal electro-optical device, and ferroelectric liquid crystal molecules are uniaxially aligned along the direction of the slopes. It is characterized by this.

The present invention was experimentally discovered as a result of the inventors' diligent efforts to solve the problems of the conventional technology as described above.

FIGS. 1A and 1B show an example of a schematic diagram and a cross-sectional view of a substrate used in a liquid crystal electro-optical device according to the present invention.

As shown in FIG. 3A, slopes are formed on the surface of the substrate, regularly arranged and aligned in one direction. Then, the smectic liquid crystal molecules are aligned square to the slope, with their long axes aligned in a direction perpendicular to the ridge line of the slope.

In Figure (A), for the sake of explanation, it is shown that only one molecule is arranged on one slope, but in reality, multiple liquid crystal molecules are oriented with their long axes roughly aligned. There is.

At this time, the layer direction of the smectic layer formed by the smectic liquid crystal and the ridge line direction of the slope formed on the substrate roughly match, so uniform alignment without defects can be obtained.

As shown in FIG. 1(B), the most convenient shape of the slope formed on the substrate surface is a sawtooth shape.
It is sufficient that slopes substantially aligned in one direction are formed on the substrate.

Also, regarding this dimension, the angle θ of the slope is 3″≦θ≦15
'', and the interval W between the ridge lines on the slope is 0.5 μm≦W≦2 μm
A good alignment state was obtained when the level difference on the slope satisfied D≦0.3 μm.

In other words, when the angle θ of the slope is less than 36 degrees or exceeds 15 degrees, the long axis direction of the molecules of the liquid crystal does not match the perpendicular direction of the ridge line of the slope, and therefore the layer direction of the smectic layer and the ridge of the slope do not match. The line directions do not match, resulting in countless defects in the alignment of the liquid crystal.

In addition, it was found that in this case, the long molecular axes of the liquid crystal are not aligned in one direction over the entire substrate, resulting in a so-called unaligned state.

Next, the interval W between the ridge lines on the slope is less than 0.5 μm or 2 μm
If it exceeds 100%, the uniaxial alignment of liquid crystal molecules cannot be obtained over the entire substrate, and the device cannot function as a liquid crystal electro-optical device (
Become.

Furthermore, if the level difference in the slope exceeds 0.3 μm, the degree of unevenness on the substrate surface is severe and a large number of defects occur.

Conversely, as long as the above-mentioned conditions of θ, W, and D are satisfied, it is not necessary to have a sawtooth shape, and it is possible to obtain the same effect as the present invention with any shape.

Examples are shown below.

〔Example〕

First, a glass substrate (2) having a transparent conductive film (2) is used as a substrate.
Using 1), approximately 0.5% of a coating solution for forming a silicon oxide film (RnSi (OH) a-), which has the function of preventing the elution of alkali metals etc. from the glass substrate or 4-electrode film, is applied onto the same substrate.
Coat to a thickness of μm.

Next, the angle of the slope θ = 10° The interval between the ridge lines of the slope W = 1μ
A mold prepared as M is brought into contact with the film through a release material to transfer the uneven shape.

Before or during this transfer process, it was effective to raise the temperature to a level that could evaporate the solvent in the coated film (for example, 100"C) because the transferred unevenness would become sharper.

Thereafter, the entire substrate was heated to about 400''C to cure the applied film to complete a film (3) having an uneven shape.

In the case of this embodiment, the uneven shape was transferred from the mold to the silicon oxide film coated on the glass substrate, but it is also possible to use a polyimide film or a pv^ film other than the silicon oxide film. Furthermore, the uneven shape may be transferred onto the glass substrate itself or the transparent wing electric film itself.

Next, stack the two pieces of base + Ji on which the unevenness was formed, with the uneven surface facing inward and the ridge lines of the slopes parallel to each other, so that the slopes are parallel to each other, and seal the outer periphery of the liquid crystal container. was formed.

Next, chiral smectic liquid crystal was injected into the container in an equi-potent state using a conventionally known liquid crystal injection method. Although there was no difference in the degree of orientation of the liquid crystals injected at this time due to differences in the molecular structure of the materials, slight differences in orientation in the smectic C phase were observed due to differences in the phase series of the liquid crystal materials.

In other words, the phase sequence of iso-lao phase - button A phase - 5mC phase is better than the phase series of iso-lao phase → nematic phase → SmA phase → 5IIIC phase, which has no defects in the orientation in the smectic C phase and has a large area and uniform orientation. It was possible to obtain

The present invention is not limited to the manufacturing method of this embodiment, and it is possible to obtain the same effects as the present invention using other materials and shapes.

〔effect〕

According to the present invention, it is possible to easily realize a uniform, defect-free liquid crystal alignment state over a large area using a smectic C phase in a device that uses chiral smectic liquid crystal to perform display, etc. by utilizing the liquid crystal electro-optic effect. became.

In addition, unlike the conventional rubbing method, which scratches the alignment film and forces the liquid crystal molecules to align in the direction of the scratches, the characteristics of the liquid crystal material itself appear inferior to those of the liquid crystal material itself during liquid crystal display. Since the liquid crystals are not forced to line up, it is possible to fully utilize the original characteristics of the liquid crystal material itself, and remarkable improvements in characteristics are seen, particularly in response speed and contrast ratio. Further, since the structure of the present invention does not generate any dust generated during rubbing, the yield of manufacturing liquid crystal containers has improved.

[Brief explanation of the drawing]

FIGS. 1(A) and 1(B) show a schematic diagram and a cross-sectional view of a substrate used in the liquid crystal electro-optical device of the present invention. FIG. 2 shows a schematic diagram of the layer structure of a smectic liquid crystal. 1...Substrate 2...Transparent conductive film 3...Alignment film 4 with unevenness...Liquid crystal molecules θ...Angle W of slope ...... Distance between the ridge lines on the slope D ...... Steps on the slope

Claims (1)

[Scope of Claims] 1. In a liquid crystal electro-optical device that uses an optically active chiral smectic liquid crystal and exhibits two states due to differences in electro-optic properties expressed depending on the direction of an externally applied electric field, the liquid crystal electro-optical device A plurality of slopes forming an angle θ with respect to the surface are provided on at least one surface of two substrates constituting a liquid crystal container of an optical device, and the angle is approximately parallel to the slope and perpendicular to the ridge direction of the slope. A liquid crystal electro-optical device characterized in that the long axes of chiral smectic liquid crystal molecules are aligned in one of the phases of the phase series of the liquid crystal. 2. A liquid crystal electro-optical device according to claim 1, characterized in that the substrate material itself forms a plurality of slopes by heating and pressure treatment. 3. The liquid crystal electro-optic according to claim 1, wherein the transparent conductive film material formed on the substrate surface forms a plurality of slopes by applying pressure or applying pressure and heat treatment. Device. 4. A liquid crystal display according to claim 1, wherein the transparent insulating film material formed on the surface of the substrate forms a plurality of slopes by applying pressure or applying pressure and heat treatment. optical equipment. 5. A liquid crystal electro-optical device according to claim 1, wherein the angle θ between the substrate surface and the slope is 3°≦θ≦15°.