JPH0772486A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide a display element using a ferroelectric liquid crystal which can be easily controlled and can give uniform and stable halftone with good orientation. CONSTITUTION:A projecting part 16 in a stripe of 4mum line width and 1500Angstrom height is formed with the interval increased from the min. 2mum to 10mum by 0.5mum increment on a transparent electrode. An extremely narrow interval of 0.9mum is formed adjacent to stripes of the narrowest interval. This substrate is used to constitute a liquid crystal display element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical modulator using liquid crystal, and more particularly to an element structure for imparting good display characteristics by using a ferroelectric liquid crystal having memory characteristics.

[0002]

2. Description of the Related Art Ferroelectric liquid crystal (hereinafter referred to as "FLC")
Has been actively used because of its advantages such as high speed and memory. Examples include an optical shutter array, a high-definition display device driven by a simple matrix, and a high-density recording light valve combined with a photoconductor. Further, there are also expectations for the same image display by active matrix driving using a thin film transistor (TFT) or the like.

[0003]

As an indispensable subject for improving the display capability of a display element using FLC, development for obtaining a good halftone is under way. For example,
As a method for creating a mixed state of black and white domains in one pixel, Japanese Patent Laid-Open No. 59-193427 discloses a method of obtaining a halftone by imparting spontaneous unevenness or an intentional fine mosaic pattern to an electrode substrate. However, Japanese Patent Application Laid-Open No. 61-166590 discloses a method of obtaining gradation by providing a stepwise distribution in the thickness of the insulating layer.
Further, Japanese Patent Laid-Open No. 64-77023 discloses a method of displaying a halftone by obtaining an alignment state having many defects. In addition to the above, many ideas have been made such as a method of displaying gray scales by providing patterned unevenness with a periodic structure.

Although it has been confirmed that a halftone state can be created by the above-mentioned method, it is further desired that these halftones are made uniform in the pixel and a controlled gradation characteristic.

Further, in order to maintain a good contrast, it is desirable that the orientation state is such that no defects are observed.

In view of the above problems, it is an object of the present invention to provide a liquid crystal display device which is easy to control and can display good alignment and uniform and stable halftone.

[0007]

SUMMARY OF THE INVENTION The present invention is a liquid crystal display device having a ferroelectric liquid crystal sandwiched between a pair of electrode substrates, and a plurality of stripes on at least one electrode in one pixel. Forming a threshold convex in the pixel by providing a convex protrusion and changing the interval between the convex protrusions,
Furthermore, the liquid crystal display element is characterized in that a region having a particularly low threshold value is formed in the lowest region of the threshold gradient.

In the liquid crystal display element of the present invention, since the stripe-shaped convex portions are provided in one pixel at different intervals to form a threshold gradient in the pixel, good inversion area control can be carried out and uniform. Gradation characteristics can be obtained. Further, a region having a particularly low threshold value is provided in the lowest threshold region to promote formation of the inversion domain.

1 and 2 show an embodiment of the electrode substrate structure of the liquid crystal display device of the present invention. 1A is a plan view, and FIG. 1B is a cross-sectional view (AA 'cross section in FIG. 1 and BB' cross section in FIG. 2). This configuration is an example in which convex portions having a gradient in the interval are provided by patterning or mask deposition as an electrode configuration on one side (a lower substrate on the scanning electrode side in FIG. 2) of a matrix substrate for multiplex driving. The shape of the convex portion is, for example, a line width of 4 μm and a distance between lines of 2 μm to 10 μm at intervals of 0.5 μm.

In FIG. 1 (upper substrate), 11 is glass,
Transparent base made of quartz, plastic, etc., 12 is IT
A transparent electrode made of O, SnO ₂ , In ₂ O ₃ or the like, 13 is a resin such as polyimide or nylon, or a polymer of which conductivity is adjusted such as polyaniline or polypyrrole, which is rubbed, or an oblique electrode such as SiO or SiO _2. It is an alignment film obtained by vacuum evaporation.

On the other hand, 14 and 15 forming the lower substrate in FIG. 2 are the same transparent bases and transparent electrodes as in the above 11, 12 and stripe-shaped convex portions 16 are formed on the transparent electrodes.

Although the alignment film 17 is provided on the convex portion 16, the alignment film may be a rubbing film or an oblique vapor deposition film similar to that of the above-mentioned 13 so as to impart uniaxial alignment to the liquid crystal therein. Alternatively, a thin film of a silane coupling agent or a non-uniaxially oriented film formed of an inorganic simple vapor deposition film may be used.

When rubbing the alignment films on both the upper and lower substrates, it is desirable that the rubbing direction be parallel to the longitudinal direction of the convex portion from the viewpoint of orientation, but even if it is not parallel, The effects of the present invention are fully recognized.

In this embodiment, the upper substrate shown in FIG. 1 and the upper substrate shown in FIG.
A polarizing plate arranged in crossed Nicols is provided outside the lower substrate shown in FIG.

In the present invention, the material for forming the convex portion as shown in FIG. 2 is Al, Ti, Au, Pt, C.
A metal such as r or a transparent conductive oxide such as SnO ₂ , In ₂ O ₃ or ITO is most preferable, but in addition to this, S
TiO _{2 and} other inorganic substances, and further polyimide, polyamide and other resins are formed by known patterning or deposition techniques.

In the present invention, the line width of the convex portion is preferably in a range larger than the thickness of the liquid crystal cell used, and 2 to 10 μm.
m. Further, it is preferable that the length of the convex portion is longer than the maximum interval, and further is about 1 pixel length or more than 1 pixel length, and is continuous over the entire electrode length of the scanning electrode as shown in FIG. 2, for example. The height of the convex part is 500Å ~
From the viewpoint of orientation, it is preferable to keep the cell thickness within the range of about 5000Å to about 5% to 30% of the cell thickness used.

Further, it is preferable that the distance between the convex portions is equal to or larger than the cell thickness in terms of orientation, and if the upper limit is changed in the range of about 20 μm, good gradation can be obtained.

The gradation effect of the stripe-shaped convex portions in the present invention will be described.

First, the convex portion has a function of making the generation points of the gradation domain uniform in each pixel. The convex portion is a portion where the electric field acting on the liquid crystal is stronger than the other portions, and a response is clearly given priority when the electric field is applied. This effect is
This is particularly large when the convex portion is formed of a conductive member, but even if it is relatively insulating, a similar electric field effect due to the capacitance ratio with other portions can be obtained.

Further, a slight change in the molecular arrangement may be considered in the vicinity of the convex portion, and in particular, the formation of a portion that easily receives an electric field as torque is also effective.

Next, in the process in which the liquid crystal molecules swung by the application of the electric field are latched (fixed) as domains, the effect of propagating the inverted response, which is prioritized to the convex portions, between the convex portions strongly acts, and the convex portions are As a whole, the narrowly spaced portions are first immobilized as inversion domains. Particularly, in the present invention, since the region having the low threshold value is intentionally provided, the region is inverted first, which facilitates the inversion of the portion having the narrow interval between the convex portions. As a result, as shown in FIG. 4, it is considered that an inversion portion having an area-controlled gradation is formed in the pixel.

Further, the gradation control performed by modulating the crest value of the applied pulse, the pulse width and other pulse waveforms by providing a gradient in the interval between the convex portions provides a smooth γ characteristic (applied signal-transmittance characteristic, VT characteristic) is shown. This is because the spread of the inversion domain area subtly picks up the propagation effect from the portion with the smallest convex interval, thereby creating continuous gradation with respect to the gradual change in the interval. Conceivable.

In the present invention, the portion having a particularly low threshold value provided in the lowest threshold gradient region is specifically formed as follows.

In particular, by intentionally forming disclinations, torque sensitivity is increased.

A special interface shape (eg height, shape) enhances the effect of the external field.

The interface regulating force is adjusted by changing the interface state such as the material, the presence or absence of uniaxiality, and the direction.

[0027]

【Example】

(Embodiment 1) FIG. 3 shows a pixel portion of an embodiment of the liquid crystal display device of the present invention. In this embodiment, the height is 1500.
Å, a convex portion having a width of 4 μm is formed of ITO, and the convex portion interval is gradually increased from 2 μm at a minimum to 10 μm at intervals of 0.5 μm to form a gradient. In addition, a region having a protrusion interval of 0.9 μm, which is narrower than the following cell thickness, was formed as a region having a particularly low threshold value adjacent to the region having the interval of 2 μm.

As an upper substrate, an IT is provided to face the lower substrate.
A transparent electrode substrate made of O was placed via a silica bead spacer having a diameter of 1.4 μm to form a liquid crystal cell in which the average thickness of the liquid crystal layer of the cell (cell thickness) was 1.5 μm.

In this embodiment, as the liquid crystal alignment treatment, a rubbing treatment was performed on both the upper and lower substrates in parallel with the longitudinal direction of the convex portion.

As a result of observing the present liquid crystal cell with a microscope, the display region has a uniform extinction position on the entire surface, whereas the above-mentioned region having a particularly low threshold has an extinction position which is slightly deviated, and has different orientations. Was showing.

The gradation characteristics of the liquid crystal cell of this embodiment were confirmed with a drive voltage pulse width of 20 μsec. The result is shown in FIG.
The T characteristic is shown by a solid line. In FIG. 4, the dotted line shows the VT characteristic of the liquid crystal cell in which the above-mentioned region having a particularly low threshold value is not provided. As shown in the figure, the gradation characteristics are obviously improved in the present invention, and in particular, the effect of increasing γ is recognized as an effect more than the electric field effect of reducing the cell thickness due to the convex portion.

Here, the slight leakage light due to the shift of the extinction position can be easily improved by shielding the region having a particularly low threshold value outside the display region according to the present invention.

The effect of the present embodiment is that the sensitivity of the torque to the external field is sensitive due to the occurrence of disclination due to the partially different orientation, the bending of the liquid crystal layer, or the extreme alignment defect. It is thought that this is the result.

(Embodiment 2) The basic structure of this embodiment is the same as that of the first embodiment, but in this embodiment, in a region with a particularly low threshold value, a height of 3000 Å and a width of 10 μm is higher than that of other convex portions. Further, a convex portion having a large height and a large width was provided, and a silica spacer having a diameter of 1.2 μm was used so that the average cell thickness was 1.5 μm.

Also in this embodiment, good gradation characteristics were obtained as in the first embodiment.

(Embodiment 3) A region having a particularly low threshold value in Embodiments 1 and 2 was subjected to a surface energy lowering treatment in order to further lower the threshold value. Specifically, after forming the convex portion, a film treatment with a fluorine-based silane coupling material was performed so as to particularly act on the low threshold region,
Further large γ characteristics and uniform area gradation characteristics were obtained.

FIG. 6 shows the structure of an image display device using the liquid crystal display element of this embodiment. This device is equipped with a 500 × 500 matrix panel 61 and a clock 6 as liquid crystal display elements.
2, a synchronization circuit 63, a shift register 64, a scanning waveform generator 66 including an analog switch 65 and the like, and an information signal generator 68 for converting and outputting video information from the frame memory 67 or the like into a drive signal. These are mounted on one side or both sides above and below the matrix substrate,
It may be distributed by being distributed to one side or both sides on the left and right. As a method of applying an information signal waveform as a halftone signal, there is voltage modulation which is usually considered as a method of giving gradation information, but in this device, in particular, the chiral smectic C phase is elastically coupled in the layer direction in the layer direction. Drive domains such as pulse width modulation and phase modulation are also effective in controlling the propagation time of the domain.

[0038]

As described above, the liquid crystal display device of the present invention can maintain good reproducibility of halftone display and perform gradation display having a desired γ characteristic. Further, good halftone display can be performed at a higher speed, a higher number of gradations, and a higher definition without complicating the structure of the element so much.

[Brief description of drawings]

FIG. 1 is a diagram showing an upper substrate of an embodiment of a liquid crystal display element of the present invention.

FIG. 2 is a diagram showing a lower substrate of an embodiment of the liquid crystal display element of the present invention.

FIG. 3 is a diagram showing a pixel portion according to an embodiment of the present invention.

FIG. 4 is a diagram showing gradation display of the liquid crystal display element of the present invention.

FIG. 5 is a diagram showing a VT characteristic of an example of the present invention.

FIG. 6 is a configuration diagram of an image display device using the liquid crystal display element of the present invention.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shinjiro Okada 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (1)

[Claims] 1. A liquid crystal display element comprising a ferroelectric liquid crystal sandwiched between a pair of electrode substrates, wherein a plurality of stripe-shaped convex portions are provided on at least one electrode in one pixel.
Further, the liquid crystal display element is characterized in that a threshold gradient is formed in the pixel by changing the interval between the convex portions, and a region having a particularly low threshold is formed in the lowest region of the threshold gradient.