JPH0348819A - Ferroelectric liquid crystal display - Google Patents

Abstract

PURPOSE:To realize a ferroelectric liquid crystal display in which display with gradation is easily obtained even in the case of using ferroelectric liquid crystal whose threshold characteristic is steep by providing a projecting part or a recessed part consisting of a minute area on the surface of at least one of two substrates on a side where the substrate contacts with the liquid crystal. CONSTITUTION:By providing the projecting part (body with level difference) 1 consisting of the minute area on the surface of one substrate 3 which contacts with the liquid crystal, differences (a) and (b) are obtained in the projecting and recessed areas of the body with level difference respectively as for the thickness of a liquid crystal layer. Since an effective voltage can be made different between the area of (a) and the area of (b) in accordance with the difference of the material (dielectric constant and resistance, etc.) and the difference of thickness of the substance with level difference, polarization and inversion always occur from the area on which the effective voltage is largely impressed at the time of impressing the voltage. Namely, the occurrence and the development of a polarized and inverted domain can be controlled according to an area that the projecting part or the recessed part occupies an image element and the height thereof, so that the gradation is easily obtained.

Description

[Detailed description of the invention] Industrial application field of the present invention 1 ↓ Related to ferroelectric liquid crystal displays, particularly related to gradation display of ferroelectric liquid crystal displays, conventional technology Bistable ferroelectric using ferroelectric liquid crystal liquid crystal (SSFL)
C) Cell cost High-speed response method Although it is expected to be used as a large screen display due to its characteristic of bistability, it is difficult to control intermediate states due to bistability. Therefore, methods for achieving multiple gradations include gradation display methods using drive waveforms, gradation display methods using pixel division, and ferroelectric Although methods of changing the threshold of liquid crystals and methods of obtaining gradation using domains that appear when polarization is reversed have been proposed, the conventional proposals go beyond the problems that the invention attempts to solve (as described in Tomo). Gradation display using drive waveforms, which had such problems, divided each frame into several subframes and drove the pixels by changing the duty ratio within each frame.However, high-speed response liquid crystal materials However, in order to obtain multiple gradations, there is still the problem that the gradation display by pixel division further subdivides each pixel to obtain gradations. This requires high-definition patterning technology and creates a complex circuit.

Furthermore, a method of changing the threshold of ferroelectric liquid crystal by creating a step L Motohisa Since the threshold of ferroelectric liquid crystal is steep, it is necessary to divide the applied voltage with very high precision. By adding steps to the substrate or TTO electrode and adding steps to the thickness of the liquid crystal layer within the pixel, the electric field strength applied to the liquid crystal layer can be changed by the steps, effectively creating different threshold voltages. However, in order to obtain multiple gradations, a fairly thick step is required, and the thickness d of the liquid crystal layer differs greatly between the part with the step and the part without. If △n is the birefringence of In the method of obtaining gradations using domains appearing in If the generation and growth can be controlled by the voltage height and width of the applied pulse, gradation display can be realized. (This is a solution to such problems,
The purpose of the present invention is to provide a ferroelectric liquid crystal display that can easily display gradations even when using a ferroelectric liquid crystal having a steep threshold characteristic. This is a liquid crystal display characterized by having a hum or recess made of a minute area on the surface of at least one of the two substrates constituting the display on the side that comes into contact with the liquid crystal. The difference is that by providing convex or concave portions consisting of minute regions on the surface of the substrate in contact with the liquid crystal, the generation of polarization-inverted domains can be controlled by differences in electric field strength, and gradation display can be easily achieved. Figure 1 shows an outline of the ferroelectric liquid crystal display according to the present invention.Here, l is a level difference having a convex or concave portion, 2 is an ITO electrode, 3 is a substrate, and a and b are The thickness of the liquid crystal layer in the convex region and the concave region of the stepped body is shown respectively.The liquid crystal layer thickness i1a and b are different in thickness, and due to the difference in the material (permittivity, resistance, etc.) of the stepped body and the difference in thickness,
Even if it is possible to make a difference in the effective voltage between region a and region b, when a voltage is applied between them, polarization reversal will always occur from the region to which a larger effective voltage is applied.In other words, polarization reversal Domain generation and growth,
This can be controlled by the area occupied by the pixel of the convex or concave part, and by the height.For example, it is possible to easily obtain gradation by creating an ITO electrode on the step body l, and in the Ca part. This effective voltage is always larger than 6 parts, and regardless of the material of the step body, a polarization inversion domain always occurs from part a.In order to obtain uniform gradation within each pixel, Each pixel may have at least one convex or concave portion, and five concave portions may be combined so that the effective voltage is different within each pixel. A combination of several types of convex portions and concave portions with different areas and heights may be used, and these may also be stacked. Strength can be obtained by controlling the occurrence of LiT. The convex and concave portions can be created using any method.

Also, the power that was tested with limited things such as their shape and height (1.X is not limited to these).

Example 1 The cell structure and manufacturing method for the ferroelectric liquid crystal display of the present invention will be explained in detail. Create the ITO electrodes 6 and 7. Create the ITO electrodes 6 and 7 so that when the two substrates are combined, the size of each pixel will be 500 μm x 500 μm, and the distance between pixels will be 100 μm. One surface of substrates 4 and 5 with TO electrodes &
A protrusion was created as a convex part using the following method. First, 5i02 was heated to 400℃, 5iHa and 02/N
2000A was prepared using the mixed gas of step 2, and after 90 minutes of cleaning and drying, a positive type resist agent was applied and etching was performed.
The size of the 5in2 protrusion 8 obtained at this time was 10μ
mX10μm, 20μmX20μm, 30μmX
30μm, 40μm×40μbi 50μm×50μ
There are 5 types of m, all with a pitch of 150μ. When the upper and lower substrates are combined, there are 16 protrusions per pixel. At this time, the area ratio of the protrusions per pixel is 1. Calculated as shown in the formula below. and (x, umX x, um)X 16+(500um
X500μm) = y% As shown in the table below, an ITO electrode 9 of about 3000A was formed again on this substrate with projections by sputtering, and an alignment film 10. As it, polyvinyl alcohol (PV Kuraray Bovar 117) was formed into a film with a film thickness of 50OA after drying, and then rubbed in one direction.
The height of the convex portion after film formation was 1500 A for all five types. After that, the PVA was pasted together through bead spacers 12 with a particle size of 2 μm so that the rubbed directions were parallel to each other, and the injection port was Then, as the liquid crystal 14, a ferroelectric liquid crystal C5-1014 manufactured by Chisso Petrochemical Co., Ltd. was injected into the element under reduced pressure in the cholesteric phase temperature range. The injection port was then slowly cooled to room temperature at a cooling rate of ℃/min, and the injection port was sealed. When this ferroelectric liquid crystal cell was observed under a polarizing microscope, it was found that uniform alignment had been obtained.
IV, 0.0. When a 5Hz triangular wave was applied, the polarization-inverted domain was always generated from the convex portion and grew uniformly and with good reproducibility within each pixel.Next, we examined the panel created in this example. In order to evaluate the gradation, the threshold characteristics were measured and the voltage waveforms used for the nine threshold characteristics are shown in FIG.

In FIG. 4, after the constant reset pulse 15 is applied,
A variable write pulse 16 of opposite polarity is applied to measure the threshold characteristic. This series of pulses is applied at regular time intervals 17.

FIG. 5 shows a voltage (V) transmittance (T) curve measured using this voltage waveform. In addition, the transmittance (the value immediately before Tomoji's reset pulse is applied) is measured. In Figure 5, the horizontal axis represents the voltage and the vertical axis represents the transmittance. (Input reset pulse at 20V, 1m5ec)
1. Variable write pulse from 0 to 20 V, 0.
5 msec, and a series of pulses were applied every 15eC.What kind of write pulse was applied?Polarization reversal always occurs from the convex part, and especially after applying a voltage of 5V to 7V, the polarization reversal occurs. The growth stopped midway, and 10 gradations were obtained. Figure 3 is a cross-sectional view of a ferroelectric liquid crystal display in Example 2. ITO electrodes 2 and 9 were created on glass substrates 4 and 5. This ITO electrode ζ, t, when two substrates are combined, the size of each pixel is 500μm x 500μ, and the distance between pixels is 100μm. The recesses 20 were created by the following method, a nine-negative type resist was applied, mask exposure was developed, and etching was performed.
Next, polyvinyl alcohol (PVA, Talarebovar 117) was formed as an alignment film 111 on both substrates to a film thickness of 50 OA after drying, and rubbed in one direction. After that, the PVA rubbed directions are parallel to each other, and the parts other than the injection port are sealed with a sealing resin 13. As the liquid crystal 14, a ferroelectric liquid crystal C5-1014 manufactured by Chisso Petrochemical Co., Ltd. was injected into the device under reduced pressure in the cholesteric phase temperature range i-0,5.
The ferroelectric liquid crystal cell was slowly cooled to room temperature at a cooling rate of °C/min, the injection port was sealed, and the cell was observed under a polarizing microscope, revealing that uniform alignment had been obtained. , 0. When a 5 Hz triangular wave was applied, it was found that the polarization-inverted domain was always generated from the concave part of the concave part, and that the domain was growing uniformly within each pixel. In the ferroelectric liquid crystal display of the present invention, the growth of polarization reversal can be controlled and eight gradations can be obtained. Although the effective voltage applied to the liquid crystal layer differs due to the difference in level between these regions, it is possible to control the generation and growth of polarization-inverted domains, and to create a strong voltage with a steep threshold. Dielectric liquid crystals can also be used to display gradation on containers.

That is, in the past, steps were added to the substrate, ■To, etc. for the purpose of changing the threshold value, resulting in a large change in Δnod and a decrease in contrast.However, according to the present invention, although there are steps, the area occupied by them is Since it is a part of the region and controls the generation of polarization-inverted domains from that region, the contrast will not become small.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a ferroelectric liquid crystal display according to the present invention, FIG. 2 is a cross-sectional view of a ferroelectric liquid crystal display according to the first embodiment, and FIG. Cross-sectional view, Figure 4 is Example 1.2
FIG. 5 is a diagram of applied pulse waveforms for gradation measurement conducted in Example 1, and FIG. 5 is a diagram of voltage (V) versus transmittance (T) measured in Example 1. 1... Step body having a convex portion or a concave portion, 2---
ITO electrode, 3.Substrate, asb", liquid crystal layer thickness in the convex and concave regions, 4,5...Glass substrate, (3,7
*Fist cloud electrode, 8・φ・protrusion, 9...ITO electric maple 1
0. II... Orientation A12... Bead spacer, 1
3...Seal resin 14...Liquid & 15. -Reset pulse included 16...Variable writing pulse included 17.
・・Pulse opening 18.19・・ ITO Denkaede 20・
・Concavity

Claims (2)

[Claims] (1) In a display using ferroelectric liquid crystal, a convex portion or a concave portion consisting of a minute area is provided on the surface of at least one of the two substrates constituting the display on the side that is in contact with the liquid crystal. A characteristic ferroelectric liquid crystal display. (2) The ferroelectric liquid crystal display according to claim 1, wherein each pixel includes at least one convex portion or concave portion.