JPH04147216A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To eliminate a difference in switching speed between longitudinal and lateral picture element gap parts, to perform switching fast uniformly, and to make a bright, high-contrast display by providing a ferroelectric liquid crystal layer in a diagonal direction of picture element by a specific orienting process. CONSTITUTION:Striped transparent electrodes 3 and 4 are formed on glass plates 1 and 2, and an orienting film 13 is formed by coating and rubbed as shown by an arrow 8 to orient liquid crystal 14. Gap parts 6 and 7 are equal in switching time and switched uniformly. The rubbing process wherein the picture elements are oriented in the diagonal direction or the oblique vapor deposition of an inorganic material in the diagonal direction of the picture elements is preferable. While the directions of orienting processes of the mentioned liquid crystal element or upper and lower substrates cross each other, the center direction of the angle of intersection may almost be aligned with the diagonal direction of the picture elements.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a liquid crystal element having a ferroelectric liquid crystal as a liquid crystal layer.

2. Description of the Related Art A conventional ferroelectric liquid crystal element includes, for example, a liquid crystal display panel having a structure as shown in FIG. One glass substrate 43
After forming a color filter 44 and a light shielding layer 45 thereon and covering it with a smoothing layer 46, a transparent electrode 42 is formed,
Furthermore, an alignment film 47 is applied. A transparent electrode 42 and an alignment film 47 are attached on the other glass substrate 43. These pair of substrates are made to face each other at a certain distance between about 1.5 μm and 5 μm using a spacer 49, and ferroelectric liquid crystal 41 is injected and oriented between them (for example, Murakami, Ishiyoshi et al.
"High-speed multicolor ferroelectric LCD," Proceedings of the 14th Liquid Crystal Symposium, pp. 88-89). Note that 48 is a polarizer and 50 is an analyzer. The thinned ferroelectric liquid crystal becomes stable in several states as shown in FIG. Fifth
Figures (a) and ■) show that the directions of the liquid crystal molecules are almost aligned.
At this time, the spontaneous polarization is directed upward and downward to the normal line of the substrate. Here, 50 is a liquid crystal molecule, 51 is a cone, and 5 is a liquid crystal molecule.
2 is an upper substrate, and 53 is a lower substrate. FIG. 5(C) shows a state in which the liquid crystal molecules are twisted in the normal direction of the substrate, and there also exists a state in which the twisting direction is reversed.

Depending on the type of alignment film, the angle of inclination of the liquid crystal molecules on the substrate and the way the liquid crystal layer is bent may differ from that shown in FIG. 5, but this schematic diagram can basically represent the stable state of the liquid crystal molecules. Figures 6(a), (b), and (C) are, respectively,
6(a) is a plan view of the liquid crystals shown in FIGS. 5(a), 5(b), and 5(C) viewed from the upper substrate. , (b) can be used to add brightness and darkness. Here, 60 indicates the direction of spontaneous polarization. When the liquid crystal molecules 63 and 64 have a twisted structure as shown in FIG. 6(C), the display becomes gray. A thin ferroelectric liquid crystal panel has such a stable state, and the transition between these states occurs very rapidly depending on the applied voltage, and the characteristics of the applied voltage and amount of transmitted light are sharp and dark. Indicates value characteristics. Therefore, it is possible to obtain a high-capacity, high-contrast display using only electrodes in a simple matrix configuration, without providing a nonlinear element such as a thin film transistor.

By the way, in FIG. 4, the color filter 44 and the light shielding layer 45 are
A smoothing layer 46 is formed on top of the color filter 44 to prevent unevenness on the color filter 44 and a stepped portion at the boundary between the color filter 44 and the light shielding layer 45 from adversely affecting the alignment of the liquid crystal. Since the ferroelectric liquid crystal 41 has a layered structure, it is more susceptible to the influence of such a step than a nematic liquid crystal, so it has such a complicated structure. Even in the case of a single color panel without a color filter 44,
In particular, when the pixel pattern becomes fine and the aperture ratio becomes small, the gaps between the pixel elements are darkened. Unless it is in a so-called black matrix state, the contrast will be very small, so normally a light shielding layer 4 is used as shown in Figure 4.
5 will be provided. However, forming the light shielding layer 45 involves complicated steps such as thin film formation and patterning by etching.

Therefore, in Japanese Patent Application No. 1-2422, we applied a predetermined pulse voltage to the electrodes forming two adjacent picture elements to switch the stable state of the picture element gap.
A liquid crystal element that can easily be brought into a black matrix state without a complicated configuration has been disclosed. In addition, depending on the cell configuration of the liquid crystal element, the gap between bright pixels can be in a bright state or an intermediate brightness state, and the gap between dark pixels can be in a dark state, so that the electrode opening It has the characteristic that the transmittance can be increased even if the transmittance is extremely small.

Problems to be Solved by the Invention When the pattern is very fine, forming a light shielding layer to create a black matrix state is difficult to align with the electrode pattern, leading to an increase in cost.

Although Japanese Patent Application No. 1-2422 solved this problem, there was a large difference in the speed at which the stable state of the liquid crystal was switched between the row electrode gap and the column electrode gap depending on the cell configuration. For this reason,
In a cell where the width of the electrode gap is as wide as about 30 μm, the stable state of the liquid crystal in the slower electrode gap may be difficult to change.

Furthermore, in order to make the pixel gap part the same as the adjacent picture elements, it is necessary that the voltage-light transmittance characteristic of the pixel gap part has a dark value characteristic, but in the cell configuration as described above, Because this dark value property was insufficient, it was not possible to drive the matrix in the gap.

Means for Solving the Problems In order to solve the above problems, the liquid crystal element of the present invention has a ferroelectric liquid crystal sandwiched between substrates having electrodes on opposing surfaces and forming matrix-like picture elements. By performing an alignment treatment on the substrate so that the layer normal direction of the liquid crystal approximately coincides with the diagonal direction of the picture elements, and applying a predetermined pulse voltage to the electrodes, the gap between the matrix-like picture elements is By switching the stable state of the gap, it is possible to stably control the display of the gap even in a liquid crystal cell with a wide pixel gap.

Patent application No. 1-242 discloses that when an electric field is applied to the active picture elements, the ferroelectric liquid crystal in the gap between the picture elements responds to the electric field and exhibits bistability.
2, it was found that there is a large difference in the speed at which the stable state changes depending on whether the direction of the pixel gap is perpendicular to the ferroelectric liquid crystal layer or horizontal. That is, when the ferroelectric liquid crystal layer is formed in the direction along the row electrodes, the stable alignment state in the column electrode gaps occurs earlier than in the row electrode gaps. The difference in switching speed described above increases as the width of the gap increases.

Equalizing the responses of the row and column electrode gaps can be achieved by aligning the layer direction of the ferroelectric liquid crystal in the diagonal direction of the picture element.

EXAMPLE Hereinafter, a liquid crystal device according to an example of the present invention will be described with reference to the drawings.

Figure 1 shows a picture element pitch of 1100u and an inter-picture element space of 30a.
FIG. 3 is a plan view of a ferroelectric liquid crystal matrix panel of FIG.

FIG. 2 is a sectional view of the panel shown in FIG. 1, in which striped transparent electrodes 3 and 4 are formed on glasses 1 and 2, and polyvinyl alcohol is applied thereon as an alignment film 13. The alignment films 13 on the upper and lower substrates were rubbed in the direction of arrow 5 in FIG. 1 to align the liquid crystal 14. The liquid crystal used is, from the high temperature side, tomoyoshi phase → chiral nematic phase → smectic A
There is a phase transition from phase to chiral smectic C phase. At this time,
A liquid crystal layer structure of a chiral smectic C phase, which is a ferroelectric liquid crystal phase, is formed in a direction perpendicular to the arrow 5 and parallel to the row electrodes 4. When a pulse is applied to the row electrode 4 and the column electrode 3, the electrode gaps 6 and 7 also respond, exhibiting memory properties. However, the pulse width required to switch the memory state, that is, the switching time, is limited to the row electrode gap 7 (parallel to the liquid crystal layer).
The column electrode gap 6 (shaded area upward to the right) was several times faster than the column electrode gap 6 (shaded area upward to the left), and a part of the gap 6 could not be switched even if the pulse width was increased.

Therefore, when we changed the rubbing direction to the diagonal direction of the pixel as shown by arrow 8 and created a cell in which the layers were oriented in the diagonal direction of the pixel, the switching times in the gaps 6 and 7 became equal, and the switching was performed uniformly. became. A sufficiently large reset pulse is applied during the reset period 20 using the drive waveform shown in FIG. 3 for this cell, so that the entire surface of the cell including the gap becomes black, and the on/off of the pixel is controlled by the pulse during the selection period. As a result, the gap functions as a black matrix. This allows a very high contrast display to be obtained with a simple configuration.

When the width of the gap is 10 μm or less, in the liquid crystal element of the present invention, the switching time of the row electrode gap and the column electrode gap is slightly less than twice the switching time of the pixel, so the gap can be used for adjacent pixels. It is also possible to make the aperture ratio substantially 100% by switching at the same time.

Depending on the alignment film, the liquid crystal layer is oriented in a direction that is not perpendicular to the rubbing direction. For example, for proteins such as albumin, the layer direction differs depending on the rubbing strength. In this case, if the rubbing directions of the upper and lower substrates intersect, the liquid crystal layer will face toward the center of the intersecting angle, so it is preferable to perform the intersecting rubbing with the diagonal direction of the picture element as the central angle. Also, the normal direction of the substrate and 80 to 85
When depositing an inorganic substance such as silicon monoxide from an angle of 100°, it is preferable to deposit it diagonally on the upper and lower substrates, as in the case of polyvinyl alcohol.

Effects of the Invention The liquid crystal element of the present invention eliminates the difference in switching speed between the vertical and horizontal pixel gaps by orienting the ferroelectric liquid crystal layer in the diagonal direction of the picture elements through a predetermined alignment process, thereby eliminating swifting in the gaps. Can be done uniformly and at high speed. This makes it possible to achieve high-contrast and bright display.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a liquid crystal device according to an embodiment of the present invention, FIG. 2 is a cross-sectional view of the same, FIG. 3 is a waveform diagram of the driving method of the liquid crystal device of the present invention, and FIG. 4 is a conventional ferroelectric liquid crystal The configuration diagrams of the panel, FIGS. 5 and 6, are schematic diagrams of the stable state of the ferroelectric liquid crystal. l...upper board, 2...lower board, 3...
... Column electrode, 4 ... Row electrode, 6 ...
・Column electrode gap, 7... Row electrode gap, 8...
. . . Rubbing direction of the present invention, 13 . . . Alignment film, 14 . . . Ferroelectric liquid crystal. Agent's name Patent attorney Haruaki Ogata Two idiots NipiL Wisdom 0 Mockery Og Fshireduction Dimensions I 4 etsuhe ～de naka 13 fig.
Molecule 5 no]-n (0) (b)
(c) Illusion 60 Simplicity of 1+2 components 6l-IiI photon

Claims (3)

[Claims] (1) A ferroelectric liquid crystal is sandwiched between substrates having electrodes on opposing surfaces and forming a matrix of picture elements, and the layer normal direction of the ferroelectric liquid crystal approximately coincides with the diagonal direction of the picture elements. A liquid crystal element characterized in that the substrate is subjected to an alignment treatment, and the stable state of the gap portions of the matrix-like picture elements is switched by applying a predetermined pulse voltage to the electrodes. (2) The liquid crystal element according to claim 1, wherein the alignment treatment is a rubbing treatment applied in the diagonal direction of the picture element, or an inorganic material is obliquely deposited from the diagonal direction of the picture element. (3) The liquid crystal element according to claim (1), wherein the directions of the alignment treatment intersect on the upper and lower substrates, and the center direction of the intersection angle and the diagonal direction of the picture element generally coincide.