JPS63142328A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To reduce the cost of a liquid crystal display device by sandwiching ferroelectric liquid crystal molecules by using a 2nd substrate which has a ferroelectric thin film, and setting dielectric thin films on 1st and 2nd substrates orthogonally to the 1st and 2nd substrates and providing self-polarization in the same direction. CONSTITUTION:The ferroelectric organic thin film is formed on an insulating substrate which has a light transmittable electrode and a lead to form the 1st substrate and a ferroelectric organic thin film is formed on an insulating substrate which has the light transmittable or non-light transmittable electrode and a lead to form the 2nd substrate. A display cell is so formed that the 1st and 2nd substrates are positioned in parallel to each other. At this point of time, the ferroelectric thin films in the display cell does not have self-polarization in a constant direction. Then when ferroelectric liquid crystal molecules are injected into the display cell, the spiral of the liquid crystal molecules is loosened by fixed charges that the cell has and the direction of the self-polarization that the liquid crystal molecules have coincides with the electric field direction that the display cell, so that the liquid crystal molecules have only one stable position. Consequently, an IC is simplified and the manufacture cost is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention proposes a structure and a driving method for a display device using ferroelectric liquid crystal.

"Conventional technology" Solid-state display devices that replace CRT are those that use liquid crystal materials,
A wide variety of devices have been developed, including those that utilize electrochromic phenomena and those that use gas discharge.

In particular, liquid crystal display devices are suitable for practical use due to their small drive size and fast response speed, and their development has been particularly active.

However, recently, as the amount of information increases, the number of pixels in one screen continues to increase. In the case of a small number of pixels, display quality could be ensured even with display devices using TN liquid crystal materials, but
For example, in the case of a matrix liquid crystal display device that has a large number of pixels (about 640 x 400 pixels), image quality is inevitably degraded due to crosstalk, etc., and even if ferroelectric liquid crystal is used as the liquid crystal material or TN liquid crystal is used, SBE mode is not used. In addition, image quality has been improved by driving semiconductor elements as switches for each pixel.

“Problem to be solved by the invention J: In a TN active matrix display device using semiconductor elements, the production cost for forming the semiconductor elements is high;
Furthermore, since the manufacturing yield of the device is low, it has been difficult to reduce the price of the display device itself. However, although the display image quality itself was good and the production price could be reduced through efforts such as mass production, the response speed of the liquid crystal material was slow,
It was unsuitable for displaying content that required high speed. Furthermore, in a ferroelectric liquid crystal display device that does not include a ferroelectric thin film within the device, it is necessary to reduce the cell thickness in order to unwind the helix of the liquid crystal molecules and make the long axis of the molecules take two stable states. Ta. Reducing the cell thickness to achieve these two stable states is a very difficult task with the current technology, and it is particularly difficult to obtain uniformly narrow cell spacing over a large area.

"Means for Solving the Problem" In the present invention, the following means were used to solve the problem.

Organic thin film CP (VDF+TrFE) exhibiting ferroelectricity on an insulating substrate with transparent electrodes and leads; copolymer of vinylidene fluoride and trifluoroethylene.

P (VDF+TeFE); copolymer of vinylidene fluoride and tetrafluoroethylene, PVDF. Vinylidene fluoride polymer, P(νDCN+VAc): Vinylidene cyanide binding nilia acetate copolymer, etc.]
A first substrate is formed by forming a first substrate. Further, a second substrate is formed by forming an organic thin film exhibiting ferroelectricity on an insulating substrate having light-transmitting or non-light-transmitting electrodes and leads.

A display cell is formed such that the first and second substrates are positioned parallel to each other. At this point, the ferroelectric thin film in the display cell does not have spontaneous polarization in a fixed direction, and an electric field is applied to the display cell from the electrodes provided on the first and second substrates in a direction perpendicular to the first and second substrates. By adding , the direction of spontaneous polarization of the thin film is made to match the direction of the electric field, so that a fixed charge is generated in the display cell even when the external electric field is removed.

(hereinafter referred to as the "cell electric field direction") When ferroelectric liquid crystal molecules are injected into this display cell, the fixed charge of the cell unwinds the helix of the liquid crystal molecules, and the direction of the spontaneous polarization of the liquid crystal molecules changes to the direction of the display cell. The liquid crystal molecules have only one stable position, matching the direction of the electric field.

According to this method, since the cell thickness is not used as a means of unwinding the helix of the liquid crystal molecules, the cell thickness does not need to be less than the pitch of the liquid crystal molecules, and since the cell thickness can be increased, the flatness accuracy of the insulating substrate used can be improved. Not only was it possible to reduce the production cost, but it also provided a margin for process control against fine dust, which had been an obstacle when forming display cells, and improved production yields.

Next, a description will be given of a method for driving the display device.

Due to the above structure, in the liquid crystal display device, as shown in FIG. The direction of the electric field in the cell is determined (position H). Also, on the other hand,
When a potential that generates an electric field opposite to the "electric field direction of the cell" is applied to the electrodes, the direction of spontaneous polarization of the liquid crystal molecules matches the direction of the electric field generated from the electrodes according to the magnitude of the interruption field in ■ and ■゛. (position ■). When no external voltage is applied, the liquid crystal molecules return to the (I[) position because they have the only stable position depending on the "cell electric field direction." For this reason, the driving voltage can be unidirectional, so there is no need to make the driving IC a bipolar output type.
Compared to conventional drive methods, this method is characterized by the ability to simplify the IC and reduce production costs.

In addition, it is possible to display contrast between gray scales, which was impossible with conventional display devices using ferroelectric liquid crystals, but according to this method, since liquid crystal molecules have only one stable direction,
Since an electric field direction opposite to that of the cell is applied from the electrodes, an intermediate gradation display is possible by adjusting the magnitude of the applied electric field.

The present invention will be explained below with reference to Examples.

"Example" FIG. 2 shows the manufacturing process of the substrate used in the present invention.

In drawing (A), after cleaning and drying a glass substrate (1) having wiring and leads (2) made of a patterned transparent conductive film, an organic alignment film material (3) such as a polyimide solution or a ferroelectric material is added to a Ny solution. Organic resin P (VDF+T
A solution in which rFE) was added at a ratio of 1:1 to the amount of resin for an organic alignment film was coated by a spin method. In another embodiment, P (VDF+TeFE), PVDF, P
We conducted an experiment using (VDCN+VAC) alone, and found that it could be used, although there was a difference in the magnitude of spontaneous polarization. Then N in a clean oven to evaporate the solvent! Beta was carried out for 20 minutes at an atmosphere of 110°C. A first substrate was produced by the above method. In addition, a second substrate having electrodes and leads orthogonal to the first substrate was manufactured by a similar method.

Next, these first and second substrates are arranged so that the surfaces of the glass substrates having wiring and leads face each other, as shown in FIG. 3B. After that, connect the circuit shown in (C) to the electrodes and leads on the side board using an external DC voltage (4).
Formed by applying . In this implementation, the thickness of the air capacitor was 3 μm, and the externally applied voltage was 80V.

The applied voltage is a value determined by the magnitude of spontaneous polarization of the ferroelectric organic resin used. In order to form a film after applying an external voltage, the
Curing was performed at 0°C for one hour.

By applying this external electric field, the spontaneous polarization of the ferroelectric resin contained in the film is aligned in a certain direction, resulting in a "cell electric field direction." After that, the surfaces of the first and second substrates are treated to align the long axis directions of liquid crystal molecules, and then the peripheries of the first and second substrates are sealed with an adhesive, and the rest is known in the art. A cell was manufactured using a liquid crystal display method.

Next, an example of driving using this cell is shown in FIG.

In the ON part, pulse of 83 μsec and width is 17 nes.
This is an example in which a voltage is applied in the direction in which an electric field is generated that is opposite to the "electric field direction of the cell" for each cell, and the pixel becomes bright. OFF
In this case, no external signals are applied, and the pixels exhibit a dark state due to the cell's only stable directionality (monostability). At this time, in another example, a voltage of about 175 to 174 was applied to the ON signal in order to generate an electric field in the same direction as the "electric field direction of the cell", and the speed of the change to darkness could be increased. Ta.

``Effect'' By providing a film with spontaneous polarization fixed in a certain direction, it is possible to create the ``cell electric field direction'', and even in cells where the cell spacing is thicker than the helical pitch length of the liquid crystal molecules, the liquid crystal molecules can be The helix can now be unraveled, allowing margins for reducing material costs such as substrate flatness.

In addition, by creating the "cell electric field direction", the liquid crystal molecules can have only one stable state (monostability), and the drive signal only needs to be applied with a voltage in a single direction.As a result, the drive I
We were able to simplify C.

Furthermore, since this cell is monostable, it was possible to obtain intermediate gray levels depending on the magnitude of the externally applied voltage.

[Brief explanation of the drawing]

FIG. 1 shows an outline of the liquid crystal display device of the present invention and the state of internal liquid crystal molecules. FIG. 2 shows a method for manufacturing a substrate for a liquid crystal display device of the present invention. FIG. 3 shows the electro-optic effect during driving of the liquid crystal display device of the present invention.

Claims (1)

[Scope of Claims] 1. A first substrate having a thin film exhibiting ferroelectricity on an insulating substrate provided with translucent electrodes and leads, and an insulating substrate provided with translucent or non-transparent electrodes and leads. Ferroelectric liquid crystal molecules are sandwiched between a second substrate having a thin film exhibiting ferroelectricity on the substrate, and the thin films exhibiting ferroelectricity on the first and second substrates are both attached to the first and second substrates. 1. A liquid crystal display device characterized by having spontaneous polarization perpendicular to and in the same direction. 2. In claim 1, the ferroelectric liquid crystal molecules existing between the first and second substrates are generated from spontaneous polarization of a thin film exhibiting ferroelectricity on the first and second substrates. A liquid crystal display device characterized in that the direction of spontaneous polarization of liquid crystal molecules is aligned in a certain direction by an electric field perpendicular to first and second substrates. 3. In claim 1, the long axes of liquid crystal molecules are arranged in a certain direction on a thin film exhibiting ferroelectricity on the first and second substrates, or on a thin film newly provided on the thin film. 1. A liquid crystal display device characterized by being subjected to an alignment treatment for aligning the images. 4. In claim 1, when no electric field is applied from the electrodes and leads provided on the first and second substrates, the direction of spontaneous polarization of the liquid crystal molecules is the same as that on the first and second substrates. The electric field generated by the electrode and lead, which is in the only stable state (monostable) and coincides with the direction of spontaneous polarization of the ferroelectric thin film, is directed in the opposite direction to the spontaneous polarization electric field generated by the ferroelectric thin film. 1. A liquid crystal display device characterized in that the direction of spontaneous polarization of liquid crystal molecules when applied is different from the direction of a spontaneous polarization electric field generated by the ferroelectric thin film. 5. A liquid crystal display device according to claim 1, comprising a thin film exhibiting ferroelectricity on at least one of the first and second substrates.