JPH0792563B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention proposes a structure and a driving method of a display device using a ferroelectric liquid crystal.

"Prior Art" Solid-state display devices that replace CRTs have been developed in a wide variety of ways, such as those using liquid crystal materials, those utilizing electrochromic phenomena, and those using gas discharge.

In particular, the liquid crystal display device is suitable for practical use because of its low driving power and high response speed, and the development of the liquid crystal display device has been particularly brisk.

However, the number of pixels in one screen has been increasing with the increase in the amount of information. In the case of a small number of pixels, the display quality could be secured even with a display device using a TN liquid crystal material, but in the case of a matrix liquid crystal display device having a large number of pixels of about 640 × 400 pixels, the deterioration of image quality due to crosstalk is avoided. However, the image quality has been improved by using a ferroelectric liquid crystal as a liquid crystal material, using an SBE mode even when using a TN liquid crystal, or driving by using a semiconductor element as a switch of each pixel.

"Problems to be solved by the invention" In the TN active matrix display device using a semiconductor element, the production cost for forming the semiconductor element is high, and the manufacturing yield of the element is low, so that the price of the display device itself is reduced. It was difficult to do. However, although the display image quality itself was good, the production cost could be reduced by efforts such as mass production, but the response speed of the liquid crystal material was slow, and it was not suitable for display contents requiring high speed. Also,
In a ferroelectric liquid crystal display device in which the ferroelectric thin film is not included in the device, it is necessary to reduce the cell thickness in order to unwind the helix of the liquid crystal molecule and to take the stable two states of the molecular long axis. Narrowing the cell thickness in order to achieve these two stable states is a very difficult task with the current technology, and it has been extremely difficult to obtain a uniform narrow cell spacing over a large area.

"Means for Solving Problems" In the present invention, the following means are used to solve such problems.

That is, the present invention relates to a first substrate having a thin film showing ferroelectricity on an insulating substrate provided with a transparent electrode and leads, and an insulating substrate provided with transparent or non-transparent electrodes and leads. A ferroelectric liquid crystal molecule is sandwiched between a second substrate having a ferroelectric thin film, and the ferroelectric thin films on the first and second substrates are both:
A spontaneous polarization electric field that is the only stable state is formed by having a spontaneous polarization that is perpendicular to the first and second substrates and has a fixed direction in the same direction. When no electric field generated by the electrodes and leads provided above is applied, the direction of spontaneous polarization of the ferroelectric liquid crystal molecules follows the spontaneous polarization electric field, and the direction opposite to the spontaneous polarization electric field is the first polarization direction. When the electric field generated from the electrodes and the leads provided on the second substrate is applied, the direction of the spontaneous polarization of the ferroelectric liquid crystal molecule has the direction of the ferroelectric liquid crystal molecule according to the spontaneous polarization electric field. A liquid crystal display device characterized by being different from the direction of spontaneous polarization.

(Hereinafter, referred to as “electric field direction of cell”) When ferroelectric liquid crystal molecules are injected into this display cell, the fixed charge of the cell unwinds the helix of the liquid crystal molecule, and the direction of spontaneous polarization of the liquid crystal molecule is The liquid crystal molecules have the only stable position because they are oriented according to the electric field direction of.

According to such a method, since the cell thickness is not used as a means for unwinding the helix of the liquid crystal molecules, it is not necessary to make the cell thickness equal to or smaller than the pitch of the liquid crystal molecules, and the cell thickness can be increased. Not only could it be alleviated, the production cost could be reduced, but a margin for process control for minute dust, which was an obstacle when forming the display cell, could also be provided, improving the production yield.

Next, a method of driving the display device will be described.

With the above structure, in the liquid crystal display device, as shown in FIG. 1, when the electrodes provided on the first and second substrates have no potential, the direction of spontaneous polarization of the liquid crystal molecules in ′ is
The orientation is according to the "direction of the electric field of the cell" (position II).
On the other hand, when a potential is applied to the electrodes that is opposite to the "direction of the electric field of the cell", the direction of the spontaneous polarization of the liquid crystal molecules in the direction of the magnitude of the new electric field is Follow (I position). When an externally applied voltage is not applied, the liquid crystal molecules return to the position (II) because they have only one stable position due to the "direction of the electric field of the cell". For this reason, the driving voltage is improved in a single direction, so there is no need to use a bipolar output type drive IC, and the IC can be simplified and production costs can be reduced compared to conventional drive methods. It is a feature.

In addition, although it is a halftone display of contrast, which is impossible in the conventional display device using the ferroelectric liquid crystal, according to this method, since the liquid crystal molecule has only one stable direction,
Since the electric field direction opposite to the electric field direction of the cell is applied from the electrodes, it is characterized in that halftone display is possible by adjusting the magnitude of the applied electric field.

The present invention will be described below with reference to examples.

[Example] FIG. 2 shows a manufacturing process of a substrate used in the present invention.

After cleaning and drying the glass substrate (1) having the wiring and the lead (2) by the transparent conductive film patterned in the drawing (A), the organic alignment film material (3), for example, a polyimide solution or a Ny solution, is added to the ferroelectric organic material. A solution in which the resin P (VDF + TrFE) was added in a ratio of 1: 1 with respect to the amount of the resin for the organic alignment film was coated by the spin method. In another embodiment, P (VDF
+ TeFE), PVDF, P (VDCN + VAc) was tested, but it was found that it could be used due to the difference in spontaneous polarization. Then, in order to evaporate the solvent, baking was performed at 110 ° C. for 20 minutes in a N ₂ atmosphere in a clean oven. The first substrate was manufactured by the above method. In addition, a second substrate having electrodes and leads orthogonal to the first substrate was manufactured by the same method.

Next, these first and second substrates are arranged so that the surfaces of the glass substrate having wirings and leads face each other as shown in FIG. Thereafter, a circuit as shown in (C) is applied to the electrodes and leads on the both substrates from the outside with a DC voltage (4).
Is formed by applying. In this embodiment, the thickness of the air capacitor is 3 μm and the externally applied voltage is 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 here, in an inert gas atmosphere at 350 ° C.
I did a cure 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, and has the "cell electric field direction". After that, a treatment for aligning the major axis directions of the liquid crystal molecules is performed on the surfaces of the first and second substrates, and then the peripheries of the first and second substrates are sealed with an adhesive. A cell was prepared by the liquid crystal display method.

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

In the ON portion, a pulse having a width of 83 μsec. Is applied every 17 msec. In a direction in which an electric field opposite to the “electric field direction of the cell” is generated, and the pixel becomes bright. In the OFF part, no signal is applied from the outside, and the pixel shows a dark state because of the only stable directionality (monostability) that the cell has. At this time, in another embodiment, it is turned on to generate an electric field in the same direction as the "cell electric field direction".
When a voltage of about 1/5 to 1/4 was applied to the signal, it was possible to increase the speed of change to dark.

"Effect" By providing a film with spontaneous polarization fixed in a certain direction, the "electric field direction of the cell" can be created, and even in a cell with a cell interval thicker than the length of the helical pitch of the liquid crystal molecule, It is possible to unwind the helicopter that it has, and it is now possible to have a margin that reduces the material cost such as the flatness of the substrate.

In addition, by creating the "direction of the electric field of the cell", the liquid crystal molecules can only have a stable state (monostable), and the drive signal only needs to be applied with a voltage in only one direction.
Was able to be simplified.

Further, since this cell is monostable, it is possible to obtain an intermediate gradation depending on the magnitude of the voltage applied from the outside.

[Brief description of drawings]

FIG. 1 shows an outline of the liquid crystal display device of the present invention and a state of liquid crystal molecules inside. FIG. 2 shows a method for manufacturing a substrate of a liquid crystal display device of the present invention. FIG. 3 shows a state of electro-optical effect when the liquid crystal display device of the present invention is driven.

 ─────────────────────────────────────────────────── ─── Continuation of the front page Judgment panel Judge General Atsushi Mitsuda Judge Ryo Maruyama Judge Hiroshi Ohara (56) References JP 61-282882 (JP, A) JP 61-159627 (JP, A) ) JP-A-54-155795 (JP, A) JP-A-53-110545 (JP, A) JP-A-51-34694 (JP, A) JP-A-62-124525 (JP, A) JP-A-62- 153836 (JP, A)

Claims (2)

[Claims] 1. A first substrate having a thin film exhibiting ferroelectricity on an insulating substrate provided with transparent electrodes and leads, and an insulating substrate provided with transparent or non-transparent electrodes and leads. Ferroelectric liquid crystal molecules are sandwiched by a second substrate having a ferroelectric thin film, and the ferroelectric thin films on the first and second substrates are both:
A spontaneous polarization electric field that is the only stable state is formed by having a spontaneous polarization that is perpendicular to the first and second substrates and has a fixed direction in the same direction. When no electric field generated by the electrodes and leads provided above is applied, the direction of spontaneous polarization of the ferroelectric liquid crystal molecules follows the spontaneous polarization electric field, and the direction opposite to the spontaneous polarization electric field is the first polarization direction. When the electric field generated from the electrodes and the leads provided on the second substrate is applied, the direction of the spontaneous polarization of the ferroelectric liquid crystal molecule has the direction of the ferroelectric liquid crystal molecule according to the spontaneous polarization electric field. A liquid crystal display device characterized by being different from the direction of spontaneous polarization. 2. The long axis of a liquid crystal molecule according to claim 1, which is formed on a thin film having ferroelectricity on the first and second substrates, or on a thin film newly provided on the thin film. A liquid crystal display device characterized by being subjected to an alignment treatment for aligning the same in a certain direction.