JPH04140720A - Ferroelectric liquid crystal element - Google Patents

Abstract

PURPOSE:To improve the memory performance and to obtain the liquid crystal element which is high in contrast by forming insulating films between electrodes of respective substrates which forms a liquid crystal cell and making the insulating films thicker than the electrodes which serve as display picture elements. CONSTITUTION:A glass substrate 11 with an ITO electrode 14 is coated with a photosensitive high polymer film as an insulating film by spin coating. Then the film is removed at picture element parts to leave the high polymer film 21 in a columnar shape at places other than the picture element parts. Then they are coated with an orienting film 15, two substrates which are rubbed are assembled across spacers, and liquid crystal is injected. Consequently, the orientation state of liquid crystal molecules at the picture element parts change uniformly as compared with the state before voltage application and the high memory performance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to the structure of a liquid crystal element using ferroelectric liquid crystal.

[Conventional technology]

Because ferroelectric liquid crystals have memory properties and high-speed response on the microsecond scale, they are expected to be put to practical use in large-capacity displays and high-speed liquid crystal shutters.

FIG. 2 is a cross-sectional view showing the structure of a liquid crystal element using ferroelectric liquid crystal. A transparent electrode 14 and an alignment film 15 are formed on the opposing surfaces of the upper and lower glass substrates 11, and both substrates face each other with a spacer 16 in between and are sealed with a sealing material 12. Inside this is a liquid crystal layer 10 made of ferroelectric liquid crystal.

Here, the alignment treatment of the liquid crystal layer 10 has a great influence on the memory property, which is one of the ferroelectric liquid crystal elements. One effective technique for improving memory performance is 'Japanese
Journal of APMied Physics
“Vo e 1 B, No 3 (1989, 4)
, p. 486. Here, after forming an organic alignment film on each of the two substrates on which electrodes are formed, a rubbing treatment is performed, and a ferroelectric liquid crystal is injected between the two substrates to create a liquid crystal element. Thereafter, an alternating electric field is applied between the electrodes of the liquid crystal element to change the alignment state of the liquid crystal molecules, thereby improving memory performance.

[Problem to be solved by the invention]

However, in the conventional cell structure as shown in Figure 2, when the alignment state is changed by applying an alternating electric field, the alignment state does not change uniformly across the entire pixel area, resulting in a decrease in contrast. There was a problem with inviting people.

The purpose of the present invention is to solve the above-mentioned problems, and to provide a liquid crystal that uniformly changes the orientation state of the entire pixel area when an alternating electric field is applied after the liquid crystal is injected, thereby realizing good memory performance. It provides a cell structure.

[Means to solve the problem]

In order to achieve the above object, the present invention provides a ferroelectric liquid crystal cell which has a rubbed alignment film and which is formed by applying an alternating electric field to change the alignment state of liquid crystal molecules. It is characterized in that an insulating film is formed between each electrode of each substrate forming a cell, and the thickness of this insulating film is made thicker than the thickness of the electrode forming a display pixel.

[Function] It is known that by applying an alternating electric field after injecting ferroelectric liquid crystal into a cell, the alignment state of the liquid crystal molecules changes, thereby achieving good memory properties. It has been difficult to uniformly change the orientation state over the entire pixel.

As a result of detailed research, we found that this is caused by the interaction between the alignment film interface and liquid crystal molecules. In other words, the stronger the interaction between the alignment film interface and the liquid crystal molecules, the more difficult it becomes to uniformly change the alignment state of the liquid crystal molecules. Generally, when liquid crystal molecules are aligned by a rubbing method, it is known that the stronger the rubbing force, the stronger the interaction between the alignment film interface and the liquid crystal molecules. Therefore, when changing the alignment state of liquid crystal molecules using an alternating electric field, it is necessary to weaken the rubbing force in order to uniformly change the alignment state within a pixel. However, excessively weak rubbing makes it impossible to align liquid crystal molecules. Therefore, by adopting the cell structure shown in Figure 1, the pixel area has a concave shape that is lower than the non-pixel area between pixels, and when rubbing is performed, the rubbing force is very weak compared to the non-pixel area. As a result, the orientation becomes weaker. On the other hand, the non-pixel area receives stronger rubbing than the pixel area, so the orientation is good. In other words, the orientation of the pixel area is weak, but the orientation of the non-pixel area surrounding the pixel is strong. Therefore, the weak alignment of the pixel part can be compensated for by its influence.In addition, since the rubbing force is weak in the pixel part, the interaction between the alignment film interface and the liquid crystal molecules is weak, and when an alternating electric field is applied, It is possible to uniformly change the alignment state of liquid crystal molecules in the pixel portion.In other words, by using the cell structure of the present invention,
The alignment state of liquid crystal molecules can be uniformly changed by an alternating electric field without weakening the alignment, and a liquid crystal cell with high memory performance and high contrast can be provided.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic cross-sectional view of one substrate of a liquid crystal element according to the present invention. A photosensitive polymer film was coated as an insulating film on the glass substrate 11 with the ITO electrode 14 using a spin cord to a controlled thickness of about 500 OA. Thereafter, the film in the pixel area was removed by an exposure process and an etching process, leaving a columnar polymer film 21 in a location other than the pixel area as shown in the figure.

Next, an alignment film 15 was coated on top thereof to a thickness of about 10 OA, and then rubbed. The other substrate constituting the liquid crystal element was prepared in the same manner, the two substrates were assembled via a spacer so that the cell thickness was approximately 2 μm, and liquid crystal was injected. Thereafter, this cell was slowly cooled from about 100°C to 25°C at 75°G/1 hour. Thereafter, alternating current with a frequency of 30 Hz and an effective voltage of 30 mm was applied for about 20 seconds.

When this liquid crystal element was observed under a polarizing microscope, it was confirmed that the alignment state of liquid crystal molecules in the pixel portion had changed uniformly compared to before voltage application. In addition, to confirm the memory property, we measured the transmittance after applying a pulse with a voltage of 25 V and a pulse width of 200 μs and the rate of change in transmittance after 2.2 ms.
As a result of measurements on the liquid crystal cell of this example and the conventional liquid crystal cell, the results shown in Table 1 were obtained. This shows that the liquid crystal cell of this example has high memory properties.

Table 1 [Effects of the Invention] As described in the above embodiments, by adopting the cell structure of the present invention, the pixel portion can have weaker leveling compared to the non-pixel portion, so it is possible to improve memory performance. Furthermore, if an alternating electric field is applied to change the orientation of the liquid crystal molecules after the liquid crystal is injected, the orientation of the liquid crystal molecules in the pixel area can be changed uniformly, making it possible to realize a liquid crystal element with high contrast.

[Brief explanation of drawings]

FIG. 1 is a schematic sectional view of a liquid crystal cell of the present invention, and FIG. 2 is a schematic sectional view of a conventional liquid crystal cell. DESCRIPTION OF SYMBOLS 10...Liquid crystal layer, 11...Glass substrate, 12...Nool material, 3...Spacer 4...Transparent electrode, 5. ...Alignment film, 1...Insulating film.

Claims (1)

[Claims] A liquid crystal element in which a ferroelectric liquid crystal is sandwiched between a pair of substrates having electrodes on opposing surfaces and alignment films formed on the electrodes and subjected to a rubbing process, and an alternating electric field is applied between the opposing electrodes. A ferroelectric liquid crystal element in which the alignment state of the ferroelectric liquid crystal is changed, characterized in that an insulating film thicker than the thickness of the electrodes is formed between the electrodes of each of the substrates.