JPH03288826A - liquid crystal electro-optical element - Google Patents

Abstract

PURPOSE:To obtain a good memory effect by bistable uniform orientation and to prevent the degradation in contrast by an orientation defect by forming grooves which are unified in a fixed direction on at least one electrode surface and further accumulating the thin films of a high-polymer compd. by a Langmuir-Blodgett's method on this surface. CONSTITUTION:The grooves which are approximately unified in the fixed direction are formed on at least one electrode 4 surface of the liquid crystal electrooptical element which crimps a ferroelectric liquid crystal 6 between a pair of substrates 1 and 2 having a scanning electrode group and a signal electrode group and further, the thin film of the high-polymer compd. formed by the Langmuir-Blodgett's method is accumulated on this surface. A glass substrate surface 1 provided with the transparent electrodes of ITO is treated by a polishing liquid contg. Al2O3, by which the fine grooves facing the fixed direction are formed on the ITO surface in such a manner that the directions thereof are paralleled in the upper and lower substrates 1, 2. The surface properties and the thickness of the oriented films are controlled. The excellent liquid crystal having the good memory effect by the bistable uniform orientation is obtd. in this way.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an electro-optical element using ferroelectric liquid crystal.

[Background Art] In recent years, information processing has become increasingly computerized, and along with this, there has been a strong desire for computers to be made smaller. In particular, CRT displays, which have held a strong position as man-machine interfaces, are heavy and large, so they are being replaced by lighter and thinner liquid crystal displays and plasma displays. Twisted nematic type liquid crystal displays are generally used. However, for high-definition displays, ferroelectric liquid crystals, which have faster response times and have memory properties, are being researched than nematic liquid crystals, which have slower responses. (For example, C1ark et al., Appl. Phys. Lett., 36,899
(1980)) Conventional methods for controlling the orientation of electro-optical elements using ferroelectric liquid crystals include a method of forming an organic polymer layer such as polyimide on the surface of a substrate and performing a rubbing treatment, a method of evaporating SiO from an oblique direction, There are methods such as a magnetic field orientation method and a method of slow cooling while applying a direct current electric field.

[Problems to be solved by the invention] The response characteristics of ferroelectric liquid crystals due to electric fields, especially the memory effect, are
Good memory is achieved according to the switching principle of the chiral smect C phase (hereinafter abbreviated as "SmC" phase), which is thought to be greatly influenced by chemical or electrochemical interactions between liquid crystal molecules and the substrate surface. In order to obtain this effect, it is desirable that the liquid crystal molecules be aligned parallel to the substrate surface and in one direction.

However, when conventional orientation control methods such as applying a polymer compound to the substrate surface and rubbing the film surface are used, the molecular orientation in the SmC'' phase is twisted, that is, the liquid crystal molecular director moves from one substrate surface to the opposite substrate surface. The ferroelectric material rotates on the side surface of the cone, and the spontaneous polarization tends to point inward or outward at both the upper and lower interfaces, making it difficult to obtain a good memory effect. It is known that when spontaneous polarization is aligned in one direction by applying an electric field, a polarized charge is generated on the surface, which forms a reverse electric field inside the ferroelectric material.In the case of ferroelectric liquid crystals, ionic impurities contained inside is localized by this reverse electric field, and if the polarization is reversed in that state, the mobility of the ions is low, so immediately after the polarization is reversed, the electric field due to these ions will be superimposed on the reverse electric field and will be applied to the liquid crystal. Bistability is lost.

The strength of this electric field (hereinafter referred to as an anti-electric field) is proportional to the spontaneous polarization value of the liquid crystal, and inversely proportional to the sum of the capacitances of the liquid crystal layer, the insulating layer, and the alignment film. In order to reduce the absolute value of the anti-electric field in order to maintain bistability, it is necessary to reduce the thickness of the insulating layer and alignment film. However, when an alignment film of polyimide or the like is formed by dipping or spin-coating as has been conventionally done, it is difficult to obtain a uniform thin film on the order of 100 Å or less.

One of the alignment film forming methods that does not involve rubbing treatment is
The Langmuir-Blodgett method (hereinafter abbreviated as LB method) has been proposed (for example, Ikeno et al.: Institute of Electronics, Information and Communication Engineers Technical Report Vol. 1.88 No.

267 (198B)). This method is suitable for film thickness control. However, in the case of conventional LB alignment films, it is known that the alignment of liquid crystals depends on the number of accumulated layers and the structure of the accumulated polymer compound, and in order to obtain satisfactory characteristics as a liquid crystal alignment film, material selection is necessary. In addition, in the case of materials that require a certain number of accumulated layers for orientation, there are problems such as the inability to control the film thickness in a region where necessary device characteristics can be obtained.

The present invention solves the above problems by improving the method for forming a liquid crystal alignment film and controlling the surface properties and the thickness of the alignment film. An object of the present invention is to provide an excellent liquid crystal electro-optical element having a memory effect.

[Means for Solving the Problems 1] In order to solve the above problems, the liquid crystal electro-optical device of the present invention is a liquid crystal electro-optic device comprising a ferroelectric liquid crystal sandwiched between a pair of substrates having a scanning electrode group and a signal electrode group. The optical element is characterized in that grooves with substantially uniform directions are formed on the surface of at least one electrode, and a thin film of a polymer compound is deposited on the same surface by the Langmuir-Prodgett method.

[Example 1] FIG. 1 is a main sectional view of an electro-optical element in an example of the present invention. The surface of the glass substrate with ITO transparent electrodes is A.
By treating with a polishing liquid containing 12O3, fine grooves oriented in a certain direction were formed on the surface of the substrate so that the directions were parallel to each other on the upper and lower substrates.

Next, an N,N-dimethylacetamide/benzene mixed solution of a compound made into a hydrophobic group by adding a long-chain alkylamine to polyamic acid was spread on the water surface to form an L membrane (Langmuir M), and the surface pressure was set to 25 dyne/benzene. The substrate was pulled up parallel to the direction of the grooves formed in the ITO at a speed of 15 mm/min while maintaining the LB film as one layer. After film formation, an imidization reaction is performed to obtain a polyimide thin film. Here, we use the method proposed by Kakimoto et al. (Chemistry Lett, 823 (1)
The imidization was carried out according to the method (see 986). The thus obtained substrates were assembled so that the pulling direction was 180 degrees at the top and bottom.

The cell thickness was approximately 2μ.

A ferroelectric liquid crystal composition was heated and sealed between the substrates, and slowly cooled to room temperature. Here, the liquid crystal is ZLI-377 manufactured by Merck.
4 was used. The liquid crystal electro-optical element obtained by the above method was sandwiched between polarizing plates whose polarization axes were orthogonal to each other, and
A driving waveform shown in FIG. 22 was applied, and the optical response shown in FIG. 22 at that time was evaluated. It is thought that the better the memory effect is, the larger the ratio I2/I+ of the amount of transmitted light when an electric field is applied (I+ in Figure 2, 22) and the amount of transmitted light after the electric field is removed (I2 in Figure 2, 22). Actual 1@ Example: Processed at 25℃ 2/
The I voltage was 0.87 and the contrast ratio was 1:12, which was good. Almost similar results were obtained when the number of laminated LB films was 3 or 5.

[Example 2] When an alternating waveform of ±25 V and 15 Hz was applied for about 10 seconds between the electrodes of the device shown in Example 1, the alignment state of the liquid crystal was found to be a dense striated structure in a direction almost perpendicular to the layer direction. It appeared in a uniform state with.

By this electric field treatment, zigzag defects formed during cooling of the encapsulation were removed. The element was held between polarizing plates whose polarization axes were perpendicular to each other, and the driving waveform shown in FIG. 21 was applied to evaluate the optical response shown in FIG. 22. In this example, at 25°C, I2/I+=0.98 and the contrast ratio was 1:37, which was good.

[5! [Bright Effects] With the above configuration, the present invention solves the drawbacks of the prior art by improving the method for forming a liquid crystal alignment film and controlling the surface physical properties and film thickness, and achieves good results by bistable uniform alignment. It was possible to provide an excellent liquid crystal electro-optical element that has a memory effect and exhibits little reduction in contrast due to alignment defects.

[Brief explanation of drawings]

FIG. 1 is a sectional view of a liquid crystal electro-optical element according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of a driving waveform used in evaluating the liquid crystal electro-optical element of the present invention and a corresponding optical response. 1.2. ,,upper and lower glass substrates 3 00. Spacer 4.5. ,,transparent electrode 6 09. Liquid crystal layer 9.10. ,,LE alignment film 11, 12. , polarizing plate 21 , , drive waveform 22 , , optical response or more

Claims (1)

[Claims] (1) In a liquid crystal electro-optical device consisting of a ferroelectric liquid crystal sandwiched between a pair of substrates having a scanning electrode group and a signal electrode group, grooves with substantially uniform directions are formed on the surface of at least one electrode. A liquid crystal electro-optical element characterized in that a thin film of a polymer compound is deposited on the same surface by the Langmuir-Prodgett method.