JPS61236526A - Optical modulation element - Google Patents

Abstract

PURPOSE:To obtain good orientation and to attain satisfactory high-speed responsiveness and bistability by orienting liquid crystal molecules in a prescribed direction by oriented films each consisting of a polystyrene high-polymer film having an insulating characteristic. CONSTITUTION:Transparent electrodes 9, 10 each consisting of an 'NESA(R)' film or ITO film, etc. are patterned and formed on transparent substrates 11, 12 and are the oriented films 7, 8 are formed thereon by the formation of the polystyrene high-polymer film and rubbing treatment. A ferroelectric chiral smectic liquid crystal 6 is sealed between the two substrates. The element formed in such a manner is heated up to the temp. at which the liquid crystal 6 turns to isotropic liquid, then the element is cooled down to the temp. at which the liquid crystal exhibits the ferroelectric chiral smectic phase to array the spiral axes of the liquid crystal molecules. Since the oriented films consisting of the high-polymer film having the insulating characteristic are used, the good orientation is obtd. and the contrast is improved. The satisfactory high speed responsiveness and stability are thus realized.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a light modulation element using a ferroelectric liquid crystal material, particularly a ferroelectric smectic liquid crystal.

<Conventional technology> Conventionally, as a liquid crystal display device, twisted nematic (tu+j, ted...e) using nematic liquid crystal has been used as a liquid crystal display device.
matic (hereinafter abbreviated as TN) field effect type, so-called TN
Cells are common and are widely used in display devices such as electronic desktop calculators and digital watches.

However, despite improvements in liquid crystal materials, cell structures, driving methods, etc., TN cells lack high-speed response, so they are used for TV image displays, portable computer displays, and optical shutter devices, which have recently attracted particular attention. for,
There was a problem with responsiveness.

Therefore, as a method to solve the problem regarding responsiveness, display elements using ferroelectric chiral smectic liquid crystals have been developed.N, A, C1ark, S, T.

It has been proposed by L aHerwal et al. (Appl.

Phys, 36, 899.1980).

Figures 2 (a), (b), and (c) show examples of ferroelectric force and tick liquid crystal cells.
It is shown schematically.

In the steady state, as shown in Figure 2 (,), the liquid crystal molecules 1
are arranged at a tilt angle θ with respect to the helical axis 2, and have a helical structure. Further, the liquid crystal molecules 1 have spontaneous polarization in a direction perpendicular to each molecule.

Now, when an electric field (E) greater than a certain critical electric field is applied between the upper and lower substrates as shown in FIG. 2(b), the helical structure of the liquid crystal molecules 1 is dissolved and all the liquid crystal molecules 1 are facing the same direction. Since the alignment of the liquid crystal molecules 1 depends on spontaneous polarization, there are two alignment directions depending on the direction of the electric field (E, -E). Liquid crystal molecules have an elongated shape and exhibit so-called birefringence, in which the refractive index differs in the major axis direction and the minor axis direction. An optical modulation element that performs a switching action can be obtained. This change in the arrangement of liquid crystal molecules simply changes the orientation of the liquid crystal molecules within the layer, so it does not involve a change in the layer structure as in the TN field effect type, and has high-speed response.

Furthermore, even in a steady state where no electric field is applied, it is possible to eliminate the helix by making the thickness of the liquid crystal layer thinner than the helical pitch of the liquid crystal molecules. In this case as well, the alignment direction of the liquid crystal molecules exhibits two directions and exhibits bistability. For example, an electric field (E) is applied to obtain the stable orientation shown in FIG. 2(b), but even when the electric field is turned off, the state shown in FIG. 2(b) continues to be maintained. Also, when applying an electric field (-E),
Although the stable state orientation shown in FIG. 2(c) is obtained, the state shown in FIG. 2(c) continues to be maintained even when the electric field is turned off.

By reducing the thickness of the liquid crystal layer in this way, high-speed response and bistability can be achieved.

In the figure, numeral 1 is the liquid crystal molecule, 2 is the helical direction, and 3.4 is the axial direction of the upper and lower polarizers, respectively.

In the optical modulation method using the above birefringence phenomenon, the incident light intensity ■. The relationship between and the transmitted light intensity I is as follows: % Condition in Figure 2 (b): 1 = 0 Condition in Figure 2 (c): 1 = (Io/2) wood sin'' (4θ) book 5in2iπ (Δn*d/λ)) Here, Δn: Refractive index anisotropy of ferroelectric smectic liquid crystal d: Thickness of ferroelectric smectic liquid crystal layer θ: Ferroelectric smectic liquid crystal is the helical tilt angle.

<Problems to be Solved by the Invention> However, at present, a ferroelectric smectic liquid crystal cell having sufficient high-speed response and bistability as a light modulation element has not been put into practical use.

SUMMARY OF THE INVENTION An object of the present invention is to provide a ferroelectric smectic liquid crystal light modulator having high-speed response and bistability.

<Means for Solving the Problems> The light modulation element of the present invention is characterized in that an insulating polystyrene-based polymer film is used as an alignment film for aligning liquid crystal molecules in a predetermined direction.

<Examples> Hereinafter, the present invention will be specifically explained with reference to illustrated examples.

FIG. 1 is a vertical cross-sectional view showing the structure of one embodiment of the light modulation element of the present invention, in which polarizers 13, 14, transparent electrodes 9, 10
, consisting of alignment films 7 and 8, a liquid crystal material 6 and a sealing material 5,
On transparent substrates 11 and 12 such as glass that are arranged opposite
Transparent electrodes 9 and 10 such as an ESA film or an ITO film are patterned, and a polystyrene polymer film is formed thereon, followed by a rubbing treatment to form alignment films 7 and 8. In between, a ferroelectric chiral smectic liquid crystal 6 is injected as a liquid crystal material and hermetically sealed with a sealing material 5, and polarizers 13.14 are disposed on the outside of both substrates 11.12.

Here, examples of the ferroelectric smectic liquid crystal 6 include the following.

p-decyloxybenzyliden-p'
amino 2 methyl-butyl c
innate (DOBAMBC) p octyl
oxybenzyl 1clene p'ami
no-2-methy-Ibutyl-α-chlo
ro-cinnamate (OOBAMBCC) p-d
ecyloxybenzylidene p'-am
ino-2-methyl-butyl-α-cyan
o-c innate(OOBAMBCC) p-t
ettradecylooxybenzylidene-
p'-amino-2-methylbutyl-α-
cyano-cinnamate (TDOBAM BCC
)p Hexyloxybenzylidene-p
'-amino-2-chlor.

-Q -propyle-cinnamate(HOB
ACPC) p-octyloxybenzyl 1de
ne-p'-amino-2-methy butyl
-α-methyl -cinnamate (OOBA
MBHC) p-azoxy-cinnamate-me
tyl-2-butanol (PACMB) p-dod
ecyloxybenzylidene-p' am
ino-2meth-yl-cinnamate (D
DOBAHBC) p-octyloxybenzyl
1den-p'-amino-2-methylb
-util -cinnamate (COBAHBC)
p-hexyloxybenzyl 1dene-p'
-amino-2-methyl-buLyl -ci
In addition, the alignment films 7 and 8 are coated with a polystyrene 2% 1 methyl acetate solution using a spinner, baked at 10°C for 1 hour, and then rubbed with a puff or the like. formed, and the film thickness is approximately 50
It is insulated and has insulating properties, and also functions as an insulating film.

Further, in the liquid crystal cell, the transparent substrates 11 and 12 are arranged so that the gap between the two transparent substrates 11 and 12, that is, the cell thickness is 2E μm.
After bonding the ferroelectric smectic liquid crystals together and injecting the ferroelectric smectic liquid crystal, the cell is heated to a temperature at which the ferroelectric smectic liquid crystal becomes an isotropic liquid, and then to a temperature at which it exhibits a ferroelectric chiral smectic phase. Approximately 0.2['C
The helical axes of the liquid crystal molecules are aligned by cooling at a cooling speed of /mlnl.

<Effects of the Invention> As described above, the light modulation element of the present invention uses an insulating polystyrene-based polymer film as an alignment film, thereby obtaining good alignment and improving contrast. It becomes possible to easily realize a ferroelectric chiral or mectic liquid crystal cell having sufficient high-speed response and bistability.

[Brief explanation of drawings]

Fig. 1 is a vertical cross-sectional view of a cell structure showing one embodiment of the present invention, and Fig. 2 (a), (b), and (c) show the molecular arrangement of ferroelectric chiral or mectic liquid crystal used in the present invention. Schematic 5... Sealing material 6... Ferroelectric smectic liquid crystal 7.8.
...Alignment film 9.10...Transparent electrode 11.12...Transparent substrate 13.14...Polarizer

Claims (1)

[Claims] In a light modulation element in which transparent electrodes are formed and a ferroelectric liquid crystal substance is sealed between the transparent electrodes, an insulating polystyrene-based film is used as an alignment film to align liquid crystal molecules in a predetermined direction. A light modulation element characterized by using a polymer film of.