JPS6361234A - Liquid crystal electro-optical device - Google Patents

Abstract

PURPOSE:To stabilize an orientation of a liquid crystal molecule between the upper and the lower substrates, and to improve the characteristic of a memory by arranging a dipole of a ferroelectric liquid crystal molecule in the vicinity of both the substrates, in a stable direction against a dipole of the substrate. CONSTITUTION:Transparent substrates 31, 32 on which an electrode and an oriented film such as a polyimide film, etc., have been formed are opposed and placed, and between them, a ferroelectric liquid crystal, a smectic liquid crystal desirably is injected. This liquid crystal molecule 33 is brought to uniaxial parallel orientation, and between one substrate and the other substrate, the molecule 33 is in a twisted orientation, and as for this twist, there exist two kinds which turn to the right and the left on a conical locus 35 on which the molecule 33 can move. However, in any state, in the vicinity of the substrates 31, 32, a dipole 34 of the molecule 33 is arranged in a stable direction against a dipole 37 of the substrate, therefore, the molecule 33 is oriented stably between both the substrates, and a good bistability is shown. Also, when an electric field is applied from the outside, oriented states of a right turn and a left turn is brought to switching, therefore, these two oriented states can be confirmed visually as a color difference.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a high-speed response temperature optical device using ferroelectric liquid crystal, and in particular, it is possible to achieve uniformity by improving the initial orientation of the liquid crystal. The present invention relates to a liquid crystal electro-optical device that has orientation and stable memory properties and is capable of storing information.

[Conventional technology]

Ferroelectric liquid crystal is Smectic C* (hereinafter referred to as SC*)
The phase has a helical structure due to the effect of asymmetric carbon atoms in the molecule. In Figure 6, which schematically depicts the helical structure of the SC* phase, that is, the orientation state of liquid crystal molecules in a thick cell, @+1, (to) is a transparent substrate, such as a glass substrate, placed opposite to each other, (To) is both claw plate t3+1
,) are ferroelectric liquid crystal molecules injected and interposed between the
These liquid crystal molecules are arranged at a predetermined interval between both claw plates a1) and (2), but in this figure, a part of them is shown for ease of understanding. μs is a conical trajectory along which the liquid crystal molecules can move. , ■ is the dipole moment in the tangential direction of the conical locus μs in the direction perpendicular to the liquid crystal molecules Q, and ⑼ is the plane parallel to the layer formed by the liquid crystal molecules, in other words, the conical locus in which the liquid crystal molecules can move ( An example is the normal direction of this plane, and the angle is the angle of inclination that indicates how much the liquid crystal molecules are tilted from the normal direction.

Furthermore, when this ferroelectric liquid crystal is injected into a thin cell, the helix unravels due to the influence of the interface, and if the tilt angle of the injected ferroelectric liquid crystal is θ, the molecules return to the original helical axis, that is, the normal direction of the layer. It faces in a direction tilted by +θ or -θ. The orientation state of the molecules at this time is shown in Fig. 7. At this time, the dipole (2) of the molecules is directed upward or downward with respect to the cell substrate 01), corresponding to the direction in which the molecular princess is tilted. .

If an electric field is applied from the outside in this state, the direction of the dipole can be reversed depending on the direction of the electric field, which means that the orientation of the molecules can be reversed between 10 and a part. This phenomenon and 2
By combining a chromatic dye and one polarizing plate or two polarizing plates, it is possible to create a contrast between light and dark in the difference when the alignment direction of the molecules is +θ and partially. Accordingly, the entire display element can be formed. The characteristics of this display element are that the switching speed is 100 to 1000 times faster than elements using conventional nematic liquid crystals, and each state is stable when the domestic direction of the molecules is +θ. If so, it means that there is a memory effect. This memory effect is indispensable when displaying with high-duty multi-branch drive. This display element is described in detail in, for example, Japanese Unexamined Patent Publication No. 107216/1983.

FIG. 8 is a schematic diagram showing the alignment state of liquid crystal molecules when an electric field is applied from the lower substrate to the lower substrate in a conventional liquid crystal electro-optical device using ferroelectric liquid crystal. (to) is in, o, or 8nO! and ITO
It is a glass substrate on which thin film transparent electrodes such as , etc. are formed to form a cellular structure, and η indicates the direction of the dipole of the substrate (a + 1 e G 埒). ■ is aligned downward, this is bottom 1i11
This shows that an electric field is applied from the first substrate (toward) to the lower substrate 3υ.

FIG. 9 is a schematic diagram showing oriented dust of liquid crystal molecules when the direction of the electric field in FIG. 8 is reversed and the electric field is applied in the direction from the upper substrate G1) to the lower fill substrate (2).

In order for a liquid crystal electro-optical device to exhibit a memory effect, both of the alignment states shown in FIGS. 8 and 9 must be stable, and each alignment state must not maintain its orientation even when the electric field is removed. must not.

For this reason, in conventional devices, a thin film cell with a gap width of, for example, 0.5 μm is used to physically press down the liquid crystal molecules (34), and when no electric field is applied, the state shown in Fig. 8 and the state shown in Fig. 9 are shown. An attempt is made to stabilize each state in FIGS. 8 and 9 by preventing molecular inversion between states.

[Problem that the invention seeks to solve]

However, the conventional device has not yet achieved a sufficient memory effect, and this is due to the dipole ■ of the liquid crystal molecule eel and the dipole (3) of the substrate opening 1) and
Paying attention to η, at the substrate interface on one side, the twin %■, 0
This is thought to be due to the occurrence of repulsion between 71 and 71. That is, in Fig. 8, the dipole - of the lower substrate (to) and the dipole ■ of the liquid crystal molecule -, and in Fig. 9, the dipole 371 of the lower substrate 0υ and the dipole ■ of the liquid crystal molecule root are respectively They interact and repel, causing destabilization of the alignment of the liquid crystal molecules. Therefore, when the electric field is removed, the alignment is disturbed near the destabilized 11111 substrate, and as a result, the alignment of the ferroelectric liquid crystal becomes unstable. Since the characteristic memory effect is difficult to appear, there is a problem in that display cannot be performed satisfactorily in high time division driving.

The present invention was made to solve the above-mentioned problems, and it is an object of the present invention to provide a liquid crystal electro-optical device having uniform alignment and good memory effect.

[Means for solving problems]

In the liquid crystal electro-optical device according to the present invention, the liquid crystal molecules are uniaxially parallel aligned on both substrates, with the long sleeve directions of the molecules aligned in a constant direction, and the liquid crystal molecules are uniaxially parallel aligned on one substrate. The axis direction of the liquid crystal molecules is different from the axis direction of the uniaxial parallel alignment on the other substrate, and the liquid crystal molecules have a twisted orientation between the one substrate and the other substrate, and this twisted state is caused by the movement of the liquid crystal molecules. There are two types of orientation: a clockwise orientation state and a counterclockwise orientation state on the conical trajectory to be obtained, and by applying an external electric field, the clockwise orientation state and counterclockwise orientation state can be changed. This is for switching.

[Effect]

In the molecular alignment in this invention, the dipoles of the liquid crystal molecules are aligned in a stable direction with respect to the dipoles of the substrates in the vicinity of the upper and lower substrates, regardless of whether they are oriented counterclockwise or clockwise. The liquid crystal molecules are stably aligned between the two plates, exhibiting good bistability, and therefore exhibiting good memory properties.Also, by applying an external electric field, the alignment state of right-handed and left-handed can be changed. Since the two types of orientation states are switched, for example, the two types of orientation states can be visually recognized as a color difference by utilizing the difference in optical rotation with respect to polarized light.

〔Example〕

FIGS. 1 and 2 are schematic diagrams showing counterclockwise and clockwise uniaxially parallel alignment states of liquid crystal molecules according to an embodiment of the present invention, and FIGS. 8 and 4 are FIGS. 1 and M2, respectively. In Figure 0, which is an explanatory diagram of the cell in the orientation state seen from the normal direction of the layer, ■ is the uniaxial parallel alignment direction of liquid crystal molecules near the substrate (3+), and Z is the liquid crystal molecule near the substrate (2). The uniaxial parallel orientation direction of q is shown.

The orientation state shown in FIGS. 1 and 2 is one of the mutually bistable orientation states, and in this example, the orientation direction of liquid crystal molecules on the upper substrate (-) and the orientation direction of the liquid crystal molecules on the lower substrate (-) The orientation direction of the molecules has an included angle that is twice the tilt angle θ of the liquid crystal. One method for obtaining such an alignment state is to perform alignment treatment on the side substrates so that the alignment treatment direction of the upper substrate fi11 and the alignment treatment direction of the upper substrate Q have a value twice the tilt angle θ of the liquid crystal molecules. As an alignment treatment method, for example, polyimide,
Polyvinyl alcohol, polyamide, and siloxane 4? Examples include a rubbing treatment method using any kind of liimide.

The orientation state shown in FIG. 1 and the orientation state shown in FIG. 2 can be switched, for example, by applying a pulsed electric field.

FIG. 5 is an exploded perspective view showing a liquid crystal electro-optical device according to an embodiment of the present invention. In FIG.
The electrodes are patterned, a polyimide alignment film is applied, and a rubbing process is applied to the glass substrates. Two of these substrates are placed facing each other and bonded with a 2.0 μm spacer (for example, a 2.0 μm spacer button) in between, and then tilted. A liquid crystal electro-optical device was constructed by injecting a ferroelectric liquid crystal with an angle of 21° and combining it with a polarizing plate (931).The arrow example shows the rubbing direction of the lower substrate, υ
4 indicates the rubbing direction of the upper board, the upper and lower boards (supports)
The angle θ formed by the rubbing direction a41·(to) is twice the tilt angle of the liquid crystal, that is, 42°. The optical axis of the polarizing plate is the same as the rubbing direction 61141 of the upper substrate for the lower polarizing plate, and the rubbing direction (61141) of the upper substrate for the upper polarizing plate.
(to) and the direction perpendicular to -. In this cell, in the initial alignment state after liquid crystal is injected, the alignment state shown in FIG. 1 and the alignment state shown in FIG. It can be done. At this time, a good display element capable of displaying navy blue on a white background can be obtained, and this element remains free for more than 1 hour.
This exhibits a good memory effect and enables display with high time division and drive.

In the above embodiment, the case where the cell gap is 2.0 μm was explained, but depending on the liquid crystal to be injected, there may be cases where the liquid crystal does not show good alignment, or may have a twisted alignment. However, this can be solved by setting the cell gap to 1 in the range of 1.6 μm to 8 μm.

Also, inject emphasis! ! As the injection liquid crystal, for example, smectic liquid crystal is suitably used, and in particular smectic C*
A liquid crystal exhibiting a phase, or a liquid crystal exhibiting a smectic C* phase and a ♂ phase is preferable.

Furthermore, it is preferable that the axial direction of the uniaxially parallel alignment of the liquid crystal molecules on both thread plates has a value in the range of twice the tilt angle of the liquid crystal molecules ±10' as an included angle, which is an angle smaller than this range. If the angle is large, many twisted orientation states of 2T41 or higher will appear, resulting in poor display quality.
This is because it gives undesirable results.

〔Effect of the invention〕

As described above, according to the present invention, the liquid crystal molecules are uniaxially parallel aligned on both thread plates with the long axis direction of the molecules substantially parallel to the substrates and aligned in a fixed direction, and The axis direction of the parallel alignment is different from the axis direction of the uniaxial parallel alignment on the other substrate, and the liquid crystal molecules have a twisted alignment between the one substrate and the other substrate, and this twisted state is different from the axis direction of the uniaxial parallel alignment on the other substrate. There are two types of states: a clockwise orientation state and a counterclockwise orientation state on a conical trajectory that can be excited, and by applying an external electric field, the above clockwise orientation state and counterclockwise orientation state By switching the alignment state, the molecules are stably aligned in the vicinity of the substrate, so that a liquid crystal electro-optical device having uniform alignment and a good memory effect can be obtained.

[Brief explanation of the drawing]

FIGS. 1 and 2 are schematic diagrams showing counterclockwise and clockwise uniaxially parallel alignment states of liquid crystal molecules according to an embodiment of the present invention, and FIGS. 8 and 4 are respectively FIG. 981 and FIG. FIG. 2 is an explanatory diagram of the cell in the oriented state viewed from the normal direction of the layers, FIG. 5 is an exploded perspective view showing a liquid crystal electro-optical device according to an embodiment of the present invention, and FIGS. 6 and 7 are conventional Figures 8 and 9 are schematic diagrams showing the alignment states of liquid crystal molecules in thick and thin cells, respectively, when an electric field is applied from the lower substrate to the upper substrate and from the upper substrate to the lower substrate, respectively. In the schematic diagram showing the alignment state of liquid crystal molecules in fil
l I E , '921 is the substrate, ■ is the liquid crystal molecule, (to) is the double lattice moment of the liquid crystal molecule, ta is the conical locus,
! 361 is the normal direction, 37) is the dipole moment of the substrate, country is the tilt angle, @11 is the spacer, line is the polarizing plate, 041
~Round is an arrow indicating the orientation direction of night crystal molecules and the optical axis of the polarizing plate. Note that the same reference numerals in each figure indicate the same or corresponding parts.

Claims (6)

[Claims] (1) In a liquid crystal electro-optical device in which transparent substrates having electrodes are arranged facing each other and a ferroelectric liquid crystal is interposed between the two substrates, the liquid crystal molecules on both substrates are substantially parallel to the substrates and the long axis of the molecule is The uniaxial parallel orientation is aligned in a certain direction, and the axial direction of the uniaxial parallel orientation on one substrate is different from the axial direction of the uniaxial parallel orientation on the other substrate, and the direction of the uniaxial parallel orientation from one substrate to the other substrate is different. The liquid crystal molecules have a twisted orientation between them,
There are two types of twisted states: a state in which the liquid crystal molecules are oriented clockwise on a conical trajectory in which they can move, and a state in which they are oriented counterclockwise. A liquid crystal electro-optical state characterized by switching between a state in which the liquid crystal is oriented in a counterclockwise direction and a state in which it is oriented in a counterclockwise direction. (2) The axis direction of the uniaxial parallel alignment of liquid crystal molecules on both substrates is
2. The liquid crystal electro-optical device according to claim 1, wherein the included angle is within a range of ±10° twice the tilt angle of the liquid crystal molecules. (3) The liquid crystal display according to claim 1 or 2, wherein the substrate is made of a polymer film of any one of polyimide, polyvinyl alcohol, polyamide, and siloxane polyimide as a uniaxial parallel alignment treatment agent. optical equipment. (4) The liquid crystal electro-optical device according to any one of claims 1 to 3, wherein the ferroelectric liquid crystal is a smectic liquid crystal. (5) The liquid crystal electro-optical device according to claim 4, wherein the smectic liquid crystal is a liquid crystal exhibiting a smectic C^* phase. (6) The liquid crystal electro-optical device according to claim 4, wherein the smectic liquid crystal is a liquid crystal exhibiting a smectic C^* phase and a liquid crystal exhibiting a smectic H^* phase.