JPS6147930A - Liquid crystal electrooptic device - Google Patents

Abstract

PURPOSE:To improve contrast and memory effect by holding a liquid crystal layer to a temp. range approximate to the upper limit temp. of a smectic C phase and impressing an electric field having a DC bias voltage thereto so that the satisfactory orientation of a ferroelectric liquid crystal is easily obtd. CONSTITUTION:Conductive films 2a, 2b and orientation control films 3a, 3b are formed respectively on the surfaces of substrates 1a, 1b. The films 2a, 2b are the electrodes for impressing the electric field to the liquid crystal 4 held between the substrates 1a, 1b. The films 3a, 3b orient horizontally the liquid crystal 4. The circumference is fixed by a sealant 5 in such a manner that the substrates 1a, 1b are held parallel at a specified spacing to form a cell. The ferroelectric liquid crystal compsn. is thereafter heated to a cholesteric phase and is packed into the cell, then the cell is sealed. Polarizing plates 6a, 6b are disposed on the outside of the cell. The cell is cooled down to the smectic C phase and is held at said temp. The electric field having the DC bias voltage is impressed to the liquid crystal layer by using the electrodes 3a, 3b. The temp. range at which the initial orientation is effected is the range approximate to the upper limit temp. of the smectic C phase.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to liquid crystal electro-optical devices such as display devices and optical shutter devices using ferroelectric liquid crystals.

[Prior art]

Display devices using nematic liquid crystals have advantages such as low power consumption, low driving voltage, and can be made thin and compact, and are often used in calculators, watches, and other devices. However, its electro-optical response is slow, and its application to fields requiring high-speed response, such as optical communications and optical shutter devices such as printer heads, has been limited.

Recently, reports have been made on electro-optical devices using ferroelectric liquid crystals. (For example, N, A, 01ark, B, T
.

Lagerwall, Appl, Phya, La
tt, 56, p, 899. (1980): This shows that the liquid crystal is in the chiral smectic C and H phases.
This takes advantage of the fact that it exhibits ferroelectricity. In these phases, the liquid crystal molecules have a layered structure, and the long axis direction of the molecules is tilted at a certain angle with respect to the layer perpendicular direction. This molecule has spontaneous polarization in a direction perpendicular to it and included in the layer plane, and by trying to align the direction of the spontaneous polarization with respect to the direction of the externally applied electric field, the orientation of the molecule changes and optical A change occurs. Its electro-optical response is 10 to 1000 times faster than that of a conventional liquid crystal device, making it applicable to high-speed optical shutter devices. Furthermore, since it is possible to provide bistability with respect to an electric field, it is possible to apply it to large-sized display devices.

[Problem to be solved by the invention]

However, to create these devices, it is necessary to create cells in which liquid crystals are uniformly aligned, but controlling the alignment of smectic liquid crystals is more difficult than that of nematic liquid crystals, which is one of the reasons for hindering their practical application. . Conventionally, there are the following methods for aligning ferroelectric liquid crystals.

(1) Cooling from the isotropic phase while applying a strong magnetic field.

(2) The two substrates constituting the cell are minutely photographed in a direction in which they are shifted.

(3) Form an orientation control film and slowly cool it from the isotropic phase.

Method (1) requires a large device to generate a strong magnetic field, and orientation control is difficult in cell thicknesses of 1011 tn or less. Regarding (2), a device for applying vibration is required, and there are still many problems to be solved, such as the method of sealing the cell. Method (3) is the most practical method, but it requires strict temperature control of the liquid crystal, requires a device to keep the cell at a constant temperature), and takes time to slowly cool down. There is a drawback.

As described above, electro-optical devices that use conventional alignment control methods for ferroelectric smectic liquid crystals require devices for controlling alignment in the periphery of the cell, so the advantage of small size of liquid crystal devices is lost. It's gone.

[Means to solve the problem]

The present invention has been made to eliminate the drawbacks of the conventional ones as described above, and it is a liquid crystal that maintains a ferroelectric liquid crystal layer having a smectic zero phase between two electrode-attached substrates that have been subjected to alignment control treatment. In an electro-optical device, in order to give an initial orientation to a liquid crystal layer, the liquid crystal layer is maintained at a temperature close to the upper limit temperature of the smectic C phase and an electric field having a DC bias voltage is applied. The present invention provides a liquid crystal electro-optical device characterized in that an initial orientation is given to a liquid crystal electro-optical device.

FIG. 1 is a sectional view of a basic liquid crystal electro-optical device of the present invention. 1 on the surface of two transparent substrates (1a), (1))
Transparent conductive films (2a) and (2b) and alignment control films C3tL) and (311) are formed, respectively.

The conductive films (2a) and (2b) are electrodes held between the substrates for applying an electric field to the liquid crystal layer (4), and are used for the purpose of adjusting the orientation and producing an electro-optical response. It is formed of a predetermined pattern, and is made of a material such as Nzos or 5nO1.
\Orientation control film (5a), (311
) is used to horizontally align liquid crystals, and a typical example is one in which an organic polymer film, particularly a polyimide polymer film, is formed and rubbed in a certain direction with a cloth.Other methods include EIiO, etc. It is also effective to apply an obliquely deposited film to the conductive film (2a) without forming an overcoat film.
, (2b) may be rubbed to form an alignment control film. In other words, the means for horizontally aligning nematic liquid crystals is as follows:
It is also effective in the present invention.

After performing such an alignment process, a spacer, for example,
Organic beads and alumina particles are sandwiched and the surrounding area is fixed with a sealant (5) to form a cell. At this time, the orientation control directions of the two substrates are set to be parallel to each other.

Thereafter, the ferroelectric liquid crystal composition is heated to a cholesteric phase or an isotropic phase, injected into a cell, and then sealed. Two polarizing plates (6a) and (6b) are placed outside the cell,
They are arranged so that their polarization axes are orthogonal to each other and one polarization axis and the orientation control direction of the substrate coincide. Substrate (1
b) Place the light source (7) on side K, so that the light is transmitted to the opposite side.

In addition, when using a reflective type, a reflective plate may be provided outside the polarizing plate (61).

When the cell is cooled to smectic 0 phase and observed,
It can be seen that liquid crystal molecules are oriented in various directions. The cell is maintained at this temperature and an electric field with a DC bias voltage is applied using electrodes (3,) and (3b).

The voltage having this DC bias voltage may be simply a DC voltage, but it is preferable to apply a voltage that is a combination of DC and AC, since the temperature range for obtaining the initial orientation is wide and a low voltage is required. .

When this direct current and alternating current are superimposed, the ratio of direct current and alternating current is 5
A ratio of 0:1 to 1:1 is preferable, and good alignment with few alignment defects can be easily obtained.

In addition, as a method to obtain the same effect as when direct current is superimposed on alternating current, the ratio of the time to apply a positive electric field to the time to apply a negative electric field (hereinafter referred to as duty) is compared to the normal 1 = removed from 1, preferably from 9:11
When the ratio is 1:20, good alignment can be obtained at a lower voltage or in a shorter time than with K. In particular, in order to obtain good alignment in a short amount of time, a duty ratio of 2:3 to 3:17 is particularly preferable.

Of course, it is also possible to superimpose a direct current on an alternating current with a duty other than 1=1. Various types of alternating current can be used, such as a sine wave, a square wave, and a triangular wave. The frequency of this alternating current is preferably 1 to 1 Hz or higher.

The applied electric field is about 2 to 100 times the threshold voltage, but it changes depending on the temperature, waveform, time, etc. at which the initial orientation is achieved, so it can be determined experimentally within a range suitable for each liquid crystal. The time required may be from several tens of seconds to several minutes.

The temperature range in which this initial orientation occurs is close to the upper limit temperature of the smectic C phase, and in particular, the upper limit temperature of the smectic C phase, for example, the smectic 0 phase-cholesteric phase transition temperature, and the temperature 10°C lower than that temperature. 1 between
A range of 0°C is preferred. When applying only a DC voltage, it is preferable to set the temperature in a higher temperature range within this temperature range.

This initial alignment is always necessary when manufacturing a liquid crystal cell, but after that it is only necessary when the alignment breaks down. Specifically, when alignment defects occur due to crystallization of the liquid crystal or high voltage application, etc. There is.

Regarding the liquid crystal to be used, if it is a liquid crystal that exhibits ferroelectricity,
Although the present invention is effective, particularly at temperatures higher than the smectic C phase, good alignment can be obtained for liquid crystals having a cholesteric phase or a nematic phase.

Examples of single liquid crystals having a smectic C phase include the following.

In the following examples, H+ represents an alkyl group or an alkoxy group having a negative carbon or a nitrogen, R represents a straight-chain alkyl group or a straight-chain alkoxy group, and the same R'' is present in one compound.
, R are not necessarily the same group.

R"-◎bottle-coo-@)-R R-◎-0H-N-■-CH=OH-Coo-R"R-
O-■-coo-◎-R" R-■-coo-■-R4! Also, other liquid crystals may be added to the liquid crystal exhibiting the smectic 0" phase as described above to improve its properties. Various known liquid crystal or non-liquid crystal additives for liquid crystals can be used for this, examples of which include the following.

R-# 0OO-◎4 R-i0008R ReOOO-(@-aoo-)u R-■(Sawa000-@xR In the present invention, at least one liquid crystal compound having a smectic 0 phase and other liquid crystals as necessary Any liquid crystal composition to which a compound or a non-liquid crystal additive for liquid crystal is added and which exhibits a smectic C phase can be used, and the above-mentioned compounds are merely examples.

[Operation] FIG. 2 is an explanatory diagram for explaining the orientation direction of molecules and electro-optical response of the present invention, and shows the orientation state of liquid crystal molecules as seen from the substrate (1a) side.

The long side direction of the liquid crystal molecule (8) indicates the long axis direction of the molecule, which coincides with the optical elastic axis. Also, the direction of (9) is the substrate (1a
) and (1b) are shown. When only an alternating electric field is applied, parts with two types of orientation states (a-1) and (1)-2) are mixed together, and uniform orientation cannot be obtained throughout. When a positive DC electric field is superimposed on an electric field with a DC bias, especially an alternating current, the entire electrode part is in a uniform orientation state (a-1).When a negative DC electric field is superimposed on an alternating current, is a uniform orientation state (1)-2) I
It becomes c.

Here, the positive electric field refers to the substrate (1b) with respect to the substrate (1b).
This refers to the case where the potential in a) is low. In addition, the type of liquid crystal material (
Therefore, the relationship between this orientation and the direction of the electric field is reversed. As described above, uniform initial orientation can be obtained by applying an electric field having a DC bias, particularly an electric field in which alternating current and direct current are superimposed.

As described above, by applying positive and negative DC electric fields to the aligned cell, the direction from (a-1) to (a-2) is changed from (a-1) to (a-2).
2) to (a-1) or (b-1) to (1)-
2) and from (b-2) to (b-1), the orientation changes depending on the direction of the electric field. (a-1) or (b-2)
In this case, the optical elastic axis of the liquid crystal layer and one of the polarization axes of the two polarizing plates are perpendicular to each other, so no light is transmitted through the uo
In (a-2) and (b-1), since the polarization axis and the optical elastic axis of the liquid crystal layer are tilted by a certain angle (2θ),
Light is transmitted through the liquid crystal layer due to its birefringence. The transmitted light intensity is expressed as the incident light intensity t- by the following equation.

Here, 2 is the refractive index anisotropy of the liquid crystal, d is the thickness of the liquid crystal layer,
λ is the optical wavelength of the incident light.

〔Example〕

Example 1 A glass substrate with a patterned transparent electrode of 1-8nO was placed by scattering alumina particles with a diameter of about 3 μm as an in-plane spacer so that the transparent electrode surfaces faced each other, and the periphery was sealed to form a cell. And so.

In this cell, a liquid crystal composition exhibiting a smectic C phase listed in Table 1 is heated to 150°C, which is a temperature higher than its smectic C phase-cholesteric phase transition temperature (hereinafter referred to as transition temperature) of 6F16°C, The injection port was sealed with epoxy resin.

Next, when the temperature of the cell was maintained at 67° C. below the transition temperature and a DC electric field of 75 V was applied for 1 minute, good orientation was obtained.

Example 2 Using the same cell as used in Example 1, maintaining the cell temperature at 63°C below the transition temperature, 50'710'KF1
When an electric field consisting of a superimposed alternating current of g and a direct current of 5 volts was applied for 30 seconds, good orientation was obtained.

Table 1 ElmYl, 9mYt: Smectic phase other than chiral smectic C phase SmO'': Chiral smectic C phase Ch: Cholesteric phase: Isotropic liquid phase Example 3 What was used in Example 1 Using the same cell as above, maintaining the cell temperature at 63° C. below the transition temperature, and applying a square wave of 50 volts 110×z1 duty-1:4 for 10 seconds, good alignment was obtained.

FIG. 3 and i4 show the electro-optical characteristics of the cell having the configuration shown in FIG. 1 in which the initial orientation was taken according to Example 2. temperature to 50℃
A halogen lamp was used as the light source, and the intensity of transmitted light was measured using a Photomaru.

FIG. 3 shows the voltage change in the transmitted light intensity of the cell when a 207.0.1 Hz triangular wave was applied. Below Ov, the orientation is (a-1), and almost no light is transmitted. Moreover, at to'7 or more, light is transmitted in the state (a-2). The contrast is very good at 20 or more. In addition, at 5 to 8V, there are two stable states: when the voltage is increased from -20V and when the voltage is decreased from +20V. Can be used.

FIG. 4 is a diagram showing the temporal change in transmitted light intensity when a 10 V, 100 Hz rectangular wave is applied. +10
If the voltage changes from '7 to -107, approximately (L 5
When the voltage changes from g5ec, -107 to +1ov, the response is as fast as about 2m5ec.

In the above embodiment, the orientation of the background portion other than the electrode portion is not uniform, resulting in a state where light is semi-transparent. If this causes deterioration in display quality, etc., a light-shielding mask that matches the background portion may be provided.

Furthermore, in the above embodiment, the electrode for adjusting the orientation and the electrode for producing an electro-optical response were the same, but they were made into different patterns, and an insulating layer was sandwiched between them. -L is also good.

Further, as a means for raising the temperature of the liquid crystal layer, heating from the outside with a heater may be used, but a simpler device can be obtained by directly heating the liquid crystal layer by passing a current through the electrodes inside or outside the cell.

The principle described above is for a transmissive type, but a reflective type with a light source placed at the top and a reflector at the bottom may also be used.The light absorption rate can be adjusted by mixing a deaf, ferroelectric liquid crystal and a dichroic dye. The present invention is also useful for types of devices that utilize change.

〔effect〕

As described above, according to the present invention, since good alignment of ferroelectric liquid crystal can be easily obtained, an inexpensive, compact, high-speed response liquid crystal electro-optical device with high contrast and a memory function can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the basic configuration of the present invention, FIG. 2 is an explanatory diagram of the influence of voltage application on the liquid crystal layer of the example, and FIGS. 5 and 4 show the electro-optical characteristics of the example. FIG. 1ζ11...Substrate, 2b...Conductive film, 3 to 3b
... alignment control film, 4 ... liquid crystal, 5 ... sealant,
6a, 6b...Polarizing plate, 7...Light source, 8...Liquid crystal molecules, Collection 1 Figure 2 (b-11 (b-21

Claims (9)

[Claims] (1) In a liquid crystal electro-optical device in which a ferroelectric liquid crystal layer having a smectic C phase is held between two substrates with electrodes that have been subjected to alignment control treatment, the liquid crystal layer is smectified to give initial alignment to the liquid crystal layer. A liquid crystal electro-optical device characterized in that an initial orientation is imparted to a liquid crystal layer by maintaining the temperature in a temperature range close to the upper limit temperature of the C phase and applying an electric field having a DC bias voltage. (2) The electric field with a DC bias voltage is a superimposition of DC on AC, and the ratio of AC voltage to DC voltage is 50:
The liquid crystal electro-optical device according to claim 1, wherein the ratio is 1 to 1:1. (3) A patent claim in which the electric field having a DC bias voltage has a duty, which is the ratio of the time for applying a positive voltage to the time for applying a negative voltage, in a range of greater than 9:11 and less than or equal to 1:20. A liquid crystal electro-optical device according to item 1 or 2. (4) The liquid crystal electro-optical device according to claim 5, wherein the duty is 2:5 to 3:17. (5) The liquid crystal electro-optical device according to claim 1, wherein the temperature range close to the upper limit temperature is lower than the upper limit temperature of the smectic C phase and at least 10° C. lower than the upper limit temperature. (6) The liquid crystal electro-optical device according to claim 1, wherein the alignment control process includes forming an organic polymer film and rubbing it. (7) A patent characterized in that the device comprises means for raising the temperature of the liquid crystal layer, and after raising the temperature of the liquid crystal layer to near the upper limit temperature exhibiting ferroelectricity, applying the electric field to adjust the orientation. A liquid crystal electro-optical device according to claim 1. (8) The liquid crystal electro-optical device according to any one of claims 1 to 7, wherein the frequency of the alternating current is 1 KHz or more. (9) The liquid crystal electro-optical device according to claim 1, wherein the liquid crystal layer is made of a liquid crystal that exhibits a chiral smectic C phase and exhibits a cholesteric phase at a temperature above that level.