JPS6398633A - Manufacture of liquid crystal electro-optical device - Google Patents

Abstract

PURPOSE:To obtain a monodomain orientation having bistable characteristic using even a ferroelectric liquid crystal having no SmA phase by cooling slowly an unoriented cell down to a SmC* phase while impressing an electric voltage which selects an orientation state having higher orientation energy out of two orientation states which can be selected by the impression of electric voltage. CONSTITUTION:A ferroelectric liquid crystal 36 having no smectic A phase is used. When polyvinyl alcohol (PVA) and polyimide (PI) is used for thin film 34 and 35 respectively, the energy of the orientation state wherein the permanent dipole 40 of the liquid crystal is directed from PVA side toward PI side as shown by the Figure (b) is the minimum and very stable energy. On the other hand, the orientation energy of the orientation state (b) is larger than that of (a) and unstable or metastable. In this state, when the liquid crystal is cooled slowly down to a chiral smectic phase (SmC* phase) while impressing a sufficiently high electric voltage from the PI side to the PVA side, molecules of liquid crystals in the SmC* phase are oriented in a manner as described by the Figure (a), and the direction of orientation coincides with the direction of rubbing.

Description

[Detailed Description of the Invention] [Industrial Application] The present invention relates to a method for manufacturing a liquid crystal electro-optical device [Prior Art] As a conventional method for aligning liquid crystal in a liquid crystal electro-optical device using ferroelectric liquid crystal, , a method is used in which a thin film of polyimide or the like is provided on two transparent substrates, rubbed in one direction, and then slowly cooled from the normal phase to the smectiraku A (8m) phase. When using a liquid crystal without physiognomy, use chiral smectic (SmO)
A method is used in which a DC voltage is further applied when slowly cooling the phase. This is because the phase series of ferroelectric liquid crystals can be roughly divided into four types as shown in Table 1, and if the SmA phase does not exist, when the transition to the SmO phase occurs, the i
As shown in Figure g5, the directions of molecules within one layer 13 are two directions 11 and 12. Therefore, when slowly cooling to the SmC* phase without applying a DC voltage, which of the molecular directions 11 and 12 in Figure 3 is the rubbing direction 14.
Since it is arbitrary whether they match, the result is a multi-domain structure as shown in FIG. 2, which deteriorates the optical properties.

[Problem that the invention seeks to solve]

However, in the conventional method, only the molecular direction (either 11 or 12) that coincides with the rubbing direction is stable, and the bistability, which is a major feature of ferroelectric liquid crystals, is lost. Therefore, an object of the present invention is to solve the above problems and to provide a liquid crystal alignment method for realizing a liquid crystal electro-optical device with bistability and good optical properties when using a ferroelectric liquid crystal that does not have an SmA phase. The goal is to provide the following.

[Means for solving problems]

The method for manufacturing a liquid crystal electro-optical device of the present invention includes (a) using a ferroelectric liquid crystal having no smectic physiognomy, and (b) using rubbing or oblique evaporation on at least one of two transparent substrates. Of the two liquid crystal molecule orientation states that can be selected by applying a pressure of 9<crit, the orientation treatment is performed and the direction is approximately parallel or approximately perpendicular to the polarization direction of the polarizing plate. It is characterized by slowly cooling to the SmC* phase while applying a voltage to select the orientation state of liquid crystal molecules.

〔Example〕

(Example 1) A schematic cross-sectional view of the liquid crystal electro-optical device used in this example is shown in FIG. 36 is a ferroelectric liquid crystal layer, 57.5B is a polarizing plate, 39 is a projection of the liquid crystal molecular axis onto the xy plane, 40 is a permanent dipole, and 41.42 are thin y! , 54°35 is a virtual dipole. Although the smectic layer is not drawn, it exists in the xy plane, and the relationship between the normal (two axes) of the smectic layer and the liquid crystal molecule axis is as shown in FIG.

Here, when polyvinyl alcohol (PTA) and polyimide (P) are used as the thin film 34.55, respectively,
The direction of each virtual dipole is as shown in FIG. The direction of the virtual dipole was determined from the direction of the permanent dipole of the liquid crystal molecules in contact with each substrate when no electric field was applied. Therefore, in the combination of PTA and P, the energy of the orientation state in which the permanent dipoles of the liquid crystal molecules are directed from the PTA side to the PI side is minimum, as shown in FIG. 1(b), and the combination is extremely stable. On the other hand, (b)
The orientation energy of the orientation state of is unstable or metastable because it is larger than that of a).Therefore, if a sufficiently large voltage is applied from the PI side to the PVA side and slowly cooled to the SmC phase, the SmO phase will be formed. The orientation of liquid crystal molecules in
The orientation is as shown in Figure (a), and the orientation direction matches the rubbing direction. However, both the upper and lower substrates are rubbed in one direction, and the directions are parallel to each other. In addition, the phase series of the liquid crystal material used is more o−+
li*→SmO*.

When oriented in this way, the alignment state shown in Figure 1 (a) is stabilized by the rubbing effect, and the alignment state shown in Figure 1 (b) is created by the permanent dipoles of liquid crystal molecules and P It is stabilized by interaction with the PTA thin film (polar interaction) and becomes bistable.

In this case, the voltages vth required to invert from (a) to (A) and from (b) to (a) are 12-5V and 12.
8V, and it can be seen that the difference in orientation energy between the two orientation states is relatively small. The symmetry of stability is α-Vth
If we express it as (a)/vth(b-α),
In this case, α=0.98.

On the other hand, when slowly cooling to the SmO phase, P
If an electric field is applied to the I side, the orientation state in Figure 3(a) is extremely unstable, and the orientation state in Figure 3(, 6) is strongly stabilized by the above two effects, making it monostable. It has become.

(Example 2) As a second example, P as the thin film 34 and 35, respectively.
TA and SiO were used, and only the upper substrate was subjected to alignment treatment. The orientation of the virtual dipole in the SiO thin film is the same as that in the P process. The liquid crystal material used in this example was H3. In this case, among the two orientation directions (a) and (b), (
Since the orientation energy of b) was lower, voltage was applied in the direction of SiO→PVA when slowly cooling to the SmC* phase. By this method, (a) also became stable and bistability could be obtained.

Further, α=(L96).However, as in the first embodiment, when the direction of the voltage was reversed, it became monostable.

(Example 3) As a third example, P treatment was used as the thin film 34 and rubbing treatment was applied to the upper substrate. The thin film 35 was not provided. As the transparent conductive thin film 33, TO was used. In addition, the liquid crystal material used has two orientation directions (a) and (b).
Among them, (a) was more stable, so bistability could be obtained by applying a voltage in the direction of TO → P during slow cooling to the SmC* phase. Also, α=1.05.

(Example 4) As a fourth example, SiO obliquely deposited at 60° was used as the thin film 34, and the thin film 35 was not provided. The following is the same as in Example 3. In this example as well, bistability could be obtained by applying a voltage in the direction from TO to SiO. α=(L95.

In the above embodiment, for simplicity, the two orientation states are illustrated as being in a uniform state, but in reality, they are in a twisted state.

〔Effect of the invention〕

When aligning a ferroelectric liquid crystal that does not have an 8 mA phase by rubbing or oblique evaporation, select the alignment state with higher alignment energy from two alignment states that can be selected by applying voltage in a cell that has not undergone alignment treatment. By slowly cooling to the SmO'' phase while applying a voltage, a monodomain alignment with bistability can be obtained even when using a ferroelectric liquid crystal that does not have an SmA phase.
Furthermore, the difference in orientation energy between the two orientation states can be reduced, (a)→(b).

The difference in voltage required to invert from Cb) to (a) becomes smaller. Furthermore, when creating a device with a large surface area, the magnitude relationship of the orientation energy between the two orientation states may be reversed locally due to deflection of the upper and lower substrates, and the driving voltage conditions of that area may change, causing the device to become inoperable. However, since the energy difference is small, even if such a reversal phenomenon occurs, the change in drive voltage conditions is small, and local unevenness in operation can be prevented.

[Brief Description of the Drawings] Figures 1(a) and (A) are cross-sectional views of a liquid crystal electro-optical device according to the present invention, and Figure 2 is a liquid crystal that does not have an SmA phase and is oriented without applying a voltage. Figure 3 shows the orientation of liquid crystal molecular axes in the 13mo* phase, and Figure 4 shows the positional relationship between liquid crystal molecular axes, permanent dipoles, and smectic layers. . 11.12... Two directions of liquid crystal molecules 13...
・・・・・・Smectic layer 14・・・・・・・・・
...Rubbing direction 15...Liquid crystal molecule 16...Permanent dipole 31...
......... Upper substrate 32... Lower substrate 33... Weekly conductive thin film 34.3
5... Organic or inorganic thin film 36... Ferroelectric liquid crystal layer 37.3
8... Polarizing plate 39... Projection of the liquid crystal molecular axis onto the xy plane 4o... Permanent dipole 41.
......Virtual dipole 42 of thin film 34
・・・・・・・・・・・・ More than the virtual dipole of the thin film 35 (Fig. 1G) Fig. 2

Claims (1)

[Scope of Claims] A liquid crystal electro-optical device, wherein a transparent conductive thin film is provided on the surfaces of two transparent substrates in contact with liquid crystal, and at least one substrate is further provided with a thin film on the transparent conductive thin film. In the manufacturing method, (a) a ferroelectric liquid crystal that does not have a smectic A phase is used; (b) at least one of the two transparent substrates is subjected to an alignment treatment by rubbing or oblique vapor deposition; is substantially parallel or substantially perpendicular to the polarization direction of the polarizing plate, and (c) to select the liquid crystal molecule alignment state with high alignment energy when no alignment treatment is performed among the two liquid crystal molecule alignment states that can be selected by applying a voltage. 1. A method for manufacturing a liquid crystal electro-optical device, which comprises slowly cooling to a chiral smectic C phase while applying a voltage of .