JP2623130B2 - Chiral smectic liquid crystal device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal device used for a display device, an optical shutter, and the like, and more particularly, to a chiral smectic liquid crystal device in which liquid crystals are well aligned.

[Prior Art] A display device of a type that controls transmitted light in combination with a polarizing element by utilizing the refractive index anisotropy of ferroelectric liquid crystal molecules is disclosed in Clark and Lagerwal.
l) (JP-A-56-107216,
U.S. Patent No. 4367924). The ferroelectric liquid crystal generally has a chiral smectic C phase (SmC ^* ) or an H phase (SmH ^* ) in a specific temperature range, and in this state, has a first optical stability in response to an applied electric field. It takes one of a state and a second optically stable state. And, when no electric field is applied, the property of maintaining that state,
That is, it has bistability and quick response to a change in electric field, and is expected to be widely used as a high-speed and storage-type display element.

When a ferroelectric liquid crystal is used as a display element, it is necessary to uniformly align the liquid crystal. Therefore, a method of using a rubbed polymer organic film as an orientation control layer has been generally adopted.

[Problems to be Solved by the Invention] According to experiments conducted by the present inventors, when the thickness of the polymer organic film used as the orientation control layer is sufficiently thick as 600 mm or more, it is sufficiently uniform over a wide area. However, it is known that when the film thickness of the polymer organic film is increased, the driving characteristics are deteriorated as compared with the case where the film thickness is small. In order to maintain the bistability of the ferroelectric liquid crystal, the thickness of the polymer organic film should be 200 μm.
It has also been proposed that it is necessary to reduce the thickness as follows (Japanese Patent Application Laid-Open No. 62-52528).

Therefore, in order to improve the driving characteristics and the bistability, it is desired that the thickness of the polymer organic film as the orientation control layer is small.

On the other hand, as the thickness of the polymer organic film, which is the orientation control layer, is reduced, alignment defects are generated, and not only uniform alignment cannot be obtained, but also the return from the alignment defects deteriorates the bistability. Occurs.

The present invention has been made in view of the above-mentioned conventional problems, and realizes good driving characteristics and bistability by reducing the thickness of a polymer organic film as an alignment control layer, and also achieves uniform alignment of liquid crystal. An object is to provide a chiral smectic liquid crystal element which can be obtained.

[Means and Actions for Solving the Problems] In order to achieve the above object, the present inventors have found that when the thickness of the polymer organic film, which is the orientation control layer, is reduced, alignment defects occur, and Regarding the inability to obtain the orientation, various investigations were conducted on the cause. As a result, this phenomenon is affected by the surface roughness of the underlying layer such as the ITO electrode, the insulating layer, and the Si coupling agent layer where the alignment of the liquid crystal is provided with the polymer organic film that is the alignment control layer. It became clear that this was the case. In addition, even if the surface roughness of the underlayer was the same, the alignment state was different if the thickness of the polymer organic film was different. Then, the relationship between the surface roughness of the underlayer and the thickness and orientation of the polymer organic film was examined, and the results shown in FIG. 2 were obtained.

In the figure, d is the thickness of the polymer organic film as the orientation control layer, and S is the average surface roughness of the underlayer on which the orientation control layer is provided. The underlayer may be any of an ITO electrode, an inorganic or organic insulating layer, a Si coupling agent layer, and the like.
In the case of FIG. 2, the underlayer is an ITO electrode, and the thickness and the surface roughness of the ITO electrode are in a proportional relationship. The average surface roughness was measured with a scanning tunneling microscope (STM, Nanoscope II, sold by Toyo Technical Co., Ltd.), and the standard deviation was calculated. When the average surface roughness was more than 100 mm, the thickness of the ITO electrode was 4000 mm or more, and the cracks were generated by the sputtering method.

From the graph of FIG. 2, it can be seen that if 0 ≦ S / d <0.7, the orientation is good even if the thickness of the organic polymer film is small.

The present invention has been made based on the above findings. That is, in the chiral smectic liquid crystal element according to the present invention, two substrates having electrodes formed in a stripe shape are arranged so that the electrodes intersect each other, and the chiral smectic liquid crystal is interposed between the two substrates via an alignment control layer. In the sandwiched chiral smectic liquid crystal cell, 0 ≦ S / d <0.7 (where d is the thickness of the alignment control layer at the intersection of the electrodes and S is the average surface roughness of the underlayer on which the alignment control layer is provided). , 0 <d ≦ 600 °, preferably 0 ≦ S ≦ 100
Ii) It is characterized by

Thereby, good driving characteristics and bistability can be realized, and uniform alignment of liquid crystal can be obtained.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing one embodiment of the ferroelectric liquid crystal device according to the present invention. The liquid crystal element shown in the figure includes a pair of upper and lower substrates 21a and 21b arranged in parallel, and transparent electrodes 22a and 22b wired to the respective substrates 21a and 21b.
A ferroelectric liquid crystal 26, preferably a non-helical ferroelectric liquid crystal having at least two stable states, is disposed between the upper substrate 21a and the lower substrate 21b. The transparent electrodes 22a and 22b are provided with an orientation control layer 23 formed of a polymer organic film such as a polyimide resin. That is, the transparent electrodes 22a, 22b
Are the underlayers of the orientation control layer 23.

The distance between the substrates is held by silica beads 24 dispersed in the liquid crystal layer 26, and the outer periphery of the substrate is sealed with an epoxy resin 25.

In the present invention, a uniaxial orientation axis can be provided to at least one orientation control layer 23. This uniaxial orientation axis can be preferably provided by a rubbing treatment. Further, an insulating film such as SiO may be further provided between the orientation control layer 23 and the transparent electrodes 22a and 22b.

Example 1 A ferroelectric liquid crystal device having the configuration shown in FIG. 1 was produced as follows. First, the transparent electrodes 22a and 22b, which are the underlying layers of the orientation control layer 23, were formed on the upper substrate 21a and the lower substrate 21b by sputtering. These transparent electrodes 22a, 22b
An ITO electrode was used, and the film thickness was 800 mm. ITO electrodes 22a, 22b
Average surface roughness S is measured by scanning tunneling microscope (STM, Nano
scope II, sold by Toyo Technica Co.) and its standard deviation S was calculated to be 36.3 °.

On the ITO electrodes 22a and 22b, a film thickness d =
100 mm of polyimide resin was provided. Thus, the ITO electrode 22
upper substrate 21a and lower substrate 21b provided with a, 22b and orientation control layer 23
Were arranged such that the electrodes intersect each other, and silica beads 24 were sealed between the substrates to form a liquid crystal cell. In this case, S / d = 0.363.

A liquid crystal having a trade name of CS-1014 (manufactured by Chisso Corporation) was injected into this cell as a ferroelectric liquid crystal under vacuum in an isotropic phase, cooled to room temperature, and cooled to room temperature in Example 1 having the structure shown in FIG. A liquid crystal element was created. Observation of the alignment state of the liquid crystal element revealed that there was no defect and good alignment.

Example 2 A cell was prepared in the same manner as in Example 1 except that the thickness of the ITO electrodes 22a and 22b was 2650 °, and the thickness of the polyimide resin as the alignment control layer 23 was 600 °. The liquid crystal element of Example 2 was prepared by injection.

At this time, the average surface roughness S of the ITO electrodes 22a and 22b is S = 72.1
Å and S / d = 0.120. In addition, when the alignment state of this liquid crystal element at room temperature was observed, good alignment without defects was observed.

Comparative Example A cell was prepared in the same manner as in Example 1 except that the thickness of the ITO electrodes 22a and 22b was changed to 2650 °, and liquid crystal was injected as in Example 1 to obtain a liquid crystal element of Comparative Example. Created.

At this time, the average surface roughness S of the ITO electrodes 22a and 22b is S = 72.1
、 And S / d = 0.721. Observation of the alignment state of this liquid crystal element at room temperature revealed that there were many defects and a favorable alignment state could not be obtained.

Example 3 Example 1 except that the thickness of the ITO electrodes 22a and 22b was 1450 °.
A cell was prepared in the same manner as described above, and liquid crystal was injected in the same manner as in Example 1 to form a liquid crystal element of Example 3.

At this time, the average surface roughness S of the ITO electrodes 22a and 22b is S = 50.6
Å, and S / d = 0.506. In addition, when the alignment state of this liquid crystal element at room temperature was observed, a favorable alignment state without defects was observed.

[Effects of the Invention] As described above, according to the chiral smectic liquid crystal device of the present invention, the thickness of the alignment control layer is reduced to achieve good driving characteristics and bistability, and to achieve uniform and defect-free operation. It is possible to obtain a good alignment state.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a ferroelectric liquid crystal device according to one embodiment of the present invention, and FIG. 2 is a graph showing the relationship between the average surface roughness of an underlayer and the thickness and orientation of a polymer organic film. is there. 21a: upper substrate, 21b: lower substrate, 22a: upper transparent electrode, 22b: lower transparent electrode, 23: alignment control layer, 24: beads, 25: sealant, 26: liquid crystal layer.

 ──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Takashi Enomoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (56) References JP-A-62-160424 (JP, A)

Claims (8)

(57) [Claims] 1. An electrode having an electrode formed in a stripe shape.
In a chiral smectic liquid crystal element in which two substrates are arranged so that the electrodes cross each other and a chiral smectic liquid crystal is sandwiched between the two substrates via an alignment control layer, at least one of the substrates has an intersection of the electrodes. The thickness d of the orientation control layer is 0 <d ≦ 600 °, and the average surface roughness of the underlayer provided with the orientation control layer on the substrate is S, and 0 ≦ S / d <0.7. Chiral smectic liquid crystal device. 2. The chiral smectic liquid crystal device according to claim 1, wherein said alignment control layer is made of an organic polymer film. 3. The chiral smectic liquid crystal device according to claim 2, wherein said organic polymer film is made of polyimide. 4. The chiral smectic liquid crystal device according to claim 1, wherein the underlayer provided with the alignment control layer is an electrode. 5. The chiral smectic liquid crystal device according to claim 1, wherein the underlayer provided with the alignment control layer is an insulating layer made of an inorganic or organic material. 6. The chiral smectic liquid crystal device according to claim 1, wherein a uniaxial alignment axis is provided to the alignment control layer. 7. The chiral smectic liquid crystal device according to claim 6, wherein the uniaxial alignment axis is provided by a rubbing treatment. 8. The chiral smectic liquid crystal device according to claim 1, wherein 0 ≦ S ≦ 100 °.