JPS63106623A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To form an oriented film which is excellent in its manufacture reproducibility and free from an uneven orientation, by forming an inorganic oriented film having a strong surface polarity on the opposed electrode surface by ion plating, or forming it by executing the ion plating, while radiating an ion beam. CONSTITUTION:An inorganic oriented film having a strong surface polarity is formed on the opposed electrode surface by ion plating, or it is formed by executing the ion plating, while radiating an ion beam. In this case, magnesium fluoride (MgF2) or magnesium oxide (MgO) is selected as a material having a large surface polarity, and by forming it by an ion plating method, a homogeneous oriented film having a good adhesion is formed on a glass substrate containing an electrode pattern. In such a way, a phase transition type liquid crystal display element having a sufficient hysteresis width and a high manufacture reproducibility can be obtained.

Description

[Detailed Description of the Invention] [Summary] This invention has been proposed as a method for obtaining a liquid crystal display element that has a voltage hysteresis width sufficient for bistable driving, has high manufacturing reproducibility, has little change over time, and has high reliability. A liquid crystal display element in which an inorganic alignment film is formed on an electrode by ion plating, or by ion plating while irradiating an ion beam.

[Industrial application field]

The present invention relates to a liquid crystal display element with high manufacturing reproducibility, little change over time, and high reliability.

FIG. 1 is a schematic diagram of a liquid crystal display element, in which a glass substrate 2 is provided with an electrode pattern 1, at least one of which is made of a transparent metal, with the electrode pattern 1 facing inside, and the electrode patterns 1 arranged in a matrix. to face the
The structure is such that a liquid crystal 3 is sealed in between and a voltage can be applied.

For example, in the case of a dot matrix type, the inner surface of the glass substrate 2 made of parallel flat plates has a line width of 200 to 3
A transparent electrode and a counter electrode are made by forming a large number of parallel electrode patterns 1 with a line spacing of about 100 μm and a line spacing of about 100 μm. Electrode patterns 1 are arranged so as to be perpendicular to each other while facing each other with a minute gap in between, and a liquid crystal 3 is sealed in this gap.

Here, the transparent electrode is formed using a solid solution (abbreviated as ITO) of indium oxide (Inz03) and tin oxide (SnO□), while the counter electrode is formed using a transmissive display structure. A transparent electrode is used, and in the case of a reflective type, a metal film with good reflectivity such as aluminum (Al) is used.

Then, the display element is driven by scanning by applying a scanning voltage and a signal voltage to the orthogonal X and Y electrodes, respectively, and applying both voltages in a superimposed manner to the selected point, creating the electric field necessary for the phase transition of the liquid crystal to occur. is configured to reach.

The present invention relates to an improvement in a display element that utilizes the voltage-light transmittance bistability associated with nematic-cholesteric phase transition caused by an electric field.

[Prior Art] A display element that utilizes the voltage-light transmittance bistability associated with nematic-cholesteric phase transition is a display method proposed by the inventors, and the liquid crystal used is nematic liquid crystal and cholesteric liquid crystal. I'm using something with the addition of.

FIG. 2 is a diagram showing the relationship between applied voltage and transmittance of such a phase change type liquid crystal.

In other words, in the absence of an electric field, liquid crystal molecules are in a cholesteric phase with a helical structure and are cloudy, and light is scattered and forms a focal conic Li (abbreviated as F state) with low transmittance.
However, as the electric field increases and the liquid crystal molecules align in the direction of the electric field and undergo a phase transition to the nematic phase, the transmittance increases and becomes transparent, resulting in a homeotropic state (abbreviated as H-shaped M) with high transmittance. become.

Next, when the electric field is decreased from this H state, the nematic phase returns to the F state consisting of a cholesteric phase, but at this time, the transmittance curve for the electric field does not go through the same process and shows hysteresis as shown in the figure. Draw a loop.

Therefore, a transparent H state and a cloudy F state exist at the same applied voltage value Vd.

Phase change type liquid crystal displays display using bistable states, and because each state is easily maintained due to the memory effect of liquid crystals, large-capacity display is possible. (Twist NematiC) A polarizing plate required for display is not required, and therefore the amount of projected light is characterized by little attenuation.

Now, a necessary condition for such a phase change type liquid crystal display element is that the voltage width (hysteresis width) Δ of the rising curve 4 and falling curve 5 of the hysteresis loop is sufficiently wide.

Here, the hysteresis width Δ is defined as the difference between the applied voltage value at which the transmittance is 90% in the falling curve 5 and the applied voltage value at which the transmittance is 20% in the rising curve 4.

Now, in a phase change type liquid crystal display element, electrode pattern 1
100 mm thick on the glass substrate 2 in contact with the liquid crystal 3.
An alignment film of 0 to 2000 layers is formed to help align liquid crystal molecules, and the hysteresis width Δ greatly influences the composition of the alignment film and the quality of its formation.

In other words, in order to increase the hysteresis width Δ, it is necessary to use a material with a large surface polarity, and it is also necessary to form the material uniformly. If there is a non-uniform part, the hysteresis width at that part will be larger than the hysteresis width Δ of the display element. I decide.

Conventionally, polyvinyl alcohol (abbreviated as PVA) and -silicon oxide (Sin) have been used as alignment films for phase change type liquid crystal display elements.
etc. were used.

Here, PVA is a material with high surface polarity and is formed into a film using the spin code method, but there are very slight stains on the surface of the glass substrate and uneven concentration of the PVA coating solution.

There is a drawback that uneven orientation occurs due to temperature distribution during heat treatment.

If alignment unevenness exists, when displaying by applying an electric field, the tilt angle of the liquid crystal molecules in that part will be different from other parts, and the display image will have brightness and darkness due to anisotropy in the refractive index of the liquid crystal molecules. will occur.

In addition, alignment films made of PVA tend to change over time.
There were reliability problems when used in environments with rapid temperature changes.

In addition, although SiO films are excellent in terms of reliability, there is a problem in that the surface condition varies due to slight contamination scratched on the glass substrate, which causes variations in the driving characteristics of phase change type liquid crystal display elements. Ta.

[Problem that the invention seeks to solve]

As mentioned above, in order to form a large hysteresis width Δ and drive stably in a phase change type liquid crystal display element, it is necessary to uniformly form an alignment film made of a material with high surface polarity on the surface of the glass substrate. However, the problem is that it is difficult to form an alignment film with excellent manufacturing reproducibility and no alignment unevenness.

[Means for solving problems]

The above problem can be solved by forming an inorganic alignment film with strong surface polarity on the opposing electrode surfaces by ion plating or by irradiating it with an ion beam in a liquid crystal display element that displays using a nematic-cholesteric phase transition liquid crystal as a medium. However, this problem can be solved by using a liquid crystal display element formed by ion plating.

[Effect]

The present invention selects magnesium fluoride (Mgh) or magnesium oxide (MgO) as a material with large surface polarity,
By forming this using an ion plating method, a highly adhesive and homogeneous alignment film is formed on a glass substrate including an electrode pattern.

Here, as the ion plating method, a high frequency excitation method is particularly suitable, and argon (Ar) is used during film formation.
It has been found that a more uniform alignment film can be formed by irradiating the glass substrate with an ion beam of an inert gas such as .

That is, an inert gas plasma is created by passing a current of 13.56 Mn2 through a high-frequency coil in a vacuum of about 10-' torr, and MgF or N4;
When the evaporated molecules of 1 gO are allowed to fly, the evaporated molecules are ionized by the ionized Ar gas, collide with the glass substrate, and generate a discharge, thereby making it possible to obtain a homogeneous evaporated film with good adhesion.

Furthermore, the inventors have discovered that a more uniform alignment film can be formed by equipping this vapor deposition apparatus with an ion gun and irradiating the glass substrate with an inert gas such as an ion beam during vapor deposition. be.

〔Example〕

Example 1: Size is 130 x 160 m, thickness is 1.1 fi,
We prepared 15 sets of glass substrates on which ITO electrode patterns were formed, and after washing and drying them, they were sequentially installed in a high-frequency excitation type ion plating apparatus, and the inside of the apparatus was heated to 2 x 10-'torr. After evacuation to a vacuum level, Ar gas was introduced and maintained at 2 × 10-'torr, and the substrate was cleaned with a plasma output of 40 W for 2 minutes. The processing conditions were then changed as follows. An alignment film was formed using the following steps, and a liquid crystal display element was manufactured.

■Ion plating was performed by passing MgF through a high-frequency coil while evaporating it using a resistance heating method.

In this case, the Ar gas pressure is 2 Xl0-'torr,
Further, the applied power for plasma formation was 100W.

(Sample A) ■ Do not irradiate the glass substrate with Ar ion beam ■
Evaporation was carried out under the same conditions. (Sample B) -gFg was evaporated using a conventional resistance heating method to form an alignment film. (
Sample C) When visually observing the alignment unevenness of the phase change type liquid crystal display elements equipped with the three types of alignment films mentioned above, no unevenness was observed in the display elements using Samples A and B, whereas no unevenness was observed in the display elements using Sample C. Many unevennesses ranging in size from several centimeters to 2 cm were detected in the elements used.

Further, when the hysteresis width Δ was measured for each of five display elements, samples A and B always had a value of 4V necessary for stable driving, while sample C showed large fluctuations.

These measured values are: Sample A: 4.1.4.0.4.0.4.1.4.0
Average 4.04V'Sample B: 4.1.4.2.4.2
．． 4.2.4.2 Average 4.18V Sample C': 4.0.
2.7.2.9.4.1.3.5 average was 3.44V.

Example 2: Using MgO instead of MgF2 as the forming material for the alignment film, an alignment film was formed on a glass substrate under the same conditions as in Example 1, and alignment unevenness was visually observed. The hysteresis width Δ was measured for the manufactured phase change type liquid crystal display element, but as in Example 1, many alignment irregularities were observed in the alignment film formed by the conventional vapor deposition method.
Also, while the variation in the hysteresis width Δ was large, the one to which the present invention was applied had no alignment unevenness, and when ion plating was performed while irradiating the ion beam, the hysteresis width Δ was larger as in Example 1. I was able to get

〔Effect of the invention〕

As described above, by carrying out the present invention, it is possible to manufacture a phase change type liquid crystal display element having a sufficient hysteresis width Δ for bistable driving, high manufacturing reproducibility, and high reliability.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view showing the structure of a liquid crystal display element, and FIG. 2 is a diagram showing the relationship between applied voltage and transmittance of a phase change type liquid crystal. In the figure, 1 is an electrode pattern, 2 is a glass substrate, and 3 is a liquid crystal.

Claims (2)

[Claims] (1) In a liquid crystal display element that performs display using a nematic-cholesteric phase transition type liquid crystal as a medium, an inorganic alignment film with strong surface polarity is formed on opposing electrode surfaces by ion plating, or while irradiating with an ion beam. A liquid crystal display element characterized by being formed by performing ion plating. (2) The liquid crystal display element according to claim 1, wherein the inorganic alignment film formed on the opposing electrode surfaces is made of magnesium fluoride or magnesium oxide.