JPH02190826A - Two-terminal element for driving liquid crystal - Google Patents

Abstract

PURPOSE:To form a low temperature formed film and to obtain excellent physical and electrical characteristics by constituting an insulating thin film by a film having specific visible light transmittivity and volume resistivity, which is formed by vapor-deposition. CONSTITUTION:An insulating thin film of a liquid crystal driving two-terminal element of an MIM constitution is constituted of a film of >=90% visible light transmittivity and >=10<13> volume resistivity, which is formed by vapor-deposition. In such a way, a breakdown strength characteristic and an I-V characteristic are improved, and also, since transparency of the insulating thin film in high, the insulating thin film can be formed on the whole surface of a picture element electrode, an MIM element is formed easily, and also, since a low temperature film formation can be executed, a plastic substrate can be used, and an active driving type liquid crystal display device being small in size, light in weight and thin is obtained.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a driving element with an MIM configuration suitable for use in a liquid crystal display device, and particularly to a driving element applicable to a liquid crystal display device using a plastic substrate. It is.

[Prior Art and Problems to be Solved by the Invention 1M] IM elements have been used as driving matrix elements using transparent electrodes in conventional liquid crystal display devices due to their ease of manufacture. The insulating film of this MI element is CVD
Silicon nitride formed by a method, aluminum oxide formed by a sputtering method, and tantalum pentoxide formed by anodizing are used for the transparent electrode. Indium oxide, etc., is used. However, all of these film forming methods require the substrate temperature to be raised to a high temperature of 300°C or higher, making it extremely difficult to form a film on substrates with low heat resistance, such as plastic substrates. Even thin films lack density, and fine depletion occurs in the film, which deteriorates the inherent physical properties of the film's constituent materials, such as light transmittance, electrical resistance,
A film with good dielectric constant could not be obtained. In particular, the insulating film has low transparency, so it cannot be formed over the entire pixel area.
It had to be formed only in the MIM element portion, which was accompanied by difficulties in manufacturing.

On the other hand, conventional liquid crystal display devices have generally been constructed using glass substrates, but there are problems with machinability.

There is a demand for the use of plastic substrates from the viewpoint of weight reduction and thinning, etc., and static drive types have already been commercialized and put into practical use, but active drive types are still insufficient. This is because, as mentioned above, it is extremely difficult to form a thin film on a plastic substrate with low heat resistance.

The present invention was made in order to solve the problems of the conventional technology as described above, and provides a two-terminal element for driving a liquid crystal that can be produced by low-temperature film formation and has excellent physical and electrical characteristics. The purpose is to provide

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a liquid crystal driving secondary structure in which a thin film transparent electrode, an insulating thin film, and a thin film electrode are sequentially laminated on a substrate. In the terminal element, the insulating thin film is formed by vapor deposition and has a visible light transmittance of 90%.
As described above, there is provided a two-terminal element for driving a liquid crystal, which is characterized by being composed of a film having a volume specific resistance of 1013 or more.

[Example code] The present invention will be explained in detail below using examples.

(Example 1) As shown in FIG. 2, an A1 thin film electrode 21 having a thickness of about 1000 wafers was formed on a PET substrate 20 by ordinary vacuum deposition.

Furthermore, an aluminum oxide film 22 with a thickness of approximately 500 densities is formed thereon by the method described below, and an indium oxide thin film electrode 23 with a thickness of approximately 850 densities is further formed thereon.
I named it Asoko.

The above aluminum oxide film 22 was formed in Japanese Patent Application Laid-Open No. 59-89.
The thin film deposition apparatus described in Japanese Patent No. 763 is used.

Here, the outline of the thin film deposition apparatus will be explained with reference to FIG.

This thin film deposition apparatus has a vacuum chamber 2, a counter electrode 10, a grid 8, a filament 6 for generating thermionic electrons, and an evaporation source 4. A film is formed by introducing a mixed gas. The evaporation source 4 may be a resistance heating type made of tungsten, molybdenum, etc. formed into a boat or coil shape, or a beam evaporation type. Counter electrode 10
is placed in a vacuum chamber 2 to hold a substrate 11, and the substrate 11 is opposed to the evaporation source 4. The grid 8 allows the vapor deposition material to pass through, and connects the evaporation source 4 and the counter electrode 1.
0 and placed at a positive potential with respect to the potential of the counter electrode lO and the filament 6, so that the grid 8 is placed in the vacuum chamber 2.
An electric field is formed from the substrate 11 toward the substrate 11 . A filament 6 for generating thermionic electrons is arranged on the evaporation source 4 side with respect to the grid 8 in the vacuum chamber 2, and the thermionic electrons generated by the filament 6 are used to ionize a part of the introduced gas and the evaporated substance. be done.

Next, the aluminum oxide film 22 is formed using the thin film deposition apparatus described above.
The formation method will be explained.

Metal A1 is held as an evaporation substance in an evaporation source 4, and a vacuum chamber 2
The degree of vacuum inside is set in advance to the order of 10-'Pa,
Oxygen gas is introduced into the vacuum chamber 2, and its pressure is set to 0, for example.
．． Maintain around IPa. In this state, for example, the counter electrode 10 is set to zero potential, a potential of 100 V is applied to the grid 8, and a power of 400 V is applied to the filament 6. Then, when power is applied to the evaporation source 4 according to a desired film formation rate, a part of the evaporated A1 is ionized and strongly combined with oxygen, and an aluminum oxide film is formed on the substrate 11.

The aluminum oxide film 22 formed by this method by introducing oxidizing gas at 1000M into the vacuum chamber 2 at a film formation rate of 5 persons/see is a dense film with a visible light transmittance of 95% or more (see Fig. 6). , the volume resistivity was 1013 or more.

Aluminum oxide,
Oxides such as tantalum pentoxide are often used. Conventionally, these films are formed by anodic oxidation after fabricating an A1 or Ta film, but anodic oxidation may make the inside of the film porous, making it difficult to form a dense film. This tendency is particularly remarkable with aluminum oxide. However, the insulating film of this example (aluminum oxide film 22) has a light transmittance of 95% or more and excellent density as described above, so M
If a material with good transmittance is used as the electrode of the IM element, MI
The M element itself becomes transparent, and when used as a liquid crystal display element, the display aperture ratio can be increased and a bright liquid crystal display device can be realized. For example, indium oxide, zinc oxide, etc. can be used as the transparent electrode. In particular, when indium oxide is also produced by the above method, it becomes a uniform film with a light transmittance of 95% or more and a surface resistance of 100 Ω/hole or less.

The IV characteristics of the MIM element created in this example are shown in Figure 3 as solid lines. In Figure 1, the thin line shows the case where aluminum oxide by anodization was used (comparative example), and the broken line shows the case where aluminum oxide was used by anodizing (comparative example), and the broken line shows the case in Example 2 described later. handle. As is clear from FIG. 3, the MIM device of this example had excellent withstand voltage characteristics, and the I-V characteristics had a sharp rise and good symmetry.

(Example 2) As shown in FIGS. 4 and 5, a transparent pixel electrode 31 of indium oxide with a film thickness of approximately 800 mm is formed on a glass substrate 30 by a method using the apparatus shown in FIG. 31, an aluminum oxide insulating film 32 having a light transmittance of 94% or more and a volume resistivity of 1014 or more is formed by the same method as in Example 1.
(film thickness approximately 500 people). Furthermore, a thin film electrode (film thickness of about 800) 3 of metal Al is provided on the end surface of the transparent pixel electrode 31.
3 was formed into a film, and an element was formed in MI using the laminated portion of each thin film.

In this MIM element, the thin film electrode 331 can also serve as a connecting electrode with an external drive circuit.

In the MIM element configured in this manner, since the insulating film 32 has high transparency, it is not necessary to form the insulating film 32 only on the MIM element portion, and it can be formed over the entire pixel portion, making the device easy to manufacture.

Although the embodiments of the present invention have been illustrated above, the present invention is not limited to these embodiments, and various modifications and changes are possible.

For example, although PET is used as the plastic substrate for forming the MIM element in the above example, a polymer film of polyester, polyethersulfone, polysulfone, polycarbonate, etc., or a glass plate may also be used. In addition to the above, the insulating film can also be made of titanium, silicon,
Oxides such as indium, nitrides such as silicon and titanium, barium titanate, etc. can be used. In addition to the above, metal electrodes include Au, Cr, NiCr, and T.
Materials such as a can be used.

[Effects of the Invention] As explained in detail above, in the present invention, the insulating thin film of the two-terminal element for liquid crystal movement having an MIM configuration is formed by vapor deposition and has a visible light transmittance of 90% or more and a volume specific resistance of 1013 or more. Since it is composed of a membrane, the following effects can be obtained.

(2) The withstand voltage characteristics and IV characteristics are improved.

■Since the insulating thin film has high transparency, it is possible to form the insulating thin film on the entire surface of the pixel electrode, making it easy to manufacture MIM elements.

■Since low-temperature film formation is possible, plastic substrates can be used, making it possible to create small, light-looking, and thin active drive type liquid crystal display devices.

■Since the insulating thin film has high transparency, the aperture ratio of the liquid crystal display device can be designed to be large, resulting in good display characteristics.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a thin film deposition apparatus used for forming an insulating film of an element according to the present invention, and FIG. 2 is a sectional view showing the structure of an IM element according to Example 1 of the present invention. FIG. 3 is a graph showing the IV characteristics of the MIM device shown in FIG. is a graph showing an example of measurement of visible light transmittance of an insulating film. 21... A1 thin film electrode 22... Aluminum oxide film 23... Indium oxide thin film electrode 31... Transparent pixel electrode 32... Insulating film 33... Thin film electrode

Claims (1)

[Claims] (1) In a two-terminal element for driving a liquid crystal with an MIM configuration in which a thin film transparent electrode, an insulating thin film, and a thin film electrode are sequentially laminated on a substrate, the insulating thin film has a visible light transmittance of 90% formed by vapor deposition. As described above, a two-terminal element for driving a liquid crystal is comprised of a film having a volume specific resistance of 10^1^3 or more.