JPS6264004A - Transparent conducting film and formation thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention] Industrial applications The present invention relates to a transparent conductive film and a method for forming the same. It is something.

Conventional technology Transparent conductive films are in great demand as essential constituent materials for flat display devices such as liquid crystal displays and solar cells, but recently they have become even more important as constituent materials for input devices such as transparent touch switches. be. In particular, with the expansion of information devices such as microcomputers into the home appliance field, the importance of this type of switch is expected to increase as a means of solving the problem of simplifying complex switch functions, and the demand for transparent conductive films will also increase in the future. expected to increase.

Currently, the most commonly used material for transparent conductive films is a thin film of indium oxide doped with tin (hereinafter referred to as
(referred to as an ITO film), and the main manufacturing methods are sputtering and vapor deposition.

This M has a specific resistance of 4 to 5 x 10''Ω,
It is hard and has good adhesion to the substrate, and satisfies the performance desired as a transparent electrode in the electronics field. However, during the manufacturing process, true 3,,-.

Since it requires a lot of science, it is difficult to uniformly form it on a large-area substrate, and this also has the disadvantage of increasing manufacturing costs.

In order to solve this drawback, a method of forming a transparent conductive film under consideration includes a method of forming the transparent conductive film by applying a forming coating liquid and baking it.

Problems to be Solved by the Invention Conventionally, this type of coating solution has been prepared by dissolving indium nitrate in acetylacetone, or its product, and dissolving tin in acetylacetone and nitric acid, using methanol,
Solutions such as solutions in ethanol and acetone, solutions in which organic acid salts of indium and tin are dissolved in solvents, and indium chloride solutions have been devised. However, although a transparent conductive film obtained by coating and baking the above-mentioned coating solution can be used in practical use in terms of resistance, there is a limit to the adhesion force of the ITO film to the substrate (mainly a glass plate), so physical
It has the disadvantage of low chemical strength, so it has not yet been put into practical use. %, when using an inexpensive soda lime glass plate as the base, the firing temperature is 500' to prevent its deformation.
Although it is desirable to lower the temperature to below 55° C., this causes the above-mentioned drawbacks to become even more problematic.

An object of the present invention is to solve the problem that a transparent conductive film formed by coating and baking has low physical and chemical durability.

The only way to solve the problem is when the ITO film is fired at a temperature of 6°C to 560°C.
It is thought that the sinterability is not sufficient and the structure is porous or layered. Evidence for this is the fact that it easily interacts with oxygen and water vapor, which causes a large change in resistance. It is clear that such a structure is the cause of low durability, so in the present invention, ITO
An attempt was made to solve this problem by making the membrane structure more dense.

Therefore, the surface of the ITO film may be covered with a compound that forms a dense film when fired at 500 to 550°C. Such a compound not only has the above-mentioned properties, but also has good light transmittance and a surface resistance of 6 bases for the ITO layer.

It is required that there be no negative impact on the

In the present invention, a mixture of tin oxide and zinc oxide was used as this compound.

Function A mixture of tin oxide and zinc oxide can be easily obtained by mixing a compound of tin and zinc in a solvent, dissolving the mixture, coating the solution on a substrate, and then firing it in the atmosphere.

At this time, a sufficiently strong thin film can be obtained even at a firing temperature of 5°C. The produced film becomes grayish-black in color as it becomes thicker, but as long as the film is thick enough to be provided for the purpose of the present invention, there is no adverse effect on its light transmittance. Further, the conductivity of the ITO transparent conductive layer provided below is not adversely affected.

Also, when applying a mixture solution of tin and zinc, this solution is
Since it is thought to penetrate into the TO film, it is effective in densifying the TO film.

Example The present invention will be explained below with reference to Examples.

Each coating solution was prepared with the composition shown in Tables 1 to 3, washed with an alkaline detergent, and rinsed with pure water. Sample specimens (commercially available soda lime glass plate, 30 mm x 3
- First, the coating solution for forming an ITO film was spin-coded at 300 Or, p, m, and 20 SeC. All of these coating solutions have a tin concentration of 6.6a.
t%. After drying at room temperature to 80° C. (change appropriately depending on the type of solvent), heat in an electric furnace at 500° C. for 60 minutes, and then form a step by etching with aqua regia, and measure the film thickness. The coating liquid used in this example had a minimum film thickness of about 600A and a maximum film thickness of about 900A.

After this, a coating solution for forming a mixture of tin oxide and zinc oxide is applied.
Spin code with 200Or, p, m, 20 lines.

After drying in the same manner, it is heated for 30 minutes in an electric furnace at 500°C. The thickness of this layer was measured by etching the film formed in the area where the ITO film was first removed by etching with aqua regia to create a step. In the coating liquid used in this example, the minimum film thickness was approximately 300 mm, and the maximum film thickness was approximately 6 mm.
The strength of the sample thus obtained was evaluated. The physical strength was expressed as the number of times the membrane was cut by scratching with a diamond tip under a load of 5. Dimensions,
The chemical strength was expressed as the dissolution time of the film (time until the film disappears due to dissolution or peeling) when immersed in 16% aqua regia at room temperature.

The results are shown in Tables 1 to 3. Table 1 uses a coating solution in which the mixing ratio of tin oxide and zinc oxide is 2:1 in terms of molar ratio, and Table 29 and Table 3 show cases where the mixing ratio of tin oxide and zinc oxide is 1:1 and 1, respectively.
:2 coating liquid was used. From these tables, it can be seen that the transparent conductive film (sample streams 1 to 6, @1o-21) having a structure in which a thin film of a mixture of tin oxide and zinc oxide is provided on an ITO film as in the present invention is different from conventional +7) ITO. It can be seen that the physical and chemical strength is greatly improved compared to the transparent conductive film having a single layer structure (sample streams 7 to 9). Moreover, its specific resistance is almost the same as that of the conventional one.

Furthermore, similar samples were tested at 40°C for durability testing.
The figure shows the change in membrane resistance when a humidity test was conducted under 90% RH conditions. In the figure, the number of each curve is the same as that of the samples in Tables 1 to 3. From this figure, it can be seen that the durability of the transparent conductive film is improved by adopting the structure of the present invention.

Furthermore, tin compounds, zinc compounds, and indium compounds other than those used in the present examples and comparative examples may be used as long as they can be dissolved in an appropriate solvent and a film can be obtained by firing.
It can be used for the purposes of the present invention. Although the mixing ratio of tin oxide and zinc oxide may be changed arbitrarily, it is not preferable to increase the content of washed zinc oxide.

(Hereinafter referred to as "white") 12 Effects of Beno Invention As described above, the present invention provides an ITO film on a substrate by applying a mixed solution of an indium compound and baking at a temperature below 560°C, and then depositing tin oxide and oxide on this film. A thin film of a zinc mixture was coated with a mixed solution of a tin compound and a zinc compound at 650°C.
It is provided by the baking process described below, and a highly durable transparent conductive film can be formed on a large-area substrate.

[Brief explanation of the drawing]

The figure is a characteristic diagram showing the results of moisture resistance tests conducted in Examples and Comparative Examples of the present invention.

Claims (3)

[Claims] (1) A transparent conductive film characterized in that a tin-doped indium oxide film is provided on a substrate, and a film made of a mixture of tin oxide and zinc oxide is provided on the film. (2) After applying a solution of an indium compound and a tin compound dissolved in a solvent onto the substrate and baking it in the air to form a tin-doped indium oxide film, a tin compound and a zinc compound are dissolved in a solvent on top of the indium oxide film. 1. A method for forming a transparent conductive film, comprising applying a solution dissolved in tin oxide and zinc oxide, and further baking in the atmosphere to form a film made of a mixture of tin oxide and zinc oxide. (3) The method for forming a transparent conductive film according to claim 2, wherein the firing temperature is 550° C. or lower.