JPS6264007A - 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 Field of the Invention The present invention relates to a transparent conductive film and a method for forming the same.

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 also become important as constituent materials for input devices such as transparent touch switches. . In particular, with the advancement of information devices such as microcomputers into the home appliance field, it is expected that the importance of this type of switch will increase as a means of solving the problem of simplifying complex switch functions37,-7. Demand is also expected to increase significantly in the future.

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

This film has a specific resistance of 4 to 6 × 10 Ωα, is hard,
It also has good adhesion to the substrate and satisfies the performance desired as a transparent electrode in the electronics field. However, since a vacuum system is required during the manufacturing process, it is difficult to uniformly form the film on a large-area substrate, and this also has the drawback 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 the transparent conductive film produced by coating and baking the above-mentioned coating solution can be used in practical applications in terms of resistance, it has insufficient sinterability and adhesion to the substrate of the ITO thin film, resulting in physical and chemical problems. It has the disadvantage of low strength and has not yet been put into practical use. In particular, when using an inexpensive soda-lime glass plate as a substrate, the firing temperature is set at 60°C to prevent its deformation.
Although it is desirable to lower the temperature from 0 to 550°C, the above disadvantages become even more problematic. An object of the present invention is to solve the problem that the physical and chemical durability of a transparent conductive film formed by coating and baking is low.

The only way to solve the problem is when the ITO film is fired at a temperature of 500 to 660°C.
A-7 is considered to be a porous or layered structure with insufficient sinterability and weak adhesion to the glass substrate. 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 properties are the cause of low durability, so in the present invention, ITO
An attempt was made to solve this problem by improving the adhesion of the film to the glass substrate and making the structure more dense.

For this purpose, a transparent layer with good adhesion to both the ITO film and the glass substrate may be provided between the ITO film and the glass substrate, and the surface of the ITO film may be covered with a substance that forms a dense transparent layer when fired at 500 to 550°C. Such a material is required not only to have the above-mentioned properties, but also to have good light transmittance and not to adversely affect the surface resistance of the ITO layer. In the present invention,
As this material, tin oxide or a mixture of tin oxide and zinc oxide was used.

FunctionA tin oxide thin film and a mixture thin film of tin oxide and zinc oxide are
It can be easily obtained by mixing a compound of tin or zinc in a solvent, dissolving it, applying this liquid to a glass substrate, and baking it in the air for 6 pages. At this time, the firing temperature was 500℃
However, it becomes a sufficiently strong thin film. The formed film becomes blackish-gray as it becomes thicker, but if the film is thick enough for the purpose of the present invention, it will not have a negative effect on its light transmittance (even if it is covered with an ITO film, its surface will not be affected). The resistance is often adversely affected.These thin films have good adhesion to both the glass substrate and the ITO film, so providing them between the IT○ film and the glass substrate strengthens the adhesion between the two. It is thought that this liquid permeates into the ITO thin film during coating, and therefore the tin oxide or the mixture of tin oxide and zinc oxide fills the pores in the IT○ film, which is effective in making it denser.

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

Each coating solution was prepared with the composition shown in Tables 1 and 2, and a sample specimen was washed with an alkaline detergent and rinsed with pure water (commercially available soda-lime glass plate, 3 on x 30 g, thickness 1.1
In step m), first, a coating solution for forming a tin oxide thin film or a coating solution for forming a thin film of a mixture of tin oxide and zinc oxide 7A-7 is spin-coded at 2000 rpm and 20%. After drying at room temperature to 80°C (varies appropriately depending on the type of solvent), heating in an electric furnace at 600°C for 3°, a portion is etched with aqua regia to form a step, and the film thickness is measured. In the coating liquid used in this example, the film thickness of
There were 8 to 00 people. This film is designated as the first film.

After this, a coating solution for forming an ITO film was applied at 300 rpm.

Spin code with 20 Yutaka. The tin concentration in the coating solution was all s, 5 at%. After drying in the same manner, it is heated in an electric furnace at 500° C. for 60 minutes to form a second film. The thickness of this layer was measured by first etching the film formed in the area where the first film was removed by etching with aqua regia to form a step. In the coating liquid used in this example, this film thickness was 5.
From 0Q onwards, he was a SOO person.

Furthermore, in the same manner as the first film was formed, a third film made of tin oxide or a mixture of tin oxide and zinc oxide, which is different from the first film, is formed thereon. The thickness of this layer was also measured in the same manner as described above.

The strength of the three-layered sample thus obtained was evaluated. The physical strength was expressed as the number of times the film was scratched with a diamond tip under a load of 6I until it was cut. The chemical strength was expressed as the dissolution time of the film (the time until the film disappears due to dissolution or peeling) when immersed in 15% aqua regia at room temperature.

The results are shown in Tables 1 and 2. Table 1 shows the first film using tin oxide and the third film using a mixture of tin oxide and zinc oxide, and Table 2 shows the first film using a mixture of tin oxide and zinc oxide. Tin oxide is used for the third film. In each case, for the mixture thin film, a coating solution was used in which the molar ratio of tin oxide to zinc oxide was 1:1. From these tables, it can be seen that the transparent conductive films (samples/Vi1-6.Vi1o-16) having a three-layer structure in which the first film and the third film are provided above and below the IT○ film as in the present invention are as follows: It can be seen that the physical and chemical strength is greatly improved compared to the conventional IT○ film single-layer transparent conductive film (sample scraps 7 to 9). Moreover, its specific resistance, 9p-7, is almost the same as that of the conventional one.

(JSU, 2nd page) Furthermore, similar samples were tested at 40°C as part of a durability test.
Figure 1 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 for the sample waste in Tables 1-2. This figure shows that the durability of the transparent conductive film is improved by using the structure of the present invention.

Note that tin compounds, zinc compounds, and indium compounds other than those used in the present examples and comparative examples may be used for the purpose of the present invention as long as they can be dissolved in an appropriate solvent and formed into a film by firing. I can do it. The thickness of the ITO layer can be arbitrarily changed depending on the concentration of the solution, but it is not preferable to make it too thick. Similarly, it is not preferable to increase the thickness of the tin oxide film and the tin oxide/zinc oxide mixture film too much.

Effects of the Invention As described above, the present invention provides a first film made of tin oxide or a mixture of tin oxide and zinc oxide on a substrate by applying a tin compound solution or a mixed solution of a tin compound and a zinc compound;
A second film made of indium oxide doped with tin is applied thereon by applying a mixed solution of an indium compound and a tin compound and baking at a temperature below 550°C. A third film made of a tin oxide thin film or a mixture of tin oxide and zinc oxide, which is different from the first film, is applied on top with a tin compound solution or a mixed solution of a tin compound and a zinc compound, and baked at 550°C or less. It is possible to form a highly durable transparent conductive film on a large-area substrate.

[Brief explanation of the drawing]

The figure shows 40
It is a characteristic diagram showing the results of a humidity test at 90% RH.

Claims (3)

[Claims] (1) A first film made of tin oxide alone or a mixture of tin oxide and zinc oxide is provided on the substrate, a second film made of tin-doped indium oxide is provided on the film, and a second film made of indium oxide doped with tin is provided on the film. A transparent conductive film characterized in that it has a three-layer structure by providing a third film made of tin oxide alone or a mixture of tin oxide and zinc oxide, which is different from the first film. (2) Applying a solution of a tin compound alone or a tin compound and a zinc compound dissolved in a solvent onto a substrate and baking it in the air,
A first film made of tin oxide alone or a mixture of tin oxide and zinc oxide is provided, and a solution in which an indium compound and a tin compound are dissolved in a solvent is applied onto the film and baked in the atmosphere.
A second film made of indium oxide doped with tin is provided, and a tin compound alone or a solution of a tin compound and a zinc compound dissolved in a solvent is applied onto these films and fired in the atmosphere to form a second film made of indium oxide doped with tin. A method for forming a transparent conductive film, which comprises providing a third film different from the film and made of tin oxide alone or 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.