JPS61227311A - Formation of transparent electroconductive film - 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 TECHNICAL FIELD The present invention relates to a method for forming a transparent conductive film on an insulating substrate such as glass or ceramic during the production of, for example, a liquid crystal display element.

"Prior Art and its Problems" It is well known that metal oxide films such as indium, cadmium, tin, and antimony formed on insulating substrates such as glass and ceramics are transparent and exhibit good conductivity. Therefore, this transparent conductive film can be used, for example, in transparent electrodes of semiconductor devices, liquid crystal display devices, electrochromic devices, electroluminescent devices, etc., as well as photoelectric conversion devices such as solar cells and image pickup tubes, and transparent surface heating elements (defroster). It is used as a functional film for transparent heat insulators, resistors, and infrared reflectors.

In recent years, transparent conductive films such as those mentioned above have been required to have lower sheet resistance values. The surface resistance value of the film is Ω/
It was a good thing to say, but as it has come to be applied to automotive panel dot matrices, LCD televisions, etc., there has been a demand for something with an extremely low sheet resistance value.

Conventionally, when forming the above-mentioned transparent conductive film, vacuum evaporation method, sputtering method, chemical spray method,
Methods such as screen printing and dipping are used. Among these, the chemical spray method, screen printing method, and dipping method are methods that utilize thermal decomposition in which a liquid containing an organic metal compound is applied and then baked.

As for the vacuum evaporation method, the mask evaporation method has recently been developed.

Although the etching process is no longer necessary, there is a problem in terms of mass production because the process is a batch process.

Like the vacuum evaporation method, the sputtering method is also a batch process, so it is not suitable for mass production and is not suitable for obtaining large area products.

Further, although the chemical spray method is advantageous in obtaining a film having a relatively large area, it requires a large amount of equipment and it is difficult to control the uniformity of the film.

Furthermore, the screen printing method has poor workability during printing.
In particular, it is difficult to print fine patterns stably, and it is difficult to obtain low resistance values.

In contrast to these methods, the immersion method allows the formation of a film of any shape on a substrate through the simple steps of ① immersion in an organic metal compound-containing liquid, ② drying, ∎ baking, and ∎ etching. Moreover, it has the advantage that it does not require a large amount of equipment and can be easily mass-produced.

However, as is common to the chemical spray method, screen printing method, and dipping method, these methods generally tend to have a high one-area resistance value. For this reason, it was not suitable as a transparent conductive coating for dot matrix, liquid crystal television, etc., which requires a very low sheet resistance value.

``Object of the Invention'' An object of the present invention is to provide a method for forming a transparent conductive film that solves the problems of the prior art described above and can be applied to fields that require a low sheet resistance value. .

"Structure of the Invention" As a result of intensive research to achieve the above object, the present inventors discovered that a transparent conductive film with a low sheet resistance value can be obtained by rapid cooling after annealing (heat treatment). , we have completed the present invention. That is, the present invention applies a transparent conductive film forming liquid to a base material, bakes it, and
This is a method of forming a transparent conductive film in which the film is annealed and then rapidly cooled.

First, the composition of the transparent conductive film forming liquid used in the present invention will be explained.

As the transparent conductive film forming liquid, a liquid containing an organometallic compound that becomes a transparent conductive metal oxide upon firing, an electrical resistance value adjusting agent, and an organic solvent is used.

The organometallic compound that becomes a transparent conductive metal oxide upon firing is not particularly limited, but is preferably an organoindium compound represented by the following general formula, for example.

In(X)3 (However, in formula 1, ) In(acac)3 and the like.

The electrical resistance value adjusting agent is not particularly limited, but for example, an organic tin compound represented by the following general formula is suitable.

(Y)2 Sn (X)2 (In the formula, X is β-diketone and Y is an alkyl group.) Examples of organic tin compounds represented by the above general formula include acetylacetone and butane bonded to tin. Dibutyltin acedope (C,H9)25n(acac)2,
Dimethyltin acedope (01%) 25n (acac
)2) Diethyltin acedope (C2H6)2Sn(a
cac)2, etc.

Organic solvents for dissolving these organic indium compounds and electrical resistance value adjusters include ketones such as acetone and methyl ethyl ketone, hydrocarbon compounds such as benzene and hexane, esters such as ethyl acetate and propyl acetate, ethanol and propatool. Alcohols such as these are used, and the low-boiling point organic solvents mentioned above are particularly suitable.

Further, a small amount of a viscous agent such as nitrocellulose may be added to and dissolved in the organic solvent, thereby allowing the liquid to be uniformly and stably applied onto the substrate with good mass productivity. In particular, the aforementioned nitrocellulose is heated at 200°C.
Since it is burnt off at a relatively low temperature before and after baking, a transparent conductive film with good properties and little residue can be obtained after baking.

In the present invention, a transparent conductive film forming liquid prepared as described above is applied to a substrate, baked, annealed, and then rapidly cooled to form a transparent conductive film.

As the base material, a plate-shaped material such as glass or ceramics or another shape is selected depending on the purpose. Any method such as a chemical spray method, a screen printing method, or a dipping method may be employed as a method for applying the transparent conductive film forming liquid to this base material.

For example, in the case of a dipping method, the substrate is immersed in a transparent conductive film forming liquid and the liquid is applied. in this case.

The concentration of the transparent conductive film forming liquid and the pulling speed are adjusted depending on the desired film thickness.

After the transparent conductive film forming liquid is applied onto the substrate in this manner, it is dried by being left at 140° C. for 10 minutes, for example. By drying, the organic solvent is sufficiently evaporated and a transparent film is formed on the substrate.

Next, this film is fired at, for example, 500° C. for 30 minutes.

By firing, a transparent conductive film of indium oxide-tin oxide is formed on the base material.

After the above firing, annealing is performed. In this case, the longer the time from the end of firing to the start of 7-annealing, the higher the sheet resistance value of the obtained transparent conductive film tends to be. Therefore, after firing, 0.5
In the present invention, annealing means heat treatment after completion of firing. The annealing conditions are preferably an atmosphere with a high nitrogen content (for example, an atmosphere containing 75% or more nitrogen); the higher the nitrogen content in the atmosphere, the larger the area of the obtained transparent conductive film. The resistance value becomes lower.

Further, the annealing temperature is preferably about 350 to 500°C.

The present invention is characterized by rapid cooling after annealing. By rapid cooling, a transparent conductive film with a low sheet resistance value can be obtained. in this case.

Although the quenching rate is not particularly limited, it is more effective to quench at a rate faster than 50° C./sin.

Note that if a sufficient film thickness cannot be obtained by applying and baking the transparent conductive film forming liquid once, the desired film thickness can be obtained by repeating the process multiple times.

"Embodiments of the Invention" 34.38% by weight of trisacetylacetonatoindium In (acac) as an organic indium compound and dibutyltin acedope (CaH
,)25n(acac)20. A conductive film-forming liquid was prepared containing 12% by weight of f1, 2.5% by weight of tenitrocellulose as a viscosity agent, and 92.5% by weight of methyl ethyl ketone (MEK) as an organic solvent.

A substrate made of soda glass is immersed in this forming solution, pulled up at a speed of 20 c layers/min, pre-dried at 140°C for 10 minutes, baked at 500°C for 30 minutes, and continuously annealed in a 100% nitrogen atmosphere. The cooling was carried out at 500° C. for 30 minutes, and then rapidly cooled at the cooling rate shown in Table 1. The area resistance values of the transparent conductive films thus obtained were measured, and the relationship between the cooling rate and the area resistance values was determined as follows.
As is clear from the table and figure shown in Figure 1, the faster the cooling rate, the lower the sheet resistance value, and when the cooling rate is 50G'0/sin, the sheet resistance value is 50Ω10
Very low.

(Hereinafter, blank spaces) Table 1 Example 2 A conductive film forming liquid having the same composition as in Example 1 was prepared. A substrate made of soda glass was immersed in this forming solution and pulled up at a speed of 20 am/min.

After pre-drying at 140°C for 10 minutes, baking is performed at 500°C for 30 minutes to form a transparent conductive film on the substrate.
Next, the thus obtained transparent conductive film was annealed at intervals of time from firing to annealing as shown in the following table. Note that annealing was performed in an atmosphere of 100% nitrogen for 5
The test was carried out at 00°C for 30 minutes. After annealing, it was rapidly cooled at 100° C./sin. The area resistance values of the transparent conductive films thus obtained were measured, and the relationship between the time from firing to 7-neal and the area resistance values was clearly shown in Table 2 and Figure 2. As shown, the sheet resistance value showed a tendency to increase as the time from firing to 7th Neal increased. Similar experiments were conducted by changing the cooling rate after annealing, and the same trend was observed. That is, it can be seen that by continuously performing baking and annealing and further increasing the cooling rate, it is possible to form a transparent conductive film with a very low sheet resistance value.

(Hereinafter, blank spaces) Table 2 Example 3 A film forming solution having the same composition as in Example 2 was prepared. A substrate made of soda glass is immersed in this forming solution,
After pre-drying at 140°C for 10 minutes by lifting at a speed of 20 cm/min, baking was performed at 500°C for 30 minutes to form a transparent conductive film on the substrate. Seven cycles were carried out under the atmosphere shown in . Annealing was performed at 500℃ for 30 minutes, and after annealing,
It was cooled at 00°C/sin. The area resistance values of the transparent conductive films obtained in this way were measured, and the relationship between the annealing atmosphere and the area resistance values was shown in Table 3. It is affected by the atmosphere, and when carried out under a nitrogen atmosphere, the resistance is 250Ω1.
0, which is lower than under other atmospheres.

Table 3 Note that although all of the above examples were based on the dipping method, the present invention can also be applied to screen printing methods, chemical spray methods, and the like.

"Effects of the Invention" As explained above, according to the present invention, the sheet resistance value can be significantly reduced by applying a transparent conductive film forming liquid, annealing it by baking it, and then rapidly cooling it. Can be done. Moreover, if annealing is performed continuously after firing, a transparent conductive film having an even lower sheet resistance value can be obtained. Furthermore, if annealing is performed in an atmosphere with a high nitrogen content ratio, a transparent conductive film having an even lower one-area resistance value can be formed. Therefore, it can also be applied to the formation of transparent conductive films that require extremely low sheet resistance values, such as automotive panels, DotFtrix, and liquid crystal televisions.

[Brief explanation of the drawing]

FIG. 1 is a chart showing the relationship between the cooling rate after annealing and the sheet resistance value, and FIG. 2 is a chart showing the relationship between the time from firing to 7th anneal and the sheet resistance value.

Claims (4)

[Claims] (1) A transparent conductive film forming liquid containing an organometallic compound that becomes a transparent conductive metal oxide when fired, an electrical resistance value adjusting agent, and an organic solvent is applied to a base material, and then fired and annealed. A method for forming a transparent conductive film, which comprises rapidly cooling after the annealing. (2) In claim 1, the rapid cooling is performed at 50%
A method for forming a transparent conductive film at a rate faster than °C/min. (3) The method for forming a transparent conductive film according to claim 1 or 2, wherein the annealing is performed within 0.5 hours after the baking. (4) A method for forming a transparent conductive film according to claim 1, 2, or 3, wherein the annealing is performed in an atmosphere containing 75% or more nitrogen.