JPH06213853A - Manufacture of gas detecting element - Google Patents

Abstract

PURPOSE:To provide a method for fabricating a gas detecting element using an n-type metal oxide semiconductor film as a gas sensitive body wherein stability with time of element resistance of the gas sensitive body is improved by providing a set of electrodes and the semiconductor film on an insulation substrate in an optional order. CONSTITUTION:In a gas detecting element wherein a set of electrodes and an n-type metal oxide semiconductor film are formed in an optional order on an insulating substrate, the n-type metal oxide semiconductor film is subjected to high temperature treatment of 350 deg.C or higher in an air current including vapor to manufacture the gas detecting element.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a gas detecting element. More specifically, it relates to a method for manufacturing a gas detection element using an n-type metal oxide semiconductor thin film as a gas sensitive body.

[0002]

2. Description of the Related Art Sintered bodies of n-type metal oxide semiconductors such as tin oxide, zinc oxide, iron oxide (II) and titanium oxide have been used as materials for detecting reducing gases such as ethylene, methane and propane. Are known. On the other hand, thin-film type gas detection elements are being put into practical use in place of these sintered type ones.

The thin-film gas detection element is a gas sensitive body formed by forming an n-type metal oxide semiconductor film on an insulating substrate having a heater on the back surface or inside by various methods. When a reducing gas comes into contact with the gas sensitive body, the electrical resistance of the gas sensitive body decreases, and the reducing gas can be detected. However, the gas detection element having the thin film gas sensitive body is The drawback is that the element resistance changes with time.

For example, when such a gas detecting element is operated in an atmosphere containing water vapor, a phenomenon appears in which the element resistance increases with time. Such a change means that the zero point (conductivity in clean air) of the detecting element changes, and as a result, it is necessary to reset the zero point all the time, which is extremely disadvantageous in terms of measurement accuracy and maintenance. Becomes

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to provide a gas detecting element which is a gas sensitive material provided with an n-type metal oxide semiconductor thin film on an insulating substrate, and whose element resistance changes with time. It is to provide a manufacturing method of the one with improved stability.

[0006]

The object of the present invention is as follows.
In a gas detection element in which a set of electrodes and an n-type metal oxide semiconductor thin film are formed on an insulating substrate in an arbitrary order, the n-type metal oxide semiconductor thin film is heated in an air flow containing water vapor for 350 This is accomplished by subjecting the gas detection element to a high temperature treatment at a temperature of ℃ or higher.

Generally, a set of electrodes is first formed on an insulating substrate, and an n-type metal oxide semiconductor thin film is provided so as to cover it. As the insulating substrate, alumina,
Aluminum nitride or the like is used, and on these substrates, a pair of electrodes, generally facing comb electrodes, is formed by, for example, printing a thick film of gold paste (about 1 to 5 μm) in a predetermined shape. It A heater is also provided on the back surface or inside.

As the n-type metal oxide semiconductor thin film covering the set of electrodes, a tin oxide thin film, a zinc oxide thin film, an indium oxide thin film, a titanium oxide thin film and the like are used, but preferably the film thickness is about 150 to 500 nm. A tin oxide thin film is used. The formation of the tin oxide semiconductor thin film is performed by the vacuum deposition method, the sputtering method,
A method of directly forming a tin oxide thin film by an ion plating method, a method of forming a metal tin thin film and the like, and then performing a heat treatment to oxidize it, or plasma polymerizing an organometallic monomer containing tin to form a plasma polymerized film. The heat treatment is performed (Japanese Patent Laid-Open No. 63-261,148). Alternatively, the semiconductor thin film may be formed by such a method, and then the electrode may be formed.

These n-type metal oxide semiconductor thin films are subjected to high temperature treatment at a temperature of 350 ° C. or higher in an air flow containing water vapor. Relative humidity for air streams containing water vapor
1.2 mg / L or more corresponding to 5% (25 ° C) is used.
Further, the high temperature treatment under such an atmosphere is performed for about 48 to 150 hours at 350 ° C. or higher which is the operating temperature of the detection element or higher.

For example, when a tin oxide thin film as a metal oxide semiconductor thin film is obtained by a method of oxidizing a metal tin thin film by heat treating it in the atmosphere, the heat treatment for oxidation is 350
It is also performed under high temperature conditions of ℃ or higher. However, under such high temperature conditions, even if water vapor is contained in the atmosphere, it is volatilized out of the system, but in the method of the present invention, by using it as an air flow containing water vapor, the temperature of 350 ° C. or higher is obtained. Even under high temperature conditions, the metal oxide semiconductor thin film effectively contacts the water vapor contained in the air. The upper limit of the water vapor concentration used is about 660 mg / L, which corresponds to a relative humidity of 90% (100 ° C.), from the viewpoint of the apparatus.

[0011]

EFFECTS OF THE INVENTION In a gas detecting element using an n-type metal oxide semiconductor thin film as a gas sensitive body, the semiconductor film is further subjected to high temperature treatment in an air flow containing water vapor so that the element resistance of the gas sensitive body changes with time. Stability can be improved and measurement reproducibility can be improved. Further, the high temperature treatment in such an atmosphere also has the effect of increasing the sensitivity to reducing gas.

It is considered that these effects are because the metal oxide is further oxidized and becomes more stable in the oxidizing atmosphere.

[0013]

EXAMPLES The present invention will now be described with reference to examples.

Example 1 A thick film of gold paste (film thickness 5 μm) was formed on the surface of an alumina substrate.
A counter comb electrode consisting of Next, a film having a thickness of about 200 nm is formed by plasma CVD using tetramethyltin as a raw material so as to cover this electrode, and the film is formed in air at 500 ° C.
A tin oxide thin film was obtained by performing heat treatment for a period of time. Then
This is placed in an air stream containing water vapor at a concentration of 13 mg / L,
It was treated at 00 ° C for 48 hours.

Comparative Example 1 In Example 1, high temperature treatment was not performed in an air stream containing water vapor.

The changes over time in the resistance of the gas detection elements using the tin oxide thin film as the gas sensitive material, which were respectively produced in Example 1 and Comparative Example 1 above, were maintained in humid air at 60% RH and 25 ° C. As a result of measurement, the results shown in the graph of FIG. 1 were obtained. That is, in the gas detection element of Example 1,
Almost no change in element resistance over time was observed, whereas the gas detection element of Comparative Example 1 showed an increase in element resistance over time, that is, the durability as a gas detection element was poor. It is shown.

Example 2 In Example 1, the high temperature treatment in an air stream containing water vapor was carried out using an air stream containing water vapor at a concentration of 10.4 mg / L.
It was performed at 144 ° C for 144 hours.

Comparative Example 2 In Example 2, high temperature treatment was not performed in an air stream containing water vapor.

The gas sensitivity (element resistance in air) of the gas detection elements produced in Example 2 and Comparative Example 2 and using the tin oxide thin film as a gas sensor, with respect to ethylene-containing gas (concentration of 2000 ppm in air). The element resistance Rgas) in the Rair / ethylene-containing gas was measured to be 4.29 and
The value of 3.22 was obtained, and the gas sensitivity of the gas detection element of Example 2 was rather increased.

[Brief description of drawings]

FIG. 1 is a graph showing changes in resistance over time of gas detection elements manufactured in Example 1 and Comparative Example 1, respectively.

Claims (1)

[Claims] 1. A gas detecting element comprising a set of electrodes and an n-type metal oxide semiconductor thin film formed on an insulating substrate in an arbitrary order, wherein the n-type metal oxide semiconductor thin film is an air containing water vapor. A method for producing a gas detection element, which comprises high-temperature treatment at a temperature of 350 ° C. or higher in a flow.