JPH10170464A - Gas sensor for detecting co - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a CO-detecting gas sensor which can continuously detect even in an ambience including an interfering alcohol gas and is improved in selectivity to CO gas. SOLUTION: An amorphous aluminosilicate coating layer is provided on a metallic oxide semiconductor thin film in the CO-detecting gas sensor. The amorphous aluminosilicate coating layer formed on the metallic oxide semiconductor thin film as a CO gas sensitive body is considered as a solid acid medium to promote a dehydration reaction of alcohol to ethylene. Since ethylene has a smaller gas sensitivity than alcohol, a CO selectivity is improved relatively. Moreover, when an operation temperature of the CO-detecting gas sensor is set to be, e.g. 300 deg.C, heating every predetermined time is eliminated, thereby enabling continuous detections.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a gas sensor for detecting CO. More specifically, the present invention relates to a gas sensor for CO detection using a metal oxide semiconductor thin film as a gas-sensitive film.

[0002]

2. Description of the Related Art A gas sensor for detecting CO used in a commercially available incomplete combustion alarm is a so-called semiconductor type sensor using a thin film of a metal oxide semiconductor such as a tin oxide sintered body as a gas sensitive body. With this sensor, the CO gas sensitivity is from room temperature to about 100
Operating temperature of 100 ° C, taking advantage of high temperature
It is set as follows.

[0003] At such a low temperature, miscellaneous gases such as water vapor in the air are adsorbed on the surface of the sensitive body, and the temporal variation in sensitivity and the like is large. Therefore, heating to desorb such miscellaneous gases is about 300-500 ° C.
It takes about 1-2 minutes. For this reason, it is impossible to detect the CO gas at the time of such heating, and during this time, the sensor becomes dead time. That is, CO
Continuous detection of gas would not be strictly possible.

On the other hand, a constant-potential electrolytic gas sensor for CO detection is commercially available as a sensor capable of continuous detection. However, in this measuring method, an electrochemical reaction is used using an electrolytic solution. Requires maintenance and is expensive.

As a result of the above studies, it has been found that the sensor must be operated at a high temperature of about 300 ° C. in order to continuously detect CO gas using an inexpensive semiconductor thin film method. However, under such high temperature conditions, CO
Since the sensitivity of the alcohol-based gas, which is the interfering gas, is higher than the gas sensitivity, in order to reduce the effect, it is necessary to add CO selectivity to the metal oxide semiconductor itself, or In general, means such as pre-adsorption of alcohol-based gas by an activated carbon layer installed in a bed is used. However, since the alcohol-based gas assumed as the interfering gas has a high concentration (about 1000 ppm), sufficient CO selectivity cannot be obtained only by these methods.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a gas sensor for CO detection capable of continuous detection even in an atmosphere containing an alcohol-based gas as an interfering gas and having improved selectivity for CO gas. To provide.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is as follows.
This is achieved by a CO detection gas sensor in which an amorphous aluminosilicate coating layer is provided on a metal oxide semiconductor thin film.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION As a metal oxide semiconductor thin film as a CO gas sensitive material, a thin film (thickness: about 150 to 500 nm) of tin oxide, zinc oxide, iron oxide, titanium oxide or the like is used. In particular, a tin oxide semiconductor thin film is preferable, and is formed by a method of directly forming a SnO ₂ thin film by a vacuum deposition method, a sputtering method, an ion plating method, or the like, or a method of forming a metal Sn thin film and then heat-treating to oxidize the thin film. Alternatively, a method of plasma-polymerizing an organometallic monomer containing Sn to form a plasma-polymerized film and heat-treating the film (Japanese Patent Application Laid-Open No. 63-2611)
No. 48).

These metal oxide semiconductor thin films are made of quartz,
It is used so as to partially or entirely cover an electrode formed on an insulating substrate such as glass or alumina.
As the electrode, a commonly used counter electrode or comb electrode is used. As a material for forming an electrode, it is most preferable to use platinum among various noble metals from the viewpoint of chemical stability. The electrodes are formed by various vapor deposition methods, sputtering methods, and the like.

[0010] An amorphous aluminosilicate coating layer is formed on the metal oxide semiconductor thin film. The formation of the amorphous aluminosilicate coating layer is performed by a sol-gel method. In the sol-gel method, tetraethoxysilane about 0.1 to 1 M (about 0.2 to 0.5 M) Aluminum triisopropoxide about 0.01 to 1 M (about 0.025 to 0.5 M) Water about 0.06 to 6 M (about 0.15 to 3 M) Triethanolamine A gas detection element on which a metal oxide semiconductor thin film is formed is immersed in a sol consisting of an isopropanol solution (preferred concentration in parentheses) dissolved at a concentration of about 0.01 to 1 M (about 0.03 to 0.65 M). 1-6
With a pulling speed of cm / min, dry in the air about 100 ~
After about 5-15 minutes at 120 ° C, about 10-60 at about 400-800 ° C
A series of operations of baking for 1 minute are generally performed about 1 to 10 times to form an amorphous aluminosilicate coating layer having a thickness of about 0.1 to 10 μm.

[0011]

The amorphous aluminosilicate coating layer formed on the metal oxide semiconductor thin film as a CO gas sensitive substance is considered to promote the dehydration reaction of alcohol to ethylene as a solid acid catalyst. It is thought that the gas sensitivity is lower than that of alcohol, so that the CO selectivity is relatively improved.

Further, by setting the operating temperature to, for example, 300 ° C., the CO detection gas sensor does not need to be heated at regular time intervals, thereby enabling continuous detection.

[0013]

Next, the present invention will be described by way of examples.

EXAMPLE A platinum electrode was formed on a quartz substrate by electron beam evaporation, and a plasma CVD method was applied to the surface of the substrate including the electrode to form a plasma CVD thin film. For the application of the plasma CVD method, a mixed gas of tetramethyltin-oxygen (volume ratio 1:10) was used.

By applying a high-frequency power of 200 W for 30 minutes while heating the substrate temperature to 200 ° C. by a thin film heater provided on the back side of the insulating substrate, a transparent and amorphous After forming the plasma CVD thin film, heat treatment for 24 hours in dry air at 700 ° C together with the substrate,
A tin oxide thin film having a thickness of 250 nm was obtained.

An amorphous aluminosilicate coating layer was formed on the tin oxide thin film by a sol-gel method. In the sol-gel method, a gas detection element in which a tin oxide thin film is formed in a sol consisting of tetraethoxysilane 0.5M aluminum triisopropoxide 0.125M water 0.75M triethanolamine dissolved at a concentration of 0.175M, respectively. Immersed, pulled up at a pulling speed of 6 cm / min, and dried in air for 11 hours.
A series of steps of baking at 0 ° C. for 10 minutes and baking at 600 ° C. for 30 minutes was performed six times to form an amorphous aluminosilicate thin film having a thickness of about 5 μm as a coating layer. The composition analysis of the amorphous aluminosilicate thin film by X-ray photoelectron spectroscopy revealed that the thin film had an element ratio of Si / Al = 4.

When the CO selectivity to ethanol gas of the amorphous aluminosilicate-coated tin oxide thin film gas detecting element thus produced was examined at a temperature of 300 ° C., the value was 0.43. Here, the CO selectivity is the CO concentration of 50pp
represented as the ratio of the sensitivity _{Rair / R EtOH (= 396 /} 88.8) of the sensitivity Rair / Rco (= 396/208 ) and ethanol 1000ppm in in m in the air.

Further, by setting the operating temperature to 300 ° C., heating at regular intervals becomes unnecessary, and continuous detection becomes possible.

Comparative Example In the example, the CO selectivity of the tin oxide thin film gas detecting element having no amorphous aluminosilicate coating layer was examined. Rair / Rco (= 226 / 56.6) and Rair / R _EtOH (= 226
/6.7), the value was 0.12.

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[Procedure amendment]

[Submission date] February 21, 1997

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0002

[Correction method] Change

[Correction contents]

[0002]

2. Description of the Related Art A gas sensor for CO detection used in a commercially available incomplete combustion alarm is a so-called semiconductor sensor using a thin film of a metal oxide semiconductor such as a tin oxide sintered body as a gas sensitive body. With this sensor, room temperature to about 100 ° C
The operating temperature is set to 100 ° C. or lower by utilizing the characteristic that the CO gas sensitivity is high at a low temperature .

Claims (2)

[Claims] 1. A gas sensor for detecting CO in which an amorphous aluminosilicate coating layer is provided on a metal oxide semiconductor thin film. 2. The gas sensor for detecting CO according to claim 1, wherein the gas sensor is used in an atmosphere containing an alcohol-based gas as an interfering gas.