JPH06148114A - Alcohol gas detecting element - Google Patents

Abstract

PURPOSE:To provide a gas detecting element with high sensitivity and selectivity to alcohol gas. CONSTITUTION:An alcohol gas detecting element comprises an insulating substrate 1, a thin film gas sensitive body 2 formed with WO3 mounted on the substrate 1, a pair of Pt electrodes 3 mounted opposedly and in contact with the gas sensitive body 2, a Pt catalyst 4 mounted on the gas sensitive body 2, and an Ag 5 formed on the surface of the gas sensitive body 2 and Pt catalyst 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas detection element having high sensitivity and selectivity for alcohol gas.

[0002]

2. Description of the Related Art Conventionally, various studies have been conducted on a gas detection element for selectively detecting alcohol gas such as C ₂ H ₅ OH (ethanol). An example thereof is that disclosed in Japanese Patent Laid-Open No. 3-102254. The element shown in this publication is on an insulating substrate,
The oxidation-treated film of the plasma-polymerized film of the organotin compound and the electrode are formed in an arbitrary order, and it is said that such a configuration improves the selectivity for alcohol gas.

[0003]

However, the gas sensitivity of this device shows a low value of about 3.5 with respect to ethanol having a concentration of 2000 ppm. Higher gas sensitivities are desired in order to measure lower concentrations of alcohol gas or to be able to work with simpler circuits.

In view of the above circumstances, the present inventor has conducted various studies in order to develop a gas detection element having high sensitivity and selectivity to alcohol gas, and as a result, the metal oxide semiconductor containing a noble metal catalyst has been Further, it was found that by adding Ag as a third component, the sensitivity and selectivity to alcohol gas were remarkably improved, and the present invention was accomplished.

[0005]

That is, an alcohol gas detecting element according to the present invention comprises an insulating substrate, a pair of electrodes, and a WO.
_A thin film gas sensor made of ₃ (tungsten oxide),
It is characterized by comprising a noble metal catalyst and an additive made of Ag (silver).

As the insulating substrate used in the present invention, a heat resistant and insulating substrate such as a ceramic substrate made of Al ₂ O ₃ (aluminum oxide) or a glass substrate made of SiO ₂ (silicon oxide) is used.

The thin-film gas sensitive material made of WO ₃ used in the present invention is formed on an insulating substrate by a vacuum deposition method, a sputtering method or the like. At this time, it is preferable that the mass film thickness of the gas sensitive body is 300 Å or more.
If it is less than 00Å, a stable continuous film cannot be formed and the sensitivity is lowered. Note that WO ₃ is formed by forming W (tungsten) on an insulating substrate by a vacuum deposition method, a sputtering method, or the like, and then performing a heat treatment or the like.
O ₃ may be formed, or WO ₃ may be formed directly on the insulating substrate by a vacuum deposition method, a sputtering method, or the like.

As the pair of electrodes used in the present invention, for example, Au (gold), Pt (platinum), etc. are used.
It is formed by a vacuum deposition method, a screen printing method, a sputtering method, or the like. The electrodes are provided in contact with and facing the gas sensitive body, and may be provided either between the gas sensitive body and the insulating substrate or on the surface of the gas sensitive body.

The noble metal catalyst used in the present invention is
For example, it is made of Pt and is formed on the surface of the gas sensitive body by a vacuum deposition method, a sputtering method, or the like. At this time, the mass film thickness of the catalyst is preferably 50 Å or less, and when it exceeds 50 Å, the gas sensitizer itself cannot maintain the property of the semiconductor and the detection characteristics are deteriorated.

The additives used in the present invention are Ag
It is formed on the surface of the gas sensitive material and the catalyst by a vacuum deposition method, a sputtering method or the like. At this time, the mass film thickness of Ag (additive) is preferably 300 Å or less, and when it exceeds 300 Å, sufficient sensitivity and selectivity cannot be obtained. In addition, Ag is a temperature condition, H ₂ (hydrogen) gas,
The oxidation state changes by contact with a reducing gas such as CO (carbon monoxide) gas. Therefore, Ag used in the present invention is not limited to either metal or oxide.

The alcohol gas detecting element of the present invention may be provided with a heating element such as a self-temperature control (PTC) heater in order to keep the element temperature at a predetermined temperature.

[0012]

The alcohol gas detecting element of the present invention having the above-described structure can selectively detect alcohol gas with high sensitivity due to the effect of adding Ag (additive).

[0013]

EXAMPLES Examples of the present invention will be described below together with comparative examples. Example First, as shown in FIG. 1, an alumina substrate having a length, width, and thickness of 8 × 7 × 0.635 mm was prepared as an insulating substrate 1, and a mass film thickness of 5 was formed on the substrate 1 by vacuum deposition.
After forming a 000Å WO ₃ thin film, 500 in air
Heat treatment was performed at 10 ° C. for 10 minutes to obtain a gas sensitive body 2. Next, a comb-shaped Pt electrode 3 having a mass film thickness of 500Å as shown in FIG. 2 was formed on the gas sensitive body 2 by a vacuum deposition method. Further, Pt was vacuum-deposited on the upper surfaces thereof so that the mass film thickness was 10 Å, to form the catalyst 4. Finally, Ag (additive) 5 having a mass film thickness of 10Å was formed on the upper surfaces of the gas sensitive body 2 and the Pt catalyst 4 by a vacuum deposition method. A heating element 6 for controlling the element temperature is provided on the back surface of the insulating substrate 1.

Here, the gas sensitivity of the device manufactured as described above was measured under the following conditions. First, the element was fixed in a closed tank, C ₂ H ₅ OH was injected into the tank so that the concentration after evaporation was 1000 ppm, and the mixture was heated and evaporated using a heater. Further, various gases such as CO gas, H ₂ gas, and C ₃ H ₈ (propane) gas were injected into the tank with a syringe so that the concentration thereof would be 1000 ppm. After sufficiently stirring these various gases with a fan, the electrical resistance value of the elements in the various gas atmospheres was measured while the element temperature was maintained at 60 to 300 ° C. The sensitivities to various gases are shown in FIG. The sensitivity was shown by [resistance value in air (R _Air ) / resistance value in gas (R _Gas )]. According to this, the device of the present invention has a C ₂ temperature range of 150 to 300 ° C.
It shows a high sensitivity of 10 ⁴ or more to H ₅ OH gas. This is various gases (CO, H) other than C ₂ H ₅ OH gas.
_2, C ₃ H ₈₎ is the value of 100 times more sensitive to,
It can be said that it shows extremely high selectivity.

<Comparative Example> Next, as a comparative example, an element containing no Ag (additive) was prepared, and the sensitivity to various gases was measured in the same manner as in the above-mentioned examples. The results are shown in Fig. 4.
Comparing FIG. 4 with the sensitivity characteristics (FIG. 3) of the elements in the above-mentioned examples, it was confirmed that the addition of Ag showed a difference of 150 ° C.
It can be seen that the sensitivity to CO gas in the temperature range below decreases and the sensitivity to C ₂ H ₅ OH gas in the temperature range of 200 ° C. or higher increases.

[0016]

As described in detail above, according to the present invention, by adding Ag to the gas sensitive material to which the noble metal catalyst is added, it is possible to obtain an extremely high resistance to alcohol gas such as C ₂ H ₅ OH. A gas detection element having high sensitivity and selectivity can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view (conceptual view) showing an embodiment of an alcohol gas detection element according to the present invention.

FIG. 2 is a plan view showing an example of a comb-shaped Pt electrode used in the present invention.

FIG. 3 is a sensitivity characteristic diagram of an alcohol gas detection element according to the present invention for various gases.

FIG. 4 is a sensitivity characteristic diagram of the element of the comparative example for various gases.

[Explanation of symbols]

 1 Insulating Substrate 2 Thin Film Gas Sensitive Body 3 Comb Pt Electrode 4 Catalyst 5 Additive 6 Heating Element

Claims (1)

[Claims] 1. An alcohol gas detection method comprising an insulating substrate, a pair of electrodes, a thin-film gas sensor made of WO ₃ (tungsten oxide), a noble metal catalyst, and an additive made of Ag (silver). element.