JPH0519944B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a combustible gas sensor, and more particularly, to a combustible gas sensor employing a field effect transistor type configuration.

<Prior art> As shown in FIG. 5, a conventional combustible gas sensor uses a DC power source 1 for an element 11 whose resistance value changes in response to a combustible gas such as SnO ₂ .
2 and an ammeter 13 are connected in series, and a power source 15 is connected in series to a heater 14 that heats the element 11 to about 100 DEG C. to 400 DEG C.

In addition, as a field effect transistor type (hereinafter abbreviated as FET type) hydrogen gas sensor, the gate electrode of the field effect transistor is made of palladium (Pd).
A composition consisting of was provided.

<Problems to be Solved by the Invention> In the flammable gas sensor having the configuration shown in FIG. 5, the element 11 for detecting the presence of combustible gas
It is essential to heat the gas to approximately 100° C. to 400° C. using the heater 14, which not only complicates the structure but also causes problems in that the heater 14 may cause a gas explosion.

Further, there is a problem in that the gas selectivity is poor and the method is similarly sensitive to similar flammable gases such as hydrogen gas and hydrocarbon gas. For example, even if a sensor is used to detect the leakage of flammable gas, it will also be sensitive to the alcohol gas generated when sake is heated, and the sensor will detect the leakage of flammable gas as well. The problem is that it can cause a condition.

In the FET type hydrogen sensor mentioned above, H ⁺ ions decomposed by the catalytic action of palladium (Pd) accumulate at the gate electrode, so the rate of change in hydrogen gas concentration due to the sequential accumulation is measured. However, there is a problem in that the absolute value of the hydrogen gas concentration cannot be measured.

<Object of the invention> This invention was made in view of the above problems, and can eliminate the risk of gas explosion, improve the selectivity of flammable gases, and further improve the selectivity of combustible gases. It is an object of the present invention to provide a combustible gas sensor that can accurately measure the concentration of flammable gas.

<Means for Solving the Problems> In order to achieve the above object, the flammable gas sensor of the present invention has one of the gate electrode and the source electrode of a field effect transistor made of platinum metal, and the other made of platinum metal. A gas-permeable proton conductor membrane is formed, which is made of a metal that does not react with flammable gas, and integrally covers both of the electrodes.

However, silver can be used as the metal that does not react with the flammable gas.

<Function> In the flammable gas sensor with the above configuration, combustible gas is guided to the electrode made of platinum metal through a gas-permeable proton conductive membrane, and is decomposed and formed by the catalytic action of platinum metal. Electrons accumulate,
The decomposed protons are free to conduct through the gas-permeable proton conductor membrane and are prevented from recombining with the electrons, while increasing the potential of the electrode made of a metal that does not react with flammable gases. A predetermined potential can be maintained without being affected by the concentration of combustible gas.

<Examples> Hereinafter, examples will be described in detail with reference to the accompanying drawings showing examples.

FIG. 1 is a schematic diagram showing an embodiment of the combustible gas sensor of the present invention, in which an n-type source region 2 and a drain region 3 are provided at predetermined positions on the surface of a p-type substrate 1.
At the same time, an n-type channel region 4 is formed between the source region 2 and the drain region 3, and the entire surface of the p-type substrate 1 except for the portion corresponding to the source region 2 is formed. It is covered with an insulating film 5. A gate electrode 6 made of platinum is placed on the insulating film 5 corresponding to the channel region 4.
A source electrode 7 made of silver is formed so as to be in contact with the source region 2, and a gas permeable proton conductive film is formed so as to cover the gate electrode 6, the source electrode 7, and the insulating film 5. A solid electrolyte membrane 8 is formed.

Note that 9 is a DC power supply, and 10 is an ammeter, which are connected in series between the source region 2 and drain region 3.

The operation of the combustible gas sensor having the above configuration is as follows.

When hydrogen gas is introduced as a measurement gas as shown by arrow A in FIG. The reaction represented by H ₂ →2H ⁺ +2e 2H ⁺ +1/2O ₂ +2e→H ₂ O takes place on the surface, and H ⁺ ions move freely in the solid electrolyte membrane 8, so the above reversible reaction occurs frequently. As the amount of hydrogen gas reaching the gate electrode 6 through the solid electrolyte membrane 8 increases, the potential becomes deeper (see FIG. 2A).

On the other hand, in the source electrode 7, since silver is not sensitive to hydrogen gas at all, it continues to be held at a predetermined potential even if the concentration of hydrogen gas changes (see FIG. 2B).

Therefore, a potential depending on the concentration of hydrogen gas is applied between the source and gate electrodes, and when a constant voltage is applied between the source and drain electrodes, the potential increases as the concentration of hydrogen gas increases. As a result, the current characteristic decreases as the current decreases (see FIG. 2C).

Furthermore, since the H ⁺ ions generated in the vicinity of the gate electrode 6 are retained without being wasted during the above operation, it is not recommended to use a particularly high impedance measuring device. Although not necessary, a regular ammeter can be used to measure the exact hydrogen gas concentration.

Further, although only the measurement of the concentration of hydrogen gas has been described above, the measurement of the concentration of carbon monoxide gas can be similarly performed.

That is, carbon monoxide gas also undergoes a reversible reaction like hydrogen gas, specifically CO+H ₂ O→CO ₂ +2H ⁺ +2e 2H ⁺ +1/2O ₂ +2e→H ₂ O. Therefore, the concentration of carbon monoxide gas can be measured using the electrons generated by the above reaction.

FIG. 3 is a schematic diagram showing another embodiment, and the only difference from the above embodiment is that the gate electrode 6 is made of silver and the source electrode 7 is made of platinum.

Therefore, the gate electrode 6 is held at a predetermined potential regardless of the concentration of hydrogen gas, and the source electrode 7 becomes a deep negative potential as the concentration of hydrogen gas increases. Then, a potential that changes inversely to that in the above embodiment is applied depending on the hydrogen gas concentration between the source and gate electrodes, and when a constant voltage is applied between the source and drain electrodes, the hydrogen gas The current characteristic increases with increasing concentration of (see FIG. 4).

Note that this invention is not limited to the above embodiments; for example, it is possible to use a calomel electrode in place of the silver electrode, or to use an electrode made of another platinum metal in place of the platinum electrode. Besides,
The measurement range is changed by changing the gas permeability of the solid electrolyte membrane 8, and a plurality of combustible gas sensors with different measurement ranges are arranged in parallel and are selectively operated by a switch or the like (not shown). etc., and various other design changes can be made within the scope of not changing the gist of the present invention.

<Effects of the Invention> As described above, the present invention configures a field effect transistor using an electrode that is sensitive to combustible gas and an electrode that is not sensitive to flammable gas. This has the unique effect of making it possible to accurately measure the combustible gas concentration using a normal measuring device while ensuring that the risk of gas explosion is eliminated.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing one embodiment of the flammable gas sensor of the present invention, Fig. 2 is a characteristic diagram explaining the operation of the combustible gas sensor, Fig. 3 is a schematic diagram showing another embodiment, and Fig. 4 is a characteristic diagram, and FIG. 5 is a schematic diagram showing a conventional combustible gas sensor. 6...gate electrode, 7...source electrode, 8...
Solid electrolyte membrane.

Claims (1)

[Claims] 1. One of the gate electrode and source electrode of a field effect transistor is made of a white metal, and the other is made of a metal that does not react with flammable gas, and both of the electrodes are integrally covered. A flammable gas sensor characterized by forming a gas-permeable proton conductor membrane. 2. The combustible gas sensor according to claim 1, wherein the metal that does not react with combustible gas is silver.