JPS6290529A - Method for detecting gas and gas sensor - Google Patents

Abstract

PURPOSE:To selectively set sensitivity corresponding to the kind of gas to be detected, by simple constitution such that specimen gas is introduced into the gap between the contact surfaces of two kinds of semiconductive substances each having a rectifying characteristic and the change in the energy level of the potential barrier of each semiconductive substance surface corresponding to the kind of the gas is detected. CONSTITUTION:N-type and P-type semiconductive substances 1, 2 are mechanically held between ceramic substrates 3, 4 by a spring 5 and voltage is applied between lead wires 32, 42 and specimen gas G is introduced into the gap between the contact surfaces of the substances 1, 2 from the direction shown by an arrow to measure a voltage-current characteristic. The specimen gas is detected by utilizing that the energy level of the potential barrier of each semiconductive substance surface changes corresponding to the kind of the specimen gas. Different gas can be selectively detected by controlling voltage to be applied or heating temp. and it is unnecessary to heat an element to high temp. and measurement can be performed even in an atmosphere wherein the concn. of oxygen varies and the specimen gas can be detected with high sensitivity by simple constitution.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is for - detecting the presence of trace amounts of carbon oxide, hydrogen, hydrocarbons, and other test gases in air or other gases; Use it for.

INDUSTRIAL APPLICABILITY The present invention can be widely used in ordinary homes or businesses that use fuel gas, workplaces that involve mining or other underground work, businesses that produce or refine gas, equipment that transports or refines petroleum, and others. .

INDUSTRIAL APPLICATION This invention can be utilized for process control which performs control based on gas detection.

〔overview〕

The present invention provides a method for detecting a sample gas contained in a sample gas by bringing a sample gas into contact with the surface of a semiconductor material having rectifying properties and detecting a change in the rectifying properties. Two types of solid materials with rectifying properties are mechanically brought into contact via a contact surface, a gap is formed in the contact surface, and a sample gas is introduced into the gap. The type of gas to be detected can be selectively detected at low temperatures (temperatures that are insufficient to oxidize the gas to be detected; the same applies hereinafter) by utilizing the fact that the potential barrier energy level of the gas changes to different values. It was made so that it could be done.

[Conventional technology]

2. Description of the Related Art Conventionally, gas sensors have been widely used to issue a warning before gas leaking into the atmosphere becomes dangerous enough to cause an explosion. In particular, even if carbon oxide is mixed into the air at a level far greater than that which causes an explosion, it poses a danger to humans or living organisms, so there is a need for something that can generate an alarm when the amount of mixed carbon is several hundred ppm. has been done.

Conventionally, a technique using a ceramic semiconductor material has been developed as a gas sensor for this purpose. This technique is described in detail in, for example, [Miyayama and Yanagida, "Zinc Oxide Gas Sensor," published by the Ceramics Association of Japan: m magazine, "Ceramics," Vol. 18, No. 11 (November 1983), pp. 941-945]. In this technology, when a reducing gas comes into contact with the surface of a ceramic semiconductor, the adsorbed oxygen on the surface of the semiconductor reacts with the gas and decreases, reducing the height and width of the potential barrier, making it easier for electrons to move. This takes advantage of the property that the specific resistance decreases. That is, a test gas is oxidized on the surface of a semiconductor, and changes in the electrical characteristics of the semiconductor are detected.

In addition, one of the inventors of the present invention noticed that the bond between a metal and a semiconductor having rectifying characteristics, or one ceramic semiconductor and a different type of ceramic semiconductor, reacts to hydrogen gas or water vapor, and he discovered that changes in rectifying characteristics can be detected by air. It was proposed that its use in detecting hydrogen or water vapor in water is promising in the future. This is [Miyayama, Yanagita [New developments in gas sensor material development] Magazine "Electrochemistry" Vol. 50 No. 1 (19
(January 1982) pp. 92-98] or [Yanagida et al., "Current-voltage characteristics of semiconductor junctions with respect to relative humidity," English journal published by the Japanese Society of Applied Physics.
al of Applied Physics) No. 22
Volume No. 12 (December 1983), page 1933].

One of the inventors of the present invention suggested in the above-mentioned known document that a semiconductor junction with rectifying properties is effective in detecting hydrogen gas and water vapor in the air, but at this stage, its effect has not been fully elucidated. Therefore, the types of gases that can be detected, the methods and equipment configurations that can be used industrially, etc. have not been disclosed.

[Problems to be Solved by the Invention] Since the conventional gas sensor described above utilizes oxidation of the gas to be detected, the temperature at which the gas to be detected can be effectively oxidized, generally a high temperature of 450°C or higher, is It is necessary to heat the detection element beforehand. For this reason, gas sensors need to be supplied with energy for heating, and they also need to have an explosion-proof structure to prevent them from becoming an explosion source.
Furthermore, a structure was needed to protect the device from heat generation. Therefore, the gas sensor becomes large and has a complicated structure, which has the disadvantage of short life.

Furthermore, since conventional gas sensors utilize the oxidation reaction of the gas to be detected, they have the property of reacting to reducing gases in general. On the other hand, -carbon oxide requires a detection alarm to be issued at an extremely low concentration compared to other reducing gases. Therefore, if the detection alarm limit is set low for a gas sensor for carbon oxide, many other gases other than carbon oxide will react at unnecessary low concentrations, making it difficult to issue reliable alarms. There was a drawback that the equipment was not available. Hitherto, a gas sensor that selectively reacts only to carbon oxide or other gases has not been available.

Conventional gas sensors utilize the oxidation reaction of a gas to be detected, so they must contain a certain concentration of oxygen in the atmosphere, and cannot be applied in an atmosphere that does not contain oxygen or in an atmosphere where the oxygen concentration fluctuates.

The present invention solves these problems by providing a device with a simple structure that operates at low temperatures, which allows sensitivity to be selectively set depending on the type of gas to be detected, and which can be used in an oxygen-free atmosphere or in an oxygen-free atmosphere. It is an object of the present invention to provide a gas sensor that can be applied even in an atmosphere where the oxygen concentration fluctuates.

[Means for solving problems]

The first aspect of the present invention is a gas detection method, in which gas detection is performed by bringing a sample gas into contact with the surface of a semiconductor and electrically detecting a change in the rectification characteristics of the semiconductor, in which at least one of the semiconductors is a semiconductor. Two types of solid substances that have rectifying properties when brought into contact with each other are brought into mechanical contact via a contact surface, a gap is formed in the contact surface, and a sample gas is introduced into the gap. Gas detection is performed by utilizing the fact that the potential barrier energy level on the surface of the semiconductor material changes to different values depending on the type of gas to be detected contained in the sample gas.

The second aspect of the present invention is a gas sensor in which two types of solid materials, at least one of which is a semiconductor material and which produce rectifying properties when brought into contact with each other, are brought into contact with each other through a contact surface with a gap through which a sample gas can enter and exit. is connected to each of these two types of solid materials, and applies a bias voltage between the two types of solid materials.
The present invention is characterized by comprising an electric circuit that detects the electric characteristics on the contact surface.

Furthermore, the third aspect of the present invention is a gas sensor in which the gas sensor described above is provided with a heating device.

[Effect]

The most important point of the present invention is to bring two different types of substances with rectifying properties into surface contact by bringing them into contact with each other, to create a small gap in the surface, and to introduce the sample gas into this gap.

The gas detection of the present invention differs from the conventional method in which a reducing gas combines with oxygen on the semiconductor surface to change the state of the semiconductor surface. It is thought that the energy level of the potential barrier changes.

This is because the inventor conducted an experiment and found that by changing the bias voltage applied between two types of substances, the type of gas causing nausea can be changed. In other words, if the test gas oxidizes, it will react broadly with reducing gases in general, as in the conventional technology, but since the amount of change in the energy level differs depending on the type of test gas, oxidation or It is possible that this is a different phenomenon that does not involve reduction directly.

The property that the type of gas to be detected can be selected by applying a bias voltage is a remarkable function and effect of the present invention. Therefore, the use of an electrical circuit that allows the bias voltage to be varied provides a device that can selectively detect different types of gas. Furthermore, in a device that detects only a specific type of gas to be detected, the most effective bias voltage for that gas to be detected may be fixedly set.

Furthermore, in the method of the present invention, the reaction with the reducing test gas occurs at a temperature that is insufficiently low to oxidize the test gas. This too,
This is one of the reasons why the detection method of the present invention is not related to redox.

Further, in the method of the present invention, if the element temperature is increased to a high temperature exceeding 500° C., the characteristic gas detection of the present invention cannot be performed. That is, at such a high temperature, the gas to be detected is oxidized, and the same oxidation and reduction actions as in the conventional device occur. Of course, if such conditions are ignored, it can also be used at temperatures exceeding 500°C.

According to the present invention, gas detection can be performed even at room temperature; however, when detecting gas in the air, water vapor in the air liquefies on the surface of the semiconductor, resulting in noise. Therefore, when detecting a low concentration test gas, gas detection is affected by the humidity in the air, and a uniform reaction depending on the type and concentration of the test gas cannot be reproduced. When the carrier of the gas to be detected is dry air or dry nitrogen that does not contain water vapor, the gas detection of the present invention can be carried out down to considerably low temperatures. Generally, in order to detect a gas in the air, it is preferable to heat the gas to be detected to be applied to the gap or the element itself, for example, to 100° C. or higher using an indirect heater to prevent water vapor from liquefying.

Although the upper limit of the temperature may vary depending on the type of substance, it is desirable that the upper limit does not exceed 300° C., at which the reducing gas easily combines with oxygen on the semiconductor surface.

Therefore, according to the present invention, the device is heated to around 200°C.
By heating to eliminate the influence of water vapor and setting the bias voltage near a value that is most sensitive to -carbon oxide, for example, a gas sensor that is significantly sensitive only to -carbon oxide can be obtained. For other types of gases, selective sensors can be obtained using similar principles.

It is necessary to provide a gap between the two types of materials at the contact surface, through which the sample gas can enter and exit. If we create a structure that seals this contact surface from the atmosphere of the test gas, no reaction to the test gas will be observed.

Experimentally, it has been found that a gap of approximately several tens of micrometers is most effective.

If this gap is smaller than 10 μm, it will be difficult for the gas to be detected to enter, which is not appropriate. Moreover, if the size exceeds 300 μm, the contact surface becomes mechanically unstable and is not suitable.

The structure of the device in the laboratory is such that the surface of the semiconductor material is roughened with sandpaper to a predetermined roughness, and a certain mechanical force is applied using this rough surface as the contact surface. . As a result, empty spaces of appropriate size can communicate with each other to form a void. A spring structure is suitable for applying a constant mechanical force. As a practical structure, one in which the element is held by a spring structure, such as a holding structure for a crystal resonator, is preferable.

Industrially, it is preferable to form semiconductor materials into thin films and control the surface roughness by etching or other methods used to produce raw conductors.

There are various methods of introducing the sample gas into the voids in the contact surface, but the simplest method is to introduce it by diffusion in the atmosphere. Although this method requires time to react, the mechanical structure of the device is simple. By creating an airflow in the sample gas using an appropriate method and exposing the voids on the contact surface to this airflow, the reaction delay can be reduced.

When heating the element, it is preferable to use a heating wire. In this case as well, the element temperature may be lower than in conventional devices, so the heating structure is simple and the heating energy may be small. It is best to connect a thermostat for temperature control to the heating wire.

Two types of solid substances that act p-type when brought into contact are sintered bodies of semiconductor substances such as copper oxide, nickel oxide, cobalt oxide, iron oxide, and chromium oxide, platinum, palladium, silver, and ruthenium. There are metals such as Examples of substances that act on the n-type include sintered bodies of semiconductor materials such as zinc oxide, titanium dioxide, silicon dioxide, and tungsten oxide, and metals such as zinc and indium. The element of the present invention can be constructed by selecting and combining materials such that at least one of the materials acting as a p-type and those acting as an n-type is a semiconductor material.

The method of the invention can be carried out in an oxygen-free atmosphere or in an atmosphere with varying oxygen concentrations. In some cases, the sensitivity is higher in an oxygen-free atmosphere than in air.

A forward or reverse bias voltage is applied to the rectifying characteristics of the two types of solid materials to detect changes in their electrical characteristics. Changes in electrical characteristics can be caused by changes in current value. It is also effective to change the electrical characteristics by changing the capacitance. In this case, the polarity of the bias voltage is preferably in the opposite direction to the rectification characteristics. In particular, it is effective to detect capacitance at a low frequency of several hundred hertz or less.

[Example 1] FIG. 1 is a diagram showing the element structure of an apparatus according to an embodiment of the present invention.

The first substance 1 and the second substance 2 are sandwiched between insulating ceramic substrates 3 and 4 and are mechanically held by a spring 5. In this example the first material is sintered ZnO
and the second material is sintered CuO. The first material is an n-type semiconductor material, the second material is a p-type semiconductor material, and when the first material 1 and the second material 2 come into contact, they exhibit rectifying properties.

Reference numerals 11 and 12 are electrodes formed on the first material and second material, respectively, and reference numerals 31 and 41 are electrodes formed on the surfaces of the ceramic substrates 3 and 4, respectively. Electrode 11 is in contact with electrode 31 and electrode 12 is in contact with electrode 41. A lead wire 32 is connected to the electrode 31, and a lead wire 42 is connected to the electrode 41.

In Figure 1, the bottom surface of the first substance 1 is drawn as uneven, but this is because the bottom surface of the first substance is formed into a rough surface and is in contact with the surface of the second substance 2. show. A gap is formed in this rough contact surface, into which the sample gas G is guided as shown by arrow G.

FIG. 2 is an electrical circuit diagram of a device according to an embodiment of the present invention.

The first substance 1 and the second substance 2 exhibit rectifying characteristics by coming into contact with each other through the contact surface as described above, and equivalently become like the diode D shown in FIG. 2.

The leads 32 and 42 of this diode D have a second
As shown in the figure, battery E, variable resistor R and ammeter A
A series circuit is connected between the lead wires 32 and 42, and a voltmeter (2) is connected between the lead wires 32 and 42.

Here, with only atmospheric gas (for example, air) present in the gap between the first substance 1 and the second substance 2, the voltage-current characteristics of this diode D are measured by changing the variable resistor R. . Next, a sample gas is introduced into the gap between the first substance 1 and the second substance 2. In this state, the voltage-current characteristics of diode D are measured again.

For equal voltages indicated by voltmeter V, if the current value when only atmospheric gas is present in the gap is Io, and the current value when sample gas is introduced into the gap is ■, then this current ratio is 1/
Io is the sensitivity to the sample gas.

FIG. 3 shows the results of measuring the current value (2) for this sample gas when the element shown in FIG. 1 was incorporated into the circuit shown in FIG. 2 and the forward bias voltage Vf applied to the diode D was varied. When -carbon oxide CO at a concentration of 8000 ppm+ (refers to the concentration in the atmospheric gas; the same applies hereinafter; the atmospheric gas is air here) is mixed as a sample gas, the characteristics as shown by the solid line in Figure 3 are obtained, and the characteristics of propane CHI with a concentration of 8000 ppm are mixed. When Hll is mixed, the result is as shown by the broken line in FIG. That is, by changing the bias voltage, the gas to be detected can be selectively detected. In this example, the sample gas was heated to 250° C. and supplied to the gap in the contact surface.

[Example 2] FIG. 4 shows the temperature characteristics when the element shown in FIG. 1 is incorporated into the electric circuit shown in FIG. 2, as in Example 1 above. However, the contact surface pressure between substance 1 and substance 2 is twice that in the case of FIG. 3.

The horizontal axis represents the temperature of the sample gas, and the vertical axis represents the sensitivity. The circle mark indicates the value for carbon monoxide at a concentration of 4000 ppm, the triangle mark indicates the value for hydrogen gas at a concentration of 8900 ppm, and the square mark indicates the value for propane gas at a concentration of 4000 ppm. Therefore, although the absolute values are not equal, it can be seen that when the bias voltage is kept constant, the sensitivity to -carbon oxide becomes maximum at a specific temperature. On the other hand, at this bias voltage, propane concentration is 4000 ppm and propane concentration is 8900 ppm.
Sensitivity is low with m hydrogen. This shows that by selecting an appropriate bias voltage, the sensor can be made selective for -carbon oxide.

[Example 3] FIG. 5 shows the measurement of the change in current value when the type of mixed gas in the supplied sample gas was changed in the apparatus used in Example 1 above. However, the temperature of the sample gas is approximately 220°C. Initially, propane gas with a concentration of 8000 ppm was mixed, but there was no response, so carbon monoxide with a concentration of 8000 ppm was mixed in about 4 minutes after the start. - Sensitivity to carbon oxides occurred after a time delay in the reed tube.

Furthermore, after about 6 minutes, at the point indicated by the upward arrow,
The atmosphere was replaced with air.

It can be seen that in this example, a sensor that is not sensitive to propane but sensitive to -carbon oxide can be constructed.

[Example 4] FIG. 6 shows the results of measuring the sensitivity to sample gas in the apparatus used in Example 1, with the forward bias voltage set to 0.3 . As sample gases, -carbon oxide, hydrogen, and propane gases heated to 250°C were used. This element has higher sensitivity to carbon monoxide than to hydrogen and propane gas. In other words, considering the sensitivity shown by the broken line in Figure 6, hydrogen and propane gas each have a sensitivity of 1500
It can be seen that even when ppn+ coexists, 1100 pp of carbon monoxide can be detected without them causing noise.

[Example 5] Figure 7 shows that Coo and ZnO (Coo/ZnO) were prepared as two solid substances using the same apparatus as in Example 1 above.
It is written as. The same description will be given below. ), the sensitivity to bias voltage (1/
It is a figure showing Io). The ambient temperature is 240°C.

The type and concentration of each sample gas are indicated in the figure.

It can be seen that high sensitivity is exhibited in a nitrogen atmosphere.

[Example 6] Fig. 8 is an example in which one of the two types of solid substances was a metal (palladium) using the same apparatus as in Example 1, and the measurement results by P d / T t OZ are shown. It is. The ambient temperature is the same <240°C. The type and concentration of each sample gas are indicated in the figure.

Nitrogen and carbon monoxide both have a molecular weight of 28,
Although it is not possible to detect carbon monoxide in nitrogen based on the difference in specific gravity, the method of the present invention can significantly detect carbon monoxide.

[Example 7] FIG. 9 shows the results of measurements for two types of solid substances, Cu 2 O/S n Oz, using the same apparatus as in Example 1 above. In this example, SnO was formed in the form of a thin film on an insulating substrate, and a platinum electrode was formed on the surface. The ambient temperature is 240°C. The type and concentration of each sample gas are indicated in the figure.

It can be seen that extremely high sensitivity is exhibited in a nitrogen atmosphere.

[Example 8] FIG. 10 shows the results of measurements on CuO/Ti0g as two types of solid substances using the same apparatus as in Example 1 above. The ambient temperature is 240"C'. The type and concentration of each sample gas are indicated in the figure.

In this example, the accuracy of this device was not sensitive in an air atmosphere.

[Example 9] FIG. 11 shows the results of measurements for two types of solid substances, NiO/ZnO, using the same apparatus as in Example 1 above. The ambient temperature is 240°C.

The type and concentration of each sample gas are indicated in the figure.

[Example 10] FIGS. 12 and 13 are diagrams showing detection sensitivity when a bias voltage is applied in a direction opposite to the rectification characteristic. Using the apparatus of Example 1, the polarity of the battery was set to be in the opposite direction to the rectification characteristics of the two types of solid materials, and similar detection sensitivity was measured. The two types of solid substances are
CuO/ZnO. In Fig. 12, the ambient temperature is 200°C, and in Fig. 13, the ambient temperature is 240°C.
It is ℃. The atmosphere was all air, and the type and concentration of each sample gas are indicated in the figure.

FIG. 14 shows the measured values when only the bias voltage to be applied was set in the forward direction of the rectification characteristics under conditions almost the same as in Example 10.

From this example, it can be seen that the detection sensitivity is also achieved depending on the reverse bias voltage. When the sample gas was propane, the sensitivity I/Io was observed to be 1 or less.

Furthermore, depending on the type of sample gas, a phenomenon in which sensitivity was reversed with respect to bias voltage was observed.

[Example 11] This example is an example in which a change in electrical characteristics between two types of solid substances was detected by a change in capacitance. Measurements were carried out using the apparatus shown in FIG. That is, the structures of the two types of solid materials 1 and 2 and the structure for introducing the sample gas into them are the same as in Example 1, but the bias voltage is applied in the opposite direction to the rectifying characteristics, and the choke It is characterized by using a coil L and a capacitor C to supply a bias voltage with high AC impedance. The interelectrode capacitance of these two types of solid materials 1 and 2 was measured using a capacitance meter 51. The power frequency for measurement was supplied from a variable frequency oscillator 52.

FIG. 16 shows an example of the measurement results. That is, CuO/ZnO are used as two types of solid substances, the temperature is 240° C. in an air atmosphere, and a reverse bias of 0.3 V is applied between the electrodes. The horizontal axis in FIG. 16 is the time axis, and the sample gas was introduced into the atmosphere at point X. This shows a state in which the interelectrode capacitance value changes over time from the point X. The vertical axis is the absolute value of capacitance. In the example of FIG. 16, the measurement frequency is constant at 1 kHz.

FIG. 17 shows the results of measurement under similar conditions using the measurement frequency as a parameter. It can be seen that in this measurement range, the lower the frequency, the larger the capacitance change, and the better the detection sensitivity.

〔Effect of the invention〕

According to the present invention, the following effects can be obtained.

■ Different types of gases to be detected can be selectively detected using different devices. In other words, the selectivity of the gas to be detected depends on the element material,
Control can be achieved by selecting the bias voltage to the element and the heating temperature of the element or the gas to be detected depending on the purpose. In particular, there has been a strong demand in industry for senna that selects -carbon oxide, as it is required for various safety devices, and this sensor satisfies this demand.

(2) Since the sensor according to the present invention does not utilize oxidation of the gas to be detected, there is no need to heat the element to a high temperature required for oxidation, and the sensor can be manufactured in a small size and at low cost.

(2) Since the method of the present invention can be carried out in an atmosphere that does not contain oxygen or in an atmosphere where the oxygen concentration fluctuates, it can be extremely usefully applied to various process controls.

(2) The method of the present invention can obtain extremely high detection sensitivity, especially by detecting changes in capacitance.

[Brief explanation of drawings]

FIG. 1 is a structural diagram of an element of an apparatus according to an embodiment of the present invention. FIG. 2 is an electrical circuit diagram of a device according to an embodiment of the present invention. FIGS. 3 to 14 are diagrams showing actual measurement results. FIG. 15 is an electric circuit diagram showing a capacitance-based detection circuit of the device according to the embodiment of the present invention. FIG. 16 and FIG. 17 are diagrams showing actual measurement results regarding capacitance. ν, ￥＞112 ￥￥＞112 ￥￥￥￥￥112 ￥￥＞１１２ ￥￥￥￥￥112 ￥￥＞１１２ ￥￥￥￥￥112
0.4 0.5 0.6-, -vt (
V ) 9 7 M 8 Fig. 4Vt (V) Straw 9 Fig. Atsushi 10 Fig.---Vf (V) Shoulder 11 Fig. CuO/ZnO20σC Red 12 Fig. 9 13 Fig. 1/l. Ichimoku V) Ka 14 figure CuO/Zn0 J￥116 figure

Claims (19)

[Claims] (1) In a method of gas detection by bringing a sample gas into contact with the surface of a semiconductor and detecting changes in the electrical characteristics of the semiconductor, at least one of them is a semiconductor material and by bringing them into contact with each other, the rectifying characteristics can be changed. Two types of solid substances are mechanically brought into contact via a contact surface, a gap is formed in the contact surface, and a sample gas is introduced into the gap. A gas detection method that electrically detects changes in the potential barrier energy level on the surface of a semiconductor material to different values. (2) Electrical detection method involves applying a bias voltage to two types of solid materials in the forward or reverse direction with respect to their rectifying characteristics, and detecting the value of the current flowing between the two types of solid materials. A gas detection method according to claim (1), which includes a method of detecting a change. (3) Electrical detection method involves applying a bias voltage to two types of solid materials in opposite directions with respect to their rectifying characteristics, and detecting changes in capacitance between the two types of solid materials. The gas detection method according to claim (1), which includes a method of: (4) An element having a structure in which two types of solid materials, at least one of which is a semiconductor material and which produce rectifying properties when brought into contact with each other, are brought into contact with each other through a contact surface with a gap through which sample gas can enter and exit; It is characterized by being equipped with an electric circuit connected to each of the types of solid substances and applying a bias voltage between the two types of solid substances, and a detection circuit that detects the electrical characteristics between the two types of solid substances. gas sensor. (5) The contact surface has a structure in which at least one surface of two types of solid substances is formed into a rough surface, and the two types of solid substances are mechanically pressurized and brought into contact via this rough surface. A gas sensor according to claim (4). (6) The gap on the contact surface is 10 to 300 μm.
The gas sensor according to claim 4, which is formed by including a large number of communicating cavities. (7) The gas sensor according to claim (4), wherein the electric circuit includes a circuit that changes the value of the bias voltage. (8) The gas sensor according to claim (4), wherein the electric circuit has a structure in which the value of the bias voltage can be set or varied depending on the type of gas to be detected. (9) The electric circuit has a structure in which a bias voltage is applied in the forward direction or reverse direction of the rectification characteristic.
Gas sensor described in ). (10) The gas sensor according to claim (9), wherein the detection circuit includes a circuit that detects a current value flowing between two types of solid substances. (11) The electric circuit has a structure in which a bias voltage is applied in the opposite direction of the rectification characteristic, and the detection circuit includes a circuit for detecting capacitance between two types of solid substances. Gas sensor described in ). (12) The gas sensor according to claim (4), wherein each of the two types of substances is a sintered semiconductor material. (13) In a patent claim, the two types of substances include one containing zinc oxide as a main component and the other containing a substance selected from among oxidized steel, nickel oxide, and cobalt oxide. Gas sensor according to range item (12). (14) The gas sensor according to claim (4), wherein one of the two types of materials is a sintered semiconductor material and the other is a metal. (15) One of the two types of substances is a substance whose main component is zinc oxide, and the other is a substance whose main component is a metal selected from silver, platinum, and palladium. 14) Gas sensor according to item 14). (16) An element having a structure in which two types of solid substances, at least one of which is a semiconductor material, which produce rectifying properties when brought into contact with each other, are brought into contact with each other through a contact surface with a gap through which sample gas can enter and exit; an electrical circuit connected to each of the solid materials, for applying a bias voltage between the two solid materials and detecting a current passing through the contact surface; and means for heating at least the contact surface. A gas sensor featuring: (17) The gas sensor according to claim (16), wherein the heating means has a structure that heats the sample gas flowing into the gap. (18) The gas sensor according to claim (16), wherein the heating means has a structure for heating an element. (19) The heating means has a structure that sets the temperature of the contact surface to 100°C or more and 300°C or less.
17) Gas sensor according to item 17).