JPH05240821A - Gas sensor and manufacturing method thereof - Google Patents

Abstract

(57) [Summary] [Objective] To obtain a gas sensor capable of detecting multi-component gas. [Structure] A plurality of sensor electrodes 2a, 2b, 2c, 2d are provided on a substrate 1, a gas sensitive layer 3 is laminated on these sensor electrodes, and a platinum catalyst and a palladium catalyst in the gas sensitive layer 3 are used as sensor electrodes. The density is changed in different patterns in the arrangement direction.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas sensor used for LP gas, city gas, carbon monoxide, hydrogen, alcohol, etc. and a method for manufacturing the same, and more particularly, it can detect two or more kinds of gases at the same time, The present invention relates to a gas sensor having high gas selectivity and a manufacturing method thereof.

[0002]

2. Description of the Related Art When an n-type metal oxide semiconductor such as tin oxide or zinc oxide is heated to a temperature of about 300 to 500 ° C. in the atmosphere, oxygen in the atmosphere is activated and adsorbed on the surface of the particles to increase the resistance. However, when the heatable gas comes into contact, the adsorbed oxygen reacts with the heatable gas to remove the adsorbed oxygen and reduce the resistance value. Utilizing such a property, a gas sensor using tin oxide is used as a gas leak alarm for LP gas, city gas, and the like.

[0003]

However, this type of sensor can detect only one gas to be detected, cannot detect two or more kinds of gases, and has a large change in resistance value against alcohol. It was difficult to selectively detect the test gas. The present invention has been made in view of the above points, and its object is to improve a metal oxide semiconductor layer that is a gas-sensitive layer and an electrode that detects a change in resistance value.
A gas sensor capable of selectively detecting a plurality of test gases and a method for manufacturing the gas sensor are provided.

[0004]

According to the first aspect of the present invention, there is provided a plurality of sensor electrodes on one main surface of a substrate and a gas sensitive layer laminated on these sensor electrodes. The gas-sensitive layer has a carrier on which a plurality of types of catalysts are carried, and the concentration of the catalyst is continuously changed in different patterns in the arrangement direction of the sensor electrodes, and according to the second invention. For example, it has a first step and a second step, the first step is a step of laminating a plurality of electrodes on the substrate, the second step is a plurality of carrier material to which different catalyst substances are added. This can be achieved by arranging the targets at different positions and stacking the gas-sensitive layer on the plurality of electrodes by a sputtering method.

[0005]

[Function] When the concentration of a plurality of types of catalysts is continuously changed in different patterns, the gas-sensitive layer partially changes its gas selectivity. Therefore, the electrode whose resistance value should be measured depending on the test gas to be detected is selected. It becomes possible to select.

[0006]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows a gas sensor according to an embodiment of the present invention,
(A) is a plan view and (b) is a sectional view taken along the line AA of (a). The substrate 1, which is the support of the sensor, has a thickness of 0.5 mm.
It is an alumina sintered body having a size of 0 mm × 4 mm. The use of alumina for the substrate has a known effect that the heat conduction from the heater to the gas-sensitive layer 3 is good, and the thin unevenness of the gas-sensitive layer makes the thin film suitable as a gas sensor due to the fine irregularities on the surface. There is also the effect. A known RF sputtering method (A) using a metal mask on one main surface of the substrate 1
r Pressure 0.5Pa, substrate temperature 350 ° C, input power 4W /
cm ² ), sensor electrodes 2a, 2b, 2c and 2d made of platinum having a thickness of 0.1 μm are formed. On the other main surface of the substrate 1, the platinum heater 4 for heating the sensor and the heater electrode 6 are the same R as previously.
It is formed with the thickness of 1 μm on the same plane by the F sputtering method. In this embodiment, platinum is used for the electrodes 2a, 2b, 2c, 2d and the heater 4, but the platinum is not limited to this, and other metals or metal oxides may be used. Also, the number of sensor electrodes can be any number.

Next, a thin film of tin oxide, which is the gas sensitive layer 3, is formed on the sensor electrodes 2a, 2b, 2c, 2d by a facing target type sputtering method using a metal mask (sputtering gas pressure 0.5P).
a, Ar / O ₂ ratio 2: 1, substrate temperature 650 ° C., input power 3 W / cm ² ) and thickness 0.3 μm to 0.5 μm
It is formed into a size of mm × 10 mm. At this time, tin oxide containing 3% of palladium is used as one of the left and right facing targets, and a tin oxide target containing 3% of platinum is used as the other target. In this case, the substrates are installed at equal distances from the left and right targets, so that the amount of palladium mixed in is larger near the target where palladium is added from the center of the substrate, and the amount of platinum is mixed near the target where platinum is added. A tin oxide film can be formed. This makes it possible to form a tin oxide film having a catalyst concentration change in the electrode arrangement direction.

FIG. 2 shows a platinum catalyst (a) in the electrode arrangement direction for the gas-sensitive layer of the gas sensor according to the embodiment of the present invention.
FIG. 3 is a diagram showing changes in concentration of palladium catalyst (II) and palladium catalyst (II). It was confirmed by X-ray microanalyzer and scanning Auger electron spectroscopy that the composition of the gas sensitive layer 3 was modulated in the electrode arrangement direction. In this embodiment, platinum and palladium were used as the catalyst added to tin oxide, but various gas sensors can be formed by changing the metal oxide semiconductor material and the catalyst material. Subsequently, heat treatment is performed at a temperature of 500 ° C. to 600 ° C. in the atmosphere or oxygen. This heat treatment has the effect of improving the temporal stability of the sensor in addition to the purpose of adjusting the crystal structure and oxidation state of the tin oxide thin film of the gas sensitive layer 3. Platinum wire lead wires 5a, 5b, 5c, 5d for detecting changes in the resistance value of the gas sensitive layer 3 are connected to the sensor electrodes 2a, 2b, 2c, 2d. Similarly, heater power supply to the heater electrode 6 is performed. Lead wires 7a and 7b are connected for. Each lead wire is connected to an external auxiliary circuit (not shown).

FIG. 3 is a diagram showing the gas sensitivity between the sensor electrodes in the gas sensor according to the embodiment of the present invention. Curve (c) is the sensitivity curve for hydrogen gas, curve (d) is the sensitivity curve for carbon monoxide gas, and curve (e)
Is a sensitivity curve for isobutane gas. The resistance of the gas sensor (gas sensitive layer 3) in air was R _o , and the resistance of the gas under test was R _g , and R _o / R _g was determined to obtain the gas sensitivity. The gas sensitivity was measured in 0.2% gas. The temperature of the gas sensor was adjusted to 350 ° C. by adjusting the voltage applied to the heater 4. Sensor electrode 2
In the region where the platinum concentration between a and 2b is high, the sensitivity to hydrogen gas is good and it hardly reacts to other gases. Sensor electrode 2
It exhibits sensitivity to carbon monoxide gas in the region where the concentrations of platinum and palladium between b and 2c are almost the same. Sensor electrode
In the high palladium concentration region between 2c and 2d, it shows sensitivity to isobutane gas.

3% gold on one of the facing targets
When the tin oxide mixed in is used and the target of tin oxide mixed with 3% of platinum is used in the other, the sensor manufactured by the same method can form a sensor that reacts with alcohol, methane, and hydrogen. In this way, a sensor having the gas sensitive layer 3 in which the catalyst concentration and the catalyst material are changed is formed,
By selecting a sensor electrode suitable for the test gas, it becomes possible to selectively detect a plurality of gas components with one sensor. When the gas to be detected is hydrogen, the sensor electrode where the platinum catalyst concentration is high is selected, and when the gas to be detected is isobutane, the sensor electrode where the palladium catalyst concentration is high is selected. In this way, by changing the combination of the sensors to be used depending on the type of target gas, it is possible to detect many types of gas with one sensor.

[0011]

According to the first aspect of the present invention, a plurality of sensor electrodes and a gas-sensitive layer laminated on these sensor electrodes are provided on one main surface of a substrate, and the gas-sensitive layer is formed on a carrier by a plurality of types. A catalyst is carried, and the catalyst continuously changes its concentration in different patterns in the arrangement direction of the sensor electrodes, and according to the second invention, the first step and the second step. The first step is a step of stacking a plurality of sensor electrodes on a substrate, and the second step is a sputtering method in which a plurality of targets obtained by adding different catalyst substances to a carrier substance are arranged at different positions. Is a step of laminating a gas-sensitive layer on the plurality of sensor electrodes, the gas-sensitive layer partially changes its gas selectivity, and a plurality of gas components can be detected simultaneously by selecting electrodes. Easy gas sensor It is.

[Brief description of drawings]

FIG. 1 shows a gas sensor according to an embodiment of the present invention,
(A) is a plan view, (b) is a sectional view taken along the line AA of (a),

FIG. 2 is a diagram showing changes in concentration of platinum catalyst (a) and palladium catalyst (b) in the electrode arrangement direction in the gas-sensitive layer of the gas sensor according to the example of the present invention.

FIG. 3 is a diagram showing gas sensitivity between sensor electrodes in a gas sensor according to an embodiment of the present invention.

[Explanation of symbols]

 1 substrate 2a sensor electrode 2b sensor electrode 2c sensor electrode 2d sensor electrode 3 gas sensitive layer 4 heater 5a lead wire 5b lead wire 5c lead wire 5d lead wire 6 heater electrode 7a lead wire 7b lead wire

Claims (5)

[Claims] 1. A substrate having a plurality of sensor electrodes on one main surface thereof and a gas-sensitive layer laminated on these sensor electrodes, the gas-sensitive layer comprising a carrier carrying a plurality of types of catalysts, A gas sensor characterized in that the catalyst has its concentration continuously changed in different patterns in the arrangement direction of the sensor electrodes. 2. The gas sensor according to claim 1, wherein the carrier of the gas sensitive layer is a metal oxide semiconductor. 3. The gas sensor according to claim 1, wherein the catalyst of the gas sensitive layer is platinum and palladium. 4. The gas sensor according to claim 1, wherein the catalyst of the gas sensitive layer is platinum and gold. 5. A first step and a second step, wherein the first step is a step of stacking a plurality of sensor electrodes on a substrate, and the second step is a carrier material and a different catalyst material. A method of manufacturing a gas sensor, which comprises the step of arranging a plurality of targets added with different amounts at different positions and laminating a gas sensitive layer on the plurality of sensor electrodes by a sputtering method.