JPH0735716A - Thick film gas sensor and manufacture thereof - Google Patents

Abstract

PURPOSE:To enhance stability and initial rumbling by forming a gas sensitive layer of a metal oxide semiconductor added with cobalt oxide, manganese oxide, etc. CONSTITUTION:Two electrodes 2, 2 are provided on a substrate 1 and a first oxidation combustion layer 3B is provided thereon. Furthermore, a gas sensitive layer 4 is formed on the oxidation combustion layer 3B and the electrodes 2, 2. A second oxidation combustion layer 3C is provided while covering the gas sensitive layer completely and the electrodes 2, 2 are connected with lead wires 7, 7. A heater 8 is formed on the other main surface of the substrate 1 and the electrodes 2A, 2A are connected with lead wires 9, 9. The oxidation combustion layers 3B, 3C are formed by supporting a noble metal catalyst on metal oxide carriers. The gas sensitive layer 4 is formed by adding at least one oxide, selected from a group of cobalt oxide, manganese oxide, nickel oxide, copper oxide, iron oxide, zinc oxide, chromium oxide, etc., into a metal oxide semiconductor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to LP gas, city gas,
The present invention relates to a thick film gas sensor for a gas leak alarm that detects hydrogen gas and the like, and particularly to a configuration of a pressure film gas sensor having a short initial ringing time.

[0002]

2. Description of the Related Art As one of gas sensors, one using a metal oxide semiconductor such as tin oxide or zinc oxide is known. When these metal oxide semiconductors are heated to about 300 to 500 ° C. in the atmosphere, oxygen in the atmosphere is activated and adsorbed on the particle surface to increase the resistance, but the reducing gas is a reducing gas in the test gas which is a reducing gas. Is adsorbed on the metal oxide semiconductor instead of adsorbed oxygen, and the electric resistance value is reduced. A gas sensor using a metal oxide semiconductor by utilizing such a property is used for a gas leak alarm device for LP gas, city gas, or the like.

FIG. 9 is a plan view showing a conventional thick film gas sensor. FIG. 10: C of FIG. 9 showing a conventional thick film gas sensor
FIG. 6 is a cross-sectional view taken along the arrow C. A conventional thick film gas sensor is formed by laminating a gas sensitive layer 4 and an oxidative combustion layer 3A on one main surface of an insulating substrate 1 made of alumina or the like. A heater 8 is formed on the other main surface of the substrate 1 to heat the thick film gas sensor to a predetermined temperature. The gas sensitive layer 4 is a layer made of tin oxide, for example. The oxidation combustion layer 3A is formed by supporting a noble metal catalyst such as platinum on tin oxide. The oxidizing combustion layer 3A enhances the temporal stability of the sensitivity of the gas sensitive layer 4 to combustible gas, and enhances the selectivity to combustible gas to reduce the sensitivity to alcohol and the like. A commercial power source is directly applied to the gas sensitive layer 4 or the heater 8 via the electrodes 2 and 2A.

[0004]

However, the conventional two-layer type thick film gas sensor as described above has a problem that the initial ringing time becomes long. FIG. 11 is a diagram showing an initial ringing characteristic of a conventional thick film gas sensor. This initial ringing causes an alarm while the resistance of the gas sensor is decreasing because the resistance of the gas sensor first decreases and then rises when the gas sensor is turned on and the gas sensor is used. Refers to the time when an alarm is issued. Therefore, during this ringing time, the gas sensor is controlled so as not to give an alarm, but if this initial ringing time becomes long, it is not preferable to start using the gas sensor. In the double-layer thick-film gas sensor, the reason why the initial ringing time is long is that the metal oxide semiconductor in the gas-sensitive layer adsorbs oxygen to increase the electric resistance value after the power is turned on, but this oxygen adsorption takes time. . Therefore, it suffices to support a catalyst that increases the oxygen adsorption rate on the metal oxide semiconductor of the gas sensitive layer, but depending on the type of catalyst, the oxygen adsorption amount of the metal oxide semiconductor is reduced due to the change in the activity, and the electrical resistance value decreases. Bring

The present invention has been made in view of the above points, and an object thereof is to provide a thick film gas sensor excellent in stability and initial ringing characteristics by using a catalyst that does not change the resistance value of the metal oxide semiconductor but increases the oxygen adsorption rate. And to provide a manufacturing method thereof.

[0006]

According to the first aspect of the present invention, there is provided a thick film gas sensor for detecting the presence or absence of gas by utilizing a change in resistance value of a metal oxide semiconductor. A pair of electrodes, a first oxidative combustion layer, a gas sensitive layer,
Including a second oxidative combustion layer, the substrate is a support for the gas sensor, the pair of electrodes is directly deposited on the substrate at a distance, and the first oxidative combustion layer is on the substrate and the pair of electrodes. , The gas-sensitive layer is selectively laminated on the first oxidation combustion layer and the pair of electrodes, and the second oxidation-combustion layer is laminated so as to cover the entire gas-sensing layer. The oxidation and combustion layer of No. 1 comprises a metal oxide carrier supporting a noble metal catalyst, the second oxidation and combustion layer comprises a metal oxide carrier supporting a noble metal catalyst, and the gas-sensitive layer comprises a metal oxide semiconductor containing cobalt oxide, Manganese oxide,
It is achieved by containing at least one selected from the group consisting of nickel oxide, copper oxide, iron oxide, zinc oxide, chromium oxide, vanadium oxide, titanium oxide and aluminum oxide.

According to a second aspect of the present invention, there is provided a thick film gas sensor for detecting the presence / absence of gas by utilizing a change in resistance value of a metal oxide semiconductor, the substrate, a pair of electrodes, and a third oxidation combustion layer. And a gas-sensitive layer, the substrate is a support of the gas sensor, the pair of electrodes is directly deposited on the substrate with a space, and the gas-sensitive layer selectively on the substrate and the pair of electrodes. The third oxidative combustion layer is laminated so as to cover the entire gas-sensitive layer, the third oxidative combustion layer is formed by supporting a noble metal catalyst on a metal oxide carrier, and the gas-sensitive layer is a metal oxide semiconductor. Is achieved by containing at least one selected from the group consisting of cobalt oxide, manganese oxide, nickel oxide, copper oxide, iron oxide, zinc oxide, chromium oxide, vanadium oxide, titanium oxide and aluminum oxide. .

According to a third aspect of the present invention, there is provided a method of manufacturing a thick film gas sensor for detecting the presence / absence of a gas by utilizing a change in the resistance value of a metal oxide semiconductor, which comprises And (2) a gas-sensitive layer forming step, the oxidizing combustion layer forming step is a step of preparing a paste of metal oxide powder carrying a noble metal catalyst, coating and drying, and heat-treating. The process of forming the gas sensitive layer is achieved by preparing a paste in which a metal powder of nickel, iron, aluminum or chromium is added to a powder of a metal oxide semiconductor, coating, drying and heat treating the paste. To be done.

The oxidative combustion layer oxidizes and burns the interference gas such as alcohol to eliminate the influence of the interference gas on the thick film gas sensor. The gas sensitive layer adsorbs a test gas such as LP gas to reduce the electric resistance value and detect the test gas. The first oxidative combustion layer and the second oxidative combustion layer increase the supply rate of air to the gas sensitive layer.

[0010]

[Function] Cobalt oxide, manganese oxide, nickel oxide,
When oxides such as copper oxide, iron oxide, zinc oxide, chromium oxide, vanadium oxide, titanium oxide, and aluminum oxide are contained in the metal oxide semiconductor of the gas-sensitive layer when the metal oxide semiconductor adsorbs oxygen. Functions as a catalyst.

The oxide catalyst does not cause grain growth in a state of being contained in the metal oxide semiconductor of the gas sensitive layer, maintains a constant catalytic activity, and has an electric resistance determined by the oxygen adsorption amount of the metal oxide semiconductor. Keep the value stable.

[0012]

Embodiments of the present invention will now be described with reference to the drawings. Embodiment 1 FIG. 1 is a plan view showing a thick film gas sensor according to an embodiment of the first invention. 2 is a sectional view taken along the line AA of FIG. 1 showing a thick film gas sensor according to an embodiment of the first invention.

The structure of the thick film gas sensor according to the embodiment of the first invention is as follows. Two electrodes 2 are provided on one main surface of the substrate 1 at a distance from each other. A first oxidative combustion layer 3B is selectively provided on the substrate 1 and the electrode 2. The gas sensitive layer 4 is selectively formed on the first oxidative combustion layer 3B and the electrode 2. The gas-sensitive layer 4 is completely covered to form the second oxidation combustion layer 3C.
Is provided. The lead wire 7 is connected to the electrode 2. An electrode 2A is formed on the other main surface of the substrate 1, a heater 8 is selectively formed on the electrode 2A and the substrate 1, and a lead wire 9 is connected to the electrode 2A.

The substrate 1 has a thickness of 0.5 mm and a length of 3 mm and a width of 3
mm polished alumina substrate. The heater comprises a ruthenium oxide resistor. Such a thick film gas sensor is prepared as follows. A platinum electrode paste was screen-printed on the two main surfaces of the substrate 1 in a predetermined pattern, dried, and then baked at a temperature of about 1100 ° C. A heater paste made of ruthenium oxide was screen-printed in a predetermined pattern and fired at a predetermined temperature.

The tin oxide powder is dried in air at a temperature of 730 ° C.
The resulting tin oxide powder was treated for 2 h with an aqueous solution of chloroplatinic acid H ₂ PtCl ₆ adjusted so that the platinum content was 2% of the tin oxide powder, kneaded, and then dried. did. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose chloroplatinic acid H ₂ PtCl ₆ to support platinum on the tin oxide powder. The obtained powder was pulverized with a ball mill, and then an appropriate amount of ethyl silicate, ethyl cellulose, carbitol, etc. was added and kneaded to obtain a paste for the first oxidative combustion layer.
The obtained paste for the first oxidative combustion layer was screen-printed with a predetermined pattern to a thickness of 20 μm and dried at 120 ° C. for 2 hours.

The tin oxide powder is dried in air at a temperature of 730 ° C.
The resulting tin oxide powder was treated with cobalt oxide Co for 2 h.
O, Manganese oxide MnO, Nickel oxide NiO, Copper oxide CuO,
Powder of iron oxide Fe ₂ O ₃ , zinc oxide ZnO, chromium oxide Cr ₂ O ₃ , vanadium oxide V ₂ O ₅ , titanium oxide TiO ₂ or aluminum oxide Al ₂ O ₃ was added to the tin oxide powder in 0.1 weight%
The mixture was added and mixed in such an amount that the ratio was 1), and then an appropriate amount of ethyl silicate, ethyl cellulose, carbitol, etc. was added and kneaded to obtain a paste for a gas sensitive layer. The obtained paste was screen-printed in a predetermined pattern to a thickness of 50 μm and dried at 120 ° C. for 2 hours.

The tin oxide powder is dried in air at a temperature of 730 ° C.
The resulting tin oxide powder was treated for 2 h with an aqueous solution of chloroplatinic acid H ₂ PtCl ₆ adjusted so that the platinum content was 2% of the tin oxide powder, kneaded, and then dried. did. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose chloroplatinic acid H ₂ PtCl ₆ to support platinum on the tin oxide powder. The obtained powder was pulverized with a ball mill, and then an appropriate amount of ethyl silicate, ethyl cellulose, carbitol, etc. was added and kneaded to obtain a paste for the second oxidative combustion layer.
The obtained paste for the second oxidative combustion layer was screen-printed in a predetermined pattern to a thickness of 20 μm and dried at 120 ° C. for 2 hours.

The first oxidative combustion layer, the gas-sensitive layer and the second oxidative combustion layer are printed and dried, and then these are simultaneously fired at a temperature of 630 ° C. for 3 hours to form a first oxidative combustion layer 3B and a gas-sensitive layer 4. , The second oxidation combustion layer 3C was formed. Then the electrode 2,
Platinum lead wires 7 and 9 were connected to 2A to obtain thick film gas sensors. Each lead wire was connected to the alarm circuit. Comparative Example 1 A sensor having the same structure as the thick film gas sensor of Example 1 was used.

Thick film gas sensor according to Comparative Example 1 is prepared as follows. Platinum electrode paste was screen-printed on the two main surfaces of the substrate 1 in a predetermined pattern, and after drying about 1
It was fired at a temperature of 100 ° C. A heater paste made of ruthenium oxide was screen-printed in a predetermined pattern and fired at a predetermined temperature. Chloroplatinic acid H ₂ was prepared by treating tin oxide powder in dry air at a temperature of 730 ° C. for 2 hours, and adjusting the content of platinum in the resulting tin oxide powder to 2% with respect to the tin oxide powder. After adding an aqueous solution of PtCl ₆ and kneading,
Dried. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose chloroplatinic acid H ₂ PtCl ₆ to support platinum on the tin oxide powder. After crushing the obtained powder with a ball mill,
Ethyl silicate, ethyl cellulose, carbitol, etc. were added in appropriate amounts and kneaded to obtain a paste for the first oxidative combustion layer. The obtained paste for the first oxidative combustion layer is screen-printed in a predetermined pattern to a thickness of 20 μm, and 12
It was dried at 0 ° C. for 2 hours.

The tin oxide powder is dried in air at a temperature of 730 ° C.
The obtained tin oxide powder was added with an appropriate amount of ethyl silicate, ethyl cellulose, carbitol and the like and kneaded to obtain a paste for a gas sensitive layer. The obtained paste was screen-printed in a predetermined pattern to a thickness of 50 μm and dried at 120 ° C. for 2 hours. Chloroplatinic acid H ₂ was prepared by treating tin oxide powder in dry air at a temperature of 730 ° C. for 2 hours, and adjusting the content of platinum in the resulting tin oxide powder to 2% with respect to the tin oxide powder. An aqueous solution of PtCl ₆ was added, and the mixture was kneaded and then dried. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose chloroplatinic acid H ₂ PtCl ₆ to support platinum on the tin oxide powder. The obtained powder was pulverized with a ball mill, and then an appropriate amount of ethyl silicate, ethyl cellulose, carbitol, etc. was added and kneaded to obtain a paste for the second oxidative combustion layer. The obtained paste for the second oxidative combustion layer was screen-printed in a predetermined pattern to a thickness of 20 μm and dried at 120 ° C. for 2 hours.

The first oxidative combustion layer, the gas-sensitive layer and the second oxidative combustion layer are printed and dried, and then these are simultaneously baked at a temperature of 630 ° C. for 3 hours to form a first oxidative combustion layer 3B and a gas-sensitive layer 4. , The second oxidation combustion layer 3C was formed. Then the electrode 2,
Platinum lead wires 7 and 9 were connected to 2A to obtain thick film gas sensors. Each lead wire was connected to the alarm circuit.

With respect to the thick film gas sensors according to Example 1 and Comparative Example 1, the initial ringing time after standing for 30 days was measured. The results are shown in Table 1.

[0023]

[Table 1]

It can be seen that the thick film gas sensor including the oxide catalyst in the gas sensitive layer has a short initial ringing time. On the other hand, it can be seen that the thick film gas sensor in which the gas sensitive layer does not contain an oxide catalyst has a long initial ringing time. FIG. 3 is a diagram showing the resistance characteristics of the thick film gas sensor according to the embodiment of the first invention. The resistance of the thick film gas sensor was measured in 0.2% isobutane gas. It can be seen that the thick film gas sensor according to the example of the first invention contains an oxide catalyst in the gas sensitive layer, but the sensor resistance value is stable for a long period of time. Embodiment 2 FIG. 4 is a plan view showing a thick film gas sensor according to an embodiment of the second invention.

FIG. 5 is a sectional view taken along the line BB in FIG. 4 showing a thick film gas sensor according to an embodiment of the second invention. The structure of the thick film gas sensor according to the embodiment of the second invention is as follows. Two electrodes 2 are provided on one main surface of the substrate 1 at a distance from each other. The gas sensitive layer 4 is selectively formed on the substrate 1 and the electrode 2. A third oxidation combustion layer 3D is provided by completely covering the gas sensitive layer 4. The lead wire 7 is connected to the electrode 2.
An electrode 2A is formed on the other main surface of the substrate 1, a heater 8 is selectively formed on the electrode 2A and the substrate 1, and a lead wire 9 is connected to the electrode 2A.

The substrate 1 has a thickness of 0.5 mm and a length of 3 mm and a width of 3 mm.
mm polished alumina substrate. The heater comprises a ruthenium oxide resistor. Such a thick film gas sensor is prepared as follows. A platinum electrode paste was screen-printed on the two main surfaces of the substrate 1 in a predetermined pattern, dried, and then baked at a temperature of about 1100 ° C. A heater paste made of ruthenium oxide was screen-printed in a predetermined pattern and fired at a predetermined temperature.

The tin oxide powder is dried in air at a temperature of 730 ° C.
The resulting tin oxide powder was treated with cobalt oxide Co for 2 h.
O, Manganese oxide MnO, Nickel oxide NiO, Copper oxide CuO,
Iron oxide Fe ₂ O ₃ , zinc oxide ZnO, chromium oxide Cr ₂ O ₃ , vanadium oxide V ₂ O ₅ , titanium oxide TiO ₂ or aluminum oxide Al ₂ O ₃ in an amount of 0.1% by weight based on the tin oxide powder. The mixture was added in proportions and mixed, and an appropriate amount of ethyl silicate, ethyl cellulose, carbitol, etc. was added and kneaded to obtain a paste for a gas sensitive layer. The paste obtained is screen-printed to a thickness of 50 μm according to a predetermined pattern and 120 ° C.
And dried for 2 h.

The tin oxide powder is dried in air at a temperature of 730 ° C.
The resulting tin oxide powder was treated for 2 h with an aqueous solution of chloroplatinic acid H ₂ PtCl ₆ adjusted so that the platinum content was 2% of the tin oxide powder, kneaded, and then dried. did. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose chloroplatinic acid H ₂ PtCl ₆ to support platinum on the tin oxide powder. The obtained powder was pulverized with a ball mill, and then an appropriate amount of ethyl silicate, ethyl cellulose, carbitol, etc. was added and kneaded to obtain a paste for the third oxidative combustion layer.
The obtained paste for the third oxidative combustion layer was screen-printed with a predetermined pattern to a thickness of 20 μm and dried at 120 ° C. for 2 hours.

After the gas-sensitive layer and the third oxidative combustion layer were printed and dried, they were simultaneously fired at a temperature of 630 ° C. for 3 hours to form a gas-sensitive layer 4 and a third oxidative combustion layer 3D. Subsequently, platinum lead wires 7 and 9 were connected to the electrodes 2 and 2A, respectively, to obtain a thick film gas sensor. Each lead wire was connected to the alarm circuit. Comparative Example 2 A sensor having the same structure as the thick film gas sensor of Example 2 was used.

Thick Film Gas Sensor According to Comparative Example 2 Prepared as follows. Platinum electrode paste was screen-printed on the two main surfaces of the substrate 1 in a predetermined pattern, and after drying about 1
It was fired at a temperature of 100 ° C. A heater paste made of ruthenium oxide was screen-printed in a predetermined pattern and fired at a predetermined temperature. The tin oxide powder was treated in dry air at a temperature of 730 ° C. for 2 hours, and an appropriate amount of ethyl silicate, ethyl cellulose, carbitol, etc. was added to the obtained tin oxide powder and kneaded to obtain a paste for a gas sensitive layer. The obtained paste was screen-printed in a predetermined pattern to a thickness of 50 μm and dried at 120 ° C. for 2 hours.

The tin oxide powder is dried in air at a temperature of 730 ° C.
The resulting tin oxide powder was treated for 2 h with an aqueous solution of chloroplatinic acid H ₂ PtCl ₆ adjusted so that the platinum content was 2% of the tin oxide powder, kneaded, and then dried. did. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose chloroplatinic acid H ₂ PtCl ₆ to support platinum on the tin oxide powder. The obtained powder was pulverized with a ball mill, and then an appropriate amount of ethyl silicate, ethyl cellulose, carbitol, etc. was added and kneaded to obtain a paste for the third oxidative combustion layer.
The obtained paste for the third oxidative combustion layer was screen-printed with a predetermined pattern to a thickness of 20 μm and dried at 120 ° C. for 2 hours.

After the gas-sensitive layer and the third oxidative combustion layer were printed and dried, they were simultaneously fired at a temperature of 630 ° C. for 3 hours to form a gas-sensitive layer 4 and a third oxidative combustion layer 3D. Subsequently, platinum lead wires 7 and 9 were connected to the electrodes 2 and 2A, respectively, to obtain a thick film gas sensor. Each lead wire was connected to the alarm circuit. The initial ringing time after leaving the thick film gas sensors according to Example 2 and Comparative Example 2 for 30 days was measured.
The results are shown in Table 2.

[0033]

[Table 2]

It can be seen that the thick film gas sensor including the oxide catalyst in the gas sensitive layer has a short initial ringing time. On the other hand, it can be seen that the thick film gas sensor in which the gas sensitive layer does not contain an oxide catalyst has a long initial ringing time. Although not shown, the resistance characteristic of the thick film gas sensor is stable for a long period of time. Although one kind of oxide is added in Examples 1 and 2, the present invention is not limited to one kind of oxide catalyst, and the same applies when a plurality of kinds of oxide catalysts are mixed and added. The effect is recognized. The heat treatment temperature of the thick film gas sensor is 630.
C., and there is no reaction between different oxides at this heat treatment temperature.

Although tin oxide is used as the metal oxide semiconductor in Examples 1 and 2, the same effect can be obtained by using zinc oxide instead of tin oxide. Zinc oxide can be produced, for example, by heat-treating an alkoxide synthesized from zinc chloride and ethyl sodium. In Examples 1 and 2, tin oxide was used to support platinum in the oxidation combustion layer, but zinc oxide ZnO, aluminum oxide Al ₂ O ₃ , magnesium oxide MgO, zirconium oxide ZrO ₂ , aluminum was used instead of tin oxide. Magnesium spinel MgAl ₂ O ₄ can be used.

Cobalt oxide was added to the gas-sensitive layer in a proportion of 0.1% by weight, and zinc oxide ZnO, aluminum oxide Al ₂ O ₃ , was added to the metal oxide carriers of the first oxidation combustion layer and the second oxidation combustion layer.
The initial ringing time after standing for 30 days was measured for a three-layer thick-film gas sensor using magnesium oxide MgO or zirconium oxide ZrO ₂ . The results are shown in Table 3.

[0037]

[Table 3]

Platinum can be used in addition to platinum for the catalyst supported on the oxidation combustion layer, and the supported amount of the catalyst is 1
It is suitable to be 10 to 10% by weight. Further, as the metal oxide carrier of the oxidation combustion layer, the cobalt oxide CoO and the manganese oxide Mn are used.
O, nickel oxide NiO, copper oxide CuO, iron oxide Fe ₂ O ₃ , zinc oxide ZnO, chromium oxide Cr ₂ O ₃ , vanadium oxide V ₂ O ₅ ,
Titanium oxide TiO ₂ or aluminum oxide Al ₂ O ₃ can be added as a catalyst. Example 3 A sensor having the same structure as the thick film gas sensor shown in Example 1 was used.

Such a thick film gas sensor is prepared as follows. Platinum electrode paste is screen-printed on the two main surfaces of the substrate 1 in a predetermined pattern, and after drying about 110
It was calcined at a temperature of 0 ° C. A heater paste made of ruthenium oxide was screen-printed in a predetermined pattern and fired at a predetermined temperature. Tin oxide powder in dry air at temperature 73
After treatment at 0 ° C. for 2 h, an aqueous solution of chloroplatinic acid H ₂ PtCl ₆ adjusted so that the platinum content is 2% with respect to the tin oxide powder is added to the obtained tin oxide powder and kneaded. Dried. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose chloroplatinic acid H ₂ PtCl ₆ to support platinum on the tin oxide powder. The obtained powder was pulverized with a ball mill, and then an appropriate amount of ethyl silicate, ethyl cellulose, carbitol, etc. was added and kneaded to obtain a paste for the first oxidative combustion layer. The obtained paste for the first oxidative combustion layer is screen-printed in a predetermined pattern to a thickness of 20 μm,
It was dried at 0 ° C. for 2 hours.

The tin oxide powder was dried in air at a temperature of 730 ° C.
The resulting tin oxide powder was treated with cobalt oxide Co for 2 h.
O, Manganese oxide MnO, Nickel oxide NiO, Copper oxide CuO,
Iron oxide Fe ₂ O ₃ , zinc oxide ZnO, chromium oxide Cr ₂ O ₃ , vanadium oxide V ₂ O ₅ , titanium oxide TiO ₂ or aluminum oxide Al ₂ O ₃ is added to the tin oxide powder in an amount of 0.008 to 1.
The mixture was added so as to have a ratio of 2% by weight, and then an appropriate amount of ethyl silicate, ethyl cellulose, carbitol, etc. was added and kneaded to obtain a gas layer paste. The obtained paste was screen-printed in a predetermined pattern to a thickness of 50 μm and dried at 120 ° C. for 2 hours.

The tin oxide powder is dried in air at a temperature of 730 ° C.
The resulting tin oxide powder was treated for 2 h with an aqueous solution of chloroplatinic acid H ₂ PtCl ₆ adjusted so that the platinum content was 2% of the tin oxide powder, kneaded, and then dried. did. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose chloroplatinic acid H ₂ PtCl ₆ to support platinum on the tin oxide powder. The obtained powder was pulverized with a ball mill, and then an appropriate amount of ethyl silicate, ethyl cellulose, carbitol, etc. was added and kneaded to obtain a paste for the second oxidative combustion layer.
The obtained paste for the second oxidative combustion layer was screen-printed in a predetermined pattern to a thickness of 20 μm and dried at 120 ° C. for 2 hours.

The first oxidative combustion layer, the gas-sensitive layer, and the second oxidative combustion layer are printed, dried, and then simultaneously baked at a temperature of 630 ° C. for 3 hours to form the first oxidative combustion layer 3B and the gas-sensitive layer 4. , The second oxidation combustion layer 3C was formed. Then the electrode 2,
Platinum lead wires 7 and 9 were connected to 2A to obtain thick film gas sensors. Each lead wire was connected to the alarm circuit.

Table 4 shows the dependency of the initial ringing time (s) on the amount of oxide catalyst added. The initial ringing time is after leaving for 30 days.

[0044]

[Table 4]

The addition amount is 0.01 regardless of the kind of oxide.
It can be seen that the initial ringing time becomes shorter in the range of 1.0 to 1.0% by weight. Example 4 Cobalt oxide CoO in preparation of paste for gas sensitive layer
, Manganese oxide MnO, Nickel oxide NiO, Copper oxide CuO,
Powder of iron oxide Fe ₂ O ₃ , zinc oxide ZnO, chromium oxide Cr ₂ O ₃ , vanadium oxide V ₂ O ₅ , titanium oxide TiO ₂ or aluminum oxide Al ₂ O ₃ was added to the tin oxide powder in 0.1 weight%
Metal nickel. Similar to Example 1 except that powder of metallic chromium, metallic iron or metallic aluminum is added in the range of 100 to 5000 ppm, and the mixture is mixed for 20 h in a ball mill using ethyl alcohol as a dispersion medium and the alcohol is naturally dried and mixed. Then, a thick film gas sensor was prepared. The above metal changes into an oxide in the metal oxide semiconductor by heat treatment and functions as a catalyst.

FIG. 6 is a diagram showing the initial ringing characteristic (A) of the thick film gas sensor according to the third embodiment of the present invention in comparison with the characteristic (A) of the conventional thick film gas sensor. The catalyst is nickel. The thick film gas sensor according to the embodiment of the present invention has a small initial ringing time regardless of the non-energization time. On the other hand, in the conventional thick film gas sensor, it can be seen that the initial ringing time increases rapidly with the non-energization time.

FIG. 7 is a diagram showing the temporal stability (c) of the sensor resistance value of the thick film gas sensor according to the embodiment of the third invention in comparison with the characteristic (d) of the conventional thick film gas sensor. The catalyst is nickel. The measurement was carried out in 0.2% isobutane gas. It can be seen that the resistance values of the thick film gas sensors according to the different embodiments of the first invention are almost stable in 7 days, but the resistance values of the conventional thick film gas sensor gradually decrease.

FIG. 8 is a diagram showing the voltage dependence (e) of the sensor resistance value of the thick film gas sensor according to the embodiment of the third invention in comparison with the characteristic (f) of the conventional thick film gas sensor. Nickel was used as the catalyst. The thick film gas sensor according to the third embodiment of the present invention has a larger sensor resistance value in air than the conventional one. As a result, in the thick film gas sensor of the present invention, the voltage exhibiting the same sensor resistance value is increased by about 5V as compared with the conventional one, and the voltage dependency of the alarm transmission of the thick film gas sensor is reduced.

Similar characteristics are observed for catalysts such as chromium, iron or aluminum.

[0050]

According to the first aspect of the present invention, there is provided a thick film gas sensor for detecting the presence or absence of gas by utilizing a change in resistance value of a metal oxide semiconductor, the substrate, a pair of electrodes, and Including an oxidative combustion layer, a gas sensitive layer, and a second oxidative combustion layer,
The substrate is a support of the gas sensor, the pair of electrodes is directly deposited on the substrate with a space therebetween, the first oxidative combustion layer is selectively laminated on the substrate and the pair of electrodes, and the gas sensitive layer is The first oxidative combustion layer and the pair of electrodes are selectively laminated, the second oxidative combustion layer is laminated so as to cover the entire gas-sensitive layer, and the first oxidative combustion layer is a metal oxide carrier and a noble metal. A catalyst is supported, the second oxidation combustion layer is a metal oxide carrier carrying a noble metal catalyst, and the gas-sensitive layer is a metal oxide semiconductor having cobalt oxide, manganese oxide, nickel oxide, copper oxide, iron oxide. , Zinc oxide, chromium oxide, vanadium oxide, titanium oxide, aluminum oxide, and at least one selected from the group, and according to the second invention, the change in resistance of the metal oxide semiconductor is used. Thick film gas sensor that detects the presence or absence of gas There, a substrate, a pair of electrodes,
A third oxidative combustion layer and a gas-sensitive layer are included, the substrate is a support of the gas sensor, the pair of electrodes is directly and separately disposed on the substrate, and the gas-sensitive layer and the substrate are paired. Selectively laminated on the electrode, the third oxidative combustion layer covers the entire gas-sensitive layer and is laminated, and the third oxidative combustion layer comprises a metal oxide carrier carrying a noble metal catalyst. The layer comprises a metal oxide semiconductor containing at least one selected from the group consisting of cobalt oxide, manganese oxide, nickel oxide, copper oxide, iron oxide, zinc oxide, chromium oxide, vanadium oxide, titanium oxide, and aluminum oxide. Then, according to the third invention, a method of manufacturing a thick film gas sensor for detecting the presence or absence of gas by utilizing the change in the resistance value of the metal oxide semiconductor,
The method includes the steps of (1) forming an oxidation combustion layer and (2) forming a gas-sensitive layer. The oxidation combustion layer is formed by preparing a paste of a metal oxide powder carrying a noble metal catalyst. The steps of coating, drying, and heat treatment are performed. In the step of forming the gas-sensitive layer, a paste prepared by adding a metal powder of nickel, iron, aluminum, or chromium to powder of a metal oxide semiconductor is prepared, coated, dried, Since this is a heat treatment step, oxide catalysts such as cobalt oxide, manganese oxide, nickel oxide, copper oxide, iron oxide, zinc oxide, chromium oxide, vanadium oxide, titanium oxide, and aluminum oxide are used for the metal oxidation of the gas-sensitive layer. A metal oxide semiconductor functioning as a catalyst when adsorbing oxygen in a state of being contained in the semiconductor, and the oxide catalyst does not cause grain growth in a state of being contained in the metal oxide semiconductor of the gas-sensitive layer, Catalytic activity Was stably maintained the oxygen adsorption amount of the metal oxide semiconductor is kept constant, a thick film gas sensor excellent result initial sounding characteristics and stability.

[Brief description of drawings]

FIG. 1 is a plan view showing a thick film gas sensor according to an embodiment of the first invention.

FIG. 2 is a sectional view taken along the line AA of FIG. 1 showing a thick film gas sensor according to an embodiment of the first invention.

FIG. 3 is a diagram showing resistance characteristics of a thick film gas sensor according to an embodiment of the first invention.

FIG. 4 is a plan view showing a thick film gas sensor according to an embodiment of the second invention.

5 is a sectional view taken along the line BB of FIG. 4 showing a thick film gas sensor according to an embodiment of the second invention.

FIG. 6 shows the initial ringing characteristic (a) of the thick film gas sensor according to the embodiment of the third invention as the characteristic (a) of the conventional thick film gas sensor.
Diagram shown in contrast to

FIG. 7 is a diagram showing the temporal stability (c) of the sensor resistance value of the thick film gas sensor according to the embodiment of the third invention in comparison with the characteristics of a conventional thick film gas sensor.

FIG. 8 is a diagram showing the voltage dependence (e) of the sensor resistance value of the thick film gas sensor according to the embodiment of the third invention in comparison with the characteristic (f) of the conventional thick film gas sensor.

FIG. 9 is a plan view showing a conventional thick film gas sensor.

10 is a sectional view taken along the line CC of FIG. 6 showing a conventional thick film gas sensor.

FIG. 11 is a diagram showing an initial ringing characteristic of a thick film gas sensor.

[Explanation of symbols]

 1 Substrate 2 Electrode 2A Electrode 3A Oxidative combustion layer 3B First oxidative combustion layer 3C Second oxidative combustion layer 3D Third oxidative combustion layer 4 Gas sensitive layer 7 Lead wire 8 Heater 9 Lead wire

Claims (10)

[Claims] 1. A thick film gas sensor for detecting the presence or absence of gas by utilizing a change in resistance of a metal oxide semiconductor, comprising: (1) a substrate, (2) a pair of electrodes, and (3) a first electrode. And (4) a gas-sensitive layer, and (5) a second oxidation-combustion layer. The substrate is a support for the gas sensor, and the pair of electrodes are directly separated from each other on the substrate. The first oxidation combustion layer is selectively laminated on the substrate and the pair of electrodes, and the gas-sensitive layer is selectively laminated on the first oxidation combustion layer and the pair of electrodes. The combustion layer is laminated so as to cover the entire gas-sensitive layer, the first oxidation combustion layer has a metal oxide carrier supporting a noble metal catalyst, and the second oxidation combustion layer has a metal oxide carrier supporting a noble metal catalyst. The gas sensitive layer is carried on the metal oxide semiconductor by cobalt oxide, manganese oxide, nickel oxide, copper oxide, iron oxide. , A thick film gas sensor comprising at least one selected from the group consisting of zinc oxide, chromium oxide, vanadium oxide, titanium oxide and aluminum oxide. 2. A thick film gas sensor for detecting the presence / absence of gas by utilizing a change in resistance value of a metal oxide semiconductor, comprising: (1) a substrate, (2) a pair of electrodes, and (3) a third electrode. And the (4) gas sensitive layer, the substrate is a support of the gas sensor, the pair of electrodes are directly and separately deposited on the substrate, and the gas sensitive layer is paired with the substrate. Is selectively laminated on the electrode of, the third oxidation combustion layer is laminated so as to cover the entire gas-sensitive layer, and the third oxidation combustion layer is formed by supporting the noble metal catalyst on the metal oxide carrier. The gas layer contains metal oxide semiconductors such as cobalt oxide, manganese oxide, nickel oxide, copper oxide, iron oxide, and zinc oxide. A thick film gas sensor comprising at least one selected from the group consisting of chromium oxide, vanadium oxide, titanium oxide and aluminum oxide. 3. The thick film gas sensor according to claim 1 or 2, wherein the metal oxide semiconductor is an n-type metal oxide semiconductor. 4. The thick film gas sensor according to claim 3, wherein
The thick film gas sensor, wherein the n-type metal oxide semiconductor is tin oxide. 5. The thick film gas sensor according to claim 3,
A thick film gas sensor, wherein the n-type metal oxide semiconductor is zinc oxide. 6. The thick film gas sensor according to claim 1 or 2, wherein the metal oxide carrier is tin oxide, zinc oxide. A thick film gas sensor comprising at least one selected from the group consisting of aluminum oxide, magnesium oxide and zirconium oxide. 7. The thick film gas sensor according to claim 1, wherein the metal oxide carrier is cobalt oxide, manganese oxide, nickel oxide, copper oxide, iron oxide, zinc oxide. A thick film gas sensor comprising at least one selected from the group consisting of chromium oxide, vanadium oxide, titanium oxide and aluminum oxide. 8. The thick film gas sensor according to claim 1, wherein the metal oxide semiconductors are cobalt oxide, manganese oxide, nickel oxide, copper oxide, iron oxide, zinc oxide. A thick film gas sensor comprising at least one selected from the group consisting of chromium oxide, vanadium oxide, titanium oxide and aluminum oxide in a proportion of 0.01 to 1.0% by weight. 9. A method of manufacturing a thick film gas sensor for detecting the presence / absence of gas by utilizing a change in resistance value of a metal oxide semiconductor, which comprises (1) a step of forming an oxidation combustion layer, and (2) a feeling. Including the gas layer forming step, the oxidizing combustion layer forming step is a step of preparing a paste of metal oxide powder carrying a noble metal catalyst, coating and drying it, and heat-treating it. The film forming step is a step of preparing a paste obtained by adding a metal powder of nickel, iron, aluminum or chromium to a powder of a metal oxide semiconductor, coating, drying and heat treating the paste, and a method for manufacturing a thick film gas sensor. . 10. The method for manufacturing a thick film gas sensor according to claim 9, wherein the addition amount of the metal powder to the powder of the metal oxide semiconductor is in the range of 100 to 5000 ppm. Production method.