JP3271635B2 - Thick film gas sensor and method of manufacturing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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 relates to a configuration of a pressure film gas sensor having a short initial sounding time.

[0002]

2. Description of the Related Art As one of gas sensors, a sensor 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 air, the oxygen in the air 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 by the metal oxide semiconductor instead of adsorbed oxygen, and the electric resistance value decreases. A gas sensor using a metal oxide semiconductor utilizing such properties is used for a gas leak alarm device for LP gas, city gas, and the like.

FIG. 7 is a plan view showing a conventional thick film gas sensor. FIG. 8 shows a conventional thick film gas sensor.
It is arrow C sectional drawing. A conventional thick-film gas sensor is formed by laminating a gas-sensitive layer 4 and an oxidized combustion layer 3A on one main surface of an insulating substrate 1 such as alumina. 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, for example, tin oxide. The oxidation combustion layer 3A is formed by supporting a noble metal catalyst such as platinum on tin oxide. The oxidizing combustion layer 3A increases the stability of the gas-sensitive layer 4 with respect to the combustible gas over time, and also increases the selectivity with respect to the combustible gas to reduce the sensitivity with respect to alcohol and the like. Commercial power 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 thick film gas sensor as described above has a problem that the initial ringing time becomes long. FIG. 9 is a diagram showing initial ringing characteristics of a conventional thick film gas sensor. When the gas sensor is turned on and the gas sensor is started to be used, the resistance of the sensor temporarily decreases and then rises, so that an alarm is issued while the resistance is decreasing. Refers to the time during which an alarm is issued. Therefore, during this ringing time, control is performed so that the gas sensor does not issue an alarm. However, if the initial ringing time is long, it takes time to start using the gas sensor, which is not preferable. The reason why the initial ringing time is long in the two-layer type thick film gas sensor is that the metal oxide semiconductor of the gas-sensitive layer adsorbs oxygen and increases the electric resistance after power-on, but this oxygen adsorption takes time. . Therefore, a catalyst that increases the oxygen adsorption rate may be supported on the metal oxide semiconductor in the gas-sensitive layer. Bring.

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

[0006]

According to a first aspect of the present invention, there is provided a thick-film gas sensor for detecting the presence or absence of a gas by utilizing a change in the resistance value of a metal oxide semiconductor. A pair of electrodes, a first oxidation combustion layer, a gas-sensitive layer,
A second oxidized combustion layer, wherein the substrate is a support for the gas sensor, a pair of electrodes are directly deposited on the substrate at a distance, and a first oxidized combustion layer is formed on the substrate and the pair of electrodes. The gas-sensitive layer is selectively laminated on the first oxidizing combustion layer and the pair of electrodes, and the second oxidizing combustion layer is laminated so as to cover all of the gas-sensitive layer. The oxidized combustion layer of No. 1 has a noble metal catalyst supported on a metal oxide carrier, the second oxidized combustion layer has a noble metal catalyst supported on a metal oxide carrier, and the gas-sensitive layer is cobalt oxide, a metal oxide semiconductor. Manganese oxide,
This is achieved by including 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 method for manufacturing a thick-film gas sensor for detecting the presence or absence of gas by utilizing a change in the resistance value of a metal oxide semiconductor. And (2) the step of forming a gas-sensitive layer. The step of forming an oxidized combustion layer is a step of preparing a paste of a metal oxide powder supporting a noble metal catalyst, coating, drying and heat-treating the paste. The process of forming the gas-sensitive layer is achieved by 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. Is done.

The oxidizing combustion layer oxidizes and combusts an 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, reduces the electric resistance value, and detects the test gas. The first oxidizing combustion layer and the second oxidizing combustion layer increase the supply rate of air to the gas-sensitive layer.

[0010]

[Action] Cobalt oxide, manganese oxide, nickel oxide,
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 in the gas-sensitive layer when the metal oxide semiconductor adsorbs oxygen. Functions as a catalyst.

When the oxide catalyst is contained in the metal oxide semiconductor of the gas-sensitive layer, it does not cause grain growth, maintains a constant catalytic activity, and has an electric resistance determined by the amount of oxygen adsorbed on the metal oxide semiconductor. Keep the value stable.

[0012]

Next, an embodiment of the present invention will 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. FIG. 2 is a cross-sectional view of the thick-film gas sensor according to the first embodiment of the present invention, taken along line AA of FIG.

The structure of the thick film gas sensor according to the embodiment of the first invention is as follows. Two electrodes 2 are provided separately on one main surface of the substrate 1. A first oxidation 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 oxidation combustion layer 3B and the electrode 2. Completely cover the gas-sensitive layer 4 to form the second oxidized 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 is 0.5 mm thick, 3 mm long and 3 mm wide.
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 fired at a temperature of about 1100 ° C. A paste for a heater made of ruthenium oxide was screen-printed in a predetermined pattern and fired at a predetermined temperature.

[0015] Tin oxide powder in dry air at a temperature of 730 ° C
For ₂ hours, and an aqueous solution of chloroplatinic acid H ₂ PtCl ₆ adjusted to have a platinum content of 2% with respect to the tin oxide powder is added to the obtained tin oxide powder, kneaded, and dried. did. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose H ₂ PtCl ₆ chloroplatinate to support platinum on the tin oxide powder. After the obtained powder was pulverized with a ball mill, an appropriate amount of ethyl silicate, ethyl cellulose, carbitol and the like were added and kneaded to obtain a paste for a first oxidation combustion layer.
The obtained paste for the first oxidation combustion layer was screen-printed in a predetermined pattern to a thickness of 20 μm, and dried at 120 ° C. for 2 hours.

[0016] Tin oxide powder in dry air at a temperature of 730 ° C
For 2 hours, and the obtained tin oxide powder is treated with cobalt oxide Co.
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 tin oxide powder in an amount of 0.1%. weight%
, And mixed with an appropriate amount of ethyl silicate, ethyl cellulose, carbitol and the like to obtain a paste for a gas-sensitive layer. The obtained paste was screen-printed to a thickness of 50 μm according to a predetermined pattern, and dried at 120 ° C. for 2 hours.

[0017] Tin oxide powder in dry air at a temperature of 730 ° C
For ₂ hours, and an aqueous solution of chloroplatinic acid H ₂ PtCl ₆ adjusted to have a platinum content of 2% with respect to the tin oxide powder is added to the obtained tin oxide powder, kneaded, and dried. did. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose H ₂ PtCl ₆ chloroplatinate to support platinum on the tin oxide powder. After the obtained powder was pulverized with a ball mill, an appropriate amount of ethyl silicate, ethyl cellulose, carbitol and the like were added and kneaded to obtain a second paste for an oxidized combustion layer.
The obtained paste for the second oxidation combustion layer was screen-printed to a thickness of 20 μm according to a predetermined pattern, and dried at 120 ° C. for 2 hours.

After printing and drying the first oxidized combustion layer, the gas-sensitive layer and the second oxidized combustion layer, they are simultaneously fired at a temperature of 630 ° C. for 3 hours to obtain a first oxidized combustion layer 3 B and a gas-sensitive layer 4. Thus, a second oxidation combustion layer 3C was formed. Then the electrodes 2,
Platinum leads 7 and 9 were connected to 2A, respectively, to obtain a thick film gas sensor. Each lead 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 is screen-printed on the two main surfaces of the substrate 1 in a predetermined pattern, and after drying, about 11
It was fired at a temperature of 00 ° C. A paste for a heater made of ruthenium oxide was screen-printed in a predetermined pattern and fired at a predetermined temperature. Tin oxide powder in dry air at a temperature of 7
The mixture was treated at 30 ° C. for ₂ hours, and an aqueous solution of chloroplatinic acid H ₂ PtCl ₆ adjusted to have a platinum content of 2% with respect to the tin oxide powder was added to the obtained tin oxide powder, followed by kneading. And dried. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose H ₂ PtCl ₆ chloroplatinate to support platinum on the tin oxide powder. After the obtained powder was pulverized with a ball mill, an appropriate amount of ethyl silicate, ethyl cellulose, carbitol and the like were added and kneaded to obtain a paste for a first oxidation combustion layer. The obtained paste for the first oxidation combustion layer was screen-printed in a predetermined pattern to a thickness of 20 μm,
It was dried at 2 ° C. for 2 hours.

[0020] Tin oxide powder in dry air at a temperature of 730 ° C
For 2 hours, and an appropriate amount of ethyl silicate, ethyl cellulose, carbitol or the like 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 to a thickness of 50 μm according to a predetermined pattern, and dried at 120 ° C. for 2 hours. The tin oxide powder for 2h at a temperature 730 ° C. in dry air, chloroplatinic acid content was adjusted to 2% with respect to tin oxide powder of platinum obtained tin oxide powder H ₂ An aqueous solution of PtCl ₆ was added, kneaded, and dried. This powder was heat-treated at a temperature of 600 ° C. for 3 hours to decompose H ₂ PtCl ₆ chloroplatinate to support platinum on the tin oxide powder. After the obtained powder was pulverized with a ball mill, an appropriate amount of ethyl silicate, ethyl cellulose, carbitol and the like were added and kneaded to obtain a second paste for an oxidized combustion layer. The obtained paste for the second oxidation combustion layer was screen-printed to a thickness of 20 μm according to a predetermined pattern, and dried at 120 ° C. for 2 hours.

After printing and drying the first oxidized combustion layer, the gas-sensitive layer and the second oxidized combustion layer, they are simultaneously fired at a temperature of 630 ° C. for 3 hours to obtain a first oxidized combustion layer 3 B and a gas-sensitive layer 4. Thus, a second oxidation combustion layer 3C was formed. Then the electrodes 2,
Platinum leads 7 and 9 were connected to 2A, respectively, to obtain a thick film gas sensor. Each lead was connected to the alarm circuit.

The initial ringing time of the thick film gas sensors according to Example 1 and Comparative Example 1 after being left 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 containing 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 having no oxide catalyst in the gas-sensitive layer has a long initial ringing time. FIG. 3 is a diagram showing 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 includes an oxide catalyst in the gas-sensitive layer, but has a stable sensor resistance value over a long period of time.

Example 2 In preparing a paste for a gas-sensitive layer, cobalt oxide CoO was used.
Manganese oxide, 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 Instead of adding and mixing the powder at a ratio of 0.1% by weight with respect to the tin oxide powder, metal nickel. Same as Example 1 except that powder of metal chromium, metal iron or metal aluminum is added in the range of 100 to 5000 ppm, mixed with ethyl alcohol as a dispersion medium in a ball mill for 20 hours, and alcohol is naturally dried and mixed. Thus, a thick-film gas sensor was prepared. The metal is converted 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 second 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. In contrast, it can be seen that the conventional thick film gas sensor rapidly increases the initial ringing time with the non-energizing time.

FIG. 5 is a diagram showing the temporal stability (c) of the sensor resistance value of the thick film gas sensor according to the second embodiment of the present invention in comparison with the characteristic (d) of the conventional thick film gas sensor. The catalyst is nickel. The measurement was performed in 0.2% isobutane gas. It can be seen that the resistance value of the thick-film gas sensor according to the different embodiment of the first invention is almost stable in 7 days, but the resistance value of the conventional thick-film gas sensor gradually decreases.

FIG. 6 is a diagram showing the voltage dependence (e) of the sensor resistance value of the thick film gas sensor according to the second embodiment of the present 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 embodiment of the second invention has a larger sensor resistance value in air than the conventional one. As a result, the voltage showing the same sensor resistance value is about 5 V higher in the thick film gas sensor of the present invention than in the prior art, and the voltage dependency of the thick film gas sensor for issuing an alarm is reduced.

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

[0050]

According to the first invention, there is provided a thick-film gas sensor for detecting the presence or absence of a gas by utilizing a change in the resistance value of a metal oxide semiconductor, comprising: a substrate; a pair of electrodes; Including an oxidizing combustion layer, a gas-sensitive layer, and a second oxidizing combustion layer,
The substrate is a support for the gas sensor, the pair of electrodes are directly deposited on the substrate at a distance, the first oxidized combustion layer is selectively laminated on the substrate and the pair of electrodes, and the gas-sensitive layer is The first oxidation combustion layer is selectively laminated on the pair of electrodes, the second oxidation combustion layer covers the entire gas-sensitive layer and laminated, and the first oxidation combustion layer is formed of a noble metal on a metal oxide carrier. A catalyst is supported, the second oxidized combustion layer is a metal oxide carrier, which carries a noble metal catalyst, and the gas-sensitive layer is a metal oxide semiconductor, which is formed of cobalt oxide, manganese oxide, nickel oxide, copper oxide, iron oxide. And at least one selected from the group consisting of zinc oxide, chromium oxide, vanadium oxide, titanium oxide, and aluminum oxide. According to the second invention, a change in the resistance value of a metal oxide semiconductor is used. Thick gas sensor that detects presence or absence of gas A manufacturing method, comprising: (1) a step of forming an oxidized combustion layer; and (2) a step of forming a gas-sensitive layer, wherein the step of forming an oxidized combustion layer comprises a metal oxide powder supporting a noble metal catalyst. In this process, a paste of the body is prepared, coated and dried, and then heat-treated. The gas-sensitive layer is formed by adding a powder of nickel, iron, aluminum or chromium to a powder of a metal oxide semiconductor. It is said that it is a process of coating, drying, and heat-treating. Therefore, oxide catalysts such as cobalt oxide, manganese oxide, nickel oxide, copper oxide, iron oxide, zinc oxide, chromium oxide, vanadium oxide, titanium oxide, aluminum oxide, etc. The metal oxide semiconductor functions as a catalyst when oxygen is adsorbed when contained in the metal oxide semiconductor of the gas-sensitive layer, and the oxide catalyst is contained in the metal oxide semiconductor of the gas-sensitive layer. Granulation The without causing the oxygen adsorption amount of maintaining the catalytic activity constant metal oxide semiconductor maintaining stable, thick film gas sensor excellent result initial sounding characteristics and stability.

[Brief description of the 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 cross-sectional view of the thick-film gas sensor according to the embodiment of the first invention, taken along the line AA of FIG. 1;

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

FIG. 4 shows the initial ringing characteristics (a) of the thick film gas sensor according to the embodiment of the second invention, and the characteristics (a) of the conventional thick film gas sensor.
Diagram shown in comparison with

FIG. 5 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 second invention in comparison with the characteristics of a conventional thick film gas sensor.

FIG. 6 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 second invention in comparison with the characteristic (f) of the conventional thick film gas sensor.

FIG. 7 is a plan view showing a conventional thick film gas sensor.

8 is a cross-sectional view of the conventional thick-film gas sensor taken along the line CC in FIG. 7;

FIG. 9 is a diagram showing initial ringing characteristics of a thick film gas sensor.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 electrode 2A electrode 3A oxidation combustion layer 3B first oxidation combustion layer 3C second oxidation combustion layer 3D third oxidation combustion layer 4 gas sensitive layer 7 lead 8 heater 9 lead

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-104396 (JP, A) JP-A-54-145200 (JP, A) JP-A-54-104395 (JP, A) JP-A-56-104396 33535 (JP, A) JP-A-60-7353 (JP, A) JP-A-5-45319 (JP, A) JP-A-1-304350 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01N 27/12

Claims (3)

(57) [Claims] 1. A thick-film gas sensor for detecting the presence or absence of a gas by utilizing a change in the resistance value of a metal oxide semiconductor, comprising: (1) a substrate; (2) a pair of electrodes; And (4) a gas-sensitive layer, and (5) a second oxidative combustion layer, wherein the substrate is a support for the gas sensor, and the pair of electrodes are directly spaced apart from the substrate. A first oxidation combustion layer is selectively deposited on the substrate and the pair of electrodes; a gas-sensitive layer is selectively deposited on the first oxidation combustion layer and the pair of electrodes; The combustion layer covers the entire gas-sensitive layer and is laminated. The first oxidation combustion layer has a noble metal catalyst supported on a metal oxide carrier, and the second oxidation combustion layer has a noble metal catalyst supported on a metal oxide carrier. The gas-sensitive layer is made of metal oxide semiconductor, 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 method for manufacturing 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, comprising: (1) a step of forming an oxidized combustion layer; And a gas layer forming step. The oxidizing and burning layer forming step is a step of preparing a paste of a metal oxide powder supporting a noble metal catalyst, coating and drying, and performing a heat treatment. The method of manufacturing a thick-film gas sensor, comprising: preparing a paste in which a metal powder of nickel, iron, aluminum or chromium is added to a powder of a metal oxide semiconductor, applying, drying and heat-treating the paste. . 3. The method of manufacturing a thick film gas sensor according to claim 2, wherein the amount of the metal powder added to the metal oxide semiconductor powder is one.
A method for manufacturing a thick film gas sensor, wherein the thickness is in the range of 00 to 5000 ppm.