CA2053049A1 - Process for the preparation of a gas sensor - Google Patents
Process for the preparation of a gas sensorInfo
- Publication number
- CA2053049A1 CA2053049A1 CA 2053049 CA2053049A CA2053049A1 CA 2053049 A1 CA2053049 A1 CA 2053049A1 CA 2053049 CA2053049 CA 2053049 CA 2053049 A CA2053049 A CA 2053049A CA 2053049 A1 CA2053049 A1 CA 2053049A1
- Authority
- CA
- Canada
- Prior art keywords
- gas
- sensitive layer
- process according
- electrodes
- catalyst
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Abandoned
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
- G01N27/02—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance
- G01N27/04—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance
- G01N27/12—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating impedance by investigating resistance of a solid body in dependence upon absorption of a fluid; of a solid body in dependence upon reaction with a fluid, for detecting components in the fluid
Landscapes
- Chemical & Material Sciences (AREA)
- Chemical Kinetics & Catalysis (AREA)
- Electrochemistry (AREA)
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- Analytical Chemistry (AREA)
- Biochemistry (AREA)
- General Health & Medical Sciences (AREA)
- General Physics & Mathematics (AREA)
- Immunology (AREA)
- Pathology (AREA)
- Investigating Or Analyzing Materials By The Use Of Fluid Adsorption Or Reactions (AREA)
Abstract
Abstract A process for the preparation of a gas sensor is described, in which two electrodes and a gas-sensitive layer connecting the two electrodes are applied to an electrically insulating carrier substrate, and a catalyst is added.
Despite its simple manufacture, a gas sensor of this kind is intended to be able to detect a specific gas at room temperature.
For that purpose, a metallic salt dissolved in water or in an alcohol is added as catalyst to the gas-sensitive layer (4) and the sensor (1) is heated to a temperature below the boiling point of the metallic salt.
Fig. 1
Despite its simple manufacture, a gas sensor of this kind is intended to be able to detect a specific gas at room temperature.
For that purpose, a metallic salt dissolved in water or in an alcohol is added as catalyst to the gas-sensitive layer (4) and the sensor (1) is heated to a temperature below the boiling point of the metallic salt.
Fig. 1
Description
20~3049 Process for the ~re~aration of a aas sensor.
The invention relates to a process for the preparation of a gas sensor, in which two electrodes and a gas-sensitive layer connecting the two electrodes are applied to an electrically insulating carrier substrate and a catalyst is added.
A process of this kind is known from DE 34 22 823 A. In that process, using a thin-film technique three electrodes are applied to the carrier substrate, two of the electrodes serving as measuring electrodes and one serving to heat the sensor. The gas-sensitive layer, which consists of tin oxide or tin oxide doped with aluminium, is arranged between the electrodes. A film that is used as catalyst is deposited by vapour-deposition on the gas-sensitive layer. This film consists of platinum or of other active metals. This gas sensor reacts in particular to hydrogen sulphide, its electrical conductivity rising as the concentration of gas increases. The gas sensor is typically operated at 280 C.
US 4 197 089 discloses a gas sensor in which three electrodes are applied to a ceramic carrier substrate, one electrode serving as the measuring electrode, the second electrode serving as the heating electrode and the third electrode serving as a common earth electrode. The gas-sensitive layer between the electrodes consists in this case of a tungsten trioxide film. In this connection, a tungsten trioxide solution is prepared, and dripped between the electrodes. A fifteen-minute heating at a temperature of 600C follows. In order to render the gas sensor 20~3~
sensitive to ammonia, a drop of platinic acid is then dripped between the electrodes, so that metallic platinuln forms. The tungsten trioxide layer is then applied. This sensor requires an operating temperature of 150 to 300~C.
EP 141 033 A describes a process for the preparation of materials for a gas sensor, in which a metallic oxide is mixed with a metallic salt acting as catalyst, for example platinic acid, to form a solution. The solution is then exposed to ultra-violet radiation. The material thus treated is slowly heated to about 300 C. After cooling and trimming to shape, the electrodes are joined on. Depending on the metallic oxide selected and the metallic salt selected, gas sensors with specific sensitivities to selected types of gas are obtained. These gas sensors are also able to operate at room temperature. Their preparation, however, is relatively costly.
The invention is based on the problem of providing an inexpensive process for preparing a gas sensor which is able to operate at room temperature and preferably reacts to a predetermined gas.
This problem is solved in a process of the kind mentioned in the introduction in that a metallic salt dissolved in water or in an alcohol is added as catalyst to the gas-sensitive layer and the sensor is heated to a temperature below the boiling point of the metallic salt.
It has been found that, by restricting the temperature to a range below the boiling point of the metallic salt, an especially sensitive catalyst layer can be produced, so that the gas sensor is able to work even at room temperature. The preparation process is relatively simple, since it is possible to work at relatively low temperatures when applying the catalyst.
The metal is not precipitated. On the contrary, the 2~3~9 metallic salt serves as the catalyst.
In a preferred embodiment, the gas sensor is dried at the temperature below the boiling point. Heating to this temperature continues until the moisture content of the sensor, in particular of the catalyst layer or the gas-sensitive layer, has dropped to a certain percentage.
It is also preferable for the catalyst to be applied to the surface of the gas-sensitive layer. In this connection the potential for reaction with the gas to be detected is greatest. Moreover, this embodiment has fewest problems in manufacture.
Advantageously, the gas-sensitive layer and/or the electrodes are provided with breaks. In this manner it is possible to trim the resistance value of the gas sensor to a specific value. The gas sensor can thus be adapted to the sensitivity of evaluating devices.
In this connection, it is preferable for the breaks to be produced with the help of a laser beam.
Very fine structures can be obtained with a laser beam so that the resistance value can be set with great accuracy.
In this connection, it is an advantage for the gas-sensitive layer to be given a meandering configuration by the breaks. In this manner, a relatively large electrical resistance value can be produced. The resistance changes caused by the gas to be detected are correspondingly large and can be readily detected.
Preferably, the breaks are produced prior to applying the catalyst layer. It is thus possible to ensure that the catalyst layer is not heated to a temperature above the required temperature.
Preferably, the two electrodes are applied by means of thick-film or thin-film technology after the carrier substrate has been cleaned. Extremely 2~3~9 -- 5 ~
accurate structures can be produced using thick-film or thin-film technology. In addition, the spatial extent of the electrodes can be limited relatively accurately.
This is of particular advantage when valuable materials, such as gold, are used for the electrodes.
It is also an advantage for the gas-sensitive layer to be vacuum-deposited. In a process of this kind the thickness of the gas-sensitive layer can be set with great accuracy. The gas sensors can be prepared consistently with great accuracy.
Advantageously, the gas sensitive layer is formed by a layer of tin which is oxidized at a temperature in the range from 400 to 500C, especially in the range from 440 to 460 C. It is easy to apply tin as a layer. Through heating to a temperature in the range mentioned, for example 450 C, an oxidation can be achieved. In this connection, a layer of tin oxide (SnOy) is obtained, which has proved to be extraordinarily useful for detecting gas through change in electrical conductivity.
In this connection, the use of platinic acid in aqueous solution (H2PtCl6(6H2O)) as catalyst is preferred. The sensor is then especially sensitive to ammonia.
It is an advantage therein for the sensor to be dried at a temperature in the range from 70 C to 150 C, in particular in the range from 105C to 115CI for several hours, in particular 20 to 28 hours. These temperatures allow a very careful drying. The catalyst is then able to develop its advantageous response to ammonia.
The invention is described in the following with reference to a preferred embodiment in conjunction with the drawing. In the drawing, Fig. 1 shows a gas sensor and 20~3~9 Fig. 2 shows a cross-section through the gas sensor on an enlarged scale.
A gas sensor 1 comprises a carrier substrate 2, which can be in the form of a ceramic substrate (Al2O,) or a Si-substrate with an insulator (nitride or oxide).
On the substrate there are two electrodes 3. A gas-sensitive layer 4 is vacuum-deposited between the electrodes 3. It consists of tin oxide (SnOy). On the gas-sensitive layer 4 there is a catalyst 5. The gas-sensitive layer 4 is provided with cutouts 6, which isolate adjacent portions of the gas-sensitive layer 4 electrically from one another, so that the gas-sensitive layer 4 follows a meandering course.
Similarly, the electrodes 3 can also be provided with cutouts (not illustrated).
To prepare the gas sensor, the substrate 2 is first of all cleaned. Then two electrodes 3 consisting of an inert metal, for example platinum or gold, are applied by means of thick-film or thin-film technology, that is to say, they are printed on and thereafter sintered at about 850C. After renewed cleaning and drying, the substrate 2 equipped with the electrodes 3 is placed in a vacuum system. There, the gas-sensitive layer 4 is vacuum-deposited, for example by means of thin-film technology (reactive vacuum-deposition). The gas-sensitive layer has an electrical connection with the two electrodes. The gas-sensitive layer here consists of tin (Sn) with a thickness of about 100 nm. After the application of the tin layer, the entire assembly is heated to about 450 C, whereby the Sn-layer is converted into a layer of tin oxide (SnOy). With the help of a laser beam the cutouts 6 are then cut into the gas-sensitive layer.
A solution of a catalyst or a catalyst mixture, 20~3~A9 sensitive layer. By this means the sensitivity to a selected type of gas is enhanced. In the present case, platinic acid in aqueous solution (H2PtC16(6H20)) is used. The gas sensor is then dried for about 24 hours at 115~C. This temperature lies below the boiling point of the platinic acid. A sensor of this kind is especially selective towards ammonia. As the concentration of ammonia increases the electrical resistance between the two electrodes 3 rises.
The invention relates to a process for the preparation of a gas sensor, in which two electrodes and a gas-sensitive layer connecting the two electrodes are applied to an electrically insulating carrier substrate and a catalyst is added.
A process of this kind is known from DE 34 22 823 A. In that process, using a thin-film technique three electrodes are applied to the carrier substrate, two of the electrodes serving as measuring electrodes and one serving to heat the sensor. The gas-sensitive layer, which consists of tin oxide or tin oxide doped with aluminium, is arranged between the electrodes. A film that is used as catalyst is deposited by vapour-deposition on the gas-sensitive layer. This film consists of platinum or of other active metals. This gas sensor reacts in particular to hydrogen sulphide, its electrical conductivity rising as the concentration of gas increases. The gas sensor is typically operated at 280 C.
US 4 197 089 discloses a gas sensor in which three electrodes are applied to a ceramic carrier substrate, one electrode serving as the measuring electrode, the second electrode serving as the heating electrode and the third electrode serving as a common earth electrode. The gas-sensitive layer between the electrodes consists in this case of a tungsten trioxide film. In this connection, a tungsten trioxide solution is prepared, and dripped between the electrodes. A fifteen-minute heating at a temperature of 600C follows. In order to render the gas sensor 20~3~
sensitive to ammonia, a drop of platinic acid is then dripped between the electrodes, so that metallic platinuln forms. The tungsten trioxide layer is then applied. This sensor requires an operating temperature of 150 to 300~C.
EP 141 033 A describes a process for the preparation of materials for a gas sensor, in which a metallic oxide is mixed with a metallic salt acting as catalyst, for example platinic acid, to form a solution. The solution is then exposed to ultra-violet radiation. The material thus treated is slowly heated to about 300 C. After cooling and trimming to shape, the electrodes are joined on. Depending on the metallic oxide selected and the metallic salt selected, gas sensors with specific sensitivities to selected types of gas are obtained. These gas sensors are also able to operate at room temperature. Their preparation, however, is relatively costly.
The invention is based on the problem of providing an inexpensive process for preparing a gas sensor which is able to operate at room temperature and preferably reacts to a predetermined gas.
This problem is solved in a process of the kind mentioned in the introduction in that a metallic salt dissolved in water or in an alcohol is added as catalyst to the gas-sensitive layer and the sensor is heated to a temperature below the boiling point of the metallic salt.
It has been found that, by restricting the temperature to a range below the boiling point of the metallic salt, an especially sensitive catalyst layer can be produced, so that the gas sensor is able to work even at room temperature. The preparation process is relatively simple, since it is possible to work at relatively low temperatures when applying the catalyst.
The metal is not precipitated. On the contrary, the 2~3~9 metallic salt serves as the catalyst.
In a preferred embodiment, the gas sensor is dried at the temperature below the boiling point. Heating to this temperature continues until the moisture content of the sensor, in particular of the catalyst layer or the gas-sensitive layer, has dropped to a certain percentage.
It is also preferable for the catalyst to be applied to the surface of the gas-sensitive layer. In this connection the potential for reaction with the gas to be detected is greatest. Moreover, this embodiment has fewest problems in manufacture.
Advantageously, the gas-sensitive layer and/or the electrodes are provided with breaks. In this manner it is possible to trim the resistance value of the gas sensor to a specific value. The gas sensor can thus be adapted to the sensitivity of evaluating devices.
In this connection, it is preferable for the breaks to be produced with the help of a laser beam.
Very fine structures can be obtained with a laser beam so that the resistance value can be set with great accuracy.
In this connection, it is an advantage for the gas-sensitive layer to be given a meandering configuration by the breaks. In this manner, a relatively large electrical resistance value can be produced. The resistance changes caused by the gas to be detected are correspondingly large and can be readily detected.
Preferably, the breaks are produced prior to applying the catalyst layer. It is thus possible to ensure that the catalyst layer is not heated to a temperature above the required temperature.
Preferably, the two electrodes are applied by means of thick-film or thin-film technology after the carrier substrate has been cleaned. Extremely 2~3~9 -- 5 ~
accurate structures can be produced using thick-film or thin-film technology. In addition, the spatial extent of the electrodes can be limited relatively accurately.
This is of particular advantage when valuable materials, such as gold, are used for the electrodes.
It is also an advantage for the gas-sensitive layer to be vacuum-deposited. In a process of this kind the thickness of the gas-sensitive layer can be set with great accuracy. The gas sensors can be prepared consistently with great accuracy.
Advantageously, the gas sensitive layer is formed by a layer of tin which is oxidized at a temperature in the range from 400 to 500C, especially in the range from 440 to 460 C. It is easy to apply tin as a layer. Through heating to a temperature in the range mentioned, for example 450 C, an oxidation can be achieved. In this connection, a layer of tin oxide (SnOy) is obtained, which has proved to be extraordinarily useful for detecting gas through change in electrical conductivity.
In this connection, the use of platinic acid in aqueous solution (H2PtCl6(6H2O)) as catalyst is preferred. The sensor is then especially sensitive to ammonia.
It is an advantage therein for the sensor to be dried at a temperature in the range from 70 C to 150 C, in particular in the range from 105C to 115CI for several hours, in particular 20 to 28 hours. These temperatures allow a very careful drying. The catalyst is then able to develop its advantageous response to ammonia.
The invention is described in the following with reference to a preferred embodiment in conjunction with the drawing. In the drawing, Fig. 1 shows a gas sensor and 20~3~9 Fig. 2 shows a cross-section through the gas sensor on an enlarged scale.
A gas sensor 1 comprises a carrier substrate 2, which can be in the form of a ceramic substrate (Al2O,) or a Si-substrate with an insulator (nitride or oxide).
On the substrate there are two electrodes 3. A gas-sensitive layer 4 is vacuum-deposited between the electrodes 3. It consists of tin oxide (SnOy). On the gas-sensitive layer 4 there is a catalyst 5. The gas-sensitive layer 4 is provided with cutouts 6, which isolate adjacent portions of the gas-sensitive layer 4 electrically from one another, so that the gas-sensitive layer 4 follows a meandering course.
Similarly, the electrodes 3 can also be provided with cutouts (not illustrated).
To prepare the gas sensor, the substrate 2 is first of all cleaned. Then two electrodes 3 consisting of an inert metal, for example platinum or gold, are applied by means of thick-film or thin-film technology, that is to say, they are printed on and thereafter sintered at about 850C. After renewed cleaning and drying, the substrate 2 equipped with the electrodes 3 is placed in a vacuum system. There, the gas-sensitive layer 4 is vacuum-deposited, for example by means of thin-film technology (reactive vacuum-deposition). The gas-sensitive layer has an electrical connection with the two electrodes. The gas-sensitive layer here consists of tin (Sn) with a thickness of about 100 nm. After the application of the tin layer, the entire assembly is heated to about 450 C, whereby the Sn-layer is converted into a layer of tin oxide (SnOy). With the help of a laser beam the cutouts 6 are then cut into the gas-sensitive layer.
A solution of a catalyst or a catalyst mixture, 20~3~A9 sensitive layer. By this means the sensitivity to a selected type of gas is enhanced. In the present case, platinic acid in aqueous solution (H2PtC16(6H20)) is used. The gas sensor is then dried for about 24 hours at 115~C. This temperature lies below the boiling point of the platinic acid. A sensor of this kind is especially selective towards ammonia. As the concentration of ammonia increases the electrical resistance between the two electrodes 3 rises.
Claims (12)
1. Process for the preparation of a gas sensor, in which two electrodes and a gas-sensitive layer connecting the two electrodes are applied to an electrically insulating carrier substrate and a catalyst is added, characterized in that a metallic salt dissolved in water or in an alcohol is added as catalyst (5) to the gas-sensitive layer (4) and the sensor (1) is heated to a temperature below the boiling point of the metallic salt.
2. A process according to claim 1, characterized in that the gas sensor is dried at a temperature below the boiling point.
3. A process according to claim 1 or 2, characterized in that the catalyst (5) is applied to the surface of the gas-sensitive layer (4).
4. A process according to one of claims 1 to 3, characterized in that the gas-sensitive layer (4) and/or the electrodes (3) are provided with breaks (6).
5. A process according to claim 4, characterized in that the breaks (6) are produced with the help of a laser beam.
6. A process according to claim 4 or 5, characterized in that the gas-sensitive layer (4) is given a meandering configuration by the breaks (6).
7. A process according to one of claims 4 to 6, characterized in that the breaks (6) are made before the catalyst layer (5) is applied.
8. A process according to one of claims 1 to 7, characterized in that the two electrodes (3) are applied by thick-film or thin-film technology after the carrier substrate (2) has been cleaned.
9. A process according to one of claims 1 to 8, characterized in that the gas-sensitive layer (4) is vacuum-deposited.
10. A process according to one of claims 1 to 9, characterized in that the gas-sensitive layer (4) is formed by a layer of tin which is oxidized at a temperature in the range from 400° to 500°C, in particular in the range from 440° to 460°C.
11. A process according to one of claims 1 to 10, characterized in that platinic acid in aqueous solution (H2PtCl6(6H2O)) is used as catalyst (5).
12. A process according to claim 11, characterized in that the sensor is dried at a temperature in the range from 70° to 115°C, in particular in the range from 105°
to 115°C, for several hours, in particular 20 to 28 hours.
to 115°C, for several hours, in particular 20 to 28 hours.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| DEP4038140.4 | 1990-11-30 | ||
| DE19904038140 DE4038140A1 (en) | 1990-11-30 | 1990-11-30 | METHOD FOR PRODUCING A GAS SENSOR |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2053049A1 true CA2053049A1 (en) | 1992-05-31 |
Family
ID=6419250
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2053049 Abandoned CA2053049A1 (en) | 1990-11-30 | 1991-10-09 | Process for the preparation of a gas sensor |
Country Status (8)
| Country | Link |
|---|---|
| JP (1) | JPH04269649A (en) |
| CA (1) | CA2053049A1 (en) |
| DE (1) | DE4038140A1 (en) |
| DK (1) | DK190091A (en) |
| FR (1) | FR2670012A1 (en) |
| GB (1) | GB2250823A (en) |
| NL (1) | NL9101879A (en) |
| SE (1) | SE9103017L (en) |
Family Cites Families (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1116943A (en) * | 1964-08-21 | 1968-06-12 | Johnson Matthey Co Ltd | Improvements in and relating to catalytic reactions and a catalyst for use therein |
| GB1345067A (en) * | 1970-12-17 | 1974-01-30 | ||
| JPS5118262A (en) * | 1974-08-06 | 1976-02-13 | Japan Gasoline | Haigasuchuno chitsusosankabutsuno jokyohoho |
| US4197089A (en) * | 1975-12-22 | 1980-04-08 | Ambac Industries, Incorporated | Reducing gas sensor |
| JPS5395097A (en) * | 1977-01-31 | 1978-08-19 | Toshiba Corp | Gas-sensitive element |
| GB2142147A (en) * | 1983-06-24 | 1985-01-09 | Standard Telephones Cables Ltd | Gas sensor |
| CH666965A5 (en) * | 1983-08-30 | 1988-08-31 | Cerberus Ag | METHOD FOR PRODUCING MATERIALS FOR GAS SENSORS. |
| JPS61110045A (en) * | 1984-11-02 | 1986-05-28 | Omron Tateisi Electronics Co | Thick film type sensor |
| US4857275A (en) * | 1986-03-19 | 1989-08-15 | Ngk Spark Plug Co., Ltd. | Thick-film gas-sensitive element |
| US4911892A (en) * | 1987-02-24 | 1990-03-27 | American Intell-Sensors Corporation | Apparatus for simultaneous detection of target gases |
| GB2234074A (en) * | 1989-07-22 | 1991-01-23 | Atomic Energy Authority Uk | Gas sensor |
-
1990
- 1990-11-30 DE DE19904038140 patent/DE4038140A1/en active Granted
-
1991
- 1991-10-09 CA CA 2053049 patent/CA2053049A1/en not_active Abandoned
- 1991-10-16 SE SE9103017A patent/SE9103017L/en not_active Application Discontinuation
- 1991-11-11 NL NL9101879A patent/NL9101879A/en not_active Application Discontinuation
- 1991-11-18 JP JP30214591A patent/JPH04269649A/en active Pending
- 1991-11-21 DK DK190091A patent/DK190091A/en not_active Application Discontinuation
- 1991-11-28 GB GB9125334A patent/GB2250823A/en not_active Withdrawn
- 1991-11-29 FR FR9114823A patent/FR2670012A1/en active Pending
Also Published As
| Publication number | Publication date |
|---|---|
| SE9103017L (en) | 1992-05-31 |
| GB9125334D0 (en) | 1992-01-29 |
| DE4038140C2 (en) | 1993-05-27 |
| GB2250823A (en) | 1992-06-17 |
| DK190091A (en) | 1992-05-31 |
| NL9101879A (en) | 1992-06-16 |
| DK190091D0 (en) | 1991-11-21 |
| DE4038140A1 (en) | 1992-06-04 |
| FR2670012A1 (en) | 1992-06-05 |
| JPH04269649A (en) | 1992-09-25 |
| SE9103017D0 (en) | 1991-10-16 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| EEER | Examination request | ||
| FZDE | Dead |