FR2670012A1 - METHOD FOR MAKING A GAS DETECTOR - Google Patents

Abstract

The invention relates to a method for producing a gas detector in which two electrodes and a gas-sensitive layer connecting the two electrodes are deposited on an electrically insulating carrier substrate, then a catalyst is added. Despite the simplicity of its manufacture, a gas detector of this type must be able to detect a predetermined gas at room temperature. As regards the catalyst, a metal salt of the layer (4) sensitive to the gas dissolved in water or in an alcohol is added and the detector (1) is heated to a temperature below the point boiling metal salt.

Description

The invention relates to a method for producing a gas detector.

  for producing a gas detector in which two electrodes and a gas-sensitive layer which connects the two electrodes are deposited on a carrier substrate

  electrically insulating and to which a catalyst is added.

  A method of this type is known from DE 34 22 823 A. Three electrodes are in this case mounted on the carrier substrate using a thick film technique, two of the electrodes serving as measuring electrodes and a detector heating electrode The gas sensitive layer is disposed between the electrodes and is

  consisting of zinc oxide or zinc oxide doped with aluminum.

  On the gas-sensitive layer is applied a film by vacuum metallization which is used as a catalyst. This film is made of platinum or other active metals. This gas detector reacts in particular with hydrogen sulfide, its electrical conductivity increasing as increases gas concentration The gas detector is typically excited at a temperature of 2800 C. US 4 197 089 discloses a gas detector in which three electrodes are deposited on a ceramic carrier substrate, an electrode serving as a The gas-sensitive layer between the electrodes is constituted in this case by a film of tungsten trioxide. A tungsten trioxide solution is produced. deposited dropwise between the electrodes Then takes place a heating for a period of fifteen minutes at a temperature of at 6000 C To make the gas detector sensitive to ammonia, it starts by depositing a drop of platinum acid between the electrodes so that the platinum metal is formed Then applies the layer of tungsten trioxide This detector requires a working temperature of between 150 and 300 C. EP 141 033 A discloses a process for producing materials for a gas detector, a metal oxide comprising a metal salt acting as a catalyst, for example platinic acid, The solution is then heated slowly to a temperature of about 3000 C. After cooling and cutting to size, the electrodes are added depending on the metal oxide selected and the selected metal salt, gas detectors having specific sensitivities with respect to the types of gas chosen are obtained. gas detectors can also operate at room temperature however, their manufacture is

relatively expensive.

  The object of the invention is to propose an economical method for producing a gas detector that operates at room temperature

  and especially that is reacts to a predetermined gas.

  With a process of the type described in the preamble, this object is achieved by adding as a catalyst a metal salt of the gas-sensitive layer dissolved in water or an alcohol, and heating the detector up to a temperature

  below the boiling point of the metal salt.

  It has been found that by limiting the temperature to a range below the boiling point of the metal salt, a particularly sensitive catalyst layer can be produced, which allows the gas detector to operate already at the ambient temperature The manufacturing process is relatively simple because it is possible to work at relatively low temperatures during the application of the catalyst. The metal does not come off.

  in addition, the metal salt serves as a catalyst.

  According to a preferred embodiment, the gas detector is dried at a temperature below the boiling point. Heating at this temperature lasts until the moisture content of the detector, in particular of the catalyst layer. or

  the gas-sensitive layer has fallen to a certain percentage.

  It is also preferable that the catalyst is deposited on the surface of the gas-sensitive layer. The reaction capacity with respect to the gas to be detected is in this case at its maximum.

  Manufacturing problems are minimized.

  Advantageously, the gas-sensitive layer and / or the electrodes are provided with recesses. It is thus possible to adjust the resistance value of the gas detector to a predetermined value. The gas detector can thus be adapted to the sensitivity of the gas detector.

evaluation devices.

  It is preferable to make the recesses with the help of a laser beam Thanks to the laser beam, very fine structures can be produced, which makes it possible to adjust the resistance value with great precision. It is advantageous for the gas-sensitive layer to have a meandering shape due to the recesses. It is thus possible to obtain a relatively high electrical resistance. The changes in resistance determined by the gas to be detected are thus

  important and can be easily detected.

  Preferably, the recesses are made before the application of the catalyst layer. It is thus ensured that the

  catalyst is not heated beyond the required temperature.

  Preferably, the two electrodes are applied by means of a thick or thin film technique after having cleaned the carrier substrate. Thanks to a thick or thin film technique, it is possible to produce very precise structures. Moreover, it is possible to limit relatively accurate expansion of the electrode space This is particularly advantageous when using for the electrodes

  valuable materials such as gold.

  It is also advantageous for the gas-sensitive layer to be applied by vacuum metallization. Thanks to a process of this type, the thickness of the gas-sensitive layer can be adjusted with great precision. It is thus possible to reproduce the gas detectors with

great precision.

  Advantageously, the gas-sensitive layer consists of a layer of zinc which oxidizes at a temperature in the range of 400 Ω to 5000,, and especially in the range of 4400 to 4600 Il It is easy to apply zinc In the form of a layer, the oxidation can be obtained by heating at a temperature in the range mentioned, and for example at 4500 C. This gives a zinc oxide (Sn Ox) layer which has proved to be extremely good. to be used for gas detection by conductivity modification

electric.

  It is advantageous that platinic acid in aqueous solution (H 2 Pt Cl 6 (6H 2 O)) is used as the catalyst. In this case,

  the sensor is particularly sensitive to ammonia.

  It is then advantageous for the sensor to be dried at a temperature in the range of 700 ° C. to 1150 ° C., and especially in the range of 1050 ° to 1150 ° C. for several hours, and in particular for a period of 20 to 28 hours. allow a particularly careful drying The catalyst can then deploy

  its advantageous effect vis-à-vis the ammonia.

  The invention will now be described in the following with the aid of a preferred embodiment, with reference to the accompanying drawings, in which: FIG. 1 represents a gas detector, and FIG. 2 is a cross-sectional view. of the detector

gas, on a larger scale.

  A gas detector 1 comprises a carrier substrate 2 which may be constituted for example by a ceramic substrate (A 1203) or by an Si substrate with an insulator (nitride or oxide). On the substrate there are two electrodes 3 between the electrodes 3 is deposited by vacuum metallization a layer 4 sensitive to gas It consists of zinc oxide (Sn Ox) On the gas-sensitive layer 4 is disposed a catalyst 5 The gas-sensitive layer 4 is provided with recesses 6 which electrically isolate each of the adjacent sections of the gas-sensitive layer 4, so that the latter has a meandering shape. Similarly, the electrodes 3 may also be provided with recesses, which

are not represented.

  For manufacturing, we first clean the substrate 2.

  Then, two electrodes 3 made of an inert metal such as platinum or gold are applied using a thick or thin film technique, this means that they are applied by pressure and then fired at about 8500 C. Afterwards a new cleaning and a new drying, the substrate 2 which is provided with the electrodes 3 is placed in a vacuum installation The gas-sensitive layer 4 is deposited therein by vacuum metallization, for example by a thin-film technique (metallization reactive) The gas-sensitive layer has an electrical connection with the two electrodes The gas-sensitive layer consists in this case of zinc (Sn) with a thickness of about 100 nn After application of the gas-sensitive layer, the set of the arrangement is heated to about 4500 C, the layer

  Sn is then transformed into a layer of zinc oxide (Sn Ox).

  Then, with the aid of a laser beam, the recesses 6 in the

gas sensitive layer.

  A solution of catalyst or a catalyst mixture which subsequently forms the layer 5 is deposited on the gas-sensitive layer. The sensitivity towards a specific type of gas is thus enhanced. In this case, Platinic acid is used in an aqueous solution (H 2 Pt Cl 6 (6 H 20)) and the gas detector is dried for about 24 hours at a temperature of 1150 C. This temperature is below the boiling point acid

  platinum A detector of this type is particularly selective

  With respect to ammonia, the electrical resistance between the two electrodes 3 increases as the concentration of the ammonia increases.

Claims (9)

  Process for producing a gas detector in which two electrodes and a gas-sensitive layer which connects the two electrodes are deposited on an electrically insulating carrier substrate and to which a catalyst is added, characterized in that it is added as a catalyst (5) a metal salt of the gas-sensitive layer (4) dissolved in water or an alcohol, and heating the detector (1) to a temperature below the boiling point of the metal salt.   Process according to Claim 1, characterized in that the gas detector is dried at a temperature below boiling point.   Process according to Claim 1 or 2, characterized in that the catalyst (5) is deposited on the surface of the sensitive layer gas (4).   Process according to one of Claims 1 to 3, characterized in   the gas-sensitive layer (4) and / or the electrodes (3) are provided with recesses (6).   Process according to claim 4, characterized in that the   recesses (6) are made using a laser beam.   6 Process according to claim 4 or 5, characterized in that the gas-sensitive layer (4) has, thanks to the recesses (6), a meander shape.   Method according to one of Claims 4 to 6, characterized in   the recesses (6) are made before the application of the catalyst layer (5).   Process according to one of Claims 1 to 7, characterized in   that the two electrodes (3) are applied by means of a thick or thin film technique after cleaning the substrate carrier (2).   Process according to one of Claims 1 to 8, characterized in   the gas-sensitive layer (4) is applied by metallization under vacuum.   Process according to one of Claims 1 to 9, characterized in   the gas-sensitive layer (4) consists of a layer of zinc which oxidizes at a temperature in the range of 4000 to 5000 C, and especially in the range of 4400 to 4600 C   Process according to one of Claims 1 to 10, characterized   in that platinic acid in aqueous solution (H 2 Pt C 16 (6H 20)) is used as the catalyst (5). Process according to Claim 11, characterized in that the sensor is dried at a temperature in the range of 700 to 1150 ° C and in particular in the range of 1050 to 1150 ° C for several hours.   hours, and in particular for a period of 20 to 28 hours.