A METHOD OF MANUFACTURING SEMICONDUCTING OXIDE BASED GAS SENSORS IN THICK FILM FORM FOR DETECTION OF COMBUSTIBLE GASES IN PRESENCE OF VOLATILE ORGANIC COMPOUNDS

摘要

In the present invention there is provided a method of manufacturing semiconducting oxide, such as tin dioxide, zinc oxide, based gas sensors in thick film form for detection of combustible gases, like methane, LPG, propane, CNG, in presence of highly reactive volatile organic compounds, which may emanate from sources such as domestic, industrial and automobile exhaust. The gas sensor is a double coated (bi-layer) sensor, wherein the top coating is essentially having an electrical resistance at least two orders of magnitude higher than that of the bottom coating. The bottom and top semiconducting oxide based coating compositions used are functionally graded tin dioxide based compositions. The composition of the top protective coating is different from that of the bottom gas sensing coating so that volatile organic compounds are preferentially reacted at the top layer and the detecting gases are reacted at the bottom layer. The top layer having an electrical resistance at least two orders of magnitude higher than that of the bottom layer makes the top layer remain electrically shunted from the bottom gas sensing layer. Thus the problem of volatile organic compounds (VOC) cross-sensitivity with the detecting gases is effectively overcome. The bi-layer sensors are highly sensitive towards detecting gases whereas their sensitivity is quite low towards highly reactive volatile organic compounds. Thus such sensors are capable of selectively detecting combustible gases even in the presence of highly reactive volatile organic compounds. The process steps for the manufacture of such sensors are also simple and cost-effective.