Research Of A New Type Gas Sensor Based On Micromachined Al₂O₃ Substrate And SnO₂ Sensing Materials

The project of this thesis involves gas sensor and its applications, which is from S863 program. All research of this thesis was cooperatively carrying out with the 49th Institute of China Electronic group Co.This thesis describes fabrication processes of two kinds of SnO2 gas sensors. They are deep-film side heating gas sensor and microstructure gas sensor array based on micromachined Al2O3 substrate plate. Sensitivity of the sensors to CO and some other disturbing gases is also experimentally and theoretical analyzed in this thesis.In general, integrated gas sensors utilize poly silicon as microheater. It is practically found that poly silicon heater is in general not stable after it operates at temperature of 260℃-350℃ for a long time. Therefore, NiCr alloy of low temperature coefficient and Au were experimentally investigated for a new heater. Then an integrated array was fabricated with combining the heater and micromachined Al2O3 substrate, by which test two sorts of gases can be detected simultaneously. A series of pulse with different amplitude and width were used to modulating the operation temperature of the sensors. The results showed that the sensors have advantages of low power consumption, higher sensitivity, multiple functions, and better shock resistance. This kind of special structure has reported the national invention patent.This thesis makes new attempt to further enhance the selective of SnO2 gas sensors by s inheriting the traditional merit of SnO2 sensitive material. In material preparation, SnO2 powder was firstly deposited by chemistry method, then some different heavy metals or oxide compound were used as additives to prepare five kinds of gas sensing materials. These sensing materials were evaluated by side heating structure. The result indicated that these SnO2 gas sensors have better enough sensitivity and speed of response, and low production cost. The optimum sensing material then was chosen by checking all the materials' response to CO and some interference gases.In new sensor development aspect, this thesis combines prepared SnO2 sensitive material with a new sort of Al2O3 substrate that can be processed with micromachining. The whole fabrication process of the new type gas sensor joint of micromachining for substrate and routine process of microelectronic for electrodes was studied and a batch of preliminary samples sensor array was manufactured successfully.