| Gas sensors prepared by tin oxide material have been widely used in many fields, because of its advantages, such as high sensitivity, long working life, good stability, strong corrosion resistance, simple structure, low cost, good mechanical property, directly putting out electric signals and so on. With the development of gas sensor market demands, in addition to the further development of the gas sensing performance of the sensor, sensor miniaturization and integration are also very necessary. In order to facilitate the miniaturization and integration of gas sensors, thin film gas sensors are the focus of the study. This paper is based on nano tin oxide thin film. Two methods, including doping and changing the film structure have been used to enhance its gas sensing properties. The main research contents and results are as follows:Nano tin oxide thin film has been prepared with sol-gel dip-coating method by using tin dichloride as precursor. The obtained thin film was formed by tin oxide grains with a tetragonal rutile structure, and the average particle size was 25.9 nm. The obtained thin film was continuous on alumina substrate, only a small amount of cracks and holes existed. The H2S sensing performances of obtained nano tin oxide thin film were systematically studied. It was found that the sensitivity of nano tin oxide thin film increased nonlinearly with increasing of the concentration of H2S gas, and with the increase in operating temperature, the sensitivity increased at first and then decreased, and the best operating temperature was 100℃.In order to further enhance the sensitivity and reduce the operating temperature of the nano tix oxide thin film, three kinds of P-type metal oxides CuO, NiO, and of Bi2O3 were doped. The results showed that the sensitivity of nano tix oxide thin film to H2S gas was greatly improved when only doping 1 at% Cu2+,Ni2+,Bi3+, and the optimum operating temperature was decreased from 100℃to 75℃. The sensitivity of nano thin film gas sensor to hydrogen sulfide could be affected by the doping amount of P-type metal oxides. Overall, the nano thin oxide thin film doped with 2 at% CuO had the highest sensitivity 1220 to 68.5 ppm H2S when working at 75℃. By doping with P-type metal oxides; although the gas sensitivity of nano thin oxide thin film was greatly enhanced and the optimal operating temperature was decreased, the recovery characteristics of the gas sensing film were not improved. Many studies have shown that gas sensors with porous structure have shorter response and recovery time. So carbonaceous polysaccharide microspheres were used as pore-forming agent to prepare macroporous nano tin oxide thin film. Compared with ordinary nano tin oxide thin film gas sensor, macroporous nano tin oxide gas sensor had slightly higher sensitivity, slightly reduced response time and greatly improved recovery time.Based on the working mechanism of tin oxide gas sensor, the test results of nano tin oxide thin film to hydrogen sulfide were explained in theory. The reason of that nano thin film gas sensor had an optimum operating temperature, was explained by the change of oxygen adsorption capacity on nano tin oxide thin film surface with temperature. Based on the reactions between oxygen adsorbed on nano tin oxide thin film surface and hydrogen sulfide, it was obtained that the sensitivity of nano thin film gas sensor was proportional to hydrogen sulfide gas concentration of 1/2 power.
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