| Summary: | 碩士 === 國立成功大學 === 化學工程學系碩博士班 === 90 === Abstract
The gas sensors consist of a thin film deposited on an electrical insulated substrate, which is sensitive to some gases. Because of the interaction of adsorbed gas with sensor, the sensor electrical properties change, and the change can be detected.
In the study, the ZnO and In2O3 thin films doped with precious metal were prepared by vacuum deposition of a thin film of zinc and indium on Al2O3 substrate followed with thermal annealing and oxidation. The sensitivity, response time, and recovery time for ethanol and CO were measured and the surface morphology is examined by SEM. The sensors were prepared at different rate of deposition, using different atomic ratio, and are oxidized under controlled condition. The effects of operation temperature on the sensitivity were measured and compared with theory. The effects of inner and surface doping of precious metal, manufacturing condition, and compositions on morphology and sensitivity were examined too.
The experimental results show that (1) the underlying mechanisms of the sensitivity probably include Schottky contact and the reactions of sensitive gases with the adsorbed oxygen ion and lattice oxygen, (2) the sensor has a higher sensitivity to ethanol than CO, (3) the sensor has a optimum sensitivity at 3450C and 5000C for ethanol and CO, respectively, (4) larger clusters are produced at higher deposition rate, (5) surface morphology and sensitivity change with atomic ratio, with the best sensitivity at an atomic ratio of Zn to In of 1/1.266 and 1/0.114 for ethanol and CO, respectively, (6) oxidation at higher rate results in a whisker structure on the oxide film, (7) inner doping leads to a decrease in sensitivity, and surface doping leads to an obvious decrease in sensitivity for ethanol and a decrease in recovery time.
Keyword：gas sensor、zinc、indium、thin film、doping
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