Fabrication And Performances Of Thin-film Tin-oxide-based Gas Sensing Materials And Devices

In order to improve the performance of Tin Oxide (SnO₂) gas sensors, devices of Ag-doped SnO₂ thin films were fabricated in a planar structure, utilizing both spin-coating and sol-gel techniques. So far to our best knowledge such devices have rarely been reported.The work described in this thesis contains the following experiments:1) Planar Al2O3 substrates with Pt heater and working electrodes were prepared and used in the experiments.2) By Sol-Gel methods Sb-doped SnO₂ thin films were prepared on Al2O3 substrates. The effect of Sb concentration on device performance (overall conductivity and gas sensitivity) was studied. The results demonstrated that the conductivity of the undoped SnO₂ films was low, and then increased with increasing amount of Sb additives, before it saturated and its value dropped with excessive amount of Sb added. Devices with 1wt% of Sb showed good sensitivity to ethanol.3) SnO₂ thin films with Ag-Sb co doping were prepared by liquid-phase doping of AgNO3 in the Sb-doped samples. The concentration of Sb-Ag additives and the sintering temperature were studied and optimized for better gas sensitivity. The results indicated the following optimal parameters: Ag and Sb concentration were 0.5wt% and 1at%, respectively, and 600℃as the best sintering temperature. The sensors were found to be excellent for alcohol detection through selectivity experiment.4) Different amount of Pt were deposited by means of sputtering to study its effect on the thin films. Results indicated that Pt can help to reduce the size of the grains, which is preferable to obtain better gas sensitivity. We found the optimal process for Pt doping to achieve both high sensitivity and fast response/recovery in the presence of low-density ethanol vapor. The samples also showed good selectivity to ethanol.5) Finally, the dependence of sample properties on the fabrication process, such as the grain resistance, the grain-boundary resistance and the capacity barrier etc., were analyzed utilizing the Complex-Impedance Spectra and in the framework of surface-adsorption theory. We also discussed the self-heating phenomenon that's revealed in the I-V characteristics of the devices...