SURFACE-MORPHOLOGY AND GAS-SENSING CHARACTERISTICS OF SNO2-X THIN-FILMS OXIDIZED FROM SN FILMS

SnO2-x gas sensors have been fabricated by thermal oxidation of Sn thi n films. Sn thin films approximately 15000 Angstrom thick for commerci al applications are deposited on a polished alumina substrate by using a high-vacuum resistance-heating evaporator. These films are oxidized at 500 degrees C in various oxygen partial pressures in order to cont rol the x value in SnO2-x. The surface morphology and quantitative com positional analysis of SnO2-x thin films as functions of oxygen partia l pressures are systematically investigated by SEM, RES and XPS. Gas s ensitivities and response times of Pd-doped SnO2-x thin films to H-2, CO, C3H8 and i-C4H10 gases are measured at 300 degrees C. The relation ship between gas sensitivities and the x value in SnO2-x thin films is discussed.