Gas response of reactively sputtered ZnO films on Si-based micro-array

ZnO thin film micro-arrays with integrated heaters were fabricated onto silicon wafers. The atmosphere-dependent electrical response of ZnO films sputtered under controlled Ar/O2 ratios onto micro-arrays was examined in response to the following gases: CO, H2, and NO2. The influence of processing conditions on the physical and electrical properties of ZnO films was investigated. The deposition conditions were found to control film morphology, while subsequent annealing at 700 °C in air had only minor effects on the microstructure. ZnO films prepared with high O2/Ar ratios during sputtering show better sensitivity to H2, NO2 and CO with sensitivity to NO2 particularly high at low temperatures. The ac impedance measurements were used to identify the two major components of the total sensor resistance including Schottky barriers at the Pt–ZnO interfaces and a dc bias-induced constriction resistance within the ZnO film. Changes induced in the impedance spectra due to dc bias pre-treatments are hypothesized to result from field-induced modifications in gas coverage of the sensor films.