Performance Improvement of Pd/ZnO-NR/Si MIS Gas Sensor Device in Capacitive Mode: Correlation With Equivalent-Circuit Elements

Abstract

Highly sensitive ethanol sensing performance of Pd/ZnO nanorods (NRs)/Si MIS device in the capacitive mode is reported in this paper. The MIS device with palladium as the top electrode and silicon as the substrate (bottom) employed ZnO-NRs as the semi-insulating sensing layer. The capacitive changes in the MIS device with exposure to ethanol vapor were measured as a function of temperatures, and 275 °C was found to be the temperature, where response is the fastest. In the capacitive mode, the response magnitude ( $\sim 7200$ % at 700-ppm ethanol) was found to be improved dramatically compared with that obtained by the conventional dc resistance measurement technique ( $\sim 45$ %). The underlying mechanism for such a significant improvement has been correlated with the corresponding change in the equivalent-circuit elements, considering the effective change in the dielectric constant of the sensing layer (consisting of ZnO-NR array, ZnO seed layer and voids) in air and in gaseous medium.