Ultrasensitive Pd–Ag/ZnO/Nickel Alloy-Based Metal–Insulator-Metal Methane Sensor on Micromachined Silicon Substrate

A novel Pd-Ag/ZnO/Nickel alloy Metal-Insulator-Metal (MIM) sensor on micromachined silicon platform, for efficient methane detection, is reported in this letter. The co-planar microheater and lower electrode of the MIM sensor were fabricated using an alloy (called DilverP1) of nickel. The Ni-alloy was found to offer an Ohmic contact with ZnO sensing layer. Nanostructured ZnO was deposited on lower electrode by a low temperature chemical process and Pd-Ag (70%) was used as the top catalytic electrode to ZnO. A study of the current-voltage characteristics of the MIM structure in pure N₂ with the presence and absence of desired concentration of methane revealed that the device can be used as a low-temperature methane sensor with ultrahigh sensitivity and fast response. The response magnitude and response/recovery time were studied at different temperatures (100, 130, 160, 190, and 220°C) for different methane concentrations. 190°C was found to be the optimum temperature for maximum response of ~316% and minimum time of response of 18 s at 1% methane in N₂.