ZnO nanoflake based metal-insulator-metal methane sensor for underground coalmine application

In this paper, the detailed methane sensing characteristics of Pd-Ag/ZnO/Ni-alloy based Metal-Insulator-Metal sensor structures on micromachined Si membrane is reported. The advantages of MEMS technology (like low power) have been successfully amalgamated with that of MIM structures (like fast and high response). A nickel alloy (Dilver P1) has been incorporated to fabricate the co-planar microheater and lower electrode of the MIM sensor. Nanoflakes like ZnO layer was deposited by a low temperature chemical deposition technique on the lower electrode and the top electrode was formed by Pd-Ag (70%) catalytic contact. The response magnitude and response/recovery time were studied at five different temperatures (100-220°C) with five different methane concentrations (0.015-1%). The maximum response of ~316% was obtained at 190°C optimum temperature with minimum response time (~18 s) at 1% methane in N₂. The stability of the sensor was also studied.