Fast response methane sensor based on Pd(Ag)/ZnO/Zn MIM structure

Metallic Zinc was deposited on thermally grown SiO2 (0.5/mu m thick) on p-Si (100) substrate. Nanocrystalline ZnO was deposited by sol-gel technique on Zn to form the active insulator of metalactive insulator-metal (MIM) structure. Pd-Ag (26%) metal contacts were deposited on ZnO to form other electrode of MIM structure. The I-V characteristics were studied at different temperatures in air and in presence of three different concentrations (0.1%, 0.5%, and 1%) of methane gas. A shift in I-V characteristics in presence of methane was observed. The sensitivity and response time were studied at different temperatures (50, 150, 200, 250, and 300 degrees C). 250 degrees C was found to be optimum temperature for maximum sensitivity of 88.6 +/- 2% and minimum time of response of 11.4 s +/- 0.5 s. The stability of the sensor structure at 250 degrees C was studied for about 21 hours in a span of three days with intermittent opening of 0.1% methane gas and the MIM sensor was found to be very stable.