Low Temperature Fabrication of a Highly Sensitive Methane Sensor with Embedded Co-Planar Nickel Alloy Microheater on MEMS Platform

In this paper, design and fabrication of MEMS based methane sensor with co-planar Nickel alloy micro heater is reported for the first time. With heater and electrodes on the same layer, less number of processing steps during fabrication was achieved. On the other hand, deposition of nano-ZnO sensing layer by a low temperature chemical deposition' technique offered circumvention of difficulties like micro-crack generation and reduced lifetime of MEMS sensor, principally originated from the high temperature processing steps like annealing of sensing layer. Thin film of zinc oxide (ZnO) having nano-needle like structure, was deposited onto coplanar heater/electrode structure using a simple and inexpensive chemical deposition technique using sodium zincate solution (0.125 M) by drop coating method and was annealed at only 150 degrees C. The fabricated sensor was tested for five different methane concentration (e.g., 0.01, 0.05, 0.1, 0.5 and 1.0%) in the temperature range of 150 degrees C-300 degrees C with N-2 as the carrier gas. The response magnitude, response time and recovery time were studied in detail. The sensor showed similar to 97% response at an optimum operating temperature of 250 degrees C with only 19 sec response time. Moreover the sensor offered appreciable response at much lower temperature (150 degrees C) range also. The short-term stability of the microheater and sensor was found to be quite promising.