Study on the MEMS-type gas sensor for detecting a nitrogen oxide gas

Abstract

In this study, MEMS-based micro gas sensors were prepared by adopting MEMS technology and using sol–gel process. These sensors can be used for application of the air quality system monitoring the automobile indoor atmosphere. An array of MEMS-based gas sensors was designed to achieve low power consumption and high efficiency; this was done by adjusting the heater pattern and line width of the microheater. The thermal efficiency and the temperature distribution for a given microheater were estimated using the finite element method (FEM). In order to prepare the material for NO x sensing, W-sol was mixed with Sn-sol, which was prepared separately, and then 1–7 wt.% WO 3 was added to the mixture; this mixture was then deposited on the MEMS platform, and the platform was heated to a temperature between 350 and 700 °C. The topography of the sensing film was studied using an FE-SEM, and it was observed that the particle sizes were approximately 10–20 nm and that they decreased with an increase in the WO 3 content. The XRD patterns showed that SnO 2–WO 3 crystallization occurred above 500 °C. The response of the gas sensor to NO 2 gas was examined at various operating temperatures and gas concentrations. The maximum response of the gas sensor, as measured in terms of the relative resistance (R gas/R air), was 37 at 300 °C for 3-ppm NO 2, and it increased almost linearly with the gas concentration. The results of this study suggest that in the future, MEMS-based gas sensors can be used as automotive-exhaust-gas sensors.