Sensing characterization of the MOS micro gas sensor array on gas mixture

Metal oxide semiconductor (MOS) gas sensors are very attractive owing to their low cost simplicity of use, large number of detectable gases and various potential application fields. However, the MOS gas sensor has a serious shortcoming of low selectivity in a mixture of gases. In this study, MOS micro gas sensors were fabricated for detecting carbon monoxide (CO), nitrogen oxide (NO2), ammonia (NH3) and formaldehyde (HCHO) gases, as well as their binary mixed gas systems. Four sensing materials, Pd-SnO2 for CO, In2O3 for NOX, Ru-WO3 for NH3, and SnO2-ZnO for HCHO were synthesized using a sol-gel method and deposited in the middle of sensor platform. The micro gas sensor platform was fabricated by using a MEMS technology. The sensing electrode and micro heater were designed to be a co-planar type structure with the Pt thin film layer. The gas sensitivity and sensing behaviors for gas mixture suggested that the selective adsorption of one gas with respect to others occurred for gas mixture and resulted in good selectivity for a particular gas species. Furthermore, the careful pattern recognition of sensing data obtained with sensor array makes it possible to distinguish a gas species from gas mixture and to measure its concentration.