A Quadrilateral Gas Sensor Cell by Complete MEMS Process for Gas Identification

This article reports for the first time a quadrilateral microelectromechanical sensor (MEMS) metal oxide (MOx) gas sensor cell with four different sensitive materials based on complete semiconductor process. In order to improve the strength, symmetry of temperature distribution, and thermal stability of the structure, the design path of the Pt heater extends to the substrate along the four supporting beams, so that the joule heat generated and heat conduction in the core area are symmetrical. Four pairs of detection electrodes and microheater are designed on the same layer and arranged in parallel; thus, the process steps are simplified and the overlapping and stacking of metals can be avoided. Each pair of detection electrodes corresponds to a type of patterned sensing material film. The sensor cell was fabricated using typical 4 in MEMS process, and four kinds of sensing materials (SnO2/Au, SnO2, In2O3/Au, and ZnO/Au) were completed by four times of sputtering process and patterned through UV lithography and lift-off, realizing the semiconductor process of the entire sensor cell. Five gases (ethanol, ethyl acetate, trimethylamine, ammonia, and hydrogen sulfide) were tested to verify the performance of the sensor cell, and the results show that the sensor cell has differential responses to the test gases. Furthermore, the k-nearest neighbor (KNN) pattern algorithm is used to distinguish the five gases with an accuracy of 99.33%. The sensor cell is promising in gas identification applications.