Study On A New MEMS Gas Sensor

Today the techniques of Microelectromechanical System (MEMS) have been developed rapidly due to microelectronical techniques. MEMS gas sensors have been becoming the main part of gas sensors. There are many advantages when MEMS techniques are use to design gas sensor, such as less bulk, power and cost, higher sensitivity, easier produced in large scale, steady-going processes, and so on. Also, it is significant of MEMS techniques for gas sensor to be integrated and intelligentized, and to improve selectivity and reliability.A new MEMS gas sensor is proposed based on the piezoresistive effect, which is composed of a silicon membrane embedded with a piezoresistive Wheatstone bridge, and a gas-sensitive polymer layer. The gas induced volume change of the gas-sensitive leads to a deformation of the silicon membrane. The bending stresses will be transformed into an output voltage by the piezoresistive Wheatstone bridge.Meanwhile, a theoretical model of the interaction between the silicon membrane and the polymer layer is presented based on elastic mechanics theory. The bending differential eguation about partly-covered double layer film is founded. The coefficient of flexural stiffness is modified, and an equivalent transverse gas load q_g is achieved .Finally an output expression of the gas sensor is proposed.After those above, analysises about the structural parameters are presented based on the theoretical model above. Besides, simple designs about the gas sensor are presented including structural parameters and manufactural processes. Theoretically, the output of the gas sensor is linear and there are some other advantages, such as simple structure, without heating elements, can be integrated with signal processing circuit using the MEMS (Microelectromechanical System) processes.