Resonant microcantilever type chemical sensors: analytical modeling in view of optimization

Silicon microcantilevers can be used as microbalances or chemical microsensors if a sensitive layer is deposited on the moving structures. Indeed, the sorption of specific species by the sensitive coating modifies the mechanical properties of the structure and then its fundamental natural frequency. In this paper, analytical expressions of the sensitivities of different structures are obtained in view of optimization of the geometrical parameters for both mass sensors or concentration gas sensors. For chemical sensors, a thin parallelepiped microcantilever with sensitive coating on the whole structure gives good performances especially regarding the sensibility. However, the frequency measurement and the active surface can be improved with a rectangular plate at the free-end of the microcantilever with little influence on the sensitivities.