Modeling of a Condenser Microphone with Structured Polysilicon Diaphragm

This work deals with the design of a silicon condenser microphone composed of a piston diaphragm stiffened by vertical ribs and a gold backplate perforated by acoustic holes. The microphone is modeled by an equivalent circuit based on a lumped element electromechanical analogy. Mathematical expressions for several interesting features of the microphone, such as the resonant frequency, the pressure sensitivity and the signal-to-noise ratio were derived. The analysis of the model allowed us to choose proper values for the air gap thickness between the electrodes, the area of the diaphragm and its mechanical compliance. The work also involved the development of a finite element model (FEM) of the piston diaphragm. The mechanical behavior of this electrode was investigated by FEM simulations, in an attempt to obtain a piston-like movement as well as the desired spring constant. Finally, we report on the design of the fixed gold electrode, which affects the damping of the diaphragm and, as a result, the frequency response of the microphone.