Design optimization of a microelectromechanical piezoresisitive microphone for use in aeroacoustic measurements Free

A microelectromechanical systems (MEMS)‐based piezoresistive microphone optimimum design is presented, with a focus on improving the minimum detectable pressure over many current technologies without sacrificing bandwidth. This microphone design addresses many of the problems associated with previous piezoresistive microphones. Here, a novel nonlinear circular composite plate mechanic model was employed to determine the stresses in the diaphragm, which was designed to be in the compressive quasibuckled state. With this model, the inherent in‐plane stresses that occur in the microelectronic fabrication process can be used to increase the sensitivity of the device. Ion‐implanted doped silicon was chosen for the piezoresistors and a fabrication recipe was made which minimizes the inherent noise characteristics of the material. The piezoresistors are arranged in a Wheatstone bridge configuration with two resistors oriented for tangential current flow and two for radial current flow. A lumped element model was created to describe the dynamic characteristics of the microphone diaphragm and the cavity/vent structure. The geometry for this device was optimized using a sequential quadratic programming scheme performed using the aforementioned novel device characteristics. Results indicate a dynamic range in excess of 120 dB for devices possessing resonant frequencies beyond 120 kHz.