Micromachined In-Plane Pressure-Gradient Piezoelectric Microphones

This paper presents the fabrication, modeling, and characterization of a micromachined piezoelectric directional microphone. The microphone structure consists of a 20-μm-thick semirigid beam structure that rotates about torsional pivots in response to in-plane pressure gradients across the length of the beam. The motion of the beam structure is transduced by piezoelectric cantilevers, which deflect when the structure rotates. While the structure has been introduced in prior publications, this is the first paper summarizing rigorous acoustic characterization of first generation prototypes. An analytical model and multimode, multiport network model utilizing finite-element analysis for parameter extraction are presented and compared with acoustic sensitivity measurements. Directivity measurements are interpreted in terms of the multimode model. A noise model for the sensor and readout electronics is presented and compared with measurements.