Characterization and Modeling of an AlN Piezoelectric Fly-Inspired In-Plane Directional MEMS Microphone Packaged With an Integrated Circuit Amplifier

The remarkable directional hearing capabilities of the fly Ormia ochracea have inspired advancements in acoustic sensing technologies. Despite the small size of the fly’s ear relative to the wavelength of audible sound, it can precisely locate crickets by detecting their chirps. This article presents the design, fabrication, testing, andmodeling of a biologically inspired MEMS microphone that leverages the fly’s unique hearing mechanism. The device consists of a two-sided cantilever beam that rotates about torsional pivots, producing two primary vibration modes: (1) a rocking mode, which responds to pressure gradients with out-of-phase motion for sound localization, and (2) a bending mode, which reacts to omnidirectional sound pressure with in-phase motion. The microphone is fabricated using a silicon-on-insulator wafer with a 2-μm-thick device layer and incorporates a 500-nm-thick aluminum nitride piezoelectric film for transduction. Multipoint scans validate the sensing modes, which are accurately modeled using finite element analysis. Signal readout is achieved through an integrated circuit amplifier with high bias resistance. Acoustic measurements in air are performed across audible and ultrasonic frequencies, with sensitivity results compared to simulations. The initial prototypes demonstrate optimal performance at ultrasonic frequencies near 20 kHz. Simulations further explore potential designs for broadband applications spanning the audio frequency range of 20 Hz to 20 kHz.