Aluminum Nitride Ultrasonic Air-Coupled Actuator

A piezoelectric micromachined ultrasonic radiator was developed using aluminum nitride (AlN) for air-coupled applications. A commercially proven CMOS-compatible fabrication process was leveraged to form the devices. The transducer design consists of a radially nonuniform circular composite diaphragm with an integrated layer of AlN between two annular electrodes. Included in the overall system design is a tunable package with back cavity depth control. A multiphysics model was developed that integrates the electrical, mechanical, and acoustic energy domains of the complete system using composite plate mechanics, lumped-element modeling, and linear acoustic theory. Acoustical, mechanical, and electrical characterization of the transducers was conducted, including acoustic far field, laser vibrometry, and electrical impedance measurements. The device characterization results showed poor quantitative match with the system-level model due to large uncertainties in film stress. However, a qualitative comparison between the device behavior and the system model with varying back cavity depth showed promising results. The overall device performance is comparable to those in previous works that utilized alternate piezoelectric films.