Development of ScAlN PMUTs for Medical Applications

In this paper, the design, fabrication and characterization of PMUTs for medical applications are discussed. Scandium (20% Sc/(Sc+Al)) doped AlN is used as the piezoelectric material. The fabrication process for PMUTs with a patterned piezoelectric layer is developed. Single-cell and linear arrays of PMUT are fabricated and electrical, mechanical and acoustic characterization is carried out. The piezo-patterning improved the performance of PMUTs. The fabricated PMUT showed excellent chip-wafer level uniformity and yield. At resonance (5.7 MHz), the ScAlN PMUT array showed transmit sensitivity of 13 kPa/V and receive sensitivity of 1.1 V/MPa. The good transmit-receive properties and the ability to operate without bias voltage make the ScAlN PMUTs best for voltage-limited medical applications.