Depletion‐mediated piezoelectric AlGaN/GaN resonators

The electromechanical properties of an acoustic wave propagating in a piezoelectric media can be tuned by modulation of the resistivity of the piezoelectric material. This is readily available in piezoelectric semiconductor materials, wherein acoustic phonons and charge carriers can interact. In this work, we employ epitaxially grown AlGaN/GaN heterostructures in bulk acoustic wave resonators with Schottky interdigitated transducers biased in the depletion region to study the interaction between piezoelectric strain and depletion charges. By modulating the impedance of the depletion layer upon application of DC voltages, we tune the acoustic properties of bulk‐mode resonators and show significant Q enhancement as the result of a depletion force added to the piezoelectric actuation force. Furthermore, we compare the performance of such resonators with pure GaN piezoelectric resonators that have the same geometry but with the AlGaN layer removed. When integrated with AlGaN/GaN HEMTs (located on the acoustic cavity or next to the resonator), such resonators can be used as frequency references in oscillator circuits in radio frequency (RF) blocks or utilized in harsh environment sensing applications.