Coupled piezoelectric micromachined ultrasonic transducers with improved pulse-echo performance

This paper presents a novel piezoelectric micromachined ultrasonic transducer (PMUT) based on mechanical coupling between a center circular resonator and an outer annular membrane. Compared to traditional circular membrane PMUTs, the design has the advantages that (1) it allows the PMUT diameter to be matched to the acoustic wavelength (λ=190μm at 8MHz) to enable high fill-factor arrays and (2) it achieves much higher TX/RX sensitivity due to mechanical amplification of the input piezoelectric force. The measured displacement is a factor of two greater than a conventional PMUT operating at the same frequency. Pulse echo measurements show a 1.9x and 6.5x increase in transmitting and receiving sensitivity at 6MHz and 8MHz when compared to a conventional PMUT array spanning the same area.