A micro-machined hydrophone employing a piezoelectric body combined on the gate of a field-effect transistor

We report a micro-machined hydrophone using piezoelectric gate on a field-effect transistor (PiGoFET), where a piezoelectric body is combined directly on the gate of a FET. The PiGoFET transduction mechanism decouples the sensitivity from the dimensions of the piezoelectric body, enabling the miniaturization of hydrophones. Here we exploit the PiGoFET mechanism for hydrophone miniaturization, which is realized via hybrid bonding integration to fabricate a micro-PiGoFET in a CMOS-compatible manner. The hybrid bonding integration employs separate wafers for the piezoelectric MEMS and CMOS processes, which are combined via eutectic wafer bonding to complete the micro-PiGoFET device. A micro-PiGoFET hydrophone was designed, fabricated and characterized with a measured sensitivity of −191.5 dB ± 1 dB (Ref. V/μPa) for frequencies in the range 50-1000 Hz. These results demonstrate the potential for high-performance miniaturized hydrophone systems for wide-band and low-frequency applications, as well as system-on-chip functionality.