A micro-machined hydrophone based on piezoelectric-gate-of-field-effect-transistor for low frequency sounds detection

Abstract

The miniaturization of conventional piezoelectric hydrophone is known to have limits in low frequencies due to high sensor impedance of micro-sized piezoelectric body. In this study, a new transduction mechanism is devised and named as piezoelectric gate of field effect transistor (PiGoFET) so that its application could solve the sensitivity limitation of a miniaturized hydrophone with a tiny piezoelectric body less than 1 mm. The PiGoFET transduction can be realized by combination of a field effect transistor and a small piezoelectric body on its gate. We connect a micro-machined membrane to the small piezoelectric body so that acoustic pressure can apply appropriate forces on the body on the FET gate. The electric field from the strained piezoelectric body modulates the channel current of FET at any frequency less than high limit of transistor; thus, the sound pressure may be transferred to the source-drain currents even at very low frequencies irrespective of the size of piezoelectric body. Under the described concept, a small hydrophone was fabricated by micromachining and calibrated using the comparison method in low frequencies to investigate its performance as a low frequency sensitive hydrophone. [Research funded by MRCnD.]