A micro-machined hydrophone using the piezoelectric-gate-of-field-effect-transistor for low frequency sounds

The micro-sized piezoelectric body for the miniaturized hydrophone is known to have the limits in low frequencies due to its high impedance and low sensitivity. In this study, a new transduction mechanism named as PiGoFET (piezoelectric gate of field effect transistor) is devised so that its application for the miniaturized hydrophone could overcome the limits of the micro-sized piezoelectric body. The PiGoFET transduction can be realized by combining a field effect transistor and a small piezoelectric body on its gate. A micro-machined silicon membrane of 2 mm diameter was connected 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 deformed piezoelectric body modulates the channel current of FET directly, thus the transduction makes the sound pressure transferred to the source–drain current effectively at very low frequencies with micro-sized piezoelectric body. Under the described concept, a hydrophone was fabricated by micro-machining and calibrated using the comparison method in low frequencies to investigate its performance. [Research funded by MRCnD.]