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A micro-machined hydrophone using piezoelectricity on gate of a field-effect transistor

This paper presents the design and fabrication of a miniaturized hydrophone made by applying the electric field of a micro-sized piezoelectric body directly on the gate of a field-effect transistor (FET). Changes in the bound surface charge density of the piezoelectric body and the corresponding changes in the electric field in response to the applied pressure affect the channel current of a FET regardless of its size. The proposed transduction overcomes the sensitivity limitations of a micro-sized piezoelectric body for various underwater applications, especially at low frequencies. A complementary metal oxide semiconductor (CMOS)-integrated underwater sensor system can also be realized by using the proposed CMOS-compatible fabrication.