A hydrophone based on the piezoelectric gate of field effect transistor for deep‐sea application in low‐frequency range. Free

A hydrophone based on the piezoelectric gate of field effect transistor(FET) for deep‐sea application in the low‐frequency range (10 Hz–20 kHz) was designed. The basic structure was piezoelectric thickness mode, which was directly applied on the gate area of a field effect transistor. Several types of sensors which used PVDF film integrated with FET have been reported. They have sensitivity limit in the low‐frequency range due to stray capacitance by extended electrodes and low coupling coefficient of PVDF film. To achieve high sensitivity, a piezoelectric ceramic was directly applied to the gate area of the FET, which resulted in decreased effect of stray capacitance. Depletion mode FET with large gate area was adopted to realize high transconductance in the operation voltage range of the piezoelectric ceramic. The head mass structure, which was motivated by the Tonpilz structure, for both sound pressure amplification and prestress was placed between the clamped diaphragm and the piezoelectric ceramic. To develop the endurance for the high hydrostatic pressure in deep‐sea, oil backing on the backside of the diaphragm was proposed. The parametric study based on the traditional FET model was performed in the design procedure. The comparison of simulation and experiment will be presented. [Research supported by MRCnd.]