Novel MEMS microshell transducer arrays for high-resolution underwater acoustic imaging applications

Presents the design, fabrication process and experimental acoustic test data for a novel MEMS-based 2-D ferroelectric ultrasound microshell transducer array. A new 3-D-micromachining technique is used to fabricate a MEMS microshell structure that acts as an ultrasound transducer in the 1-5 MHz range. A rounded sacrificial carbon structure generated by a two-step photo-resist reflow and pyrolysis process provides the shape for the microshell. The variation of process parameters and their affect on the microshell shape are. discussed The piezoelectric monomorph layer is composed of a sol-gel PZT as the active ferroelectric layer deposited on insulating layers of ZrO₂ and SiN or SiO₂. A novel in-plane polarization of the PZT is used to maximize sensitivity, while trading off output capacitance to match the CMOS buffer electronics that are required for an arrayed imaging device. Polyimide layers are used to electrically isolate the device from the fluid test environment. Finite element analysis was used to generate expressions describing resonant frequency, volume compliance and receive sensitivity.