Piston-Shaped CMOS-MEMS CMUT Front-End Featuring Force-Displacement Transduction Enhancement

This work presents a novel capacitive micromachined ultrasonic transducer (CMUT) receiver front-end with optimized force-displacement relation in CMOS-MEMS platform. In this work, the proposed piston-shaped CMUT is composed of a deformable silicon nitride membrane (Si 3 N 4 ), a suspended electrode, and a cross-shaped neck structure in between. By optimizing the electrode dimension, improved displacement uniformity is achieved for transduction efficiency enhancement. The proposed CMUT front-end is designed and fabricated in standard CMOS process along with a low-power and low-noise interface sensing circuit. The device is characterized in vegetable oil with the integrated amplifier under 5V of dc-bias, showing its center frequency of 2.14 MHz, 6-dB fractional bandwidth of 76%, and sensitivity of 9.6 mV/kPa, respectively. Compared with the conventional CMUT design on the same chip with the same device capacitance, the sensitivity of the piston-shaped CMUT design is enhanced by 1.7 times.