A CMOS-MEMS Ultrasonic Transceiver With Bipolar-Biased Differential CMUT Transducers

In this work, a capacitive micromachined ultrasonic transducer (CMUT) transceiver prototype, comprising independent transmitter (TX) and receiver (RX) channels, is designed and characterized using a standard CMOS platform. For the RX, a fully differential integrator-differentiator transimpedance amplifier (ID-TIA) with inherent time-gain compensation (TGC) functionality is vertically integrated beneath the bipolar-biased differential CMUT structure, with sub-mW power consumption. The CMUT elements are implemented using a titanium nitride composite (TiN-C) CMOS-MEMS process to achieve a transduction gap of 400 nm, aiming for high electrostatic transduction efficiency. The proposed CMUT RX occupies an area of 0.11 mm² per channel and features a center frequency of 5.2 MHz, a 3 dB/6 dB fractional bandwidth (FBW) of 68% and 93%, respectively, and can operate under a DC bias from 5 V to 60 V. Furthermore, the CMUT TX and RX functionalities are characterized via burst-echo self-test. The proposed CMOS-MEMS CMUT chip is implemented using the TSMC 0.18 μm standard CMOS process.