A Sub-mW/Pixel Zero-Bias CMUT-in-CMOS Receiver Front-End with TiN Electrode

In this work, a sub-mW/pixel monolithic zero-bias CMOS-MEMS capacitive micromachined ultrasound transducer (CMUT) receiver front-end is demonstrated based on a titanium nitride composite (TiN-C) structure for low-voltage applications. The fabricated CMUT device exhibits a center frequency of 3 MHz immersed in water while having an operation bandwidth of roughly 90%. The front-end low noise amplifier of each CMUT pixel ($180\times 550\ \mu \mathrm{m}^{2}$) features gain of 25 dB and bandwidth of 14 MHz while only consuming 0.965 mW from a 2.5V supply, showing a great potential for high speed and low power imaging applications. The sensitivity of the proposed CMUT front-end was characterized with 0.4 mV/kPa and 1.4 mV/kPa with DC-bias of 0V (i.e., zero-bias) and 2V, respectively, which is benefitted from the efficient electrostatic transduction offered by TiN-C MEMS platform (transducer gap size < 400 nm) in $0.35\ \mu \mathrm{m}$ CMOS.