Abstract
This study introduces a novel 1-D CMOS-MEMS capacitive micromachined ultrasonic transducer (CMUT) array, featuring dual transduction gaps (180 nm and 400 nm) on a standard CMOS platform. The design prioritizes excellent transceiving efficiency at low DC bias voltages, despite a slight reduction in maximum output pressure capability. Detailed fabrication processes and functionality tests validate the performance of the proposed CMUT on CMOS. Experimental results indicate a high electromechanical coupling strength and superior ultrasonic transmitting efficiency of 16.7 kPa/V/mm2, alongside a receiving sensitivity of 57 mV/kPa in underwater acoustic tests. The dual-gap device's efficiency was further confirmed in self-Tx-Rx experiments. Integration with a monolithic amplifier results in an impressive noise efficiency factor (NEF) of 0.39 mPav’(mW/Hz), outperforming existing technologies. These findings underscore the potential of the dual-gap CMUT on CMOS for advanced ultrasonic applications.