188+188 Row–Column Addressed CMUT Transducer for Super Resolution Imaging

A capacitive micromachined ultrasonic transducer (CMUT), 8 MHz resonance frequency, λ/2 cell pitch 188+188 row-column addressed (RCA) array for super resolution imaging is presented. The top- and bottom electrode design features a zig-zag shaped pattern to increase the active cell area for fixed plate thicknesses. The RCA CMUT has been fabricated utilising a deposit, remove, etch, multistep (DREM) process to fully separate the bottom electrodes electrically as well as anodic bonding the array to an insulating borosilicate glass wafer. Linear test elements have been characterized. Electrical measurements show a center frequency of approximately 5.5 MHz and a coupling coefficient of 7.8% for -80 V DC bias and 50 mV AC. Acoustic measurements made in immersion with a single cycle 4 MHz pulse with a -90 V DC bias demonstrate that the fabricated CMUT arrays can emit broadband ultrasound pulses.