1Center for Nanosale Science and Technology, Stanford University, Stanford CA, USA
The capacitive micromachined ultrasonic transducer (CMUT), in its present most widely used configuration, was first presented at the IEEE International Ultrasonic Symposium in 1994. The last 17 years have seen international adoption of the device and technology, and have seen the realization of CMUT as a platform technology. This presentation will start with a brief introduction of the CMUT and its merits in comparison to other ultrasound transducers. This will be followed by a summary of the various activities necessary to realize devices: theory (analytic solution, finite element modeling); technology (sacrificial release, direct bonding); modes of operation (conventional, pull-in, permanent pull-in); electronic integration (CMUT on ASIC, flip-chip on ASIC, interposer); packaging (backing, focusing lens); and system integration. Finally, we present a number of examples of using CMUTs in airborne ultrasound applications such as gas flow (pressure up to 20 atm, and temperature up to 1000 C), non-destructive testing, gravimetric sensing (50 MHz); and immersion application such as medical imaging with ring array catheters, 2-D array for 3-D volumetric imaging, photoacoustic imaging, and high intensity focused ultrasound therapy.