Diamond-based capacitive micromachined ultrasonic transducers

Abstract Capacitive micromachined ultrasonic transducers (CMUTs) employing diamond membranes are demonstrated. The design, finite element modeling, microfabrication, and experimental characterization of diamond-based CMUTs are reported. Ultrananocrystalline diamond having a chemical mechanical polished silicon dioxide interlayer deposited via high temperature oxide (HTO) process at 850 °C in a low pressure chemical vapor deposition (LPCVD) furnace is employed as the membrane to form vacuum sealed cavities using plasma-activated direct bonding technology. Electrical impedance, deflection, and transmission measurements of a fabricated CMUT are performed in air using an impedance analyzer, a white light interferometer and a hydrophone, respectively. Experimental results verify the accuracy of finite element modeling. Diamond-based CMUTs possess 3-dB fractional bandwidth of 3% at a center frequency of 1.74 MHz in air. Our experimental results demonstrate diamond as an alternate membrane material for CMUTs, and that diamond can be employed in novel microelectromechanical devices.