Collapsed Regime Operation of Capacitive Micromachined Ultrasonic Transducers based on Wafer-Bonding Technique

We report experimental results from collapsed regime operation of capacitive micromachined ultrasonic transducers (cMUTs) fabricated by a wafer bonding technique. The results show that a cMUT operating in the collapsed regime produces a maximal output pressure higher than a cMUT operating in the precollapse regime at 90 % of its collapse voltage, 1.79 kPa/V vs. 9.72 kPa/V at 2.3 MHz. In collapsed regime operation the fractional bandwidth (pulse echo) is increased compared to that obtained in precollapsed regime operation 140 % vs. 83 % with a bias 90 % of the collapse voltage. Characterization of 1-D cMUT arrays operating in oil was done by ultrasonic pulse echo and pitch catch measurements.