Collapsed regime operation of capacitive micromachined ultrasonic transducers based on wafer-bonding technique

We report experimental results from collapsed regime operation of the 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, 1.79kPa/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.