Multiple Moving Membrane CMUT With Enlarged Membrane Displacement and Low Pull-Down Voltage

A multiple moving membrane capacitive micromachined ultrasonic transducer ( M³-CMUT) has been fabricated and is shown to exhibit a significantly enlarged total membrane displacement ( ~ 280 nm) compared with the displacement of a conventional CMUT ( ~ 85 nm) for the same bias voltage. The M³-CMUT exhibits a significant reduction of the device pull-down voltage, while showing a much higher capacitance change, 100 fF for the M³-CMUT compared with only 20 fF for CMUT, at a dc bias of 25 V. The device performance, sensitivity, and acoustic power generation capability are primarily associated with the magnitude of the displacement of the membrane, and therefore, are enhanced through employing multiple deflectable membranes in M³-CMUT device. This high performance M³-CMUT is a promising candidate for high resolution ultrasonic imaging application.