High Sensitivity and Wide Bandwidth Airborne CMUTs with Low Driving Voltage

Abstract

This paper presents a novel method to significantly broaden the bandwidth of airborne capacitive micromachined ultrasonic transducers (CMUTs) by introducing a gaseous squeeze film as a damping mechanism. The damping and stiffening effects of the squeeze film can be tuned to lower the pull-in voltage while improving the sensitivity by optimizing fluidic trenches of various heights within the gap. By only adjusting the trench height, we can control the bandwidth from 0.89% to 8.1% while keeping the pull-in voltage under 55 V and achieving the minimum detectable pressure (MDP) from 2.2 μPa/√Hz to 4.88 μPa/√Hz. We also present a vacuum CMUT with high sensitivity and extremely low MDP as low as to 1.2 μPa/√Hz with 0.93 kHz bandwidth, in which a thick plate is chosen to reduce the geometric nonlinearity. This demonstration of the high sensitivity and wide bandwidth CMUTs with low driving voltage make them applicable to medical imaging, thermoacoustics, and nondestructive testing.