The influence of eliminating the fixed electrode from an air-coupled, dual deflectable membrane, capacitive micromachined ultrasonic transducer

Multiple moving membrane, capacitive micromachined ultrasonic transducers (M
³
-CMUTs) benefit from a multiple vibrating membrane configuration that enhances the transducer properties. In this work, further improvement in the device displacement amplitude is achieved through eliminating the transducer fixed electrode. Two M
³
-CMUT devices have been fabricated and their electrical impedances are compared. It is demonstrated that the 50 μm radius transducer without the fixed electrode shows a 70% increase in the membrane displacement amplitude at a DC voltage of 20 V compared with the M
³
-CMUT with a fixed bottom electrode of the same dimension.