Design and Characterization of a Capacitive Micromachined Transducer With a Deflectable Bottom Electrode

Multiple moving membrane capacitive micromachined ultrasonic transducers (M
³
-CMUTs) employ a multiple vibrating plate configuration. The presence of an additional plate improves the transducer properties. In this letter, the device displacement amplitude is further enhanced through eliminating the transducer fixed electrode and employing a deflectable plate as the bottom electrode. A set of air-coupled transducers with the effective plate radius of 65 μm has been fabricated. Electrical and optical measurements were conducted. It is demonstrated that the transducer with a deflectable bottom electrode exhibits larger top plate displacement amplitude compared with the conventional CMUTs as well as the M
³
-CMUT with a fixed bottom electrode. A maximum of a 57% and 4% increase in the plate displacement is achieved at a dc bias level of 27 V for the transducer with vibrating bottom electrode compared with the conventional CMUT and M
³
-CMUT with a fixed bottom electrode, respectively.