Design and measurement of MEMS capacitive ultrasonic transducer

Since the proposing of capacitive micromachined ultrasonic transducer by Khuri Yakub group in 1994 that this kind of transducer occupying the advantages of wide bandwidth, impedance matching well with the propagation medium especially in fluid and air and high sensitivity, has shown a great potential for a wide range of applications such as medical imaging, medical ultrasound diagnosis, therapy and underwater ultrasonic imaging. This paper presents a kind of MEMS capacitive ultrasonic transducer with the novel cavities embedded in the device layer of Silicon On Insulator. Firstly, the geometric dimensions are derived from the theoretical analysis of the vibrating membrane and the electrical analysis of the transducer. Secondly, Finite Element Analysis is adopted to confirm the operation mode and the deflection and equivalent stress under operation/collapse voltage are obtained. Then, the fabrication process is depicted and the fabricated transducer is shown. The test results show that the electromechanical coupling coefficient is 69.65%.