Capacitive micromachined ultrasonic transducers and their application

Today's ultrasound technology covers a wide range of measurements, diagnostic, and other applications, e.g. from non-destructive testing to medical ultrasonic imaging or from surveillance in process plants to distance measurement. Capacitive micromachined ultrasonic transducers (cMUT) receive increasing acceptance as an alternative to piezoelectric transducers for certain fields of applications due to a number of distinctive features. Some of these cMUT applications recently presented are reviewed. Besides, the present paper focuses on novel technological aspects regarding the improvement in performance of cMUT consisting of silicon membranes. Within this context a partial doping of silicon membranes is introduced to confine the effective electrode area to an indispensable extent and, therefore, to reduce the offset and parasitic capacitance. Though the objective of this paper emphasizes applications and technology of cMUT, some further attention is paid to a frequently applied electrical equivalent circuit.