Characterization of capacitive micromachined ultrasonic transducers

This paper describes numerical and experimental characterization of capacitive micromachined ultrasonic transducers (CMUTs) for ultrasound transmission. Simulations based on a finite elements method to model the electromechanical behaviour of CMUTs and to determine the dimensions of elementary cells are presented. In particular, we analyse how the collapse voltage and the capacitance are affected by different parameters of a circular cell and by different bias voltages. The fill factor is defined as the ratio of the top electrode radius to the membrane radius and we study the influence of the fill factor in the performances of CMUTs. The fabrication process of a CMUT uses anodic bonding of a SOI wafer on a borosilicate glass substrate and we compare experimental results with numerical results in terms of eigenfrequencies, bandwidth, quality factor and capacitance for non-metallized and metallized membranes.