Capacitive Ultrasonic Transducers for medical applications: technological optimization at FBK

Silicon surface micromachining can be successfully used in the fabrication of ultrasonic transducers (cMUT) which exhibit promising performance improvements with respect to the PZT devices for medical applications such as echographic systems. The micro-fabrication of these transducers is still affected by a number of critical steps, among which wafer bonding, through-silicon via (TSV) interconnects, critical patterning of the vibrating membrane and bad acoustic properties of the silicon substrate. In order to address these problems a new fabrication sequence was introduced by Caliano et. al., in which the fabrication approach is top-down (“reverse technology”). Advantages of this fabrication are: no membrane patterning, low temperature processing (which avoids mechanical instability introduced by high temperature treatments), complete removal of the silicon substrate, reverse packaging with standard wire bonding (no need for TSV). This technology was developed and patented at Roma Tre University.