MEMS-based transducers (CMUT) for medical ultrasound imaging

Capacitive micromachined ultrasonic transducers (CMUTs) are micro-electromechanical devices (MEMS) fabricated using silicon micromachining techniques. In the past decade, their use has proved to be attractive mainly in the field of medical ultrasound imaging as active elements in ultrasound probes. The interest of this novel technology relies on its full compatibility with standard integrated circuit technology that makes it possible to integrate, on the same chip, the transducers and the electronics, thus enabling the realization of extremely low-cost and high-performance devices. From an operational point of view, CMUTs have been widely recognized as a valuable alternative to piezoelectric transducer technology in a variety of medical imaging applications, thanks to a higher sensitivity, a wider bandwidth, and an improved thermal efficiency. In this chapter, the design and fabrication of a 192-element linear array CMUT probe operating in the range 6-18 MHz, designed for vascular, small parts, rheumatology and anesthesiology imaging applications, is reported. The CMUT array is microfabricated and packed using a novel fabrication concept specifically conceived for imaging transducer arrays. The performance optimization of the probe is performed by connecting the CMUT array with multichannel analog front-end electronic circuits housed into the probe body. Characterization and imaging results are used to assess the performance of CMUTs with respect to conventional piezoelectric transducers.