CMUT - Capacitive micromechanical ultrasonic transducerr

Business Unit »Intelligent Sensor and Actuator Systems«

Silicon CMUT in acoustically matched housing for high temperature applications.
© Fraunhofer ENAS
Silicon CMUT in acoustically matched housing for high temperature applications.
Silicon CMUT chip (10 x 10 mm²).
© Fraunhofer ENAS
Silicon CMUT chip (10 x 10 mm²).

The capacitive micromechanical ultrasonic transducer (CMUT) is an alternative device to conventional ultrasonic transducers, which can be fabricated in silicon technology. Therefore, CMUTs can be highly miniaturized, manufactured cost-effectively in batch processes, and combined with driving electronics. CMUTs have a wide bandwidth as well as low acoustic impedance. The latter has an advantageous effect on matching the surrounding medium. Thus, CMUTs can be more easily adapted for different applications. In addition, the performance of CMUTs is less dependent on the ambient temperature and they also have no self-heating. This makes CMUTs preferable for certain applications.

A CMUT element is basically a MEMS capacitor in which one electrode is solid and immobile and the other (membrane) is thin and mobile. Depending on the application and required performance, the membrane can be made of different materials such as silicon, graphene or metallic glass. A CMUT transducer usually consists of many CMUT cells connected in parallel (in single-element transducers) or arranged in multiple elements that can be controlled separately (in multi-array transducers). The capacitive ultrasonic transducer is a complex component that combines several physical aspects, such as: Structural mechanics, electrostatics and acoustics. Therefore, before CMUTs are fabricated, several modeling and simulation experiments are performed to investigate a design (including geometries and materials) that provides the optimal performance (including acoustic pressure at the resonant frequency) in the target application area.

CMUTs have a proven track record in medical imaging and therapeutic applications. The ability to fabricate CMUTs with different device configurations and materials, and the advantages mentioned above, allow CMUTs to be used for a wide variety of applications.