A cavity is formed in a silicon substrate, and a thin layer suspended on the top of the cavity serves as a membrane on which a metallized layer acts an electrode, together with the silicon substrate which serves as a bottom electrode.
If an AC signal is applied across the biased electrodes, the vibrating membrane will produce ultrasonic waves in the medium of interest.
The properties to use in high frequency with large bandwidth makes it a good choice to use as a transducer in medical imaging, especially in an intravascular ultrasound (IVUS).
[3] The major limitations of this method include complicated manufacturing process for constructing and sealing etch/drainage channels of the sacrificial material; the need for sacrificial-release channels reduces the available space for transducers, thereby reducing the achievable sound generation capability; limited control of layers' thickness during the manufacturing process; limited cavity thickness due to residues of fluid inside the cell cavity, which can cause stiction between the upper and lower parts of the cell, if the cell is not thick enough.
CMUTs manufactured in the multi-user MUMPS were reported to have reduced performance, such as relatively low resonating frequency.
CMUT performance is benchmarked using pitch-catch and pulse-echo experiments, and operation uniformity is tested in air and in immersion.
The CMUT-on-CMOS technology and the flip-chip process allows tight integration of CMUTs with front-end electronics, which is necessary for miniature medical imaging devices, such as IVUS.