Micromachined Ultrasonic Transponders in Post-CMOS Technology
Fraunhofer IPMS develops micromachined ultrasonic components for various areas of application. These elements are uniquely capable of being integrated into CMOS processes as post-CMOS modules, paving the way for highly-miniaturized components with integrated evaluation electronics. Therefore, Fraunhofer IPMS is focused on the development of capacitive micromachined ultrasonic transducers (CMUTs).
CMUTs are basically MEMS structures which consist of two electrodes. One of the electrodes is fixed, the other is movable. The electrodes are separated by an insulating layer and a vacuum-sealed gap. CMUTs can both send and receive by converting electric energy to acoustic energy or vice versa through the displacement of the movable electrode. When a CMUT is sending sound, an electronic potential is established between the electrodes in order to deflect the electrostatic force from the movable electrode to its fixed counterpart. This movement generates a sound wave. Using the opposite procedure, the CMUT is also able to act as a receiver.
At Fraunhofer IPMS, CMUT production implements a unique method that allows for CMUTs to be manufactured as so-called Back-end-of-Line (BeoL) process modules. Here, amorphous metals in particular are used for the CMUT plates to provide elements high long-term stability and reproducibility. Furthermore, the CMUT module can be integrated into standard CMOS processes, a unique feature of this technology. In the institute's clean room, highly-integrated CMUTs are developed on 200mm wafers and manufactured for pilot production.