Fabrication of embossed capacitive micromachined ultrasonic transducers using sacrificial release process

An embossed capacitive micromachined ultrasonic transducer (CMUT) is a device with embossed membrane that works in the collapse mode to improve output pressure in transmission. In this paper, a six-mask sacrificial release process is proposed for fabricating embossed CMUT arrays. Based on this process, the embossed pattern CMUTs were firstly fabricated. By using of electroplating methods, annular embossed patterns made of nickel were grown on the full top electrodes of CMUTs. The dimensions of the embossed pattern were about 3.0µm in width and 1.4 µm in height. The resonant frequencies of the embossed CMUT array were 6.4MHz and 8.7MHz when the device worked in the conventional and the collapse mode, respectively.