A novel stretchable CMUT array using liquid-metal electrodes on a PDMS substrate

This paper introduces a new method for fabricating a stretchable capacitive micromachined ultrasonic transducer (CMUT) array with liquid-metal (Ga-In-Sn) electrodes on a polydimethylsiloxane (PDMS) substrate. A stretchable CMUT array can make it fully comply with a 3D curved surface for biomedical applications. The transducer membrane and cavity are fabricated separately using PDMS and bonded together by using O2 plasma, which allows us to form the concave bottom electrodes on top of the reflowed photoresist. By using concave bottom electrodes, the effective capacitance will be increased by reducing the gap distance on the membrane edge, especially when pulled in by a DC bias. This can increase the device sensitivity, fill factor and output pressure. The device is designed to operate in the range of 100 kHz to 500 kHz for low frequency applications. The preliminary experimental results show a resonant frequency at around 200 kHz by using an impedance analyzer.