Flexible Polymer-based Capacitive Micromachined Ultrasound Transducers (polyCMUTs): Fabrication and Characterization

Flexible components have always been an attraction in all engineering fields; ultrasound transducers are no exception to this. Capacitive micromachined ultrasound transducers (CMUTs) have started to challenge the piezoelectric dominance in ultrasound imaging industry due to their wider bandwidth and excellent integration with electronics. We present a new fabrication technique for making flexible polymer-based CMUTs that is simple, inexpensive, and robust. The proposed technique includes forming CMUT cells through four lithography steps on a polyimide substrate, and then chemically releasing it from the silicon carrier (by a sacrificial layer) to reduce residual stress. The fabricated 1D, 8-element flexible array showed similar resonant response at 5.8 MHz on flat and curved surfaces without compromising functionality. Our finite element analysis also confirmed the minimal change in resonant frequency. The proposed device could be used for conformal ultrasound imaging of anatomical features.