Demonstration of PolyimideBased Flexible CMUT Operation on Curved Substrates

Capacitive micromachined ultrasonic transducers (CMUTs) represent a class of ultrasonic devices widely investigated for several applications such as medical imaging and non-destructive material inspections. Although many improvements, the possibility to successfully operate on nonplanar surfaces still remains challenging. In this respect, flexible electronics can represent a unique ally to enable the manufacturing ultra-thin highly conformable CMUTs. In this paper, we demonstrate a fully flexible fabrication process for a PI based CMUT device and a preliminary characterization. This flexible CMUT technology was conceived to achieve a final device composed of only two materials, i.e., Titanium for the electrodes and PI for the membrane and the backplate. The CMUT cavities were realized by Aluminium sacrificial release. We fabricated flexible CMUT test devices consisting of 7 membranes 50µm in diameter laying onto an 8µm-thick backplate. This configuration can allow the bending of the devices on very small curvature radii (down to 1 mm).