Fabrication of High-Frequency 2D Flexible pMUT Array

This paper reports an 8x8 2D flexible pMUT array fabrication process along with preliminary characterization results. The top-down fabrication process uses a Silicon wafer as a temporary carrier from which a flexible pMUT array is released by DRIE. The flexible pMUT membrane consists of a 1 µm PZT and 6 µm polyimide layers. A 14 µm thick polyimide sidewall with a cavity of 100 µm in diameter is defined by reactive ion etching (RIE). The released structure is bonded to PDMS for making the assembly mechanically robust. The flexible pMUTs demonstrate a 5 mm bending radius, 40% fractional bandwidth of the 4.2 MHz center frequency in-air, and 7 mm•s
^-1
•V
^-1
transmission sensitivity.