Fig. 1: Lithium Niobate (LN) pMUTs.

a Design of a single element LN pMUT- dimensions of its cavity, electrodes, and bonding pads. b Design of a 15×15 LN pMUT array. c Cross section of LN pMUT with Scanning Electron Microscope (SEM). We can distinguish top electrode (Al), piezoelectric layer (LN), un-patterned bottom electrode (Pt), structural layer (SiO₂), and the unreleased substrate (Si). d Optical image of the fabricated 15×15 LN pMUT array. This is wire-bonded to a PCB and coated in Parylene for ultrasonic testing in a de-ionized water tank and then in a tissue phantom. The Parylene acts as a matching layer between the acoustic impedance of the pMUT membrane and the acoustic impedance of the medium, in this case, the tissue phantom. e Array directivity based on theoretical ultrasonic wave propagation in the XZ plane from the array (left figure) as well as the cross section in the X plane (right figure) at different distances from the pMUT array (1, 5, 10, and 13 cm).