Characterization of Curved Piezoelectric Micromachined Ultrasound Transducers Fabricated by Chip-Scale Glass Blowing Technique

This letter presents the development of curved piezoelectric micromachined ultrasound transducers (pMUTs) using a novel chip-scale glass-blowing method on suspended glass templates. This new approach allows for controllable diaphragm curvature and high fill-factor arrays of varying sizes, making it possible to study the impact of the curvature on the performance of the pMUTs. A finite element analysis (FEA) model was built to guide the design. Thirty percent Scandium-doped Aluminum Nitride (Sc-AlN) was chosen for good piezoelectrical coefficient and biocompatibility. The 100 nm platinum/750 nm Sc-AlN/100 nm gold films are sputtered on the curved glass membrane with diameters ranging from 75 to 750
μ
m. pMUT with a diameter of 150 μm with 5.6
μ
m depth of curvature had resonance frequencies of 2.2 MHz along with center displacements up to 154 nm/V in air. Impedance measurements at resonance on the pMUTs show
$k_{\text{eff}}^2$
of 1.31%. Optimal curvatures were found experimentally and matched the FEA model. Changes in mode shapes were found when curvatures were deeper than the optimal value.