Real-time 3D imaging with 11×11 rigid PMUT array on conventional silicon wafer

Piezoelectric micromachined ultrasonic transducers (PMUTs) can push medical imaging forward by enabling smaller pitch sizes and reduced sidelobes for sharper resolution. However, earlier research on ultrasound imaging with PMUTs primarily used linear phased arrays, which are limited to 2D imaging, or row-column (RC) arrays, which present challenges for 3D imaging due to circuit complexity. Existing PMUT arrays for 3D imaging suffer from a complex fabrication process, raising yield and reliability concerns. Here, we demonstrate real-time 3D ultrasound imaging using an 11×11 PMUT array fabricated on a low-cost conventional silicon wafer with a polyimide membrane, a first in the literature. Operating at 2 MHz in tissue-mimicking media, an array element achieves 50 Pa/V output pressure at 2.5 cm and 5 µV/V round-trip sensitivity with 5 V DC bias. Up to 4 cm deep imaging results are recorded with a voltage as low as 10 VAC+10 VDC. Unlike prior SOI-based PMUTs, this approach drastically reduces fabrication expenses while maintaining performance for low-frequency imaging. The novel interconnect scheme enables simplified fabrication and packaging processes, opening a pathway for on-probe electronics. This technology offers a cost-effective solution for low-frequency real-time 3D ultrasound.