Lateral-Field-Excited PMUTs Based on Bilayer X-Cut Lithium Niobate

This work demonstrates the design, fabrication, and characterization of the first piezoelectric micromachined ultrasonic transducers (PMUTs) based on bilayer X-cut lithium niobate (LiNbO3). A comparison of PMUT materials based on different figures of merit (FoMs) is presented, highlighting LiNbO3as a promising and well-balanced alternative to more conventional materials. To leverage its superior material properties, PMUTs were designed based on bilayer X-cut LiNbO3to fully harnesses the in-plane stress associated with the bending of the structure, thereby enhancing transduction. The fabricated devices show high electromechanical coupling ($k_{t}^{2}$) of$4.6{\,}\%$, albeit significantly lower than the simulated value due to parasitic effects. Mechanical vibration characterization shows a high static displacement of$0.88{\,}\mathrm {nm/V}$and excellent linear dynamic range. Based on this design, an$8\times 1$array is demonstrated showing excellent consistency among the elements, with a frequency spread of$0.006{\,}\mathrm {MHz}$and a displacement sensitivity spread of$0.15{\,}\mathrm {nm/V}$. Our devices show comparable performance to monocrystalline PZT-based PMUTs, and substantially outperform ScAlN-based PMUTs in terms of static displacement sensitivity by a factor of 5. These results underscore the strong potential of LiNbO3for high-performance PMUTs.[2026-0008]