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

Abstract

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 LiNbO3 as a promising and well-balanced alternative to more conventional materials. To leverage its superior material properties, PMUTs were designed based on bilayer X-cut LiNbO3 to fully harnesses the in-plane stress associated with the bending of the structure, thereby enhancing transduction. The fabricated devices show high electromechanical coupling (k2t ) 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 nm=V and excellent linear dynamic range. Based on this design, an 8 × 1 array is demonstrated showing excellent consistency among the elements, with a frequency spread of 0:006 MHz and a displacement sensitivity spread of 0:15 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 LiNbO3 for high-performance PMUTs.