Inherent Suppression of Transverse Modes on LiTaO₃/AT-Quartz SAW Devices

Featuring a pronounced leakage suppression of acoustic energy, the construction of multilayer stacks offers an effective avenue for surface acoustic wave (SAW) devices to remain competitive in fifth-generation (5G) applications. While the target modes experience significant enhancement due to the waveguide effect, transverse spurious responses are also confined and amplified, leading to severe in-band ripples and limited rejection in the corresponding filter. Guided by the slowness dispersion analysis, commercially available AT-Quartz was identified as the optimal substrate that inherently suppresses these unwanted modes without additional countermeasures. The mechanism of slowness manipulation by combining several substrates including AT-Quartz, Si, SiC, and Sapphire with LiTaO(3 )was studied through the finite-element method (FEM), validating the superior potential of AT-Quartz for transverse mode suppression. Furthermore, the curvature dispersion characteristic of the slowness curve on the 42 degrees Y-X LiTaO3 (LT)/AT-Quartz platform as functions of hLT/A, and hAl/A, were investigated, which revealed a substantial parameter space devoid of spurious responses. Under the guidance of the suppression window, a series of spurious-free resonators with pure spectrum were successfully implemented without any treatment of interdigital transducer (IDT), with a typical one maintaining a remarkable maximum Bode-Q value of 2891 and a large figure of merit (FoM) of 334. The demonstrated LT/AT-Quartz platform has shown strong potential for high-performance, spurious-free, and compact acoustic components for front-end applications.