Inherent Suppression of Transverse Modes on LiTaO<sub>3</sub>/AT-Quartz SAW Devices
Boyuan Xiao, Sulei Fu, Rongxuan Su, Huiping Xu, Peisen Liu, Xinchen Zhou, Shuai Zhang, Rui Wang, Cheng Song, Fei Zeng, Weibiao Wang, Feng Pan
Abstract
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 LiTaO3 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 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$42^{\circ }{Y}$ </tex-math></inline-formula> – <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${X}$ </tex-math></inline-formula> LiTaO3 (LT)/AT-Quartz platform as functions of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${h}_{\text {LT}}/\lambda $ </tex-math></inline-formula> and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${h}_{\text {Al}}/\lambda $ </tex-math></inline-formula> 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- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}$ </tex-math></inline-formula> 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.