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

• Published in: IEEE transactions on electron devices 2023-12, p.1-8
• Main Authors: Xiao, Boyuan, Fu, Sulei, Su, Rongxuan, Xu, Huiping, Liu, Peisen, Zhou, Xinchen, Zhang, Shuai, Wang, Rui, Song, Cheng, Zeng, Fei, Wang, Weibiao, Pan, Feng
• Format: Article
• Language: English
• Subjects: Anisotropy; quartz; slowness curve; surface acoustic wave (SAW); transverse mode suppression
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2023.3340663

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 _{\text{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 ^{\circ}\textit{Y} - X LiTaO _{\text{3}} (LT)/AT-Quartz platform as functions of \textit{h}_{\text{LT}} / \uplambda and \textit{h}_{\text{Al}} / \uplambda 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.