Suppressed Transverse Mode Generation in TF-SAW Resonators Based on LiTaO₃/Sapphire

Abstract

Thin-film surface acoustic wave (TF-SAW) devices are important for wireless communication systems in the new age. Nevertheless, there are still some technical challenges including transverse mode suppression. To find out a practical solution for the challenge, this work theoretically and experimentally investigates transverse mode generation in TF-SAW devices based on LiTaO3/sapphire in which only mature and commercial materials are adopted. The devices with various Al thicknesses and wavelengths are simulated, and slowness curves, admittance curve and displacement distributions are all analyzed. A large range of wavelength from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.6~\mu $ </tex-math></inline-formula>m to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$4~\mu $ </tex-math></inline-formula>m or even larger is found for the devices to have flat slowness curves. TF-SAW resonators based on LiTaO3/sapphire without any designs for transverse mode suppression are fabricated. The transverse modes in the resonators with wavelength from <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.6~\mu $ </tex-math></inline-formula>m to <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$3.8~\mu $ </tex-math></inline-formula>m are all dramatically suppressed, agreeing well with the theoretical results. We believe that the suppression is sufficient, even though the transverse modes still exist. This work proposes a method to obtain TF-SAW devices with suppressed transverse mode generation, showing the strengths of LiTaO3/sapphire structure and promoting the development of TF-SAW technology.