Tilted IDT Designs for Spurious Modes Suppression in LiNbO₃/SiO₂/Si SAW Resonators

Abstract

High-performance wideband acoustic filters are urgently needed for communication systems with large volumes of data. Recently, multilayered surface acoustic wave (SAW) resonators have attracted wide attention as key components of acoustic filters. In our previous work, we proposed a shear-horizontal SAW (SH-SAW) resonator based on a 30° YX -LiNbO3/SiO2/Si substrate. This resonator achieved an effective electromechanical coupling coefficient ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}^{{2}}_{\text {eff}}$ </tex-math></inline-formula> ) of 24.4% and a Bode- <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${Q}_{\text {max}}$ </tex-math></inline-formula> of 1092. However, the admittance/conductance showed obvious transverse and longitudinal modes spurious that degraded the resonator’s performance. To address this issue, we adopted a tilted interdigital-transducer (IDT) design in this article, which combined dispersion/slowness characteristic analysis and tilted angle optimization using the finite-element method (FEM). The simulations and experimental results have verified the successful suppression of both transverse and longitudinal modes when the tilted angle of the IDT reaches 16°. Moreover, the adoption of the tilted IDT designs for spurious modes suppression does not result in the evident sacrifice of the <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${k}^{{2}}_{\text {eff}}$ </tex-math></inline-formula> . The proposed resonator has the potential to be used in the development of acoustic filters with large bandwidth, low loss, and no ripples.