Spurious-Free TF-SAW Resonators Improved Q Using Double Busbar and Thermal Annealing

In this work, high performance surface acoustic wave (SAW) resonators are proposed, using piston mode to suppress transverse modes, and double busbar structure together with thermal annealing to improve quality factor (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i>). Firstly, the effectiveness of the electrode structure design was validated through a combination of finite element method (FEM) simulations and experimental measurements. Secondly, a performance comparison on 4H-SiC and Si substrates reveals the impact of substrate material properties on device performance with parasitic surface conduction (PSC) effects suppressed. The SiC-based resonators exhibit enhanced separation between the shear-horizontal (SH) mode and high-order spurious modes compared to their Si counterparts. Additionally, the SiC-based device achieves a higher Bode-<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 2350, compared to 2022 for the Si-based resonator. Furthermore, thermal annealing of resonators on both substrates helps relieve residual stress, resulting in nearly 10% <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i> enhancement of SAW resonators, with the SiC resonators reaching a Bode-<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Q</i><sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 2550.