Spurious-Free Shear Horizontal Surface Acoustic Wave Filters Based on 36Y-Cut LiNbO₃/SiO₂/Si Substrates

High-performance surface acoustic wave (SAW) filters are essential for meeting modern demands for ubiquitous wireless connectivity and rapid data transmission. This study first explores the design and optimization of shear-horizontal-SAW (SH-SAW) multilayer resonators on 36Y-cut LiNbO3/SiO2/Si substrates, addressing spurious mode suppression, energy dispersion characteristics, and filter applications. To mitigate interference between the transverse and longitudinal modes, a new tilted interdigital transducer (IDT) design and the reflector period ratio <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${\lambda }_{R}$ </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">${\lambda }\lt {1}$ </tex-math></inline-formula> were implemented. Dispersion analysis identified the optimal wavelength for mode suppression at <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$1.8~\mu $ </tex-math></inline-formula>m, addressing out-of-band (OoB) interference from Rayleigh and high-order SH (SH1) modes. Studies of phase velocity (<inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${v}_{p}$ </tex-math></inline-formula>) and energy distribution revealed that metal layers significantly affect acoustic energy dissipation, reducing <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${v}_{p}$ </tex-math></inline-formula> and quality factor (Q) at higher frequencies than 2 GHz. These findings were finally applied to design a spurious-free filter with a center frequency near 2 GHz and a fractional bandwidth (FBW) of 9.9%, demonstrating its potential for high-performance acoustic filters in communication systems.