Insights Into High-Frequency Spurious Suppression of LLSAW Devices Based on Cu-Grating/X-Cut LiNbO 3 /SiC

This article presents the first systematic study on the collaborative high-frequency suppression of spurious modes in longitudinal leaky surface acoustic waves (LLSAWs) devices on the Cu-grating/X-cut LiNbO3/SiC stack, including the first-order shear-vertical (SV1), shear-horizontal (SH1), and longitudinal spurious signals (LSSs). Through detailed modal and dispersion analysis, we clarify the role of cutoff frequencies in the high-order mode suppression mechanism using distance-to-cutoff as a quantitative design margin. Resonators with Al and Cu electrodes are compared through systematic simulations under matched mass-loading conditions, supported by measurements on fabricated devices with different stack configurations. The Cu-electrode LLSAW resonators achieve a maximum Bode- $Q_{\mathrm {max}}$ of 512 and a figure of merit of 107 at 6 GHz. A synchronous LLSAW, filter prototype demonstrates a 3-dB fractional bandwidth (FBW) of 11.9%, a minimum insertion loss of 1.6 dB, and spurious suppressed responses both in-band and out-of-band (OoB) signals. This work provides a scalable design paradigm enabling spurious-free wideband LLSAWdevices in future 5G systems.