6 GHz Lithium Niobate on Insulator Low-Loss Saw Delay Line Adapting Non-Leaky Composite Waveguide Mode

In this study, a high-performance C-band surface acoustic wave (SAW) delay line is demonstrated on a thin-film lithium niobate on insulator (LNOI) platform. By optimizing the thickness ratio of the LN and SiO2 layers, a non-leaky composite waveguide (CWG) mode with shear-horizontal (SH) surface motion is achieved. This mode offers inherently high electromechanical coupling and effectively confines acoustic energy within the thin-film LN layer. The resulting CWG-mode acoustic delay line (ADL), with a wavelength of 0.7 μm, achieves an insertion loss (IL) of 7 dB, a fractional bandwidth (FBW) of 3.14%, and a group delay (GD) of 21.8 ns at a center frequency of 6 GHz, demonstrating competitive performance compared to state-of-the-art time-delay devices operating in the same frequency range.