Low Propagation Loss Acoustic Delay Lines based on YX-LiNbO3/SiO2/Sapphire

In this work, we investigated the design of low loss and wideband shear horizontal surface acoustic wave (SH-SAW) acoustic delay lines (ADLs) on a sapphire-based thin-film lithium niobate on insulator (LNOI) platform. The SH-SAW propagates in a Y-cut LN/SiO
2
double-layer thin film atop the sapphire substrate, where the significant acoustic impedance mismatch between the thin film and the substrate confines the acoustic energy at the surface, thus minimizing the propagation loss. The single-phase unidirectional transducers (SPUDT) used in this work is implemented with gold (Au) to maximize the electromechanical coupling as well as the directionality. The proposed ADLs based on YX-LN/SiO
2
/Sapphire centered at 830 MHz showed a minimum insertion loss (IL) of 3 dB, a wide fractional bandwidth (FBW) of 4.19%, and a low propagation loss (PL) of 2.51 dB/mm, which yields an effective quality factor (Q
PL
) exceeds 2,700. These results demonstrate the competitive performance of the proposed devices compared to state-of-the-art thin film LN ADLs, offering extremely low propagation loss for RF signal processing.