Low Loss Acoustic Delay Lines Based on Solidly Mounted Lithium Niobate Thin Film

In this work, acoustic delay lines (ADLs) based on solidly mounted structures were studied to achieve low insertion loss (IL) and wide fractional bandwidth (FBW). By adopting the guided shearhorizontal wave (SH-wave) in thin-film lithium niobate on insulator (LNOI) configuration, the acoustic energy is constrained near the surface to attain high piezoelectric coupling (K
²
) to yield low IL and wide FBW. Proposed ADLs were designed with Au electrodes in X-cut LNOI to obtain sufficient K
²
> 27% up to 1-GHz, thus allowing a better IL-FBW tradeoff. Fabricated prototype ADLs with wavelength (λ) of 4 μm (940 MHz) and 6 μm (640 MHz) achieve IL around 10 dB and FBW around 9% simultaneously using conventional bidirectional transducers. Such a performance is comparable to suspended plate wave ADL counterparts while retains enhanced mechanical robustness for batch-manufacturing and packaging.