8.5 GHz and 11.5 GHz Acoustic Delay Lines Using Higher-Order Lamb Modes in Lithium Niobate Thin Film

摘要

We present the first group of X-band acoustic delay lines (ADLs) in lithium niobate (LiNbO3) thin films. The fabricated miniature ADLs exploit the high phase velocities ($v_{p}$) and large electromechanical couplings ($k^{2}$) of the 2^nd-order symmetric (S2) mode and the 3^rd-order antisymmetric (A3) mode in Z-cut LiNbO3. The S2 passband centered at 8.55 GHz shows a minimum insertion loss (IL) of 13.3 dB, a 3-dB fractional bandwidth (FBW) of 1.20% and group delays between 11.5 ns and 93.6 ns, while the A3 passband centered at 11.5 GHz shows a minimum IL of 11.6 dB, an FBW of 1.14% and group delays between 9.0 ns and 65.1 ns. The $v_{p}$, group velocity ($v_{g}$), and propagation loss (PL) have been experimentally extracted. The demonstrated X-band ADL platform could potentially enable high-frequency passive signal processing functions for 5G applications.