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

We present the first group of X-band acoustic delay lines (ADLs) in lithium niobate (LiNbO
₃
) 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 (S
₂
) mode and the 3
^rd
-order antisymmetric (A3) mode in Z-cut LiNbO
₃
. The S
₂
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.