A Solidly Mounted Resonator Fabricated by LiNbO₃ Single-Crystalline Film on Flexible Polyimide Substrate

A solidly mounted resonator on flexible polyimide (PI) substrate with high-effective coupling coefficient ( K_t² ) of 14.06% is reported in this article. This high K_t² is resulting from the LiNbO₃ (LN) single-crystalline film and [SiO₂/Mo]³ Bragg reflector. The quality of LN film fabricated by the crystal-ion-slicing (CIS) technique using benzocyclobutene (BCB) bonding layer was close to the bulk crystalline LN. The interfaces of the Al/LN/Al/[SiO₂/Mo]³ Bragg reflector/BCB/PI multilayer are sharp, and the thickness of each layer is consistent with its design value. The resonant frequency and K_t² keep stable when it is bent at different radii. These results demonstrate a feasible approach to realizing RF filters on flexible polymer substrates, which is an indispensable device for building integrated and multifunctional wireless flexible electronic systems.