Ultrahigh Frequency SAW Devices Based on 128°Y-X LiNbO₃/SiO₂/Sapphire Structure

Surface acoustic wave (SAW) devices based on multilayer structures herald dawns in satisfying stringent high-frequency demands of 5G and sub-6G wireless systems. However, SAW devices for X-band via lithography have not been realized. This work targets at boosting the operating frequency of SAW devices to the X-band simply by standard photolithography and lift-off techniques. Based on 128°Y-X LiNbO3 (LN)/SiO2/Sapphire heterostructure, a high-order thickness shear (TS) SAW as the intended mode is successfully excited. Theoretical and experimental optimization of LN cut orientation, LN and SiO2 thickness, and wavelength ( $\lambda \text {)}$ enable the resonators and filters to cover most partial X-band. The resonators achieve an ultrahigh center frequency ( ${f}_{\text {c}}\text {)}$ of 10.53 GHz, with a large coupling coefficient ( ${K}^{{2}}\text {)}$ of 11.05% and Bode- ${Q}_{\max }$ of 372. The corresponding filters covering 8.9–10.3 GHz exhibit a minimum insertion loss ( ${\mathrm {IL}}_{\min }\text {)}$ of 3.06–3.31 dB. This first prototype of X-band SAW devices fabricated via standard lithography highlights enormous potential of SAW technology for next-generation wireless systems.