High-performance SH-SAW resonator using optimized 30° YX-LiNbO₃/SiO₂/Si

With the rapid development of 5G technology, acoustic wave filters with large bandwidths are urgently required to deal with the explosive increase in data traffic. Recently, there is extensive attention paid to shear-horizontal (SH) surface acoustic wave (SAW) resonators based on lithium niobate (LiNbO₃) substrates, thanks to its large effective coupling coefficient (k²_eff). However, because of the bulk acoustic wave (BAW) energy radiation into the LiNbO₃ substrate, it is very challenging to obtain a high quality factor (Q) for SH-SAW resonators. In this study, a 30° YX-LiNbO₃/SiO₂/Si SAW resonator with the SH mode is proposed to achieve a large coupling and a high Q simultaneously. By bonding a LiNbO₃ thin film onto a thermally oxidized Si(100) substrate, the velocity mismatch between the piezoelectric layer and the SiO₂/Si substrate could significantly reduce the BAW energy leakage. Finite element method simulation is employed to optimize the cut angle of the LiNbO₃ film and the thickness of each layer. The fabricated SH-SAW resonators with a resonant frequency of 924 MHz yield a k²_eff of 24.8% and a maximum of Bode-Q (Bode-Q_max) of 1107. In comparison with the previously reported same-type SAW resonators, a higher Bode-Q_max is demonstrated in this work when their k²_eff is larger than 20%, providing a potential solution to enable wideband tunable filters in the 5G communication system.