High-performance wideband acoustic filters are urgently needed for communication systems with large volumes of data. Recently, multilayered surface acoustic wave (SAW) resonators have attracted wide attention as key components of acoustic filters. In our previous work, we proposed a shear-horizontal SAW (SH-SAW) resonator based on a 30° YX -LiNbO3/SiO2/Si substrate. This resonator achieved an effective electromechanical coupling coefficient ( ${k}^{{2}}_{\text {eff}}$ ) of 24.4% and a Bode- ${Q}_{\text {max}}$ of 1092. However, the admittance/conductance showed obvious transverse and longitudinal modes spurious that degraded the resonator’s performance. To address this issue, we adopted a tilted interdigital-transducer (IDT) design in this article, which combined dispersion/slowness characteristic analysis and tilted angle optimization using the finite-element method (FEM). The simulations and experimental results have verified the successful suppression of both transverse and longitudinal modes when the tilted angle of the IDT reaches 16°. Moreover, the adoption of the tilted IDT designs for spurious modes suppression does not result in the evident sacrifice of the ${k}^{{2}}_{\text {eff}}$ . The proposed resonator has the potential to be used in the development of acoustic filters with large bandwidth, low loss, and no ripples.

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.

Phononic crystals (PnC) are a remarkable example of acoustic metamaterials with superior wave attenuation mechanisms for piezoelectric micro-electro-mechanical systems (MEMS) resonators to reduce the energy dissipation. Herein, a spider web-like PnC (SW-PnC) is proposed to sufficiently isolate the wave vibration. Finite-element analysis is performed to gain insight into the transmission property of finite PnC, and band characteristics by infinite periods. In comparison with the circle hole PnC at a similar bandgap, due to its already very lightweight PnC structure compared with previously reported PnCs, the proposed PnC offers a significantly lighter weight, smaller lattice constant, and greater energy leakage inhibition. More specifically, the resonator with the SW-PnC plate as the anchoring substrate exhibited a quality factor as high as 66569.7 at 75.82 MHz.