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.

With the rapid development of 5G communication technology, high-performance acoustic filters are urgently required to cope with the increasing number of frequency bands. Recently, an extensive attention has been paid to the advancement of lithium niobate (LiNbO $_{\text{3}}$ )-based thin-film acoustic resonators due to their large electromechanical coupling factor. In this article, a fundamental (0th) shear-horizontal plate acoustic wave (SH $_{\text{0}}$ -PAW) resonator based on a 30 $^{\circ}$ Y -cut LiNbO $_{\text{3}}$ /SiO $_{\text{2}}$ thin film is proposed. Using the finite element method (FEM), the effective electromechanical coupling coefficient ( $\textit{k}^{\text{2}}_{\text{eff}}$ ) and phase velocity as the function of the rotation angle $^{^{^{}}}$ of the LiNbO $_{\text{3}}$ film and the layer thicknesses are extracted. Meanwhile, the dispersion characteristic of the SH $_{\text{0}}$ mode is analyzed. The fabricated resonators yield a $\textit{k}^{\text{2}}_{\text{eff}}$ of 24.8%, a Bode- $\textit{Q}_{\text{max}}$ of 688, and a figure of merit (FoM $=$ $\textit{k}^{\text{2}}_{\text{eff}} \cdot \text{Bode-}\textit{Q}_{\text{max}}$ ) of 170. Furthermore, a tilted interdigital-transducer (IDT) method is adopted to suppress the spurious modes of the proposed resonators. It has been experimentally verified that most of the transverse modes are suppressed, and the longitudinal modes are suppressed effectively. The proposed resonator provides an effective solution to design a wideband, low loss, and unrippled acoustic filter for communication systems.

This study introduces shear horizontal (SH) surface acoustic wave (SAW) resonators based on a multilayered structure of lithium tantalate (LiTaO3 or LT)/silicon dioxide (SiO2)/4H-silicon carbide (4H SiC). SiC exhibits high resistivity (HR) ( $\rho \gt 10^{{10}}~\Omega \cdot $ cm), effectively suppressing the parasitic surface conduction (PSC) effect. The suppression of the PSC effect by 4H-SiC substrates is demonstrated by extracting the substrate loss of SiO2/4H-SiC and SiO2/Si substrates in a coplanar waveguide (CPW) structure. Consequently, SAW resonators based on 4H-SiC substrates demonstrate a superior quality factor (Q) compared to the conventional SH SAW resonators based on Si substrates. The fabricated resonators with 4H-SiC and Si substrates achieved Bode- ${Q} _{\max }$ of 3916 and 1836, ${Q} _{\text {p}}$ of 3402 and 590, and admittance ratios ( ${Y} _{\text {r}}$ ) of 92 and 74 dB, respectively. The ${Q} _{\text {p}}$ of the 4H-SiC-based resonator is 5.7 times higher than that of the Si-based resonator. Substituting the Si substrate with the 4H-SiC substrate increases Q without compromising the effective electromechanical coupling ( ${k} ^{{2}}_{\text {eff}}$ ) and temperature coefficient of frequency (TCF). To suppress the transverse mode of the SAW resonators, tilted interdigital transducers (IDTs) at various titled angles were fabricated. A 12° tilt angle IDT demonstrated the most effective transverse mode suppression. When the tilted IDT was employed, the ${Q} _{\text {p}}$ of the SAW resonator based on the 4H-SiC substrate surpassed that of Si substrate. Compared to the Si substrate, the 4H-SiC substrate resulted in a higher ${Q} _{\text {p}}$ , making this technique promising for application in filters, oscillators, and sensors.

In this article, a new high quality factor ( ${Q}$ ) inductor with piezoacoustic plate acoustic wave (PAW) resonators is presented. As indicated by the investigation of the acoustic wave propagation characteristics and transducer materials, the coupling coefficient ( ${k}^{{2}}$ ) of the shear-horizontal plate (SH ₀ ) mode that propagates in the LiNbO ₃ plate increases to 55.7%, which leads to a wide inductive bandwidth of 29%. The longitudinal and transversal spurious modes are inhibited through novel edge reflector design and transducer engineering. The peak inductor quality factor ( ${Q}_{L \text {,peak}}$ ) of the acoustic resonator–inductor is obtained as 347, and a large range of inductance values are achieved to be up to 49 nH by regulating the interdigital transducer (IDT) number of fingers (NF). It is noteworthy that a larger inductance is realized in a more miniaturized device. Furthermore, the wavelength-scaling-induced physics is investigated for frequency tuning in 1–5 GHz, which reveals the multifrequency ability on a single chip of the SH ₀ acoustic resonator–inductor.

In this work, high performance surface acoustic wave (SAW) resonators are proposed, using piston mode to suppress transverse modes, and double busbar structure together with thermal annealing to improve quality factor (Q). Firstly, the effectiveness of the electrode structure design was validated through a combination of finite element method (FEM) simulations and experimental measurements. Secondly, a performance comparison on 4H-SiC and Si substrates reveals the impact of substrate material properties on device performance with parasitic surface conduction (PSC) effects suppressed. The SiC-based resonators exhibit enhanced separation between the shear-horizontal (SH) mode and high-order spurious modes compared to their Si counterparts. Additionally, the SiC-based device achieves a higher Bode-Q_max of 2350, compared to 2022 for the Si-based resonator. Furthermore, thermal annealing of resonators on both substrates helps relieve residual stress, resulting in nearly 10% Q enhancement of SAW resonators, with the SiC resonators reaching a Bode-Q_max of 2550.