The fast development of the fifth-generation (5G) wireless systems and substantial growth of data usage have imposed stringent requirements for high-frequency and wideband radio frequency devices. Here, it is reported on a longitudinal leaky surface acoustic wave (LLSAW) mode acoustic resonator with a large electromechanical coupling factor ($k_{\mathrm{t}}^2$ ), high operating frequency, and efficient spurious suppression. Through systematical finite element method simulations, available design spaces such as supporting substrate, propagation angle, and lithium niobate (LN) thickness have been fully investigated with the aim of stimulating the intended LLSAW and suppressing spurious modes concurrently. Optimization results reveal that the LLSAW mode wave propagating in X-35°Y LN/SiC piezoelectric-on-insulator (POI) bilayer structure possesses a large $k_{\mathrm{t}}^2$ without significant interference from other spurious modes. To verify the theoretical analyses, LLSAW resonators were fabricated and exhibited a near spurious-free response with the operating frequency over 6 GHz, and $k_{\mathrm{t}}^2$ as large as 22.7%. This work demonstrates a high-performance LLSAW resonator on the POI platform with a simple prototype as well as potentially providing a high-frequency filtering solution for 5G applications in the 6-GHz spectrum.

There is less “clearance” for the antenna for full-screen mobile phones, which is a higher challenge to antenna miniaturization in radio frequency. Magnetoelectric (ME) antenna stands out as a promising solution to the antenna miniaturization in the fifth generation (5G) wireless communication technology for its superior miniaturization capability compared with conventional electrical antennas. Although many structures of ME antennas have been proposed, their resonant frequency stay below 3 GHz, which cannot satisfy 5G communication. Here we report a magnetoelectric antenna with 445 nm AlN coupled with FeGaB/SiO ₂ multilayers based on the solidly mounted resonator (SMR) structure with Bragg reflectors of SiO ₂ /W/SiO ₂ /W/SiO ₂ , which resonates at 4.97 GHz consistent with theoretical analysis of the reflection performance of the ME antenna. The far-field radiation performance with different FeGaB thicknesses and near-field polarization of the ME antenna were tested. The experimental data demonstrate that the SMR-based ME antenna with 270 nm-thick FeGaB film displays the highest far-field performance with a gain of –25.1 dBi, quality factor of 1207, and radiation efficiency of 0.53% with a circular resonating disk of 300 μm in diameter. Such a compact and high-frequency ME antenna is potentially suitable for the 5G wireless communication systems.

Compensated synthetic antiferromagnets (SAFs) stand out as promising candidates to explore various spintronic applications, benefitting from high precession frequency and negligible stray field. High-frequency antiferromagnetic resonance in SAFs, especially the optic mode (OM), is highly desired to attain fast operation speed in antiferromagnetic spintronic devices. SAFs exhibit ferromagnetic configurations above saturation field; however in that case, the intensity of OM is theoretically zero and hard to be detected in well-established microwave resonance experiments. To expose the hidden OM, the exchange symmetry between magnetic layers must be broken, inevitably introducing remanent magnetization. Here, we experimentally demonstrate a feasible method to break the symmetry via surface acoustic waves with the maintenance of compensated SAF structure. By introducing an out-of-plane strain gradient inside the Ir-mediated SAFs, we successfully reveal the hidden OM. Remarkably, the OM intensity can be effectively modulated by controlling strain gradients in SAFs with different thicknesses, confirmed by finite-element simulations. Our findings provide a feasible scheme for detecting the concealed OM, which would trigger future discoveries in magnon-phonon coupling and hybrid quasiparticle systems.

In the rapidly evolving fifth-generation (5G) communication system, there is an urgent need for high-performance surface acoustic wave (SAW) filters to address challenges such as frequency band congestion and smaller gaps between adjacent frequency bands. In this study, we focused on investigating longitudinal leaky SAW (LLSAW) devices based on the LiTaO $_{\text{3}}$ /SiO $_{\text{2}}$ /SiC hetero-structure, specifically designed for narrowband applications. A comprehensive analysis of the intrinsic electromechanical coupling coefficients ( K $^{\text{2}}_{\textit{ij}}$ ) of shear horizontal SAW (SH-SAW) and LLSAW on LiTaO $_{\text{3}}$ (LT) thin films was conducted. Via carefully adjusting the LT cut angle $\theta $ and propagation angle $\psi$ , strong excitation of LLSAWs was achieved. Through elaborated parameter optimization, LLSAW resonators were fabricated based on a 50 $^{\circ}\textit{Y}$ - $\text{45}^{\circ}\textit{X}$ LT/SiO $_{\text{2}}$ /SiC platform, demonstrating excellent performance on frequencies and quality factors ( Q ). These resonators exhibited small effective electromechanical coupling coefficients ( $\textit{K}_{\text{eff}}^{\text{2}}$ ) ranging from 4.6% to 5.9% and scalable resonance frequencies ranging from 2887 to 6050 MHz. In addition, a high maximum Bode- Q of 2121 was attained. Finally, filters were numerically simulated using LLSAW resonators and a narrowband filter with fractional bandwidth (FBW) of 2.3% and minimum insertion loss (IL $_{\text{min}}$ ) of 1.4 dB was successfully fabricated. The developed LT/SiO $_{\text{2}}$ /SiC structure emerges a great prospect of high-performance narrowband applications in the 5G era.

To meet the demands of highly integrated and miniaturized radio frequency front-end (RFFE) modules, multi-passband filters which support multi-channel compounding come to the foreground. In this work, we proposed a new design of a dual-passband surface acoustic wave (SAW) filter based on a 32°YX-LiNbO₃ (LN)/SiO₂/SiC multilayered structure. The filter is of a standalone ladder topology and comprises dual-mode resonators, in which the shear horizontal (SH) mode and high-order SH mode are simultaneously excited through electrode thickness modulation. The impact of electrode thickness on the performance of the dual-mode resonator was systematically investigated by the finite element method (FEM), and resonators were prepared and verified the simulation results. The electromechanical coupling coefficients (K²) of the SH modes are 15.1% and 17.0%, while the maximum Bode-Q (Q_max) values are 150 and 247, respectively, for the fabricated resonators with wavelengths of 1 μm and 1.1 μm. In terms of the high-order SH modes in these resonators, the K² values are 9.8% and 8.4%, and Q_max values are 190 and 262, respectively. The fabricated dual-band filter shows the center frequencies (f_c) of 3065 MHz and 4808 MHz as two bands, with 3-dB fractional bandwidths (FBW) of 5.1% and 5.9%, respectively. Such a dual-band SAW filter based on a conventional ladder topology is meaningful in terms of its compact layout and diminished area occupancy. This work provides a promising avenue to constitute a high-performance dual-passband SAW filter for sub-6 GHz RF application.

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.