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A wideband 5G millimeter-wave multiple-input multiple-output (MIMO) magneto-electric (ME) dipole antenna integrated with partially reflective surfaces (PRSs) is proposed. Each ME dipole consists of a planar electric dipole and an equivalent magnetic dipole. Owing to dual radiation modes of the ME dipole antenna, the wide bandwidth can be obtained. To increase the radiation gain, a dielectric slab with planar PRSs is placed over the ME dipole antenna. The PRS and the metal ground plane form a Fabry-Perot cavity which can increase the radiation gain. Meanwhile, four dielectric cylindrical rings with rotationally symmetric PRSs can construct multiple Fabry-Perot cavities and a further increase of the radiation gain can be obtained. The metal sidewalls and the polarization diversity are applied to reduce mutual coupling. The measured impedance bandwidth at -10 dB reflection coefficient is 24-43.5 GHz (57.8%). The measured transmission coefficients \S21\, \S31\, and \S32\ are less than -27, -37.9, and -46.4 dB, respectively. The simulated and measured maximum radiation gains are 17.3 and 16.1 dBi, respectively. Thus, the proposed 5G millimeter-wave MIMO ME dipole antenna integrated with PRSs features wide bandwidth, high isolation, and high radiation gain. IEEE

This focuses on developing a new platform for the thin-film bulk acoustic wave (BAW) resonator, which features predefined sealed cavities, self-formed acoustic boundaries, and compatibility with subsequent fabrication. Different from conventional BAW resonator fabrication methods, this work has simplified fabrication by using silicon migration technology: building freely predefined cavities with self-formed acoustic boundaries without patterning the piezoelectric layer in only two steps (etching and annealing). Additionally, the sealed cavity is sturdy enough to be compatible with subsequent hetero-integrating with other devices. For higher frequency and better electromechanical coupling ( K2 ), the proposed platform can excite the second-order asymmetric Lamb wave mode (A2) in scandium-doped aluminum nitride (Al1–xScxN) film with an optimized stress field. The fabricated devices demonstrate S1 and A2 resonant modes at 1.58 GHz and 3.52 GHz with electromechanical coupling coefficients of 1.47% and 5.12%, respectively. [2023-0185]

This paper reports on the demonstration of a 6.2 GHz acoustic filter with an over-1 GHz bandwidth, a 30 dB out-of-band rejection, and a sharp roll-off. The demonstrated filter employs the first-order antisymmetric (A1) lamb wave in Y-128° cut lithium niobate thin film to maximize the electromechanical coupling (k2t=48%). Amorphous Si is utilized to decrease the parasitic conductor effect and feedthrough for better out-of-band rejection of the filter. The ultrawide passband proves the promising potential of lithium niobate thin films in WIFI 7 and 6G applications.

This paper presents a new method to suppress spurious modes in lithium niobate thin-film acoustic devices by twisting the piezoelectric coupling properties of the spurious modes. The excellent piezoelectric properties of lithium niobate (LiNbO3) advance performance but lead to significant spurious modes accompanied by the targeted main mode. To harvest the benefits and avoid the spurious modes, this work investigates solidly mounted LiNbO 3 thin films with different substrates to twist the zero-coupling orientations of spurious modes to be close to the maximum-coupling orientation of the targeted main mode. The fabricated devices, based on the solidly mounted LiNbO 3 -sapphire structure and surface guided acoustic wave, show an operating frequency of 2.4 GHz with a large electromechanical coupling of 22% and a spurious-free response in the wide frequency range. This work could overcome a significant bottleneck in commercializing LiNbO 3 thin-film acoustic devices.

This paper presents different frameworks of lithium niobate (LiNbO 3 ) thin films for piezoelectric acoustic devices covering from GHz to mmWave. Lithium niobate thin film can be either solidly mounted on carrier substrates or suspended to address the limitations in traditional piezoelectric acoustic devices. Various devices, including a spurious-free resonator, a Wi-Fi 6E passband filter, 5.7 GHz acoustic delay lines, and mmWave resonators, are investigated and fabricated to present the excellent potential of LiNbO 3 thin films.

This paper presents a new method to improve the performance of SAW devices based on transferred lithium niobate thin films. Amorphous silicon replaces the single-crystal silicon to eliminate a conductive layer generated in the thin-film transfer processes. As a result, the electromechanical coupling of the surface-guided acoustic wave is maximized, and the substrate loss is reduced in the amorphous-silicon-based hybrid wafer. The fabricated resonator shows an extracted electromechanical coupling coefficient of 22% with over 60 dB impedance radio, which is 30 dB higher than the resonator with parasitic surface conductive effect. The fabricated delay lines show excellent propagation properties of the excited surface-guided acoustic wave with a minimum propagation loss of 18.1 dB/mm at 2.35 GHz, which further demonstrate the elimination of the conductive layer and outstanding acoustic energy confinement between lithium niobate and amorphous silicon. This work has shown the strong potential of the silicon-SAW platform for front-end signal processing. © 2022 IEEE.

This work presents an acoustic platform using solidly mounted thin-oriented lithium niobate (LiNbO3) film on silicon (Si). A thin layer of amorphous Si eliminates a conductive layer generated in the thin-film bonding processes and contributes to acoustic energy confinement and thermal frequency stability. The gigahertz operating frequency is achieved by resorting to the guided acoustic wave shear-horizontal wave (SH0) in a 400-nm-thick X-cut LiNbO3 thin film. Due to the elimination of the parasitic surface conduction (PSC) effect, the electromechanical coupling of the guide acoustic wave is maximized in the Si-based heterogeneous wafer. Due to the minimized acoustic impedance mismatch between surface material and substrate, longitudinal and higher order spurious modes are suppressed. Due to the stiff substrate with a small temperature expansion coefficient (TEC), the solidly mounted structure features a reduced temperature coefficient of frequency (TCF) and improved power handling. The fabricated resonator shows an extracted electromechanical coupling coefficient of 22.8%, a high loaded Q of 1208 at 1.6 GHz, and a TCF of -36 p/min/K. The compressed filter is demonstrated with a minimum insertion loss (IL) of 0.6 dB, a fractional bandwidth (FBW) of 8%, an out-of-hand rejection of 30 dB, a TCF of -38.5 p/min/K at roll-off, and a miniaturized footprint of 0.4 mm(2). The performance has shown the strong potential of the LiNbO3-Si platform for front-end applications in 5G.

This paper demonstrates a 160 nm thick first- and third-order antisymmetric mode Lithium Niobate resonator. The presented device maintains feature sizes on the order of micrometers by thinning the piezoelectric resulting in a first-order mode at 11.77 GHz through direct scaling of state-of-the-art design approaches. Thinning leverages an Argon-based low-power physical etch, with attention paid specifically to surface roughness. The fabricated device demonstrates a first-order antisymmetric series resonant frequency of 11.77 GHz with an electromechanical coupling of 23.6% and a mechanical quality factor of 148 for a Figure of Merit of 35.1. In addition, the resonator's third-order antisymmetric mode achieves an electromechanical coupling of 3.7% and a mechanical quality factor of 66 at a frequency of 34.7 GHz.

In this work, we present the low-loss acoustic delay lines (ADLs) at 5 GHz, using the first-order antisymmetric (A1) mode in 128° Y-cut lithium niobate thin films. The ADLs use a single-phase unidirectional transducer (SPUDT) design with a feature size of quarter acoustic wavelength. The design space is analytically explored and experimentally validated. The fabricated miniature A1 ADLs with a feature size of show a high operating frequency at 5.4 GHz, a minimum insertion loss (IL) of 3 dB, a fractional bandwidth (FBW) of 1.6%, and a small footprint of 0.0074 mm 2 . The low IL and high operating frequency have significantly surpassed the state-of-the-art performance of ADLs. The propagation characteristics of A1 acoustic waves have also been extracted. The demonstrated designs can lead to low-loss and high-frequency transversal filters for future 5G applications in the sub-6-GHz bands.