Chengjie Zuo

This work reports on the first experimental demonstration of piezoelectric micromachined ultrasonic transducers (PMUTs) based on the intrinsic piezoelectricity of c-axis 4H-silicon carbide (4H-SiC), establishing its viability for acoustic transduction in extreme environments. Fabricated on silicon carbide on insulator (4H-SiCOI) substrates via standard microelectromechanical-system processes, the devices exhibit distinct flexural resonant modes verified by laser Doppler vibrometry, confirming effective electromechanical transduction. The measured fundamental resonant frequencies adhere strictly to classical thin-plate vibration theory across a broad range of diaphragm geometries. Furthermore, the analysis of a PMUT array reveals exceptional inter-unit uniformity with tightly controlled frequency distributions. These results validate 4H-SiC as a compelling alternative to conventional AlN and PZT, paving the way for integrated piezoelectric sensing systems in high-temperature and high-radiation scenarios.

Acousto‐optic (AO) interactions provide a powerful interface between the microwave and optical domains, enabling optical switching, non‐reciprocal propagation, and efficient microwave‐to‐optical transduction. Here, we demonstrate high‐efficiency AO modulation on a non‐suspended lithium‐tantalate‐on‐insulator (LTOI) platform. LTOI combines intrinsically low birefringence, a high optical‐damage threshold, strong electro‐optic and Kerr nonlinearities, and favorable acoustic properties. Our Mach–Zehnder interferometers achieve , while racetrack resonators reach , enabling microwave‐to‐optical conversion without suspended structures. Measurements across six in‐plane propagation directions identify propagation along the crystal Z axis as the most efficient tested configuration, where the higher‐order R1 mode produces the strongest MZI response. Temperature‐dependent acoustic measurements and continuous RF‐driven optical testing further demonstrate material‐related operating stability. These results establish non‐suspended LTOI as a robust platform for integrated acousto‐optics with broad applications in communications, signal processing, and quantum information technologies.

High-frequency acoustic resonators are key elements in radio-frequency (RF) front ends that enable signal selection, filtering, and spectral reconfiguration in modern wireless communication systems. However, achieving both large electromechanical coupling (k²) and high quality factor (Q) in 5G/6G bands (3 to 7 GHz, or sub-7 GHz) remains a critical challenge for acoustic wave devices. Here, we propose and demonstrate a new type of self-aligned nanorod bulk acoustic wave (SN-BAW) resonator fabricated from single-crystal piezoelectric lithium niobate (LiNbO₃ or LN) thin film on silicon carbide (SiC) substrate. The resonator features an array of solidly mounted piezoelectric nanorods defined by one step of a self-aligned nanoscale etching process, which eliminates the need for suspended membranes, bottom electrodes, or reflective gratings, as normally required in traditional bulk acoustic wave (BAW) or surface acoustic wave (SAW) devices. This unique nanorod LiNbO₃ structure, solidly mounted on SiC substrate, ensures strong acoustic energy confinement within the piezoelectric material and excellent mechanical stability while enabling a good thermal path for heat dissipation, which favors the thermal handling capability of the realized resonators. The fabricated SN-BAW resonators exhibit outstanding performances, with high quality factors (Q) up to 1943 in the 3 to 5 GHz range, scalable electromechanical coupling coefficients (k²) from 23% to 43% depending on design, and a record-high figure of merit (FoM = k² × Q) of 626 at 3.46 GHz. These results demonstrate a practical route toward wafer-level, low-loss, and frequency-agile acoustic filters with good thermal handling and low cost aimed for next-generation 5G and 6G RF front ends, and highlight LiNbO₃ nanostructures as a unifying platform linking photonics, acoustics, and high-frequency electronics.

Herein, based on MOCVD-regrown ohmic contacts (ROCs), a GaN HEMT with ultra-low noise figure and superior power merit is reported. Thanks to the ROCs, a low contact resistance of 0.13 Ω·mm is achieved, benefiting 26% reduced parasitic source resistance compared to the devices with alloyed ohmic contacts. As such, the ROC-HEMT shows reduced thermal noise and ultra-low minimum noise figures within a wide bandwidth, featuring 0.38/0.71/1.19 dB at 10/18/30 GHz with associated gain of 12.5/9.8/6.6 dB. In addition, remarkable output power and efficiency at Ku-band can be delivered by the ROC-HEMT, verifying the feasibility of MOCVD-ROC techniques to advance noise & power performance of GaN HEMTs towards compact all-GaN RF front-end modules.

In this work, we present a newly proposed concept of engineering the anchor fins in a suspended Lamb wave resonator and using it as an important design parameter to optimize the resonator performance. The exploration was conducted on antisymmetric Lamb wave resonators based on 128° Y-cut lithium niobate (LN or LiNbO ${}_{\mathbf {3}}$ ) and the deformation was adjusted by introducing different anchor fin designs that mount the suspended structure to the supporting substrate. The proposed design methodology was validated by the demonstration of first-order antisymmetric Lamb wave (A1-mode) resonators operating at 12GHz, and also third-order antisymmetric Lamb wave (A3-mode) resonators operating at 36GHz. It has been proved that special anchor fin design serves as an effective means to improve the power handling or linearity of Lamb wave resonators. Therefore, this work opens up a brand new design space for acoustic resonators based on a suspended thin-film structure, which makes it possible to realize further performance enhancement and optimization for Lamb wave resonators especially at centimeter wave (cmWave) and millimeter wave (mmWave) frequencies. [2025-0117]

Ultra-wide bandgap/wide bandgap (UWBG/WBG) materials have revolutionized power electronics and ultraviolet solid-state lighting, attracting significant attention from researchers. However, beyond active devices, UWBG/WBG materials have also made remarkable contributions to radio frequency (RF) passive acoustic devices over the past decades. This paper provides a systematic and critical review of UWBG/WBG materials in RF passive acoustic applications, categorizing them into two functional groups: acoustic wave generators and acoustic wave restrainers. UWBG/WBG piezoelectric materials, including Al(Sc)N, LiNbO3 (or LN), GaN, and ε-Ga2O3, are explored as effective acoustic wave generators, while SiC and diamond are evaluated as acoustic wave restrainers due to their high phase velocity and thermal conductivity. This review examines the crystal structures, electrical, and acoustic (mechanical) properties of these materials, as well as their synthesis methods and chronological advancements in RF passive acoustic applications. By integrating recent research findings and technological trends, this review highlights the transformative potential of UWBG/WBG materials in developing next-generation RF communication technologies.

The signal of spin-torque ferromagnetic resonance (ST-FMR) primarily consists of microwave absorption resonance in the ferromagnetic layer and spin–orbit torque (SOT) absorption resonance, with SOT efficiency strictly dependent on the applied current. Based on this, we propose an ST-FMR-based filter that not only enables the selection of specific frequency signals through magnetic field modulation but also allows precise tuning of signal linewidth via current control. This study provides insights into using spintronic devices for advanced signal processing applications.