Self-aligned assembly of piezoelectric nanorods for 6G wireless communications.

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.