Nanosheet Lithium Niobate Acoustic Resonator for mmWave Frequencies

As wireless communication evolves into millimeter wave (mmWave) frequencies, it becomes extremely challenging to realize compact and integrated radio frequency (RF) front-end components with wide bandwidth and high energy efficiency. Here we propose a new fin-mounted acoustic resonator design based on nanosheet (thickness < 100 nm) Z-cut single-crystal lithium niobate (LiNbO3) thin film for large-bandwidth filtering applications in the 5G NR Frequency Range 2 (FR2) band. The fabricated fin-mounted acoustic resonator operating at 25.03 GHz exhibits a high electromechanical coupling coefficient ( ${k}^{{2}}{)}$ of 16% and quality factor ( ${Q}_{p}{)}$ of 132 at parallel resonant frequency (without any de-embedding), which achieves the highest Figure of Merit (FoM = ${k}^{{2}} \times {Q}{)}$ in the 5G FR2 band among all reported resonators to date. This demonstration provides a new solution to the internal stress problem of nanosheet piezoelectric thin film devices and opens up more possibilities in enabling piezoelectric nanostructures for filtering, sensing, and timing applications.