36.8-GHz Fin-Mounted Lithium Niobate Resonator with High Electromechanical Coupling Coefficient of 33.8%

In this study, we carefully reduced the thickness of single-crystal Y128° lithium niobate (LN) thin films to approximately 50 nm through low-power physical etching using argon gas. This process was adopted to construct a finmounted Lamb wave resonator operating above 30 GHz. The fabricated fin-mounted nanosheet LN resonator, operating at 36.84 GHz, achieved an electromechanical coupling coefficient (k<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>) of 33.82%, along with series and parallel 3-dB quality factors (Q<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> and Q<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">p</inf>) of 13 and 83, respectively. These results demonstrate the highest figure of merit (FoM) of 28, surpassing other millimeter-wave (mmWave) resonators within the same frequency range.