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 (k²) of 33.82%, along with series and parallel 3-dB quality factors (Qs and Qp) 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.

I. Introduction

With radio frequency (RF) bands below 7 GHz fully allocated, exploration of millimeter-wave (mmWave) bands, ranging from 10 to 100 GHz as defined by 3GPP standards, is essential to support the escalating mobile data traffic [1]. The need for effective mmWave filtering solutions is becoming a critical bottleneck in the further deployment of 5G networks [2]. Various countries and regions, including Europe, China, and the United States, have released several mmWave bands for 5G New Radio (NR) communications across the Ka-band, Q-band and even E-band [3]. As the primary filter solution below 7 GHz in mobile systems, the performance of micro-acoustic devices at mmWave frequencies is crucial to meeting the stringent requirements set by 5G standards [4].