Frequency Scaling Acoustic Resonators into Millimeter Wave Using Thin-Film Lithium Niobate*

Recent studies have aimed to reproduce the success of acoustic resonators at sub-6 GHz at higher frequencies, e.g., into millimeter waves. However, such frequency scaling calls for innovation from both the material-level development and device-level design. In this talk, we will examine the fundamental limits of mm-wave acoustic resonators, then showcase transferred thin-film lithium niobate (LiNbO3) as a promising platform. More specifically, periodically poled piezoelectric film (P3F) LiNbO3 will be used for frequency scaling without losing quality factor (Q) or electromechanical coupling (k2). Finally, we report a 50.74 GHz lithium niobate (LiNbO3) acoustic resonator with a high quality factor (Q) of 237 and an electromechanical coupling (k2) of 5.17% resulting in a figure of merit (FoM, Q·k2) of 12.2. The device also shows a Q of 159, k2 of 65.06%, and FoM of 103.4 for the 16.99 GHz tone. This result shows promising prospects of P3F LiNbO3 towards mm-wave front-end filters.