Realization of high-Q Lamb wave resonator with smooth vertical etching profile for thin film lithium niobate

In this work, Lamb Wave Resonators (LWRs) based on 2 μm thin Y-cut LiNbO3 films have been fabricated using integrated fabrication process that defines IDTs (Inter Digital Transducers) on top surface and a partial Si cavity for a sacrificial layer on the bottom surface. We discuss the etch quality and its effects on the device's performance. For the first time, we present an optimized high-quality etched MEMS (Micro-electromechanical Systems) Resonator with smooth and vertical sidewalls on this material system, reporting the maximum Q-factor of 2500 at 846 MHz frequency. We observed that the resonator system has a Q-factor of 480 over the same frequency range when the etched surface has significant roughness and non-verticality. Q values of the device are greatly diminished by the presence of surface roughness and non-verticality of the etched edges. This truly highlights how important it is to have a high-quality etch profile for a piezoelectric material system like this so that the designed resonators can perform at their best.