High Coupling Two-port Lithium Niobate MEMS Resonators using Capacitive Ground Concept

The most important bottleneck for the use of lithium niobate (LN) films for making MEMS resonators is related to the fabrication process and it is particularly challenging when a bottom electrode needs to be included in the film stack to increase the resonator's capacitance per unit area. In this work, we propose to access the bottom electrode by using capacitive coupling rather than a direct resistive coupling. We utilize the high dielectric constant available from the Y-cut LN thin film to implement this concept. In this practical demonstration, we ground the bottom electrode, hence we call it "capacitive ground" concept. This approach eliminates the need for additional patterning of the bottom electrode and selective etching of the LN film over the bottom electrode. This demonstration is critical in the development of resonators with high out-of-band rejection and piezoelectric transformers.