Frequency scaling capabilities of single layer LiNbO3 film bulk acoustic resonators

We investigate the capability of LiNbO3 film bulk acoustic resonators to scale up in frequency through the selection of second and third order overtones. With the same piezoelectric layer thickness (300 nm), but different electrode thicknesses, resonators reach antiresonance frequencies of respectively 9, 10.1 and 12.1 GHz when considering fundamental mode, second overtone and third overtone longitudinal resonators. Electromechanical coupling factors of respectively 21%, 8% and 11% are obtained, indicating that satisfying electromechanical coupling factors can be reached without requiring complex structures such as periodically poled resonators. This offers promising perspectives towards further frequency scaling with thinner piezoelectric layers.