Enhancement of high-frequency harmonics in resonators using multilayered structures with polarity-inverted layers

Periodically Poled Piezoelectric Film (P3F) stacks have recently been reported as a promising platform for next-generation radio-frequency acoustic filters that extend into cm- and mm-wave bands. By demonstrating the potential for developing high-performance acoustic devices with frequencies up to 20 GHz, P3F structures based on lithium niobate (LiNbO3) films have opened up new possibilities. In this study, the influence of key parameters such as the number of layers, crystal orientation, duty factor, and variation in thicknesses between the layers on the efficiency of the n-th harmonic excitation and spurious modes was examined. To enhance higher-order harmonics, which are suppressed in P3F structures, a novel multilayered stack with Aperiodically Polarized Piezoelectric Films (APPF) is proposed. Optimizing the ratio between layer thicknesses can enhance higher-order harmonics. An optimization principle is described and illustrated by examples of three-layered APPF structures optimized for the generation of antisymmetric Lamb wave harmonics A3-A17, with electromechanical coupling continuously decreasing with frequency. High-frequency modes excited in APPF structures fill the gaps in frequencies and electromechanical coupling coefficients between the modes generated in P3F stacks and can provide greater diversity of device performance.