Localized Modes in Asymmetric Phononic Crystals

This paper reports on a localized mechanical resonance induced by a novel phononic crystal (PnC) design demonstrated in a $1\ \mu \mathrm{m}$ aluminum nitride (AlN) thin film. An asymmetric PnC with diagonal beam bridging discs in a square lattice generates an isolated mode inside the PnC bandgap defined by the flexural mode of the connecting beam. Here we investigate the properties of the PnC dispersion relations as a function of key design parameters, defining resonance cavities to excite the localized mode. PnC resonators with localized mode at 156 MHz are characterized as a function of central bar rotation angle ($\theta$), number of actuation layers ($\mathrm{N}_{act}$) and lateral periods (P). This analysis of electromechanical modes with designed flat dispersion relation is an important first step toward Density-Near-Zero (DNZ) metamaterials and resilient elastic wave manipulation on chip.