Investigation of Elastic Topological Protected Interface Modes on RF Piezo-Electric MEMS Technology

Since their discovery, topological insulators have attracted significant research interest due to their nontrivial topological properties. These properties give rise to the emergence of edge states that propagate along the interface between inversed topological invariants. These edge states assume great relevance because of their ability to resist perturbations and so being immune to back-scattering. For these reasons, they are referred to as topologically protected states. The discovery of this phenomenon in quantum systems and the potential of this unidirectional transport with negligible attenuation inspires and led to the demonstration of the equivalent topological edge states in acoustic technologies. The aim of this work is to investigate the existence of topological protected states at the interface of a Piezo-Electric MEMS device working in the RF range. A topological edge mode is formed when a break of the symmetry of a periodic system with a topologically non-trivial bandgap happens. To achieve this outcome, we examined a piezoelectric metamaterial based on AlScN, which has a spatially periodic structure that ensures a symmetric band-structure. A detailed examination of the band structure of the device's single unit-cell was conducted. The presence of topologically-protected modes was initially investigated through numerical methods, specifically the finite element method (FEM). The Floquet boundary condition was applied to the single unit-cell during this study. The existence of this state was then verified by calculating the Zak phase, which is a geometric phase characterizing the topological properties of bulk bands in a 1D periodic system. To investigate the presence of topological-protected modes in a device with a finite number of unit cells, a numerical study was again carried out using FEM simulations.