Contribution of Ribbon-Structured SiO₂ Films to AlN-Based and AlN/Diamond-Based Lamb Wave Resonators

New designs based on S₀ Lamb modes in AlN thin layer resonating structures coupled with the implementation of structural elements in SiO₂, are theoretically analyzed by the Finite Element Method (FEM). This study compares the typical characteristics of different interdigital transducer (IDTs) configurations, involving either a continuous SiO₂ cap layer, or structured SiO₂ elements, showing their performance in the usual terms of electromechanical coupling coefficient (K²), phase velocity, and temperature coefficient of frequency (TCF), by varying structural parameters and boundary conditions. This paper shows how to reach temperature-compensated, high-performance resonator structures based on ribbon-structured SiO₂ capping. The addition of a thin diamond layer can also improve the velocity and electromechanical coupling coefficient, while keeping zero TCF and increasing the solidity of the membranes. Beyond the increase in performance allowed by such resonator configurations, their inherent structure shows additional benefits in terms of passivation, which makes them particularly relevant for sensing applications in stern environments.