PMBAR* - shear mode TFBAR based on (001)AlN thin film

A novel concept for shear mode Bulk Acoustic Resonators (BAR) is presented. It is based on c-axis oriented AlN thin films grown on silicon dioxide thin films, combined with interdigitated electrodes. Such a structure leads to an excitation of mainly shear mode displacements in the AlN film. However, a more pure mode is expected if only every second electrode section would contain active AlN, thus requiring means to selective disabling the piezoelectricity in AlN. In this article, such piezo-modulated BAR structures are studied by the finite element method to evaluate the theoretical performance. Preliminary experimental results show the practical feasibility of the new concept. A first test device delivers a quality factor of 1100 in air.