High SAW velocity and high electromechanical coupling coefficient with the new three layered structure: ZnO/AlN/diamond

A new diamond based SAW device layered structure, combining high acoustic velocity (Vφ) and high electromechanical coupling coefficient (K^-), is investigated for GHz-band applications. In fact, to overcome the trade-off relationship between Vφ and K², we propose the use of a three-layer structure ZnO/AlN/diamond that combine the advantages of both piezoelectric materials: high K² of ZnO and high velocity of AlN. A theoretical study based on the Campbell and Jones model was performed to calculate the phase velocity and K² dispersion curves of the Rayleigh mode; its higher modes as well as the leaky waves generated in this structure. Three configurations depending on IDT position in the structure: ZnO surface, ZnO/AlN or AlN/diamond interfaces were calculated considering various thicknesses of ZnO and AlN layers. Both high values of K² larger than 4%, and of Vφ more than 15 km/s are expected on this new structure according to the theoretical results.