Induced surface roughness to promote the growth of tilted-AlN films for shear mode resonators

Two methods currently used to induce surface roughness that promotes the growth of AlN tilted grains to fabricate shear mode resonators have been investigated. The first one involves the use of a rough substrate to provide tilted facets on which the AlN grains will grow with a certain angle. The second method is based on using a thin non-piezoelectric AlN seed layer that exhibits high populations of {10·3} and {10·2} planes. The influence of the power applied to the Al target and the total gas pressure during the deposition process of the AlN seed layer has been studied and correlated with the k²_shear of the resonators. The best fabricated devices show a shear mode resonance frequency at around 1.45 GHz, a k²_shear up to 3.64% and a Q_shear above 230 when operating in air, which reduces to 108 when operating in liquid.