Seed layer controlled deposition of ZnO films with a tilted c-axis for shear mode resonators

We investigate different procedures for achieving ZnO films with the c-axis tilted with respect to the normal for their application in acoustic resonators operating in the shear modes. The approach consists in combining the use of textured surfaces of different nature with off-axis sputtering, which promotes the growth of ZnO with inclined microcrystals. The rough surfaces investigated are porous-SiO₂ and AlN and ZnO seed layers films specifically prepared to exhibit textured surfaces. The suitability of these films for the intended applications is tested by analyzing the frequency response of ZnO-based solidly mounted resonators. Electromechanical coupling factors for the shear modes up to 3.3% are achieved.