This invention relates to an improved method of making crystal films, and more particularly it relates to an improved method of making piezoelectric films with a high electro-mechanical coupling coefficient by using a cathodic sputtering step, the films being especially useful for manufacturing thin film acoustic devices.
Crystal films have been used widely for making solid state devices, and crystal films having piezoelectric characteristics are usable for fabricating thin film acoustic devices. Various films having piezoelectric characteristics such as films of ZnO, ZnS, ZnSe, CdS, CdSe, AlN GaN, LiNbO.sub.3 and the sillenite family of bismuth oxides have been investigated by various workers, which films have been formed by means of vacuum evaporation, chemical vapor deposition or cathodic sputtering. These piezoelectric films, however, cannot be used in practice for the production of acoustic devices because their crystallographic properties cannot be controlled with high reproducibility.