The morphology of unconventional sputter deposited Ba(1-x)SrxTiO3 thin films

Thin films of Ba(1-x)SrxTiO3 (BST) have been deposited on (100) MgO substrates by off-axis cosputtering targets of SrTiO3 and BaTiO3 for several Ba/Sr metals fractions. The surface morphology and crystal structure were strongly dependent on the Ba/Sr metals fraction. For small x values (< 0.3), the films were multi-textured and of a tetragonal structure. At greater x, the films became predominantly (110) orientated and for x > 0.5 became strongly (200) orientated. The surface roughness was smooth for x < 0.5 and became progressively rougher with increasing x (greater Sr). Interdigitated capacitors fabricated on these films showed greater tuning for films having low x values and greater Q for those having higher x values. A comparison of the lattice parameter with that for bulk BST shows the films to be under compressive stress for x < 0.45 and under tensile stress for x > 0.45. This film stress has a strong influence on the Curie temperature and the resulting dielectric properties of the films.