Crystallization trend in STO-seeded sputtered PZT thin films: Effects of seed layer thickness and post-annealing temperature

Based on the results of X-ray diffractometry (XRD) and analytical scanning/transmission electron microscopy (S/TEM), the crystallization trend and local chemistry of sputtered PZT films on SrTiO3 (STO) coated corning glass substrates have been scrutinized as functions of STO layer thickness (∼20-150 nm) and post-annealing temperature (450  C-650 °C). It is shown that as a seed layer, STO thin films promote perovskite PZT nucleation at the PZT/STO interface at a temperature of ∼450 °C. Irrespective of STO seed layer thickness, PZT films evolve as a bi-layered structure comprising of tetragonal perovskite and disordered fcc fluorite upon post-annealing. The perovskite crystals are found to be enriched with Pb and lean in Zr and oxygen than fluorite structures. During the post-crystallization growth, Zr atoms get preferentially segregated from perovskite structures and accumulate in top fluorite zone resulting in Zr-enrichment in the latter. Thinner STO seed layers are observed to be more effective in realizing better perovskite growth while crystallographic orientation selection of perovskite is dependent on both seed layer thickness and post-annealing temperature. Transverse compositional homogeneity of the grown perovskite PZT and the level of Pb-diffusion from film to the seed layer and glass substrate are also observed to be seed layer thickness dependent.