Phase formation and crystal growth of Sr–Bi–Ta–O thin films grown by metalorganic chemical vapor deposition

The crystallization process of SrxBiyTa2O5+x+3y/2 thin films grown by metalorganic chemical vapor deposition was investigated. Phase formation and crystal growth is greatly affected by the film composition and crystallization temperature. Phase diagrams for varying Sr or Bi contents were determined as a function of the crystallization temperature. The higher the Sr or Bi content in the film, the lower the phase transition temperature from the amorphous to the fluorite-type phase and from the fluorite-type to the Bi-layered Aurivillius phase. Low Sr and Bi contents support pyrochlore-type phase formation as a second phase. During annealing, excess Bi is not lost due to evaporation, but due to migration to the bottom electrode. Contrary to the fluorite-type phase, the Aurivillius phase is not able to incorporate the excess of Bi atoms. Decreasing grain size and pyrochlore-type phase formation entail decreasing remanent polarization.