Influence of ultrathin tantalum buffer layers on microstructure and ferroelectric properties of SrBi ₂ Ta ₂ O ₉ thin films

The effects of buffer layers on the crystallization process of strontium bismuth tantalite (SBT) thin films, using a metallorganic decomposition technique, are investigated in this study. Ultrathin tantalum (Ta) buffer layers of various thicknesses were deposited onto Pt/TiO₂ /SiO₂ /Si substrates using magnetron sputtering. The crystallinity, microstructure, and electrical properties of the resulting SBT films on top of the Ta layer were found to be strongly dependent on the thickness of the buffer layer. By optimizing this buffer layer thickness, a homogeneous bismuth-layered structure with uniformly distributed fine grains, it was clearly evident that the SET film, annealed at 750°C for 1 min, and the corresponding remanent polarization (2P_r), can be as large as 18.8 μC/cm² at an applied voltage of 5 V. It is suggested that these buffer layers cause the SBT composition to depart from stoichiometry to an enriched Ta condition. During the crystallization procedure in oxygen ambient, the excess Ta atoms in local regions easily reacted with O atoms to form TaO_x, centers. They are believed to serve as the nucleation sites that cause the reduction of the activation energy of SBT crystallization.