Parametric study of sputtered Sr-deficient SrBi₂ Ta ₂O₉ thin films

Sr-deficient Sr Bi2 Ta2 O9 (SBT) thin films for nonvolatile ferroelectric random access memory applications were deposited by radio-frequency magnetron sputtering on PtTaSi O2 Si substrates. The effect of deposition parameters on microstructures and chemical composition were studied using x-ray diffraction (XRD), field emission scanning electron microscopy, and x-ray photoelectron spectroscopy (XPS). The composition of the films was dependent on the sputtering conditions. The undesirable pyrochlore phase could be eliminated by adjusting process pressure, target power density, and target-to-substrate distance. The evolution of microstructures at various deposition conditions was attributed to changes in the BiTa and SrTa ratios. When Sr became deficient and Bi excessive (Sr0.74 Bi2.2 Ta2 O9+x as determined by XPS), no pyrochlore phase was detected with XRD. Under an electric field of 240 kVcm, the Sr-deficient SBT film demonstrated a remnant polarization (2 Pr) of 11.6 μC cm2 and a coercive field (2 Ec) of 96 kVcm.