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Role of Excess Bi in SrBi2Ta2O9 Thin Film Prepared Using Chemical Liquid Deposition and Sol-Gel Method

We studied the role of excess Bi, added to improve ferroelectirc properties of SrBi2Ta2O9 (SBT) thin film whose Bi-layered structure is fatigue-free characteristics for Nonvolatile memory. The lost of Bi by annealing process was not observed even after annealing at 850° C in chemical liquid deposition (mixed alkoxide solution system). In SBT films composed of fluorite and Bi-layered structure grains, Bi-layered structure grains had a higher Bi content than that in fluorite grains. Excess Bi was added to promote crystallization of fluorite to the Bi-layered structure easy. SBT film close to stoichimometric composition formed by a hydrolyzed, condensed solution (sol-gel method) had superior ferroelectric properties despite its closely stoichiometric Sr0.9Bi2.1Ta2O9 composition. Closely stoichiometric Sr0.9Bi2.1Ta2O9 SBT film shows no fatigue even after 3×1012 switching cycles. The improved SBT formation solution that is hydrolyzed, condensed solution makes excess Bi unnecessary.