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

Abstract

We studied the role of excess Bi, added to improve ferroelectirc properties of SrBi 2 Ta 2 O 9 (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 Sr 0.9 Bi 2.1 Ta 2 O 9 composition. Closely stoichiometric Sr 0.9 Bi 2.1 Ta 2 O 9 SBT film shows no fatigue even after 3×10 12 switching cycles. The improved SBT formation solution that is hydrolyzed, condensed solution makes excess Bi unnecessary.