Development of sputtered SrBi2Ta2O9 thin films for nonvolatile random access memory application

Utilization of ferroelectric thin films for nonvolatile random access memory (NvRAM) applications has been under intensive investigation. Films for transistor-type memory require possessing these properties: a large remnant polarization, a low coercive field (2Ec), sufficient fatigue endurance against repetitive polarization switching. Layered perovskite structure SrBi2Ta2O9 (SBT) thin film has attracted ever increasing attention because it exhibits fatigue-free property up to 1012 cycles (even on Pt bottom electrode), excellent retention characteristics, and low leakage current density. However, two shortcomings are involved in SBT thin films: the low remnant polarization (2Pr800?). Substitution at A or B site can effectively modify polarization properties. Trivalent elemental substitution such as Bi3+, La3+ and Nd3+ with the Sr2+ site induces A-site cation vacancies to satisfy charge neutrality, which significantly improves the low-field polarization.DOCTOR OF PHILOSOPHY (MAE