(1-x)SrBi2Ta2O9-xBi3Ti(TayNb1-y)O9 Layered Structure Solid Solutions for Ferroelectric Random Access Memory Devices

Abstract

ABSTRACTThin films of layered-structure solid-solution material, (1−x)SrBi2Ta2O9−xBi3Ti(TayNb1−y)O9, have shown much improved ferroelectric properties compared to SrBi2Ta2O9, a leading candidate material for ferroelectric random access memory applications. The higher Pr, higher Tc, and lower crystallization temperature of the thin films of solid solution material promise to solve many problems with the present materials of interest. The films were fabricated by metalorganic solution deposition technique using room temperature processed alkoxide-carboxylate precursor solution and characterized in terms of structural, dielectric, and ferroelectric properties. It was possible to obtain a pyrochlore free crystalline phase at an annealing temperature of 600 °C. The effects of annealing temperature and excess Bi content on the film microstructure and properties were analyzed. The electrical measurements were conducted on metal-ferroelectric-metal (MFM) capacitors using Pt as the top and bottom electrode. It was possible to obtain good ferroelectric properties on films annealed at 650 °C. For example, thin films with 0.7SrBi2Ta2O9-0.3Bi3TiTaO9 composition, which were annealed at 650 °C, exhibited typical 2Pr and Ec values of 12.4 μC/cm2 and 80 kV/cm, respectively. The films exhibited low leakage current density, good fatigue characteristics under bipolar stressing at least up to 1010 switching cycles, and good memory retention characteristics after about 106 s of memory retention indicating a favorable behavior for memory applications.