S. O. Ryu

Properties of SrBi2Ta2O9 ferroelectric thin films prepared by a modified metalorganic solution deposition technique

Polycrystalline SrBi2Ta2O9 thin films having a layered-perovskite structure were fabricated by a modified metalorganic solution deposition technique using room temperature processed alkoxidecarboxylate precursor solution. It was possible to obtain a complete perovskite phase at an annealing temperature of 650 °C and no pyrochlore phase was observed even up to 600 °C. In addition, the SrBi2Ta2O9 thin films annealed at 750 °C exhibited better structural, dielectric, and ferroelectric properties than those reported by previous techniques. The effects of postdeposition annealing on the structural, dielectric, and ferroelectric properties were analyzed. The electrical measurements were conducted on Pt/SrBi2Ta2O9/Pt capacitors. The typical measured small signal dielectric constant and dissipation factor at 100 kHz were 330 and 0.023 and the remanent polarization and the coercive field were 8.6 μC/cm2 and 23 kV/cm, respectively, for 0.25-μm-thick films annealed at 750 °C. The leakage current density was lower th...

Thin films of layered-structure (1−x)SrBi2Ta2O9−xBi3Ti(Ta1−yNby)O9 solid solution for ferroelectric random access memory devices

We report on the thin films of solid–solution material (1−x)SrBi2Ta2O9−xBi3Ti(Ta1−yNby)O9 fabricated by a modified metalorganic solution deposition technique for ferroelectric random access memory devices. Using the modified technique, it was possible to obtain the pyrochlore free crystalline thin films at an annealing temperature as low as 600 °C. The solid–solution of layered perovskite materials helped us to significantly improve the ferroelectric properties, higher Pr and higher Tc, compared to SrBi2Ta2O9; a leading candidate material for memory applications. For example, the films with 0.7 SrBi2Ta2O9–0.3Bi3TiTaO9 composition and annealed in the temperature range 650–750 °C exhibited 2Pr and Ec values in the range 12.4–27.8 μC/cm2 and 68–80 kV/cm, respectively. The leakage current density was lower than 10−8 A/cm2 at an applied electric field of 200 kV/cm. The films exhibited good fatigue characteristics under bipolar stressing.

Low temperature processed 0.7SrBi2Ta2O9–0.3Bi3TaTiO9 thin films fabricated on multilayer electrode-barrier structure for high-density ferroelectric memories

Thin films of solid-solution material 0.7SrBi2Ta2O9–0.3Bi3TaTiO9 (0.7SBT–0.3BTT) were fabricated on n+-polycrystalline (n+-poly) Si substrates by a metalorganic solution deposition technique at a low processing temperature of 650 °C using a Pt–Rh/Pt–Rh–Ox electrode-barrier structure. The Pt–Rh/Pt–Rh–Ox structure was deposited using an in situ reactive radio frequency sputtering process. The electrodes had a smooth and fine-grained microstructure and were excellent diffusion barriers between the 0.7SBT–0.3BTT thin film and Si substrate. The ferroelectric (0.7SBT–0.3BTT) test capacitors using these electrode-barrier grown directly on Si showed good ferroelectric hysteresis properties, measured through n+-poly Si substrate, with 2Pr and Ec values of 11.5 μC/cm2 and 80 kV/cm, respectively, at an applied electric field of 200 kV/cm. The films exhibited good fatigue characteristics (<10% decay) under bipolar stressing up to 1011 switching cycles and the leakage current density was lower 10−7 A/cm2 at an applied...

Fabrication and characterization of (1−x)SrBi2Ta2O9–xBi3TaTiO9 layered structure solid solution thin films for ferroelectric random access memory (FRAM) applications

Abstract We report on the properties of (1−x)SrBi2Ta2O9–xBi3TaTiO9 solid solution thin films for ferroelectric non-volatile memory applications. The solid solution thin films fabricated by modified metalorganic solution deposition technique showed much improved properties compared to SrBi2Ta2O9. A pyrochlore free crystalline phase was obtained at a low annealing temperature of 600°C and grain size was found to be considerably increased for the solid solution compositions. The film properties were found to be strongly dependent on the composition and annealing temperatures. The measured dielectric constant of the solid solution thin films was in the range 180–225 for films with 10–50% of Bi3TaTiO9 content in the solid solution. Ferroelectric properties of (1−x)SrBi2Ta2O9–xBi3TaTiO9 thin films were significantly improved compared to SrBi2Ta2O9. For example, the observed remanent polarization (2Pr) and coercive field (Ec) values for films with 0.7SrBi2Ta2O9–0.3Bi3TaTiO9 composition, annealed at 650°C, were 12.4 μC/cm2 and 80 kV/cm, respectively. The solid solution thin films showed less than 5% decay of the polarization charge after 1010 switching cycles and good memory retention characteristics after about 106 s of memory retention. The improved microstructural and ferroelectric properties of (1−x)SrBi2Ta2O9–xBi3TaTiO9 thin films compared to SrBi2Ta2O9, especially at lower annealing temperatures, suggest their suitability for high density FRAM applications.