Effect of V2O5 B-site substitution on the microstructure, Raman spectrum, and dielectric properties of SrBi2Ta2O9 ceramics

Strontium bismuth tantalate vanadate [SrBi2(Ta2−xVx)O9, SBTV] ceramics, which are bismuth-layered perovskite ferroelectrics, were synthesized through the solid-state reaction method. The effects of different sintering temperatures and V2O5 contents on the structure of the microstructure, Raman spectrum, and dielectric properties of the SBTV ceramics were investigated. As sintered at high temperature (980–1040 °C) and different V2O5 contents (x = 0.1 − x = 0.4), only disk-like grains of the SBTV ceramics were observed in the scanning electron micrographs. Preferential orientation of the crystals of the SBTV ceramics was confirmed through X-ray diffraction studies. The higher dielectric constant and Curie temperature of the SBTV ceramics compared with those of strontium bismuth tantalite (SrBi2Ta2O9, SBT) ceramics are ascribe to the partial replace of Ta5+ ions by V5+ ions in the B sites. The Curie–Weiss law and the modified Curie–Weiss law were used to discuss the normal-type or relaxor-type ferroelectric characteristic of the SBTV ceramics. The Ta5+ ion replaced by V5+ ion site in SBT ceramics to form SBTV ceramics exerted a pronounced effect on the BO6 mode, as demonstrated by Raman spectrum results.

Characteristics of BiFeO3 Thin Films on a LaAlO3 Substrate by RF Sputtering

In this paper, BiFeO3 (BFO) films were grown on LaAlO3 (LAO) substrate by a RF magnetron sputtering system. Fabrication parameters, such as work pressure, sputtering atmosphere, and post annealing were examined in terms of their influences on characteristics of the ferroelectric films. X-Ray diffraction, Raman scattering and scanning electron microscope measurements were employed to characterize the microstructure and the morphology of these films. At last, the ferroelectric characteristic of BFO has been studied, and the film has a large saturated polarization of 40 μC / cm2 under an applied field of 12 kV /cm.

The size effect of the polarization of SrBi2Ta2-xNbxO9 Capacitor

ABSTRACTIt is known that the ferroelectric characteristic drastically changes between the bulk crystal state and the thin film state, fabricated for the high density FeRAM. Therefore, the theoretical clarification of the high density FeRAM characteristic has become very important to realize the next generation FeRAM devices on time.The size dependence of the polarization of SrBi2Ta2-xNbxO9 (SBTN) ferroelectric capacitor was calculated in the two-dimensional capacitor system considered with two different mechanisms, the depolarization effect and the surface effect due to the change of the long-range interaction between the polarization in the vicinity of the surface and interface. The free energy expression of thepolarization is described as a function of position of polarization using the Landau phenomenological theory.The simulations of the size effect of the polarization were performed. The simulated result shows that the polarization is stable down to capacitor size of 0.01um2 which can be applied for next generation FeRAM devices.

The effects of capping barrier layers on the compositional and structural variations of integrated Pb(Zr, Ti)O3 ferroelectric capacitor having the dimension 3 × 3 μm2

Structure and composition of the ferroelectric Pb(Zr, Ti)O3 layers in a capacitor of the ferroelectric random-access memory (FeRAM) device having a density of 64 k were investigated by transmission electron microscopy (TEM) together with the energy-dispersive spectroscopy (EDS) technique. The 250 nm thick PZT layer derived by the sol-gel route showed a 2–3% Pb-deficient, 3–4% Ti-deficient, and 5–7% Zr-excess composition at the top electrode interface compared to the bulk composition when they were as-fabricated. The local compositional nonuniformity became more critical as the integration process proceeded, which seriously degraded the ferroelectric hysteresis and the device yield. The major cause of the compositional variation was the outward diffusion of Pb through the capping barrier TiO2 layer during annealing at 650 °C. The AlN capping barrier layer was also not effective in suppressing the diffusion of Pb. However, the Al2O3/TiO2 double capping layer was very effective in suppressing the outward diffusion of Pb, and excellent ferroelectric characteristic was expected.