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The stress influence of the structural and ferroelectric properties of polycrystalline BiFeO3 (BFO) thin films has been investigated using a membrane substrate for relaxing stress. Reciprocal space mapping (RSM) measurement has been performed to confirm the stress dependence of the crystal structure of polycrystalline BFO thin films on the Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (625 μm) substrate (stress-constrained BFO film) and the Pt (200 nm)/TiO2 (50 nm)/SiO2 (600 nm)/Si (15 μm) membrane substrate (stress-relaxed BFO film). The BFO thin films prepared by pulsed laser deposition were polycrystalline and mainly exhibit a texture with (001) and (110) plane orientations. From the RSM results, the crystal structure of the (001)-oriented domain changes from Pm monoclinic to Cm monoclinic or to R3c rhombohedral due to stress relaxation. Moreover, at room temperature as well as at 150 K, remanent polarization (Pr) increases and double coercive field (2Ec) decreases (in the latter case from 88 to 94 μC/cm2 and from 532 to 457 kV/cm, respectively) due to relaxing stress. The enhancement of ferroelectricity is attributed to the crystal structural deformation and/or transition and angle change between the polarization direction and film plane. [ABSTRACT FROM AUTHOR]

We have investigated effects of the postmetallization annealing and the electric field application on ferroelectric properties of BiFeO3 thin films prepared by chemical solution deposition. The leakage current is reduced after the postmetallization annealing although the crystallinity of the polycrystalline BiFeO3 is unchanged. In addition, double coercive field is reduced at about 90 kV/cm after the postmetallization annealing, while remanent polarization of 90 μC/cm2 is almost the same at 80 K. The postmetallization annealing is considered to lead the improvement of contact between the BiFeO3 film and the Pt electrode or the reduction in defects near the interface between the BiFeO3 film and the Pt electrode. Moreover, once a high electric field of 2.8 MV/cm is applied, the ferroelectric property of BiFeO3 thin films is dramatically improved. This effect may be due to the relaxation of pinned domains or locked polarizations in the BiFeO3 film. The postmetallization annealing and the electric field application are effective to improve ferroelectric properties of BiFeO3 thin films. [ABSTRACT FROM AUTHOR]

Polycrystalline BiFeO3(BFO) films on Pt/TiO2/SiO2/Si substrate have been prepared by a pulsed laser deposition (PLD) method with various repetition rates. The X-ray diffraction (XRD) pattern observes single-phase perovskite structure with a small secondary phase. While the film-thickness is increased with increasing repetition rates, the grain size increases, and the leakage current reduces. Also, good polarization versus electric field (P-E) hysteresis loops of all polycrystalline BFO films were obtained at room temperature (RT). It is seen that the polarization value (Pr) practically remains almost constant for all the BFO films, and the coercive field (Ec) decreases with increasing the film thickness. [ABSTRACT FROM PUBLISHER]

Sr-substituted BiFeO3 thin films (BSFO) have been prepared on Pt/TiO2/SiO2/Si substrate by pulsed laser deposition using 15% Bi-excess targets (Bi1.15(1-x)SrxFeO3). Some XRD peaks shift to low angle with increasing Sr, and grain sizes decrease. Leakage current densities of BSFO thin films are almost same or a little larger compared to that of BiFeO3 thin film, but P-E hysteresis loops were obtained at RT and 80 K. M-H hysteresis loops of BSFO thin films show weak ferromagnetism at RT and 80 K. BSFO thin film for x = 0.05 shows good multiferroic properties including ferroelectricity and ferromagnetism. [ABSTRACT FROM AUTHOR]

Multiferroic 350-nm-thick BiFeO3 thin films have been prepared on Pt/TiO2/SiO2/ Si(54 μm) membrane substrates by pulsed laser deposition. To confirm the influence of stress from substrate, ferroelectric and magnetoelectric properties of BiFeO3 thin films have been evaluated with applying stress. For applying stress, we tried to pump out backside of the membrane structure at various pressures. From ferroelectric hysteresis loops, the remanent polarization at the pumping pressure of 0.01 atm increase from 105 to 110 μC/cm2, comparing to that without pumping. Under magnetic field of 0.4 T, polarization at zero electric field at pumping pressure of 0.01 atm with maximum applied voltage of 15 V increased from 100 μC/cm2 to 103 μC/cm2. [ABSTRACT FROM AUTHOR]

BiFeO3 thin films have been prepared on Pt/TiO2/SiO2/Si substrates by sol-gel method using precursor solutions of various elemental ratio (Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1). The θ < eqid2 > 2θ scan XRD patterns show all the films consist mainly of polycrystalline perovskite and the crystallinity of Bi:Fe = 1.1:1.0 is better than the others. SEM and AFM images show all BiFeO3 film have rosette structures, which consist of perovskite phase and matrix phase. The leakage current density measured at the temperature of 80 K is lower than 10-4 A/cm2 in all the films when the electric field reaches 1.6 MV/cm. The leakage mechanism of BiFeO3 thin film is dominated by Schottky conduction at 80 K. At 80 K, the remanent polarizations at maximum applied voltage of 2.8 MV/cm are 100, 49, and 44 μC/cm2 for the ratio of Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1, respectively. The saturated magnetization of BiFeO3 thin films at 80 K were found to be 14, 22.5, 15 emu/cm3 for the ratio of Bi:Fe = 1.1:1.0, 1.0:1.0, and 1.0:1.1, respectively. Among these ratio, BiFeO3 thin film deposited from precursor of Bi:Fe = 1. 1:1.0 gives the best ferroelectric property. [ABSTRACT FROM AUTHOR]