Preparation And Characterization Of BiFeO₃ Thin Films

In recent years, ferroelectromagnetics materials have been attracting considerable attention, which shows coexistence of ferroelectric order and magnetic order, have potential applications in ferroelectric and magnetic devices. BiFeO3 was one of the few ferroelectromagnetics materials with the existence of ferroelectricity and antiferromagnetism simultaneously at room temperature, has potential applications in memory devices, Integrated circuits, transducer, spin electronics devices and so on. BiFeO3 possess perovskite structure at room temperature, which has ferroelectric properties with curie temperature (TC=1103K) and antiferromagnetism with Neel temperature (TN=643K).The main contents of this paper are as this following:1. BiFeO3 ceramics prepared by Solid State Reaction. Investigate different ratio influence on microstructure and polarization of ceramics. As the excess percentage of Bi2O3 decrease (from 10% to 3%), impurity peak decrease clearly and polarization increase gradually. Pure ceramic phase Bi2Fe4O9 can be obtained by high-temperature sintering when the ratio of Fe2O3 and Bi2O3 is 2:1. Polarization of Bi2Fe4O9 ceramic is smaller ,which is due to the microstructure of Bi2Fe4O9.2. BiFeO3 thin films were prepared on LaNiO3-electrodized thermally oxidized silicon substrate by sol-gel method. The main results are:(1). BiFeO3 and LaNiO3 thin films are perovskite structure, with (110) preferential orientation from the XRD patterns;(2). The typical surface morphology of BiFeO3 thin films were smooth and dense, the thin films with thickness of about 380 nm was confirmed by cross-sectional SEM;(3). The double remanent polarization (2Pr) and double coercive field (2Ec) of BiFeO3 thin films are identified to be 90.9?C/cm2 and 744.6KV/cm under the applied voltage of 25V, respectively;(4) The dielectric constant of BiFeO3 thin films decreases gradually as the frequency increasing. The dielectric loss increases slowly at low frequency range, and increases rapidly when the frequency above 100 kHz. The dielectric constant and dielectric loss at 10 kHz are 202 and 0.045, respectively;(5) Under the applied voltage of 10 V, the leakage current density was identified to be about 1.41mA/cm2. On basis of the analysis of the leakage current, the transport of carriers inside the BiFeO3 thin films deposited LNO electrode was well in agreement with the trap-control space charge limited current mechanism.