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Synthesis and Multiferroic Properties of BiFeO3 Thin Films

Author: MaJiKui
Tutor: ZhaoQingXun
School: Hebei University
Course: Plasma Physics
Keywords: BiFeO3 BiFe0.95Mn0.05O3 Magnetron sputtering Multiferroelectric Bi4Ti3O12
CLC: TB383.2
Type: Master's thesis
Year: 2011
Downloads: 125
Quote: 1
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Abstract


Multiferroics are multifunctional materials which exhibits coexistence of at least two of the ferroelectricity, ferromagnetism and ferroelasticity. BiFeO3（BFO） is the only candidate of multiferroic materials which can be used at room temperature, possesses both ferroelectricity and ferromagnetism. It provides potential applications in new type of nonvolatile Ferroelectric random access memories（FeRAM）, integrated circuits, transducer, modulators, spin electronic and driver system. Therefore, this paper focused on the research of BFO thin film.Polycrystalline and epitaxial BFO thin films have been successfully prepared by rf magnetron sputtering. The microstructure and morphology of BFO thin films as well as the ferroelectric and ferromagnetic properties of the capacitors have been investigated by X-ray diffraction （XRD）, atomic force microscopy （AFM）, ferroelectric tester （Precision LC Unit） and Vibrating Sample Magnetometer （VSM）. The main results are follows:1. BFO polycrystalline thin films have been prepared on Pt/Ti/SiO2/Si（111） substrates by rf magnetron sputtering. Fabrication parameters, such as sputtering pressure, annealing temperature were examined in terms of their influences on the microstructure of the BFO film. The ferroelectric properties, leakage current density and its conduction mechanism of the Pt/BFO/Pt capacitor were investigated.2. Epitaxial BFO thin films have been successfully deposited on SrTiO3 （001） substrates. The influence of substrates temperature on the microstructure of BFO thin film was discussed. The optimal deposition conditions for BFO thin film was concluded though the experiment results. In addition, ferroelectric, ferromagnetic and leakage current density were investigated with different metal top electrode. The physical properties, leakage current and its conduction mechanism of SrRuO3/BiFeO3/SrRuO3 heterostructure capacitor was detailed studied.3. 5% Mn-doped BFO thin film was prepared using magnetron sputtering. The influence of growth temperature on the microstructure and properties of BiFe0.95Mn0.05O3 was investigated. It is found that the polarization of Mn-doped BFO thin film was effectively improved. SrRuO3/BiFe0.95Mn0.05O3/SrRuO3 capacitor have excellent hysteresis loop, fatigue-free and retention characteristics.4. Degradation of ferroelectric materials Bi4Ti3O12 ferroelectricity during forming gas annealing was investigated by first-principles method. We calculated the variation of the total energy, electron density and total density of states in hydrogen-free and hydrogenated models. The results show that the introduction of hydrogen during forming gas annealing hinders phase transition of the Bi4Ti3O12 from tetragonal paraelectricity to orthogonal ferroelectricity, electrical conductivity of Bi4Ti3O12 is increased. This may be an important factor causing severe degradation of Bi4Ti3O12 ferroelectricity.

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