异价元素掺杂BiFeO3薄膜带电缺陷扩散机制研究

The goal of the project was to explore the diffusion mechanism of charged defects in doped BiFeO3(BFO) films and to improve the quality of BFO thin films. First of all, the heterovalent doped BiFeO3 films were deposited on Si and Pt/Ti/SiO2/Si substrates using a sol-gel method combined with layer by layer rapid thermal annealing process. We then studied the influence of A-site, B-site and both sites doping effects on structures and electrical properties. The leakage currents and ferroelectric properties of the doped BiFeO3 films were measured by a standard ferroelectric tester. The piezoelectric properties of the films were investigated using an atomic force microscope (AFM) system working in piezoelectric-mode. The dielectric properties of the samples were analysed by a precision impedance analyzer. The surface morphologies and roughness of the films were detected using SEM and AFM, respectively, in tapping mode. The valence state of Fe in the samples was analyzed by x-ray photoelectron spectroscopy (XPS).The phase structure, the ferroelectric domain structure and ion defects were determined by high transmission electron microscope (HTEM).Finally,a physical model of charged defects diffusions mechanism for doped BiFeO3 thin films was developed by using materials physics theory and analytical studies. Through this project, we were able to understand the intrinsic physical origin of diffusions mechanism of charged defects in heterovalent doped BiFeO3 films. Our work will lay a solid foundation to further improve the performance of the BiFeO3 film and to provide a reliable theoretical basis and technical support for the development and application of the integrated iron voltage chip data storage and microelectronic mechanical systems based on BiFeO3 films.

本项目以探索BiFeO3(BFO)掺杂薄膜带电缺陷的扩散机制、改善BFO薄膜性能为目标，采用溶胶凝胶法，利用层层快速退火的工艺，以单晶Si片和Pt/Ti/SiO2/Si为衬底基片，制备A位，B位以及A、B位异价元素掺杂的BFO薄膜，用铁电测试系统以及压电模式原子力显微镜系统测试样品的漏电流密度及铁电压电性能，用阻抗分析仪测试系统测试样品的介电性能；用SEM、AFM分析薄膜的表面形貌和表面粗糙度，用XPS分析样品中Fe 的价态，重点用HTEM等来表征样品的相结构、铁电畴结构及离子缺陷分布情况，深入探索BFO掺杂薄膜中带电缺陷扩散机制，阐明带电缺陷的扩散对改善BFO薄膜性能的作用机理，揭示带电缺陷扩散与薄膜的显微结构和性能之间的内在关系，建立物理模型，为进一步提高BFO薄膜的各项性能、为BFO薄膜在集成铁电压电芯片数据存储及微电子机械系统的开发应用提供可靠的理论依据和技术支撑，具有重要的理论和

本项目用溶胶-凝胶法，结合层层快速退火的工艺，以ITO/glass衬底基片，在优化纯相BiFeO3（BFO）薄膜的制备工艺基础上对其进行异价元素掺杂和带电缺陷扩散机制研究，结果表明，制备BFO薄膜的最佳温度应为500℃，Bi过量10%；B位引入适量的异价元素可改善BFO薄膜的抗击穿性能，但BiFe1-xMnxO3（BFMO）薄膜老化现象严重，BiFe1-xZnxO3（BFZO）薄膜矫顽场不对称性较高，BiFe1-xMnxO3（BFTO）的漏电流密度曲线表现出明显的二极管效应，Mn、Ti高低价元素共掺可有效抑制漏电流改善薄膜性能，BiFe0.96Mn0.02Ti0.02O3(BFMTO)薄膜的导电机制也由空间电荷限制传导（SCLC）转变为欧姆传导；A位Sr元素掺杂对BFMO薄膜的相结构和电性能有较大影响，导致其漏电的主要因素是自由移动的氧空位 或取代铋位的锶离子 ，而不是缺陷电子对 ；将具有较低漏电流密度的Sr2Bi4Ti5O18（SBTO）薄膜作为过渡层与BSFMO形成双层结构，有利于薄膜材料抗击穿性能的提高以及漏电流的抑制，漏电流密度由无过渡层时的3.23×10-7A/cm2逐渐降为4.68×10-9A/cm2，提高了BSFMO薄膜的抗击穿性能，开阔了制备更薄BFO基薄膜的新思路；为改善BFO陶瓷的电学性能，将BFO作为插层插入SBTO类钙钛矿中形成6层BLSF相的Sr2Bi5FeTi5O21（SBFT）陶瓷，具有较大晶格畸变，较小的漏电流，并在室温下表现出弱的铁磁性能，这为制备室温下具有强磁电耦合效应的单相多铁性化合物开拓了一个新思路；基于第一性原理和冻声子方法构建了具有Bi缺陷的晶体模型，计算了该缺陷模型的声子态性质，声子分波态密度分析和低温区热容研究加深了对BFO非本征态的认识，对于进一步了解应用这类晶体材料提供了重要的理论基础和参考价值。