镧系和过渡族元素共掺杂取向生长的BiFeO3薄膜制备及多铁性能增强的机理研究

BiFeO3 is one of few materials with both ferroelectric and ferromagnetic properties at room temperature. It has the potential application in the fields of the spinning electronic devices, sensors, the multimode storage and multifunctional electronic equipment. But the lanthanides or transition group elements doped separately at Bi site and Fe site could not continually decrease the leakage current and enhance the multiferroic properties of the thin films, which could not meet the requirements of the microelectronic devices. This project intends to adopt the sol-gel spin coating method to regulate the ratio of the raw materials and solvents, the short-wave ultraviolet light to irradiate the substrates and the wet films, and layer-by-layer rapid annealing technique to prepare BiFeO3 thin films co-doped by the lanthanides and transition group elements and oriented growing on (110) crystal plane on the FTO/glass and LaNiO3/Si substrates respectively. The effects of the doping causing electron orbital hybridization between ions, exchange interaction among electrons and the oriented growth on the microstructure and the leakage current of BiFeO3 thin films will be studied. The effects of oriented growth and the microstructural changes on the co-doping morphotropic phase boundary (MPB) on the domain structure, polarization turnover mechanism, depolarization effect and ferroelectric polarization maintaining characteristics of BiFeO3 thin films will be also studied so as to obtain the mechanisms of the cooperation between co-doping and oriented growth for decreasing the leakage current and intensifying the ferroelectric and ferromagnetic properties of BiFeO3 thin film, which will lay a solid theoretical basis for researching and developing the microelectronic devices.

BiFeO3是少数室温下同时具有铁电性和铁磁性的材料之一，在自旋电子器件、传感器、多态存储和多功能电子设备等方面有着潜在的应用。但在Bi位和Fe位单独掺杂镧系或过渡族元素已无法继续降低薄膜的漏电流和增强多铁性能，难以满足微电子器件的要求。本项目拟用溶胶-凝胶旋涂法，调控原料和溶剂的配比、短波紫外光辐照衬底和湿膜、逐层快速退火工艺，在 FTO/glass 和LaNiO3/Si衬底上制备镧系和过渡族元素共掺杂（110）晶面取向生长的BiFeO3薄膜；研究掺杂导致的离子间电子轨道杂化和电子间的交换作用与取向生长对BiFeO3薄膜微结构、漏电流的影响；研究取向生长和共掺杂的准同型相界处微结构变化对BiFeO3薄膜的畴结构、极化翻转机理、退极化效应和铁电极化保持特性的影响，获得共掺杂和取向生长的协同作用对BiFeO3薄膜漏电减小的机制、铁电和铁磁性能增强的机理，为微电子器件的研发打下坚实的理论基础。

BiFeO3作为典型的在室温下具有多铁性能的材料，虽掺杂改性和复合磁性材料层在一定程度上提高了BFO材料的性能，然而掺杂所提高的铁磁性能微弱，磁性相材料层会对复合薄膜的铁电性能的破坏，使BFO材料的多铁性能没有得到大的改变。因此，本课题将多元掺杂与复合磁性相这两种方法结合起来研究其对BFO薄膜的结构和多铁性能的影响。Bi1-xErxFeO3薄膜由BFO薄膜的菱方R3c:H结构变为菱方R3c:H与R3m:R两相共存的结构，且薄膜中存在着丰富的Fe2+和大量的氧空位；薄膜的漏导电流随着Er3+掺入而增大，但Bi1-xErxFeO3薄膜中有铁电转换存在； BiFe1-xMnxO3薄膜Mn2+诱导BFO三方相转变为三方和四方相共存。Mn2+掺杂降低薄膜的漏电流密度，获得Pr为76.20 μC/cm2和Ms为4.45 emu/cm3；Mn-Co、Mn-Ni和Mn-Cu共掺杂使薄膜向四方扭曲的伪立方相转变。Fe2+含量减少的同时出现少量Mn3+，致薄膜中氧空位等缺陷浓度随着掺杂而降低，泄漏电流减小。Mn-Co共掺BFO获得的最大Pr为197.8 µC/cm2；Tb和Cr、Mn、Co共掺杂能诱导Bi0.89Tb0.11Fe1-xTMxO3薄膜由菱方相向三斜扭曲的伪立方相转变。BTFCoO薄膜的Pr和Ec分别为127.8 µC/cm2和468.1 kV/cm，共掺体系中Co2+和Mn2+对BFO薄膜多铁性能的改善最明显；四元共掺比单掺杂更易诱导薄膜相结构变化，随着掺杂离子种类的增多，薄膜中的四方相结构逐渐增多，且沿(110)晶面择优趋向，Bi0.89Sm0.11Fe0.96Mn0.04Cr0.02O3薄膜Pr为89.42 μC/cm2，Ms为1.22 emu/cm3； Bi0.9Er0.1Fe0.96Co0.02Mn0.02O3/Co1-αMnαFe2O4薄膜呈优异的多铁性能。Pr为157.8μC/cm2， Ec为497 kV/cm，Ms为51.47 emu/cm3，Mr 为23.53 emu/cm3，且具有良好的可读写性能和铁电翻转特性。铁电性能的变化来源于底层Mn2+掺杂使CMαFO层由立方Fd-3m:2向三方R-3m:H转变诱导了BEFMCO层中三斜-P1向三方-R3c:H转变，三斜P1结构含量的改变和两相共存有利于复合薄膜铁电性能的提高，磁电性变化主要来源CMαFO磁性能。