直接在金属底电极上取向控制生长Bi系层状钙钛矿型多铁薄膜

Multiferroic materials exhibiting ferroelectric and magnetic orderings simultaneously have been attracted much attention during the past decade. It is mainly attributed to the possibility of cross-controlling between magnetic field/electric field and polarization/magnetization in multiferroic materials, which provides a route in advanced memory devices. There has been an intense search for room-temperature magnetoelectric multiferroics within which the coupling of ferroelectric and ferromagnetic polarizations might be remarkably demonstrated. One of the most effective ways to obtain the excellent multiferroic properties in single-phase matters is to incorporate magnetic species of perovskite like YFeO3 into ferroelectric Bi4Ti3O12 matrix of layered perovskite. For their applications in high-density devices, it is necessary to grow uniformly a/b-axes-oriented (or near-a/b-axes-oriented) multiferroic thin films of Bi-layered perovskite on standard-type Pt/Ti/SiO2/Si substrates. Our previous research indicates that the nucleation and growth of oriented grains in the thin films can be effectively controlled by adjusting thermal stress during crystallization using different heating rates and by applying in-situ electrical field. In this work, we plan prepare Bi4Ti3O12-nAFeO3、Bi4Ti3O12-nAFe0.5Co0.5O3 (A = Y、La or Bi, n = 0.5、1.0、1.5 or 2.0) multiferroic thin films of uniform a/b-axes (or near-a/b-axes) orientation grown on Pt/Ti/SiO2/Si through sol-gel method. A key route for the controlled growth of uniformly-oriented multiferroic thin films with Bi-layered perovskite directly on metal electrodes will be find out. The mechanism of such orientation-controlled growth will be understood by establishing the growth process ? preferred orientation ? microstructure relation for these thin films. Single-phase multiferroic thin films exhibiting excellent magnetoelectric coupling properties at room temperature will be obtained. These oriented multiferroic thin films of Bi-layered perovskite are expected to match applications in high-density memory devices.

目前探寻在室温同时具有铁电和铁磁性且磁电耦合强的单相多铁材料是研究热点。在层状钙钛矿型Bi4Ti3O12铁电体中插入YFeO3等磁性基团是获得单相多铁物质的有效途径。实用要求在标准型Pt/Ti/SiO2/Si衬底上实现此类多铁薄膜沿近a/b轴均匀取向生长。我们的前期研究表明，薄膜晶化时用升温速率调整热应力和原位外加电场都可有效诱导晶粒取向成核成长。本申请拟用溶胶-凝胶工艺在Pt/Ti/SiO2/Si上制备沿近a/b轴均匀取向生长的Bi4Ti3O12-nAFeO3、Bi4Ti3O12-nAFe0.5Co0.5O3 (A = Y、La或Bi, n = 0.5、1.0、1.5或2.0) 多铁薄膜，摸索出一套在金属电极上控制Bi系层状钙钛矿型多铁薄膜取向生长的关键技术；建立制膜工艺-取向生长-显微结构关系，理解这种取向控制生长机制；筛选出在室温同时具有优良铁电、铁磁和磁电耦合特性的单相多铁薄膜。

探寻在室温同时具有铁电和铁磁性且磁电耦合强的单相多铁材料是研究热点。在层状钙钛矿型Bi4Ti3O12铁电体中插入LaFeO3等磁性基团是获得单相多铁物质的有效途径。实用要求在标准型Pt/Ti/SiO2/Si衬底上实现此类多铁薄膜沿近a/b轴均匀取向生长。. 当薄膜升温晶化时原位外加电场，用溶胶-凝胶工艺在Pt/Ti/SiO2/Si上制备了86%近a/b轴取向和60%近(104)/(014)取向的Bi4Ti3O12薄膜，其剩余极化2Pr值分别高达61 uC/cm2和57 uC/cm2。与随机取向薄膜相比，两取向膜中极化开关的速度和稳定性都有增强，适合铁电存储器应用。薄膜的择优取向度是用XRD极图可靠测量估算，经透射电镜观察验证。两取向膜都主要由穿透整个薄膜厚度的柱状晶密排组成，柱状晶受外电场有效诱导在Pt底电极上择优取向成核。更重要的是，通过薄膜晶化时快速升温调整热应力，在Pt/Ti/SiO2/Si上分别获得了a/b轴择优、c轴择优和随机取向的Bi4Ti3O12-BiFeO3多铁薄膜。进一步的取向生长工艺仍在优化中，期待制备出均匀取向生长的多铁薄膜。. 在Bi4Ti3O12中成功插入0.5、1或1.5层LaFeO3，制备了三种新型层状钙钛矿型Bi4Ti3O12-nLaFeO3薄膜，果然均有室温多铁性和磁电藕合效应。用Fe0.5Co0.5替换Fe，还制备了Bi4LaFe0.5Co0.5Ti3O15薄膜。通过Fe-O-Co耦合作用，其磁性果然比Bi4LaTi3FeO15薄膜提高了7倍。在Bi4Ti3O12中插入YFeO3或BiFeO3磁性基团，制备了Bi4YFeTi3O15薄膜和Bi5Ti3FeO15薄膜。比较上述多铁薄膜，Bi4LaFe0.5Co0.5Ti3O15薄膜的室温多铁性能相对最优，且表现出室温磁介电效应。当外加低磁场0.25T，磁介电耦合系数为3.8%。. 同时，在以下三方面做了富有成果的研究工作：Bi4Ti3O12铁电单晶中畴壁类型、构形及其可动性的原位观察；BaTiO3基铁电二极管和铁电隧道结的阻变特性研究；几种铁电、压电和电光陶瓷的制备与关键性能研究。