四方相BiFeO3薄膜的外延生长及其铁电性质研究

Due to its large polarization, low dielectric constant and environmental friendliness, tetragonal bismuth ferrite (T-BiFeO3) has a wide range of potential applications in spintronic and nonvolatile memory devices and therefore has become extensively focused in recent years. However, due to its narrow growth window and lack of electrode materials, it is rather difficult to realize the applications of T-BiFeO3. In order to solve this issue, we propose to epitaxially grow T-BiFeO3 on Al2O3 by using aluminium-doped zinc oxide (AZO) buffer layer. AZO has lower lattice misfits and better interfacial chemical stability with both Al2O3 substrate and T-BiFeO3 epilayer, which makes it feasible to obtain pure T-BiFeO3 with few defects and larger critical thickness. In the meantime, AZO has excellent conductivity, offering us a possible way to directly explore the macroscopic ferroelectric properties of T-BiFeO3. The goal of the present project is to achieve the growth of T-BiFeO3 epilayer on AZO, to elucidate the mechanism of epitaxy, and to make clear the structural relaxation process. It also gives us the chances to clarify the microscopic ferroelectric properties of T-BiFeO3 and look for suitable ways of reducing the leakage current, and therefore offers a possibility to fundmentally study and commercialize T-BiFeO3.

四方相铁酸铋具有极化强度大、介电常数低及环境友好等特点，在自旋电子学及非易失存储等领域极具应用前景，是当前无铅铁电材料研究的热点。纯四方相铁酸铋薄膜的外延生长较为困难，适合其外延的底电极材料更是缺乏，这已成为当前制约四方相铁酸铋薄膜走向应用的主要瓶颈之一。针对该研究困境，我们拟采用Al掺杂的ZnO（AZO）作为缓冲层，在Al2O3衬底上外延生长纯四方相铁酸铋薄膜。AZO缓冲层与Al2O3衬底及四方相铁酸铋外延薄膜的晶格失配度均较小且界面稳定，有利于外延生长缺陷少、临界厚度大的纯四方相铁酸铋薄膜；同时，AZO兼具优异的导电性，可用作底电极探究四方相铁酸铋薄膜的宏观电学性质。通过该项目的实施，我们期望实现AZO底电极上四方相铁酸铋薄膜外延生长，揭示其外延生长机理及结构弛豫规律；探明四方相铁酸铋薄膜的宏观铁电性质，同时探寻减小薄膜漏电的有效途径，为四方相铁酸铋的基础研究和应用奠定基础。

四方相铁酸铋具有极化强度大、介电常数低及环境友好等特点，在自旋电子学及非易失存储等领域极具应用前景，是当前无铅铁电材料研究的热点。纯四方相铁酸铋薄膜的外延生长较为困难，适合其外延的底电极材料更是缺乏，这已成为当前制约四方相铁酸铋薄膜走向应用的主要瓶颈之一。在本项目中，我们采用Al掺杂的ZnO（AZO）作为缓冲层，在Al2O3衬底上外延生长四方相铁酸铋薄膜。我们发现，在Al2O3 (0001)衬底之上，通过ZnO(0001)缓冲层可以得到正四方相铁酸铋外延薄膜，但样品中始终存在少量的Bi2O3杂相。通过压电力显微镜表征，得到了正四方相铁酸铋的矫顽场与压电系数。而借助于ZnO(11-20)缓冲层，我们在Al2O3 (10-12)衬底上得到了无任何杂相的正四方相BiFeO3。而且，在ZnO(11-20)缓冲层上正四方相铁酸铋的临界厚度高达120nm，数倍于类钙钛矿衬底上MC相铁酸铋的文献报道值，对今后的实际推广应用具有重要的意义。四方相铁酸铋与发展成熟、成本低廉的半导体平台集成于一体，为包括铁电场效应晶体管在内的多功能器件发展提供了一条新的途径。更进一步，我们对铁酸铋-铁酸钴复合薄膜相界局域电导进行研究，采用磁控溅射法制备了铁酸铋-铁酸钴复合薄膜，通过不同温度的样品研究了其生长行为，发现了其中的相界局域导电特性，通过系统测试分析，澄清了其导电机制为界面调控的PF机制，为多铁材料开关的多场调控研究奠定了基础。我们的研究丰富了对铁电及多铁材料的新兴特性的理解，并证明了开发未来纳米电子器件的可能性。