基于铁电极化的阻变效应和器件性能研究

Nonvolatile memories are important foundations for the rapid development of current information technology, but the present flash is approaching a technology limit. For ferroelectric memories, it is inevitable to readout the polarization states destructively and difficult to increase the storage density, whereas the chemical alteration is difficult to control in resistive switching memories. These problems can be avoided by using the resistive switching effect based on ferroelectric polarization recently found. However, there are some questions urgent to be resolved, for example, how to identify the behaviors of ferroelectric resistive switching and normal resistive switching, clarify the physical processes in resistive switching based on ferroelectric polarization, clarify the internal relationship between them, reveal the effect of conduction, interface layer and band bending at the electrode/ferroelectric thin film interfaces on the ferroelectric resistive switching. Based on the previous work on the growth, interface band alignment and electrical properties in perovskite ferroelectric oxide thin films, in this project, we will grow ferroelectric thin films with different conductive characteristics by contolling the growth condition, distiguish the ferroelectric displacement charge and leakage charge by pulse measurement and so on, further realize the ferroelectric resistive switching based on polarization, explore the factors and laws influencing the ferroelectric resistive switching devices, and reveal the internal relationships between ferroelectric polarization and resistive switching. The proposed research will provide an experiment foundation and theory basis for promoting the development and application of ferroelectric resistive switching nonvolative memories.

非挥发存储器是现代信息技术快速发展的重要基础，但目前所用的闪存已经接近技术极限，而铁电存储器具有数据破坏性读出和存储密度难以提高的缺点，阻变存储器则面临着电阻开关中难以控制的化学变化等问题。最新发现的基于铁电极化的阻变效应可以避免上述困难。然而，如何鉴别铁电阻变与普通阻变行为，弄清铁电极化反转诱导电阻转换的物理过程、铁电极化与阻变行为之间的内在关联，以及材料导电特性、电极-铁电薄膜界面层结构和界面带弯等因素对铁电阻变性能的影响，是目前急待深入研究的问题。本项目拟在钙钛矿氧化物铁电薄膜生长、界面能带排列、电学等性能研究的基础上，通过控制生长条件获得不同导电特性的铁电薄膜，采用脉冲电压法等技术区分铁电位移电荷和漏电荷，进而实现极化相关的铁电阻变，探索影响铁电阻变器件性能的因素，揭示铁电极化与阻变的内在联系。这些研究将为推动铁电阻变新型存储器件的研发和应用提供实验依据和理论基础。

铁电极化的阻变效应和器件性能研究 是近年来信息科学领域的研究热点之一。本项目利用脉冲激光沉积 (PLD) 技术制备了SrTiO3、YMnO3、PrBa2Cu3Ox(PBCO)、BaTiO3、Eu2O3等薄膜，并采用真空溅射法制作三明治或铁电异质结构的器件：Au/p-NiO/n-SrTiO3(STO)/Pt、YMnO3/Nb:SrTiO3 (YMO/NSTO、Pt/PrBa2Cu3Ox(PBCO)/Pt、SrTiO3:Nb/ZnO、Pt/BaTiO3/Nb-SrTiO3、Au/BaTiO3/FTO、ITO/Eu2O3/FTO等。利用二端引线和四端引线方法结合测试I-V和电化学阻抗谱研究样品的阻变行为和存储特性，特别是利用压电力显微镜进行了研究，发现铁电极化和界面与电阻开关性能紧密相关。.PLD外延法生长在Nb-掺杂 SrTiO3(SNTO)(001)衬底上的铁电BaTiO3薄膜制成Pt/BaTiO3/Nb-SrTiO3器件，测试发现该器件呈现出较为明显的铁电阻变效应和忆阻效应。在两种不同的极化态下呈现出不同的阻态，和其他的阻变器件相比较会发现该器件的I-V曲线是非线性的，不对称的和不连续的。另外该器件的电阻可以通过改变脉冲电压的宽度被连续调节，可调范围可以达到1.3×105％。分析发现，由于铁电材料的极化所控制的BaTiO3/Nb-SrTiO3界面间的势垒高度的变化是引起该现象的主要原因。.具有台阶一样的YMnO3/Nb:SrTiO3 (YMO/NSTO) 铁电异质结构也表现出与铁电紧密相关的电阻开关性能。YMnO3层和YMO/NSTO界面的电阻开关性能使用了四端引线伏安法进行独立量化测试，结果显示在电阻开关过程中它们的电阻都变化了三个数量级。压电力显微镜结果显示出有效的铁电电阻开关特性，其对应于异质结的宏观I/V特性。我们结合能带结构提出了铁电极化翻转可以调整界面耗尽区宽度，导致了YMO/NSTO异质结构的电阻开关行为。