铁电隧道结阻变循环耐久性及其失效机理研究

As a promising candidate for new emerging nanoelectronic memories, ferroelectric tunnel junctions (FTJs) have attracted great attention because of their excellent performances, such as nondestructive readout, high-density data storage, fast write/read speed in nanosecond scale, and ultralow power consumption. Recently, almost all efforts have been devoted to optimize the tunneling electroresistance properties of FTJ devices. There are, however, few works addressing the write/erase endurance, which is a critical performance character for the commercialization of prototypical memories. Therefore, we plan to investigate cycling endurance and the failure mechanisms of FTJs in this proposal. Pulsed laser deposition is employed to grow ultrathin ferroelectric barriers and electrodes with atomically smoothing surface. Tunnel junctions are fabricated based on these high quality heterostructures. The endurance characteristics are studied by applying different cycling voltage sequences on the FTJ devices. The polarization fatigue and electrochemical effects, i.e., the migration and aggregation of charged defects, confined in nanoscale of the FTJs are discussed. The physical mechanisms of endurance failure are clarified by carefully studying the development of the high and the low resistance states with increasing cycling number and the evolution of ferroelectric properties, dielectric characteristics, and transport behaviors after the switching measurement. Artificial microstructure engineering is adopted to achieve the devices with enhanced cycling endurance. The present proposal not only facilitates the emergence of new theoretical models and new device structures in ferroelectric and resistive switching communities but also provides substantial basis for the application of ferroelectric tunneling structures in high-performance non-volatile memory technology.

铁电隧道结具有非破坏性数据读出，高存储密度，纳秒级读/写速度和超低功耗等卓越性能，作为新兴纳米电子学存储方案而备受关注。当前，该领域工作主要集中在隧穿电致电阻优化，而存储原型器件商业化的关键环节-数据循环擦写耐久性研究至今尚未起步。因此，本项目拟开展铁电隧道结阻变循环耐久性及其失效机理研究。我们将采用脉冲激光沉积制备原子级平整的高质量铁电超薄膜和电极，形成隧道结器件。通过考察不同测试参数下高、低阻态随循环次数增加的演变，以及比较测试前后器件的铁电、介电、输运等电学行为，探讨铁电隧道结这一受限体系中，纳米尺度极化疲劳与荷电缺陷迁移、聚集等电化学效应的关系，以及它们在耐久性中的作用，澄清阻变翻转失效的物理机制。并开展人工微结构调控来获得耐久性能优越的结构。本项目研究不仅有利于铁电和阻变领域新理论和新结构的出现，更为铁电隧穿结构在高性能非挥发信息存储技术上的应用打下基础。

项目执行期间，围绕铁电隧道结与外延薄膜异质结构，开展了如下研究工作。我们基于微结构优化策略，获得了Pt/BaTiO3/Nb:SrTiO3和(La,Sr)MnO3/BaTiO3/CoFe2O4/Nb:SrTiO3等多种铁电/多铁隧道结。获得了高达10^6的ON/OFF电流开关比，外推超过10年的时间保持性，以及超过10^6循环次数的有效阻态翻转。对这些隧道结的阻变循环耐久性开展了系统研究，结合扫描透射电子显微镜，压电力显微镜，阻变性能表征以及成核限制理论、电输运理论等，总结了阻变翻转耐久性随工艺参数、材料特性、激励脉冲波形等的变化规律。在原子尺度上揭示了晶格氧缺失导致的铁电死层以及局部钙钛矿型晶格结构破坏是造成铁电隧道结ON/OFF开关比值下降和耐久衰退的物理机制，阐释了强外加电场下超薄铁电膜的极化疲劳起因。并且，我们还研究了CMOS兼容的铁电HfO2超薄膜体系，发现其疲劳效应主要来自于荷电缺陷导致的畴璧钉扎，氧空位在其中并没有显示主导作用，这可能源于钙钛矿结构和萤石结构中氧离子配位情况的不同。这些进展为铁电隧道结等低维电子器件的工业化发展打下了实验基础。另外，我们将研究拓展到了面向新一代信息存储的忆阻器和相关的神经态计算领域，基于双层神经网络和向后传播算法获得了对手写数字的高识别率。. 项目资助发表SCI论文13篇，均是以主持人为通讯作者的研究成果，包括《Science Advances》1篇，《Advanced Materials》1篇，《Nano Letters》1篇，中国卓越期刊计划《Journal of Materiomics》1篇，《Applied Physics Letters》5篇，《ACS Applied Materials & Interfaces》2篇等。总共被他引201次，其中一篇文章为ESI高被引用。授权发明专利1项。. 完成了本课题的研究任务。

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