Collaborative: Reliability of Ferroelectric Thin Films: A Systematic Study of Point Defect Phenomena and Local Electronic Structure Effects

合作：铁电薄膜的可靠性：点缺陷现象和局域电子结构效应的系统研究

• 批准号: 0205949
• 负责人: Paul McIntyre
• 金额: $ 67.5万
• 依托单位: Stanford University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-06-15 至 2006-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0205949&HistoricalAwards=false
• 关键词: Collaborative; Reliability; Ferroelectric; Thin; Films

This proposal describes a coherent, collaborative research project on the connections between the point defect chemistry and electronic structure of ferroelectric thin films and the fatigue and imprint processes that limit their reliability in non-volatile memory (FeRAM) devices. A key objective of the research program is to understand the relative contributions of field-induced electronic charge injection/trapping and charged oxygen vacancy redistribution during fatigue and imprint of state-of-the-art Pb(Zr,Ti)O3 (PZT) films. Fatigue and imprint testing under optical illumination and DLTS measurements will be pursued in order to characterize both optically- and electrically-active carrier traps in the films. Atomic resolution STEM/EELS studies will be performed on both undegraded and fatigued/imprinted specimens in order to look for degradation-induced changes in bonding arrangements and local electronic structure at the electrode interfaces with PZT. Oxygen isotope depth profiling through ferroelectric capacitors subjected to various electrical biasing conditions will be used to characterize oxygen vacancy motion. Ab initio calculations of the local electronic structure at ferroelectric/metal interfaces, the energies of carrier trap states associated with point defects, and defect formation and migration energies will be performed to properly interpret the experimental results.Ferroelectric materials exhibit a spontaneous polarization, which can be used in a variety of different applications in microelectronics and communications. For example, thin film ferroelectric materials are the key enabler for a new generation of non-volatile semiconductor memories which are currently being developed (and, increasingly, brought to market) by major microelectronics firms worldwide. The physics of switching the ferroelectric polarization state in small-dimension, thin film structures is also an important topic of fundamental scientific interest. Both the science and the technology of ferroelectric thin films provide motivation for better-understanding phenomena that interfere with reliable polarization switching in these materials. Such phenomena include ferroelectric fatigue, the loss of switchable polarization after repeated switching by applied voltage pulses, and imprint, a shift in coercive voltage resulting from repeated voltage pulses of one polarity. A host of experimental observations and theoretical models for ferroelectric fatigue and imprint have been reported over the years. However, the detailed mechanisms responsible for these reliability-limiting processes remain uncertain. This research program will investigate the underlying mechanisms of ferroelectric fatigue and imprint in state-of-the art ferroelectric films provided by our collaborators in the semiconductor industry. The research will be directed by three co-principal investigators based at Stanford University and the University of Illinois at Chicago (UIC). The program builds on our complimentary expertise in measurements of charged defect migration and polarization switching characteristics of ferroelectric thin films, atomic resolution imaging and spectroscopy using the electron microscope, and simulations of the electronic properties of solids. It will strengthen existing educational outreach activities to Chicago-area high school students, and will include summer research projects for UIC undergraduates at Stanford. These summer projects will be well-integrated with the research program objectives and will strengthen the collaboration between our two institutions.

该提案描述了一个连贯的，合作的研究项目之间的连接点缺陷化学和铁电薄膜的电子结构和疲劳和压印过程，限制其在非易失性存储器（FeRAM）设备的可靠性。该研究计划的一个关键目标是了解场致电子电荷注入/捕获和带电氧空位再分布在疲劳和最先进的Pb（Zr，Ti）O3（PZT）薄膜的压印过程中的相对贡献。 疲劳和压印测试下的光学照明和DLTS测量将进行，以表征光学和电活性载流子陷阱的薄膜。 原子分辨率STEM/EELS研究将在未降解和疲劳/压印试样上进行，以寻找在与PZT的电极界面处的键合安排和局部电子结构中降解引起的变化。 氧同位素深度剖析通过铁电电容器进行各种电偏置条件下将被用来表征氧空位运动。 铁电/金属界面的局部电子结构、与点缺陷相关的载流子陷阱态能量、缺陷形成和迁移能的从头计算将被执行以正确地解释实验结果。铁电材料表现出自发极化，这可以用于微电子和通信中的各种不同应用。 例如，薄膜铁电材料是新一代非易失性半导体存储器的关键使能器，其目前正由全球主要微电子公司开发（并且越来越多地推向市场）。 在小尺寸薄膜结构中，铁电极化态的切换物理也是一个重要的基础科学研究课题。 铁电薄膜的科学和技术为更好地理解这些材料中干扰可靠极化切换的现象提供了动力。 此类现象包括铁电疲劳、通过施加电压脉冲重复切换后可切换极化的损失，以及印记、由一个极性的重复电压脉冲引起的矫顽电压的漂移。 铁电疲劳和压痕的实验观察和理论模型的主机已经报道了多年。 然而，负责这些可靠性限制过程的详细机制仍然不确定。 本研究计划将探讨铁电疲劳的基本机制，并在我们的合作者提供的最先进的铁电薄膜在半导体行业的印记。这项研究将由斯坦福大学和伊利诺伊大学芝加哥分校（UIC）的三名联合主要研究人员指导。 该计划建立在我们在带电缺陷迁移和铁电薄膜的极化开关特性，原子分辨率成像和光谱使用电子显微镜，以及固体的电子性质的模拟测量的互补专业知识。它将加强对芝加哥地区高中生的现有教育推广活动，并将包括为斯坦福大学的UIC本科生开展的暑期研究项目。 这些暑期项目将与研究计划目标很好地结合起来，并将加强我们两个机构之间的合作。