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协作研究项目，该项目涉及铁电薄膜的点化学与电子结构之间的连接以及限制其在非挥发性记忆（FERAM）设备中的可靠性的疲劳和烙印过程。研究计划的一个关键目的是了解疲劳期间野外诱导的电子电荷注入/捕获和带电的氧空位再分配的相对贡献，以及最先进的PB（ZR，TI）O3（PZT）膜的烙印。 为了表征膜中的光学和电动载体陷阱，将进行光照明和DLTS测量下的疲劳和烙印测试。 原子分辨率的茎/鳗鱼研究将对未基础和疲劳/烙印样品进行，以寻找降解诱导的粘结布置和局部电子结构在带有PZT的电极界面的变化。 氧同位素深度分析通过经受各种电偏置条件的铁电容器进行，将用于表征氧空位运动。 将对铁电/金属界面的局部电子结构进行始终计算，与点缺陷相关的载体陷阱状态的能量以及缺陷形成和迁移能的能量，以正确解释实验结果。Ferroelectric材料可以自发极化，可以在各种不同的Microelectronics和Communcotions中使用自发的极化。 例如，薄膜铁电材料是新一代非易失性半导体记忆的关键推动力，这些记忆目前正在全球主要的微型微型公司（越来越多地推向市场）。 在小维度中切换铁电化状态的物理学，薄膜结构也是基本科学兴趣的重要主题。 铁电薄膜的科学和技术都为更好地理解现象提供了动力，从而干扰了这些材料中可靠的极化转换。 这种现象包括铁电疲劳，通过施加的电压脉冲重复切换后可切换极化的损失以及烙印，这是由一种极性的重复电压脉冲导致的强制电压的变化。 多年来，已经报道了许多用于铁电疲劳和烙印的实验观察和理论模型。 但是，负责这些可靠性限制过程的详细机制仍然不确定。 该研究计划将研究我们在半导体行业的合作者提供的最先进的铁电膜中铁电疲劳和烙印的潜在机制。这项研究将由斯坦福大学和伊利诺伊大学芝加哥大学（UIC）的三名联合主要研究人员指导。 该计划基于我们的免费专业知识，用于测量铁电薄膜的电荷缺陷迁移和极化开关特性，使用电子显微镜以及固体电子特性的模拟，原子分辨率成像和光谱。它将加强对芝加哥地区高中学生的现有教育外展活动，并将包括斯坦福大学UIC本科生的夏季研究项目。 这些夏季项目将与研究计划的目标充分融合，并将加强我们两个机构之间的合作。