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: 0335364
• 负责人: Nigel Browning
• 金额: $ 22.5万
• 依托单位: University of California-Davis
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-01-01 至 2006-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0335364&HistoricalAwards=false
• 关键词: Collaborative; Reliability; Ferroelectric; Thin; Films

This is the University of California at Davis (UCD) portion of a 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 devices. A key objective of the research program is to understand the relative contributions of field-induced electronic charge injection/carrier trapping and charged oxygen vacancy redistribution during fatigue and imprint of state-of-the-art Pb(Zr,Ti)O3 (PZT) films. We will use atomic resolution STEM and EELS to study the changes in atomic arrangements and local electronic structure that result from ferroelectric fatigue and imprint electrical testing. Examples of such changes might include development of locally-high oxygen non-stoichiometry near electrode interfaces and grain boundaries, and changes in bonding arrangements and the local density of states at these interfaces. Atomic structure determinations will be made using the Z-contrast imaging technique. Simultaneous acquisition of electron energy loss spectra will allow electronic structure information in the spectrum to be correlated with individual atomic columns in PZT thin film specimens. Electrical testing of the PZT capacitors prior to STEM/EELS studies will be performed by our collaborators at Stanford. Quantitative interpretation of EELS features will be facilitated by ab initio calculations (also performed at Stanford) of the local electronic structure at ferroelectric/electrode interfaces and the energies of carrier trap states associated with point defects.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 UCD with complimentary expertise in measurements of charged defect migration and polarization switching of ferroelectric thin films, atomic resolution imaging and spectroscopy using the electron microscope, and simulations of the electronic properties of solids. The UCD portion of the research will focus on direct examination of local bonding and electronic structure changes induced by fatigue and imprint electrical testing of PZT thin films. A new outreach program will be established at UCD that is modeled after the successful program initiated by the PI at U IL at Chicago. In that program, research positions were provided for 32 Chicago-area high school students, from groups typically under-represented in engineering and the natural sciences. The program at UCD will make use of the strong links between the Davis campus and high-schools in the Sacramento area.

这是加利福尼亚大学戴维斯分校（UCD）的一部分，是一个协作研究项目的，介绍了点缺陷化学与铁电薄膜的电子结构之间的联系，以及限制其在非挥发性存储器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现场诱导的电子电荷注入/载体捕获和带电的氧气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。 我们将使用原子分辨率茎和鳗鱼来研究由铁电疲劳和烙印电测试导致的原子布置和局部电子结构的变化。这种变化的例子可能包括在电极接口和晶界附近的局部高氧气非化学计量以及在这些接口处的粘结布置和状态的局部密度变化。 原子结构将使用Z-Contrast成像技术进行确定。 电子能量损失光谱的同时采集将允许光谱中的电子结构信息与PZT薄膜标本中的单个原子柱相关。 我们在斯坦福大学的合作者将对PZT电容器进行PZT电容器的电测试。 从头开始计算（也在斯坦福大学进行的）将促进对铁/电极接口的局部电子结构的定量解释，以及与点缺陷相关的载波陷阱状态的能量。 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UCD的三名联合主要研究者指导，并具有免费的专业知识，以使用电子显微镜的原子分辨率成像和光谱型的铁电薄膜，原子分辨率成像和光谱膜的极化切换，以及固体电子特性的模拟。研究的UCD部分将集中于疲劳和PZT薄膜的烙印电测试引起的局部键合和电子结构变化。 UCD将建立一个新的外展计划，该计划是在PI在芝加哥U IL成功发起的成功计划之后建立的。 在该计划中，为32名芝加哥地区高中学生提供了研究职位，这些学生通常是工程学和自然科学的成员。 UCD的计划将利用戴维斯校园与萨克拉曼多地区的高中生之间的牢固联系。