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Critical Scaling of Domain Dynamics in Ferroelectric Nanoelements

铁电纳米元件中域动力学的临界尺度

基本信息

批准号：
EP/H047093/1
负责人：
J M Gregg
金额：
$ 41.35万
依托单位：
Queen's University Belfast
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2010
资助国家：
英国
起止时间：
2010 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FH047093%2F1
关键词：
Critical Scaling Domain Dynamics Ferroelectric

项目摘要

The potential for ferroelectric materials to influence the future of small scale electronics cannot be overstated. At a basic level, this is because ferroelectric surfaces are charged, and so interact strongly with charge-carrying metals and semiconductors - the building blocks for all electronic systems. Since the electrical polarity of the ferroelectric can be reversed, it can both attract and repel charges in nearby materials, exerting complete control over both the charge distribution and movement within the device. It should be no surprise, therefore, that microelectronics industries have already looked very seriously at harnessing ferroelectric materials in a variety of applications, from solid state memory chips (ferroelectric random access memories, or FeRAMs) to field effect transistors (ferroelectric field effect transisitors, or FeFETs). In all such applications, switching of the direction of the polarity of the ferroelectric is the most important aspect of functional behaviour. The mechanism for switching invariably involves the field-induced nucleation and growth of domains. Domain coarsening, through domain wall propagation, eventually causes the entire ferroelectric to switch its polar direction. It is therefore the existence and behaviour of domains under the influence of an external bias field that determine the switching response, and ultimately the performance of the ferroelectric in any given electronic device. Understanding domains and domain dynamics is therefore the key to fully understanding switching behaviour and eventually rationalizing and predicting device performance.However, integrating ferroelectrics into commercial devices has not been altogether straightforward. One of the major issues has been that the properties associated with ferroelectrics, in bulk form, appear to change quite dramatically and unpredictably when at the nanoscale: new modes of behaviour, and different functional characteristics appear. For domains, in particular, the proximity of surfaces and boundaries has a dramatic effect: surface tension and depolarizing fields both serve to increase the equilibrium density of domains, and domain walls, such that minor changes in scale or morphology at the nanoscale can have major ramifications for domain redistribution. Given the importance of domains in dictating the overall switching characteristics of a device, the need to fully understand how size and morphology affect domain behaviour in small scale ferroelectrics is obvious. That the near future plans for microelectronic ferroelectric devices are to move from simple planar 2D to more complex 3D architectures, only increases the imperative for study. This proposal seeks to map and understand the manner in which reduced size and increased morphological complexity affect the switching behaviour of small scale ferroelectrics. Our revolutionary approach will be to make devices in which single crystal ferroelectric material has been machined to thin film dimensions using focused ion beam milling (FIB). 'Stroboscopic Piezo-Force Microscopy (PFM)' will be used to map the dynamics of domain wall motion during in-plane switching, induced by an external electric field dropped between coplanar electrodes. Observations made on nanoscale domain dynamics can then be meaningfully correlated to the measured 'macroscopic' functional behaviour of the devices. Using FIB to machine holes and slits into the thin ferroelectric slabs will allow us to directly investigate the manner in which physical defects alter the nucleation and propagation of domain walls. The study will also be extended to investigate axial switching of discrete FIBed single crystal ferroelectric nanowires with and without topographic complexity (in terms of notches, antinotches and kinks). Prior support on static domain states in passive ferroelectric nanoshapes has enabled this research, but there is no overlap - this new work concerns domain dynamics in active devices.

铁电材料对未来小规模电子产品的潜在影响怎么强调都不为过。在基本层面上，这是因为铁电表面是带电的，因此与携带电荷的金属和半导体-所有电子系统的构建块-强烈相互作用。由于铁电体的电极性可以反转，它可以吸引和排斥附近材料中的电荷，对器件内的电荷分布和运动进行完全控制。因此，毫不奇怪，微电子工业已经非常认真地研究了在各种应用中利用铁电材料，从固态存储器芯片（铁电随机存取存储器，或FeRAM）到场效应晶体管（铁电场效应晶体管，或FeFET）。在所有这些应用中，铁电体极性方向的切换是功能行为的最重要方面。开关的机制总是涉及领域的场诱导成核和增长。通过畴壁传播，畴粗化最终导致整个铁电体切换其极性方向。因此，在外部偏置场的影响下，畴的存在和行为决定了开关响应，并最终决定了任何给定电子器件中铁电体的性能。因此，理解畴和畴动力学是完全理解开关行为并最终合理化和预测器件性能的关键。其中一个主要问题是，与铁电体相关的性质，在散装形式，似乎在纳米级时发生了相当显着和不可预测的变化：新的行为模式和不同的功能特性出现。对于域，特别是，接近的表面和边界有一个显着的效果：表面张力和去极化场都有助于增加域的平衡密度，和域壁，使微小的变化在纳米尺度或形态可以有域重新分布的主要分支。鉴于畴在决定器件的整体开关特性方面的重要性，显然需要充分了解尺寸和形态如何影响小尺度铁电体中的畴行为。微电子铁电器件的近期计划是从简单的平面2D转向更复杂的3D架构，这只会增加研究的必要性。这项建议旨在映射和理解的方式，减少尺寸和增加形态的复杂性影响小尺度铁电体的开关行为。我们的革命性方法将是使设备中的单晶铁电材料已被加工成薄膜尺寸使用聚焦离子束铣削（FIB）。“频闪压电力显微镜（PFM）”将被用来映射畴壁运动的动态在平面内切换，由共面电极之间的外部电场下降引起。观察纳米级域动力学，然后可以有意义地与测量的“宏观”的功能行为的设备。使用FIB机孔和狭缝到薄的铁电板将使我们能够直接调查的方式，其中物理缺陷改变畴壁的成核和传播。这项研究还将扩展到调查轴向开关离散FIBed单晶铁电纳米线和没有地形复杂性（在缺口，antinotches和扭结）。先前对被动铁电纳米形状中静态畴态的支持使这项研究成为可能，但没有重叠-这项新工作涉及有源器件中的畴动力学。