Critical Scaling of Domain Dynamics in Ferroelectric Nanoelements

铁电材料影响小规模电子产品未来的潜力怎么强调都不为过。从根本上说，这是因为铁电表面是带电的，因此与带电金属和半导体--所有电子系统的基石--相互作用强烈。由于铁电的电极性可以反转，它既可以吸引也可以排斥附近材料中的电荷，从而完全控制器件内的电荷分布和运动。因此，毫不奇怪，微电子行业已经非常认真地考虑在各种应用中利用铁电材料，从固态存储芯片(铁电随机存取存储器，或FeRAM)到场效应晶体管(铁电场效应过渡器，或FeFET)。在所有这些应用中，铁电体的极性方向的切换是功能行为的最重要的方面。开关的机制总是涉及到场诱导的磁畴形核和长大。磁区粗化，通过磁区壁的传播，最终导致整个铁电材料改变其极性方向。因此，在外部偏置场的影响下，铁电体的存在和行为决定了开关响应，并最终决定了铁电体在任何给定电子器件中的性能。因此，了解电畴和电畴动力学是全面了解开关行为并最终合理化和预测器件性能的关键。然而，将铁电材料集成到商业器件中并不是一帆风顺的。其中一个主要问题是，在纳米尺度下，与块状铁电材料相关的性质似乎发生了相当戏剧性的和不可预测的变化：新的行为模式和不同的功能特征出现。特别是对于磁区，表面和边界的接近具有显著的影响：表面张力和去极化场都有助于增加磁区和磁区壁的平衡密度，因此在纳米尺度上尺度或形态的微小变化可以对磁区重新分布产生重大影响。鉴于电畴在决定器件整体开关特性方面的重要性，很明显，有必要充分了解尺寸和形态如何影响小规模铁电材料中的电畴行为。微电子铁电器件的近期计划是从简单的平面2D结构转向更复杂的3D结构，这只会增加研究的紧迫性。这一提议试图描绘和理解尺寸减小和形态复杂性增加对小规模铁电材料开关行为的影响方式。我们革命性的方法将是制造单晶铁电材料已经使用聚焦离子束铣削(FIB)加工到薄膜尺寸的器件。“频闪压电力显微镜(PFM)”将被用来描绘共面电极之间的外加电场引起的面内转换过程中的磁化壁运动的动力学。然后，在纳米尺度领域动力学上所做的观察可以有意义地与所测量的设备的“宏观”功能行为相关联。使用FIB在铁电薄片上加工孔洞和狭缝，将使我们能够直接研究物理缺陷改变域壁形核和扩展的方式。这项研究还将扩展到研究具有和不具有地形复杂性(就缺口、反缺口和扭结而言)的离散FIBed单晶铁电纳米线的轴向开关。先前对无源铁电纳米形状中静态磁畴状态的支持使这项研究成为可能，但没有重叠-这项新工作涉及到有源器件中的磁畴动力学。

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.