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Non-equilibrium electron-ion dynamics in thin metal-oxide films

金属氧化物薄膜中的非平衡电子-离子动力学

基本信息

批准号：
EP/K003151/1
负责人：
Keith Mckenna
金额：
$ 86.01万
依托单位：
University of York
依托单位国家：
英国
项目类别：
Fellowship
财政年份：
2013
资助国家：
英国
起止时间：
2013 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FK003151%2F1
关键词：
Non equilibrium electron ion dynamics

项目摘要

Recent estimates suggest there are now over 3 billion mobile phones and 1 billion personal computers in use worldwide. The total energy consumption associated with such devices is growing and is predicted to triple by 2030, becoming equivalent to the current residential electricity consumption of the US and Japan combined (Gadgets and Gigawatts - Policies for Energy Efficient Electronics, 2009). Given the environmental costs associated with energy generation and storage, improving the energy efficiency of electronic devices is now an urgent priority.The key to reducing the energy consumption of electronic devices is better control of the electric currents flowing within them. Crucially, this is often dependent on the properties and robustness of thin metal-oxide (MO) films. For example, insulating MO films are used to separate metallic and semiconducting electrodes in transistors. During operation, the voltage applied between the electrodes causes current to leak through the MO film, causing wasteful energy consumption. Over time, leakage current can grow and lead to a more terminal problem whereby the MO film abruptly becomes highly conducting, a process known as breakdown. These deleterious effects are becoming increasingly important as transistors are ever further miniaturised to meet consumer demand for increasingly powerful devices. On the other hand, the reversible switching of a MO film between insulating and conducting states by applying voltages has recently received interest as the basis for a non-volatile and low-power memory technology. For transistors, memristors and many other oxide-based electronic devices there is speculation that electron trapping by defects, polycrystallinity, electric fields and redox reactions at the electrode, all play important roles, however, there are few theoretical models which take these factors into account.The main aims of this fellowship are to learn how structure and composition are related to the electrical properties of thin MO films sandwiched between conducting electrodes, and to understand the mechanisms responsible for the transformation of these properties by application of a voltage. This will provide a framework for understanding leakage current and resistive switching in MO films, and allow strategies to control these effects to be investigated. Materials modelling can play a crucial role in addressing these aims by elucidating processes taking place over a wide range of time- and length-scales, and identifying the critical material parameters. The usual modelling approach is first to determine the equilibrium structure, then to calculate the corresponding electronic properties and current. However, this does not allow for the possibility that the non-equilibrium flow of electrons can modify the structure of the material, e.g. by field driven ion diffusion and local heating. Considering such non-equilibrium effects is essential to be able to model breakdown and resistance switching, and is also important for other processes involving correlated electron-ion dynamics, such as radiation damage. Therefore, the development of a new integrated approach is proposed that can describe the feedback between electron and ion dynamics consistently, resulting in dynamically evolving non-equilibrium structure and properties. It will combine several levels of theoretical modelling to describe the polycrystalline film structure, including defects and interfaces, the associated electronic and thermodynamic properties, and the coupled non-equilibrium dynamics of both electrons and ions. Through close collaboration with project partners, models will be tested and refined. Ultimately, this will feed into the electronics industry, leading to the design of more efficient and more reliable devices. In the later stages of the project the methodologies developed will be extended to address related materials challenges for applications including solid oxide fuel cells and batteries.

最近的估计表明，目前全球有超过 30 亿部移动电话和 10 亿部个人电脑在使用。与此类设备相关的总能源消耗正在增长，预计到 2030 年将增加两倍，相当于美国和日本目前住宅用电量的总和（小工具和千兆瓦 - 节能电子产品政策，2009 年）。考虑到与能源生成和存储相关的环境成本，提高电子设备的能源效率已成为当务之急。降低电子设备能耗的关键是更好地控制电子设备内流动的电流。至关重要的是，这通常取决于金属氧化物 (MO) 薄膜的特性和坚固性。例如，绝缘 MO 膜用于分隔晶体管中的金属电极和半导体电极。在操作过程中，施加在电极之间的电压导致电流通过MO膜泄漏，造成能源浪费。随着时间的推移，漏电流会增加并导致更严重的问题，即 MO 薄膜突然变得高度导电，这一过程称为击穿。随着晶体管进一步小型化以满足消费者对功能日益强大的设备的需求，这些有害影响变得越来越重要。另一方面，通过施加电压来实现 MO 薄膜在绝缘状态和导电状态之间的可逆切换，作为非易失性和低功耗存储技术的基础，最近引起了人们的兴趣。对于晶体管、忆阻器和许多其他基于氧化物的电子器件，人们推测电极上的缺陷、多晶性、电场和氧化还原反应引起的电子捕获都发挥着重要作用，然而，很少有理论模型考虑到这些因素。本奖学金的主要目的是了解结构和成分如何与夹在导电电极之间的 MO 薄膜的电性能相关，并了解通过施加电压来转变这些特性的机制。这将为理解 MO 薄膜中的漏电流和电阻开关提供一个框架，并允许研究控制这些效应的策略。材料建模可以通过阐明在广泛的时间和长度范围内发生的过程并识别关键材料参数来实现这些目标，从而发挥至关重要的作用。通常的建模方法是首先确定平衡结构，然后计算相应的电子特性和电流。然而，这并没有考虑到电子的非平衡流动可以改变材料结构的可能性，例如通过场驱动离子扩散和局部加热。考虑这种非平衡效应对于能够模拟击穿和电阻切换至关重要，并且对于涉及相关电子-离子动力学的其他过程（例如辐射损伤）也很重要。因此，提出了一种新的集成方法的开发，该方法可以一致地描述电子和离子动力学之间的反馈，从而动态演化非平衡结构和性质。它将结合多个层次的理论模型来描述多晶薄膜结构，包括缺陷和界面、相关的电子和热力学性质，以及电子和离子的耦合非平衡动力学。通过与项目合作伙伴的密切合作，模型将得到测试和完善。最终，这将进入电子行业，从而设计出更高效、更可靠的设备。在该项目的后期阶段，开发的方法将得到扩展，以解决固体氧化物燃料电池和电池组等应用的相关材料挑战。