RUI: Structural and compositional modification of memristive niobium oxide films for neuromorphic computing applications

在过去的七十年中，电子电路的快速和看似无情的改进在很大程度上是由电子元件的小型化所驱动的。然而，在极小的长度尺度上，不利的量子效应对这些电路的缩小提出了一个即将到来的限制，许多研究人员已经将目光投向生物系统，以寻求进一步改进的灵感。神经形态，或大脑启发，计算有潜力提高性能和计算速度，同时通过模仿神经元的生物功能降低功耗。来自纽约州立大学布罗克波特分校和伊萨卡学院本科物理系的研究小组，以及来自美国海军研究实验室的合作者，正在研究用于神经形态电路的氧化铌薄膜。薄膜氧化铌是神经形态电路的理想候选者，因为它储量丰富，价格低廉，无毒，并且可以模拟大脑的神经元和突触行为。本项目重点关注薄膜的生长，在薄膜中加入其他元素（如锌和铝），生长后的热退火，并制作成电子电路元件。研究小组正致力于将各种材料变化（例如，氧化物成分、厚度、生长参数）与设备产生的电子行为联系起来。最终，该项目的目标是开发基于氧化铌的电子元件，可以与当前最先进的硅基电子元件无缝集成。本科生是研究团队不可或缺的一员，参与这项研究通常对物理学中代表性不足的群体具有吸引力。研究团队的本科生成员在夏季和学年期间参与研究项目的各个方面，并在地区和国家会议上展示他们的工作。pi定期出现在学生来自弱势群体地区的当地学校，包括材料科学和计算机科学方面的成功、挑战和机遇的信息，以激发人们对科学和技术的兴趣。技术描述氧化铌是一种多晶材料，根据化学计量，具有许多有趣的和潜在有用的电学和光学性质。特别是，晶体二氧化铌（NbO2）表现出挥发性记忆电阻行为，是将传统的金属氧化物半导体元件与大脑启发的神经形态电路元件融合在一起的架构的主要候选者，这些元件通常需要具有突触样和神经元样组件。该项目的重点是更好地了解NbO2， NbO2在800摄氏度左右经历了从高电阻到低电阻的挥发性相变。一旦达到温度阈值，这种转变通过突然改变电阻来模拟神经元的尖峰电行为。该研究小组由两名主要研究人员组成，他们的专业是材料开发和电传输，他们的本科生和来自美国海军研究实验室的合作者，他们正在研究材料沉积和沉积后处理过程，以及所得薄膜的光学和电学行为。在材料方面，研究团队使用原子层沉积（ALD）、掺杂和生长后结晶技术，以与现有半导体制造工艺完全兼容的方式制造高质量的NbO2。具体来说，该项目研究了ALD过程中掺杂剂的添加，以促进与低功耗设备操作兼容的热预算结晶。结晶后，利用超高真空系统对材料进行相变热循环，同时观察反射和传输的光信号，快速确定生长条件或掺杂剂对相变温度的影响。在器件方面，进行电气测量以确定材料制备和性能对关键器件操作参数的影响，例如在故障前可以执行的转换次数、器件良率和开关功率要求。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Non-technical abstractThe rapid and seemingly relentless improvement in electronic circuitry over the last seven decades has been driven in large part by miniaturization of the electronic components. However, adverse quantum effects at extremely small length scales present an impending limit to shrinking of these circuits, and many researchers have looked to biological systems for inspiration for further improvement. Neuromorphic, or brain-inspired, computing has the potential to enhance performance and computational speed while reducing power consumption by mimicking the biological function of neurons. The research team from the undergraduate-only physics departments at SUNY Brockport and Ithaca College, along with collaborators from the U.S. Naval Research Laboratory, are studying thin films of niobium oxide for use in neuromorphic circuits. Thin-film niobium oxide is an ideal candidate for neuromorphic circuits, as it is plentiful, inexpensive, non-toxic, and can mimic both the brain’s neuronal and synaptic behaviors. This project focuses on the growth of the thin films, incorporation of other elements (such as zinc and aluminum) in the films, post-growth thermal annealing, and fabrication into electronic circuit components. The research team is focusing their effort on correlating the various material changes (e.g., oxide composition, thickness, growth parameters) with the device’s resulting electronic behavior. Ultimately, the project’s goal is to develop niobium oxide based electronic components that can seamlessly integrate with the current state-of-the-art silicon-based electronics. Undergraduate students are integral members of the research team, and participation in this research is often attractive to members of groups underrepresented in physics. Undergraduate student members of the research team participate in all aspects of the research project during both the summer and during the academic year, and present their work at regional and national conferences. The PIs regularly present at local schools in areas with students from underrepresented groups and include information on successes, challenges, and opportunities in materials science and computer science to ignite interest in science and technology.Technical descriptionNiobium oxide is a polymorphic material that, depending on stoichiometry, has a number of interesting and potentially useful electrical and optical properties. Crystalline niobium dioxide (NbO2), in particular, displays volatile memristive behavior, and is a leading candidate for architectures that merge traditional metal-oxide-semiconductor components with brain-inspired neuromorphic circuit elements, which are generally required to have both synapse-like and neuron-like components. This project focuses on developing a better understanding of NbO2, which undergoes a volatile phase transition from high to low resistance around 800 degrees Celsius. This transition mimics the spiking electrical behavior of neurons by abruptly changing resistance once a temperature threshold is achieved. The research team – which consists of two principal investigators, with specialties of materials development and electric transport, their undergraduate research students, and collaborators from the U.S. Naval Research Laboratory – is studying both the material deposition and post-deposition treatment processes, as well as the optical and electrical behavior of the resulting films. On the materials side, the research team uses atomic layer deposition (ALD), doping, and post-growth crystallization techniques to fabricate high-quality NbO2 in a way that is fully compatible with existing semiconductor manufacturing processes. Specifically, the project examines the addition of dopants during ALD to encourage crystallization with a thermal budget compatible with low-power device operation. Following crystallization, an ultra-high vacuum system is used to thermally cycle the material through its phase transition while observing reflected and transmitted optical signals to quickly establish the effect of growth conditions or dopants on the phase transition temperature. On the device side, electrical measurements are performed to establish the effect that material preparation and properties have on key device operation parameters, such as the number of transitions that can be performed before failure, the device yield, and the switching power requirements.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.