Effect Of Small Size, Stress Localization And Stress Gradient On The Strength Of Silicon

小尺寸、应力局部化和应力梯度对硅强度的影响

• 批准号: 1562694
• 负责人: Taher Saif
• 金额: $ 35.57万
• 依托单位: University of Illinois at Urbana-Champaign
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-05-01 至 2020-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1562694&HistoricalAwards=false
• 关键词: Effect; Small; Size; Stress; Localization

This award supports an investigation of the failure behavior of silicon at small scales. Most micro-nano mechanical systems use silicon beams as their structural components. These beams are typically subjected to bending during operation. But silicon is brittle at room temperature. This limits the design space of silicon devices. Bending, however, localizes high stresses near the surface of the beams close to the anchors. In addition, the stresses decrease from the surface towards the middle plane of the beam, giving rise to stress gradients. The effects of small size, stress localization and stress gradient on the failure mechanisms of silicon remain elusive to date. Recent evidence suggests that silicon at small scale can be ductile (i.e., not brittle) at very high yield stresses. If so, then small size, stress localization and stress gradients together may offer the virtues of both ductility and high strength to silicon. Such failure resistance would present a yet untapped paradigm to the design space of silicon devices. A detailed understanding of the failure and deformation mechanisms of silicon at small scale under bending would be transformative for both semiconductor physics and industry, and will be a fundamental advance for the field of mechanics. The goal of this project is to explore the mechanics and mechanisms of deformation and failure in small silicon samples under bending by combining theory and experiments. The working hypothesis of the project is that dislocation is the primary mechanism of deformation in silicon under bending at small scale. Small samples are dislocation free. Small size and stress localization in bending offer high flaw tolerance against fracture. This is due to the low probability of flaw incidence in the small stressed region. Bending results in dislocation nucleation from the surface before any flaw induced fracture. These dislocations enter the bulk yielding the silicon. But the yield stress increases with decreasing size due to stress gradient. This hypothesis will be tested by undertaking three tasks: (1) mechanistic modeling and molecular dynamics simulations of silicon samples under bending, (2) bending experiments on micro-nano fabricated single crystal silicon samples with various sizes and at different temperatures, and (3) in situ bending experiments in transmission electron microscopes (TEM) to reveal the mechanisms of deformation (in collaboration with Max Planck Institute at Dusseldorf, Germany). A novel micro mechanical stage will be developed for tasks 2 and 3. The research will be integrated with education and outreach activities involving K-12 to graduate students.

该奖项支持在小尺度上对硅的失效行为进行研究。大多数微纳机械系统使用硅梁作为其结构部件。这些梁通常在操作期间经受弯曲。但是硅在室温下很脆。这限制了硅器件的设计空间。然而，弯曲使高应力集中在靠近锚的梁表面附近。此外，应力从梁的表面朝向中间平面减小，从而产生应力梯度。迄今为止，小尺寸、应力局部化和应力梯度对硅材料失效机制的影响仍然是难以捉摸的。最近的证据表明，小规模的硅可以是可延展的（即，不脆）。如果是这样的话，那么小尺寸、应力局部化和应力梯度一起可以为硅提供延展性和高强度的优点。这种故障抵抗性将为硅器件的设计空间提供一个尚未开发的范例。详细了解硅在小尺度弯曲下的失效和变形机制将对半导体物理和工业产生变革性影响，并将成为力学领域的根本性进步。本课题旨在通过理论与实验相结合的方法，探索硅小试样在弯曲条件下的变形和破坏机理。该项目的工作假设是位错是硅在小尺度弯曲下变形的主要机制。小样品无位错。小尺寸和弯曲时的应力局部化提供了高的抗断裂缺陷容限。这是由于在小应力区域内发生缺陷的可能性较低。弯曲导致在任何缺陷诱导断裂之前从表面的位错成核。这些位错进入块体，产生硅。但由于应力梯度的存在，屈服应力随着尺寸的减小而增大。将通过以下三项任务来检验这一假设：（1）弯曲条件下硅样品的力学建模和分子动力学模拟，（2）不同尺寸和不同温度下微纳加工单晶硅样品的弯曲实验，透射电镜（TEM）原位弯曲实验，揭示变形机理（与德国杜塞尔多夫马克斯·普朗克研究所合作编写）。将为任务2和任务3开发一种新型微机械工作台。这项研究将与涉及K-12研究生的教育和外联活动相结合。