Viscoelastic and Viscoplastic Behavior of Thin Metal Films for MEMS

这项研究是关于在手机等应用中使用的微型机电设备中经常存在的金属问题的基本机制。尽管这些微小的金属部件在制造后可能立即表现良好，但随着时间的推移，这种行为可能会改变，设备可能会失效。特别是，某些金属部件中所需的张力可以逐渐松弛，就像吉他弦随着时间的推移松弛一样。然而，与吉他弦不同的是，不可能周期性地拧紧金属微电子机械部件来恢复最佳功能。已经找到了许多解决方法，但缺乏基本的了解会导致设备更复杂、成本更高、功能更少。这项研究的方法是系统地探索不良行为的根本原因，通过一次改变一个方面的金属结构，而保持其他方面不变。大约一微米厚的金膜将作为一个模型系统，可以在表面和内部进行修改，以模拟微机械设备中使用的其他金属(包括铝、铜和铂)常见的条件。如果成功，这项研究的好处将包括极大地改善对用于微型机电设备的金属的不希望的随时间变化的理解。这将指导金属合金和表面处理的未来发展，以减少或消除依赖时间的变化。这项研究中观察到的趋势的数学描述将为设备设计人员提供加速设备开发和降低成本所需的建模工具。2012年，微电子机械设备的市场规模约为120亿美元，即使只影响一小部分设备，也可能产生显著的经济影响。特别是，手机、小型显示器和汽车雷达的微型机电设备将受益。与微型机电设备相关的概念和研究中使用的方法将通过一年一度的外展活动与K-12年级的孩子们分享，激发他们对科学和工程的兴趣。

This research is about the basic mechanisms that underlie a problem that often exists with the metals in micro-electromechanical devices used for applications like cell phones. Although the behavior of these tiny metal components may be fine immediately after fabrication, over time the behavior can change and the device may fail. In particular, the required tension that exists in certain metallic components can gradually relax, much like a guitar string relaxes over time. Unlike a guitar string, however, it is not possible to periodically tighten a metallic micro-electromechanical component to regain optimum functionality. A number of workaround solutions have been found, but the lack of basic understanding leads to greater device complexity, greater cost, and less capability than would otherwise be possible. The approach of this research is to systematically explore the root cause of the undesirable behavior by altering aspects of metal structure one at a time while holding the other aspects constant. Gold films approximately one micrometer thick will serve as a model system that can be modified on the surface and in the interior in order to simulate conditions that are common to other metals used in micro-electromechanical devices, including aluminum, copper, and platinum. If successful, the benefits of this research will include a greatly improved understanding of the undesirable time-dependent changes in metals used for micro-electromechanical devices. This will guide future development of metallic alloys and surface treatments to reduce or eliminate time-dependent changes. Mathematical descriptions of the trends observed in this research will provide device designers with the modeling tools needed to accelerate device development and reduce cost while doing so. With a micro-electromechanical devices market of approximately $12 billion US dollars in 2012, influencing even a fraction of devices can have a significant economic effect. In particular, micro-electromechanical devices for cell phones, small displays, and automotive radars will benefit. Concepts related to micro-electromechanical devices and the methods used in this research will be shared with children in grades K-12 through an annual outreach event, stimulating their interest in science and engineering.