Micro Scale Experiments and Modeling of MEMS RF-Switches

0120866埃斯皮诺萨Agoali奖支持与无线应用中的微电子机械系统(MEMS)和IC元件集成相关的材料特性和问题的研究。与其他技术相比，这些系统具有独特的优势，因为它们的低功耗、高灵敏度、物理尺寸和低成本。该技术是下一代手机、无线系统基站和用于军事通信的高效软件控制数字无线电的理想选择。在这些应用中，MEMS器件通常用作滤波器或开关。可以使用Q因子为94,000的滤波器来预先选择通信频带和该频带内的特定信道。每个开关的插入损耗小于0.1d B的开关可用于雷达天线的电磁波束控制，这种方法是通过移相实现的。此功能使天线无需物理重新定向即可发送和接收信号。然而，尽管这项技术在工业上有很大的兴趣，但它在商业上还不可行，因为首先必须克服一些技术障碍。其中的关键是微米级的MEMS材料的封装和机械建模。例如，在射频开关的情况下，环境的影响可能会由于湿度或其他来源而导致薄膜粘连。这就需要开发一种廉价的密封包装。从可靠性的观点来看，有必要考虑塑性极限及其与材料的温度相关性。在卫星和飞机无线应用中，温度低至零下50摄氏度，而在设备封装过程中，温度可能达到数百摄氏度。另一个重要的失效机制是由过多的驱动循环引起的疲劳。这些器件中的大多数都是被驱动的万亿次循环，推动了设计极限和我们目前对材料行为的了解，超出了已知参数。在这个项目中，我们将研究电容式RF-MEMS开关材料和元件的可靠性。对于铝合金和掺杂纳米晶金刚石薄膜，将考察温度和循环次数对由于缺陷产生和演化而导致的材料退化的影响。同样，内置应力的演变将通过扫描电子显微镜中使用的纳米压痕技术来识别，该技术最近在PI的实验室中开发。实验将包括独立薄膜的偏转，以评估薄膜的弹性和非弹性特性，以及通过连续的静电激励进行疲劳分析。固有应力和材料微观结构的演变将作为驱动循环次数的函数进行评估。实验的建模将在几个长度尺度上进行，从从头计算和分子动力学到离散位错和连续分布的位错网络；广泛的模拟将把建模和实验联系起来。

0120866EspinosaA GOALI award supports study of materials properties and problems relevant to the integration of micro-electro-mechanical systems (MEMS) with IC components for wireless applications. These systems offer unique advantages over other technologies because of their low power consumption, high sensitivity, physical size, and low cost. The technology is ideal for next generation of cell phones, base stations for wireless systems, and highly-efficient software-controlled digital radio for military communications. In these applications the MEMS devices are typically used as filters or switches. Filters with Q-factors of 94,000 can be employed to pre-select a communication band and a specific channel within that band. Switches with insertion losses bellow 0.1 dB per switch can be used for electromagnetic beam steering in radar antennas, accomplished through phase shifting. This feature enables antennas to transmit and receive signals without the need for physical reorientation. However, despite the large industrial interest, the technology is not yet commercially viable because a number of technical obstacles have to be overcome first. Key among these are packaging and mechanical modeling of MEMS materials at the micron scale. For instance, in the case of RF-switches, the effect of the environment can result in stiction of the membranes due to humidity or other sources. This requires the development of a cheap hermetic package. From a reliability standpoint, it is necessary to consider the plasticity limit and its temperature dependence with the materials involved. Temperatures as low as minus 50 degrees Celcius can be reached in satellite and airplane wireless applications while temperatures of a few hundred degrees can be present during device packaging. Another important failure mechanism is fatigue caused by excessive actuation cycles. Most of these devices are actuated trillions cycles pushing the design envelope and our current knowledge of material behavior beyond known parameters.In this project the reliability of capacitive RF-MEMS switch materials and components will be investigated. The effect of temperature and number of cycles on material degradation as a result of defects generation and evolution will be examined for aluminum alloy and doped nanocrystalline diamond films. Likewise, the evolution of the built-in stresses will be identified with a nanoindentation technique for use in the SEM, recently developed in the PI's laboratory. Experiments will consist of the deflection of freestanding films, to assess the elastic and inelastic properties of the films, and fatigue analysis by means of successive electrostatic actuation. Evolution of built-in stresses and material microstructure will be assessed as a function of the number of actuation cycles. Modeling of the experiments will be performed at several length scales, from ab initio calculations and molecular dynamics to discrete dislocation and continuously distributed dislocation networks; extensive simulations will link modeling and experiment.***