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Long term mechanical performance of MEMS in liquid environments.

机译:MEMS在液体环境中的长期机械性能。

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摘要

Micro-electro-mechanical systems (MEMS) are exposed to a variety of liquid environments in applications such as chemical and biological sensors, and microfluidic devices. Environmental interactions between the liquids and micron-sized structures can lead to unpredictable long-term performance of MEMS in liquid environments. The present understanding of long-term mechanical performance of MEMS is based on studies conducted in air or vacuum. The objective of this study was to extend the present understanding of long-term mechanical performance of MEMS to liquid environments. Two broad categories of long-term mechanical failures reported in the literature were experimentally investigated-operational failures and structural fatigue failures. Typically operational failures are observed to occur at low stress levels, while fatigue failures are reported at higher stress levels. In order to investigate these failure modes, two different designs of test specimens and experimental techniques were developed. Low stress level (0-5 MPa) tests to investigate operational failures of MEMS in liquids were performed on microcantilever test specimens. Higher stress level (∼ 0.2 GPa) tests were conducted on MEMS tensile specimens for investigating fatigue failures in liquids. Microcantilever specimens were made of silicon and silicon nitride. In addition, performance of silicon microcantilevers coated with common MEMS coating materials such as Titanium and SU-8 was also investigated. Microcantilever specimens were tested in liquids such as de-ionized water, saline, and glucose solution and compared with results in air. The microcantilevers were subjected to long-term cyclic actuation (108 -109 cycles) in liquid filled enclosures. Mechanical performance of the microcantilevers was evaluated by periodically monitoring changes in resonant frequency. Any unpredictable change in resonant frequency was deemed to constitute an operational failure. Despite low stress levels, mechanical performance of microcantilever test specimens was affected to a varying degree depending on environmental interactions between the structural/ coating material and the liquid environment. The changes in resonant frequency, often to the extent of ∼1%, were attributed to factors such as mineral deposition, corrosion fatigue, water absorption, and intrinsic stresses. Tensile-tensile fatigue tests (high stress level) were performed on aluminum MEMS tensile specimens, in air and saline solution. Fatigue life was observed to range between 1.2 x 106 to 2.2 x 106 cycles at mean and alternating stresses of 0.13 GPa. The effect of saline environment on fatigue failures of aluminum tensile specimens was inconclusive from the experiments performed in this study. In conclusion, experimental results indicate subtle operational failures to be a potential critical failure mode for MEMS operating in liquid environments. Long-term mechanical failures in MEMS are expected to depend on the particular combination of material, stress level, and environment.
机译:在诸如化学和生物传感器以及微流体装置的应用中,微机电系统(MEMS)暴露于各种液体环境中。液体和微米级结构之间的环境相互作用可能导致MEMS在液体环境中的长期性能无法预测。对MEMS长期机械性能的当前了解是基于在空气或真空中进行的研究。这项研究的目的是将目前对MEMS的长期机械性能的理解扩展到液体环境。文献中报道了两大类长期机械故障,它们是通过实验研究的,即操作故障和结构疲劳故障。通常观察到在低应力水平下会发生操作故障,而在较高应力水平下会报告疲劳故障。为了研究这些失效模式,开发了两种不同的测试样本设计和实验技术。在微悬臂梁试样上进行了低应力水平(0-5 MPa)测试,以研究MEMS在液体中的运行故障。在MEMS拉伸试样上进行了更高的应力水平(约0.2 GPa)测试,以研究液体的疲劳破坏。微悬臂试样由硅和氮化硅制成。此外,还研究了用常见的MEMS涂层材料(如钛和SU-8)涂层的硅微悬臂梁的性能。微悬臂梁样品在去离子水,盐水和葡萄糖溶液等液体中测试,并与空气中的结果进行比较。使微悬臂梁在充满液体的外壳中进行长期循环驱动(108 -109个循环)。通过定期监测共振频率的变化来评估微悬臂梁的机械性能。谐振频率的任何不可预测的变化都被认为是操作失败。尽管应力水平较低,微悬臂梁试样的机械性能还是受到不同程度的影响,具体取决于结构/涂层材料与液体环境之间的环境相互作用。共振频率的变化通常约为1%,这归因于诸如矿物沉积,腐蚀疲劳,吸水率和固有应力等因素。在空气和盐溶液中对铝MEMS拉伸试样进行了拉伸-拉伸疲劳测试(高应力水平)。在平均应力和交替应力为0.13 GPa的条件下,疲劳寿命为1.2 x 106至2.2 x 106个循环。盐环境对铝拉伸试样疲劳破坏的影响尚不确定。总之,实验结果表明,微妙的操作故障是在液体环境中运行的MEMS的潜在关键故障模式。预期MEMS中的长期机械故障取决于材料,应力水平和环境的特定组合。

著录项

  • 作者

    Ali, Shaikh Mubassar.;

  • 作者单位

    University of Minnesota.;

  • 授予单位 University of Minnesota.;
  • 学科 Engineering Mechanical.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 237 p.
  • 总页数 237
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类 机械、仪表工业;
  • 关键词

  • 入库时间 2022-08-17 11:37:36

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