Reliability of MEMS in Liquid Environments

摘要与液体相互作用的微机电系统在生物医学、制药、化工、消费品和国防工业中具有重要意义。MEMS在液体环境中的操作是特别具有挑战性的，因为（1）需要显著的驱动力来移动潜在的大的流体“附加质量”，以及（2）液体粘度阻尼振荡运动。 此外，液体和MEMS材料之间的化学相互作用可能导致结构或电气故障。 对于浸没在流动液体中的MEMS，颗粒和气泡可能会改变器件性能。 在整个器件寿命（可靠性）期间，一致和可预测的操作对于MEMS的商业化至关重要。 拟议的研究的主要目的是调查和了解液体和颗粒或充满气泡的液体对微器件的短期和长期性能的影响。 第二个目的是证明有效的设计和设计限制，在液体中的可靠性能。为了实现这些目标，振荡微悬臂梁的性能将在充满液体的空腔和流动的液体进行研究。 梁将使用典型的MEMS结构膜材料和电绝缘涂层构造。器械将在其谐振频率下振荡最多1010个周期，并记录性能的任何变化。为了将由结构故障引起的性能损失与短路故障隔离开来，将对非导电和导电液体环境的影响进行研究。该研究将包括旨在量化结构和流体运动的实验。 在透明液体中，光束谐振频率、品质因数和位移将通过激光测振仪测量。 集成到光束中的传感元件将用于监测不透明、充满颗粒或气泡的液体中的谐振频率。流动液体环境中的颗粒和气泡运动将通过显微镜可视化，并用高分辨率数码相机记录。 图像处理将用于确定液体速度变化以及颗粒和气泡速度。 实验结果将与现有的气体环境中的可靠性研究进行比较，以确定影响器件性能的因素的共性和差异。 智力价值：这是第一个已知的调查可靠性的MEMS器件在液体环境中工作。 由于此类设备在各个行业中都非常受欢迎（并且已经在开发中），因此实验数据和分析对许多应用中的工程师来说都很有用。这项基础研究的结果可以推广到MEMS结构材料和涂层的实用指南，以确保在各种液体环境中可靠，长期运行。 拟议的研究将利用P.I.的跨学科专业知识。是制定这些指导方针。 广泛的影响：拟议的工作对工业的意义如上所述。 两个博士学生将获得该项目的资助。 此外，本科研究人员和高中物理教师将在夏季进行和参与短期调查。 教师们将把他们在尖端测量技术和工程应用方面的经验带回课堂。

AbstractMEMS that interact with liquids are of great interest in the biomedical, pharmaceutical, chemical, consumer product and defense industries. MEMS operation in liquid environments is particularly challenging because (1) significant driving forces are required to displace the potentially large 'added mass' of fluid and (2) liquid viscosities damp oscillatory motion. Also, chemical interaction between the liquid and MEMS materials may lead to structural or electrical failure. For MEMS immersed in flowing liquids, particles and bubbles may alter the device performance. Consistent and predictable operation throughout the device lifetime (reliability) is critical for commercializing MEMS. The primary objective of the proposed study is to investigate and understand the effects of liquids and particle- or bubble-laden liquids on microdevice short- and long-term performance. A second objective is to demonstrate effective designs and design limitations for reliable performance in liquids. To achieve these goals, the performance of oscillating micro-cantilever beams will be studied in liquid-filled cavities and in flowing liquids. The beams will be constructed using typical MEMS structural film materials and electrically insulating coatings. The devices will be oscillated at their resonant frequency for up to 1010 cycles, and any changes in performance will be noted. To isolate loss in performance caused by structural failures from shorting failures, the effects of both nonconducting and conducting liquid environments will be examined.The study will incorporate experiments designed to quantify both structural and fluid motion. In transparent liquids, beam resonant frequency, quality factor, and displacement will be measured by laser vibrometry. Sensing elements integral to the beams will be used to monitor resonant frequency in opaque, particle-laden or bubbly liquids. The particle and bubble motion in flowing liquid environments will be visualized through a microscope and recorded with a high-resolution digital camera. Image processing will be used to determine liquid velocity variations as well as particle and bubble velocities. Experimental results will be compared with existing reliability studies in gaseous environments to determine commonalities and differences in the factors affecting device performance. Intellectual merit: This is the first known investigation of reliability for MEMS devices operating in liquid environments. Since such devices are extremely desirable (and already under development) in a variety of industries, the experimental data and analysis will be useful to engineers in many applications. The results of this basic study can be generalized to practical guidelines for MEMS structural materials and coatings to ensure reliable, long-term operation in various liquid environments. The proposed study will draw on the interdisciplinary expertise of the P.I.'s to develop these guidelines. Broad impact: The significance of the proposed work to industry is described above. Two Ph.D. students will be funded by this project. Also, undergraduate researchers and high school physics teachers will perform and participate in short-term investigations during the summers. The teachers are expected to bring their experiences with cutting edge measurement techniques and engineering applications back to the classroom.