Failure Investigation of Polymer Mechanical Micromponents
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0975-DD06-09
Failure Investigation of Polymer Mechanical Micromponents Yi Zhao1, and Xin Zhang2 1 Department of Biomedical Engineering, The Ohio State University, 294 Bevis Hall, 1080 Carmack Road, Columbus, OH, 43210 2 Department of Manufacturing Engineering, Boston University, 15 Saint Mary's Street, Bookline, MA, 02446 ABSTRACT This paper reports typical failure modes of polymer microstructures. Polydimethylsiloxane (PDMS) microstructures were fabricated using replication-based methods. The mechanical collapses of these structures were observed using scanning electron microscopy. In this work, we classified the mechanical collapses based on their individual geometries and discussed the mechanism of each failure mode. We also worked on solutions to recover these failed PDMS structures. This work helps us to better understand the collapsing mechanism and to facilitate the development of control strategies to enhance the mechanical reliability of polymer microdevices.
INTRODUCTION Polymer microstructures have been increasingly used in the rapidly developing biological microelectromechanical systems (BioMEMS). They not only serve as structuring materials, such as microchannels and microreservoirs, but also as mechanosensing and actuating components, such as pumps, valves and cantilevers. This is due to the unique advantages of polymers over conventional materials, including good biocompatibility, optical transparency and small elastic modulus (about 100 ~ 10,000 times smaller than that of conventional semiconductor materials). Among these advantages, the low elastic modulus allows the polymers to serve as sensing materials for detection of minute mechanical forces at small scales, especially the forces generated by cellular and subcellular units. The directions and magnitudes of the forces are measured from deformation of subject polymer microstructures. For this application, polymer microstructures need to be fabricated with certain geometries, and usually with high aspect ratios, to obtain sufficient mechanical sensitivities along one or multiple directions. Recent study [1,2] has shown that the unique geometries of these mechanical polymer microcomponents may give rise to mechanical reliability problems, causing the structures to collapse to each other or to the ground substrate in one way or another. The low elastic modulus and the dielectric characteristics of polymer materials make this concern even more crucial. The collapsed polymer structures either lose mechanical sensitivities that they have been designed for, or fail to serve as structuring materials. So far, there is little systematic work on primary failure modes of these polymer mechanical components. Therefore, in this paper, we investigate experimentally the failures of polymer microstructures fabricated using soft lithography technologies. Each failure mode is discussed for its mechanism and its unique geometries, with an aim to increase fabrication yield and to provide practical strategies for polymer microfabrication.
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