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Utilizing On-Chip Testing and Electron Microscopy to Study Fatigue and Wear in Polysilicon Structural Films

Published online by Cambridge University Press:  15 March 2011

D.H. Alsem ,
E.A. Stach ,
C.L. Muhlstein ,
M.T. Dugger  and
R.O. Ritchie
D.H. Alsem
Affiliation:
Department of Materials Science and Engineering, University of California, Berkeley Materials Sciences Division, Lawrence Berkeley National Laboratory National Center for Electron Microscopy, Lawrence Berkeley National Laboratory
E.A. Stach
Affiliation:
National Center for Electron Microscopy, Lawrence Berkeley National Laboratory
C.L. Muhlstein
Affiliation:
Department of Materials Science and Engineering, Pennsylvania State University
M.T. Dugger
Affiliation:
Materials and Process Sciences Center, Sandia National Laboratory, Albuquerque
R.O. Ritchie
Affiliation:
Department of Materials Science and Engineering, University of California, Berkeley Materials Sciences Division, Lawrence Berkeley National Laboratory
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Abstract

Wear and fatigue are important factors in determining the reliability of microelectromechanical systems (MEMS). While the reliability of MEMS has received extensive attention, the physical mechanisms responsible for these failure modes have yet to be conclusively determined. In our work, we use a combination of on-chip testing methodologies and electron microscopy observations to investigate these mechanisms. Our previous studies have shown that fatigue in polysilicon structural thin films is a result of a ‘reaction-layer’ process, whereby high stresses induce a room-temperature mechanical thickening of the native oxide at the root of a notched cantilever beam, which subsequently undergoes moisture-assisted cracking. Devices from a more recent fabrication run are fatigued in ambient air to show that the post-release oxide layer thicknesses that were observed in our earlier experiments were not an artifact of that particular batch of polysilicon. New in vacuo data show that these silicon films do not display fatigue behavior when the post release oxide is prevented from growing, because of the absence of oxygen. Additionally, we are using polysilicon MEMS side-wall friction test specimens to study active mechanisms in sliding wear at the microscale. In particular, we have developed in vacuo and in situ experiments in the scanning electron microscope, with the objective of eventually determining the mechanisms causing both wear development and debris generation.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 821: Symposium P – Nanoscale Materials & Modeling-Relations Among Processing, Microstructure and Mechanical Properties , 2004 , P2.5
Copyright
Copyright © Materials Research Society 2004

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