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Microstructural and Geometrical Factors Influencing the Mechanical Failure of Polysilicon for MEMS

Published online by Cambridge University Press:  01 February 2011

Krishna Jonnalagadda  and
Ioannis Chasiotis
Krishna Jonnalagadda
Affiliation:
[email protected], University of Illinois at Urbana-Champaign, Aerospace Engineering, 104 S. Wright Street, Urbana, IL, 61801, United States
Ioannis Chasiotis
Affiliation:
[email protected], University of Illinois at Urbana-Champaign, Aerospace Engineering, 104 S. Wright Street, Urbana, IL, 61801, United States
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Abstract

The failure strength of polycrystalline silicon is discussed in terms of activation of critical flaws, as well as the material microstructure and inhomogeneity. The Weibull probability density function parameters were obtained to deduce the scaling of material and component strength and to identify critical flaw populations, especially when two or more flaw sets are concurrently active. It was shown that scaling of strength changes for small feature sizes, which limits the applicability of strength data from large MEMS components to self-similar small MEMS components. On the other hand, the probability of failure of small components is described by a larger Weibull material stress parameter, which makes uniaxial strength data a conservative design approach. Furthermore, according to mode I and mixed mode I/II fracture studies for polysilicon, it is concluded that microstructural inhomogeneity alone accounts for 50% scatter in strength (with reference to the minimum recorded value). Thus, the conditions for applicability of the Weibull probability density function are rather weak in polycrystalline silicon, because flaws of the same length that are subjected to the same macroscopic stresses are not always critical.

Keywords

microelectro-mechanical (MEMS)fracturestrength
Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 1052: Symposium DD – Microelectromechanical Systems–Materials and Devices , 2007 , 1052-DD02-01
Copyright
Copyright © Materials Research Society 2008

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