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Mechanical Characterization of Thin Films Using Full-Field Measurement of Diaphragm Deflection

Published online by Cambridge University Press:  15 February 2011

R. I. Pratt  and
G. C. Johnson
R. I. Pratt
Affiliation:
Department of Mechanical Engineering, University of California, Berkeley, CA 94720.
G. C. Johnson
Affiliation:
Department of Mechanical Engineering, University of California, Berkeley, CA 94720.
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Abstract

A new method for evaluating the elastic moduli and residual stresses in thin films is presented. This technique is based on measurement of the complete deflected shape of pressurized diaphragms made of the material to be evaluated. It offers important advantages over previous techniques in which only the displacement of the center of the diaphragm is measured as a function of pressure. The experimental apparatus uses a laser beam and its reflection from the sample surface to determine relative height. Measurements are made over an area of the sample by performing a two-dimensional scan of the sample under the laser beam. The most important advantage of determining the entire deformed shape of the diaphragm is that the shape is known rather than assumed. This way, the particular theory chosen to analyze the structural response does not also dictate a deformed shape based solely on the maximum deflection at the midpoint. Plate theory, as opposed to the more traditional membrane theory, is used to account for the dominance of bending behavior at low pressure and near the diaphragm edges. An energy method is employed to estimate stiffness and residual stress. The accuracy of this approximate method is directly related to how closely the assumed mode shape used in the analysis approximates the true response of the structure. Since these surface profiles are measured experimentally, the resulting property estimates are obtained with increased confidence.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 308: Symposium M1 – Thin Films: Stresses and Mechanical Properties IV , 1993 , 115
Copyright
Copyright © Materials Research Society 1993

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References

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