A new in situ residual stress measurement method for a MEMS thin fixed-fixed beam structure

A new method is described to measure the in situ residual stress state in a thin fixed-fixed beam structure used in microelectromechanical systems (MEMS). The methodology can be applied to devices at the anticipated operational and environmental temperatures. The new technique makes use of differenc...

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Bibliographic Details
Published in:	Journal of microelectromechanical systems Vol. 11; no. 4; pp. 309 - 316
Main Authors:	Chen, S., Baughn, T.V., Yao, Z.J., Goldsmith, C.L.
Format:	Journal Article
Language:	English
Published:	New York, NY IEEE 01-08-2002 Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
Subjects:	Beams (structural) Exact sciences and technology Finite element method Finite element methods Fundamental areas of phenomenology (including applications) Instruments, apparatus, components and techniques common to several branches of physics and astronomy Mathematical analysis Mathematical models Measurement and testing methods Measurement methods Measurement methods and techniques in continuum mechanics of solids Mechanical instruments, equipment and techniques Microelectromechanical devices Microelectromechanical systems Micromechanical devices Micromechanical devices and systems Natural frequencies Physics Radio frequency Residual stress Residual stresses Solid mechanics Stress concentration Stress measurement Stresses Structural and continuum mechanics Studies Substrates Temperature Thermal expansion Thermal stresses Topology Suspended structure In situ In situ test Numerical method Residual stresses Experimental study Radiofrequency Switching Finite element method Thermal expansion Model matching Strain gradient Modelling Microelectromechanical device Stress measurement
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Summary:	A new method is described to measure the in situ residual stress state in a thin fixed-fixed beam structure used in microelectromechanical systems (MEMS). The methodology can be applied to devices at the anticipated operational and environmental temperatures. The new technique makes use of differences in the thermal expansion coefficient between the thin beam and the substrate. The residual stress distribution is determined by matching the thermal deflections from a finite element model (FEM) to measured deflections of the beam. All previous residual stress measurement methods for MEMS suspended structures reported a uniformly distributed residual stress. Experimental data coupled with the new analytical method suggests that this may not be adequate for the case of a suspended thin structure with nonplanar surface topology. A stress gradient through the thickness must be included in the determination of the stress state of the beam. The new method indicates a spatially varying residual stress distribution and is capable of de-coupling the mean stress and the stress gradient through the thickness. It was found through an extensive literature review that the quantification of the stress gradient in a thin suspended structure has never been reported. The de-coupling makes the prediction of the stress state at different temperature points possible. Details of the new method are demonstrated and discussed by the use of a capacitive radio frequency (RF) MEMS switch.
Bibliography:	ObjectType-Article-2 SourceType-Scholarly Journals-1 ObjectType-Feature-1 content type line 23
ISSN:	1057-7157 1941-0158
DOI:	10.1109/JMEMS.2002.800936