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Surface Oxide Effects on Static Fatigue of Polysilicon MEMS

Published online by Cambridge University Press:  11 February 2011

H. Kahn
Affiliation:
Dept. of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, U.S.A.
R. Ballarini
Affiliation:
Dept. of Civil Engineering, Case Western Reserve University, Cleveland, OH 44106, U.S.A.
A.H. Heuer
Affiliation:
Dept. of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106, U.S.A.
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Abstract

Static fatigue – crack growth causing delayed failure under constant stress and involving stress corrosion cracking – was investigated in polysilicon MEMS using two different surface-micromachined devices. One exploited residual tensile stresses to create stress concentrations at micromachined notches, and the other involved a single-edge notched beam specimen integrated with an electrostatic comb-drive microactuator. Tests with both devices revealed that polysilicon is not susceptible to static fatigue in humid environments. However, when a relatively thick (45 to 140 nm) surface oxide was thermally grown on the microactuator devices, the specimens demonstrated delayed fracture in a humid ambient, presumably due to static fatigue of the surface SiO2. The stress intensities at the resulting cracks in the SiO2 were then sufficient to cause catastrophic crack propagation through the polysilicon specimens. The implications of our data on the issue of fatigue in polysilicon is discussed.

Type
Research Article
Copyright
Copyright © Materials Research Society 2003

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References

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