This paper reports on a tensile-mode fatigue test in a constant humidity, even in a very high humidity, to reveal the mechanism of fatigue fractures of MEMS materials. A newly developed tensile-mode fatigue tester using the electrostatic grip can control the humidity from 25%RH to 90%RH. Using this tester, the fatigue life and strength of single crystal silicon (SCS) thin films and their dependence on the humidity were evaluated. In addition, using the statistical analysis for the fatigue test results, the fatigue parameter of SCS was obtained. The scale parameter, Weibull modulus, and fatigue parameter in the high humidity (85-90%RH) were 2.9×10{sup}9Pa, 13.6, and 86.3, respectively. With these parameters, the fatigue life prediction of SCS was performed for the long-term reliability assessment of MEMS devices.
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