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Proceedings Paper

Long-term reliability of single-crystal silicon thin films: the influence of environment on the fatigue damage accumulation rate
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Paper Abstract

Single-crystal silicon thin films were forced to resonate at high frequency (~40 kHz) in different environments to study the long-term durability of this structural material used in microelectromechanical (MEMS) devices. The fatigue characterization structure consists of a notched cantilever beam attached to a plate shaped mass and is actuated at resonance, creating fully reversed, constant amplitude, sinusoidal stresses at the notch root. The dynamic behavior of the resonating structure has been meticulously quantified to allow accurate stress measurements from the knowledge of the driving voltage amplitude and the calculation of the quality factors in air and vacuum. In addition, the change in resonant frequency is periodically monitored for long-life specimens. Fatigue failure was observed for specimens tested in humid air and medium vacuum. In air, the stress-life (S-N) curve confirms the unique fatigue behavior already attributed to silicon thin films. In vacuum, the strength of the specimens appears to increase, and fatigue failure is delayed. Fracture surface examination reveals distinct features on the fracture surfaces of long-life fatigued specimens, not found in quasistatic failure, that are clear indications of initiation regions. The decrease rate in resonant frequency during cycling is demonstrated to be related to damage accumulation rate, and is strongly sensitive to both stress amplitude and humidity. The different currently proposed mechanisms are discussed in light of this new set of experimental evidence.

Paper Details

Date Published: 22 January 2005
PDF: 10 pages
Proc. SPIE 5716, Reliability, Packaging, Testing, and Characterization of MEMS/MOEMS IV, (22 January 2005); doi: 10.1117/12.591219
Show Author Affiliations
Olivier N. Pierron, The Pennsylvania State Univ. (United States)
Christopher L. Muhlstein, The Pennsylvania State Univ. (United States)

Published in SPIE Proceedings Vol. 5716:
Reliability, Packaging, Testing, and Characterization of MEMS/MOEMS IV
Danelle M. Tanner; Rajeshuni Ramesham, Editor(s)

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