Abstract
Reliability issues such as crack propagation and lifetime are more and more crucial in commercial microelectromechanical systems (MEMS). Because conventional assessment methods have significant limitations in MEMS applications due to their very small scale, more advanced methods are required. This study focuses on a new methodology based on an analytical and statistical analysis of time-dependent degradation behavior of resonating structures. To predict reliability from the degradation behavior, we introduced a new concept, degradation rate. A single silicon tether-type resonating structure with a small sharp notch, fabricated by micromachining, was operated electrostatically at resonance mode and the decrease in resonant frequency with operation cycles was measured. We identified the degradation/failure mode and mechanism by analyzing the fracture surface. To investigate the effect of a notch as a local defect on failure, we deduced a relation between the stiffness of a notched beam and the resonant frequency of the structure and used it to quantify the effect of notch depth ratio and crack growth near the notch tip on stiffness degradation and ultimate time to failure. Finally, this degradation rate concept was used in a statistical analysis of the measured resonant frequency to evaluate the reliability function and hazard rate and predict the failure time of the structure. These predictions were compared with experiments to verify the validity of the proposed methodology.
