Feedback of MEMS reliability study on the design stage: A step toward Reliability Aided Design (RAD)

Abstract

This paper presents recent experimental evidence of stiffness evolution under cyclic loading. This is part of a MEMS reliability study aiming at the modelling of the fatigue phenomenon. Dynamic response of polycrystalline structural layers during operation has been studied by using benches based on M-Test. Clamped-clamped beams have been designed and fabricated in order to serve as sample to which elementary bending solicitations have been applied. The fabrication process of in situ test benches is detailed. Finite Element Method computations have been performed to estimate features such as the pull-in voltage, the resonant frequency and the Von Mises stress induced while applying a bending stress. Next, cyclic actuation has been achieved and two different characterization methods have been used: pull-in voltage measurement and mechanical determination of the stiffness via the use of an Atomic Force Microscope. Then, a description of the fatigue phenomenon is proposed and, from experimental results, a predictive modelling has been made and compared to other set of characterization results in order to validate it; the prediction error is 19%. This phenomenological modelling allows predicting the evolution of clamped-clamped beam stiffness vs. the number of functioning cycles. Such methodology, "Reliability Aided Design" (RAD) could be applied to other couples "material-structure" leading to think already at the MEMS design stage in term of reliability. © 2003 Elsevier Ltd. All rights reserved.