Evaluation of nanoindentation load-depth curve of MEMS bridge structures by calculating the critical elastic-plastic bending deflections

Abstract

This paper proposes a correction method to accurately evaluate the nanoindentation load-depth (P-h) curve of MEMS double clamped micro bridge structures. Critical elastic and plastic deflections of the bent bridge are extracted from the overall elastic-plastic deflection, respectively. Through subtracting the elastic-plastic deflection of the micro bridge from the total displacement of the Berkovich indenter’s tip, the effect of constraint condition (double clamped) on the P-h curve of micro bridge is corrected. Nanoindentation P-h curves of routine and micro bridge C11000 Cu specimens are respectively obtained and compared with each other through both finite element analysis and experiments. Meanwhile, cross-sectional profiles along the symmetry axis of local indentation locations respectively obtained from the nodal deformations and scanned images of routine and micro bridge specimens are also compared and explained. Furthermore, a theoretical model is proposed to analyze the effect of the equivalent flow area induced by the elastic-plastic deflection on maximum indentation depth, the corrected values of Young’s modulus, maximum and residual depths of micro bridge specimens are essentially in agreement with that of routine fixed specimens.