Influence of the frequency on fatigue of directly wafer-bonded silicon

Fatigue tests on directly wafer-bonded silicon samples were performed using pre-cracked Micro-Chevron samples applying cycling loading frequencies between 0.3 and 40 Hz. The experimental lifetime results were compared with a theoretical prediction using measured subcritical crack growth parameters under static loading conditions. The experimental investigations revealed that the number of cycles required to break the samples increased with frequency. In contrast, the corresponding time-to-failure values did not depend on frequency. Both the qualitative behavior and the quantitative life-time results agreed very well with a prediction based on a fracture mechanical model. Therefore, it could be concluded that fatigue behavior in the considered frequency range is solely controlled by stress corrosion in the bonded interface. Furthermore, the results demonstrate an available approach for lifetime prediction of wafer-bonded micro-electro-mechanical systems components stressed by cycling loading.