Tensile properties and fatigue crack growth in LIGA nickel MEMS structures

The tensile and fatigue properties of LIGA (Lithographie, Galvanformung, Abformung) nickel microelectromechanical systems (MEMS) structures were evaluated using a microtensile/fatigue device. The feature size of the specimens was 10 μm. The stress-strain results obtained by microtensile tests showed comparatively brittle, and the variation in ultimate tensile strength was explained by the specimen geometry. Stress-cycle curves were also measured by tension-tension fatigue tests. The notch effect on fatigue was discussed in terms of notch-sensitivity factor. Crack propagation rates were measured by the unloading compliance method and the Paris parameter was obtained. The cycles to failure predicted from the crack propagation rate at various stress intensity factors were compared with the measured values.