Nanoindentation study of plasticity length scale effects in LIGA Ni microelectromechanical systems structures

This paper presents the results of a nanoindentation study of the effects of strain gradient plasticity on the elastic-plastic deformation of lithographie, galvanoformung, abformung (LIGA) Ni microelectromechanical systems (MEMS) structures plated from sulfamate baths. Both Berkovich and North Star/cube corner indenter tips were used in the study to investigate possible effects of residual indentation depth on the hardness of LIGA Ni MEMS structures between the micro- and nanoscales. A microstructural length scale parameter, l̂ = 2.2 μm, was determined for LIGA nickel films. This is shown to be consistent with a stretch gradient length-scale parameter, l_s, of approximately 0.9 μm.