Role of oxide thickening in fatigue crack initiation in LIGA nickel MEMS thin films

This paper presents the results of a combined experimental and theoretical study of the fatigue crack initiation in LIGA Ni thin films with a thickness of 270μm. The potential roles of surface oxide thickening and slip bands are explored for fatigue crack initiation. Surface oxides and roughness are characterized using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM). The underlying crack driving forces associated with pop-in in surface oxide layers are then compared to those associated with the early stages of fatigue crack growth. The implications of the results are discussed for the modeling of fatigue in LIGA Ni micro-electro-mechanical-systems (MEMS) structures.