Ultra high-cycle fatigue in pure Al thin films and line structures

The requirements of mechanical devices (micro electro mechanical systems, MEMS, and surface acoustic wave filter, SAW) increase due to shrinking size, rising frequencies and driving power. This paper focuses on novel fatigue mechanisms stemming from the combination of small dimensions (100 nm) and ultrahigh frequencies (GHz). Quantitative post-test analysis of in situ experiments showed a correlation between extrusion density and device performance. Qualitative microstructural analysis showed a good correlation between the location of defect formation and stress concentrations as calculated by finite element analysis. In situ measurements of the characteristic damage formation revealed a combined extrusion/void formation mechanism that operates on a short time scale. The underlying mechanism was assumed to be a combination of a dislocation and stress induced diffusion process, leading to the observed void and extrusion formation.