Cu/Si interface fracture due to fatigue of copper film in nanometer scale

In order to investigate the fatigue behavior of metals in nanoscale, a cyclic bending experiment is carried out using a nano-specimen. The specimen includes a copper film with a thickness of 20 nm constrained by highly rigid materials, which yields a high strain region with a size of a few nanometers near the interface edge. The specimen broke before the maximum load in the 7th cycle under fatigue (load range of 18 μN). The load-displacement curve shows nonlinear behavior and a distinct hysteresis loop, indicating plasticity in the Cu film. Reverse yielding appearing after the 2nd cycle suggests the development of a cyclic substructure in the Cu film. The cumulative plastic strain in the Cu film at fracture is more than three times larger than that under monotonic loading. These results indicate that the specimen breaks owing to fatigue of the Cu film on the nanoscale.

Research highlights▶ The fatigue fracture of bulk metals is generally induced by characteristic dislocation structures with micron scale through the self-organization process. ▶ However, there is not enough space to for the formation of the structure in a small component where the size is close to the one of the fatigue dislocation structure. ▶ This paper tries to clarify the existence of fatigue in a nanometer scale metal component. ▶ The component is definitely broken by a cyclic loading, and the cyclic load-displacement curves show obvious hysteresis and shape variation, which indicate the formation of specific fatigue structure.