Forming long Ag thin wires by using stress migration

Ag thin wires in the 1-2 μm diameter range with lengths of up to ~680 μm were fabricated in a metallic multilayer sample using stress migration. The sample, which was heated under atmospheric conditions, was a thin Ag film deposited on a Cu foil with an adhesion film of Ti and covered with a TiN passivation film. A compressive stress gradient, formed in the Ag film during the heating treatment, was the driving force for atomic diffusion. A tensile stress was produced in the TiN film, and brittle fracture occurred to cause cracks after the tensile stress exceeded the fracture strength of TiN. The cracks provided pathways for atomic discharge to generate long Ag thin wires. It was noted that a thick TiN passivation film was indispensable for wire formation. The long Ag thin wires may provide great potential applications as component materials in flexible transparent electrodes, integrated circuits and electromagnetic systems.