Fabrication of aluminum microwires through artificial weak spots in a thick film using stress-induced migration

Abstract

With recent advances in technology, micro/nanomaterials have attracted a great deal of attention because of their superior properties compared with the bulk materials. Stress-induced migration (SM) has been used to fabricate micro/nanomaterials because of its advantages of simple processing, mass production, and the possibility of fabricating reactive materials such as aluminum. Stress-induced migration is a physical phenomenon of atomic diffusion driven by compressive stress gradients. When a multilayer structure that includes a passivation layer, a metallic film, and a substrate is heated, hydrostatic thermal stress gradients in the metallic film drive atoms to migrate and discharge through weak spots in the passivation layer. As a result, a large number of nanowhiskers and hillocks grow spontaneously at those locations. However, two problems exist in SM fabrication. First, the position, size, and shape of the growing materials are random because of the randomness of the weak spots. Second, fabricating microwires is difficult because migration of a large number of atoms is needed. In this study, 1- m m-diameter aluminum microwires were successfully grown at intended positions on thick aluminum film by using SM. The thick aluminum film was used to provide a sufficient number of atoms to form microwires. In addition, the positions of the microwires were controlled by introducing artificial weak spots. The parameters that are related to the intentional growth of microwires were investigated, and an optimum condition for growing aluminum microwires was presented.