Analysis of failure mechanisms in electrically stressed Au nanowires

An analysis of polycrystalline Au thin film interconnects of widths ranging from 850 to 25 nm, and lengths ranging from 1.0 μm to 20 nm which have been electrically stressed to the point of failure is presented. For the longer wires (widths 60–850 nm), the failure current density is typically found to be ${10}^{12} {\mathrm{A m}}^{\mathrm{-2}},$ essentially independent of the wire width, and then rapidly approaching zero for thinner wires. For the wider wires, failure occurs at the end towards the negative electrode; for narrow wires, failure tends to occur towards the center of the wire, as observed using scanning electron microscopy and atomic force microscopy. The mean time to failure for fixed current density is seen to decrease with decreasing wire width. The failure current density for a given wire width increases as the length decreases. An analysis of the temperature profile based on calculations of a simple model is presented which shows that this width-dependent behavior of narrow lines is not anticipated from the assumption of a homogeneous line subject to thermally-assisted electromigration alone.