  Granular aluminium is a high kinetic inductance thin film superconductor
which, when formed into nanowires can undergo an intrinsic electromigration
process. We use a combination of experimental and computational approaches to
investigate the role of grain morphology and distribution in granular aluminium
thin films, when formed into nanowire constrictions. Treating the granular
aluminium film as a network of randomly distributed resistors with parameters
motivated by the film microstructure allows us to model the electrical
characteristics of the nanowires. This model provides estimates of the
dependence of sheet resistance on grain size and distribution, and the
resulting device to device variation for superconducting nanowires. By
fabricating a series of different length nanowires, we study the
electromigration process as a function of applied current, and then compare
directly to the results of our computational model. In doing so we show that
the electromigration is driven by the formation of quantum point contacts
between metallic aluminium grains.
