The physical mechanisms which were responsible for the dependence of the electromigration-induced failure lifetime upon the NiFe thin film thickness were studied in order to determine the maximum allowable current density. Based upon measured median times-to-failure, a maximum current density of 108 to 2 x 108A/cm2 was found to be safely usable in 3 to 5nm-thick films. Grain size analyses, using transmission electron microscopy, suggested that the longer lifetimes of thinner films were due mainly to the smaller numbers of grain boundaries and triple junctions; which resulted in less atomic flux divergence.

Dependence of Electromigration-Induced Failure Lifetimes on NiFe Thin-Film Thickness in Giant Magnetoresistive Spin-Valve Read Heads. S.Bae, J.H.Judy, I.Tsu, M.Davis, E.S.Murdock: Applied Physics Letters, 2001, 79[22], 3657-9