Effects of Cu Interdiffusion on the Electromigration Failure of FM/Cu/FM Tri-Layers for Spin Valve Read Sensors

Electromigration-induced failure (EIF) lifetime characteristics of FM/Cu/FM (FM: NiFe or Co) tri-layers, which are currently used in GMR spin-valve read sensors, have been investigated to verify the fundamental failure mechanisms. It is found that the lifetime of NiFe/Cu/NiFe tri-layers was dramatically increased by decreasing the Cu spacer thickness. The obvious shorter lifetime of NiFe/Cu/NiFe tri-layers compared to that of Co/Cu/Co tri-layers was mainly thought to be attributed to the formation of current paths resulted from the electromigration-induced Cu interdiffusion into the top or bottom NiFe layer during electrical stressing caused by the Ni-Cu intermixing. The activation energy (E_a) and current density factor, "n" value of the NiFe/Cu/NiFe tri-layers were found to be 0.23-0.25eV and 1.23-1.32, respectively. It is suggested that the control of Cu spacer interdiffusion and chemical roughness at the FM/Cu interface is crucial in determining the electrical reliability of FM/Cu/FM based GMR spin valve read sensors