Electromigration-induced failure characteristics of GMR spin- valves and magnetic multilayers for the electrical reliability of spintronic devices

Abstract

This dissertation focuses on the electromigration (EM)-induced failure characteristics of FM/Cu/FM/(FeMn) based magnetic multi-layer (ML) and giant magnetoresistance (GMR) spin valves (SV) devices, especially when they are stressed by both the electrical and magnetic fields. The lifetime dependence of FM/Cu/FM tri-layers on Cu spacer thickness and FM/Cu chemical interface was investigated. Both lifetime and magnetic (VSM or MR) measurement of NiFe/(Co)/Cu/(Co)/NiFe/(FeMn) based SV-ML devices demonstrated that EM-induced Cu inter-diffusion is the dominant failure mechanism and an ultrathin Co or CoFe insertion layer is an effective diffusion barrier in improving the lifetime and magnetic stability. Cross-sectional HR-TEM and EDX were employed to directly compare the failure characteristics and interfaciall mixing. The activation energy and current dependence factor values were also graphically determined for numerically confirming the blocking effect of diffusion barriers. The effect of magnetic field on accelerating the EM-induced failures in SV-MLs was also demonstrated. A newly developed physical model confirmed that Hall effect-induced Lorentz force driven to the perpendicular-to-the-film-plane direction is primarily responsible for the severe acceleration of EM failures due to its dominant contribution to abruptly increasing local temperature and current density. The proposed failure model and the theoretical calculations were demonstrated to agree well with the experimental observations.