Characteristics of electrostatic discharge induced damage on magnetic tunnel junctions

We report on the investigation of electrostatic discharge (ESD) sensitivity of current perpendicular to plane (CPP) magnetic tunnel junction (MTJ) heads used in hard disk drives (HDD). Our results show that MTJs have different degradation characteristics and mechanisms from current in-plane (CIP) giant magnetoresistive (GMR) heads when exposed to cumulative ESD current transients. Both MTJ and GMR beads show gradual amplitude degradation as a result of increasing ESD levels, but MTJs are more robust than GMR heads in terms of sensor stack magnetic stability, such as polarity flip. Large ESD voltages could change stability state of the MTJ heads, which shows up as random telegraph noise associated with transfer curve magnetic distortions in low-frequency regime and noise spikes several times above baseline noise in high-frequency regime. This MTJ instability is likely a result of defects in the multilayer reader magnetics and disturbances, as well as degradation of tunnel oxide barrier.