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 junctions (MTJ) used in hard disk drives (HDD). The newer generations of HDDs increasingly use MTJs while the current in plane (CIP) giant magnetoresistive (GMR) heads are being gradually phased out. We have found that, in general, the ESD sensitivity of CPP MTJs and CIP GMR readers is comparable at the same areal density point. The difference is in the details of degradation. With increasing ESD voltage pulse applied across the two terminals of the reader, the amplitude of a GMR reader degrades first, while resistance remains stable to higher ESD voltage levels and ultimately increases. With the MTJ reader it is the resistance that decreases first, while the amplitude remains stable to higher ESD voltage levels and ultimately decreases. In addition to its effect on resistance and amplitude, ESD can also change the state of stability of MTJs. In this paper, we report on our investigations of instability generation in MTJs with increasing ESD levels. We describe the experimental method, record the observations, and analyze them to understand the source of instability.