Study of a Permanent Shunt Across a TMR Reader With an Ultralow RA Barrier

This paper experimentally presents the permanent-shunt resistance (PSR) effect on electrostatic discharge (ESD) threshold of a MgO-based tunnel magnetoresistance reader with an ultralow resistance-area (RA) barrier. Parallel-connected permanent shunts of different values are designed for the experiment. The PSR shunt can improve the ESD threshold, but it also brings some degradations on the dynamic performance of the read signal, and a tradeoff is needed between the ESD protection and the read signal. “Barrier defect enlargement” mode was found effective to explain the ESD damage mechanism in the low RA reader, and the slope factor between normalized amplitude and normalized magnetic reader resistance is related to the PSR value strongly. Based on the RA value, PSR shunt value, and slope factor between normalized amplitude and normalized magnetic reader resistance, the RA of the defective area can be determined to be around one quarter of RA of the magnetic tunnel junction RA.