Heavy-Ion-Induced Displacement Damage Effects in Magnetic Tunnel Junctions With Perpendicular Anisotropy

• Published in: IEEE transactions on nuclear science 2021-05, Vol.68 (5), p.581-587
• Main Authors: Xiao, T. Patrick, Bennett, Christopher H., Mancoff, Frederick B., Manuel, Jack E., Hughart, David R., Jacobs-Gedrim, Robin B., Bielejec, Edward S., Vizkelethy, Gyorgy, Sun, Jijun, Aggarwal, Sanjeev, Arghavani, Reza, Marinella, Matthew J.
• Format: Article
• Language: English
• Subjects: Anisotropy; Displacement; Displacement damage; heavy ion irradiation; Heavy ions; Interfaces; Ions; Junctions; magnetic random access memory; magnetic random access memory (MRAM); magnetic tunnel junction; magnetic tunnel junction (MTJ); Magnetic tunneling; Magnetoresistance; Magnetoresistivity; MRAM; non-volatile memory; nonvolatile memory; NUCLEAR PHYSICS AND RADIATION PHYSICS; Perpendicular magnetic anisotropy; perpendicular magnetic anisotropy (PMA); Polarization (spin alignment); Propagation modes; Radiation effects; Random access memory; Resistance; Scatter propagation; spin-transfer-torque MRAM (STT-MRAM); Structural damage; STT-MRAM; Switches; Tunnel junctions
• ISSN: 0018-9499; 1558-1578
• DOI: 10.1109/TNS.2021.3057348

We evaluate the resilience of CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy (PMA) to displacement damage induced by heavy-ion irradiation. MTJs were exposed to 3-MeV Ta 2+ ions at different levels of ion beam fluence spanning five orders of magnitude. The devices remained insensitive to beam fluences up to 10^{11} ions/cm 2 , beyond which a gradual degradation in the device magnetoresistance, coercive magnetic field, and spin-transfer-torque (STT) switching voltage were observed, ending with a complete loss of magnetoresistance at very high levels of displacement damage (>0.035 displacements per atom). The loss of magnetoresistance is attributed to structural damage at the MgO interfaces, which allows electrons to scatter among the propagating modes within the tunnel barrier and reduces the net spin polarization. Ion-induced damage to the interface also reduces the PMA. This study clarifies the displacement damage thresholds that lead to significant irreversible changes in the characteristics of STT magnetic random access memory (STT-MRAM) and elucidates the physical mechanisms underlying the deterioration in device properties.