Annealing stability of magnetic tunnel junctions based on dual MgO free layers and [Co/Ni] based thin synthetic antiferromagnet fixed system

摘要

We study the annealing stability of bottom-pinned perpendicularly magnetizedmagnetic tunnel junctions based on dual MgO free layers and thin fixed systemscomprising a hard [Co/Ni] multilayer antiferromagnetically coupled to thin a Coreference layer and a FeCoB polarizing layer. Using conventional magnetometryand advanced broadband ferromagnetic resonance, we identify the properties ofeach sub-unit of the magnetic tunnel junction and demonstrate that thismaterial option can ensure a satisfactory resilience to the 400$^\circ$Cthermal annealing needed in solid-state magnetic memory applications. The dualMgO free layer possesses an anneal-robust 0.4 T effective anisotropy andsuffers only a minor increase of its Gilbert damping from 0.007 to 0.010 forthe toughest annealing conditions. Within the fixed system, the ferro-couplerand texture-breaking TaFeCoB layer keeps an interlayer exchange above 0.8mJ/m$^2$, while the Ru antiferrocoupler layer within the syntheticantiferromagnet maintains a coupling above -0.5 mJ/m$^2$. These two strongcouplings maintain the overall functionality of the tunnel junction upon thetoughest annealing despite the gradual degradation of the thin Co layeranisotropy that may reduce the operation margin in spin torque memoryapplications. Based on these findings, we propose further optimization routesfor the next generation magnetic tunnel junctions.