High thermal stability tunnel junctions

Abstract

The thermal stability of CoFe/Al2O3/CoFe/MnIr spin-tunnel junctions fabricated by ion beam, using two oxidation methods is studied for annealing temperatures up to 450 °C. Tunnel magnetoresistance (TMR) is 40% after annealing at 300 °C, and a TMR of 15% is still achieved after annealing at 380 °C. The TMR decay with anneal depends on the oxidation process (O2 beam or remote plasma) and on the thickness of the MnIr exchange layer. Overoxidation of the Al, or higher kinetic energy of the O2 ions, during oxidation, lead to faster thermal degradation of the TMR. Thinner MnIr retards thermal degradation. Rutherford backscattering shows a strong interdiffusion of Mn into the CoFe electrode above 300 °C, but no significant changes are detected at the CoFe/Al2O3/CoFe interfaces, even after annealing at 435 °C (the junction resistance remains high confirming barrier stability). The pinned layer moment decreases upon annealing as expected from Mn incorporation. Also, the strong TMR decrease may indicate polarization loss when Mn reaches the Al2O3/CoFe interface. At 410 °C, the TMR is still 5%, with the fast switching characteristics of the free layer unchanged.