Study of the oxygen migration versus anneal in Co/AlOx/Fe–FeOy/Ti tunnel junctions

Abstract The thermal stability of junctions of the type Co 40 A/Al 9 A+plasma oxidation/Fe 25 A+plasma oxidation/Ti 30 A has been studied by X-ray photoelectron spectroscopy. Results suggest that the enhancement of the thermal stability of the room-temperature tunneling magnetoresistance (TMR) of magnetic tunnel junctions (MTJs) with the main structure of Ni 80 Fe 20 70 A/Co 80 Fe 20 30 A/Al 9 A+plasma oxidation/Fe ( t Fe )+plasma oxidation/Co 80 Fe 20 40 A/Mn 76 (Fe,Ir) 24 250 A ( t Fe =0–25 A), up to annealing temperatures of 380°C (TMR=39%), is related to the oxygen diffusion from the inserted Fe+FeO y layer to the AlO x barrier. This may yield metallic Fe at the interface with the top-pinned CoFe electrode, and some ferrimagnetic, half-metallic Fe 3 O 4 with strong polarization at the top of the AlO x barrier, enhancing TMR. Oxygen diffusion from the initial FeO y layer to the barrier causes the over-oxidation of the latter, further enhancing barrier quality and TMR. This is relevant for the application of MTJs to magnetic random access memories.