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

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 Ni80Fe20 70 A/Co80Fe20 30 A/Al 9 A+plasma oxidation/Fe (tFe)+plasma oxidation/Co80Fe20 40 A/Mn76(Fe,Ir)24 250 A (tFe=0-25 A), up to annealing temperatures of 380 deg. C (TMR=39%), is related to the oxygen diffusion from the inserted Fe+FeOy layer to the AlOx barrier. This may yield metallic Fe at the interface with the top-pinned CoFe electrode, and some ferrimagnetic, half-metallic Fe3O4 with strong polarization at the top of the AlOx barrier, enhancing TMR. Oxygen diffusion from the initial FeOy 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