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 Angstrom/Al 9 Angstrom + plasma oxidation/Fe 25 Angstrom + plasma oxidation/Ti 30 Angstrom 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 Angstrom/Co80Fe20 30 Angstrom/Al 9 Angstrom + plasma oxidation/Fe (t(Fe)) + plasma oxidation/Co80Fe20 40 Angstrom/ Mn-76(Fe,Ir)(24) 250 Angstrom (t(Fe) = 0-25 Angstrom), up to annealing temperatures of 380degreesC (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. (C) 2003 Elsevier Science B.V. All rights reserved.