Annealing effect of magnetic tunnel junctions with one FeOx layer inserted at the Al2O3/CoFe interface

Spin tunnel junctions with one interposed Fe oxide layer between the Al2O3 barrier (t(Al) = 8-9 Angstrom) and the top CoFe pinned layer show large tunneling magnetoresistance (TMR) values (39%) after 40 min anneal at 380 degreesC. The as-deposited TMR is low and does not increase until 350 degreesC (< 10%), but then increases sharply, peaking at 380 degreesC. Further anneals at this temperature (380 degreesC), lead to TMR decrease to 20% with a diffusion constant of 34 min. At 360 degreesC, the diffusion constant is about 60 min. Samples without this inserted FeOx layer show TMR <5% after prolonged anneals at 380 degreesC. The different techniques utilized to probe the barrier and electrode changes during the annealing processes indicate that from the initial Fe-FeOx layer, part of the Fe diffuses into the CoFe electrode, and the remaining FeOx probably decomposes into a pure interfacial Fe layer at high temperature, responsible for the large TMR. The observed TMR values and barrier parameters, seem consistent with a standard CoFe/Al2O3/CoFe barrier formed at high temperature. (C) 2001 American Institute of Physics.