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 (tAl=8–9 Å) and the top CoFe pinned layer show large tunneling magnetoresistance (TMR) values (39%) after 40 min anneal at 380 °C. The as-deposited TMR is low and does not increase until 350 °C (<10%), but then increases sharply, peaking at 380°C. Further anneals at this temperature (380 °C), lead to TMR decrease to 20% with a diffusion constant of 34 min. At 360 °C, the diffusion constant is about 60 min. Samples without this inserted FeOx layer show TMR<5% after prolonged anneals at 380 °C. 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.