Annealing effect on low-resistance ferromagnetic tunnel junctions

The stacking structure and fabrication process of tunnel junctions were investigated. The stacking structure of the tunnel junctions fabricated was Ta/(Cu,Pt)/Fe20Ni80/IrMn/Co75Fe25/Al-oxide/Co75Fe25/Fe20Ni80/Ta. When the Al thickness, oxidation rime, and annealing temperature were 0.8 nm, 15 s (10 s), and 300 degreesC (250 degreesC), the tunnel magnetoresistance (TMR) ratio and the resistance obtained were 49% (31%) and 1.1 k Ohm mum(2) (230 Ohm mum(2)), respectively. In order to investigate the annealing temperature dependence of the TMR ratio, the local electrical properties were measured for a Ta/Fe20Ni80/Pt/Fe20Ni80/IrMn/Co-75/Fe-25/Al-oxide multilayer. The current image became very homogeneous after annealing at around 300 degreesC for Ih. The increase of the TMR ratio of the junction after annealing can be well explained by taking into account both an increase of barrier height and a decrease of barrier height fluctuation. After further annealing at above 350 degreesC, the barrier height decreased and leakage currents were detected.