Annealing Effect on Low-Resistance Ferromagnetic Tunnel Junctions

Abstract

The stacking structure and fabrication process of tunnel junctions were investigated. The stacking structure of the tunnel junctions fabricated was Ta/(Cu,Pt)/Fe 20 Ni 80 /IrMn/Co 75 Fe 25 /Al-oxide/Co 75 Fe 25 /Fe 20 Ni 80 /Ta. When the Al thickness, oxidation time, and annealing temperature were 0.8 nm, 15 s (10 s), and 300°C (250°C), the tunnel magnetoresistance (TMR) ratio and the resistance obtained were 49% (31%) and 1.1 kΩµm 2 (230 Ωµm 2 ), respectively. In order to investigate the annealing temperature dependence of the TMR ratio, the local electrical properties were measured for a Ta/Fe 20 Ni 80 /Pt/Fe 20 Ni 80 /IrMn/Co 75 Fe 25 /Al-oxide multilayer. The current image became very homogeneous after annealing at around 300°C for 1 h. 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°C, the barrier height decreased and leakage currents were detected.