60% magnetoresistance at room temperature in Co–Fe/Al–O/Co–Fe tunnel junctions oxidized with Kr–O2 plasma

The influence of the mixed inert gas species for plasma oxidization process of a metallic Al layer on the tunnel magnetoresistance (TMR) was investigated for a magnetic tunnel junction (MTJ), Ta 50 A/Cu 200 A/Ta 200 A/Ni–Fe 50 A/Cu 50 A/Mn75Ir25 100 A/Co70Fe30 25 A/Al–O/Co70Fe30 25 A/Ni–Fe 100 A/Cu 200 A/Ta 50 A. Using Kr–O2 plasma, a 58.8% of TMR ratio was obtained at room temperature after annealing the junction at 300 °C, while the achieved TMR ratio of the MTJ fabricated with usual Ar–O2 plasma remained 48.6%. A faster oxidization rate of the Al layer by using Kr–O2 plasma is a possible cause to prevent the over oxidization of the Al layer, which depolarizes the surface of the underlaid ferromagnetic electrode, and to realize a large magnetoresistance.