Local transport properties of Co-Fe/Al-O/Co-Fe tunnel junctions with high thermal stability

Abstract In order to investigate the annealing temperature dependence of the tunnel magnetoresistance ratio (TMR) for ferromagnetic tunnel junction, the local transport properties were measured for Ta 5 nm/Cu 20 nm/Ta 5 nm/Ni76Fe24 2 nm/Cu 5 nm/Mn75Ir25 10 nm/Co71Fe29 4 nm/Al-O junction with metal Al thickness of 0.8 nm and oxidization time of 7 s. The current histogram statistically calculated from the electrical current image was in good accordance with the fitting result considering the Gaussian distribution of barrier height and Fowler-Nordheim conductance. At high annealing temperature of 340°C, where the TMR ratio of the corresponding MTJ had the maximum value of 44%, the average barrier height φ ave increased to 1.12 eV and the standard deviation σ φ decreased to 0.1 eV. The increase of TMR ratio after annealing was attributed to the increase of average barrier height and decrease of the barrier height variation. After further annealing at 360 °C, the standard deviation σ φ increased up to 0.2 eV and the TMR decreased to 10%.