Characterization of the magnetic tunnel junction with an AlOx barrier fabricated by using tilted plasma oxidation

Abstract

Tilted plasma oxidation was found to induce a gradual change in the extent of oxidation of an insulating layer, which consequently led to a gradual change in the tunneling magnetoresistance (TMR) and the specific junction resistance (RA) of the magnetic tunnel junction (MTJ). At a high annealing temperature of 280 degrees C, TMR ratio was observed to decrease due to a degradation of the interface between the barrier and the ferromagnetic layer when the tilted plasma oxidation was carried out, easily resulting in a micro-structural fluctuation at the interface. In order to modify the interface, we synthesized MTJs that contained a nano-oxide layer (NOL) on the top surface of the bottom pinned CoFe and a gradually over-oxidized AlOx layer. The properties of the TMR and the RA values were investigated after thermal annealing at T = 280 degrees C and were compared with those of normal MTJs without an NOL, showing different tendencies for the behavior of the TMR and the RA values. The oxygen molecules at the NOL layer are thought to be redistributed after thermal annealing, inducing a well-formed interface.