Influence of annealing on the bias voltage dependence of tunneling magnetoresistance in MgO double-barrier magnetic tunnel junctions with CoFeB electrodes

Double-barrier magnetic tunnel junctions with two MgO barriers and three CoFeB layers exhibiting tunneling magnetoresistance (TMR) values of more than 100% were fabricated. The bias voltage dependence of the TMR ratio is highly asymmetric after annealing at low temperatures, indicating dissimilar CoFeBMgO interfaces. The TMR effect decays very slowly for positive bias and is only reduced to half of its maximum value at V12 =1.88 V when the junctions are processed at 200 °C. The largest output voltage, 0.62 V, is obtained after annealing at 300 °C, a temperature that combines high TMR ratios with a considerable asymmetric bias dependence.