Dynamic conductance of Ni80Fe20/AlOx/Ni80Fe20 tunnel junctions

Abstract

The shape of the dynamic conductance versus voltage of NiFe/AlOx/NiFe tunnel junctions is correlated with the intensity and duration of oxidation. A shift of the conductance minimum towards positive voltage (up to 100 mV) indicates that the Al layer is only partially oxidized. In contrast, a shift of the conductance minimum towards negative voltage indicates oxidation of the bottom electrode and/or damage to the top surface of the barrier. Annealing of the junctions makes the tunnel barrier effectively thinner and taller, as implied by a fit to the parabolic conductance. These qualitative trends are observed for Al layers ranging from 10 to 35 Å in thickness. In conjunction with these effects, we observe the highest magnetoresistance (up to 26.6%) and the best bias dependence of the magnetoresistance when the conductance is symmetric.