Magnetic tunnel junction performance versus barrier thickness: NiFe/AlOx/NiFe junctions fabricated from a wedged Al layer

The resistance-area product (R*A) and the magnetoresistance (MR) of NiFe/Al Ox/NiFe spin-dependent tunnel junctions exhibit a strong dependence on the thickness of Al before oxidation. We obtain these data from wafers where we uniformly oxidize an Al layer with a wedged thickness profile, enabling us to reliably characterize the effect of Al thickness variations with subang strom precision. The R*A drops from 10(4) to 10(2) Omega mu m(2) as the Al thickness decreases from 9 to 4 Angstrom, respectively. The MR is highest ( 21%) for an Al thickness of 7 Angstrom, where the Al layer is fully oxidize d and the oxidation of the bottom NiFe electrode is minimal. (C) 2000 Ameri can Institute of Physics. [S0003-6951(00)01926-4].