Failure of exchange-biased low resistance magnetic tunneling junctions upon thermal treatment

Abstract

Transmission electron microscopy (TEM) and Rutherford backscattering spectroscopy (RBS) were used to characterize low resistance (100-1000 Omega mum(2)) tunneling junctions consisting of Ta/NiFe/Cu/NiFe/IrMn/CoFe/Al (6.6 and 7.7 Angstrom)-oxide/CoFe/NiFe/Ta multilayers after annealing at temperatures ranging from 250 to 500 degreesC. The Al (7.7 Angstrom) junction showed continual improvement in the magnetoresistance (MR) ratio when annealed up to 300 degreesC while the MR ratio of the Al (6.6 Angstrom) junction dropped sharply above 250 degreesC in spite of the only 1 A difference in the deposited thickness of aluminum metal prior to plasma oxidation. TEM measurement provided evidence that the annealing process improves, in general, structural uniformity in the insulation layer, but thermal treatment can also degrade junction performance at a relatively low temperature due to current leakage through the electrodes. Current leakage can be problematic for a junction whose insulation barrier may be too thin (less than similar to 10 Angstrom). Both RBS and TEM analyses indicated that the maximum annealing temperature of exchange biased junctions lies between 400 and 500 degreesC above which the multilayer structure in the pinned electrode is destroyed by interdiffusion. (C) 2002 American Institute of Physics.