Influence of Ta antidiffusion barriers on the thermal stability of tunnel junctions

Previous work on spin-dependent tunnel junctions based on NiFe/CoFe/Al2O3/CoFe/MnIr reported structural thermal stability upon anneals up to 300 or 320 degrees C. Above 320 degrees C, the tunneling magnetoresistance (TMR) starts to decrease, and interdiffusion occurs at the MnIr/CoFe interface. MnIr diffuses into CoFe and reduces its magnetic moment. It was proposed that this mechanism could be partially responsible for the observed loss of TMR, due to the decrease in interface polarization. In this letter, tunnel junctions were prepared with a 2 Angstrom-thin Ta antidiffusion barrier inserted at the CoFe/MnIr interface, to stop MnIr diffusion into the pinned electrode. Structural and magnetization measurements indicate that the CoFe and MnIr layers remain unchanged with anneals up to 440 degrees C, and that the antidiffusion barrier is working. However, the TMR degradation above 320 degrees C was not avoided, which suggests that improving the thermal stability of the junctions will probably require changes in the barrier itself. (C) 2000 American Institute of Physics. [S0003-6951(00)04825-7].