Microstructure and chemical analysis of the magentic tunnel junction

Abstract

To investigate the thermal breakdown mechanism of low resistance magnetic tunneling junctions(MTJ) with 100∼1000Ω㎛2,Ta/NiFe/Cu/NiFe/IrMn/CoFe/Al(6.6Åand 7.7Å)-oxide/CoFe/NiFe/Ta multi-layer was fabricated and heat treated at temperatures ranging from 200℃ to 500℃ under vacuum. Both Al(6.6Å)and Al(7.7Å)-oxide junctions showed the expected annealing behavior, exhibiting optimal MR ratio at 200∼300℃ after which MR ratio dropped rapidly. However, in spite of only 1Å difference in Al-deposited thickness, MR behavior for the Al(6.6Å)-oxide junction was lost at a much lower temperature compared to the Al(7.7Å)-oxide junction. Transmission Electrom Microscopy(TEM) of the MTJ's revealed that the Al(6.6Å)-oxide junction is likely to have suffered high current leakage due to the short-circuiting of the electrodes. We have also carried out Auger Electron Spectroscopy(ASE) and Rutherford Backscattering Spectroscopy(RBS) analysis to elucidate the extent of interdiffusion during thermal treatment in the bottom electrode of the Ta/NiFe/Cu/NiFe/IrMn/CoFe/Al-oxide/CoFe/NiFe/Ta junction and separately prepared Ta/NiFe/IrMn/CoFe multi-layerwith and without the Ta oxidation protection layer on top of CoFe. Specially, Mn diffusion to the insulationlayer, which is mainly believed to be the source of the MTJ failure, could be enhanced by the ptrsence of free oxygen at the insulator ibnterface.