Interdiffusion in exchange biased NiFe/IrMn/CoFe electrode in magnetic tunnel junctions.

Abstract

Auger Electron Spectroscopy(AES) and Rutheford Backscattering Spectroscopy(RBS) analysis were carried out to elucidate the extent of interdiffusion during thermal treatment of the pinned electrode(Ta/NiFe/IrMn/CoFe)of the magnetic tunnel junction multi-layer. From concentration profile results from RBS and AES, a significant amount of Mn-CoFe interdiffusion was observed when the sample was annealed at 200-400deg. under vacuum. The multi-layer we com;letely intermixed at 400deg., losing the exchange bias between IrMn and CoFe layers. It was showed that the migration of Mn was enhanced by the preferential oxidation of Mn of the Surface. When Ta oxidation protection was deposited on top of the electrode, the Mn diffusion wasminimized up to 300deg. Our experiment suggests that the Mn diffusion to the insulation layer could be enhanced by the presence of the free oxygen radicals in the insulation layer remanining from the plasma oxidation fo the Al layer in magnetic tunneling junctions.