Mn diffusion in plasma oxidized AlOx insulation layer in the magnetic tunnel junctions.

Abstract

The pinned electrode of the exchange biased magnetic tunneling junction(MTJ), consisting of Ta/NiFe/IrMn/CoFe/(Ta) layer was deposited and annealed at various temperatures under vacuum to elucidate the thermal decay of ther MTJ due to the interdiffusion within the pinned electrode. When there is no oxidation-preventing layer, in spite of the vacuum enviroment, a significant amount of Mn-Co inter-diffusion at 300℃was observed from the compositional analysis using Auger Electron Spectroscopy(AES) and Rutherford Backscattering Spectroscopy(RBS). Also observed was the Mn-oxide at the surgace and the loss of the exchange bias field in conjunction layer was deposited on top of the electrode, a minimal amount of Mn-Co interdiffusion was detected up to 400℃. Our results suggest that the Mn-Co interdiffusion is greatly promoted through the surface oxidation of the pinned electrode. Hence, the residual oxygen radical in the Al-oxide insulation layer in MTJ, of present, could accelerate the Mn-Co interdiffusion. In fact, when a multi-layer structure, Ta/NiFe/IrMn/CoFe/Al-oxide/Ta wasannealed at 300℃, the AES depth profile showed a considerable degree of Mn diffusion compared to the electrede with the Ta protedtion layer, which confirms that the presence of oxygen can enhance the Mn-Co interdiffusion due to the oxygen affinity of Mn. From the experiment, it can be concluded that the oxidation condition of the insulation layer will affect the Mn-Co interdiffusion and the thermal response of the MTJ when annealed above 300℃.