Spin-tunnel-junction thermal stability and interface interdiffusion above 300 °C

Spin tunnel junctions (CoFe/Al2O3/CoFe/MnIr) were fabricated with tunneling magnetoresistance (TMR) of 39%-41% after anneal at 300 degrees C, decreasing to 4%-6% after anneal at 410 degrees C. Junction resistance decreases from (0.8-1.6) to (0.5-0.8) M Omega mu m(2) during anneal. The pinned-layer moment decreases by 44% after anneal at 435 degrees C, but the free-layer moment does not change. The current-voltage characteristics change significantly and become asymmetric above 300 degrees C. Rutherford backscattering analysis (RBS) shows that above 300 degrees C, strong interdiffusion starts at the CoFe/MnIr interface with Mn moving into CoFe, causing the electrode moment to decrease. Mn eventually reaches the Al2O3/CoFe interface contributing to the TMR decrease. RBS analysis of a separate CoFe/Al2O3/CoFe structure shows only minor structural changes at the CoFe/Al2O3 interfaces after anneal at 435 degrees C, possibly leading to a second mechanism for the loss of interface polarization and TMR. (C) 2000 American Institute of Physics. [S0003-6951(00)01605-3].