Low resistance and high thermal stability of spin-dependent tunnel junctions with synthetic antiferromagnetic CoFe/Ru/CoFe pinned layers

In this work, submicron-size (down to 0.273 mu m(2)) spin-dependent tunnel junctions with resistance as low as similar to 30 Omega mu m(2) have been f abricated, where the tunneling barrier of AlOx was formed by in situ natura l oxidation. These junctions annealed at 250 degrees C for 5 h showed tunne ling magnetoresistance (TMR) of 14.3% and 25.8% for the pinned layers of Co Fe/RuRhMn and CoFe/PtMn, respectively, while the TMR is further increased t o 31.6% for a synthetic antiferromagnetic pinned layer of CoFe/Ru/CoFe/PtMn due to less interdiffusion at CoFe/Ru interface. The investigation has ind icated that the growth of ultrathin Al layer is very sensitive to the surfa ce roughness of bottom ferromagnetic electrode, and large surface roughness leads to small junction resistance. (C) 2000 American Institute of Physics . [S0003-6951(00)03117-X].