Fabrication of high-magnetoresistance tunnel junctions using Co75Fe25 ferromagnetic electrodes

Temperature dependence of tunnel magnetoresistance (TMR) ratio, resistance, and coercivity from 4.2 K to room temperature and applied voltage dependence of the TMR ratio and resistance at room temperature for a tunnel junction, Ta (5 nm)/Ni79Fe21 (3 nm)/Cu (20 nm)/Ni79Fe21 (3 nm)/Ir22Mn78 (10 nm)/Co75Fe25 (4 nm)/Al (0.8 nm)-oxide/Co75Fe25 (4 nm)/Ni79Fe21 (20 nm)/Ta(5 nm), were investigated. TMR ratio, effective barrier height and width, and breakdown voltage of the junction can be remarkably enhanced after annealing at 300 degrees C for an hour. High TMR ratio of 49.7% at room temperature and 69.1% at 4.2 K were observed. The value of spin polarization of Co75Fe25, P = 50.7%, deduced from the TMR ratio at 4.2 K was corresponding well to the experimental data measured at 0.2 K in a spin polarized tunneling experiment using a superconductor/insulator/ferromagnet tunneling junction. (C) 2000 American Institute of Physics. [S0003-6951(00)05028-2].