Tunnel magnetoresistance of 604% at 300 K by suppression of Ta diffusion in CoFeBMgOCoFeB pseudo-spin-valves annealed at high temperature

The authors observed tunnel magnetoresistance (TMR) ratio of 604% at 300 K in Ta Co20 Fe60 B20 MgO Co20 Fe60 B20 Ta pseudo-spin-valve magnetic tunnel junction annealed at 525 °C. To obtain high TMR ratio, it was found critical to anneal the structure at high temperature above 500 °C, while suppressing the Ta diffusion into CoFeB electrodes and in particular to the CoFeBMgO interface. X-ray diffraction measurement of MgO on Si O2 or Co20 Fe60 B20 shows that an improvement of MgO barrier quality, in terms of the degree of the (001) orientation and stress relaxation, takes place at annealing temperatures above 450 °C. The highest TMR ratio observed at 5 K was 1144%.