Thermal stability of the exchanged biased CoFe/IrMn electrode for the magnetic tunnel junction as a function of CoFe thickness

Pinned electrodes of the magnetic tunnel junction (MTJ) consisting of Ta/AlOx/CoFe(x)/IrMn/NiFe/Ta, where 35 Angstrom<x<87.5 Angstrom, were thermally annealed and analyzed using Auger electron spectroscopy and transmission electron microscopy in order to study the effects of the CoFe thickness on the interdiffusion of elements in the pinned electrode. Increasing CoFe thickness reduced the Mn migration out of the IrMn layer towards the tunnel barrier. An 87.5-Angstrom-thick CoFe layer completely blocked the Mn diffusion up to 350 degreesC with minimal reduction of the tunneling magnetoresistance (TMR) ratio when full junction was fabricated. Although other mechanisms could be responsible for the thermal degradation of the MTJ, the Mn diffusion appears to be related to the reduction of the TMR at 300 degreesC. Since the presence of Mn in the tunnel barrier as an impurity is detrimental to the junction performance, reduction of Mn migration towards the tunnel barrier by increasing the CoFe electrode should improve the postannealed performance of the junction. (C) 2002 American Institute of Physics.