Thermal stability of Ir-MnCo-Fe-BAl-OCo-Fe-B tunnel junctions

The thermal stability of magnetic tunnel junctions with structures of Ta (5) Cu (30) Ta (5) Ni79 Fe21 (5) Ir22 Mn78 (12) Co62 Fe20 B18 (4) Al (0.8) -oxide Co62 Fe20 B18 (4) Cu (30) Ta (5) (thicknesses unit in nanometers) has been investigated. The tunnel magnetoresistance (TMR) shows a large increase up to 54.4% after annealing at 265 °C due to the improved characteristic properties of the barrier and the interface between the barrier and the ferromagnetic electrodes. The TMR was observed to decrease drastically above the annealing temperature of 310 °C accompanied by a notable increase of junction resistance and coercivity of the free layer. The amorphous Co62 Fe20 B18 layers seem to behave as a barrier of diffusion, preventing the migration of Mn or Cu atoms into the interface between the barrier and the ferromagnetic layers. This may cause the drastic decrease of TMR due to the deterioration of the barrier and its interface with Co62 Fe20 B18 layers. The observed crystallization in the amorphous Co62 Fe20 B18 layers is considered to contribute to the increase in coercivity of the free layer.