Thermal stability of magnetic tunnel junctions with new amorphous ZrAl alloy films as under and capping layers

This study investigated the effects of ZrAl under layers and capping layers on the thermal stability and structural stability behavior of MTJs with ZrAl-oxide barrier at elevated temperatures. The results were compared with conventional Ta-based MTJs with Al-oxide barrier. Magnetron sputtering was used to prepare an MTJ consisting of Si/SiO₂/ZrAl 2 nm(or Ta 5 nm)/NiFe 4 nm/IrMn 7.5 nm/CoFe 3 nm/ZrAl 1.6 nm(or Al)-oxidation/CoFe 3 nm/ZrAl 2 nm(or Ta 5 nm). AFM and TEM analysis showed that the ZrAl under layer improved interface uniformity, developed fine and dense grain structure, and retarded the development of texture of upper layers due to their noncrystallinity. Also, the ZrAl-oxide barrier is found to be not only a structurally stable, high-quality barrier, but is also thermally stable. TMR ratio variation were measured as a function of annealing temperatures.