Ta thickness-dependent perpendicular magnetic anisotropy features in Ta/CoFeB/MgO/W free layer stacks

• We observed changes in the diffusion behavior with regard to Ta seed layer thickness.
• It was observed that a thinner Ta seed layer induced more annealing-stable features.
• However, ultra-thin (0.75 nm) Ta shows unstable characteristics about the annealing process.
• It was possibly due to a rugged interface of the Ta layer by the island growth process.

We describe Ta underlayer thickness influence on thermal stability of perpendicular magnetic anisotropy in Ta/CoFeB/MgO/W stacks. It is believed that thermal stability based on Ta underlay is associated with thermally-activated Ta atom diffusion during annealing. The difference in Ta thickness-dependent diffusion behaviors was confirmed with X-ray photoelectron spectroscopy analysis. Along with a feasible Ta thickness model, our observations suggest that an appropriate seed layer choice is needed for high temperature annealing stability, a critical issue in the memory industry.