Abstract:
In most of the MRAM research, the spin-torque structure consists of two CoFeB layers separated by a very thin MgO insulator layer [1]. Upon annealing, one important issue is that B diffuses to the insulating layer and causes a magnetic dead layer, which degrades the performance of MRAM [2-4]. Thus, to avoid this issue, an additional capping layer, such as Ta or Zr acted as B absorber can be put next to the CoFeB layers. This experiment explores the influence of B diffusion behavior by changing the annealing time, capping layer thickness, and capping materials.
The X-ray reflectivity shows that the overall thickness of the film of the Ta (Zr)/CoFeB interface is significantly reduced, and the roughness becomes smoother. The density of CoFeB (CoFe) and capping layer are both increased. The XPS depth profile also provided the information that B has transported to the Ta (Zr) capping layer rather than moving to the MgO layer after the annealing process. It has confirmed the capping layer is sufficient method. To further enhance the signal of B atoms by taking the advantage of extra-large neutron absorption cross section, polarized neutron reflectivity (PNR), provides the advantage of understanding the magnetic contribution with the B diffusion after annealing. with above result, the experiment provides a sufficient way to understand the relationship between the B diffusion and change of magnetic moment with capping layers during annealing process.