Boron diffusion in magnetic tunnel junctions with MgO (001) barriers and CoFeB electrodes

Abstract

Boron diffusion out of the CoFeB layers in model systems with thick CoFeB and MgO layers grown by radiofrequency sputtering or electron-beam evaporation and in MgO-based magnetic tunnel junctions (MTJs) is probed after annealing by x-ray photoemission spectroscopy (XPS) and electron energy loss spectroscopy. Successive interfaces are exposed by ion milling the stacks, layer by layer, in the XPS system. Despite the presence of thick CoFeB and a high annealing temperature of 400 °C, we found no boron in the MgO or at the MgO/CoFe interfaces. Similar results are also obtained in the MTJs.