Study of boron diffusion in MgO in CoFeB∣MgO film stacks using parallel electron energy loss spectroscopy

Boron diffusion in MgO has been investigated in annealed film stacks of sputtered CoFeB∣MgO using transmission electron microscopy and parallel electron energy loss spectroscopy. The analyses show significant B movement when the films are annealed, with the formation of B O x complexes. Characteristic diffusion lengths have been estimated in films annealed at the commonly employed temperature range of 300 - 400 ° C for the fabrication of magnetic tunnel junctions. An activation energy of 1.3 eV ( ± 0.4 eV ) has been extracted from these data that represent B diffusion in MgO through vacancies and defect states mediated by the formation of B O x complexes.