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 BOx 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 1.3eV (±0.4eV) has been extracted from these data that represent B diffusion in MgO through vacancies and defect states mediated by the formation of BOx complexes.