On the role of Ta cap in the recrystallization process of CoFeB layers

Abstract

To understand the role of Ta capping on the tunneling magnetoresistance of CoFeB/MgO/CoFeB tunnel junctions, we performed an atom probe study on model CoFeB/Ta junctions. In as-prepared state, CoFeB exhibits chemically and structurally homogeneous amorphous structure. The nanoanalysis demonstrates that B segregation to the Ta cap enforces crystallization to start at the opposite interface towards the MgO barrier and so warrants the correct orientation relation. Carrying out isothermal and isochronal heat treatments, the diffusion coefficient of Boron in amorphous CoFeB could be determined.