Investigation on the structural property of the sputtered hcp-phase boron nitride tunnel barrier for spintronic applications

Recently, two-dimensional (2D) materials have attracted considerable interest for use in spintronic applications, especially hexagonal close-packed (hcp)-phase boron nitride (BN) as a tunnel barrier. In this paper, we experimentally investigated the structural properties of a sputtered hcp-BN thin film. By optimizing the experimental conditions, we obtained the stoichiometric BN thin film with a ratio of 1:1 of the Ar/N2 sputtering gas. Then the Co/BN/Co magnetic tunnel junction (MTJ) stacks were prepared to study the crystalline structure of the BN tunnel barrier and their epitaxial relationship. We found that the as-deposited BN tunnel barrier layer follows the texture of the bottom Co layer and forms a polycrystalline structure. After the high-temperature treatment of the MTJ stack, texturing of the BN tunnel barrier layer is observed, however, this annealing process makes the BN tunnel barrier noncontinuous and induces serious interdiffusion between layers. These results will open the door for development of spintronic devices based on MTJs with hcp-phase BN tunnel barrier and hcp-phase perpendicular magnetic anisotropy ferromagnetic layer.