Texture development and magnetoresistance properties of CoFeB/MgO/CoFeB-based magnetic tunnel junction depending on capping layer crystallinity

Abstract

We investigated the effects of the crystallinity of the capping layer materials on the crystallization of amorphous top CoFeB (t-CoFeB) and the magnetoresistance properties and temperature sensitivities of the magnetic tunnel junctions (MTJs). When a (002)-textured hcp Ru capping layer was used, the amorphous t-CoFeB was crystallized to bcc-CoFe (110) during annealing. Using the CoFe (110)/Ru (002) texture relation is the best way to reduce the lattice mismatch down to 5.6%. However, when a polycrystalline TiAl (two phase: amorphous and fine polycrystalline) or amorphous ZrAl capping layer was used, the amorphous t-CoFeB was crystallized to bcc-CoFe (002) during annealing due to the MgO (001) template effect. The tunneling magneto resistance ratios of the annealed MTJs capped with Ru, TiAl, and ZrAl were 46.7%, 71.8%, and 72.7%, respectively, which depended on the texture and the epitaxiality of t-CoFeB/MgO (001). Consequently, the texture evolution of the amorphous t-CoFeB during annealing can be controlled by adjusting the crystallinity of the adjacent capping layer which, in turn, affects the magnetoresistance properties and temperature sensitivities of the MTJs.