Investigation of atomic layer deposition of magnesium oxide on a CoFeB layer for three-dimensional magnetic tunneling junctions

In this study, we comparatively investigated thermal- and plasma-enhanced atomic layer deposition (Th- and PE-ALD) of MgO on a CoFeB layer. MgCp ₂ (Bis(cyclopentadienyl)magnesium) was used as a Mg precursor and H₂O and O₂ plasma were employed as reactants for the Th- and PE-ALD process, respectively. Th- and PE-ALD MgO formed interlayer between MgO and CoFeB layer due to the oxidation of CoFeB by H₂O and O ₂ plasma during the Th- and PE-ALD process. While interlayer formation was observed to be less than 1 nm for Th-ALD MgO, the PE-ALD MgO process resulted in an approximately 5 nm thick, predominantly FeO_x oxidation of CoFeB. This was due to the high reactivity of the O radicals and the higher driving force of Fe for oxidation when compared with Co. Our results show that the Th-ALD MgO process has a better potential as a deposition technique to form tunnel barrier of magnetic tunneling junctions (MTJs).