Interlayer-assisted atomic layer deposition of MgO as a magnetic tunneling junction insulators

Highlights: • ALD Mg interlayer suppresses oxidation of sublayer against the oxidant in ALD MgO. • Oxidized ALD Mg interlayer has (200)-preferred orientation essential for MTJ barrier. • ALD MgO on Mg interlayer is grown with (200)-preferred orientation. • Insertion of ALD Mg interlayer is effective method to form ALD MgO barrier in MTJ. The growth behavior of MgO deposited on a Mg interlayer by plasma-enhanced atomic layer deposition (PE-ALD) was investigated to improve the MgO layer quality for magnetic tunneling junction (MTJ) applications. The Mg interlayer was inserted beneath the PE-ALD MgO film to prevent the oxidation of the bottom substrate layer. The chemical bonding status, elemental depth profile, and electron microscopy results for the PE-ALD Mg/MgO stack indicate that the Mg interlayer successfully blocked the oxidation of the substrate via its transformation to MgO. In addition, a change of the preferred orientation from (111) to (200) was observed in the X-ray diffraction pattern when the Mg interlayer was applied. This was attributed to the (200)-preferred orientation of the MgO formed through the oxidation of the Mg interlayer. The use of Mg interlayer is aim to prevent the degradation of the tunneling magneto-resistance properties by not only protecting the bottom layer (i.e., = CoFeB film in MTJs) from oxidation but also changing the preferred orientation from (111) to (200).