Oxidation mechanism of the insulation layer in NiFe/Co/Al(Ta)-oxide /Co magnetic tunnel junctions

Ferromagnetic tunneling junctions with Al-oxide and Ta-oxide as the insulating layer were fabricated using metal mask and Inductively Coupled Plasma (ICP) sputtering system. To interpret growth mechanism of the insulating layer during plasma oxidation process, the microstructure of the oxide layers was investigated with cross-sectional TEM. TEM analysis showed Al-oxide had different microstructures depending on the thickness of the layer. At 13 إ, the Al-oxide layer was flat while the Al-oxide layer became progressively wavy with regular periodicity of 20 nm at increasing oxide thickness. Ta-oxide layer was partially oxidized under equal oxidizing conditions, but remained flat regardless of the thickness. Growth mechanism for the two different oxide layers is proposed in terms of oxidation kinetics and oxygen plasma.