Surface flattening processes of metal layer and their effect on transport properties of magnetic tunnel junctions with Al-N barrier

In order to form ultrathin insulating layer in magnetic tunnel junctions (MTJs), two surface flatting processes of metal films are investigated. Oxygen-additive sputter-deposition process was applied to the bottom Cu electrode and the Al layer to be nitrided. Dry-etching process was applied for the surface treatment of lower Co-Fe layer. As a result, the surface roughness of stacked ultrathin Al layer to be nitrided is reduced from 3.2 angstrom to 1.7 angstrom, and the tunnel magnetoresistance (TMR) ratio of the MTJs increases from 1% to 26% while maintaining resistance-area product (R X A) less than 5 10(2) Omega mu m(2) in the Co-Fe/Al(6A)-N/Co-Fe MTJs. We conclude that the decrease of the surface roughness of Al layer is one of the key factors to realize high performance MTJs with low R X A and high TMR ratio. (c) 2005 American Institute of Physics.