Artificial antiferromagnetic tunnel junction sensors based on Co/Ru/Co sandwiches

A novel method is used for pinning the magnetization of the magnetically hard subsystem in micron-size magnetic tunnel junctions: the so-called artificial antiferromagnetic structure. The latter uses the strong antiparallel exchange coupling between two Co layers through a Ru spacer layer to ensure a high rigidity of the hard subsystem magnetization. The tunnel barriers were formed by sputter etching previously deposited Al layers in a rf Ar/O2 plasma. Wafers, 3 in. in diameter, were patterned into arrays of square junctions with lateral sizes of 20 and 50 μm. All junctions of a given size show resistances reproducible within several percents. The tunnel magnetoresistance (TMR) is found to be independent of the junction size and TMR ratios of 14%–16% are achieved at room temperature.