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

A novel method is used for pinning the magnetization of the magnetically ha rd subsystem in micron-size magnetic tunnel junctions: the so-called artifi cial antiferromagnetic structure. The latter uses the strong antiparallel e xchange coupling between two Co layers through a Ru spacer layer to ensure a high rigidity of the hard subsystem magnetization. The tunnel barriers we re formed by sputter etching previously deposited Al layers in a rf Ar/O-2 plasma. Wafers, 3 in. in diameter, were patterned into arrays of square jun ctions with lateral sizes of 20 and 50 mu m. All junctions of a given size show resistances reproducible within several percents. The tunnel magnetore sistance (TMR) is found to be independent of the junction size and TMR rati os of 14%-16% are achieved at room temperature. (C) 1999 American Institute of Physics. [S0021-8979(99)49508-8].