Effect of Milling Depth of the Junction Pattern on Magnetic Properties and Yields in Magnetic Tunnel Junctions

We fabricated magnetic tunnel junctions of Ta (3 nm)/Ni81Fe19(2)/Fe50Mn50(10)/Co90Fe10(6)/Al(2.2)-oxide/Ni81Fe19(5)/Ta(5) with two different structures, the "just-etched junction" and the "over-etched junction", using a secondary ion mass spectroscopy apparatus during the milling process of a junction pattern: the milling was stopped at the Al-oxide barrier layer in the former case and at either the CoFe or the FeMn layers in the latter. For the "over-etched junction", both the demagnetization field of the pinned layer and magnetostatic coupling between the pinned and free layers increased with increasing milling depth of the junction pattern. The yield for a sampling of 48 junctions was much higher in the case of the "just-etched junction" than in that of the "over-etched junction".