Magnetic tunnel junction sensor with AP-coupled free layer

摘要

A differential magnetic tunnel junction (MTJ) sensor is provided having a first MTJ stack, a second MTJ stack and a common AP-coupled free layer. The AP-coupled free layer comprises a ferromagnetic first sense layer and a ferromagnetic second sense layer with an antiferromagnetic coupling (APC) layer disposed between the two sense layers providing strong antiferromagnetic coupling. The thickness of the first sense layer is chosen to be different (greater or smaller) than the thickness of the second sense layer so that the AP-coupled free layer has a net magnetic moment oriented parallel to the ABS and free to rotate in the presence of a signal magnetic field. Antiferromagnetic (AFM) layers in the first and second MTJ stacks are set to pin the magnetizations of pinned layers in each stack perpendicular to the ABS and in the same direction with respect to one another. Having both AFM layers set in the same direction allows both AFM layers to be formed of the same antiferromagnetic material and both AFM layers may be set in the same process step during fabrication.