CPP Sensor With In-Stack Longitudinal Biasing of Free Layer Using Self-Stabilized LBL2 Extending Beyond Sensing Region
Original Publication Date: 2003-Feb-28
Included in the Prior Art Database: 2003-Jun-21
Disclosed is an alternative in-stack longitudinal bias scheme for forming a resetable in-stack longitudinal bias stack using synthetic anti-parallel (AP) coupling through a thin conducting layer such as Ru and the shape anisotropy of ferromagnetic materials. Prior art in-stack bias schemes uses a second AFM and a ferromagnetic longitudinal bias layer (LBL), resulting in about 250 Angstrom of additional sensor thickness. Prior art also requires a complicated thermal annealing process to set the two AFM layers orthogonally. Also weaker magnitude of the AFM-FM exchange coupling in prior art (compared to the stronger antiferromagnetic exchange coupling across Ru in the present invention) results in a smaller range of LBL thicknesses possible. In our invention, the sense layer is stabilized by a LBL layer through magnetostatic interactions, as in the prior art. Here, however, the LBL layer is pinned through strong AP coupling through the Ru spacer to the LBL2 layer. The layer closest to the sensor free layer is patterned with the sensor stack to form a longitudinal bias layer. The other layer in the bilayer is formed into a large aspect-ratio shape which is self-stabilized due to shape anisotropy, and also stabilizes the longitudinal bias layer through antiferromagnetic exchange coupling across a thin metallic layer. The resulting in-stack biased sensor can be advantageously fabricated by this method with a much smaller shield-to-shield gap spacing, and be easily magnetically reset without the need for a high-temperature annealing step. Micromagnetic calculations have been performed which demonstrate the magnetic performance of the resulting sensor structure.