CPP sensors with hard bias structures that shunt sense current towards a shield
View Patent ↗Read sensors and associated methods of fabrication are disclosed. A read sensor as disclosed herein includes a first shield, a sensor stack including an antiparallel (AP) free layer, and insulating material disposed on the sensor stack. A aperture is formed through the insulating material above the sensor stack so that a subsequently deposited second shield is electrically coupled to the sensor stack through the aperture. The width of the aperture controls the current density that is injected into the top of the sensor stack. Also, hard bias structures may be formed to be electrically coupled to the sensor stack. The electrical coupling of the sensor stack and the hard bias structures allows current to laterally spread out as it passes through the sensor stack, and hence, provides a non-uniform current density.
1. A read sensor comprising:
a first shield;
a sensor stack including an antiparallel (AP) free layer, a first surface of the sensor stack electrically coupled to a surface of the first shield;
insulating material disposed on an opposing second surface of the sensor stack; and
a second shield disposed on the insulating material,
wherein the insulating material has an aperture providing electrical coupling of the sensor stack and the second shield; and
hard bias structures electrically coupled to the sensor stack on opposing sides of the sensor stack, and electrically coupled to the surface of the first shield so as to direct sensing current away from the sensor stack and towards the first shield.
2. The read sensor of claim 1 wherein a width of the aperture is substantially smaller than a width of the AP free layer.
3. The read sensor of claim 1 , wherein:
the sensor stack comprises a reference layer; and
the hard bias structures are adapted to acquire sensing current from the sensor stack and to direct the sensing current to the surface of the first shield, reducing current density of sensing current at the reference layer in relation to current density of sensing current at the AP free layer.
4. The read sensor of claim 3 wherein the hard bias structures comprise:
a seed layer electrically coupled to the first shield; and
a hard bias layer electrically coupled to the seed layer.
5. The read sensor of claim 1 wherein
the sensor stack comprises:
an antiferromagnetic (AFM) layer;
a reference layer formed directly on the AFM layer;
a non-magnetic spacer layer formed directly on the reference layer;
the AP free layer formed directly on the non-magnetic spacer layer; and
a cap layer formed directly on the AP free layer, and connected to the second shield through the aperture, wherein a width of the cap layer is substantially smaller than a width of the AP free layer.
6. The read sensor of claim 5 wherein widths of the AFM layer, the reference layer, the non-magnetic spacer layer, and the AP free layer are substantially the same.
7. The read sensor of claim 5 wherein a resistance of the hard bias structures is less than or equal to a resistance of the AFM layer.
8. The read sensor of claim 5 wherein heights of the hard bias structures are substantially planar with a top surface of the AP free layer.