Magnetic sensor having hard bias structure for optimized hard bias field and hard bias coercivity
View Patent ↗A magnetic read sensor having a hard bias structure that extends beyond the back edge of the sensor stack by a controlled, distance that is chosen to maximize both hard bias field and hard bias magnetic coercivity and anisotropy. The hard bias structure has a back edge that is well defined and that has a square corner at its innermost end adjacent to the sensor stack. The magnetic sensor can be constructed by a process that includes a separate making an milling process that is dedicated to defining the back edge of the hard bias structure.
1. A magnetic read sensor, comprising:
a sensor stack having a front edge disposed at an air bearing surface and a back edge opposite the air bearing surface, the distance between the front edge and the back edge defining a sensor stack stripe height; and
a hard bias structure formed adjacent to the sensor stack and having a back edge opposite the air bearing surface, the distance between the air bearing surface and the back edge of the hard bias structure defining a hard bias length, the hard bias length being greater than the sensor stripe height; and
a bi-layer insulation structure formed behind the back edge of the sensor stack, the bi-layer insulation structure including a layer of material that is resistant to ion milling and a layer of material that has an ion milling rate that is about the same as an ion milling rate of the sensor stack.
2. The magnetic read sensor as in claim 1 wherein the hard bias structure has a straight back edge and a straight inner edge adjacent to the sensor stack.
3. The magnetic read sensor as in claim 1 wherein the back edge of the hard bias structure and an inner edge of the hard bias structure meet at a junction that is substantially square.
4. The magnetic read sensor as in claim 1 wherein the hard bias structure extends beyond the back edge of the sensor stack by a distance that is greater than 0 and no greater than 250 nm.
5. The magnetic read sensor as in claim 1 wherein the hard bias structure is separated from the sensor stack by a thin, non-magnetic, electrically insulating layer.
6. The magnetic read sensor as in claim 1 wherein the hard bias structure and the sensor stack is formed over a magnetic shield, and wherein the hard bias structure is separated from the sensor stack and from the magnetic shield by a first thin insulation layer, and further comprising a second insulation layer disposed between the hard bias structure and the magnetic shield only in regions where the hard bias structure extends beyond the back edge of the sensor stack.
7. The magnetic read sensor as in claim 6 wherein the first insulation layer comprises alumina.
8. The magnetic read sensor as in claim 6 wherein the second insulation layer comprises alumina.
9. The magnetic read sensor as in claim 6 wherein the first and second insulation layers both comprise alumina.
10. The magnetic read sensor as in claim 6 wherein both the first and second insulation layers are disposed between the hard bias structure and the magnetic shield in regions where the hard bias structure extends beyond the sensor stack and the second insulation layer is between the first insulation layer and the magnetic shield.