Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2002-05-13
2004-05-11
Letscher, George J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06735061
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic read head sensor with a reactively sputtered pinning layer structure and more particularly to a pinning layer structure that has a nickel oxide (NiO) first film and an iron oxide (Fe
2
O
3
) or (Fe
3
O
4
) second film that are reactively sputtered for increasing an exchange coupling field between the pinning layer structure and a pinned layer structure.
2. Description of the Related Art
A spin valve sensor is employed by a read head for sensing magnetic signal fields from a moving magnetic medium, such as a rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning a magnetic moment of the pinned layer 90° to an air bearing surface (ABS) which is an exposed surface of the sensor that faces the magnetic disk. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. A magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or bias point position in response to positive and negative magnetic field signals from a rotating magnetic disk. The quiescent position, which is typically parallel to the ABS, is the position of the magnetic moment of the free layer with the sense current conducted through the sensor in the absence of signal fields.
The thickness of the spacer layer is chosen so that shunting of the sense current and a magnetic coupling between the free and pinned layers are minimized. This thickness is typically less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons are scattered at the interfaces of the spacer layer with the pinned and free layers. When the magnetic moments of the pinned and free layers are parallel with respect to one another scattering is minimal and when their magnetic moments are antiparallel scattering is maximized. Changes in scattering changes the resistance of the spin valve sensor as a function of cos &thgr;, where &thgr; is the angle between the magnetic moments of the pinned and free layers. The sensitivity of the sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in the resistance of the sensor as the magnetic moment of the free layer rotates from a position parallel to the magnetic moment of the pinned layer to an antiparallel position thereto and R is the resistance of the sensor when the magnetic moments are parallel.
Because of the interfacing of the pinning and pinned layers the pinned layer is exchange coupled to the pinning layer. A unidirectional orientation of the magnetic spins of the pinning layer pins the magnetic moment of the pinned layer in the same direction. The orientation of the magnetic spins of the pinning layer are set by applying heat at or above a blocking temperature of the material of the pinning layer in the presence of a field that is directed in the desired pinned direction. The pinned direction is typically perpendicular to the ABS. The blocking temperature is the temperature at which all of the magnetic spins of the pinning layer are free to rotate in response to an applied field. During the setting, the magnetic moment of the pinned layer is oriented parallel to the applied field and the magnetic spins of the pinning layer follow this orientation. When the heat is reduced below the blocking temperature the magnetic spins of the pinning layer pin the orientation of the magnetic moment of the pinned layer. The pinning function is effective as long as the temperature remains substantially below the blocking temperature.
Nickel oxide (NiO) is a desirable material for the aforementioned pinning layer structure. Since nickel oxide (NiO) is insulating it can function as a portion of the first read gap layer thereby enhancing the insulating properties of the first read gap of the read head. Unfortunately, nickel oxide (NiO) has a relatively low blocking temperature which is about 220° C. In a magnetic disk drive the operating temperature may exceed 150° C. A portion of the magnetic spins of the nickel oxide NiO) pinning layer rotate below the blocking temperature because of a blocking temperature distribution below the blocking temperature where portions of the magnetic spins of the pinning layer commence to rotate. Accordingly, a portion of the magnetic spins of the nickel oxide (NiO) pinning layer can rotate at operating temperatures in the presence of a magnetic field, such as a signal field from the rotating magnetic disk, the write field from the write head or an unwanted electric static discharge (ESD) caused by contact with a statically charged object. The problem is exacerbated when the slider contacts an asperity on the magnetic disk which can raise the temperature above the disk drive operating temperature.
In the presence of some magnetic fields the magnetic moment of the pinned layer can be rotated antiparallel to the pinned direction. The question then is whether the magnetic moment of the pinned layer will return to the pinned direction when the magnetic field is relaxed. This depends upon the strength of the exchange coupling field and the coercivity of the pinned layer. If the coercivity of the pinned layer exceeds the exchange coupling field, the exchange coupling field will not be strong enough to bring the magnetic moment of the pinned layer back to the original pinned direction. Until the magnetic spins of the pinning layer are reset the read head is rendered inoperative. Accordingly, there is a strong felt need to increase the exchange coupling field between a nickel oxide (NiO) pinning layer and a pinned layer so that the sensor has improved thermal stability.
SUMMARY OF THE INVENTION
The present invention includes a pinning layer structure that has a reactively sputtered nickel oxide (NiO) first film that underlies a reactively sputtered iron oxide (Fe
2
O
3
) or (Fe
3
O
4
) second film. The iron oxide second film interfaces a pinned layer so that the pinned layer is exchange coupled to the pinning layer. In a preferred embodiment the pinned layer includes a cobalt (Co) or cobalt iron (CoFe) layer sputter deposited on the iron oxide layer. With a pinned layer structure comprising a nickel iron (NiFe) layer and a cobalt iron (CoFe) layer on the aforementioned pinning layer structure the magnetoresistive coefficient dr/R was 5.07% after setting the magnetic moment of the pinned layer structure perpendicular to the ABS and before annealing, and was 4.72% after annealing at a temperature of 230° C. for 11 hours in the presence of a field of 500 Oe. With a nickel iron (NiFe) pinned layer on a typical nickel oxide (NiO) pinning layer the magnetoresistance coefficient dr/R was 5.28% after setting and before annealing and was 4.50% after annealing. Accordingly, the magnetoresistive coefficient dr/R of the read head with the improved pinning layer structure increased from 4.50% to 4.72% after annealing. This is due to the improvement of the exchange coupling field between the pinned layer and the present pinning layer structure. In still a further preferred embodiment the pinned layer is cobalt (Co) or cobalt iron (CoFe). When the pinned layer was a single cobalt iron (CoFe) layer on the present pinning layer structure the initial magnetoresistive coefficient dr/R was 5.54% and after annealing the magnetoresistive coefficient dr/R was 5.42%. This embodiment demonstrates a significant improvement in the magnetoresistive coefficient dr/R.
The improved pinning layer structure is formed in a sputtering chamber that has an ion beam gun for directing a beam of an ionized noble gas, such as argon (Ar), on a target. In a preferred embodiment of the method of making, the first target is nickel (Ni) and the second target is iron (Fe). Oxygen is provided in the chamber either through an ion gun or an inlet. When
Hitachi Global Storage Technologies - Netherlands B.V.
Johnston Ervin F.
Letscher George J.
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