Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-03-29
2001-02-06
Heinz, A. J. (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C324S252000, C365S158000
Reexamination Certificate
active
06185080
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a dual tunnel junction sensor with a single antiferromagnetic layer and, more particularly, to dual sensor components that share a single antiferromagnetic layer.
2. Description of the Related Art
A read head employing a read sensor may be combined with an inductive write head to form a combined magnetic head. In a magnetic disk drive, an air bearing surface (ABS) of the combined magnetic head is supported adjacent a rotating disk to write information on or read information from the disk. Information is written to the rotating disk by magnetic fields which fringe across a gap between the first and second pole pieces of the write head. In a read mode, the resistance of the read sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a current is conducted through the read sensor, resistance changes cause potential changes that are detected and processed as playback signals in processing circuitry.
One type of read sensor is a tunnel junction sensor. The details of tunnel junction have been described in a commonly assigned U.S. Pat. No. 5,650,958 to Gallagher et al., which is incorporated by reference herein. A typical tunnel junction sensor has two ferromagnetic layers (i.e., the pinned and free layers) separated by a thin barrier layer which relies upon the phenomenon of spin-polarized electron tunneling. The free and pinned layers, which may be NiFe or CoFe, are separated by a non-magnetic electrically insulating barrier layer that is thin enough that quantum mechanical tunneling occurs between the free and pinned layers. The pinned layer has a magnetic moment that is pinned in its orientation by exchange coupling with a pinning layer that is made of an antiferromagnetic material. The tunneling phenomenon is electron spin dependent, making the magnetic response of the tunnel junction sensor a function of the relative orientations and spin polarization of the conduction electrons between the free and pinned layers. Ideally, the magnetic moment orientation of the pinned layer should be pinned 90° to the magnetic moment orientation of the free layer, with the magnetic direction of the free layer being able to respond to external magnetic fields. It is possible to improve the sensitivity of a tunnel junction head structure by using multiple tunnel junction sensors. One problem with this scheme is that it requires multiple antiferromagnetic layers. Since the antiferromagnetic layers are relatively thick, using multiple antiferromagnetic layers increases the size of the read gap of the tunnel junction read head which equates to a reduced linear read bit density along a track of the rotating disk. Therefore, it may not be possible to insert more than one antiferromagnetic layer within the read gap for future ultra high areal density heads. There is a strong-felt need of increasing the sensitivity of the tunnel junction head structure with multiple tunnel junction sensors without significantly increasing the size of the read gap.
SUMMARY OF THE INVENTION
The present invention is directed to a dual tunnel junction read sensor having two tunnel junction sensors that share a single antiferromagnetic layer, thereby increasing the read sensitivity of the tunnel junction read head. In addition, by making the thickness of the ferromagnetic layers in the dual tunnel junction sensor about one half the thickness of ferromagnetic layers used in a single tunnel junction sensor, the dual tunnel junction sensor will not significantly increase the read gap of the tunnel junction read head. The dual tunnel junction sensor includes a first free layer and a first pinned layer separated by a first barrier layer, a second free layer and a second pinned layer separated by a second barrier layer; and an antiferromagnetic(AFM) pinning layer between the first and second pinned layers. The first and second pinned layers are adjacent to the AFM layer and their magnetic moments are pinned by exchange coupling in a first direction, typically normal to the air bearing surface (ABS). For the dual tunnel junction head to work efficiently, the orientation of the magnetic moment of the first and second free layers should be perpendicular to the orientation of the magnetic moment of the pinned layers.
Another embodiment of the present invention is an antiparallel (AP) dual tunnel junction sensor. This AP dual tunnel junction sensor is similar to the dual tunnel junction sensor described above but utilizes first and second AP pinned layers in place of the first and second pinned layers. Each AP pinned layer has a spacer made of ruthenium (Ru) between pinned film layers, preferably made of cobalt (Co). Because of the antiparallel features of the AP layers due to the Ru spacer layer, the magnetic moment of the one pinned film is antiparallel to magnetic moment of the other pinned film, which increases the effect of the sensor when the magnetic moment of the free layers rotate. In other embodiments, a combinations of pinned and AP pinned layers may be used.
A tunneling current I
T
flows through the dual tunnel junction head, perpendicular to the plane of the films or layers. The amount of current I
T
that flows through is dependent on the relative magnetic moment directions of the pinned and free layers and magnetic moments. Since the magnetic moments of the free and pinned layers are in-phase for both tunnel junctions, the resistance change due to tunneling is additive and, therefore, provides sensitivity enhancement. As the tunnel junction sensor is positioned over a rotating magnetic disk, external magnetic fields sensed from the rotating disk moves the direction of magnetic moments of the first and second free layers up or down, changing the resistance through the tunnel junction sensor. As the direction of the magnetic moments of the first and second free layers rotate up from the ABS (i.e., going toward the opposite direction of a downwardly directed magnetic moments of the first and second pinned layer), the amount of electron tunneling decreases (i.e., the resistance increases). As the direction of the magnetic moments of the first and second free layers rotate down toward the ABS (i.e., going toward the same direction as the magnetic moments of the first and second pinned layers) the amount of electron tunneling increases (i.e., the resistance decreases). As the tunnel current I
T
is conducted through the sensor, the increase and decrease of electron tunneling (i.e., increase and decrease in resistance) are manifested as potential changes. These potential changes are then processed as readback signals by the processing circuitry of the disk drive. Optionally, the directions of the magnetic moments of the free and pinned layers may be opposite to that described hereinabove.
Other objects and advantages of the present invention will become apparent upon reading the following description taken together with the accompanying drawings.
REFERENCES:
patent: 6108177 (2000-08-01), Gill
Gray Cary Ware & Freidenrich LLP
Heinz A. J.
International Business Machines - Corporation
Johnston Ervin F.
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