Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
1999-03-29
2001-01-30
Ometz, David L. (Department: 2754)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
Reexamination Certificate
active
06181537
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tunnel junction structure and, more particularly, to a tunnel junction structure in which the tunnel junction layer is embedded in amorphous ferromagnetic layers.
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 spacer layer which relies upon the phenomenon of spin-polarized electron tunneling. The free and pinned layers, which may be NiFe or CoFe, are crystalline in structure and are separated by an electrically insulating spacer layer that is thin enough that quantum mechanical tunneling occurs between the free and pinned layers. 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. 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. Large ferromagnetic coupling (>20 Oe) occurs between the pinned and free layers. This large coupling causes improper magnetic bias for the free ferromagnetic layer which results in a distorted readback signal. One reason for this ferromagnetic coupling between the pinned and free layers is interfacial roughness. This roughness results from thin film crystalline texture as a result of epitaxy type growth of these films.
There is a strong felt need for a tunnel junction structure that reduces the ferromagnetic coupling between the pinned and free ferromagnetic layers, which thereby reduces distortion in the read back signal.
SUMMARY OF THE INVENTION
The present invention is directed toward a tunnel junction structure in which the tunnel junction barrier layer is embedded in amorphous ferromagnetic layers. Major reasons of ferromagnetic coupling between ferromagnetic layers is interfacial roughness due to the crystallinity of the material. To avoid this problem, the present invention discloses the use of amorphous ferromagnetic layers on each side of the tunnel junction layer. These amorphous ferromagnetic layers suppress any epitaxial growth between them as well as have a high saturation flux density. This will reduce the magnetic bias of the free ferromagnetic layer, thereby reducing distortion in the read back signal.
The tunnel junction sensor includes an antiferromagnetic (AFM) pinning layer, a crystalline pinned layer, an amorphous pinned layer, a tunnel junction barrier layer, an amorphous free layer and a crystalline free layer (optional). The tunnel junction barrier layer being embedded between the amorphous pinned layer and the amorphous free layer. For the tunnel junction head to work efficiently, the orientation of the magnetic moment of the crystalline and amorphous free layers should be perpendicular to the orientation of the magnetic moment of the crystalline and amorphous pinned layers.
A tunneling current I
T
flows through the 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. 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 free layers up or down, changing the resistance through the tunnel junction sensor. 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: 5446613 (1995-08-01), Rottmayer
patent: 5668688 (1997-09-01), Dykes et al.
patent: 5898548 (1999-04-01), Dill et al.
patent: 5966012 (1999-10-01), Parkin
patent: 5986858 (1999-11-01), Sato et al.
patent: 6023395 (2000-02-01), Dill et al.
patent: 6078484 (2000-06-01), Sakakima
patent: 9-251618 (1997-09-01), None
patent: 10-162326 (1998-06-01), None
patent: 11-316919 (1999-11-01), None
Gray Cary Ware & Freidenrich LLP
International Business Machines - Corporation
Johnston Ervin F.
Ometz David L.
LandOfFree
Tunnel junction structure with junction layer embedded in... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Tunnel junction structure with junction layer embedded in..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Tunnel junction structure with junction layer embedded in... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2557233