Dynamic magnetic information storage or retrieval – Head – Magnetoresistive reproducing head
Reexamination Certificate
2000-07-12
2003-01-07
Evans, Jefferson (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Magnetoresistive reproducing head
C360S324120
Reexamination Certificate
active
06504689
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a tunnel junction read head with a flux guide coupled to and magnetically extending a recessed free layer to an air bearing surface and, more particularly, to such a flux guide which permits both a free layer and a pinned layer to be recessed from the ABS so as to prevent shorting therebetween by conductive material which is smeared across the ABS by lapping during construction of the read head.
2. Description of the Related Art
The heart of a computer is a magnetic disk drive which includes a rotating magnetic disk, a slider that has read and write heads, a suspension arm above the rotating disk and an actuator arm that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent an air bearing surface (ABS) of the slider causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic signal fields from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
An exemplary high performance read head employs a tunnel junction sensor for sensing the magnetic signal fields from the rotating magnetic disk. The sensor includes an insulative tunneling or barrier layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning the magnetic moment of the pinned layer 90° to an air bearing surface (ABS) wherein the ABS is an exposed surface of the sensor that faces the rotating disk. The tunnel junction sensor is located between ferromagnetic first and second shield layers. First and second leads, which may be the first and second shield layers, are connected to the tunnel junction sensor for conducting a tunneling current therethrough. The tunneling current is conducted perpendicular to the major film planes (CPP) of the sensor as contrasted to a spin valve sensor where the sense current is conducted parallel to the major film planes (CIP) of the spin valve sensor. A magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or zero bias point position in response to positive and negative magnetic signal fields from the rotating magnetic disk. The quiescent position of the magnetic moment of the free layer, which is preferably parallel to the ABS, is when the tunneling current is conducted through the sensor without magnetic field signals from the rotating magnetic disk.
When the magnetic moments of the pinned and free layers are parallel with respect to one another the resistance of the tunnel junction sensor to the tunneling current (I
T
) is at a minimum and when their magnetic moments are antiparallel the resistance of the tunnel junction sensor to the tunneling current (I
T
) is at a maximum. Changes in resistance of the tunnel junction sensor is a function of cos &thgr;, where &thgr; is the angle between the magnetic moments of the pinned and free layers. When the tunneling current (I
T
) is conducted through the tunnel junction sensor resistance changes, due to signal fields from the rotating magnetic disk, cause potential changes that are detected and processed as playback signals. The sensitivity of the tunnel junction sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in resistance of the tunnel junction sensor from minimum resistance (magnetic moments of free and pinned layers parallel) to maximum resistance (magnetic moments of the free and pinned layers antiparallel) and R is the resistance of the tunnel junction sensor at minimum resistance. The dr/R of a tunnel junction sensor can be on the order of 40% as compared to 10% for a spin valve sensor.
Magnetic head assemblies, wherein each magnetic head assembly includes a read head and a write head combination, are constructed in rows and columns on a wafer. After completion at the wafer level, the wafer is diced into rows of magnetic head assemblies and each row is lapped by a grinding process to lap the row to a predetermined air bearing surface (ABS). In a typical tunnel junction read head all of the layers are exposed at the ABS, namely first edges of each of the first shield layer, the seed layer, the free layer, the barrier layer, the pinned layer, the pinning layer and the second shield layer. The second edges of these layers are recessed in the head. The barrier layer is a very thin layer, on the order of 20 Å, which places the free and pinned layers very close to one another at the ABS. When a row of magnetic head assemblies is lapped there is a high risk of magnetic material from the free and pinned layers being smeared across the ABS to cause a short therebetween. Accordingly, there is a strong-felt need to construct magnetic head assemblies with tunnel junction heads without the risk of shorting between the free and pinned layers at the ABS due to lapping.
SUMMARY OF THE INVENTION
The present invention overcomes the problem of shorting between the free and pinned layers due to smeared conductive material between these layers at the ABS by recessing both of the free and pinned layers into the head from the ABS with first edges close to the ABS and second edges further recessed into the head. In order to conduct the signal fields from the ABS to the free layer a flux guide is magnetically coupled to the free layer and extends to the ABS. Accordingly, a first edge of the flux guide is exposed at the ABS and preferably a second edge of the flux guide abuts the first edge of the free layer. In order to achieve the abutting junction between the flux guide and the free layer, first and second spaced apart insulation layers may be provided with the first insulation layer extending to the ABS and the second insulation layer extending into the head. The free layer is located in the space between the first and second insulation layers and overlaps a portion of the first insulation layer. The overlapping portion of the free layer then provides the free layer with its first edge for connection to the second edge of the flux guide.
In a still further preferred embodiment the free layer also overlaps a portion of the second insulation layer and a first edge of a second flux guide abuts the second edge of the free layer. The barrier layer may then extend over the first and second flux guides and over the free layer with the pinned layer on top of the barrier layer and the pinning layer on top of the pinned layer. Each of the pinned and pinning layers have first and second edges which are recessed from the ABS and third and fourth insulation layers may be provided with the third insulation layer abutting the first edges of the pinned and pinning layers and extending to the ABS and with the second insulation layer abutting the second edges of the pinned and pinning layers and extending away from the ABS. The second shield layer may then overlay the third insulation layer, the pinning layer and the fourth insulation layer. By electrical contact between the first shield layer and the free layer and electrical contact between the second shield layer and the pinning layer, the first and second shield layers may serve as first and second leads for conducting a sense current perpendicular to the film surfaces of the layers of the tunnel junction sensor. The second flux guide will serve as an extension of the free layer into the head for minimizing flux decay between the free layer and the first and second shield layers.
An object of the present invention is to provide a tunnel junction read head which can be constructed, in part, by lapping to an
Gill Hardayal Singh
Werner Douglas Johnson
Evans Jefferson
Johnston Ervin F.
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