Abstract:
A tunnel junction read head is provided with free and pinned layers which are recessed from the ABS with the free layer being connected to a flux guide which extends the free layer to the ABS for conducting signal fields to the free layer from a rotating magnetic disk. With this arrangement the typical narrow spacing between the free and pinned layers at the ABS is obviated so that upon lapping of the read head during its construction, conductive material will not be smeared between these layers so as to cause shorting therebetween.

Description:
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 θ, where θ 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 ABS without the risk of smearing conductive material between the free and pinned layers to cause shorting therebetween. 
     Other objects and attendant advantages of the invention will be appreciated upon reading the following description taken together with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a plan view of an exemplary magnetic disk drive; 
     FIG. 2 is an end view of a slider with a magnetic head of the disk drive as seen in plane  2 — 2  of FIG. 1; 
     FIG. 3 is an elevation view of the magnetic disk drive wherein multiple disks and magnetic heads are employed; 
     FIG. 4 is an isometric illustration of an exemplary suspension system for supporting the slider and magnetic head; 
     FIG. 5 is an ABS view of the magnetic head taken along plane  5 — 5  of FIG. 2; 
     FIG. 6 is a partial view of the slider and a piggyback magnetic head as seen in plane  6 — 6  of FIG. 2; 
     FIG. 7 is a partial view of the. slider and a merged magnetic head as seen in plane  7 — 7  of FIG. 2; 
     FIG. 8 is a partial ABS view of the slider taken along plane  8 — 8  of FIG. 6 to show the read and write elements of the piggyback magnetic head; 
     FIG. 9 is a partial ABS view of the slider taken along plane  9 — 9  of FIG. 7 to show the read and write elements of the merged magnetic head; 
     FIG. 10 is a view taken along plane  10 — 10  of FIGS. 6 or  7  with all material above the coil layer and leads removed; 
     FIG. 11 is an ABS illustration of the tunnel junction read head; and 
     FIG. 12 is a view taken along plane  12 — 12  of FIG.  11 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Magnetic Disk Drive 
     Referring now to the drawings wherein like reference numerals designate like or similar parts throughout the several views, FIGS. 1-3 illustrate a magnetic disk drive  30 . The drive  30  includes a spindle  32  that supports and rotates a magnetic disk  34 . The spindle  32  is rotated by a spindle motor  36  that is controlled by a motor controller  38 . A slider  42  has a combined read and write magnetic head  40  and is supported by a suspension  44  and actuator arm  46  that is rotatably positioned by an actuator  47 . A plurality of disks, sliders and suspensions may be employed in a large capacity direct access storage device (DASD) as shown in FIG.  3 . The suspension  44  and actuator arm  46  are moved by the actuator  47  to position the slider  42  so that the magnetic head  40  is in a transducing relationship with a surface of the magnetic disk  34 . When the disk  34  is rotated by the spindle motor  36  the slider is supported on a thin (typically, 0.05 μm) cushion of air (air bearing) between the surface of the disk  34  and the air bearing surface (ABS)  48 . The magnetic head  40  may then be employed for writing information to multiple circular tracks on the surface of the disk  34 , as well as for reading information therefrom. Processing circuitry  50  exchanges signals, representing such information, with the head  40 , provides spindle motor drive signals for rotating the magnetic disk  34 , and provides control signals to the actuator for moving the slider to various tracks. In FIG. 4 the slider  42  is shown mounted to a suspension  44 . The components described hereinabove may be mounted on a frame  54  of a housing, as shown in FIG.  3 . 
     FIG. 5 is an ABS view of the slider  42  and the magnetic head  40 . The slider has a center rail  56  that supports the magnetic head  40 , and side rails  58  and  60 . The rails  56 ,  58  and  60  extend from a cross rail  62 . With respect to rotation of the magnetic disk  34 , the cross rail  62  is at a leading edge  64  of the slider and the magnetic head  40  is at a trailing edge  66  of the slider. 
     FIG. 6 is a side cross-sectional elevation view of a piggyback magnetic head  40 , which includes a write head portion  70  and a read head portion  72 , the read head portion employing a tunnel junction sensor  74  of the present invention. FIG. 8 is an ABS view of FIG.  6 . The tunnel junction sensor  74  is sandwiched between ferromagnetic first and second shield layers  80  and  82 . In response to external magnetic fields, the resistance of the tunnel junction sensor  74  changes. A tunneling current (I T ) conducted through the sensor causes these resistance changes to be manifested as potential changes. These potential changes are then processed as readback signals by the processing circuitry  50  shown in FIG.  3 . The tunneling current (I T ) may be conducted through the tunnel junction sensor  74  perpendicular to the planes of its film surfaces by the first and second shield layers  80  and  82  which serve as first and second leads, which will be discussed in more detail hereinafter. 
     The write head portion  70  of the magnetic head  40  includes a coil layer  84  sandwiched between first and second insulation layers  86  and  88 . A third insulation layer  90  may be employed for planarizing the head to eliminate ripples in the second insulation layer caused by the coil layer  84 . The first, second and third insulation layers are referred to in the art as an “insulation stack”. The coil layer  84  and the first, second and third insulation layers  86 ,  88  and  90  are sandwiched between first and second pole piece layers  92  and  94 . The first and second pole piece layers  92  and  94  are magnetically coupled at a back gap  96  and have first and second pole tips  98  and  100  which are separated by a write gap layer  102  at the ABS. An insulation layer  103  is located between the second shield layer  82  and the first pole piece layer  92 . Since the second shield layer  82  and the first pole piece layer  92  are separate layers this head is known as a piggyback head. As shown in FIGS. 2 and 4, first and second solder connections  104  and  106  connect leads from the spin valve sensor  74  to leads  112  and  114  on the suspension  44 , and third and fourth solder connections  116  and  118  connect leads  120  and  122  from the coil  84  (see FIG. 10) to leads  124  and  126  on the suspension. 
     FIGS. 7 and 9 are the same as FIGS. 6 and 8 except the second shield layer  82  and the first pole piece layer  92  are a common layer. This type of head is known as a merged magnetic head. The insulation layer  103  of the piggyback head in FIGS. 6 and 8 is omitted. 
     FIG. 11 shows an ABS illustration of the present tunnel junction read head  200 . The read head  200  includes a tunnel junction sensor  202  which is located between ferromagnetic first and second shield layers (S 1 ) and (S 2 )  204  and  206 . The tunnel junction sensor includes an insulative barrier layer  208  which is between a ferromagnetic free layer  210  and a ferromagnetic pinned layer  212 . The pinned layer  212  is exchange coupled to an antiferromagnetic (AFM) pinning layer  214  so that the pinning layer  214  pins a magnetic moment  216  perpendicular to the ABS, such as into the head as shown in FIG.  12 . The magnetic moment  218  of the free layer is parallel to the ABS and may be directed into the paper, as shown in FIG.  12 . When a signal field from a rotating magnetic disk rotates the magnetic moment  218  into the head, it becomes more parallel to the magnetic moment  216 , which reduces the resistance of the tunnel junction sensor, and when a signal field from the rotating magnetic disk rotates the magnetic moment  218  toward the ABS, the magnetic moments  218  and  216  become more antiparallel, which increases the resistance of the tunnel junction sensor. These resistance changes cause potential changes in the processing circuitry  50  in FIG. 3, which are processed as playback signals. A seed layer  220  is typically located between the free layer  210  and the first shield layer  204  to improve magnetoresistance and magnetic properties. 
     As shown in FIG. 12, the tunnel junction sensor may have first and second spaced-apart insulation layers (Ins.)  222  and  224  with the first insulation layer  222  having a first edge  224  at the ABS and a second edge  226  recessed in the head and spaced from a first edge  228  of the second insulation layer. The seed layer  220  and the free layer  210  are preferably located within the space between the first and second insulation layers  222  and  224  and have forward portions with first edges  230  and  232 , which overlap a recessed end portion of the first insulation layer  222 . A first flux guide (FG 1 )  234  has a first edge  236  which is located at the ABS and a second edge  238  which abuts the first edges  230  and  232  of the seed and free layers. In a still further preferred embodiment the seed and free layers have rear portions which overlap the second insulation layer  224  with second edges  240  and  242  which abut a first edge  244  of a second flux guide (FG 2 )  246 . The second flux guide  246  extends a stripe height of the free layer  210  into the head for minimizing flux decay from the free layer when it receives signal fields from the rotating magnetic disk. 
     The barrier layer  208  extends over the first flux guide  234 , the free layer  210  and the second flux guide  246 . On top of the barrier layer  208  is the pinned and pinning layers  212  and  214 . The pinned and pinning layers may be located between spaced apart third and fourth insulation layers (Ins.)  248  and  250  with the first insulation layer having a first edge  252  which is located at the ABS. The pinned and pinning layers may be located between the space between the third and fourth insulation layers with first edges  254  and  256  abutting a recessed second edge  258  of the third insulation layer and having second edges  260  and  262  which abut a first edge  264  of the fourth insulation layer. 
     Typical thicknesses and materials of the layers are 2 μm of nickel iron (NiFe) for the first shield layer  204 , 10 Å of copper (Cu) for the seed layer  220 , 30 Å of nickel iron (NiFe) for the free layer  210 , 10 Å of aluminum oxide (Al 2 O 3 ) for the barrier layer  208 , 30 Å of cobalt iron (CoFe) for the pinned layer  212 , 200 Å of a metal such as nickel manganese (NiMn) for the pinning layer  214  and 2 μm of nickel iron (NiFe) for the second shield layer  206 . Each of the first and second flux guides  234  and  246  may be 100 Å thick and constructed of nickel iron (NiFe). Each of the first, second, third and fourth insulation layers  222 ,  224 ,  248  and  250  may be aluminum oxide (Al 2 O 3 ). Optionally, the free layer  210  may include a 15 Å thick nickel iron (NiFe) film and a 15 Å thick cobalt iron (CoFe) film with the cobalt iron (CoFe) film located between the nickel iron (NiFe) film and the barrier layer  208  for increasing the magnetoresistance. 
     It can be seen from FIG. 12 that because of the very thin barrier layer  208 , which is on the order of 10 Å thick, there is a very small distance between the free and pinned layers  210  and  212 . If the first edges  232  and  254  of these layers extended all the way to the ABS, there would be a risk that conductive material would be smeared across the barrier layer at the ABS shorting the free and pinned layers. This has been overcome in this invention by recessing the first edges  230  and  232  of the free and pinned layers, as well as the first edges  230  and  256  of the seed and pinning layers. By magnetically connecting the first flux guide  234  to the free layer  210 , the spacing between the conductive layers, which are the flux guide  234  and the first and second shield layers  204  and  206 , at the ABS are located farther apart. The thickness of the first insulation layer  222  may be on the order of 100 Å and the thickness of the third insulation layer  248  may be on the order of 100 Å. The first insulation layer  222  is located between the first shield layer  204  and the flux guide  234  at the ABS and the barrier layer  208  and the third insulation layer  248  are located between the flux guide  234  and the second shield layer  206  at the ABS. With this additional spacing there is less risk of smearing of conductive material between the conductive layers at the ABS. 
     It should be understood that the thicknesses and materials of the layers are exemplary, except the first insulation layer  222  should be thicker than the barrier layer  208 . It should be noted from FIG. 11 that the track width (TW) of the read head is defined by the width of the flux guide  234  at the ABS. 
     Clearly, other embodiments and modifications of this invention will occur readily to those of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.