Abstract:
A read head, which can be submicron, has an antiparallel (AP) coupled flux guide which is located at an air bearing surface and guides field signals from a rotating magnetic disk to a tunnel junction sensor which is recessed in the head. Because of the highly stable characteristics of the AP flux guide, first and second hard bias layers at the side edges of the flux guide are not required in order to stabilize the magnetization of the flux guide. The AP flux guide has first and second AP layers with oppositely oriented magnetizations so that the flux guide has a net magnetization which is the difference between the magnetizations of the first and second AP layers. These thicknesses are designed to provide a desired uniaxial anisotropy H K  and magnetic softness of the AP flux guide.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a tunnel junction sensor with an antiparallel (AP) coupled flux guide wherein the flux guide does not require stabilization by hard bias layers.  
           [0003]    2. Description of the Related Art  
           [0004]    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 rea d 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.  
           [0005]    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 sense current therethrough. The sense 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 parallel to the ABS, is when the sense current is conducted through the sensor without magnetic field signals from the rotating magnetic disk.  
           [0006]    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 sense current (I S ) is at a minimum and when their magnetic moments are antiparallel the resistance of the tunnel junction sensor to the sense current (I S ) 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 sense current (I S ) 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.  
           [0007]    The first and second shield layers may engage the bottom and the top respectively of the tunnel junction sensor so that the first and second shield layers serve as leads for conducting the sense current Is through the tunnel junction sensor perpendicular to the major planes of the layers of the tunnel junction sensor.  
           [0008]    The tunnel junction sensor has first and second side surfaces which are normal to the ABS. First and second hard bias layers abut the first and second side surfaces respectively of the tunnel junction sensor for longitudinally biasing the magnetic domains of the free layer. This longitudinal biasing maintains the magnetic moment of the free layer parallel to the ABS when the read head is in a quiescent condition.  
           [0009]    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. Opposite 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.  
           [0010]    A scheme for preventing shorts across the barrier layer of the tunnel junction sensor is to recess the tunnel junction sensor within the head and provide a flux guide between the ABS and the sensor for guiding flux signals from the rotating magnetic disk. Typically, the ferromagnetic material of the flux guide is required to be stabilized by hard bias layers on each side of the flux guide. With track widths of 1 μm or more this stabilization of the flux guide has been acceptable. However, with submicron track widths, such as 0.1 μm to 0.2 μm, the hard biasing of the flux guide renders the magnetization of the flux guide too stiff to adequately respond to flux signals from the rotating magnetic disk. The reason for this is because flux guides, regardless of the track width, are magnetically stiffened about 0.1 μm on each side of the flux guide by the hard biasing layers. When the track width is above 1 μm, this does not render the flux guide unacceptable since a remainder of the width of the flux guide remains relatively soft for responding to field signals from the rotating magnetic disk. Another way of stating the problem is that with submicron track widths the hard bias renders the flux guide with low permeability. Since a flux guide needs a height of approximately 0.25 μm to 0.5 μm the field signal from the rotating magnetic disk is nonexistent or insignificant at the tunnel junction sensor because of the lack of permeability of the flux guide. Accordingly, there is a strong-felt need to provide a submicron track width tunnel junction sensor with a flux guide that has high permeability.  
         SUMMARY OF THE INVENTION  
         [0011]    The present invention provides a highly permeable flux guide for a submicron tunnel junction sensor. As background, the tunnel junction sensor is recessed from the ABS and has front and back recessed surfaces. The flux guide has a front surface that forms a portion at the ABS and a back surface that is magnetically coupled to the front surface of the tunnel junction sensor. The flux guide is provided with high permeability by making it an antiparallel (AP) coupled structure. The AP coupled structure includes first and second antiparallel (AP) layers and an antiparallel coupling (APC) layer that is located between and interfaces each of the first and second AP layers. Each of the first and second AP layers has a magnetic moment. Magnetic moments of the AP layers are antiparallel with respect to each other and are parallel to the ABS and the major planes of the first and second AP layers. The magnetic moment of one of the first and second AP layers, such as the second AP layer, has a magnetic moment that is greater than the magnetic moment of the other of the first and second AP layers, such as the first AP layer. The free layer of the tunnel junction sensor has a magnetic moment that is parallel to the magnetic moment of the AP layer which has the greater magnetic moment, such as the second AP layer.  
           [0012]    With the present invention hard bias layers on each side of the flux guide are not required in order to stabilize the magnetization of the flux guide. The AP coupled flux guide is more stable than a single layer flux guide without hard biasing since the ends of the AP coupled flux guide have reduced demagnetization. This is because of flux closure between the first and second AP layers. The AP flux guide also has high permeability which means that the flux decay length of the field signal from the rotating magnetic disk can be long which improves the efficiency of the read head. The effective thickness of the AP flux guide is the difference in the thicknesses of the first and second AP layers. For instance, if the first AP layer is 50 Å thick and the second AP layer is 200 Å thick the effective thickness is 150 Å. Assuming that the uniaxial anisotropy H K  for each layer is 5 Å the uniaxial anisotropy H K  for the AP flux guide can be calculated by the formula H K =(H K1 t 1 +H K2 t 2 )÷(t 2 −t 1 ). With the above parameters H K =5×50+5×200+200−50=8.2 Oe. Accordingly, the effective uniaxial anisotropy H K  of the AP flux guide is 8.2 Oe which renders the AP flux guide relatively soft with high permeability.  
           [0013]    An object of the present invention is to provide a submicron track width tunnel junction sensor with a highly permeable flux guide.  
           [0014]    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  
       [0015]    [0015]FIG. 1 is a plan view of an exemplary magnetic disk drive;  
         [0016]    [0016]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;  
         [0017]    [0017]FIG. 3 is an elevation view of the magnetic disk drive wherein multiple disks and magnetic heads are employed;  
         [0018]    [0018]FIG. 4 is an isometric illustration of an exemplary suspension system for supporting the slider and magnetic head;  
         [0019]    [0019]FIG. 5 is an ABS view of the magnetic head taken along plane  5 - 5  of FIG. 2;  
         [0020]    [0020]FIG. 6 is a partial view of the slider and a piggyback magnetic head as seen in plane  6 - 6  of FIG. 2;  
         [0021]    [0021]FIG. 7 is a partial view of the slider and a merged magnetic head as seen in plane  7 - 7  of FIG. 2;  
         [0022]    [0022]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;  
         [0023]    [0023]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;  
         [0024]    [0024]FIG. 10 is a view taken along plane  10 - 10  of FIG. 6 or  7  with all material above the coil layer and leads removed;  
         [0025]    [0025]FIG. 11 is a longitudinal cross-section of the present tunnel junction read head; and  
         [0026]    [0026]FIG. 12 is an ABS illustration of the tunnel junction read head. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
     Magnetic Disk Drive  
       [0027]    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  55 , as shown in FIG. 3.  
         [0028]    [0028]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.  
         [0029]    [0029]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 spin valve 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.  
         [0030]    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.  
         [0031]    [0031]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.  
       The Invention  
       [0032]    [0032]FIG. 11 is a longitudinal cross-sectional view of the present read head  72  with the sensor  74  located between the first and second shield layers  80  and  82 . A tunnel junction sensor  200  has front and back surfaces  202  and  204  and is recessed in the head from the ABS. A flux guide  206  has front and back surfaces  208  and  210  wherein the front surface  208  forms a portion of the ABS and the back surface  210  is magnetically coupled to the front surface  202  of the tunnel junction sensor  200 .  
         [0033]    The tunnel junction sensor has an electrically nonconductive barrier layer  212  which is located between a pinned layer (P)  214  and a free layer (F)  216 . The pinned layer  214  has a magnetic moment  218  which is pinned by an antiferromagnetic (AFM) pinning layer  220  perpendicular to the ABS in a direction from left to right or from right to left, as shown in FIG. 11. A cap layer  222  may be provided on top of the free layer  216  for protecting it from subsequent processing steps. The free layer  216  has a magnetic moment  224  which is oriented parallel to the ABS and to the major planes of the layers. When a field signal H AP  from a rotating magnetic disk is sensed by the tunnel junction sensor  200  the magnetic moment  224  of the free layer rotates. When the free layer  224  is rotated upwardly into the head by the field signal from the rotating magnetic disk the magnetic moments  224  and  218  become more parallel which reduces the resistance of the sensor to a tunneling current I T  and when the field signal from the rotating magnetic disk rotates the magnetic moment  224  outwardly from the head, the magnetic moments  224  and  218  become more antiparallel which increases the resistance of the tunnel junction sensor to the tunneling current I T . These increases and decreases in the resistance of the tunnel junction sensor are processed as playback signals by the processing circuitry  50  in FIG. 3. The tunneling current I T  may be conducted through the tunnel junction sensor by the first and second shield layers  80  and  82  which are electrically conductive. The connection of the source of the tunneling current I T  to the first and second shield layers is not shown.  
         [0034]    As shown in FIGS. 11 and 12, the flux guide  206  is an antiparallel (AP) coupled structure without any hard bias layers at the first and second side surfaces  226  and  228  for stabilization. The AP coupled flux guide  206  is self-stabilized. The AP coupled flux guide  206  includes first and second antiparallel (AP) layers (AP 1 ) and (AP 2 )  230  and  232  and an antiparallel coupling (APC) layer  234 . The APC layer  234  is located between and interfaces each of the first and second AP layers  230  and  232 . The first AP layer  230  has a magnetic moment  236  and the second AP layer has a magnetic moment  238  wherein each of the magnetic moments  236  and  238  are oriented parallel to the ABS and to the major planes of the layers. By strong antiparallel coupling between the first and second AP layers the magnetic moments  236  and  238  are antiparallel with respect to each other. Accordingly, there is flux closure between the first and second AP pinned layers  230  and  232  which highly stabilizes the AP flux guide  206 . Further, because of the lack of hard bias layers at the side surface  226  and  228  of the AP flux guide the ferromagnetic materials of the first and second AP coupled layers remain magnetically soft. A preferred material for the first and second AP layers  230  and  232  is nickel iron (Ni 83 Fe 17 ). The APC layer  234  is typically ruthenium (Ru).  
         [0035]    The magnetic moment  238  of one of the AP layers, such as the second AP layer  232 , has a greater magnetic moment than the magnetic moment  236  of the other AP layer, such as the first AP layer  230 . Assuming that the magnetic moment  238  is oriented into the paper, as shown in FIG. 11, the net magnetic moment, which is the difference between the magnetic moments  236  and  238 , will be oriented into the paper and parallel to the magnetic moment  224  of the free layer. Accordingly, as the field signal HAP from the rotating magnetic disk rotates the net magnetic moment of the AP flux guide  206  upwardly into the head the magnetic moment  224  of the free layer will likewise be rotated upwardly into the head or vice versa.  
         [0036]    The flux guide  206  is insulated on all sides except the side that faces a portion of the ABS. An insulation layer  240 , which may be multiple layers, provides insulation about the flux guide  206  and an insulation layer  242  insulates the back surface  210  of the flux guide from the front surface  202  of the tunnel junction sensor. Another insulation layer  244 , which may be multiple layers, insulates the back surface  204  of the tunnel junction sensor. Each of the insulation layers may be aluminum oxide. The insulation layer  242  should be thin, such as 10 Å to 20 Å. Sufficient insulation may be obtained at  242  by oxidizing the front edges of the tunnel junction sensor.  
       Discussion  
       [0037]    The materials for the layers of the tunnel junction sensor  200  may be platinum manganese for the pinning layer  220 , cobalt iron for the pinned layer  214 , aluminum oxide for the barrier layer  212 , nickel iron for the free layer  216  and tantalum for the cap layer  222 .  
         [0038]    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.