Abstract:
A seed layer is provided for a pinning layer which increases the pinning field H PIN  between a pinning layer and a pinned layer of a spin valve sensor. In an example the seed layer structure included a first seed layer of cobalt iron boron (CoFeB), a second seed layer of nickel manganese oxide (NiMnO) and a third seed layer of aluminum oxide (Al 2 O 3 ) with the first seed layer interfacing the pinning layer and the second seed layer being located between the first and third seed layers. A pinning field between the pinning and pinned layers was 600 Oe and the magnetoresistive coefficient of the spin valve sensor was 8.8%. The pinned layer can be a single pinned layer or an antiparallel (AP) pinned layer structure. If the pinned layer structure is a single pinned layer the cobalt iron boron (CoFeB) first seed layer provides a second significant function of at least partially counterbalancing the demagnetizing field from the pinned layer.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a seed layer for improving the pinning field of a spin valve sensor and more particularly to a seed layer structure that improves the pinning field between pinning and pinned layers and promotes a higher magnetoresistive coefficient of a spin valve sensor. 
     2. Description of the Related Art 
     A spin valve sensor is employed by a read head for sensing magnetic signal fields from a moving magnetic medium, such as a rotating magnetic disk. The sensor includes a nonmagnetic electrically conductive first spacer layer sandwiched between a ferromagnetic pinned layer and a ferromagnetic free layer. An antiferromagnetic pinning layer interfaces the pinned layer for pinning a 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 magnetic disk. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. A magnetic moment of the free layer is free to rotate upwardly and downwardly with respect to the ABS from a quiescent or bias point position in response to positive and negative magnetic field signals from a rotating magnetic disk. The quiescent position, which is preferably parallel to the ABS, is the position of the magnetic moment of the free layer with the sense current conducted through the sensor in the absence of signal fields. 
     The thickness of the spacer layer is chosen so that shunting of the sense current and a magnetic coupling between the free and pinned layers are minimized. This thickness is typically less than the mean free path of electrons conducted through the sensor. With this arrangement, a portion of the conduction electrons are scattered at the interfaces of the spacer layer with the pinned and free layers. When the magnetic moments of the pinned and free layers are parallel with respect to one another scattering is minimal and when their magnetic moments are antiparallel scattering is maximized. Changes in scattering changes the resistance of the spin valve sensor as a function of cos θ, where θ is the angle between the magnetic moments of the pinned and free layers. The sensitivity of the sensor is quantified as magnetoresistive coefficient dr/R where dr is the change in the resistance of the sensor as the magnetic moment of the free layer rotates from a position parallel with respect to the magnetic moment of the pinned layer to an antiparallel position with respect thereto and R is the resistance of the sensor when the magnetic moments are parallel. 
     A read head in a magnetic disk drive of a computer includes the spin valve sensor as well as nonconductive nonmagnetic first and second read gap layers and ferromagnetic first and second shield layers. The spin valve sensor is located between the first and second read gap layers and the first and second read gap layers are located between the first and second shield layers. In the construction of the read head the first shield layer is first formed followed by formation of the first read gap layer, the spin valve sensor, the second read gap layer and the second shield layer. Spin valve sensors are classified as a top or a bottom spin valve sensor depending upon whether the pinning layer is located at the bottom of the sensor next to the first read gap layer or at the top of the sensor closer to the second read gap layer. Spin valve sensors are further classified as simple pinned or antiparallel pinned depending upon whether the pinned layer structure is one or more ferromagnetic layers with a unidirectional magnetic moment or a pair of ferromagnetic layers that are separated by a coupling layer with magnetic moments of the ferromagnetic layers being antiparallel. Spin valve sensors are still further classified as single or dual wherein a single spin valve sensor employs only one pinned layer and a dual spin valve sensor employs two pinned layers with the free layer structure located therebetween. 
     Because of the interfacing of the pinning and pinned layers the pinned layer is exchange coupled to the pinning layer. A unidirectional orientation of the magnetic spins of the pinning layer pins the magnetic moment of the pinned layer in the same direction. The orientation of the magnetic spins of the pinning layer are set by applying heat close to or above a blocking temperature of the material of the pinning layer in the presence of a field that is directed perpendicular to the ABS. The blocking temperature is the temperature at which all of the magnetic spins of the pinning layer are free to rotate in response to an applied field. During the setting, the magnetic moment of the pinned layer is oriented parallel to the applied field and the magnetic spins of the pinning layer follow the orientation of the pinned layer. When the heat is reduced below the blocking temperature the magnetic spins of the pinning layer pin the orientation of the magnetic moment of the pinned layer. The pinning function is effective as long as the temperature remains substantially below the blocking temperature. 
     In the presence of some magnetic fields the magnetic moment of the pinned layer can be rotated antiparallel to the pinned direction. The question then is whether the magnetic moment of the pinned layer will return to the pinned direction when the magnetic field is relaxed. This depends upon the strength of the exchange coupling field and the coercivity of the pinned layer. If the coercivity of the pinned layer exceeds the exchange coupling field between the pinning and pinned layers the exchange coupling field will not be strong enough to bring the magnetic moment of the pinned layer back to the original pinned direction. Until the magnetic spins of the pinning layer are reset the read head is rendered inoperative. Accordingly, there is a strong felt need to increase the exchange coupling field between the pinning layer and the pinned layer so that the spin valve sensor has improved thermal stability. 
     Another parameter that indicates the performance of the pinning of the pinned layer is the pinning field H p  between the pinning and pinned layers. The pinning field, which is somewhat dependent upon the exchange coupling field H ex , is the applied field at which the magnetic moment of the pinned layer commences to rotate in a substantial manner. If the pinning field H p  is low the orientation of the pinned layer will not be controlled thereby degrading performance of the read head. Accordingly, it is desirable to maximize the pinning field H p . 
     SUMMARY OF THE INVENTION 
     I have provided a seed layer structure for the pinning layer which increases the pinning field H PIN  between the pinning layer and the pinned layer. In an example, which will be described in detail hereinafter, I obtained a pinning field H PIN  of 600 Oe which is excellent in the spin valve sensor art. In the example the seed layer structure included a first seed layer of cobalt iron boron (CoFeB), a second seed layer of nickel manganese oxide (NiMnO) and a third seed layer of aluminum oxide (Al 2 O 3 ) with the first seed layer interfacing the pinning layer and the second seed layer being located between the first and third seed layers. My invention also includes employing a seed layer structure which includes only the first seed layer of cobalt iron boron (CoFeB) since it directly interfaces the pinning layer and is primarily responsible for the improvement in the pinning field H PIN . The pinned layer can be a single pinned layer or an antiparallel (AP) pinned layer structure. The cobalt iron boron (CoFeB) seed layer provides a second significant function of at least partially counterbalancing the demagnetizing field from the pinned layer. Accordingly, the seed layer improves readback asymmetry of the read head by promoting a centering of a bias point of the spin valve sensor on its transfer curve. As will also be seen from the following example the spin valve sensor with the seed layer structure provided a magnetoresistive coefficient of 8.8% which is excellent in the spin valve art. 
     An object is to provide a seed layer for a spin valve sensor which improves the pinning field H PIN  between pinning and pinned layers and the magnetoresistive coefficient dr/R of the sensor. 
     Another object is to provide a seed layer for a spin valve sensor which improves the texture of layers constructed on the seed layer for improving performance of the spin valve sensor. 
     A further object is to accomplish the aforementioned objectives while employing the seed layer to provide a sense current field for counterbalancing a demagnetization field from a pinned layer or pinned layer structure of the spin valve sensor. 
     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 planar 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 ; 
     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 slider 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 isometric ABS illustration of an exemplary read head which employs a spin valve sensor longitudinally biased by hard biasing layers; 
     FIG. 12 is an ABS illustration of a first embodiment of the present spin valve sensor; and 
     FIG. 13 is an ABS illustration of a second embodiment of the present spin valve sensor. 
    
    
     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  supports 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 . 
     FIG. 5 is an ABS view of the slider  42  and the magnetic head  40 . The slider has a center rail  56 , which 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 spin valve sensor  74  of the present invention. FIG. 8 is an ABS view of FIG.  6 . The spin valve sensor  74  is sandwiched between nonmagnetic electrically insulative first and second read gap layers  76  and  78 , and the read gap layers are 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 sense current I s  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 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 is an isometric ABS illustration of a read head  72  which has a spin valve sensor  130  with a pinning layer  132  which is typically nickel oxide (NiO). First and second hard bias and lead layers  134  and  136  are connected to first and second side edges  138  and  140  of the spin valve sensor. This connection is known in the art as a contiguous junction and is fully described in commonly assigned U. S. Pat. No. 5,018,037. The first hard bias and lead layers include a first hard bias layer  140  and a first lead layer  142  and the second hard bias and lead layers  136  include a second hard bias layer  144  and a second lead layer  146 . The hard bias layers  140  and  144  cause magnetic flux to extend longitudinally through the spin valve sensor  130  for stabilizing magnetic domains of the free layer. The spin valve sensor  130  and the first and second hard bias and lead layers  134  and  136  are located between nonmagnetic electrically insulative first and second read gap layers  148  and  150 . The first and second read gap layers  148  and  150  are, in turn, located between first and second shield layers  152  and  154 . 
     The Invention 
     The read head embodiment  400  shown in FIG. 12 includes a spin valve sensor  402  which may be constructed on the first read gap layer  148 . The spin valve sensor  402  includes a nonmagnetic conductive spacer layer (S)  404  which is located between a free layer structure  406  and a pinned layer (P)  408 . The pinned layer  408  is exchange coupled to an antiferromagnetic (AFM) pinning layer  410 . The pinning layer  410  pins a magnetic moment  412  of the pinned layer perpendicular to the ABS in a direction away from the ABS, as shown in FIG. 12, or optionally toward the ABS. 
     The free layer structure  406  includes a free layer (F)  414  and a nanolayer (NL)  416  with the nanolayer located between the spacer layer  404  and the free layer  414  for increasing the magnetoresistive coefficient dr/R of the spin valve sensor. The free layer structure has a magnetic moment  418  which is directed parallel to the ABS from left to right, as shown in FIG. 12, or optionally from right to left. The magnetic moment  418  is rotated upwardly and downwardly by signal fields from the rotating magnetic disk. When the sense current Is is conducted through the spin valve sensor a rotation of the magnetic moment  418  upwardly decreases the resistance of the sensor and a rotation of the magnetic moment  418  downwardly increases the resistance of the sensor which resistance changes are processed as playback signals by the processing circuitry  50  in FIG. 3. A cap layer  420  is located on the free layer  414  for protecting it from subsequent processing steps. 
     A seed layer structure  422  was provided for the spin valve sensor which included 10 Å of cobalt iron boron (CoFeB) for a first seed layer  424 , 30 Å of nickel manganese oxide (NiMnO) for a second seed layer  426  and 30 Å of aluminum oxide (Al 2 O 3 ) for a third seed layer  428  with the second seed layer located between the first and third seed layers. The spin valve sensor  402  is located on the seed layer structure  422  with the pinning layer  410  interfacing the first seed layer  424 . 
     The thicknesses and materials of the layers of the spin valve sensor  402  are 250 Å of platinum manganese (PtMn) for the pinning layer  410 , 35 Å of cobalt iron (CoFe) for the pinned layer  408 , 20 Å of copper (Cu) for the spacer layer  404 , 15 Å of cobalt iron (CoFe) for the nanolayer  416 , 45 Å of nickel iron (NiFe) for the free layer  414  and 50 Å of tantalum (Ta) for the cap layer  420 . 
     Upon testing the embodiment  400  shown in FIG. 12 the magnetoresistive coefficient dr/R of the spin valve sensor was 8.8% and the pinning field H PIN  between the pinning layer  410  and the pinned layer  408  was 600 Oe. Both of these values are considered to be excellent in the spin valve sensor art. 
     Another embodiment of the present invention is illustrated in FIG. 13 which is same as the embodiment  400  in FIG. 12 except an antiparallel (AP) pinned layer structure  502  is substituted for the pinned layer  408  in FIG.  12 . The AP pinned layer structure  502  includes first and second AP pinned layers (AP 1 ) and (AP 2 )  504  and  506  with an AP coupling layer  508  located between the first and second AP pinned layers. The first and second AP pinned layers  506  and  508  have first and second magnetic moments  510  and  512  which are antiparallel with respect to one another. Because of this relationship the AP pinned layer structure  502  produces a net demagnetizing field which is less than the demagnetizing field of the pinned layer  408  in FIG.  12 . Exemplary thicknesses and materials for the AP pinned layer structure are 23 Å of cobalt iron (CoFe) for the first AP pinned layer  504 , 26 Å of cobalt iron (CoFe) for the second AP pinned layer  506  and 8 Å of ruthenium (Ru) for the AP coupling layer  508 . 
     Discussion 
     The percentage composition of the various elements of the materials are Co 88 Fe 9 B 3 , Ni 50 Mn 50 O, Pt 50 Mn 50 , Co 90 Fe 10  and Ni 82 Fe, 18 . All of the layers embodiments shown in FIGS. 12-15 were deposited in situ except for the first gap layer  148  wherein in situ means that all of the layers are deposited in a ion beam sputtering chamber without breaking the vacuum. 
     The spin valve sensors  402  and  502  in FIGS. 12 and 13 are bottom spin valve sensors since the pinning layer  410  is located at the bottom of the spin valve sensor closer to the first read gap layer  408  than the free layer structure  406  is to the first read gap layer. It should be understood that the thicknesses for the various layers are exemplary and can be varied. Further, while cobalt iron (CoFe) is preferred for the pinned and nanolayers, cobalt (Co) could be substituted therefor. Still further, while platinum manganese (PtMn) is preferred for the pinning layers, other metallic antiferromagnetic materials may be employed such as iridium manganese (IrMn), nickel manganese (NiMn), iron manganese (FeMn), palladium platinum manganese (PdPtMn) and nickel manganese (NiMn). 
     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.