Abstract:
Apparatus and method for providing a magnetic head that includes a magnetoresistive read sensor disposed between first and second magnetic shields. The shields are configured to reduce protrusion of the shields from a polished flat air bearing surface of the magnetic head upon increases in temperature. This configuration for the shields therefore at least reduces differences in thermal expansion of the shields relative to other parts of the magnetic head forming the air bearing surface. These shields according to some embodiments include one or more ferromagnetic layers exchange coupled with an antiferromagnetic layer. Further, in a particular embodiment, all the ferromagnetic layers within each of the shields can have a combined thickness per shield of less than 500 angstroms.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     Embodiments of the invention generally relate to electronic data storage and retrieval systems having magnetic heads capable of reading recorded information stored on magnetic media.  
         [0003]     2. Description of the Related Art  
         [0004]     In an electronic data storage and retrieval system, a magnetic head typically includes a reader portion having a magnetoresistive (MR) sensor for retrieving magnetically-encoded information stored on a magnetic recording medium or disk. The MR sensor operates based on a change of electrical resistivity of certain materials of the MR sensor in the presence of a magnetic field. During a read operation, a bias current is passed through the MR sensor. Magnetic flux emanating from a surface of the recording medium causes rotation of a magnetization vector of a sensing layer of the MR sensor, which in turn causes the change in electrical resistivity of the MR sensor. Since a voltage across the MR sensor is equal to the bias current that is supplied times the resistivity, the change in electrical resistivity of the MR sensor can be detected by measuring a voltage across the MR sensor to provide voltage information that external circuitry can then convert and manipulate as necessary.  
         [0005]     To efficiently read data from a data track of the recording medium, the MR sensor of the magnetic head must be shielded from extraneous magnetic fields, such as those generated by a write head or adjacent data tracks. Accordingly, the MR sensor is sandwiched between a pair of magnetic shields within the read head portion. During the read operation, first and second read shields ensure that the MR sensor reads only the information stored directly beneath it on a specific track of the recording medium by. absorbing any stray magnetic fields.  
         [0006]     Each of the shields typically includes one or more layers of ferromagnetic materials such as a nickel iron alloy. The ferromagnetic materials within the shields possess high coefficients of thermal expansion relative to most other materials in the magnetic head. Further, the amount of thermal expansion of the shields occurs proportionally to the volume of the shield, especially since a bulk of the volume is typically the ferromagnetic materials. The MR sensor is relatively small in volume compared to the shields. Consequently, an expansion differential occurs between the MR sensor and the shields as the temperature of the magnetic head increases. Specifically, the shields experience relatively more expansion than the MR sensor with increasing temperature. The difference in expansion results in the MR sensor becoming recessed along an air bearing surface of the magnetic head relative to the protruding shields at the air bearing surface. This recessing of the MR sensor due to thermal expansion of the shields adversely effects separation of the MR sensor from the recording medium resulting in increased read errors.  
         [0007]     A contributing factor to the problem of shield expansion is that the shields conforming to conventional structures utilize thickness of the layers of the ferromagnetic materials to maintain a magnetic stiffness desired. Ensuring shield magnetic stability avoids non-linear response of the MR sensor and increases in write induced instability/popcorn noise. The magnetic stiffness of the shields according to prior configurations for the shields decreases with a reduction in thickness of the shields. Accordingly, this thickness of the ferromagnetic materials adds to the volume of the shields, thereby contributing to relatively large thermal expansion of the shields.  
         [0008]     Therefore, there exists a need for an improved shield structure that eliminates or reduces temperature dependent protrusion of the shield into a planar air bearing surface common with an end surface of an MR sensor.  
       SUMMARY OF THE INVENTION  
       [0009]     In one embodiment, a magnetic head includes a non-magnetic insulating portion, a magnetoresistive read sensor, and a shield disposed adjacent the magnetoresistive read sensor. Additionally, the shield includes a ferromagnetic first layer, an antiferromagnetic second layer, and a non-magnetic third layer. The non-magnetic third layer can define an outermost layer of the shield in contact with the non-magnetic insulating portion.  
         [0010]     According to a further embodiment, a magnetic head includes a non-magnetic insulating portion, a magnetoresistive read sensor, and a shield disposed adjacent the magnetoresistive read sensor. The shield includes an antiferromagnetic layer and at least one ferromagnetic layer disposed between the magnetoresistive read sensor and a distal boundary of the shield where the shield interfaces the non-magnetic insulating portion. All layers of the at least one ferromagnetic layer can have a combined thickness less than 500 angstroms.  
         [0011]     In another embodiment, a magnetic head includes a magnetic resistive sensor means for reading data from a magnetic storage medium, and a shield means for magnetically shielding the sensor means. The shield means can include a non-magnetic means, a ferromagnetic means disposed between the magnetic resistive sensor means and the non-magnetic means, and an antiferromagnetic means for exchange coupling with the ferromagnetic means. The non-magnetic means can have a thickness between 500 angstroms (Å) and 1000 Å.  
         [0012]     For yet a further embodiment, a method of forming a magnetic head includes depositing a non-magnetic insulating portion, depositing a magnetoresistive read sensor, and depositing a shield disposed adjacent the magnetoresistive read sensor. Depositing the shield can include depositing a ferromagnetic first layer, depositing an antiferromagnetic second layer, and depositing a non-magnetic third layer. Additionally, the non-magnetic third layer can define an outermost layer of the shield in contact with the non-magnetic insulating portion.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]     So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.  
         [0014]      FIG. 1  is a top plan view of a hard disk drive including a magnetic head, according to embodiments of the invention.  
         [0015]      FIG. 2  is a cross-sectional, diagrammatic side view of the magnetic head, according to embodiments of the invention.  
         [0016]      FIG. 3  is a diagrammatic bottom view of the magnetic head, according to embodiments of the invention.  
         [0017]      FIG. 4  is a diagrammatic bottom view of a magnetic head, according to another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0018]     In the following, reference is made to embodiments of the invention. However, it should be understood that the invention is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the invention. Furthermore, in various embodiments the invention provides numerous advantages over the prior art. However, although embodiments of the invention may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the invention. Thus, the following aspects, features, embodiments and advantages are merely illustrative and, unless explicitly present, are not considered elements or limitations of the appended claims.  
         [0019]      FIG. 1  illustrates a hard disk drive  10  that includes a magnetic media hard disk  12  mounted upon a motorized spindle  14 . An actuator arm  16  is pivotally mounted within the hard disk drive  10  with a magnetic head  20  disposed upon a distal end  22  of the actuator arm  16 . During operation of the hard disk drive  10 , the hard disk  12  rotates upon the spindle  14  and the magnetic head  20  acts as an air bearing slider adapted for flying above the surface of the disk  12 . As described hereinafter, the magnetic head  20  includes a substrate base upon which various layers and structures that form the magnetic head  20  are fabricated. Thus, magnetic heads disclosed herein can be fabricated in large quantities upon a substrate and subsequently sliced into discrete magnetic heads for use in devices such as the hard drive  10 .  
         [0020]      FIG. 2  shows a side diagrammatic cross-sectional elevation view of the magnetic head  20 , which includes a read head portion  204  employing a magnetoresistive (MR) sensor  201 . Additionally, the read head portion  204  includes first and second shields  200 ,  202  that the MR sensor  201  is sandwiched between. A spacer layer  210  disposed about the MR sensor  201  separates the first shield  200  from the second shield  202 . Ends of the shields  200 ,  202  and the MR sensor  201  are polished to at least partially define an air bearing surface (ABS)  208 . During operations, a thin cushion of air (e.g., 0.01 micrometers) between the disk  12  and the ABS  208  supports the head  20 .  
         [0021]     The magnetic head  20  can additionally include a write head portion  206  if desired to form a combination read and write head. The write head portion  206  of the magnetic head  20  includes a coil layer  216  sandwiched between first and second insulation layers  214 ,  218 . The coil layer  216  and the first and second insulation layers  214 ,  218  are sandwiched between a first pole layer  220  and the second shield  202  that doubles as a second pole layer when the head  20  is a merged magnetic head. A back gap  222  magnetically couples the first pole layer  220  and the second shield  202  while a write gap layer  212  separates the first pole layer  220  and the second shield  202  at the ABS  208 . For some embodiments, the second shield  202  can be separated by an insulation layer from a separate second pole layer to provide a piggyback head (not shown).  
         [0022]      FIG. 3  illustrates a diagrammatic bottom view of the magnetic head  20 . First and second regions  335 ,  336  on either side of the MR sensor  201  typically include insulation layers, such as aluminum oxide (Al 2 O 3 ), and hard bias layers that cause magnetic fields to extend longitudinally through the MR sensor  201  for stabilizing a free layer  322 . The MR sensor  201  can define a current perpendicular to the plane (CPP) sensor or a current in plane (CIP) sensor. When the MR sensor  201  is configured as the CPP sensor, the shields  200 ,  202  can serve as first and second leads connected to processing circuitry (not shown) for conducting a current I through the MR sensor  201  perpendicular to major planes of the layers of the MR sensor  201 , as shown in  FIG. 3 . The MR sensor  201  and the hard bias layers are located between the first and second shields  200 ,  202 .  
         [0023]     As an exemplary sensor configuration for use with the shields described herein, the MR sensor  201  includes a first tantalum (Ta) layer  308  deposited on the first shield  200  followed by a first ruthenium (Ru) layer  310  and a sensor antiferromagnetic (AFM) layer  312 , such as iridium manganese (IrMn). An antiferromagnetic (AFC) coupling layer  316 , such as Ru, separates first and second pinned layers  314 ,  318  disposed above the sensor AFM layer  312 . The first pinned layer  314  can be a cobalt iron layer, such as CoFe25, while the second pinned layer  318  can be a cobalt iron boron (CoFeB) layer. The sensor AFM layer  312  can be exchange coupled to the first pinned layer  314  for pinning a magnetic moment  315  of the first pinned layer  314  in a direction either out of the head or into the head. By a strong antiparallel coupling between the magnetic moment  315  and a magnetic moment  319  of the second pinned layer  318 , the direction of the magnetic moment  319  is antiparallel to the magnetic moment  315 . Additionally, the MR sensor  201  includes an insulator (INS) layer  320 , such as magnesium oxide (MgO), located between the second pinned layer  318  and the free layer  322 . Further, a second Ta layer  324  and a second Ru layer  326  complete the MR sensor  201  prior to deposition of the second shield  202  onto the second Ru layer  326 .  
         [0024]     The free layer  322  provides a magnetic moment  323  directed from right to left or from left to right. When a field signal from a rotating magnetic disk rotates the magnetic moment  323  into the head, the magnetic moments  323  and  319  become more antiparallel increasing the resistance of the MR sensor  201  to the current (I). Alternatively, the magnetic moments  323  and  319  become more parallel to decrease the resistance of the MR sensor  201  when the field signal rotates the magnetic moment  323  out of the head. These resistance changes cause potential changes that are processed as playback signals.  
         [0025]     For some embodiments, the first shield  200  is deposited onto a substrate base  333  of the magnetic head. The substrate base  333  can be a non-magnetic material such as A 1   2 O 3 —TiC (alumina titanium carbide) and can include an undercoating, such as aluminum oxide (Al 2 O 3 ), deposited prior to deposition of the first shield  200 . A first non-magnetic layer  300  is formed onto the substrate base  333 . The first non-magnetic layer  300  can be either Ta or rhodium (Rh) or a combination of these materials in separate layers as illustrated in  FIG. 4 . Since Ta and Rh have relatively small thermal coefficients of expansion, the first non-magnetic layer  300  can be thicker without tending to protrude from the ABS  208  as temperature increases. For example, the first non-magnetic layer  300  can be between 500 angstroms (Å) and 1000 Å.  
         [0026]     The first shield  200  additionally includes a seed layer  302 , a first antiferromagnetic (AFM) layer  304  and a first ferromagnetic (FM) layer  306 . The seed layer  302  can be about 15 Å and can include nickel iron chromium (NiFeCr) and/or nickel iron (NiFe) or Ru. The first AFM layer  304  of the first shield  200  can be IrMn and can have a thickness of 50 Å to 75 Å. Other antiferromagnetic materials such as palladium manganese (PdMn) or nickel manganese (NiMn) can also be used for the AFM layer  304 . The first AFM layer  304  induces an exchange coupling between the first AFM layer  304  and the first ferromagnetic layer  306  formed on the first AFM layer  304 . Therefore, the first AFM layer  304  fixes the direction of a magnetization  307  of the first ferromagnetic layer  306  substantially in a direction directed from right to left or from left to right.  
         [0027]     The first ferromagnetic layer  306  can be a NiFe alloy or cobalt iron (CoFe) and can have a thickness of less than 500 Å. For some embodiments, the thickness of the first ferromagnetic layer  306  is between 100 Å and 500 Å. The exchange coupling between the first AFM layer  304  and the first ferromagnetic layer  306  stabilizes a magnetic domain configuration of the first ferromagnetic layer  306 . Accordingly, the first ferromagnetic layer  306  is as magnetically stiff as a much thicker ferromagnetic layer lacking the exchange coupling. This stability assures that the first ferromagnetic layer  306  does not saturate with an applied external field and that a return to the desired magnetic domain configuration of the first ferromagnetic layer  306  occurs upon relaxation of the external magnetic field. Further, the layers  300 ,  302 ,  304 ,  306  of the first shield  200  together with the second shield  202  provide substantially all the shielding for the MR sensor  201 .  
         [0028]     In addition to a small thickness of the first ferromagnetic layer  306  aiding in reducing an extent of thermal expansion of the first shield  200 , the small thickness enables more flexibility in selecting a composition of the ferromagnetic material within the first shield  200 . Thick films normally require plating to deposit a desired layer while thin films permit use of sputtering. For some embodiments, the first ferromagnetic layer  306  can include sendust (FeSiAl) or iron nitride (FeN). The first ferromagnetic layer  306  according to some embodiments can include a first sputtering of CoFe followed by a second sputtering of NiFe to improve magnetic coupling with the first AFM layer  304  since CoFe provides a larger exchange constant than NiFe.  
         [0029]     After completing deposition of the first shield  200 , the MR sensor  201  can be deposited onto the first ferromagnetic layer  306 . The second shield  202  can be formed on top of the second Ru layer  326  of the MR sensor  201 . For some embodiments, the second shield  202  includes a second ferromagnetic layer  328 , a second AFM layer  330  and a second non-magnetic layer  332 , which can be analogous to corresponding ones of the layers  300 ,  304 ,  306  of the first shield  200 .  
         [0030]     Accordingly, the second ferromagnetic layer  328  can include NiFe/CoFe and can have a thickness of less than 500 Å. Additionally, the second AFM layer  330  of the second shield  202  can include IrMn and can have a thickness of 50 Å to 75 Å. The second AFM layer  330  fixes the direction of a magnetization  329  of the second ferromagnetic layer  328  substantially in a direction directed from right to left or from left to right. Similar to the first shield  200 , exchange coupling between the second AFM layer  330  and the second ferromagnetic layer  328  magnetically stabilizes the second shield  202 . Furthermore, the second non-magnetic layer  300  can be between 500 Å and 1000 Å and can include Ta/Rh.  
         [0031]     An encapsulation layer  334 , such as Al 2 O 3 , disposed on the second non-magnetic layer  332  provides a coating on the second shield  202 . The encapsulation layer  334  can provide a magnetic gap utilized by the write head portion  206  that can be disposed on the second shield  202 , such as illustrated in  FIG. 2 . For example, the encapsulation layer  334  can function as the write gap layer  212  to separate the first pole layer  220  and the second shield  202  adjacent the ABS  208 . For some embodiments, the encapsulation layer  334  separates the second shield  202  from a separate write head of a piggyback head since the separate write head can be deposited directly onto the encapsulation layer  334 . When the shields  200 ,  202  and the MR sensor  201  are part of a read only head, the encapsulation layer  334  can define an outermost layer that remains exposed.  
         [0032]     Magnetic setting of all the AFM layers  304 ,  312 ,  330  can occur in a single setting process. The setting process can include heat treatment while applying a magnetic field (e.g., 10,000 oersted (Oe)) perpendicular to the substrate base  333  (i.e., the direction of the magnetic moment  315 ). Thus, the direction of the magnetic moment  315  of the first pinned layer  314  of the MR sensor  201  fixes in the direction of the applied magnetic field by exchange coupling with the sensor AFM layer  312 . Subsequently, the magnetic field applied is decreased and its direction changed to a direction parallel to the substrate base  333  (i.e., the direction of the magnetic moments  307 ,  329 ). This lower magnetic field (e.g., 1000 Oe) induces exchange coupling between the first ferromagnetic layer  306  and the first AFM layer  304  of the first shield  200  and exchange coupling between the second ferromagnetic layer  328  and the second AFM layer  330  of the second shield  202  without effecting the pinned layers  314 ,  318  since the pinned layers  314 ,  318  are magnetically stiff due to the antiferromagnetic coupling provided by the AFC layer  316 .  
         [0033]     Each of the ferromagnetic layers  306 ,  328  represent substantially all of the ferromagnetic material in each of the shields  200 ,  202 , respectively. Accordingly, a total thickness of ferromagnetic material within each of the shields can be less than 500 angstroms to limit the amount of expansion differential that occurs between the MR sensor  201  and the shields  200 ,  202  as the temperature of the magnetic head  20  increases. The foregoing embodiment(s) is merely exemplary. Persons skilled in the art will recognize other embodiments within the scope of the present invention. For example, other embodiments can divide the first ferromagnetic layer  306  into two layers disposed on each side of the first AFM layer  304 , as described below.  
         [0034]      FIG. 4  shows a diagrammatic bottom view of a magnetic head  420  according to another embodiment of the invention. The head  420  includes a first shield  400 , a MR sensor  401  and a second shield  402 . A first conductor layer  450  is formed onto a substrate base of the head  420 . The first conductor layer  450  can be Rh with a thickness of about 500 Å. A first non-magnetic layer  452  is formed onto the first conductive layer  450 . The first non-magnetic layer  452  can be Ta and can have a thickness of about 30 Å.  
         [0035]     The first shield  400  additionally includes a seed layer  454 , a first ferromagnetic layer  456 , a first AFM layer  458  and a second ferromagnetic layer  460 . The seed layer  454  can be about 15 Å and can include NiFeCr/NiFe or Ru. The first and second ferromagnetic layers  456 ,  460  can include NiFe/CoFe and can each have a thickness of less than 250 Å. The first AFM layer  458  can include IrMn and can have a thickness of 50 Å to 75 Å. The first AFM layer  458  fixes the direction of a magnetization  457  of the first ferromagnetic layer  456  and a magnetization  461  of the second ferromagnetic layer  460  substantially in a direction directed from right to left or from left to right.  
         [0036]     Magnetic coupling of the ferromagnetic material within the first shield  400  with the first AFM layer  458  depends on amount of surface area of the ferromagnetic material in contact with the first AFM layer  458 . Advantageously, the first and second ferromagnetic layers  456 ,  460  enable contact with two faces of the first AFM layer  458 . Therefore, the first and second ferromagnetic layers  456 ,  460  disposed on both sides of the first AFM layer  458  enhance stability of the first shield  400 .  
         [0037]     After completing deposition of the first shield  400 , the MR sensor  401  can be deposited onto the second ferromagnetic layer  460  followed by the second shield  402 . For some embodiments, the second shield  402  includes a third ferromagnetic layer  462 , a second AFM layer  464 , a fourth ferromagnetic layer  466 , a second non-magnetic layer  468  and a second conductor layer  470  that can all be analogous to corresponding layers of the first shield  400 . Hence, the third and fourth ferromagnetic layers  462 ,  466  can include NiFe/CoFe and can each have a thickness of less than 250 Å. The second AFM layer  464  can include IrMn and can have a thickness of 50 Å to 75 Å. The second AFM layer  464  fixes the direction of a magnetization  463  of the third ferromagnetic layer  462  and a magnetization  467  of the fourth ferromagnetic layer  466  substantially in a direction directed from right to left or from left to right.  
         [0038]     Furthermore, the second non-magnetic layer  468  can be about 30 Å and can include Ta. The second conductor layer  470  can include Rh and have a thickness of about 500 Å. For configurations where the second shield  402  is not exposed, an encapsulation layer (not shown) can be disposed on the second shield  402 , as described above.  
         [0039]     All of the embodiments disclosed herein can have a total thickness of ferromagnetic material within each of the shields less than 500 angstroms to limit the amount of expansion differential that occurs between the MR sensor and the shields as the temperature of the magnetic head increases. Accordingly, protrusion of the shields at the air bearing surface is at least reduced. The shields disclosed herein maintain magnetic stiffness/stability even with the thickness of the ferromagnetic material within each of the shields being less than 500 angstroms due to exchange coupling with an AFM layer.  
         [0040]     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.