Abstract:
A magnetoresistive read sensor has amagnetoresistive element, first and second bias elements, first and second current guides, and first and second overlaid leads. The magnetoresistive element has a center region and end regions separated by the center region. The first and second bias elements are positioned on the end regions of the magnetoresistive element. The first and second current guides are positioned on respective first and second bias elements. Each of the first and second current guides extends a guide overlay distance onto the center region of magnetoresistive element. The first and second overlaid leads are positioned on respective first and second current guides. Each of the first and second overlaid leads extends a lead-insulator offset distance onto the center region of the magnetoresistive element. The first and second overlaid leads are separated by a lead separation distance.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     None. 
     BACKGROUND OF THE INVENTION 
     The present invention relates generally to the field of magnetic data storage and retrieval systems. More particularly, the present invention relates to a magnetoresistive read sensor having a magnetoresistive element, a pair of overlaid leads and a current guiding layer for directing substantially all of bias current through a narrow region close to an active central area of the magnetoresistive element. 
     A transducing head of a magnetic data storage and retrieval system typically includes a magnetoresistive (MR) reader portion for retrieving magnetic data stored on a magnetic media. The reader is typically formed of several layers which include a MR sensor positioned between two gap layers, which are in turn positioned between two shield layers. The MR sensor may be any one of a plurality of MR-type sensors, including, but not limited to, AMR, GMR, spin valve and spin tunneling sensors. 
     To operate the MR sensor properly, the sensor must be stabilized against the formation of edge domains because domain wall motion results in electrical noise that makes data recovery impossible. A common way to achieve stabilization is with a permanent magnet abutted junction design. Permanent magnets have a high coercive field (i.e., are hard magnets). The magnetostatic field from the permanent magnets stabilizes the MR sensor and prevents edge domain formation, and provides proper bias. 
     Tabs of antiferromagnetic material, sometimes called “exchange tabs,” have also been used to stabilize the MR sensor. Exchange tabs are deposited upon the outer regions of the MR sensor and are exchange coupled thereto. Functions of the exchange tabs include pinning the magnetization of the outer regions of the MR sensor in the proper direction, preventing the formation of edge domains and defining the width of an active area of the MR sensor by preventing rotation of the magnetization at of the outer regions of MR sensor. 
     When the transducing head is placed near a magnetic medium, a resistance of the MR sensor fluctuates in response to a magnetic field emanating from written transitions in the magnetic medium. By providing a sense current through the MR sensor, the resistance of the sensor can be measured and used by external circuitry to decipher the information stored on the magnetic medium. The sense current is provided to the MR sensor via a pair of current contacts. 
     In prior art transducing heads, the current contacts were deposited on the biasing elements (either the abutted junction permanent magnets or the exchange tabs), such that the sense current passes through the MR sensor via the biasing elements. This arrangement of current contacts and biasing elements in prior art transducing heads allows for the sense current and the magnetic bias to share a common path through the biasing elements. It was previously believed that a shared magnetic and electrical path would occupy less physical space to allow for a smaller transducing head to be built. However, to be electrically reliable, the interface between the biasing elements and the MR sensor needs to be large in surface area to minimize the electrical resistance and to minimize the possibility of open contacts caused by the manufacturing process. 
     More recently, the use of overlaid current contacts have been used. As with the traditional current contact configurations, the pair of overlaid current contacts are deposited upon the biasing elements. However, the overlaid current contacts differ from the traditional current contacts in that the overlaid current contacts are also deposited directly on portions of the MR sensor. To ensure that most of the sense current flows directly into the MR sensor, rather than passing first through the biasing elements, the relative conductivities of the overlaid current contacts, the MR sensor, and the biasing elements can be controlled. Nonetheless, some of the sense current will still pass through the biasing elements before entering the MR sensor, contributing to side-reading in intermediate areas of the MR sensor in which the bias field exerted by the biasing elements has dropped off. 
     Accordingly, there is a need for a means of forcing the sense current through the active regions of the MR sensor. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is a magnetoresistive sensor having overlaid leads and an insulating current guide layer for preventing diversion of current through the biasing means. 
     A magnetoresistive read sensor has a magnetoresistive element, first and second bias elements, first and second current guides, and first and second overlaid leads. The magnetoresistive element has a center region and end regions separated by the center region. The first and second bias elements are positioned on the end regions of the magnetoresistive element. The first and second current guides are positioned on respective first and second bias elements. Each of the first and second current guides extends a guide overlay distance onto the center region of magnetoresistive element. The first and second overlaid leads are positioned on respective first and second current guides. Each of the first and second overlaid leads extends a lead-insulator offset distance onto the center region of the magnetoresistive element. The first and second overlaid leads are separated by a lead separation distance. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional view of a prior art transducing head having an overlaid current contacts and permanent magnet abutted junction biasing. 
     FIG. 2 is a cross-sectional view of a prior art transducing head having overlaid current contacts and exchange tab biasing. 
     FIG. 3 is a cross-sectional view of a transducing head in accord with the present invention and having overlaid current contacts and permanent magnet abutted junction biasing. 
     FIG. 4 is a cross-sectional view of a transducing head in accord with the present invention and having overlaid current contacts and exchange tab biasing. 
     FIG. 5 is a graph of current distribution curves produced by transducing heads with varying lead-insulator offsets. 
     FIG. 6 is a graph illustrating decay range of a transducing head&#39;s current distribution curve versus the lead-insulator offset of the transducing heads. 
     FIG. 7 is a graph illustrating contact resistance of a MR sensor of a transducing head versus the lead-insulator offset of the transducing heads. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 is a cross-sectional view of prior art transducing head  10  taken along a plane parallel to an air bearing surface (ABS) of transducing head  10 . Transducing head  10  includes MR sensor  12 , permanent magnet seed layer  14 , first and second permanent magnets  16  and  18 , and first and second overlaid current contacts  20  and  22 . 
     MR sensor  12  may be any one of a plurality of MR-type sensors, including, but not limited to, AMR, GMR, spin valve and spin tunneling sensors. MR sensor  12  has two end regions separated by a central region. 
     First and second permanent magnets  16  and  18 , which are grown on seed layer  14 , are positioned on the end regions of MR sensor  12  to provide longitudinal magnetic bias to MR sensor  12 . First and second permanent magnets  16  and  18  form abutted junctions with MR sensor  12 . Seed layer  14  separates first and second permanent magnets  16  and  18  from MR sensor  12  and provides proper crystallographic orientation of permanent magnets  16  and  18 . 
     First and second overlaid current contacts  20  and  22  are deposited over respective first and second permanent magnets  16  and  18 . Additionally, each of first and second overlaid current contacts  20  and  22  overlays MR sensor  12  by lead overlay distance X LO . First and second overlaid current contacts  20  and  22  are separated from each other by lead separation distance X LS . 
     When transducing head  10  is placed near a magnetic medium (not shown in FIG.  1 ), a resistance of MR sensor  12  fluctuates in response to a magnetic field emanating from written transitions in the magnetic medium. During a read operation, first and second overlaid current contacts  20  and  22  provide a sense current to MR sensor  12 . By measuring the voltage across MR sensor  12 , the information stored on the magnetic medium can be deciphered through use of external circuitry. 
     FIG. 2 is a cross-sectional view of prior art transducing head  30  taken along a plane parallel to an air bearing surface (ABS) of transducing head  30 . Transducing head  30  includes MR sensor  32 , first and second exchange tabs  34  and  36 , and first and second overlaid current contacts  38  and  40 . 
     MR sensor  32  may be any one of a plurality of MR-type sensors, including, but not limited to, AMR, GMR, spin valve and spin tunneling sensors. MR sensor  32  has two end regions separated by a central region. 
     First and second exchange tabs  34  and  36 , which are formed of an antiferromagnetic material, are exchange coupled to the end regions of MR sensor  32  to provide longitudinal magnetic bias to MR sensor  32 . First and second exchange tabs  34  and  36  pin the magnetization of the outer regions of MR sensor  32  in a desired direction to prevent the formation of edge domains and to define the width of an active region of MR sensor  32  by preventing rotation of the magnetization at the outer regions of MR sensor  32 . 
     First and second overlaid current contacts  38  and  40  are deposited over respective first and second exchange tabs  34  and  36 . Additionally, each of first and second overlaid current contacts  38  and  40  overlays MR sensor  32  by lead overlay distance X LO . First and second overlaid current contacts  38  and  40  are separated from each other by lead separation distance X LS . 
     When transducing head  30  is placed near a magnetic medium (not shown in FIG.  2 ), a resistance of MR sensor  32  fluctuates in response to a magnetic field emanating from written transitions in the magnetic medium. During a read operation, first and second overlaid current contacts  38  and  40  provide a sense current to MR sensor  32 . By measuring the voltage across MR sensor  32 , the information stored on the magnetic medium can be deciphered through use of external circuitry. 
     In prior art transducing head  10  having overlaid current contacts  20  and  22 , most of the sense current flowing between contacts  20  and  22  will flow directly into MR sensor  12 ; however, there will be some leakage of sense current into MR sensor  12  through permanent magnets  16  and  18 . Similarly in prior art transducing head  30  having overlaid current contacts  38  and  40 , there will be some leakage of sense current through exchange tabs  34  and  36 . This leakage of sense current into MR sensor  12  through the biasing elements (either permanent magnets  16  and  18  or exchange tabs  34  and  36 ) results in side-reading and a wider read width of the MR sensor than if there were no leakage of sense current through the biasing elements. Accordingly, there is a need to minimize the amount of sense current leaked through the biasing elements. 
     FIG. 3 is a cross-sectional view of transducing head  50  in accord with the present invention, the cross-section being taken along a plane parallel to an air bearing surface (ABS) of transducing head  50 . Transducing head  50  includes MR sensor  52 , seed layer  54 , first and second permanent magnets  56  and  58 , first and second current guides  60  and  62 , and first and second overlaid current contacts  64  and  66 . 
     MR sensor  52  may be any one of a plurality of MR-type sensors, including, but not limited to, AMR, GMR, spin valve and spin tunneling sensors. MR sensor  52  has two end regions separated by a central region. 
     First and second permanent magnets  56  and  58 , which are grown on seed layer  54 , are positioned on the end regions of MR sensor  52  to provide longitudinal magnetic bias to MR sensor  52 . First and second permanent magnets  56  and  58  form abutted junctions with MR sensor  52 . Seed layer  54  separates first and second permanent magnets  56  and  58  from MR sensor  52  and provides proper crystallographic orientation of permanent magnets  56  and  58 . 
     First and second current guides  60  and  62  are deposited upon respective first and second permanent magnets  56  and  58 . Additionally, each of first and second current guides  60  and  62  overlays a small portion of MR sensor  52 . Preferably, first and second current guides  60  and  62  are each formed of an insulating material, such as an oxide or a nitride. Most preferably, first and second current guides  60  and  62  are formed of aluminum-oxide. Also in a preferred embodiment, a thickness of first and second current guides  60  and  62  is in the range of about 50 Å to about 100 Å. 
     First and second overlaid current contacts  64  and  66  are deposited over respective first and second current guides  60  and  62 . Additionally, each of first and second overlaid current contacts  64  and  66  overlays a small portion of MR sensor  52 . Lead-overlay distance X LO , lead-insulator offset X LI , and lead-separation distance X LS  are three parameters used to define the interrelations of MR sensor  52 , current guides  60  and  62 , and current contacts  64  and  66 . Lead-overlay distance X LO  is the distance that either of first or second current contact  64  or  66  would overlay MR sensor  52  if respective current guide  60  or  62  were not present. Lead-insulator offset X LI  is the distance that either of first or second current contact  64  or  66  actually overlays (or directly contacts) MR sensor  52 . Finally, lead separation distance X LS  is the distance between first and second overlaid current contacts  64  and  66 . 
     In a preferred embodiment, lead-overlay distance X LO  is greater than about 0.1 micrometers, lead-insulator offset X LI  is in the range of about 0.05 micrometers to about 0.2 micrometers, and lead separation distance X LS  is less than about 0.3 micrometers. Lead-insulator offset X LI  is more preferably in the range of about 0.09 micrometers to about 0.11 micrometers. 
     When transducing head  50  is placed near a magnetic medium (not shown in FIG.  3 ), a resistance of MR sensor  52  fluctuates in response to a magnetic field emanating from written transitions in the magnetic medium. During a read operation, first and second overlaid current contacts  64  and  66  provide a sense current to MR sensor  52 . By measuring the voltage across MR sensor  52 , the information stored on the magnetic medium can be deciphered through use of external circuitry. First and second current guides  60  and  62  minimize the amount of sense current leaked into MR sensor  52  through either of first and second permanent magnets  56  and  58 . 
     FIG. 4 is a cross-sectional view of transducing head  70  in accord with the present invention, the cross-section being taken along a plane parallel to an air bearing surface (ABS) of transducing head  70 . Transducing head  70  includes MR sensor  72 , first and second exchange tabs  74  and  76 , first and second current guides  78  and  80 , and first and second overlaid current contacts  82  and  84 . 
     MR sensor  72  may be any one of a plurality of MR-type sensors, including, but not limited to, AMR, GMR, spin valve and spin tunneling sensors. MR sensor  72  has two end regions separated by a central region. 
     First and second exchange tabs  74  and  76 , which are formed of an antiferromagnetic material, are exchange coupled to the end regions of MR sensor  72  to provide longitudinal magnetic bias to MR sensor  72 . First and second exchange tabs  74  and  76  pin the magnetization of the outer regions of MR sensor  72  in a desired direction to prevent the formation of edge domains and to define the width of an active region of MR sensor  72  by preventing rotation of the magnetization at the outer regions of MR sensor  72 . 
     First and second current guides  78  and  80  are deposited upon respective first and second exchange tabs  74  and  76 . Additionally, each of first and second current guides  78  and  80  overlays a small portion of MR sensor  72 . Preferably, first and second current guides  78  and  80  are each formed of an insulating material, such as an oxide or a nitride. Most preferably, first and second current guides  78  and  80  are formed of aluminum-oxide. Also in a preferred embodiment, a thickness of first and second current guides  78  and  80  is in the range of about 50 Å to about 100 Å. 
     First and second overlaid current contacts  82  and  84  are deposited over respective first and second current guides  78  and  80 . Additionally, each of first and second overlaid current contacts  82  and  84  overlays a small portion of MR sensor  72 . Lead-overlay distance X LO , lead-insulator offset X LI , and lead-separation distance X LS  are three parameters used to define the interrelations of MR sensor  72 , current guides  78  and  80 , and current contacts  82  and  84 . Lead-overlay distance X LO  is the distance that either of first or second current contact  82  or  84  would overlay MR sensor  72  if respective current guide  78  or  80  were not present. Lead-insulator offset X LI  is the distance that either of first or second current contact  82  or  84  actually overlays (or directly contacts) MR sensor  72 . Finally, lead separation distance X LS  is the distance between first and second overlaid current contacts  82  and  84 . 
     In a preferred embodiment, lead-overlay distance X LO  is greater than about 0.1 micrometers, lead-insulator offset X LI  is in the range of about 0.05 micrometers to about 0.2 micrometers, and lead separation distance X LS  is less than about 0.3 micrometers. Lead-insulator offset X LI  is more preferably in the range of about 0.09 micrometers to about 0.11 micrometers. 
     When transducing head  70  is placed near a magnetic medium (not shown in FIG.  4 ), a resistance of MR sensor  72  fluctuates in response to a magnetic, field emanating from written transitions in the magnetic medium. During a read operation, first and second overlaid current contacts  82  and  84  provide a sense current to MR sensor  72 . By measuring the voltage across MR sensor  72 , the information stored on the magnetic medium can be deciphered through use of external circuitry. First and second current guides  78  and  80  minimize the amount of sense current leaked into MR sensor  72  through either of first or second exchange tabs  74  or  76 . 
     To illustrate, the effectiveness of current guides  60  and  62  in transducing head  50  of the present invention, a transducing head (having abutted-junction permanent magnet biasing) was modeled with a 600 Å PtMn-pinned dual spin valve sensor, a 50 Å Cr seed layer, 400 Å CoCrPt permanent magnets, 50 Å Al 2 O 3  current guides, 100 Å Cr/1000 Å Ta overlaid current contacts, a lead-separation distance X LS  of 0.2 μm, and a variable lead-insulator offset X LI  in the range of 0.5 μm to 0.2 μm. With lead insulator offset X LI  equal to 0.2 μm in this embodiment, the current guides do not overlay the MR sensor. 
     FIG. 5 is a graph of current distribution curves produced by transducing heads with varying lead insulator offsets. Current distribution curve  90  was produced by a nominal transducing head having no current guides, current distribution curve  92  was produced by a transducing head having a lead-insulator offset X LI  of 0.18 μm, current distribution curve  94  was produced by a transducing head having a lead-insulator offset X LI  of 0.1 μm, and current distribution curve  96  was produced by a transducing head having a lead insulator offset X LI  of 0.05 μm. As shown in FIG. 5, a smaller lead insulator offset X LI  results in a tighter current distribution curve. The tighter the current distribution curve, the less side-reading occurs and the narrower the read width. 
     FIG. 6 is a graph illustrating decay range of a transducing head&#39;s current distribution curve versus the lead-insulator offset X LI  of the transducing heads. Decay range for a particular distribution curve is defined as the difference between a nominal reader width of 0.2 μm and the cross-track position of the 10% value of the current distribution curve. As shown in FIG. 6, the decay range equals 0.16 μm when the lead-insulator offset X LI  equals 0.2 μm, and equals 0.055 μm when the lead-insulator offset X LI  equals 0.05 μm. Accordingly, the decay range is directly related to the lead-insulator offset X LI . 
     FIG. 7 is a graph illustrating contact resistance of a MR sensor of a transducing head versus the lead-insulator offset X LI  of the transducing heads. The contact resistance of a MR sensor is affected by the surface area of the junction between the current contacts and the MR sensor. If the surface area of that junction becomes too small, the contact resistance of the MR sensor rapidly increases, negatively affecting the performance of the MR sensor. As FIG. 7 illustrates, for values of the lead-insulator offset X LI  less than 0.1 μm, the contact resistance of the MR sensor rapidly increases; whereas, for values of the lead-insulator offset X LI  greater than 0.1 μm, there is relatively little change in the contact resistance of the MR sensor. A significant increase in resistance of the MR sensor may not only result in increased head amplitude values, it may contribute to thermal reliability problems with the sensor. 
     As illustrated in FIGS. 5-7, there is a trade-off in selecting a value of lead-insulator offset X LI ,. As X LI  decreases, the current distribution curve becomes more desirable, but the contact resistance of the MR sensor undesirably increases. Conversely, as the lead-insulator offset X LI  increases, the current distribution becomes less desirable, but the contact resistance of the MR sensor remains more stable. 
     In conclusion, the present invention is a novel current guide layer positioned between the biasing elements and the overlaid current contacts of a transducing head. The use of this novel current guide layers minimizes the amount of sense current leaked into the MR sensor via the biasing elements, resulting in a tighter current distribution curve and a narrower reader width. 
     Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.