Abstract:
A magnetic sensing device includes a first electrode, a second electrode, a first magnetic shield, a second magnetic shield, and a sensor. The first magnetic shield forms at least a portion of the first electrode. The second magnetic shield includes a first region that forms at least a portion of the first electrode and a second region that forms at least a portion of the second electrode. The sensor is positioned between the first and second magnetic shields and is electrically connected in series between the first and second electrodes.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates generally to the field of magnetic data storage and retrieval systems. In particular, the present invention relates to a magnetic read head having a shield/electrode structure in which the magnetic and electrical functions thereof have been separated from one another.  
         [0002]     In a magnetic data storage and retrieval system, a magnetic recording head typically includes a reader portion, or read head, having a magnetoresistive (MR) sensor for retrieving magnetically encoded information stored on a magnetic medium, such as a magnetic disc. To retrieve information from a track of the magnetic disc, the read head is positioned over that track as the disc is rotated at a high speed. This rotation causes the read head to be supported over an air bearing surface (ABS) of the magnetic disc by a thin cushion of air. To ensure that the MR sensor reads only the information that is stored directly beneath it on a specific track of the magnetic disc, first and second magnetic shields are placed on either side of the MR sensor.  
         [0003]     During a read operation, magnetic flux from the surface of the disc causes rotation of the magnetization vector of a sensing layer or layers of the MR sensor, which in turn causes a change in electrical resistivity of the MR sensor. The change in resistivity of the MR sensor can be detected by passing a current through the MR sensor and measuring a voltage across the MR sensor. Depending on the geometry of the device, the sense current may be passed in the plane (CIP) of the layers of the device or perpendicular to the plane (CPP) of the layers of the device.  
         [0004]     To provide current to the MR sensor of a CPP read head, the first and second magnetic shields conventionally perform double duty as both magnetic shields and electrodes. Optimization of the various electrical and magnetic functions required of the magnetic shields for a CPP MR sensor requires conflicting demands on their physical structure. There is thus a need for a magnetic shield/electrode structure for a MR sensor of a CPP read head in which both the magnetic and electrical functions of the CPP read head can be optimized.  
       BRIEF SUMMARY OF THE INVENTION  
       [0005]     A magnetic sensing device in accord with the present invention includes a first electrode, a second electrode, a first magnetic shield, a second magnetic shield, and a sensor. The first magnetic shield forms at least a portion of the first electrode. The second magnetic shield includes a first region that forms at least a portion of the first electrode and a second region that forms at least a portion of the second electrode. The sensor is positioned between the first and second magnetic shields and is electrically connected in series between the first and second electrodes. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]      FIG. 1  is a cross-section view of a magnetic read head and a magnetic disc taken along a plane substantially normal to an air bearing surface (ABS) of the magnetic read head.  
         [0007]      FIG. 2A  is an exploded perspective view,  FIG. 2B  is a medium-facing view,  FIG. 2C  is a top view, and  FIG. 2D  is a side view of a magnetic shield/electrode structure in accord with a first embodiment of the present invention for a CPP MR sensor.  
         [0008]      FIG. 3A  is an exploded perspective view,  FIG. 3B  is a medium-facing view,  FIG. 3C  is a top view, and  FIG. 3D  is a side view of a magnetic shield/electrode structure in accord with a second embodiment of the present invention for a CPP MR sensor.  
         [0009]      FIG. 4A  is an exploded perspective view,  FIG. 4B  is a medium-facing view,  FIG. 4C  is a top view, and  FIG. 4D  is a side view of a magnetic shield/electrode structure in accord with a third embodiment of the present invention for a CPP MR sensor.  
         [0010]      FIG. 5A  is an exploded perspective view,  FIG. 5B  is a medium-facing view,  FIG. 5C  is a top view, and  FIG. 5D  is a side view of a magnetic shield/electrode structure in accord with a fourth embodiment of the present invention for a CPP MR sensor.  
         [0011]      FIG. 6  is a top view of a prior art magnetic shield/electrode structure for a CPP MR sensor.  
         [0012]      FIG. 7  is a top view of a magnetic shield/electrode structure in accord with the present invention for a CPP MR sensor. 
     
    
     DETAILED DESCRIPTION  
       [0013]      FIG. 1  is a cross-sectional view of magnetic read head  10  and magnetic disc  11  taken along a plane substantially normal to an air bearing surface (ABS) of magnetic read head  10 . Magnetic disc  11  may be either a perpendicular or longitudinal recording media, with magnetic read head  10  corresponding thereto. Magnetic read head  10  is carried on slider body  12  and separated therefrom by gap  14 . Magnetic read head  10  includes first magnetic shield  16 , current-perpendicular-to-plane (CPP) magnetoresistive (MR) sensor  18 , insulating layers  20 , and second magnetic shield  22 . CPP MR sensor  18  and insulating layers  20  are positioned between bottom and top shields  16  and  22 , with MR sensor  18  being adjacent the ABS of magnetic head  10 .  
         [0014]     To provide current to CPP MR sensor  18 , first and second magnetic shields  16  and  22  conventionally perform double duty as both magnetic shields and electrodes. Thus, first and second magnetic shields  16  and  22  are forced to serve the dual functions of providing electrical connection to MR sensor  18  and providing magnetic shielding from stray magnetic fields. Design goals for optimizing these two functions include the minimization of: (1) stray field sensitivity, (2) the likelihood of MR sensor short circuits at the ABS, (3) shield-to-shield (technically, electrode-to-electrode) capacitance, and (4) capacitive pickup of common mode noise. As detailed below, it is near impossible to fully optimize all four of these goals in designing prior art magnetic shield/electrode structure  50 .  
         [0015]     I. Stray Field Sensitivity  
         [0016]     First and second magnetic shields  16  and  22  of magnetic head  10  ideally permit remanent magnetic fields from a selected track of magnetic media  11  to reach CPP MR sensor  18 , while preventing stray magnetic fields originating elsewhere from reaching MR sensor  18 . Consequences of MR sensor  18  picking up stray magnetic fields is alteration of the sensor&#39;s bias point, the addition of noise to the signal sensed from the selected track, a decreased signal-to-noise ratio, and a greater probability that errors will occur in reading back the data recorded on the selected track. Experimental investigations have shown that magnetic shields  16  and  22  having too narrow a cross-track direction width have poor stray field rejection. It has further been shown that shields  16  and  22  will better reject stray fields if their edges (or at least the ABS and a back edge opposite the ABS) are coincident with each other. By coincident edges, it is meant that corresponding edges of the shields lie in the same plane as each other. Thus, to improve stray field rejection, first and second magnetic shields  16  and  22  are preferably wide shields having coincident edges at least at the ABS and the back edge.  
         [0017]     II. MR Sensor Short Circuits  
         [0018]     Slider body  12  upon which read head  10  is disposed is maintained in close proximity to disc  11 , with first and second magnetic shields  16  and  22  being the closest held elements to magnetic disc  11 . As a result, any surface imperfection on disc  11 , such as an asperity, can result in a momentary contact between read head  10  and spinning disc  11 . This contact can damage first and second magnetic shields  16  and  22 , resulting in a metallic smear from one to the other. Further, this resultant smear may have an electrical resistance low enough to effectively short circuit MR sensor  18 , thus rendering read head  10  inoperable. The probability of a damaging event depends on many factors, but is clearly proportional to a cross-track width of first and second magnetic shields  16  and  22 . Thus, reducing the probability of a short circuit of MR sensor  18  at the ABS requires narrow shields.  
         [0019]     III. Electrode-To-Electrode Capacitance  
         [0020]     Because first and second magnetic shields  16  and  22  of CPP MR sensor  18  serve as the electrical connections to MR sensor  18 , they essentially form a capacitor. In an electrical circuit representation of read head  10 , this electrode-to-electrode capacitor appears in parallel with a resistance of MR sensor  18 , thus limiting the bandwidth of MR sensor  18  at high frequencies. At a given disc rotational velocity, the bandwidth of MR sensor  18  imposes a substantial limit on the number of magnetic transitions allowed per track length, and consequently, on the areal data storage density of magnetic disc  11 . To improve the high frequency response of MR sensor  18 , it is important that this electrode-to-electrode capacitance be minimized, which in turn requires that an overlapping area of first and second magnetic shields  16  and  22  be minimized.  
         [0021]     IV. Capacitive Pickup of Common Mode Noise  
         [0022]     Not only do first and second magnetic shields (electrodes)  16  and  22  form a capacitor between each other, but each also forms a capacitor between itself and slider body  12  upon which read head  10  is formed. The capacitance of each electrode-to-slider body capacitor is determined mostly by the area of a slider body-facing surface of the shield (electrode) and the spacing between the two. A further capacitance is added between each of shields (electrode)  16  and  22  and magnetic disc  11 , with the capacitance of each being primarily dependent upon the area on the ABS of the shield (electrode).  
         [0023]     In the electrical circuit representative of read head  10 , MR sensor  18  appears in parallel with the capacitor formed between first and second magnetic shields (electrodes)  16  and  22 . The additional capacitances introduced by each of shields (electrodes)  16  and  22  appear at opposite ends of MR sensor  18  between MR sensor  18  and a ground terminal. A preamplifier (not shown) configured to differentially amplify a voltage across MR sensor  18  rejects any interference that appears simultaneously as voltages on both shields (electrodes)  16  and  22  (i.e., “common mode” noise). However, if the two electrode-to-slider body (and electrode-to-magnetic disc) capacitances are not equal, common mode noise will be capacitively coupled unequally to the inputs of the preamplifier, appearing as differential mode noise and degrading the signal-to-noise ratio of the MR sensor signal.  
         [0024]     In a conventional configuration of read head  10 , one of first and second shields (electrodes)  16  and  22  is positioned much closer to slider body  12  than the other, with the result being that the two electrode-to-slider body capacitances are unequal. One method for balancing these electrode-to-slider body capacitances is by adding a balancing capacitor electrically coupled between one of shields (electrodes)  16  and  22  and a slider “bond pad” used for external connection to a power source. But, this added capacitance also increases the electrode-to-electrode capacitance caused between shields (electrodes)  16  and  22 . Thus, the addition of a balance capacitor to minimize electrode-to-slider body capacitance (and improve rejection of common mode noise) extracts a penalty in the high frequency response of MR sensor  18 .  
         [0025]     A second way to equalize the electrode-to-slider body capacitances is to vary a size of first and second magnetic shields (electrodes)  16  and  22  such that the first shield (electrode)  16  closest to slider body  12  is smaller than second shield (electrode)  22  farthest from the slider body  12 . Thus, reducing electrode-to-slider body capacitance mismatch to improve common mode rejection requires first and second shield (electrodes)  16  and  22  to have non-coincident edges.  
         [0026]     Another contributor to the capacitive pickup of common mode noise is the mismatched electrode-to-disc capacitances of first and second magnetic shield  16  and  22 . This mismatch is caused by differences in the areas on the ABS of first and second shields (electrodes)  16  and  22   s . Thus, reducing electrode-to-disc capacitive mismatch requires that the ABS cross-sectional areas of shields (electrodes)  16  and  22  to be equal.  
         [0027]     V. Additional Factors  
         [0028]     To enhance their shielding performance, first and second magnetic shields  16  and  22  preferably each have a width (measured in the plane of the ABS) to depth (measured normal to the ABS) ratio sufficient to provide a shape anisotropy in shields  16  and  22  that makes it difficult to saturate the magnetization of shields  16  and  22 .  
         [0029]     To further enhance the shielding performance of shields  16  and  22 , domain wall movement near the areas of shields  16  and  22  adjacent MR sensor  18  is preferably avoided. The ideal width-to-height ratio to prevent such domain wall movement is dependent upon various material characteristics including anisotropy, magnetic moment, and film thicknesses. However, it has been found that, for any material, the ideal height of shields  16  and  22  should equal the height of one or two domain periods for any feature width. This can be determined by calculation or by empirical study of domains on rectangular features of varying width and height. Thus, shields  1   b  and  22  are also preferably short in the direction perpendicular to the ABS.  
         [0030]     In sum, minimization of stray field sensitivity requires shields  16  and  22  to be wide and short and to have coincident edges (at least at the ABS and back edge), minimization of the likelihood of shorts of MR sensor  18  requires narrow shields  16  and  22 , minimization of electrode-to-electrode capacitance requires shields  16  and  22  to have a small area, and minimization of capacitive pickup of common mode noise requires shields  16  and  22  to have mismatched areas. With prior art designs, these requirements contradict each other, thus preventing optimization of all four design goals of first and second magnetic shields  16  and  22 .  
         [0031]     The present invention introduces a novel design for a magnetic shield/electrode structure that allows all four design goals specified above to be simultaneously optimized. Four embodiments of the present invention are described herein.  FIGS. 2A, 2B ,  2 C, and  2 D are views of magnetic shield/electrode structure  60  in accord with a first embodiment of the present invention for CPP MR sensor  62 . In particular,  FIG. 2A  is an exploded perspective view,  FIG. 2B  is a medium-facing view,  FIG. 2C  is a top view, and  FIG. 2D  is a side view of structure  60 . In these figures, insulation and spacing layers have been removed for clarity.  
         [0032]     Magnetic shield/electrode structure  60  includes fragments  64 ,  66 ,  68 , and  70 ; gaps  72  and  74 , and electrical contacts  76  and  78 , all of which come together in various combinations to form the magnetic shields and electrodes needed for MR sensor  62 . In particular, coplanar fragments  64  and  66 , which are spaced apart by gap  72 , are magnetostatically coupled to each to form top shield  64 / 66 . Similarly, coplanar fragments  68  and  70 , which are spaced apart by gap  74 , are magnetostatically coupled to each other to form bottom shield  68 / 70 . Top shield  64 / 66  and bottom shield  68 / 70 , which are separated from one another by spacing layers (not shown) to prevent exchange coupling, are positioned on opposite sides of MR sensor  62  to shield MR sensor  62  from magnetic fields. MR sensor  62  is positioned adjacent or near medium-facing surface  80  of structure  60  for receipt of magnetic fields from a medium (not shown), such as a magnetic disc, spaced a short distance from medium-facing surface  80 .  
         [0033]     Fragments  64  and  68  are electrically coupled to one another via contact  76  to form top electrode  64 / 68 . Similarly, fragments  66  and  70  are electrically coupled to each other via contact  78  to form bottom electrode  66 / 70 . Although not shown in the figures, contacts  76  and  78  extend away from MR sensor  62  to electrically connect electrodes  64 / 68  and  66 / 70  to an external power source in a conventional manner. Top electrode  64 / 68  and bottom electrode  66 / 70 , which are otherwise electrically insulated from one another by gaps  72  and  74 , supply current to MR sensor  62  in a direction perpendicular to a plurality of layers of MR sensor  62 . Fragments  64 ,  66 ,  68 , and  70  are shaped such that MR sensor  62  is physically between fragments  64  of top electrode  64 / 68  and fragment  70  of bottom electrode  66 / 70 . In this way, current directly enters and leaves MR sensor  62  through fragments  64  and  70 .  
         [0034]     Fragments  64 ,  66 ,  68 , and  70  are each preferably formed of an electrically-conductive material having high magnetic permeability and low coercivity. Gaps  72  and  74  are preferably formed of electrically-insulating material. Gaps  72  and  74  preferably have a width large enough to electrically decouple the fragments on either side thereof, but small enough to allow for the magnetostatic coupling of the fragments. Accordingly, this width is specific to the materials and dimensions used throughout magnetic shield/electrode structure  60 . In most embodiments, gaps  72  and  74  will preferably have a width less than about 20 micrometers, but greater than zero. Contacts  76  and  78  are preferably formed of a non-magnetic, electrically-conductive material.  
         [0035]     Magnetic shield/electrode structure  60  in accord with the present invention separates its magnetic and electrical properties, thereby allowing for optimization the design goals of minimizing: (1) stray field sensitivity, (2) the likelihood of MR sensor short circuits at the ABS, (3) electrode-to-electrode capacitance, and (4) shield capacitive pickup of common mode noise.  
         [0036]     I. Stray Field Sensitivity  
         [0037]     As discussed above, to minimize stray field sensitivity of MR sensor  62 , top shield  64 / 66  and bottom shield  68 / 70  are preferably wide, but short, shields having coincident edges (at least at medium-facing surface  80  and back surface  86  of structure  60  opposite medium facing surface  80 ). Here, fragments  64  and  66  behave magnetically as a single wide feature, namely top shield  64 / 66 , and fragments  68  and  70  similarly behave magnetically as a single wide feature, namely bottom shield  68 / 70 . Additionally, external edges  82  of top shield  64 / 66  are coincident with (or are coplanar with) external edges  84  of bottom shield  68 / 70 . Thus, the design of magnetic shield/electrode  60  satisfies the first design goal, and allows for MR sensor  62  to have improved stray field sensitivity.  
         [0038]     II. MR Sensor Short Circuits  
         [0039]     Top shield  64 / 66  and bottom shield  68 / 70  are preferably narrow at medium-facing surface  80  of structure  60  to minimize the likelihood of a smear between shields  64 / 66  and  68 / 70  caused by contact with the medium spaced a short distance from medium-facing surface  80 . Structure  60  accomplishes this goal. Because fragment  64  of top shield  64 / 66  and fragment  68  of bottom shield  68 / 70  are electrically coupled to one another, a smear that occurs between fragments  64  and  68  will not short circuit MR sensor  62 . Similarly, no fear exists of a smear between fragments  66  and  70  short circuiting MR sensor  62 . A small risk exists of a smear at skew between fragments  64  and  66  and between fragments  68  and  70 . However, gaps  72  and  74  may be made wide enough to minimize this risk. Thus, the primary risk of a short circuit exists between fragment  64  of top shield  64 / 66  and fragment  70  of bottom shield  68 / 70 . And then, this risk resides only in the area where there two fragments overlap one another, which need be only as wide as a width of MR sensor  62 . This overlap is substantially more narrow than the width required of top shield  64 / 66  and bottom shield  68 / 70  to minimize stray field sensitivity.  
         [0040]     III. Electrode-To-Electrode Capacitance  
         [0041]     To improve the high frequency response of MR sensor  62 , the electrode-to-electrode capacitance between top shield  64 / 66  and bottom shield  68 / 70  is preferably minimized. This goal has been accomplished with magnetic shield/electrode structure  60 . The electrode-to-electrode capacitance is proportional to the area of overlap between top electrode  64 / 68  and bottom electrode  66 / 70 , which here is very small in comparison to the area of overlap between top shield  64 / 66  and bottom shield  68 / 70 .  
         [0042]     Gap  72  of top shield  64 / 66  extends from medium-facing surface  80  towards back surface  86  of structure  60  opposite medium-facing surface  80  at an angle, such that fragment  64  is wider at medium-facing surface  80  than it is at back surface  86  while fragment  66  is narrower at medium-facing surface  80  than it is at back surface  86 . Likewise, gap  74  of bottom shield  68 / 70  extends from medium-facing surface  80  toward back surface  86  at an angle, such that fragment  84  is narrower at medium-facing surface  80  than at back surface  86 , while fragment  84  is wider at medium-facing surface  80  than at back surface  86 . Thus, the only overlap between top electrode  64 / 68  and bottom electrode  66 / 70  is a small wedge between fragments  64  and  70 .  
         [0043]     IV. Capacitive Pickup of Common Mode Noise  
         [0044]     To minimize capacitive pickup of common-mode noise, which degrades the signal-to-noise ratio of MR sensor  62 , any mismatches in the capacitances between each of top electrode  64 / 68  and bottom electrode  66 / 70  and the substrate (or slider body) upon which shield/electrode structure  60  is formed and in the capacitances between each of top electrode  64 / 68  and bottom electrode  66 / 70  and the medium likewise must be minimized. Magnetic shield/electrode  60  design allows for this goal to be met.  
         [0045]     In magnetic shield/electrode structure  60 , the two electrode-to-substrate capacitances can be equalized by equalizing both the areas of electrodes  64 / 68  and  66 / 70  and their spacing to the substrate. Here, the total area of fragments  64  and  68  of top electrode  64 / 68  can be substantially matched to the total area of fragments  66  and  70  of lower electrode  66 / 70 . For instance, the area of fragment  64  can be matched to the area of fragment  70 , and the area of fragment  66  can be matched to the area of fragment  68 . Likewise, the spacing can be equalized between each of electrodes  64 / 68  and electrodes  66 / 70  and the substrate. The two electrode-to-medium capacitances can be equalized by equalizing the areas of top electrode  64 / 68  and bottom electrode  66 / 70  at medium-facing surface  80 . Thus, magnetic shield/electrode  60  design allows for minimization of capacitive pickup of common mode noise.  
         [0046]     In sum, magnetic shield/electrode  60  allows for all four of the shield/electrode design goals listed above to be met by separating the electrical and magnetic functions thereof—thus enabling each to be optimized separately. The particular configuration of magnetic shield/electrode  60  is intended as exemplary of the invention only, and many alternative configurations are possible. Further, the present invention contemplates that some of the design goals may be sacrificed for other reasons.  
         [0047]      FIGS. 3A, 3B ,  3 C, and  3 D illustrate magnetic shield/electrode structure  90  in accord with a second embodiment of the present invention for CPP MR sensor  92 .  FIG. 3A  is an exploded perspective view,  FIG. 3B  is a medium-facing view,  FIG. 3C  is a top view, and  FIG. 3D  is a side view of magnetic shield/electrode structure  90 . In these figures, insulation and spacing layers have been removed for clarity.  
         [0048]     Magnetic shield/electrode structure  90  includes fragments  94 ,  96 ,  98 , and  100 , gaps  102  and  104 , and electrical contacts  106  and  108 , all of which come together in various combinations to form the magnetic shields and electrodes needed for MR sensor  92 . In particular, fragment  94  forms top shield  94 , while coplanar fragments  96 ,  98 , and  100 , which are spaced apart by gaps  102  and  104 , are magnetostatically coupled to each other to form bottom shield  96 / 98 / 100 . Top and bottom shields  94  and  96 / 98 / 100 , which are separated from one another by spacing layers (not shown) to prevent exchange coupling, are positioned on opposite sides of MR sensor  92  to shield MR sensor  92  from magnetic fields. MR sensor  92  is positioned adjacent or near medium-facing surface  110  of structure  90  for receipt of magnetic fields from a medium (not shown), such as a magnetic disc, spaced a short distance from medium-facing surface  110 .  
         [0049]     Fragments  94 ,  96 , and  100  are electrically coupled to one another via contacts  106  and  108  to form top electrode  96 / 94 / 100 . Fragment  98  simply forms bottom electrode  98 . Although not shown in the figures, contacts  106  and  108  extend away from MR sensor  92  to electrically connect top electrode  96 / 94 / 100  to an external power source in a conventional manner. Bottom electrode  98  is similarly connected to the external power source. Top electrode  96 / 94 / 100  and bottom electrode  98 , which are otherwise electrically-insulated from one another by gaps  102  and  104 , supply current to MR sensor  92  in a direction perpendicular to a plurality of layers of MR sensor  92 . Fragments  94 ,  96 ,  98 , and  100  are shaped such that MR sensor  92  is physically between fragments  94  of top electrode  96 / 94 / 100  and bottom electrode  98 . In this way, current directly enters and leaves MR sensor  92  through fragments  94  and  98 .  
         [0050]     Fragments  94 ,  96 ,  98 , and  100  are each preferably formed of an electrically-conductive material having high magnetic permeability and low coercivity. Gaps  102  and  104  are preferably formed of electrically-insulating material. Gaps  102  and  104  preferably have a width large enough to electrically decouple the fragments on either side thereof, but small enough to allow for the magnetostatic coupling of the fragments. Accordingly, this width is specific to the materials and dimensions used throughout magnetic shield/electrode structure  90 . In most embodiments, gaps  102  and  104  will preferably have a width less than about 20 micrometers, but greater than zero. Contacts  106  and  108  are preferably formed of a nonmagnetic, electrically-conductive material.  
         [0051]     Magnetic shield/electrode structure  90  meets most of the above-listed design goals. Top shield  94  and bottom shield  96 / 98 / 100  are wide shields having coincident edges (at least at medium-facing surface  110  and a back surface opposite surface  110 ) to reduce stray field sensitivity. The risk of short circuits is limited to a relatively short width between fragments  94  and  104 . The electrode-to-electrode capacitance in structure  90  is greater than the electrode-to-electrode capacitance in structure  60 , but still less than in prior art designs. Electrode-to-disc capacitance can be partially equalized by top electrode  96 / 94 / 100  being thinner than bottom electrode  98 . However, the electrode-to-substrate capacitance of this embodiment suffers over that of magnetic shield/electrode structure  60 . This increase in capacitance common mode pickup is the result of a simpler top shield design. Certain manufacturing methods make it difficult to form a gap in the top shield of a magnetic head. In those applications, this solution may be preferred as it still provides many benefits over prior art designs.  
         [0052]      FIGS. 4A, 4B ,  4 C, and  4 D illustrate magnetic shield/electrode structure  120  in accord with a third embodiment of the present invention. Because of the similarity in shield/electrode structures  90  and  120 , common elements between the two are like numbered.  FIG. 4A  is an exploded perspective view,  FIG. 4B  is a medium-facing view,  FIG. 4C  is a top view, and  FIG. 4D  is a side view of magnetic shield/electrode structure  120  in accord with the present invention for CPP MR sensor  92 .  
         [0053]     Structure  120  introduces a minor modification of magnetic shield/electrode structure  90  to reduce the capacitive common mode pickup at the expense of a slight gain in differential capacitance. Specifically, structure  120  adds dummy element  122  having segments  124  and  126  and electrical contact  128  positioned therebetween. Segment  124  is coplanar with segment  94 , while segment  126  is coplanar with segments  96 ,  98 , and  100 . Dummy element  122  is electrically coupled to bottom electrode  98 , but magnetically insulated from top shield  94  and bottom shield  96 / 98 / 100 .  
         [0054]     The area of dummy element  122  adds to the capacitance of lower electrode  98 , making it possible to accurately balance the electrode-to-substrate capacitances. Additionally, Because of the additional area at media-facing surface  110 , a thickness of top shield  94  can be increased without significantly unbalancing the electrode-to-disk capacitances.  
         [0055]      FIGS. 5A, 5B ,  5 C, and  5 D present a minor modification of magnetic shield/electrode structure  90 . Because of the similarities in shield/electrode structures  90  and  120 , common elements between the two are like numbered.  FIG. 5A  is an exploded perspective view,  FIG. 5B  is a medium-facing view,  FIG. 5C  is a top view, and  FIG. 5D  is a side view of magnetic shield/electrode structure  130  in accord with a fourth embodiment of the present invention for MR sensor  92 .  
         [0056]     Magnetic shield/electrode structure  130  is nearly identical to structure  90 , with the change being the geometric shape of segments  96 ,  98 , and  100 . In this change, the width of segment  98  of structure  130  is reduced over that in structure  90 , while the widths of segment  96  and  100  of structure  130  are increased over that of structure  90 . This modification will further reduce the likelihood of short circuits of MR sensor  92  caused by smearing.  
       Experiment Results  
       [0057]      FIG. 6  is a top view of prior art magnetic shield/electrode structure  140  for CPP MR sensor  142 . Structure  140  includes top shield  144 , top shield contact  146 , bottom shield  148 , and bottom shield contact  150 . MR sensor  142  is positioned between top and bottom shields  144  and  148  adjacent a media bearing surface structure  140 . Top shield contact  146  electrically couples top shield  144  to an external power source. Likewise, bottom shield contact  150  electrically couples bottom shield  148  to an external power source. Top and bottom shields  144  and  148  double as electrodes for MR sensor  142 , and thus, are electrically insulated from one another, except through MR sensor  142 .  
         [0058]      FIG. 7  is a top view of magnetic shield/electrode structure  160  in accord with the present invention for CPP MR sensor  162 . Structure  160  includes top shield  164 ; top shield contact  166 ; first, second, and third bottom shield fragments  168 ,  170 , and  172 ; and first and second bottom shield contacts  174  and  176 . MR sensor  162  is positioned between top shield  164  and second bottom shield fragment  170  adjacent a media facing surface of structure  160 . Top shield contact  166  electrically couples top shield  164  to an external power source, thereby forming top electrode  164 . First, second, and third bottom shield fragments  168 ,  170 , and  172  are coplanarly positioned with second bottom shield fragment  170  positioned between fragments  168  and  172 . First and second bottom shield contacts  174  and  176  electrically couples top shield  164  to a respective one of first and third bottom shield fragments  168  and  172 , thereby forming top electrode  168 / 164 / 172 . First bottom shield contact  174  further serves to couple top electrode  168 / 164 / 172  to the external power source. Top electrode  164  and bottom electrode  168 / 164 / 172  are electrically insulated from one another, except through MR sensor  162 .  
         [0059]     Performance of prior art magnetic shield/electrode structure  140  of  FIG. 6  was experimentally compared to the performance of magnetic shield/electrode structure  160  of  FIG. 7  in accord with the present invention. In the experiment, structures  140  and  160  had equal widths. Because stray field sensitivity is more pronounced in perpendicular recording performance structures  146  and  160  were designed for reading from perpendicular recording medium. A test of reader sensitivity to externally applied fields shows that structures  140  and  160  had equal immunity to stray fields applied to an underlayer of the perpendicular recording medium. The experimental results further show that the electrode-to-electrode and electrode-to-substrate capacitances in structure  160  were substantially lower than those in structure  140 . Little difference was seen in the electrode-to-medium capacitances in structures  140  and  160 . Further, an overlap of between top electrode  168 / 164 / 172  and bottom electrode  170  is significantly less than the overlap between top and bottom electrodes  144  and  148  of structure  140 ; thus, the likelihood of a MR sensor short circuit will be less in structure  160  than in structure  140 .  
         [0060]     Thus, by separating the electrical and magnetic properties of a magnetic shield/electrode structure, it becomes possible to simultaneously optimize all four design goals for magnetic shield/electrode structures for use with a sensor, including a CPP MR sensor.  
         [0061]     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.