Abstract:
An onboard electronic lapping guide for lapping a magneto-resistive head having a magneto-resistive sensor element disposed for electrical communication with a pair of sensor electrical leads. The lapping guide includes an electronic lapping guide resistive element disposed for electrical communication with the sensor electrical leads. The resistive element has a predetermined height in a lapping direction and is adapted to produce an electrical resistance in the presence of a lapping current that increases as said resistive element height is reduced during lapping. A lapping method and a method of forming the onboard electronic lapping guide are also disclosed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to magnetoresistive and giant magnetoresistive sensors for reading magnetically-recorded information from data storage media, and particularly to methods for lapping such heads during manufacturing.  
           [0003]    2. Description of the Prior Art  
           [0004]    By way of background, magnetic media-based DASD systems, such as disk drives, use magnetoresistive and giant magnetoresistive sensors (hereinafter collectively referred to as “MR” sensors) to read data recorded on the storage media. An MR sensor is a magneto-electrical device that produces a variable voltage output in response to magnetic field fluctuations emanating from the recorded magnetic domains that represent stored information. The MR sensors used in disk drives are commonly integrated with inductive write heads to form merged read/write heads. Such heads are conventionally formed by building thin film layer structures on a wafer substrate. The wafer substrate is then divided into multiple slider bars that each carry a row of multiple (e.g., 60) read/write heads. Processing of the slider bars into finished read/write heads requires lapping along one longitudinal edge of the slider bar to precisely define an air bearing surface (ABS) of each read/write head, followed by division of the slider bar into individual heads.  
           [0005]    Slider bar lapping is typically performed as a wet grinding process in which material is removed to define a read head parameter known as “stripe height” for each of the read/write heads on the slider bar. Stripe height is the distance from the ABS to the back of each MR sensor. It is a parameter that greatly influences sensor responsiveness to recorded magnetic domains, and thus must be carefully controlled. The conventional technique used to monitor slider bar lapping is by way of one or more electronic lapping guides (ELGs) formed in kerf areas of the slider bar. Each ELG includes an electrically conductive sensor structure whose ends are connected to electrical leads that carry current from a control circuit. Lapping is controlled by sensing resistance increases in the ELG as sensor material is removed by the grinding process. The ELG resistance increases are used to determine changes in MR sensor stripe height so that the lapping process can be terminated at the required stripe height.  
           [0006]    It is to improvements in the ELG art that the present invention is directed. In particular, the invention addresses the need for increased lapping accuracy and reduced variability in final stripe height from one slider to another during manufacturing.  
         SUMMARY OF THE INVENTION  
         [0007]    The foregoing problems are solved and an advance in the art is obtained by an onboard electronic lapping guide for lapping a magneto-resistive head having a magneto-resistive sensor element connected between a pair of sensor electrical leads. The lapping guide includes an electronic lapping guide resistive element that is also connected between the sensor electrical leads so as to form part of the in-process head structure. The lapping guide resistive element has a predetermined height in a lapping direction and is adapted to produce an electrical resistance in the presence of a lapping current that increases as the resistive element height is reduced during lapping. The lapping process ultimately consumes the ELG and produces a finished MR sensor.  
           [0008]    In preferred embodiments of the invention, the resistive element is disposed between the sensor element and a portion of the head that will receive a lapping tool, and comprises two resistive elements providing a coarse lapping guide and a fine lapping guide. The coarse lapping guide has a greater width and height than the fine lapping guide. The coarse lapping guide is separated from the fine lapping guide by a gap that is of sufficient height to support a lapping clean-up phase. The fine lapping guide may have a height corresponding to a height of the sensor element, and has a width corresponding to a track width of the sensor element. The sensor electrical leads can be shaped to define the width of the fine lapping guide and the track width of the sensor element, and to further define a width of the coarse lapping guide that is larger than the fine lapping guide width and the sensor element track width. The resistive element and the sensor element may comprise identical thin film layers.  
           [0009]    The invention further contemplates a lapping method and a method of forming the onboard electronic lapping guide. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0010]    The foregoing and other features and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying Drawing, in which:  
         [0011]    [0011]FIG. 1 is a perspective view showing a disk drive incorporating an MR read head constructed in accordance with the invention;  
         [0012]    [0012]FIG. 2 is a side elevational view showing the interior of the disk drive of FIG. 1;  
         [0013]    [0013]FIG. 3 is a plan view of the disk drive of FIG. 1;  
         [0014]    [0014]FIG. 4 is a plan view of an integrated read/write transducer for use in the disk drive of FIG. 1;  
         [0015]    [0015]FIG. 5 is a side elevational view of the transducer of FIG. 4;  
         [0016]    [0016]FIG. 6 is a cross-sectional view taken along line  6 - 6  in FIG. 4;  
         [0017]    [0017]FIG. 7 is an ABS view of the transducer of FIG. 3 taken in the direction of arrows  7 - 7  in FIG. 6;  
         [0018]    [0018]FIG. 8 is a cross-sectional view showing an exemplary MR sensor layer structure following cap layer deposition and prior to formation of an onboard lapping guide in accordance with the invention;  
         [0019]    [0019]FIG. 9 is a plan view showing a track width-defining, photoresist etch mask formed over the structure of FIG. 8;  
         [0020]    [0020]FIG. 10 is a cross-sectional view taken along line  10 - 10  in FIG. 9;  
         [0021]    [0021]FIG. 11 is a cross-sectional view as in FIG. 10 following a track width defining etching step;  
         [0022]    [0022]FIG. 12 is a cross-sectional view as in FIG. 10 following the deposition of sensor lead material in the etched areas of FIG. 11;  
         [0023]    [0023]FIG. 13 is a plan view showing a stripe height-defining, photoresist etch mask formed over the structure of FIG. 12;  
         [0024]    [0024]FIG. 14 is a plan view showing an MR sensor structure with an onboard ELG in accordance with the invention following etching to remove sensor material outside the stripe height-defining, photoresist mask of FIG. 13;  
         [0025]    [0025]FIG. 15 is a plan view of the structure of FIG. 14 following a first coarse lapping phase;  
         [0026]    [0026]FIG. 16 is a plan view of the structure of FIG. 14 following a second clean-up lapping phase;  
         [0027]    [0027]FIG. 17 is a plan view of the structure of FIG. 14 following a third rate-determining lapping phase;  
         [0028]    [0028]FIG. 18 is a plan view of the structure of FIG. 14 following a fourth fine trim lapping phase.  
         [0029]    [0029]FIG. 19 a  is a first graph showing change in ELG resistance versus stripe material removal when lapping the sensor structure of FIG. 14 using its onboard ELG;  
         [0030]    [0030]FIG. 19 b  is a second graph showing the first derivative of the curve of FIG. 19 a ; and  
         [0031]    [0031]FIG. 19 c  is a third graph showing the second derivative of the curve of FIG. 19 a;   
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0032]    Turning now to the figures (which are not necessarily to scale), wherein like reference numerals represent like elements in all of the several views, FIGS.  1 - 3  illustrate an exemplary disk drive  2  that incorporates an MR read head constructed in accordance with the invention. Note that the disk drive  2  is shown in greatly simplified schematic form, with only those construction details that are necessary for an understanding of the invention being represented. As to these illustrated components, it should be understood that all are conventional in nature unless otherwise indicated below.  
         [0033]    The disk drive  2  conventionally includes a base casting  4  made from aluminum or other suitable material. A cover  5  is removably mounted thereto via a hermetic seal (not shown). The base casting  4  supports a conventional spindle drive motor  6  having an associated drive spindle  8 . The drive spindle  8  carries a set of disks  10  for high speed rotation therewith. The disks  10  form a spaced vertically stacked disk platter arrangement. Each disk  10  is conventionally formed from an aluminum or glass substrate with appropriate coatings being applied thereto such that at least one, and preferably both, of the upper and lower surfaces of the disks are magnetically encodable and aerodynamically configured for high speed interaction with a read/write transducer (described below).  
         [0034]    Data access to the disk surfaces is achieved with the aid of an actuator  12  that is mounted for rotation about a stationary pivot shaft  14 . The actuator  12  includes a set of rigid actuator arms  16  that respectively carry either one or two flexible suspensions  18  (see FIG. 2). Each suspension  18  supports a slider  20  and a transducer  22  that are positioned to interact with an associated disk surface, representing the transducer&#39;s recording medium. The sliders  20  are aerodynamically designed so that when the disks  10  are rotated at operational speed, an air bearing develops between each slider and its associated disk surface. The air bearing is very thin (typically 0.05 μm) so that the transducers  22  are positioned in close proximity to the recording media. A conventional voice coil motor  24  is provided for pivoting the actuator  12 . This motion sweeps the actuator arms  16  and their slider-carrying suspensions  18  generally radially across the respective surfaces of the disks  10 , allowing the transducers  22  to be positioned from one concentric data track to another during seek, settle and track following operations of the drive  2 .  
         [0035]    As described in more detail below, each transducer  22  is an integrated device that includes a magnetic write head and an MR sensor read head constructed in accordance with the invention. Data is read from the disks  10  by the read head portion of each transducer  22 . This data is processed into readback signals by signal amplification and processing circuitry (not shown) that is conventionally located on each actuator arm  16 . The readback signals carry either customer data or transducer position control information depending on whether the active read head is reading from a customer data region or a servo region on one of the disks  10 . The readback signals are sent to the drive controller  25  for conventional processing. Data is recorded on the disks  10  by the write head portion of each transducer  22 . This data is provided by write data signals that are generated by the controller  25  during data write operations. The write data signals are delivered to whichever write head is actively writing data. The active write head then records the positive and negative magnetic domains representing digital information to be stored onto the recording medium.  
         [0036]    Turning now to FIGS.  4 - 7 , an exemplary one of the transducers  22  is shown as including a transducer write head portion  26  and a transducer read head portion  28 . In FIGS.  4 - 6 , the transducer  22  is shown as being lapped at  29  to form an air bearing surface (ABS) where the transducer magnetically interacts with the adjacent rotating disk surface. The ABS  29  is spaced from the disk surface during drive operations by virtue of the above-described air bearing. FIG. 7 depicts the transducer  22  from the vantage point of the disk surface, looking toward the ABS  29 .  
         [0037]    The write head  26  conventionally includes a first insulative layer  30  (commonly referred to as “I 1 ”) supporting a second insulative layer  32  (commonly referred to as “I 2 ”) that carries plural inductive coil loops  34 . A third insulative layer  35  (commonly referred to as “I 3 ”) can be formed above the coil loops  34  for planarizing the write head  26  to eliminate ripples in the I 2  insulative layer  32  caused by the coil loops. The coil loops  34  inductively drive first and second pole pieces  36  and  38  that form the yoke portion of the write head  26 . The pole pieces  36  and  38  respectively extend from a back gap  39  to pole tips  36   a  and  38   a  located at the ABS  29 . An insulative gap layer  40  (commonly referred to as “G 3 ) is sandwiched between the pole pieces  36  and  38  to provide a magnetic write gap at the pole tips  36   a  and  38   a . Note that the pole piece  36  is commonly referred to as a “P 1 ” pole piece. The pole piece  38  may be referred to as a “P 2 ” or “P 3 ” pole piece depending on how the pole tip  38   a  is formed. It is labeled as “P 2 ” in FIG. 5. During data write operations, electrical current passing through a pair of electrical leads E 1  and E 2  to the coil loops  34  generates a magnetic field that induces a magnetic flux in the P 1  and P 2  layers  36  and  38 . As shown in FIG. 6, this magnetic flux propagates from the yoke to the pole tips  36   a  and  38   a , where it fringes across the gap layer  40  at the ABS  29 . This causes magnetic domains to be formed on an adjacent recording surface of one of the disks  10 . The orientation of each recorded magnetic domain is dependent on the magnetization direction of the pole tips  36   a  and  38   a , which in turn is determined by the direction of the electrical current passing through the coil loops  34 . Reversing the coil&#39;s electrical current reverses the magnetization direction of the pole tips  36   a  and  38   a , and consequently reverses the orientation of the next recorded magnetic domain. This magnetization reversal process is used to encode data on the recording medium.  
         [0038]    The read head  28  lies between insulative gap layers  42  and  44  at the ABS  29 , where it is influenced by magnetic flux emanating from the adjacent disk surface. The gap layers  42  and  44  are commonly referred to as “G 1 ” and “G 2 ” gap areas, and are sandwiched between a first magnetic shield layer  46  (commonly referred to as an “S 1 ” shield) and second magnetic shield layer  48  (commonly referred to as an “S 2 ” shield). In some designs, including that of FIG. 5, the S 2  shield layer  48  also provides the P 1  pole piece  36 . The P 1  shield layer  46  is conventionally formed over the slider  20 , which is only partially shown in FIGS. 5 and 6 for clarity.  
         [0039]    As mentioned above by way of background, one important dimension of the read head  28  that must be carefully controlled is its stripe height (SH), as best shown in FIG. 5. The stripe height dimension is established by lapping the face of the transducer  22  while carefully monitoring the amount of material removed using an ELG. Applicants have determined that it would be desirable to define an ELG lithographically using the same lithographic stepper tool and mask used to define the stripe height of an MR sensor portion of the read head  28  (i.e., the back edge of the sensor that is remote from the ABS). This would reduce the variability in final stripe height induced by the lapping process. For reasons that will become clear from the ensuing description, the stripe height must be defined at very high resolution in order to maximize the overlap of the stripe height-defining mask with the mask used to define the sensor&#39;s track width. As explained in more detail below, this will ensure that there is a minimal increase in electrical resistance due to undesired removal of lead material as a result of etching the ferromagnetic layers of the sensor.  
         [0040]    Conventional high resolution stepper tools do not offer large enough field sizes (˜26 mm) to accommodate typical lapping row lengths (˜50 mm). As such, if it is desired to lap an entire slider bar using high resolution steppers, multiple fields that are separately lithographically defined must be stitched together to form a lapping row. Inevitable stitching errors at the field boundaries would add to tolerances of stripe height after lapping the row. Lapping of sliders individually would solve the stitching problem, but requires a method of controlling lapping progress on an individual slider basis. Applicants thus propose the use of onboard ELGs formed on individual sliders, allowing for per-slider lapping, or optionally for the lapping sliders in small groups no larger than the stepper tool&#39;s field of view.  
         [0041]    Turning now to FIG. 8 (in which the vertical scale is greatly exaggerated), an exemplary process of forming an onboard ELG may begin with conventional formation of the sensor layer structure  50  shown therein. As in the case of FIG. 7, the view of FIG. 8 is taken on a plane that is parallel to the ABS of the sensor to be constructed from the sensor layer structure  50 . The “x” axis in FIG. 8 represents the radial track width direction of the sensor to be formed. The “y” axis in FIG. 8 represents the gap width direction of the sensor. The “z” axis represents the direction pointing perpendicularly away from the sensor ABS and toward the disk medium that the sensor will read.  
         [0042]    The sensor layer structure  50  begins with an S 1  shield layer  52  that will provide the S 1  shield layer  46  of FIG. 5 and a G 1  gap layer  54  that will provide the G 1  gap layer  42  of FIG. 5. As is conventional, the shield layer  54  is made from a non-ferromagnetic electrically conductive material, while the G 1  gap layer  54  is made from an electrically insulative material. By way of example only, the sensor layers  50  are arranged to provide a “bottom-type” spin valve sensor. The first ferromagnetic layer of the sensor to be formed is a ferromagnetic pinned (P) layer  56  whose magnetization direction is fixed perpendicular to the plane of FIG. 8. Although the pinned layer  56  could be self pinned, for example, by forming it with very high positive magnetostriction and very large compressive stress (according to existing techniques), FIG. 8 shows an implementation wherein the pinned layer  56  is externally pinned by an optional antiferromagnetic (AFM) pinning layer  58 . The pinning layer  58  is deposited to a suitable thickness on one or more conventional seed layers (not shown) that are formed on top of the G 1  gap layer  54 . The pinning layer  58  can be made from platinum-manganese (Pt—Mn), nickel-manganese (Ni—Mn), iridium-manganese (Ir—Mn), or any other suitable antiferromagnetic material that is capable of exchange biasing the ferromagnetic material in the pinned layer  56 .  
         [0043]    The pinned layer  56  can be implemented in conventional fashion as a single layer ideally having one magnetization direction, or as plural sub-layers ideally having parallel and antiparallel magnetization directions. FIG. 8 shows an example of the latter configuration, with the pinned layer  56  being formed by growing a first sublayer  56   a  of cobalt-iron (CoFe), a second sublayer  56   b  of ruthenium (Ru), and a third sublayer  56   c  of cobalt-iron (CoFe). These sublayers are formed on top of the pinning layer  58  at suitable thickness. The magnetic moment of the first sublayer  56   a  is shown by the arrow tail  60   a , which points into the plane of FIG. 8. The magnetic moment of the third sublayer  56   c  is shown by the arrowhead  60   b , which points out of the plane of FIG. 8. The magnetic moments  60   a  and  60   b  are thus antiparallel to each other and oriented generally perpendicular to the plane of FIG. 8.  
         [0044]    As stated, the pinned layer  56  will have its magnetic moment fixed by interfacial exchange coupling with the pinning layer  58 . The magnetization direction(s) of the pinned layer  56  will be sufficiently fixed by the exchange-biasing pinning layer  58  to prevent rotation thereof in the presence of relatively small external magnetic fields, such as the fields produced by magnetic domains recorded on the adjacent disk surface.  
         [0045]    A spacer layer  62  is formed on top of the pinned layer  56  as a suitably thick deposit of an electrically conductive, non-ferromagnetic material, such as Cu.  
         [0046]    The sensor&#39;s free layer  64  is formed above the spacer layer  62 . The free layer  64  can be made by covering the spacer layer  62  with a single layer of Co, Co—Fe, Ni—Fe or other suitable ferromagnetic material grown to a suitable thickness. In an alternative configuration, the free layer  64  can be formed from multiple layers, such as a bilayer structure comprising a bottom sublayer of Co—Fe and a top sublayer of Ni—Fe, or a trilayer structure comprising a bottom sublayer of Co—Fe, a middle sublayer of Ni—Fe and a top sublayer of Co—Fe.  
         [0047]    The arrow  66  in FIG. 8 shows the preferred zero bias point magnetization direction of the free layer  64  when the free layer is in a quiescent state with no magnetic field incursions thereon. A protective cap layer  68  is formed on the surface of the free layer  64  in order to protect the free layer prior to the deposition of subsequent structural layers. The cap layer  68  is conventionally made from tantalum or other suitable material.  
         [0048]    It should be noted that the sensor layer structure  50  of FIG. 8 is a full wafer structure that is used to form a large number of sensors. As such, the next sensor fabrication step is the definition of individual sensors on the wafer, with each sensor having its own onboard ELG. Alternatively, if multiple sensors will be lapped as a group, at least one of the sensors will be constructed with an onboard ELG.  
         [0049]    The process begins with the formation of a track width-defining, photoresist etch mask  70 , as shown in FIGS. 9 and 10. The mask  70  can be constructed according to conventional techniques by first spin coating the cap layer  68  with a positive photoresist material. Then, with the aid of a high resolution lithographic stepper tool and a pattern mask, the photoresist is pattern-developed by optically exposing the areas  72   a  and  72   b  of FIG. 9. The material in the areas  72   a  and  72   b  is thereafter chemically removed by a photoresist developer solution (e.g., KOH, NaOH, or tetramethyl ammonium hydroxide) to expose the cap layer  68 , as shown in FIG. 10.  
         [0050]    It will be seen that the areas  72   a  and  72   b  are relatively narrowly spaced from each other along much of their adjacent inner edges ( 73   a ,  73   b ) to define a sensor track width dimension (TW). The areas  72   a  and  72   b  are then stepped at their ABS end to form relatively narrow legs  74   a  and  74   b  that will be used to provide part of the onboard ELG, as further described below.  
         [0051]    Turning now to FIGS. 11 and 12 (in which the vertical scale is again greatly exaggerated), the top of the sensor layer structure  50  is etched using a suitable etching process to remove sensor layer material down to the G 1  gap layer  54  within the areas  72   a  and  72   b . This forms a pair of trenches  76   a  and  76   b , as shown in FIG. 11. As shown in FIG. 12, after removal of the photoresist mask  70 , the trenches are filled by way of a suitable deposition process with a magnetic biasing material (e.g., CoPtCr) and an electrically conductive material, such as copper, to define a pair of sensor leads  78   a  and  78   b.    
         [0052]    Turning now to FIG. 13, a stripe height-defining etch mask  80  is ready to be formed on top of the sensor structure  50 . The mask  80  can be constructed according to conventional techniques by first spin coating the cap layer  68  with a positive photoresist material. Then, with the aid of a high resolution lithographic stepper tool and a pattern mask, the photoresist is pattern-developed by optically exposing all but the area  82  of FIG. 13. The material outside the area  82  is thereafter chemically removed by a photoresist developer solution (e.g., KOH, NaOH, or tetramethyl ammonium hydroxide) to expose the cap layer  68 .  
         [0053]    The material of layers  58 - 68  of the sensor layer structure  50  is now ready to be etched to define the back edge of the sensor stripe height dimension and complete the formation of the onboard ELG. To that end, it will be seen in FIG. 13 that the area  80  includes a pair of large generally rectangular mask regions  82   a  and  82   b  that substantially cover the sensor leads  78   a  and  78   b . Extending between the regions  82   a  and  82   b  are three horizontal mask sections  84 ,  86  and  88 . As described in more detail below, the section  84  is used to define a sensor stripe height back edge location and the sections  84  and  86  are used to define an onboard ELG in conjunction with the sensor leads  78   a  and  78   b . Importantly, it will be seen that there are small filets where the horizontal sections  84 ,  86  and  88  meet the rectangular regions  82   a  and  82   b . These filets are present as a result of resolution limitations of the stepper tool used to define the mask  80 . The lower the resolution, the larger the filets, and visa versa. This limitation is of particular concern with respect to the filets  90   a  and  90   b , where the upper edge of the horizontal section  84 , which defines the back edge of the sensor stripe height dimension, meets the horizontal regions  82   a  and  82   b . Because of the filets  90   a  and  90   b , the inner opposing edges the rectangular regions  82   a  and  82   b , respectively shown by reference numerals  92   a  and  92   b , cannot be brought into alignment with the inner opposing edges of the sensor leads  78   a  and  78   b , which are shown by reference numerals  94   a  and  94   b . To do so would cause the stripe height to flare out at the filets  90   a  and  90   b.    
         [0054]    Recessing the edges  92   a  and  92   b  of the mask  80  from the edges  94   a  and  94   b  of the sensor leads  78   a  and  78   b  solves the foregoing problem. However, the sensor lead edges  94   a  and  94   b  are exposed to subsequent etching (described below) and will therefore be thinned. This tends to undesirably increase sensor leads resistance. Therefore, it is desirable to employ a stepper tool with the highest possible resolution, so that the amount of edge recessing of the mask  80  is minimized, and sensor leads etching and resultant resistance increase is not excessive.  
         [0055]    Turning now to FIG. 14, the top of the sensor layer structure  50  is etched using a suitable etching process to remove sensor layer material down to the G 1  gap layer  54  outside the mask  80 . This forms a composite structure  100  that combines an MR sensor with an onboard ELG. The composite structure  100  includes the sensor leads  78   a  and  78   b . It also includes an untapped MR sensor element  102  and ELG resistive elements  104  and  106 , all of which are in electrical communication with the sensor leads  78   a  and  78   b . The MR sensor element  102  has a defined sensor track width (TW) and stripe height (SH) back edge as a result of the processing steps described above. All that is required to transform the composite structure  100  into a completed MR sensor is lapping to remove material and define an ABS along an lapped edge of the sensor element  102 . The ELG resistive elements  104  and  106  are used for this purpose. In particular, by attaching the sensor leads  78   a  and  78   b  to a conventional lapping apparatus (not shown), a lapping current may be passed through the ELG resistive elements  104  and  106 . The ELG resistive elements  104  and  106  are disposed between the MR sensor element  102  and the lapping tool that engages the composite structure  100 . Each has a corresponding electrical resistance to the lapping current that is dependent on the height of each element in the lapping direction. By programming the control system of the lapping apparatus, lapping can be performed in the manner described in more detail below, with the ELG resistive element  104  providing a coarse lapping guide that is used during a first coarse lapping phase and the ELG resistive element  106  providing a rate-determining guide that is used during a third rate-determining lapping phase.  
         [0056]    A four-phase lapping procedure will now be described for transforming the composite structure  100  into a finished MR sensor. Initially, it will be appreciated that the composite structure  100  may be removed from the other like structures on the full wafer layer structure  50  using conventional techniques. The composite structure  100  and all of its companions may then be lapped individually. Alternatively, a group of composite structures  100  formed by the same lithographic process within the resolution of the stepper tool and comprising part of a single slider bar may be lapped as a group. Note that in the latter case, it is not necessary to form an onboard ELG in association with each MR sensor. Instead, it may be enough to form onboard ELGs on one or two sensors of the lapping group.  
         [0057]    The four zones labeled A, B, C and D in FIG. 14 correspond to the four lapping phases. The first lapping phase corresponding to zone A is a coarse lapping phase in which a large amount of material is removed. Note that the ELG resistive element  104  has a relatively long span for maximum sensitivity. FIG. 15 shows the result of the first lapping phase. The ELG resistive element  104  has been removed to eliminate zone A and zone B has been reached.  
         [0058]    The second lapping phase corresponding to zone B is a clean up phase in which smeared material is removed to reduce noise during subsequent lapping phases. By way of example only, the height of zone B (in the lapping direction) may be approximately 500 nm. FIG. 16 shows the result of the second lapping phase. Material has been removed to eliminate zone B and the lapping tool is ready to begin lapping zone C.  
         [0059]    The third lapping phase corresponding to zone C is used to establish a fine phase lapping rate for the final lapping phase. To that end, the height of the ELG resistive element  106  (in the lapping direction) is carefully controlled (e.g., at 200 nm) with clear starting and ending points. Preferably, the height of the ELG resistive element  106  corresponds to the height of the MR sensor element  102 . The time required to lap through zone C is monitored and compared to the zone height to calculate the fine-phase lapping rate. FIG. 17 shows the result of the third lapping phase. The ELG resistive element  106  has been removed to eliminate zone C.  
         [0060]    The fourth lapping phase is used to trim a prescribed amount of the sensor element  102  from a starting width by a desired amount (e.g., approximately 200 nm) to form the final stripe height. The amount of material removed is calculated based on the fine-phase lapping rate determined in phase  3  and the elapsed time. FIG. 18 shows the result of the fourth lapping phase.  
         [0061]    [0061]FIGS. 18 a ,  18   b  and  18   c  show descriptive plots of resistance and derivatives thereof through each of the four lapping regions A, B, C and D. In FIG. 18 a , ELG resistance is plotted directly against elapsed lapping time. FIG. 18 b  shows the first derivative of the resistance plot and FIG. 18 c  shows the second derivative. It will be seen that the lithographically defined edges of the MR sensor element  102  and the ELG resistive elements  104  and  106  provide clear starting and ending points (see second derivative plot) for lapping each region.  
         [0062]    Accordingly, an MR sensor with an onboard ELG has been disclosed, together with a lapping method and an onboard ELG fabrication method. While various embodiments of the invention have been described, it should be apparent that many variations and alternative embodiments could be implemented in accordance with the invention. It is understood, therefore, that the invention is not to be in any way limited except in accordance with the spirit of the appended claims and their equivalents.