the following description is of the best embodiments presently contemplated for carrying out this invention . this description is made for the purpose of illustrating the general principles of this invention and is not meant to limit the inventive concepts claimed herein . referring now to fig1 , there is shown a disk drive 100 in which the present invention may be embodied . as shown in fig1 , at least one rotatable magnetic disk 112 is supported on a spindle 114 and rotated by a disk drive motor 118 . the magnetic recording on each disk is in the form of annular patterns of concentric data tracks ( not shown ) on the magnetic disk 112 . at least one slider 113 is positioned near the magnetic disk 112 , each slider 113 supporting one or more magnetic head assemblies 121 . as the magnetic disk rotates , slider 113 moves radially in and out over the disk surface 122 so that the magnetic head assembly 121 may access different tracks of the magnetic disk where desired data are written . each slider 113 is attached to an actuator arm 119 by way of a suspension 115 . the suspension 115 provides a slight spring force which biases slider 113 against the disk surface 122 . each actuator arm 119 is attached to an actuator means 127 . the actuator means 127 as shown in fig1 may be a voice coil motor ( vcm ). the vcm comprises a coil movable within a fixed magnetic field , the direction and speed of the coil movements being controlled by the motor current signals supplied by controller 129 . during operation of the disk storage system , the rotation of the magnetic disk 112 generates an air bearing between the slider 113 and the disk surface 122 which exerts an upward force or lift on the slider . the air bearing thus counter - balances the slight spring force of suspension 115 and supports slider 113 off and slightly above the disk surface by a small , substantially constant spacing during normal operation . the various components of the disk storage system are controlled in operation by control signals generated by control unit 129 , such as access control signals and internal clock signals . typically , the control unit 129 comprises logic control circuits , storage means and a microprocessor . the control unit 129 generates control signals to control various system operations such as drive motor control signals on line 123 and head position and seek control signals on line 128 . the control signals on line 128 provide the desired current profiles to optimally move and position slider 113 to the desired data track on disk 112 . write and read signals are communicated to and from write and read heads 121 by way of recording channel 125 . with reference to fig2 , the orientation of the magnetic head 121 in a slider 113 can be seen in more detail . fig2 is an abs view of the slider 113 , and as can be seen the magnetic head including an inductive write head and a read sensor , is located at a trailing edge of the slider . the above description of a typical magnetic disk storage system , and the accompanying illustration of fig1 are for representation purposes only . it should be apparent that disk storage systems may contain a large number of disks and actuators , and each actuator may support a number of sliders . with reference now to fig3 , a magnetoresistive sensor 300 according to an embodiment of the invention includes a magnetoresistive sensor element or sensor stack 302 , sandwiched between first and second non - magnetic , electrically insulating gap layers 304 , 306 , which can be constructed of , for example alumina ( al 2 o 3 ). first and second hard bias layers ( hb ) 305 , 307 constructed of , for example , coptcr are formed at either side of the sensor to provide a magnetic bias field to bias the magnetic moment of the free layer in a direction parallel with the abs . first and second electrically conductive lead layers 308 , 310 are formed above the first and second hb layers , and extend laterally from the sides of the sensor stack 302 between the first and second gap layers 304 , 306 . insulation layers 309 , 311 prevent current flow from the leads 308 , 310 through the sides of the sensor 330 , 332 . the construction of the leads 308 , 310 and insulation layers 309 , 311 will be described in greater detail below . with continued reference to fig3 , the sensor stack 302 includes a magnetic free layer 312 , a pinned layer structure 314 and a non - magnetic , electrically conductive spacer layer 316 , constructed of , for example cu . the free layer 312 can be constructed of several magnetic materials such as co , nife or cofe , or of a combination of layers of different magnetic materials . the pinned layer structure 314 may be a simple pinned structure or an antiparallel pinned ( ap pinned ) structure , and may be either self pinned or afm pinned . for purposes of illustration , the pinned layer structure 314 , will be described as an afm pinned , ap pinned layer structure having first and second ferromagnetic layers 318 , 320 , which are antiparallel coupled across a non - magnetic , electrically conductive ap coupling layer 322 such as ru . the first and second magnetic layers 318 , 320 can be constructed of , for example cofe , nife or some combination of these or other materials . a layer of antiferromagnetic material ( afm layer ) 324 is disposed beneath the pinned layer structure 314 , and can be for example ptmn , irmn or some other antiferromagnetic material . the afm layer 324 is exchange coupled with the first magnetic layer 318 and strongly pins the magnetic moments of the magnetic layers as indicated by symbols 319 , 321 . the sensor stack 302 also may include a seed layer 326 formed at the bottom of the sensor stack 302 , which can be used to initiate a desired crystalline growth in the layers of the sensor stack 302 . a capping layer 328 , such as for example ta or some other suitable material may be provided at the top of the sensor stack 302 to protect the layers of the sensor stack from damage during manufacturing processes such as annealing . the innermost edges of the leads 308 , 310 are separated by a distance w 1 . the sensor 300 has a track width tw that is substantially defined by the leads 308 , 310 . although the actual effective track width tw is defined by the distance w 1 between the leads , it is not equal to this width w 1 , due to the fact that not all of the sense current will enter the sensor stack at the very end of the lead . therefore , the effective trackwidth of the sensor is wider than w 1 . the sensor stack 302 has first and second lateral sides 330 , 332 that extend significantly beyond w 1 and also beyond the effective track width ( tw ) of the sensor . the distance w 2 between the sides 330 , 332 of the sensor stack is preferably at least 1 . 5 times w 1 and is preferably 2 - 4 times w 1 . the free layer 312 has a magnetic moment 331 that is biased in a desired direction parallel with the abs . biasing of the moment 331 is achieved by a bias field provided by the first and second hard bias layers 305 , 307 . the leads 308 , 310 each include a thin first lead layer 334 ( bottom lead ) and a thicker second lead layer 336 ( top lead ). the first thin lead layer 334 extends inward to define the track width tw of the sensor 300 . because , the first lead layers 334 are thin , they can be accurately patterned to a very narrow track width . forming a thick structure requires the use of a thick mask structure . because , the first lead layer is thin , it can be patterned using a thin mask structure , resulting in a greatly improved , accurate photolithography . this will be better appreciated upon reading a method for constructing a sensor according to an embodiment of the invention , described herein below . the thicker lead layers 336 provide improved conduction of sense current to the sensor stack 302 , and since they do not extend inward to the track width tw , the photolithographic alignment used to pattern the thicker leads 336 is much less critical than the that of the thinner leads 334 . with reference to fig4 , it can be seen that the free layer 312 extends from the abs a first stripe height distance sh 1 , whereas the pinned layer 314 and possibly a portion of the spacer layer 316 extend much further from the abs to a second stripe height distance sh 2 . sh 2 is preferably at least larger than sh 1 , and is more preferably at least two times or several times sh 1 . as those skilled in the art will appreciate , the abs or air bearing surface is the portion of the head that faces the magnetic medium during operation . as fly heights become ever smaller , the fly height may approach a distance where the head could be considered to be in contact with the medium . therefore , the term “ abs ” should be understood to describe the surface of the head that faces the magnetic medium regardless of the distance from the medium during operation . an insulation fill layer 402 is provided in the area beyond sh 1 to fill the space between the gap layers 305 , 306 and between the spacer 316 and second gap layer 306 . with reference to fig5 , the sensor stack 302 extends laterally beyond the active area of the sensor 300 ( as discussed with reference to fig3 ). preferably the sensor stack 302 has a width w 2 that is at least 1 . 5 times sh 1 . more preferably the width w 2 is 2 - 5 times sh 1 . the pinned layer 314 extends in the stripe height direction as described with reference to fig4 . the hard bias layers 305 , 307 are separated from the laterally extending portions of the sensor stack 302 by the conformal insulation layers 309 , 311 . the insulation fill layer 402 fills the space at either side of the pinned layer in the area beyond sh 1 . the insulation fill layer 402 can be , for example alumina . the insulation layers 309 , 311 can also be alumina , but are preferably deposited by a conformal deposition method as will be described in greater detail herein below . the hard bias layers 305 , 307 can be constructed of several different hard magnetic materials , such as copt or coptcr . with continued reference to fig5 , the first lead layers 334 can be seen formed over the sensor layers 302 . as mentioned above , the leads have inner edges 502 , 504 that define the track width ( tw ) of the sensor . the inner ends 502 , 504 of the first thin lead layers 334 may , but need not be , aligned perfectly with the sides 506 , 508 of the extended portion 510 of the pinned layer 314 and possibly the spacer 316 . a method for constructing the sensor 300 described herein below provides for alignment of the sides 506 , 508 of the extended pinned layer 314 with the inner ends 502 , 504 of the thin first leads 334 . with reference to fig6 , the second thicker leads 336 can be seen formed over a portion of the first lead 334 and over a portion of the hard bias layers 305 , 307 . with reference now to fig7 - 20 , a method for constructing a sensor 300 according to an embodiment of the invention will be described . with particular reference to fig7 , a plurality of sensor layers 702 are deposited full film on a substrate 704 , which can be , for example a non - magnetic , electrically insulating gap layer 706 . then , with reference to fig8 , a first mask structure 802 is formed over the sensor layers 702 . the first mask structure 802 may include a cmp stop layer 804 , an image transfer layer such as durimide ® 806 and a photoresist layer 808 . the mask structure 802 has a back edge 812 that is disposed away from the location where the future abs will be formed . this back edge defines a back stripe height of an extended pinned layer portion as will be better understood upon further reading of the described method for constructing a sensor . it should be pointed out that , while the location of the air bearing surface ( abs ) is shown in fig8 , it is for purposes of illustration only as the abs will be formed by a lapping processes after the sliders have been cut from the wafer into slider rows as will be familiar to those skilled in the art . with continued reference to fig8 , with the mask 802 in place , an ion mill 814 can be performed to remove portions of the sensor material that are not covered by the mask structure 802 . this ion mill defines the back stripe height of the extended pinned layer portion . an insulation fill layer such as alumina ( not shown in fig8 ) can then be deposited and a chemical mechanical polishing process can be performed to planarize the insulation layer . with reference now to fig9 , a second mask structure 902 , as viewed from the abs direction in fig9 , is formed over the sensor layers . this mask has first and second laterally opposed sides 904 , 906 that define the effective track width of the sensor , although the actual effective track width may be wider than the distance between the sides 904 , 906 , as will be seen . the second mask structure 902 may include a first layer 908 constructed of a material that is resistant to removal by chemical mechanical polishing ( cmp stop layer ) 908 . this cmp stop layer may be constructed , for example , of diamond like carbon ( dlc ). a second layer , constructed of a material that is resistant to removal by chemical mechanical polishing and also resistant to removal by reactive ion etching ( rie ) is formed over the first layer 908 . this second layer ( rie stop layer 910 ) may be constructed of , for example rh . an image transfer layer 912 may be formed over the rie stop layer 910 , and may be constructed of durimide ®. a layer of photosensitive material such as photoresist 914 forms the top of the mask structure 902 . the mask structure 902 can be formed by first depositing the layers 908 - 914 as full film layers . the photoresist layer 914 can then be photolithgoraphically patterned by methods that will be familiar to those skilled in the art . then , a rie process can be performed to transfer the image of the photoresist layer 914 onto the image transfer layer 912 . a short ion mill can then be performed to remove uncovered portions of the rie stop layer 910 , transferring the image of the layers 912 , 914 onto the rie stop layer 910 . then , another rie can be performed to transfer the image of the layers 910 , 912 , 914 onto the cmp stop layer 908 . with reference now to fig1 , a relatively thin electrically conductive lead material 1002 is deposited full film . a layer of cmp resistant material 1004 , such as diamond like carbon ( dlc ) can then be deposited full film over the electrically conductive lead material 1002 . with reference to fig1 , a chemical mechanical polishing process ( cmp ) can be performed to remove portions of the mask structure , with the cmp stop layer 910 and rie stop layer 908 remaining . the resulting structure can be seen with reference to . fig1 , with the rie stop layer 910 remaining , and cmp stop layer 1004 formed over the thin lead layers covering the rest of the structure 1002 ( not shown ). with reference now to fig1 , a third mask structure 1302 is formed . the third mask structure has a back edge 1304 that will define the stripe height of the active portion of the sensor . the third mask structure can be seen more clearly with reference to fig1 a and 15a and includes : a cmp stop layer 1402 , such as dlc ; an image transfer layer 1404 , such as durimide ® and a photosensitive layer 1406 , such as photoresist . the formation of the third mask structure includes the use of a reactive ion etch to transfer the image of the photoresist layer 1406 onto the underlying mask layers 1402 , 1404 . this rie also removes the cmp stop layer 1004 from over the leads 1002 , however the rh rie stop layer 910 remains in the track area . fig1 a shows the structure as viewed from the side in the region outside of the track width as indicated by line 14 - 14 of fig1 . fig1 a shows a cross section taken from the center of the structure within the track width region as indicated by line 15 - 15 of fig1 , and shows the remaining second mask structure 902 including the cmp stop layer 908 and rie stop layer 910 . with reference now to fig1 b and 15b , an ion mill is performed to remove lead and sensor material in areas not covered by the remaining second mask structure ( layers 908 , 910 ) and third mask structure 1302 . fig1 b shows a section from outside the track and shows that the sensor material has been removed in these regions . fig1 b shows a section from within the track ( from line 15 - 15 of fig1 ). as can be seen in fig1 b , the sensor material remains under the cmp stop layer 908 . the rh layer is however removed by the ion mill . with reference to fig1 c , another rie 1502 can be performed to remove the remaining cmp stop layer 908 from within the track layer in areas uncovered by the third mask 1302 , and then a short ion mill 1504 can be performed to remove the cap layer 328 , free layer 312 and possibly a portion of the spacer layer 316 from areas beyond the stripe height defined by the third mask 1302 . in this way , the free layer can be removed , while leaving the pinned layer extending to the extended stripe height location defined in the first masking step ( fig8 ). the structure formed can be seen in a top down view in fig1 . an insulating fill layer 1602 can then be deposited . the fill layer 1602 can be , for example alumina ( al 2 o 3 ) or some other non - magnetic , electrically insulating material , and is preferably deposited by atomic layer deposition or some other conformal deposition . the insulation layer is preferably deposited thick enough to completely fill the areas at either side of the track , and also to cover the remaining spacer 316 in the extended portion and pinned layer 314 hidden there under . the third mask structure 1302 can then be lifted off either by a chemical lift off process or by a physical lift process such as chemical mechanical polishing . with reference now to fig1 , a fourth mask structure 1702 is deposited . the mask structure 1702 can include a layer of diamond like carbon , an image transfer layer such as durimide ® and a patterned photoresist layer . the mask structure 1702 has first and second laterally opposed sides 1704 , 1706 . the sides 1704 , 1706 define the outermost width of the sensor layer stack 302 ( fig3 ) after completion of the sensor . in fig1 it can be seen that portions of the first lead layers 1002 , and the insulation layer 1602 extend beyond the sides 1704 , 1706 of the fourth mask structure 1702 . with reference to fig1 a and 18b , an ion mill can be performed to remove these exposed portions of the first lead layers 1002 and insulation layer 1602 that extend beyond the sides 1704 , 1706 of the fourth mask structure 1702 . then , thin layer of conformally deposited insulation material 1802 can then be deposited , followed by a layer of hard magnetic material 1804 . the insulation layer 1802 can be , for example , alumina ( al 2 o 3 ) or some other non - magnetic , electrically insulating material , and is preferably deposited by a conformal deposition method such as atomic layer deposition , chemical vapor deposition , etc . the conformal deposition of the insulation layer 1802 results in an insulation layer that covers the sides of the sensor stack , 702 , and also extends over the substrate 704 . the hard magnetic material 1804 can be , for example , copt , coptcr or some other hard magnetic material . with reference to fig1 , a chemical mechanical polishing process ( cmp ) can be performed to planarize the hard bias material 1804 , and insulation layer 1802 , and to remove the fourth mask structure 1702 . with reference now to fig2 , a fifth mask structure 2002 is formed . this mask structure 2002 has first and second openings 2004 , 2006 that expose a portion of the hard bias layer 1804 , insulation 1802 first lead layer 1002 and insulation layer 1602 near the abs location . the opening can be in the form of a square or rectangle , and is configured with a shape to define the second lead layers 336 described in fig3 . with reference to fig2 , a layer of electrically conductive lead material 2102 is deposited into the openings 2004 , 2006 in the fifth mask structure 2002 to form the leads 336 of fig3 . the mask 2002 can then be lifted off , resulting in the structure shown in fig2 . a layer of electrically insulating , non - magnetic material ( not shown ) can then be deposited to complete the formation of the sensor 300 shown in fig3 . with reference now to fig2 , a method for constructing a sensor according to an embodiment of the invention includes , in a step 2202 , providing a substrate . then , in a step 2204 , a plurality of sensor layers 702 ( fig8 ) is deposited onto the substrate . the sensor layers may include a pinned layer structure , free layer and a non - magnetic spacer layer sandwiched between the free and pinned layers . in a step 2206 , a first mask structure 802 ( fig8 ) is formed , having a back edge at a distant stripe height location to define the back edge of the pinned layer 314 ( fig4 ) in the final sensor 300 . in , a step 2208 a first ion mill can be performed to remove sensor material not covered by the first mask structure . the first mask can then be removed . in a step 2210 , a second mask structure can be formed . the second mask structure 902 ( fig9 ) may include a cmp stop ( such as diamond like carbon ), a rie stop ( such as rh ), an image transfer layer ( such as durimide ®), and a photosensitive layer ( such as photoresist ). the second mask structure has first and second sides that define a track width of the sensor 300 . then , in a step 2212 a layer of electrically conductive lead material can be deposited . a layer of cmp stop material , such as diamond like carbon ( dlc ) may also be deposited . in a step 2214 a third mask structure 1302 ( fig1 a ) is formed having a back edge that defines an active area of the sensor in the stripe height direction . then , in a step 2216 a second ion mill is performed to remove lead and sensor material not covered by the second and third mask structures . in a step 2218 , a rie can be performed to remove portions of the cmp stop layer of the second mask structure that extend beyond the third mask structure . then , in a step 2220 a quick third ion mill can be performed to remove portions of the free layer that extend beyond the third mask structure . an electrically insulating fill material , such as alumina , is deposited to fill the space left by the removed lead and sensor material . the third mask can then be removed . then , in a step 2222 a fourth mask structure can be formed having a width that is significantly wider than the second mask structure . a fourth ion mill can be performed to remove lead , sensor and insulation material not covered by the fourth mask . then , in a step 2224 a thin layer of conformally deposited insulation material , such as alumina can be deposited . then , in a step 2226 a layer of hard magnetic material such as copt or coptcr can be deposited . the fourth mask can then be lifted off . in a step 2228 a fifth mask structure can be formed having a width that is between that of the second and fourth mask structures . then , in a 2230 a second layer of lead material can be deposited . the resulting sensor structure , shown with reference to fig3 - 6 , provides several advantages over previous magnetoresistive sensors . for example , during the ion milling processes used to form the outer edges of the sensor , a certain amount of damage inevitably occurs to the sensor layers at the outer edge of the sensor stack 302 . however , the effective track width in a lead overlay sensor according to the present invention is removed from the actual outer edges of the sensor stack 302 in the active area of the sensor . therefore , the effect of such damage at the outer edges 330 , 332 is mitigated by removing it from the active area of the sensor . moving the outer edges 330 , 332 of the sensor stack 302 outside of the active area ( beyond the tw ) also improves free layer sensitivity in the active area of the sensor . the hard bias layers 305 , 307 provide magnetic biasing to the free layer 312 by magnetostatically coupling with the outer edges of the free layer 312 . however , such biasing results in pinning or near pinning of the free layer 312 at the outer edges 330 , 332 . moving this pinned region of the free layer 312 outside of the active area of the sensor improves free layer sensitivity in the active area of the sensor . another advantage to a sensor according to the present invention is that the thin leads define the effective track width of the sensor 300 and can be easily photolithgraphically patterned . because the thin leads 334 are very thin , the mask structure 902 ( fig9 ) used to define the leads can be much thinner and more accurately photolithographically patterned than a mask structure that would be used to defining the width of an entire sensor stack in a prior art sensor design . therefore , the distance between the inner portion of the first leads 334 can be accurately patterned to a very narrow width . the insulation layers 309 , 311 that separate the hard bias layers 305 , 307 from the sides 330 , 332 of the sensor stack prevent sense current from leaking from the hard bias layers 305 , 307 to the sensor stack 302 . this channels the sense current through the leads to more accurately define the track width . with reference to fig4 , it can be seen that the pinned layer 314 extends much further in the stripe height direction ( ie . away from the abs ) than the rest of the sensor stack 302 . this extension of the pinned layer 314 provides a strong magnetic anisotropy that greatly improves the pinning of the pinned layer 314 . this shaped induced anisotropy can be several hundred oe or larger . furthermore , this strong magnetic anisotropy is advantageously unaffected by other factors such as the size of the sensor or by mechanical stresses . what &# 39 ; s more , this anisotropy is completely additive to other pinning mechanisms such as ap pinning , afm pinning or pinning with a hard magnet . in a similar manner , the free layer has a shape enhanced anisotropy parallel to the abs ( ie . perpendicular to that of the pinned layer ). as can be seen with reference to fig3 and 4 , the free layer is much wider in the track width direction than it is in the stripe height direction . a free layer 312 having this shape has a magnetic anisotropy in a direction parallel with the abs , ( ie . left to right in fig3 ) that may improve free layer stability . while various embodiments have been described above , it should be understood that they have been presented by way of example only , and not limitation . other embodiments falling within the scope of the invention may also become apparent to those skilled in the art . thus , the breadth and scope of the invention should not be limited by any of the above - described exemplary embodiments , but should be defined only in accordance with the following claims and their equivalents .