Abstract:
A magnetoresistive sensor having a lead overlay defined trackwidth and a pinned layer that extends beyond the stripe height defined by the free layer of the sensor. The extended pinned layer has a strong shape induced anisotropy that maintains pinning of the pinned layer moment. The extended portion of the pinned layer has sides beyond the stripe height that are perfectly aligned with the sides of the sensor within the stripe height. This perfect alignment is made possible by a manufacturing method that uses a mask structure for more than one manufacturing phase, eliminating the need for multiple mask alignments. The lead overlay design allows narrow, accurate trackwidth definition.

Description:
FIELD OF THE INVENTION 
     The present invention relates to magnetoresistive sensors and more particularly the construction of a magnetoresistive sensor having a pinned layer that is extended in the stripe height direction to increase shape induced magnetic anisotropy and thereby improve pinning, and that has a lead overlay structure for improved trackwidth control and sensor performance. 
     BACKGROUND OF THE INVENTION 
     The heart of a computer&#39;s long term memory is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions. 
     The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks on the moving media, such as in circular tracks on the aforementioned rotating disk. 
     In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer. 
     The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals. 
     When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve. When a spin valve employs an antiparallel (AP) pinned layer it is referred to as an AP pinned spin valve. An AP pinned spin valve includes first and second magnetic layers separated by a thin non-magnetic coupling layer such as Ru. The thickness of the spacer layer is chosen so as to antiparallel couple the magnetizations of the ferromagnetic layers of the pinned layer. A spin valve is also known as a top or bottom spin valve depending upon whether the pinning layer is at the top (formed after the free layer) or at the bottom (before the free layer). 
     The spin valve sensor is located between first and second nonmagnetic electrically insulating read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers. 
     Magnetization of the pinned layer is usually fixed by exchange coupling one of the ferromagnetic layers (AP 1 ) with a layer of antiferromagnetic material such as PtMn. While an antiferromagnetic (AFM) material such as PtMn does not in and of itself have a magnetization, when exchange coupled with a magnetic material, it can strongly pin the magnetization of the ferromagnetic layer. 
     The push for ever increased data rate and data capacity has lead a drive to make magnetoresitive sensors ever smaller. For example, designing a sensor with a narrower track width means that more tracks of data can be fit onto a given area of magnetic medium. The various dimensions of a sensor must scale together, so if the trackwidth is decreased, then the stripe height dimension (perpendicular to the ABS) must also be decreased. As sensors become ever smaller, one problem that arises is that the pinned layer becomes impracticably unstable. In fact, future generation sensors will very soon become so small that the pinned layer cannot be adequately pinned by current pinning mechanisms. 
     It is known that shape can induce magnetic anisotropy in magnetic materials, which can improve the stability of the pinning. Such shape induced anisotropy could be provided by, for example, extending the pinned layer in the stripe height direction (perpendicular to the ABS) so that the pinned layer structure has a narrow deep rectangular structure. 
     However, the use of such designs has been prevented by such factors as: the limitations on the stripe height dimension of the free layer (to avoid shape induced anisotropy in the wrong direction on the free layer); the need to avoid shunting of sense current across the extended portion of the pinned layer, and also by currently available photolithographic techniques, such as the alignment of multiple mask structures in very small structures. 
     There are also other challenges to making a sensor with an extremely small track width. For example, currently used biasing mechanisms used for biasing the magnetic moment of the free layer are not desirable for use in extremely narrow sensors. Standard biasing mechanisms include a hard magnetic layer at each side of the sensor. This hard magnetic layer is magnetostatically coupled with the sides of the free layer and this magnetostatic coupling orients the magnetic moment in a desired direction parallel with the ABS. However, as can be appreciated, this biasing is not uniform across the width of the free layer. The sides, where the magnetostatic coupling primarily acts, are strongly biased, or even pinned, while the center portion of the sensor has more freedom to respond to a magnetic field from the medium. As sensors become very narrow, the entire free layer can be pinned by the bias layers and the sensor becomes insensitive to magnetic fields. 
     In addition, manufacturing processes such as ion milling used to form the sensor stack damage the magnetic layers at the sides of the sensor layer. As sensor track widths become smaller, this damaged portion of the sensor layer becomes a large proportion of the sensor stack, and sensor performance suffers. 
     Therefore, there is a need for a sensor structure that can provide a high signal output. Such a sensor structure and method of constructing such a sensor structure must overcome the photolithographic and structural challenges faced by current sensor designs. 
     There is also a strong felt need for a sensor design, and a method of making such a sensor that will provide a strong pinned layer anisotropy perpendicular to the ABS, such as by a design that provides a shape induced anisotropy. Such a design must not, however, result in a significant amount of current shunting. Preferably, a method for manufacturing such a sensor would overcome current photolithographic limitations involved in aligning separate mask structures which has prevented the use of such pinned layer structures. 
     SUMMARY OF THE INVENTION 
     The present invention provides a magnetoresistive sensor having a shape enhanced pinned layer that extends in the stripe height direction for increased pinning strength and an enhanced lead overlay design, and a lead overlay structure that improves sensor performance. 
     The sensor includes a sensor stack with a pinned layer, a free layer and a spacer layer sandwiched between the free and pinned layers. First and second lead layers are formed over the sensor stack, and the distance between the lead layers substantially defines the track width. The sensor stack has a width that is substantially greater than the track width defined by the lead layers. The sensor stack has a back edge that defines a first stripe height (SH 1 ) of the active area of the sensor. A portion of the pinned layer extends beyond the first stripe height SH 1  to a second stripe height SH 2 . 
     In a possible method of constructing a sensor according to the present invention, a plurality of sensor layers is deposited over a substrate. Then, a mask structure is formed to define the track width of the sensor. Then, an electrically conductive lead material is deposited. Another mask structure that has a width greater than the track width is then formed and an ion mill is performed to remove sensor material at the sides not covered by this mask structure. This second mask structure can also have a back edge that defines the first stripe height (SH 1 ) of the sensor by defining the back edge of the free layer. A thin layer of insulation material is then deposited, followed by a layer of hard bias material. Another mask structure can then be formed having a width less than the previous mask structure, but greater than the track width. With this mask structure in place, another layer of electrically conductive lead material can be deposited to provide improved sense current conductivity. 
     The method of the present invention provides a sensor having excellent pinned layer pinning, because the pinned layer is extended significantly beyond the active area of the sensor in the stripe height direction. This produces a strong shape enhanced magnetic anisotropy. 
     The senor also has an advantageous lead overlay design that improves sensor performance by removing the sensor edges away from the active area of the sensor. The effective track width of the sensor is defined by the overlying leads, and the sensor layers extend laterally, substantially beyond the track width. Since the ion milling used to define the edges of the sensor may cause damage to the edges of the sensor layers, moving the sensor edges away from the active area of the sensor ensures that the sensor layers within the active area of the sensor (track width) will be free from damage. 
     Furthermore, extending the sensor layers beyond the active area of the sensor (beyond the track width) improves free layer sensitivity. Free layers are biased by hard magnetic bias layers at either edge that magnetostatically couple with the edges of the free layer. This results in strong biasing or pinning at the edges and greater free layer sensitivity at the center of the free layer away from the edges. Moving the edges beyond the track width means that the portions of the free layer within the active area or track width will be very sensitive, thereby improving sensor performance, dr/R. 
     The extended pinned layer has a shape that provides a strong magnetic anisotropy in a direction perpendicular to the ABS as desired to assist pinning. This shape enhanced anisotropy field can be several hundred Oe. 
     These and other features and advantages of the invention will be apparent upon reading of the following detailed description of preferred embodiments taken in conjunction with the Figures in which like reference numerals indicate like elements throughout. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a fuller understanding of the nature and advantages of this invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings which are not to scale. 
         FIG. 1  is a schematic illustration of a disk drive system in which the invention might be embodied; 
         FIG. 2  is an ABS view of a slider illustrating the location of a magnetic head thereon; 
         FIG. 3 ; is an ABS view, taken from circle  3  of  FIG. 2  illustrating a sensor according to an embodiment of the invention; 
         FIG. 4  is a side cross sectional view, taken from line  4 - 4  of  FIG. 3 ; 
         FIG. 5  is a plan view of a sensor according to an embodiment of the invention taken from line  5 - 5  of  FIG. 4 ; 
         FIG. 6  is a plan view of a sensor according to an embodiment of the invention taken from line  6 - 6  of  FIG. 4 ; 
         FIGS. 7-21  are views of a magnetoresitive sensor according to an embodiment of the invention, shown in various intermediate stages of manufacture to illustrate a method of manufacturing a device according to an embodiment of the present invention; and 
         FIG. 22  is a flowchart illustrating a method of using a multiuse mask structure to construct a device according to an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     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  FIG. 1 , there is shown a disk drive  100  in which the present invention may be embodied. As shown in  FIG. 1 , 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  FIG. 1  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  FIG. 2 , the orientation of the magnetic head  121  in a slider  113  can be seen in more detail.  FIG. 2  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  FIG. 1  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  FIG. 3 , 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  FIG. 3 , 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  FIG. 4 , 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  FIG. 5 , the sensor stack  302  extends laterally beyond the active area of the sensor  300  (as discussed with reference to  FIG. 3 ). 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  FIG. 4 . 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  FIG. 5 , 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  FIG. 6 , 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  FIG. 7-20 , a method for constructing a sensor  300  according to an embodiment of the invention will be described. With particular reference to  FIG. 7 , 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  FIG. 8 , 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  FIG. 8 , 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  FIG. 8 , 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  FIG. 8 ) can then be deposited and a chemical mechanical polishing process can be performed to planarize the insulation layer. With reference now to  FIG. 9 , a second mask structure  902 , as viewed from the ABS direction in  FIG. 9 , 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  FIG. 10 , 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  FIG. 11 , 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.  FIG. 12 , 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  FIG. 13 , 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  FIGS. 14A 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. 
       FIG. 14A  shows the structure as viewed from the side in the region outside of the track width as indicated by line  14 - 14  of  FIG. 13 .  FIG. 15A  shows a cross section taken from the center of the structure within the track width region as indicated by line  15 - 15  of  FIG. 13 , and shows the remaining second mask structure  902  including the CMP stop layer  908  and RIE stop layer  910 . 
     With reference now to  FIGS. 14B 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 .  FIG. 14B  shows a section from outside the track and shows that the sensor material has been removed in these regions.  FIG. 15B  shows a section from within the track (from line  15 - 15  of  FIG. 13 ). As can be seen in  FIG. 15B , the sensor material remains under the CMP stop layer  908 . The Rh layer is however removed by the ion mill. With reference to  FIG. 15C , 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 ( FIG. 8 ). The structure formed can be seen in a top down view in  FIG. 16 . 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  FIG. 17 , 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  ( FIG. 3 ) after completion of the sensor. In  FIG. 17  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  FIGS. 18A 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  FIG. 19 , 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  FIG. 20 , 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  FIG. 3 . With reference to  FIG. 21 , 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  FIG. 3 . The mask  2002  can then be lifted off, resulting in the structure shown in  FIG. 21 . A layer of electrically insulating, non-magnetic material (not shown) can then be deposited to complete the formation of the sensor  300  shown in  FIG. 3 . 
     With reference now to  FIG. 22 , 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  ( FIG. 8 ) 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  ( FIG. 8 ) is formed, having a back edge at a distant stripe height location to define the back edge of the pinned layer  314  ( FIG. 4 ) 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  ( FIG. 9 ) 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  ( FIG. 14A ) 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  FIGS. 3-6 , 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  ( FIG. 9 ) 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  FIG. 4 , 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  FIGS. 3 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  FIG. 3 ) 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.