Abstract:
A magnetically stable, read sensor uses low-coercivity magnetic material without seed layers in side shields for longitudinal biasing in order to improve micro-magnetic read width of the sensor. The sensor is formed between an upper and lower shield and includes a symmetric pair of abutting side shields adjacent to the sides of the sensor. In one configuration the side shields are partially covered by a layer of high magnetic moment material that extends along a bottom surface and side surface of the side shields and is contiguous and conformal with the layer of insulating material, but does not cover the backside of the sensor. The high moment layer focuses flux at the sensor sides and also improves the micro-magnetic read width. The side shields include a multiplicity of horizontal ferromagnetic layers that are antiferromagnetically coupled to each other and magnetically coupled to the upper shield.

Description:
RELATED PATENT APPLICATIONS 
     This application is related to Ser. No. 13/785,227, Filing Date Mar. 5, 2013; Ser. No. 13/785,255, Filing Date Mar. 5, 2013 and Ser. No. 13/863,269, Filing Date Apr. 18, 2013, all assigned to the same assignee and all fully incorporated herein by reference. 
     BACKGROUND 
     1. Technical Field 
     This disclosure relates generally to thin-film magnetoresistive (MR) read sensors (i.e. read heads) and particularly to the enhancement of micro-magnetic read width of such sensors by the use of different shield materials and configurations. 
     2. Description 
     The demand for data storage capacity in today&#39;s information technology has driven the increase of recording density in magnetic storage. One of the components in magnetic storage that determines the recording density is the read head sensor, which is based on a spin valve magnetoresistance (SVMR) configuration. As the recording density increases to the level of Gb/in 2 , the size of the recording bit in the magnetic storage medium shrinks into the nanometer range. The size of the read head sensor, therefore, needs to be of that same dimensional order in order to read the bit signal accurately. Typically the cross-sectional area of the read sensor is smaller than 0.1×0.1 microns at the air bearing surface (ABS) of the read/write head for recorded media areal density of 100 Gb/in 2  and above. 
     Current technology utilizes the tunneling magnetoresistive (TMR) effect in the SVMR sensor. Typically, the sensor has a bottom spin valve configuration. This sensor structure includes two ferromagnetic layers, a top and a bottom, separated by an ultra-thin dielectric tunneling layer. The top ferromagnetic layer is a free layer (FL) whose magnetic moment is free to respond to the changing fields produced by the recorded media, whereas the bottom ferromagnetic layer is a reference layer (denoted AP1, for “first antiparallel layer”) whose magnetic moment is fixed in space. The dielectric tunneling layer is usually made of MgO or AlOx. 
     The layer AP1 is pinned by yet another ferromagnetic layer (AP2, for “second antiparallel layer”) through a synthetic anti-ferromagnetic (SAF) effect which creates antiparallel magnetic moments in AP1 and AP2. The magnetic moment of the AP2 layer is pinned in spatial direction by an anti-ferromagnetic layer at its bottom surface. When an external magnetic field is applied to the sensor by passing it over a recording medium at its ABS, the FL magnetization will rotate corresponding to the direction of the magnetic field it experiences. Depending upon the memory state (“0” or “1”) of the magnetic medium closest to the FL, which translates into the direction of its magnetic field, the magnetization (magnetic moment) of the FL will rotate to a direction either parallel or anti-parallel to that of the AP1. When an electric current passes through the sensor in order to read the FL state of magnetization, the resistance R will change in accord with the joint magnetization states of FL and An R is low when the magnetization of the FL is parallel to the AP1 and high when antiparallel. Thus the read head sensor will register a bit as a “0” or “1”. 
     The typical design of a read head sensor is based on an abutting junction configuration in which the sensor is surrounded by shields (bottom shield S1, top shield S2 and side shields) to isolate it from unwanted external fields. The sensor is also etched at the back edge to produce an island shape with dimensions in nm×nm range. At this size range, the FL of the sensor will encounter significant demagnetization interference from outside. Therefore, a longitudinal biasing field from side shields is necessary to anchor the magnetization of the FL and keep it from fluctuation. Conventionally, the side shields consist of a hard bias layer (a layer of “hard” magnetic material) formed adjacent to each side of the free layer of the sensor at the ABS. As the critical dimensions of the sensor element become smaller, the FL becomes more volatile and more difficult to bias. This biasing scheme using a hard bias layer has become problematic due to randomly distributed hard magnetic grains within the hard bias layer. To mitigate the problem, we have proposed in related applications Ser. Nos. 13/785,227 and 13/865,269 (which are fully incorporated herein by reference) a different scheme to use soft magnetic layers (permalloy, supermalloy, MU metal, etc) to form the side shields. 
     Referring to  FIG. 1 , there is shown a schematic graphical illustration of a read-back cross track profile (denoted the “micro read width” or μMRW) which is obtained by scanning the read head across the width of a given data track and plotting the read-back amplitude vs. the off-track distance (distance from track center). The 100% amplitude is the relative strength of the read-back signal when the head is positioned perfectly at the track center. μMRW-10% (the x-axis distance −x1 and x1) and μMRW-50% (the x-axis distance −x2 and x2) are the 10% and 50% micro magnetic read widths that are defined by the width of the cross track profile in  FIG. 1  at relative amplitudes corresponding to 10% and 50% of the track center amplitude, respectively. A higher cross track resolution requires a small μMRW and better μMRW sharpness which means the ratio of μMRW-10% and μMRW-50% should be as close to 1 as possible. 
     In this disclosure, we propose a shield scheme to improve the μMRW sharpness by using high magnetic moment wrap shields on the side and top shields. 
     The prior arts disclose various attempts at resolving sensor performance problems by the use of various shield structures and materials. Examples are: Lin, (U.S. Pat. No. 7,599,153); Lin, (U.S. Pat. No. 7,606,009) and Nishida et al. (U.S. Pat. No. 7,450,349). However, none of these attempts have addressed the problem in the same manner and with the same effect as the method to be summarized below and then described in further detail herein. 
     SUMMARY 
     It is a first object of the present disclosure to provide a shielded MR read sensor in which the side shield is coupled to the top shield for improved stability. 
     It is a second object of the present disclosure to provide such a shielded MR read sensor in which a side shield of soft magnetic material replaces a hard bias layer so that a smaller domain size is obtained which, thereby, improves overall sensor stability. 
     It is a third object of the present disclosure to provide a side shield formed of a soft magnetic material that combines low coercivity with high magnetic moment to produce the desired sensor stability. 
     It is a fourth object of the present disclosure to provide the stability enhancing shields described above while also wrapping layers of high magnetic moment about the shields in order to obtain better μMRW (micro magnetic red width) sharpness. 
     It is a fifth object of the present disclosure to sharpen said μMRW by reducing the gap between the sensor free layer and the biasing layer. 
     It is a sixth object of the present disclosure to prevent any pinning by a metal seed layer onto the high magnetic moment layer coupled with soft magnetic shields. 
     It is a seventh object of the present disclosure to provide a method by which the anisotropy of the high magnetic moment layer&#39;s magnetization is aligned with that of the soft magnetic shield material of the side shields through an annealing process in the presence of a longitudinal magnetic field, for efficient biasing of the free layer. 
     It is an eighth object of the present disclosure to provide a side shield formed of a magnetic material alloy composition that will exhibit high overall magnetic moment and low coercivity, while also enhancing μMRW of the sensor. 
     Conventionally, the longitudinal biasing scheme exploits the properties of a hard bias by using hard magnetic materials (hard magnets=high coercivity) such as CoPt, FePt, and the like, formed adjacent to both sides of the sensor at the ABS. In our previous referenced applications, fully incorporated herein by reference, (Ser. Nos. 13/785,227, 13,785,255, 13/863,269), we first proposed (but did not fully exploit) a different scheme that exploits the properties of a soft magnetic material (soft magnet=low coercivity) for the longitudinal biasing layers, in order to improve the sensor stability. This soft material biasing layer could be a single soft magnetic layer such NiFe and NiFeMe (where Me=Mo, Cr, Cu, etc) or laminated layers of magnetic layers and non-magnetic layers to form a stronger AFM (anti-ferromagnetic) coupling layer to the top shield. 
     In this disclosure, we propose yet another design for the shields, differing from the previous approaches, in that: (1) the soft magnetic layers are formed without the use of a seed layer, and (2) the sensor is wrapped with a thin layer of high magnetic moment Fe (“high-moment” material). Moreover, the disclosed structure has the added capability of being magnetically aligned in the longitudinal direction by annealing. Other high moment materials that have the same property as Fe may also be used. These materials may include FeNi where the Fe content is above 30%. The thickness of the high moment layer is between approximately 10 A and 50 A. Preferably, the high moment wrap layer is formed in the closest proximity with the FL of the sensor and beneath and in contact the soft magnet side shields. 
     Preferably, the high moment Fe layer is integrated into the longitudinal biasing scheme as described in related application Ser. No. 13/785,227. In a preferred embodiment, the sensor has a bottom spin valve configuration with an intrinsic AFM layer, SAF (Synthetic Antiferromagnetic) reference layer, non-magnetic spacer layer, ferromagnetic free layer, and capping layer sequentially formed on a bottom shield, so that the bottom surface of the AFM layer contacts the bottom shield and the top surface of the capping layer interfaces with the top shield. 
     The high moment layer (or layers) are formed directly on an insulation layer such as a layer of AlOx, MgO, SiNx, SiO2, etc., that isolates the sensor side walls from the side shields without any intervening metal seed layer. The advantages of forming the high moment Fe layer directly on the insulation layer without the seed layer typical of the prior art are: (1) to reduce the width of the gap between the side of the FL and the biasing layer so that the μMRW sharpness is improved; (2) to prevent the seed layer from pinning the magnetic flux of the free layer to the soft magnet side shields; and (3) to be able to align the anisotropy or the magnetization of the high moment layer and the soft magnetic layer in the side shields with annealing under magnetic field along the longitudinal direction for efficient biasing for the FL. These properties will all improve the sensor stability. 
     Layers of a magnetically soft material such as permalloy, supermalloy, or MU-metal is sequentially formed on the high moment layer. The typical thickness of this layer is approximately 50 A-300 A. This high moment and soft (low coercivity) magnetic layer composite will exhibit high permeability or low coercivity yet it contains a high flux density due to the high moment layer in close proximity to the sensor FL. These properties are essential for good device performance with good stability and better μMRW sharpness. 
     The present disclosure also includes a method of forming a sensor that is stabilized with side shields having an AFM coupling configuration, and forming the wrap shield structure comprised of the high moment layer Fe or other materials with similar properties. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic graphical profile showing the cross-track read-back signal amplitude of a prior art read head vs. the distance from a track center. 
         FIG. 2  is a schematic cross-sectional view (in a plane perpendicular to the ABS plane) of a prior art bottom spin-valve read head configuration showing a typical top and bottom shield configuration. 
         FIG. 3A  is a schematic representation, in an ABS plane, of a first embodiment of the present shielded read head including only a side shield structure formed with no seed layers. 
         FIG. 3B  is a schematic representation of a prior-art shielded read head showing the presence of a seed layer. 
         FIG. 4  is a schematic representation, in an ABS plane, of a second embodiment of a shielded read head of the present disclosure. 
         FIG. 5  is a top-down view of the read head of  FIG. 4 , with the top shield removed to show additional structure of the side shields. 
         FIG. 6  is a schematic illustration of the first step in a fabrication process of the present read head. 
         FIG. 7  is a schematic illustration of a subsequent step to that shown in  FIG. 6 , showing results of an ion-milling process or an ion beam etch (IBE) here being applied in the formation process of the presently disclosed read head. 
         FIG. 8  is a schematic illustration showing results of further steps in the fabrication process of the read head presently disclosed. 
     
    
    
     DETAILED DESCRIPTION 
     The conventional design of a read head typically uses a hard bias layer in the longitudinal biasing. In related applications Ser. Nos. 13/785,227, 13/785,255, 13/863,269; all fully incorporated herein by reference, it was proposed to use a soft magnetic layer for longitudinal biasing, with that layer formed as a composite of multiple soft magnetic layers coupled to the top shield to improve the stability of the read sensor. 
     In the present disclosure, in addition to proposals previously implemented in above designated applications Ser. Nos. 13/785,227, 13/785,255, 13/863,269, we further propose to wrap the sensor about its sides and bottom periphery with a thin layer of high moment Fe or Fe-containing material and, in addition, to eliminate all seed layers from the soft magnetic biasing layers. 
     As will be shown below, the high moment layer is formed directly on an insulation layer that isolates the sensor side walls from the side shields. Unlike the prior art, no metal seed layer is needed for the high moment layer. Preferably, the high moment layer should be as close to the FL (free layer) as possible on both the side and the top of the sensor, a condition which would not have been possible if using a seed layer. The insulation layer in between the FL side walls and the high moment layer should be as thin as possible yet thick enough for effective electrical isolation. This is to increase the magnetic flux density around the FL so that the μMRW (micro-magnetic read width) sharpness, as shown in  FIG. 1 , is improved. 
     Referring to prior art  FIG. 2 , there is shown a cross-sectional view (in a y-z plane, perpendicular to the x-z ABS plane) of a bottom spin valve read head shielded only at its top and bottom. The stack includes composite layer  6   d , which is a reference layer, layer  6   f , which is a free layer and layer  6   h , which is a capping layer. The bottom shield  4  and top shield  7  both extend in a y-axis direction, away from the ABS plane, beyond the sloped back side edge  6   s   1  of the sensor. In the x-direction, the shields are above and below the patterned sensor stack in the ABS plane. It is noted that in this cross-sectional view, side shields are not seen since they would be in front of and behind the plane of the cross-section. It is further noted that the sensor may be of a tunneling magnetoresistive type (TMR), in which case the free layer is separated from the reference layer by a dielectric layer, or it may be a giant magnetoresistive type sensor (GMR), in which case the free layer is separated from the reference layer by a non-magnetic, but electrically conducting, spacer layer. 
     According to the configuration shown, an insulation layer  31  made of AlOx, MgO, or SiO2, for example, is formed on insulation layer  5  that lies along (conformally abutting) the back side edge  6   s   1 . Also shown in cross-sectional  FIG. 2  are the portions of the insulation layers  5 ,  31  that are formed on a portion of the top surface of bottom shield  4 . The insulation layers  5 ,  31 , however, could also be formed on any of the layers of the sensor below the free layer  6   f . In an alternative embodiment, layers  5 ,  31  may be combined into a single insulation layer  5 . Note that other layers  6   d ,  6   h  within the sensor are formed below and above the free layer  6   f , respectively, and may each contain one or more layers. 
     In a bottom spin valve configuration as is shown in  FIG. 2 , layer  6   h  comprises at least a capping layer (not shown), and composite layer  6   d  typically includes a bottom seed layer  6   d   1 , a reference layer  6   d   2  with a fixed magnetization direction (often called a pinned layer), and a non-magnetic spacer  6   d   3  that is between the reference layer and free layer  6   f  (if the sensor is a GMR sensor). In another aspect, bottom layer  6   d   1  may be a composite layer including a lower seed layer and an upper antiferromagnetic (AFM) layer that contacts the reference layer. The AFM layer may be comprised of IrMn, MnPt, or the like and is used to pin the magnetization direction in the reference layer  6   d   2  (often called a pinning layer). 
     Referring next to  FIG. 3A , there is shown a schematic illustration of a stabilized side shield sensor design illustrating a first embodiment of the present disclosure. A schematic design, shown in  FIG. 3B , shows a prior-art structure, presented here for contrast only, that was previously disclosed in related applications Ser. Nos. 13/785,227 and 13/785,255. The structure in  FIG. 3B  would not meet the objects of the present disclosure because, as shown in  FIG. 3B , it includes a seed layer, shown as layer  40 , which is interposed between (and contiguous with) an insulation layer  5  and a shield layers  42 ,  43 ,  44 ,  45  and  46 , collectively denoted  47 . 
     The present disclosed first embodiment in  FIG. 3A  is found to provide advantages of the shield structure in the inset, with additional advantages that include (but are not limited to) a significantly improved cross-track read profile or micro-magnetic read width, μMRW. This improvement is obtained by the elimination of that seed layer ( 40  in  FIG. 3B ) from the side shield structure, which narrows the width of the shield without degrading its magnetic properties (as discussed above). This narrowed shield width is reflected in the improvement in μMRW. In addition to the physical narrowing of the structure because the seed layer  40  is absent, there are also advantages that are a result of the absence of the alloys typically used to form the seed layer, such as bilayers of Ta/Ru. The presence of these alloys adjacent to the edges of the free layer can adversely affect the magnetic properties of the sensor. 
     The first embodiment shielded sensor of  FIG. 3A  is shown in a cross-sectional view from an ABS perspective. The multiply-layered side shield structure, collectively denoted  47 , is formed on both sides of the patterned sensor (shown here as three layers  6   d ,  6   f  and  6   h , in a trapezoidally patterned shape) between the top,  7 , and bottom,  4 , shields. The side shields  47  provide longitudinal biasing to the free layer  6   f  in adjacent sensor stack  6   d ,  6   f  and  6   h.    
     The bottom shield  4  has a magnetization (arrow) m1 aligned in a cross-track (x-axis) direction, and top shield  7  has a magnetization (arrow) m5 aligned in the same direction as m1. In this exemplary configuration, free layer  6   f  has a magnetization (not shown) that would be either parallel or anti-parallel to m1 depending on the magnetic state (“0” or “1”) of the sensor. The m1 direction in the shield is typically set by a first anneal step that is performed before the layers in the sensor are deposited. 
     An aspect of the sensor is that the side shield structure  47  has sidewalls  47   s  formed adjacent to sides  6   s   2  of the sensor itself and the sensor free layer  6   f . The sidewalls are separated from the sensor sides by the insulation layer  5 . The side shield structure extends rearward from the ABS, in the positive y-direction, for a distance of between 30 nm to 2 microns toward a back end of the read head. 
     The two side edges  6   s   2  of the patterned sensor connect with a single backside edge  6   s   1  (not visible in this figure, but shown in  FIG. 2 ) at a certain distance behind the ABS and thereby form a continuous sidewall around the side and rear periphery of the sensor. This is shown clearly in an overhead view of the sensor periphery illustrated in  FIG. 5  below and discussed there. 
     As is seen in the schematic illustration of the shielded sensor of  FIG. 3A , an insulation layer  5  is formed on a top surface of bottom shield  4  except over the portion of the bottom shield surface, denoted  6   b , on which sensor layer  6   d  is formed. Thus, the bottom of layer  6   d  directly contacts the upper surface of the bottom shield,  4 , along the surface portion  6   b . The insulation layer  5  then extends upward along sidewalls  6   s   2  to separate the sensor from the side shields  47 . The distinction of the present disclosure from either of our previous disclosures Ser. Nos. 13/785,227 and 13/785,255 as shown in  FIG. 3B , is that those previous disclosures exploit a seed layer  40  abutting the side shield structure  47 , interposed between structure  47  and insulation layer  5 . In  FIG. 3A , the seed layer is omitted and its absence is found to improve the performance of the shielded sensor for several reasons discussed below. 
     In order to further improve the μMRW sharpness as illustrated in  FIG. 1 , the present disclosure eliminates this seed layer so that the longitudinal biasing layer is in the closet possible proximity with the free layer. The elimination of the seed layer, which would typically be a bi-layer of Ta/Ru of about 20 A total thickness, has several important advantages for the performance of the sensor, particularly when the side shields also include a high magnetic moment layer as will be discussed in a second embodiment shown in  FIG. 4 . First, in both the embodiments of  FIG. 3A  and  FIG. 4 , the absence of the seed layer reduces the gap between the free layer of the sensor and the biasing layers within the shield so that the micro-magnetic read width is improved by this gap reduction. Second, pinning of the high moment layer flux by the seed layer (see particularly the second embodiment of  FIG. 4 ) and by the soft magnetic shields is therefore prevented. Such pinning is undesirable because it is uncontrollable. It is much preferred that the magnetization of the high moment layer and of the shields as a whole be set by the subsequent annealing of the completed sensor under magnetic field conditions which are controllable. It becomes much easier to align the anisotropy or magnetization of the high moment layer and the soft magnetic layers in the side shields by annealing in a longitudinal magnetic field. 
     Above the insulation layer  5 , which is a layer of AlOx, MgO, SiNx, SiO 2  or the like, typically formed to a thickness between 20 A and 50 A, there is sequentially formed a first magnetic layer  42 , a first antiferromagnetic (AFM) coupling layer  43 , s second magnetic layer  44 , a second AFM coupling layer  45 , and a third magnetic layer  46 . These layers abut the insulation layer against the sides of the sensor. As a result, the magnetization (arrow m2) of the first magnetic layer  42  is aligned anti-parallel to magnetization (arrow m3) of the second magnetic layer  44  while magnetization (arrow m4) of the third magnetic layer  46  is also aligned anti-parallel to m3. The first magnetic layer preferably has a greater thickness than the second and third magnetic layers and thereby provides a majority of the longitudinal biasing to free layer  6   f . Third magnetic layer  46  contacts a bottom surface of the top shield  7  which induces m4 to be aligned in the same direction as (arrow m5) the magnetization of top shield  7 . Consequently, the top shield plays an important role in stabilizing the magnetization m2 and m4, respectively, which are parallel to m5. 
     AFM coupling between first magnetic layer  42  and second magnetic layer  44 , and between second magnetic layer  44  and third magnetic layer  46  also contributes to overall stabilization of the magnetic moments within the side shields  47 . Enhanced stabilization of the side shields leads to high output sharpness and improved magnetic read width. Moreover, side shields  47  prevent stray magnetic fields produced by a magnetic medium from inadvertently switching the magnetization direction of the free layer. 
     Preferably, the first, second, and third magnetic layers are comprised of one or both of the alloys CoFe and NiFe wherein the Ni content is between 70 and 90 atomic % to yield a soft magnetic layer. The alloys: NiFeMe (Me=Mo, Cr or Cu) can replace the NiFe in one of more the magnetic layers. As an example, the first magnetic layer  42  may be a NiFe/CoFe composite wherein the lower NiFe has a thickness from 50 to 300 A, while the CoFe layer preferably has a thickness between 5 to 20 A. Preferably, the second magnetic layer  44  is made of CoFe or a CoFe/NiFe/CoFe composite that has a thickness from 5 to 50 A, respectively. The third magnetic layer  46  may have a CoFe/NiFe configuration wherein the lower CoFe layer contacts the second AFM coupling layer  45  and has a thickness between 5 to 20 A, and the upper NiFe layer preferably has a thickness from 50 to 200 A. According to this embodiment, the NiFe layer in the first magnetic layer provides a majority of the longitudinal biasing to the free layer. The biasing strength can be tuned by adjusting the thickness of the NiFe layer. 
     In a further aspect, the AFM coupling layers  43 ,  45  are made of Ru and have a thickness of 7 to 9 A to promote maximum AFM coupling (i.e., maintaining antiparallel magnetizations) between adjacent magnetic layers in the side shields. 
     Referring now to  FIG. 4 , a further embodiment of the present disclosure is schematically illustrated that retains all of the elements comprising the first embodiment structure in  FIG. 3A , and, in addition, includes a high magnetic moment layer  41  (also denoted, for simplicity, a “high moment” layer) that is formed covering a portion of the peripheral surfaces of the side shields. The position of the high moment layer over the side shields effectively interposes it between the side shields  48  and the layer of insulation  5 . In this position, the high moment layer is able to concentrate magnetic flux from the side shields to the magnetic layers of the sensor. We will call this high moment layer  41  the “first” high moment layer where we wish to distinguish it from other high moment layers. 
     Additional high moment layers (additional to the first high moment layer  41 ) are formed as part of the upper and lower shields. Specifically, as a lower layer  7   a  of the top shield  7  and as an upper layer  4   b  of the bottom shield  4 . All of these high moment layers serve to stabilize the sensor and the first such layer  41  surrounding the bottom and sides of the side shield  48 , also concentrates flux onto the sides of the sensor stack further improving the micro-magnetic read width sharpness. 
     The first high moment layer  41  is formed directly on the insulation layer  5  and is thereby contiguous with and conformal to layer  5 . The high moment layer continuously follows the shape of layer  5  but does not extend to cover the portion of layer  5  that covers the backside of the sensor. 
     Insulation layer  5  is formed above a top layer  4   b  of the bottom shield  4  and is contiguous with and conformal to patterned sensor sides  6   s   2 . Layers  41  and  42  form a composite magnetic layer  49  that provides a majority of the longitudinal biasing to the free layer  6   f  in the sensor element. Note that magnetization vectors m2a and m2b in the high moment layer  41  and bottom shield layer  42  respectively are parallel to each other. The high moment layer  41  has a thickness between approximately 5 A and 50 A, but preferably from approximately 10 A to 30 A. In one embodiment, the high moment layer  41  is Fe. In another embodiment, the high moment layer  41  may be formed of other materials that have similar properties to Fe, such as FeNi alloy in which the Fe content is greater than 30 atomic %. 
     Layers  42 - 46  in each side shield  48  are sequentially formed on the first high moment layer  41 . Magnetic layers  42 ,  44 ,  46  are made of one or both CoFe and NiFe as described previously. Note also that layers  44 ,  45  and  46  may form a synthetic antiferromagnetic structure where magnetizations m3 and m4 are antiparallel. 
     The top shield  7  is a composite structure having a second high moment layer  7   a  that contacts a top surface  6   t  of the sensor element and forms an interface with side shields  48  along a top surface of the second magnetic layer  46 . The top shield also comprises an upper magnetic layer  7   b  which may have the same material composition as the bottom layer  4   b  in the bottom shield. 
     As yet another embodiment of this disclosure, layers  7   a  and  4   b  are both also layers of high magnetic moment material, so that the sensor stack is completely encased in such high magnetic moment material, along its sides and bottom, by layer  41 , and along its top by layer  7   a  and its bottom by layer  4   b . The layers  7   a  and  4   b  act in an advantageous manner in improving μMRW due to their close proximity to the sensor stack and their strengthening of the magnetic interactions that bias and stabilize the sensor. 
     Referring now to  FIG. 5 , there is shown an overhead view of the embodiment of  FIG. 4 , where top shield  7  has been removed to show a top surface  48   t  of the side shield structure  48 . Note, the entire shield is labeled  48  in  FIG. 4 , but its upper layer is  46 , so  48   t  could equally well be labeled  46   t  in  FIG. 5 . 
       FIG. 5  also shows a top surface, labeled  6   t , of the patterned sensor (which would be the top surface of layer  6   h  in  FIG. 4 ). Also shown in  FIG. 5  are the two parallel side edges of the sensor,  6   s   2  that extend rearward in the +y direction and the backside edge of the sensor,  6   s   1 . The side shield sidewalls  48   s , which form the periphery of the top edges of layers  5  and  41 , extend parallel to sides  6   s   2  of the patterned sensor, towards a backside  6   s   1  of the sensor wherein the sensor backside is located a distance d of 30 nm to 2 microns in a positive y-axis direction from the ABS. Note that the space between  6   s   2  and  48   s  will contain the edges of the contiguous pair  5  and  41 , the layer of insulation and the high moment layer. However, while layer  5  extends around the backside,  6   s   1 , of the sensor, layer  41  abuts only the side  6   s   2 . 
     In addition, the present disclosure also anticipates an embodiment wherein side shields  48  extend rearward (+y direction) for a greater distance than d from the ABS. Preferably, the sidewalls  48   s  extend at least a distance d to provide a maximum biasing effect to the free layer in the sensor. 
     The present disclosure also discloses a method of forming a sensor with a wrap-around shield configuration that is stabilized by AFM coupling between the magnetic layers in the side shields, and includes a high moment layer in each shield to enable a better μMRW for improved read head performance. This fabrication method will be described below. 
     In  FIG. 6 , a first step in a fabrication process is illustrated wherein bottom shield layer  4  (i.e. the bi-layer  4   a  and  4   b ) is formed on a substrate (not shown) by a sputtering method of physical vapor deposition (PVD), for example. The bottom shield is annealed by a conventional process to set the magnetization m1a, m1b, shown in  FIG. 4 , in an x-axis direction. Thereafter, layers  6   d   1 ,  6   d   2 ,  6   d   3 ,  6   f , and  6   h  in the sensor stack are sequentially formed by PVD, with the bottom surface  6   b  of layer  6   d   1  contacting a top surface of the bottom shield. Layer  6   d   3  may be a non-magnetic, but electrically conductive metal such as Cu in a giant magnetoresistvie (GMR) sensor or a non-conducting oxide such as MgO in a tunneling magnetoresistive (TMR) sensor. Free layer  6   f  may be a single layer or a composite including a plurality of magnetic layers. A composite free layer may have a synthetic antiferromagnetic configuration wherein two ferromagnetic layers are separated by a coupling layer such as Ru and aligned with antiparallel magnetizations. The uppermost layer  6   h  is a capping layer that may be one or more of Ta and Ru, or other materials used in the art. 
     During the following step in the fabrication sequence, a photoresist layer is spin coated and patterned on the sensor top surface  6   t  by a conventional photolithography process to generate a pattern including a photoresist island  60  having a width w, typically between 20 nm-50 mm in the cross-track (x) direction after photoresist trimming. The photoresist pattern typically includes a plurality of islands arranged in rows and columns that, from a top-down view, are each similar to the sensor top surface  6   t  shown in  FIG. 5 . There are openings  61  on either side of the photoresist island that expose a substantial portion of top surface  6   t . It should be understood that a portion of top surface  6   t  is also uncovered along a back side (not shown) of layer  60  to completely isolate adjacent islands in the photoresist pattern. 
     Referring to schematic  FIG. 7 , an ion milling process or ion beam etch (IBE) process as disclosed in related patent application Ser. No. 13/803,362 and fully incorporated herein by reference is performed to transfer the shape of the photoresist island  60 , in the negative z direction, down through the sensor stack of layers. In particular, the IBE includes a step wherein incident ions have an angle of 0 to 10 degrees with respect to a plane (not shown) that is perpendicular to top surface  6   t . The IBE process stops on a top surface  62  of reference layer  6   d   2 . 
     In an alternative embodiment, the first IBE step is extended downward to produce an over-etch that penetrates beyond  62  and etches into the SAF reference layer  6   d   2 . The over-etch is to insure that the free layer  6   f  is completely etched away so that no remnants produce shunting problems. The IBE process may include a second step that features an IBE side trim at an angle of 45 to 75 degrees to reduce the free layer width and, incidentally, to shape the sides of the sensor element. 
     When the width dimension w is substantially less than 100 nm, then sloped sides  6   s   2  are usually desirable to prevent collapse of the sensor during a subsequent milling step. An IBE process is generally preferred as the etch method to generate sloped sidewalls since the ions can be angled with respect to the z-axis direction. As a result, the cross-track distance between sides  6   s   2  at the position of the non-magnetic spacer  6   d   3  is generally greater than the track width w at the top surface of upper layer  6   h.    
     In schematic  FIG. 8 , insulation layer  5  is deposited along the sides  6   s   2  by ion beam deposition (IBD), PVD (physical vapor deposition), or atomic layer deposition (ALD) to a thickness between approximately 20 A-50 A. Next, the side shields  48  are formed adjacent to sides  6   s   2  by consecutively depositing the high moment layer  41  over the insulation layer, then forming the first magnetic layer  42 , the first AFM layer  43 , the second magnetic layer  44 , the second AFM layer  45 , and the third magnetic layer  46  by IBD or PVD method. When an IBD method is used for depositing the insulation layer  5  and the side shield layers, the deposition angle may be varied to fine tune the sidewall coverage of the side shields. When the IBD angle is close to normal with respect to the plane of the wafer, the insulation layer  5  coverage is the thinnest at sides  6   s   2 . In PVD, the process pressure may be varied to fine tune the sidewall coverage. The photoresist layer  60  is then removed by a standard liftoff process. A chemical mechanical polish (CMP) process may be employed to form a top surface  46   t  that is essentially coplanar with a top surface  6   t  of the sensor. 
     Thereafter, a top shield is formed by IBD or PVD to complete the shield structure illustrated in  FIG. 4 . A second anneal step may be performed to set the magnetization direction of layers  7   a ,  7   b  in top shield  7 , and layers  41 ,  42 ,  44 ,  46  in the side shields. 
     In summary, we have disclosed a wrapped shield structure and its method of fabrication. The structure provides biasing to a free layer in an adjacent sensor stack and improved stabilization. Furthermore, micro magnetic read width performance is enhanced compared with the prior art. 
     As is understood by a person skilled in the art, the present description is illustrative of the present disclosure rather than limiting of the present disclosure. Revisions and modifications may be made to methods, materials, structures and dimensions employed in forming and providing a read sensor having a wrapped shield structure formed without seed layers for improved micromagnetic read width performance and enhanced magnetic stability, while still forming and providing such a read sensor and its method of formation in accord with the spirit and scope of the present disclosure as defined by the appended claims.