Abstract:
Approaches to improving hard disk drive far track interference problems include utilizing a wrap-around shield having recessed high magnetic moment layer(s). Embodiments include tapering the high-moment portion away from the air bearing surface (ABS) in the cross-track direction away from the write pole, thereby reducing exposure of high moment layers at the ABS to reduce the risk of unwanted track erasure away from the main pole. Embodiments include positioning the high magnetic moment layers in their entirety away from the ABS, such as with a laminate structure of high magnetic moment and low magnetic moment materials laid down in a direction away from the pole tip trailing edge.

Description:
FIELD OF THE INVENTION 
       [0001]    Embodiments of the invention relate generally to perpendicular magnetic recording and more particularly to improving far track interference performance. 
       BACKGROUND 
       [0002]    A hard-disk drive (HDD) is a non-volatile storage device that is housed in a protective enclosure and stores digitally encoded data on one or more circular disks having magnetic surfaces. When an HDD is in operation, each magnetic-recording disk is rapidly rotated by a spindle system. Data is read from and written to a magnetic-recording disk using a read/write head that is positioned over a specific location of a disk by an actuator. 
         [0003]    A read/write head uses a magnetic field to read data from and write data to the surface of a magnetic-recording disk. Write heads make use of the electricity flowing through a coil, which produces a magnetic field. Electrical pulses are sent to the write head, with different patterns of positive and negative currents. The current in the coil of the write head induces a magnetic field across the gap between the head and the magnetic disk, which in turn magnetizes a small area on the recording medium. 
         [0004]    A perpendicular magnetic recording (PMR) system records data as magnetizations oriented perpendicular to the plane of the magnetic-recording disk. The magnetic disk has a magnetically soft underlayer covered by a thin magnetically hard top layer. The perpendicular write head has a main pole with a very small cross section at the pole tip, tapered down from the cross section along the length of the yoke from which the pole tip protrudes, and a return pole having a much larger cross section along the length. A write head may also include a wrap-around shield for assisting in focusing the magnetic field emitting from the pole tip by managing the magnetic leakage from the pole tip, and a back gap. A strong, highly concentrated magnetic field emits from the writer main pole in a direction perpendicular to the magnetic disk surface, magnetizing the magnetically hard top layer of the disk. The resulting magnetic flux then travels through the soft underlayer of the magnetic disk, returning to the return pole where it is sufficiently spread out and weak that it will not erase the signal recorded by the main pole when it passes back through the magnetically hard top layer of the disk on its way back to the return pole. 
         [0005]    However, there remains a risk associated with a write operation, that the highly concentrated magnetic field emitted from the writer main pole tip will interfere with the data integrity of adjacent tracks (referred to as “adjacent track interference”, or “ATI”) and tracks beyond adjacent (referred to as “far track interference”, or “FTI”), typically manifesting as soft errors. Because a significant amount of magnetic flux is generated in the relatively wide cross section main pole and channeled into the very small cross section pole tip, magnetic leakage occurs which can cause ATI and FTI. While there are teams of scientists and engineers designing solutions to reduce such leakage, a couple general approaches to this issue are to optimize the design of the main pole (e.g., the geometry, the flare point, etc.) and, as mentioned, to utilize a wrap-around shield (“WAS”) to “catch” and redirect the flux leakage. A WAS is typically positioned at and wrapping around the main pole tip, and is constructed of magnetic material having a lower magnetic moment than the main pole material. 
       SUMMARY OF EMBODIMENTS OF THE INVENTION 
       [0006]    Embodiments of the invention are directed to improving hard disk drive (HDD) far track interference (FTI) problems by utilizing a wrap-around shield (WAS) having recessed high magnetic moment layer(s). 
         [0007]    Embodiments include tapering the high-moment portion of the WAS away from the air bearing surface (ABS) in the cross-track direction away from the write pole, thereby reducing exposure of high-moment layers at the ABS to reduce the risk of unwanted track erasure away from the main pole. 
         [0008]    Embodiments include positioning the high-moment layers in their entirety away from the ABS, such as with a monolithic high-moment structure leading away from the main pole tip trailing edge side or with a laminate structure of high-moment and low-moment materials laid down in a direction away from the pole tip trailing edge. 
         [0009]    Embodiments discussed in the Summary of Embodiments of the Invention section are not meant to suggest, describe, or teach all the embodiments discussed herein. Thus, embodiments of the invention may contain additional or different features than those discussed in this section. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    Embodiments of the invention are illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings and in which like reference numerals refer to similar elements and in which: 
           [0011]      FIG. 1  is a plan view of a hard disk drive (HDD), according to an embodiment of the invention; 
           [0012]      FIG. 2  is a cross-sectional side view of a perpendicular magnetic recording head, according to an embodiment of the invention; 
           [0013]      FIG. 3  is an air bearing surface (ABS) view of a conventional wrap-around shield (WAS) structure; 
           [0014]      FIG. 4A  is an ABS view of a recessed WAS structure, according to an embodiment of the invention; 
           [0015]      FIG. 4B  is a top view of a recessed WAS structure, according to an embodiment of the invention; 
           [0016]      FIG. 5  is a cross-sectional side view of a recessed WAS structure, according to an embodiment of the invention; and 
           [0017]      FIG. 6  is a cross-sectional side view of a recessed laminated WAS structure, according to an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0018]    Approaches to a recessed wrap-around shield in a magnetic write head, with applicability to incorporation into a hard disk drive, are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention described herein. It will be apparent, however, that the embodiments of the invention described herein may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form in order to avoid unnecessarily obscuring the embodiments of the invention described herein. 
       PHYSICAL DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS OF THE INVENTION 
       [0019]    Embodiments of the invention may be used in the context of a magnetic writer for a hard-disk drive (HDD). In accordance with an embodiment of the invention, a plan view of a HDD  100  is shown in  FIG. 1 .  FIG. 1  illustrates the functional arrangement of components of the HDD including a slider  110   b  that includes a magnetic-reading/recording head  110   a . Collectively, slider  110   b  and head  110   a  may be referred to as a head slider. The HDD  100  includes at least one head gimbal assembly (HGA)  110  including the head slider, a lead suspension  110   c  attached to the head slider, and a load beam  110   d  attached to the lead suspension  110   c . The HDD  100  also includes at least one magnetic-recording disk  120  rotatably mounted on a spindle  124  and a drive motor (not visible) attached to the spindle  124  for rotating the disk  120 . The head  110   a  includes a write element and a read element for respectively writing and reading information stored on the disk  120  of the HDD  100 . The disk  120  or a plurality (not shown) of disks may be affixed to the spindle  124  with a disk clamp  128 . 
         [0020]    The HDD  100  further includes an arm  132  attached to the HGA  110 , a carriage  134 , a voice-coil motor (VCM) that includes an armature  136  including a voice coil  140  attached to the carriage  134 ; and a stator  144  including a voice-coil magnet (not shown). The armature  136  of the VCM is attached to the carriage  134  and is configured to move the arm  132  and the HGA  110  to access portions of the disk  120  being mounted on a pivot-shaft  148  with an interposed pivot-bearing assembly  152 . In the case of an HDD having multiple disks, or platters as disks are sometimes referred to in the art, the carriage  134  is called an “E-block,” or comb, because the carriage is arranged to carry a ganged array of arms that gives it the appearance of a comb. 
         [0021]    With further reference to  FIG. 1 , in accordance with an embodiment of the present invention, electrical signals, for example, current to the voice coil  140  of the VCM, write signal to and read signal from the head  110   a , are provided by a flexible interconnect cable  156  (“flex cable”). Interconnection between the flex cable  156  and the head  110   a  may be provided by an arm-electronics (AE) module  160 , which may have an on-board pre-amplifier for the read signal, as well as other read-channel and write-channel electronic components. The AE  160  may be attached to the carriage  134  as shown. The flex cable  156  is coupled to an electrical-connector block  164 , which provides electrical communication through electrical feedthroughs (not shown) provided by an HDD housing  168 . The HDD housing  168 , also referred to as a casting, depending upon whether the HDD housing is cast, in conjunction with an HDD cover (not shown) provides a sealed, protective enclosure for the information storage components of the HDD  100 . 
         [0022]    With further reference to  FIG. 1 , in accordance with an embodiment of the present invention, other electronic components (not shown), including a disk controller and servo electronics including a digital-signal processor (DSP), provide electrical signals to the drive motor, the voice coil  140  of the VCM and the head  110   a  of the HGA  110 . The electrical signal provided to the drive motor enables the drive motor to spin providing a torque to the spindle  124  which is in turn transmitted to the disk  120  that is affixed to the spindle  124  by the disk clamp  128 ; as a result, the disk  120  spins in a direction  172 . The spinning disk  120  creates a cushion of air that acts as an air-bearing on which the air-bearing surface (ABS) of the slider  110   b  rides so that the slider  110   b  flies above the surface of the disk  120  without making contact with a thin magnetic-recording medium of the disk  120  in which information is recorded. 
         [0023]    The electrical signal provided to the voice coil  140  of the VCM enables the head  110   a  of the HGA  110  to access a track  176  on which information is recorded. Thus, the armature  136  of the VCM swings through an arc  180  which enables the HGA  110  attached to the armature  136  by the arm  132  to access various tracks on the disk  120 . Information is stored on the disk  120  in a plurality of stacked tracks (not shown) arranged in sectors on the disk  120 , for example, sector  184 . Correspondingly, each track is composed of a plurality of sectored track portions, for example, sectored track portion  188 . Each sectored track portion  188  is composed of recorded data and a header containing a servo-burst-signal pattern, for example, an ABCD-servo-burst-signal pattern, information that identifies the track  176 , and error correction code information. In accessing the track  176 , the read element of the head  110   a  of the HGA  110  reads the servo-burst-signal pattern which provides a position-error-signal (PES) to the servo electronics, which controls the electrical signal provided to the voice coil  140  of the VCM, enabling the head  110   a  to follow the track  176 . Upon finding the track  176  and identifying a particular sectored track portion  188 , the head  110   a  either reads data from the track  176  or writes data to the track  176  depending on instructions received by the disk controller from an external agent, for example, a microprocessor of a computer system. 
         [0024]      FIG. 2  is a cross-sectional side of a perpendicular magnetic recording (PMR) head, according to an embodiment of the invention.  FIG. 2  illustrates a PMR head  200  in recording relation with a perpendicular magnetic recording medium such as disk  210 . PMR head  200  comprises a reader  220  and a writer  230 . 
         [0025]    PMR writer  230  comprises a main pole  231 , an auxiliary pole  232  (also at times referred to as a “stitch pole”), a writer coil  235 , a magnetic wrap-around shield (WAS)  234 , and a return pole  233 . Main pole  231  is exposed at the air bearing surface (ABS), faces disk  210 , and forms recording bits by reversing the magnetization of magnetic particles in the disk  210 . Auxiliary pole  232  is magnetically connected to the main pole  231  but is not typically exposed at the ABS. Writer coil  235  is for exciting the main pole  231  and the auxiliary pole  232 , i.e., the electricity flowing through the coil  235  produces a magnetic field. The WAS  234  is positioned at the periphery of the main pole  231  tip for assisting with focusing the magnetic flux emitting from main pole  231 , and a return pole  233  is positioned for providing means for the magnetic flux to return to the writer structure to complete the magnetic circuit. 
         [0026]    As mentioned, electrical pulses are sent to the coil  235  of writer  230  with different patterns of positive and negative currents and the current in the coil  235  induces a magnetic field across the gap between the main pole  231  and the disk  210 , which in turn magnetizes a small area on the recording medium. A strong, highly concentrated magnetic field emits from the main pole  231  in a direction perpendicular to the  210  disk surface, magnetizing the magnetically hard top layer  211 . The resulting magnetic flux then travels through the soft underlayer  212 , returning to the return pole  233  where it is sufficiently spread out and weak that it will not erase the signal recorded by the main pole  231  when it passes back through the magnetically hard top layer  211  on its way back to the return pole  233 . 
       Magnetic Write Head with a Recessed Wrap-Around Shield 
       [0027]    As mentioned, a risk associated with write operations in a hard disk drive (HDD) is that the highly concentrated magnetic field emitted from the writer main pole tip will interfere with the data integrity of adjacent tracks and/or tracks beyond adjacent (“far track interference”, or “FTI”). While the known approaches to this issue are to optimize the design of the main pole and to implement a wrap-around shield (“WAS”) to control the flux leakage, challenges still remain with combating FTI. Therefore, embodiments of the invention are directed to improving HDD FTI problems by utilizing a WAS having recessed high magnetic moment layers. 
       Tapered Recessed High-Moment Wrap-Around Shield Layer 
       [0028]      FIG. 3  is an air bearing surface (ABS) view of a conventional wrap-around shield (WAS) structure.  FIG. 3  illustrates a portion of a magnetic write head  300 , which comprises a magnetic pole tip  302  of a main pole (e.g., main pole  231  of  FIG. 2 ). The pole tip  302  is wrapped by a WAS structure comprising a relatively thin high magnetic moment material layer  306  (also referred to simply as the “high-moment layer” and the “high-moment portion” as it may comprise multiple thin layers or films) and some bulk low magnetic moment material  308  (also referred to simply as “low moment portion”). The high-moment portion  306  has a higher magnetic moment than the low-moment portion  308 . A thin layer  304  of magnetic insulating/isolating material, such as Ru, separates the pole tip  302  from the WAS structure. The remaining material under the isolating layer is primarily filler, such as alumina. As mentioned, a WAS is used to “catch” and redirect flux leakage from the main pole and pole tip  302  to the return pole (e.g., return pole  233  of  FIG. 2 ), and is constructed of magnetic materials having a lower magnetic moment than the main pole material so that the WAS materials are less likely to generate their own magnetic flux from the excitation of the main pole. 
         [0029]    Note that the layer  304 , high-moment portion  306 , and low-moment portion  308  not only wrap around a significant portion of the pole tip  302  surfaces, but also flare in both lateral (cross-track) directions for some distance away from the pole tip  302  area. Such a configuration is mainly a result of attempting to limit the complexity of some of the thin film manufacturing processes used to fabricate a magnetic write head such as write head  300 . However, manufacturing simplicity comes at the expense of FTI in this context. It has been found that FTI “hot spots” are created away from the pole tip  302  close to the high-moment layer  306 , for example, near a location  310 . 
         [0030]      FIG. 4A  is an ABS view of a recessed WAS structure, according to an embodiment of the invention.  FIG. 4A  illustrates a portion of a magnetic write head  400 , which comprises a magnetic pole tip  402  of a main pole (e.g., main pole  231  of  FIG. 2 ). The pole tip  402  is wrapped by a WAS structure comprising a relatively thin (e.g., but not limiting, approximately 50-100 nm) high magnetic moment material layer  406  (also referred to simply as the “high-moment layer” and the “high-moment portion” as it may comprise multiple thin layers or films) and some bulk low magnetic moment material  408  (also referred to simply as “low moment portion”). The high-moment portion  406  has a higher magnetic moment than the low-moment portion  408 , and is typically positioned closer to the pole tip  402  than the low-moment portion  408  to enable a sharp magnetic recording field gradient or pulse. A thin layer  404  of magnetic insulating/isolating material, such as Ru, separates the pole tip  402  from the WAS structure. The remaining material under the isolating layer is primarily filler, such as alumina. 
         [0031]    With further reference to  FIG. 4A , according to an embodiment, the WAS is configured such that at least a portion of high-moment portion  406  is recessed from the air bearing surface. Thus, being an ABS view,  FIG. 4A  illustrates the absence of high-moment layer  406  along the lateral flares of the WAS structure because the high-moment portion  406  is recessed from the ABS in these regions. Generally, high-moment WAS material is functionally most effective at the trailing edge (the top side of the pole tip  402  as depicted in  FIG. 4A ) to improve the magnetic recording field gradient and thus better track SER, and secondarily at the sides of the pole tip  402  to improve side-field gradient which well defines the edges of the track. Therefore, removing or foregoing the deposition of the high-moment portion  406  in areas beyond the trailing edge and possibly the sides of the pole tip does not significantly degrade the WAS function, but provides a counteraction to the FTI risk. 
         [0032]      FIG. 4B  is a top view of a recessed WAS structure according to an embodiment of the invention, such as the recessed WAS structure of magnetic write head  400  along line A-A of  FIG. 4A . Visible in this top view A-A of the WAS structure are the low-moment portion  408 , extending to the ABS and along the surface of the ABS, and the recessed high-moment portion  406  covering the top of the pole tip  402  of the main pole. The recessed high-moment portion  406  is depicted extending a small distance laterally beyond the pole tip  402 , consistent with its width depicted in  FIG. 4A , and tapering away from the ABS starting around the area at which high-moment portion  406  meets with the layer  404  ( FIG. 4A ). 
         [0033]    With the conventional write head  300  of  FIG. 3 , it was noted that each of layer  304 , high-moment portion  306 , and low-moment portion  308  flare in both lateral (cross-track) directions for some distance away from the pole tip  302  area, and that research has determined that FTI “hot spots” are created away from the pole tip  302  close to the high-moment layer  306 , for example, near location  310 . Returning to  FIG. 4A , according to an embodiment, the WAS is configured such that at least a portion of high-moment portion  406  is recessed from the air bearing surface. For example, a different mask may be used to fabricate high-moment portion  406  than would be used to fabricate high-moment portion  306 . Thus, being an ABS view,  FIG. 4A  illustrates the absence of high-moment layer  406  along the lateral flares of the WAS structure because the high-moment portion  406  is recessed from the ABS in these regions. Consequently, the FTI hot spots generated in the magnetic write head  300  are likely reduced or eliminated in the magnetic write head  400  of the present embodiment. 
         [0034]    With further reference to  FIG. 4B , high-moment portion  406  tapers away from the ABS in the cross-track direction away from the pole tip  402 , to a distance X from the ABS, from where the high-moment portion  402  continues in the cross-track direction substantially parallel to the ABS. The exact configuration and dimensions associated with the taper portion and the ultimate cross-track portion of high-moment portion  406  may vary from implementation to implementation depending, for example, on the design of the main pole, pole tip, drive coil and magnetic write head, generally. However, for example and according to an embodiment, research and development has determined that a reasonable and functional configuration to comprise an ultimate recess distance X of approximately 100 nm from the ABS and a taper angle α of approximately 30°-45°, to be sufficient to effectively eliminate the FTI risk. Furthermore, the present embodiment for a recessed WAS high-moment portion may be implemented using a dry-pole fabrication process and/or the snore complex Damascene fabrication process. 
       Complete Recessed High-Moment Wrap-Around Shield Layer 
       [0035]      FIG. 5  is a cross-sectional side of a recessed WAS structure, according to an embodiment of the invention.  FIG. 5  illustrates a magnetic write head comprising a writer  530 . The write head depicted in  FIG. 5  is largely similar to the head  200  depicted in  FIG. 2 , with some notable differences as follows. Like elements are labeled with the same element numbers as in  FIG. 2  and for purposes of clarity the associated descriptions of these elements are not repeated here. Reference is made to the description of  FIG. 2  for such descriptions. 
         [0036]    The write head of  FIG. 5  comprises a main pole  502  wrapped by a WAS structure comprising a low-moment portion  508  and a recessed high-moment portion  506 . In contrast to the write head  400  illustrated in  FIGS. 4A and 4B , the high-moment portion  506  of the write head illustrated in the embodiment of  FIG. 5  is completely and entirely recessed from the ABS, with the low-moment portion  508  being flush with the ABS and in front of the high-moment portion  506 . This embodiment extends the idea of recessing the high-moment portion of the WAS away from the ABS by adding additional layers of high-moment portion  506 , all of which are entirely recessed from the ABS. The additional high-moment layers improve the ability of the WAS structure to carry away the stray magnetic flux from the main pole without leaking it to the ABS. The plurality of high-moment layers of high-moment portion  506  are constructed essentially as a high-moment monolith or tower recessed from the ABS and deposited in layers in a direction leading away from the pole tip trailing edge side. 
       Laminated Recessed Wrap-Around Shield Layers 
       [0037]      FIG. 6  is a cross-sectional side view of a recessed laminated WAS structure, according to an embodiment of the invention.  FIG. 6  illustrates a magnetic write head comprising a writer  630 . The write head depicted in  FIG. 6  is largely similar to the head  200  depicted in  FIG. 2 , with some notable differences as follows. Like elements are labeled with the same element numbers as in  FIG. 2  and for purposes of clarity the associated descriptions of these elements are not repeated here. Reference is made to the description of  FIG. 2  for such descriptions. 
         [0038]    The write head of  FIG. 6  comprises a main pole  602  wrapped by a WAS structure comprising a low-moment portion  608  and a recessed high-moment portion  606 . In contrast to the write head  400  illustrated in  FIGS. 4A and 4B , the high-moment portion  606  of the write head illustrated in the embodiment of  FIG. 6  is completely and entirely recessed from the ABS, with the low-moment portion  608  being flush with the ABS and in front of the high-moment portion  606 . This embodiment extends the idea of recessing the high-moment portion of the WAS away from the ABS by adding additional layers of high-moment portion  606 , all of which are entirely recessed from the ABS. The high-moment layers of high-moment portion  606  are configured in a laminate structure with low-moment layers of low-moment portion  608 . The additional high-moment layers improve the ability of the WAS structure to carry away the stray magnetic flux without leaking it to the ABS, and the laminated low-moment layers serve generally as filler. According to a related embodiment, layers corresponding to the high-moment portion  606  and layers corresponding to the low-moment portion  608  are deposited in a laminate structure having alternating high-moment and low-moment portions in a direction leading away from the trailing edge side of the pole tip. 
         [0039]    The foregoing embodiments for completely recessed WAS high-moment portions may be implemented using a dry-pole fabrication process and/or the more complex Damascene fabrication process. 
         [0040]    In the foregoing specification, embodiments of the invention have been described with reference to numerous specific details that may vary from implementation to implementation. Thus, the sole and exclusive indicator of what is the invention, and is intended by the applicants to be the invention, is the set of claims that issue from this application, in the specific form in which such claims issue, including any subsequent correction. Any definitions expressly set forth herein for terms contained in such claims shall govern the meaning of such terms as used in the claims. Hence, no limitation, element, property, feature, advantage or attribute that is not expressly recited in a claim should limit the scope of such claim in any way. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.