Patent Publication Number: US-2022223176-A1

Title: Perpendicular Magnetic Recording (PMR) Writer with Recessed Leading Shield

Description:
This is a Divisional application of U.S. patent application Ser. No. 16/209,136 filed on Dec. 4, 2018, which is herein incorporated by reference in its entirety and assigned to a common assignee. 
    
    
     BACKGROUND 
     1. Technical Field 
     This disclosure relates generally to a writer used in perpendicular magnetic recording (PMR) and particularly to the design of shields that improve their performance. 
     2. Description 
     In today&#39;s PMR design, an important role of the Leading Shield (LS) is to prevent Side Shield (SS) saturation and leading side induced adjacent track interference (ATI). In current (i.e., prior art) writer designs the LS is exposed at the ABS to support the SS, however the downside of this exposure is that the LS will attract the main pole (MP) field that is returned from the disk soft underlayer (SUL) and reduce the trailing side return field. Keeping in mind the important measures of “bits per inch” (BPI) and “tracks per inch” (TPI), in this disclosure we propose a PMR writer design where OW/BPI will be enhanced, while ATI/TPI can be preserved. 
     Examples are taught in U.S. Patent Application 2018/0005648 (Fujii et al—TDK) discloses recessing part of the leading shield from the ABS. U.S. Pat. No. 9,036,299 (Chembrolu) discloses a portion of a wrap-around shield recessed from the ABS. U.S. Pat. No. 8,385,020 (Min) teaches recessed leading shield, side shield, and write shield. U.S. Pat. No. 8,345,388 (Guan et al.) shows recessed edges of shields at the ABS. None of these examples provide the effectiveness and degree of control that we provide in this disclosure. 
     SUMMARY 
     We disclose a PMR writer with a leading shield (LS) layer and a contiguous “leading shield taper” (LET) layer, both having distal edges (distal referring to an edge closest to the air-bearing surface (ABS)) in planes parallel to the ABS plane but not coplanar with the ABS plane so that both layers may be independently recessed from the ABS plane. As main pole (MP) magnetic flux emitted from the MP returns from the SUL of an adjacent magnetic recording medium, the flux distribution is very sensitive to spacing from the ABS to the SUL. Therefore, a larger gap between the LS and the SUL of the magnetic recording media can guarantee the maximum return field shifting to the trailing side of the main pole. As the overall LS volume and LS/SS connection is kept the same, TPI loss in this design configuration is minimized. 
       FIG. 1A  shows a cross-sectional plane (perpendicular to the ABS plane  10 ) cut through the center of the main pole (MP)  20 , of a prior art PMR writer (one currently in use) and  FIG. 1B  shows the same illustration for the presently disclosed PMR writer. Note, edges of the elements of the PMR (shields, etc.) extending closest to the ABS  10  will be referred to as distal edges. Opposite edges and other portions further away from the ABS will be considered as proximal. 
     Referring first to  FIG. 1A , there is shown the MP  20 , extending to the ABS  10  where its tip  25  has a trapezoidal shape (not shown here) in the ABS plane (shown in  FIGS. 5A &amp; 5B ). The cross-section of a trailing-edge shield (TS) is shown as two layers; layer  30  is low moment (B s ) material, typically 1 kG to 22 kG, and  35  is a high moment material, typically 16 kG to 24 kG. The leading-edge shield (LS), is shown as  40  and its material has a moment between 1 kG and 19 kG, typically lower than the side shields (not shown here). 
     A leading-edge taper (LET) layer is shown as  50  and it can have a moment that is independent of the leading-edge shield material. The LET taper is separated from the side of the MP by a narrow gap  51 , but the taper is conformal to a complementary taper along the side of the MP as shown in the figure. A soft underlayer (SUL)  60  of a magnetic recording medium is shown beneath the ABS  10 . Magnetic flux lines  70  are shown emerging from the tip of the main pole  25 , striking the SUL  60  and returning from the SUL  60  to enter the various shields. The flux intensity is represented schematically by the number of flux lines, which is here shown to be equal in number returning on the leading-edge side and trailing edge side of the main pole. Surrounding filler material,  90  is dielectric or, can be non-magnetic metals. 
     Referring now to  FIG. 1B , the presently disclosed design shows a TS with two layers,  30  and  35  as in  FIG. 1A . There is also the cross-section of a MP  20  extending to the ABS  10 . The leading-edge side of the MP now shows two independently positioned layers adjacent to it, a LET  50  and a LS  45 . The distal surface of the leading-edge shield  45  is now recessed (raised) above the ABS  10 , although still parallel to the ABS, and is tapered to have an inner edge  55  coplanar with the inner edge of the LET  50  and conformal to the taper of the MP, although the tapered edges of the LS and LET are now shifted alongside and relative to each other. In this design configuration, the recess amount of the LET and LS can be independent of each other. Thus, there are three options for this recess configuration: LS recessed only, LET recessed only, and LS and LET both recessed independently.  FIG. 1B  shows the LS recess-only configuration, configuration 1. 
     Referring now to  FIGS. 2A and 2B , there is shown schematically the LS-LET-SS configuration in a cross-sectional view through the central plane of the MP  20  in  2 A (as in  FIG. 1B ). The difference between this configuration and that of  1 B is that the LS  45  is now recessed from the ABS by 200 nm and is vertically separated from the LET layer  50 , which remains coplanar with the ABS plane.  FIG. 2B  shows the same configuration as  FIG. 2A , but the cross-sectional plane of the figure is sufficiently off the central axis that a portion of the side-shield (SS)  80  is visible along with the recessed LS  45 . Note that  FIG. 5A  is an ABS view of the writer that shows all the shields (side shields (SS)  80 , TS  30 , LS  40  so that the connection between the SS and the LS in this  FIG. 2A  may be visualized. As the LS throat height (thickness measured vertically from the ABS) is 150 nm in  2 A and LS recess height away from the ABS is 200 nm, the LS and LET appear as disconnected in the  FIG. 2A  view. However, as the SS throat height (vertical thickness) is 600 nm in this sketch which is off-center at the SS-LS connection area, the area of connection between SS and LS is kept the same, with LET connection to SS unchanged, and LS connection to SS shifted up the perpendicular direction. 
     Referring to  FIGS. 3A, 3B, 3C and 3D  there is shown the results of simulations conducted using the Finite Element Method (FEM), to validate the performance of the disclosed design. The different graphical figures show the FEM simulation result for writer heads with different LS recess height. With larger amount of LS recess, the head field is slightly enhanced and the trailing shield gains much more return field (which goes much more negative), thereby fulfilling the design purpose as expected. 
     The vertical axis in  FIG. 3A  measures perpendicular field strength; in  FIG. 3B  it measures erasure width (EWAC); in  FIG. 3C  it measures trailing shield return field; and in  FIG. 3D  it measures the side shield return field. Horizontal axes measure recess height of the LS. The black dot in each figure refers to the exemplary prior-art writer case with LS exposed at ABS (0 recess height). In this simulation, LS volume is kept the same for different recess amount, meaning LS thickness minus recess height is kept at 150 nm for the three different cases. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1A  is a schematic representation of a side, cross-sectional slice through the center of the main pole (MP) and leading (LS) and trailing (TS) shields, up to the ABS, of a prior-art PMR writer and also showing the soft magnetic underlayer (SUL) of a recording disk beneath the ABS with a depiction of flux lines passing from the MP and returning to the shields. 
         FIG. 1B  is a schematic representation of a side, center cross-sectional slice through the main pole (MP) and leading (LS) and trailing (TS) shields, up to the ABS, of the presently disclosed PMR writer and also showing the SUL of a disk beneath the ABS with a depiction of flux lines passing from the MP and returning to the shields. The figure shows a recessed LS that now includes a leading edge taper (LET) which can be implemented in several different configurations (only one being shown). 
         FIG. 2A  is a schematic representation of a side cross-sectional view through the center of the presently disclosed PMR writer (as in  FIG. 1B ) with the LET being recessed further from the ABS than in  FIG. 1A . 
         FIG. 2B  is a schematic representation of an ABS view of the presently disclosed PMR writer, configured as in  FIG. 2A  but with the cross-sectional plane being off-center so that the SS can also be seen. 
         FIGS. 3A, 3B, 3C and 3D  are FEM simulation result for the proposed structure. Vertical axis refers to (a) perpendicular field strength; (b) erasure width; (c) trailing shield return field; (d) side shield return field. Horizontal axes refer to recess height of the LS. The black dot in each figure refers to current prior-art case with LS exposed at ABS (0 recess height). In this simulation, LS volume is kept the same for different recess amount, meaning LS TH minus recess height is kept 150 nm for the three different cases. 
         FIGS. 4A, 4B and 4C  are, respectively, top-down view sketches of the LS in ( 4 A) present (prior art) writer; ( 4 B) recess configuration 1, LS recess all the way in the cross-track direction, and ( 4 C) recess configuration 2, LS recess only in the center track. Arrow  103  shows recess height, arrow  102  shows LS throat height, and arrow  101  shows cross track recess width. The angle θ is the recess tilt angle, which can range from 10 degrees to 90 degrees. 
         FIGS. 5A, 5B, 5C and 5D  are, respectively, schematic ABS views of the LS in ( 5 A) the prior art writer; ( 5 B) recess configuration 1, LS recess all the way in the cross-track direction; ( 5 C) recess configuration 2, LS recess only in the center track and ( 5 D) recess of the LS and LET by different amounts. 
         FIG. 6  schematically shows a perspective view of a head arm assembly of the present recording apparatus utilizing the disclosed PMR writer. 
         FIG. 7  schematically shows a side view of a head stack assembly of the present recording apparatus. 
         FIG. 8  schematically shows a plan view of the magnetic recording apparatus within which are mounted the components shown in  FIGS. 6 and 7 . 
     
    
    
     DETAILED DESCRIPTION 
     Several recess configurations will now be described. The simple recess configuration (configuration 1) is to recess the entire LS along its full cross-track width (up to 20 um). A second configuration (configuration 2) recesses only a center track portion of the LS, so cross-track recess width will range from 100 nm (nanometers) to 5 um (microns). In the second configuration, while the LS volume at track center is recessed from ABS, the region laterally outside of cross track recess width is still exposed to (not recessed from) the ABS. A third configuration permits recessing the LS and a leading edge taper (LET) by independent amounts. 
     As the MP field is primarily concentrated in the track center, the SUL return field (and corresponding flux) also depends primarily on the center area. By controlling the cross-track recess width, the majority of the SUL return flux path will still be shifted to the trailing side, but the balance between the (SS saturation/EWAC growth) and TS (return field gain/OW gain) can be fine-tuned. In addition, the down-track thickness of the recessed area can also range from 50 nm to 1 um, which also provides an extra control variable for tuning TPI/BPI balance. The throat height (TH) of the LS can also range from 200 nm to 1 um. Under fixed recess height and cross track recess width, a thicker LS TH can provide better protection for SS saturation and EWAC confinement, while thinner LS TH can further enhance TS return field and OW. 
     Referring to  FIGS. 4A-4C , there is shown a sequence of schematic top-down views of the LS  40 . In ( 4 A) there is shown a prior art PMR writer where the entire shield  40  reaches the ABS  10 ; in ( 4 B) there is shown the first recess configuration where the entire LS  40  is recessed (double ended vertical arrow) from the ABS  10  across its entire cross track direction (width of the figure), and, in ( 4 C) there is shown the second recess configuration, where the LS  45  is recessed from the ABS  10  (small double arrow  103 ) only in a center portion  43  of the track. Here, the small double arrow  103  shows recess height (distance vertically above the ABS), the longer vertical arrow  102  shows LS throat height, and horizontal arrow  101  shows cross track recess width. The angle θ is the recess tilt angle, which can range from 10 degrees to 90 degrees. 
     Referring now to  FIG. 5A , there is shown an ABS view of the face of a prior art PMR writer, as though looking up from the SUL of the recording media, showing the TS  30 , the LS  40 , two horizontally disposed SS  80 , the face of the MP tip is  25 , two dielectric filled side gap regions (SG)  87 , a leading gap LG  47  just above the LS  40  and, in this case, a small high saturation magnetic moment shield (B s =24 kG)  35  positioned above the write gap WG  97 . This high moment shield is not a necessary component of the design, however, and the design performs equally well in its absence. Note that the TS  30  is formed of a low saturation moment material with B s =between approx. 16-19 kG and the LS  40  is formed of magnetic material with B s =between approximately 10-19 kG. Note also that the leading shield LS  40  is not recessed from the ABS at any point. 
     Referring next to  FIG. 5B , there is shown the presently disclosed PMR writer in its first recessed LS configuration where an entire portion of LS  40 , is now uniformly recessed away from the ABS plane in the proximal direction, along its entire cross-track extent. The recessed portion is shown as a space by the double arrow  104 , where the double arrow indicates the width of the recessed portion in the down-track direction. The height of the recess (its distance away from the ABS) is shown as a double-ended arrow in  FIG. 4B , which can be in the range between 200 nm and 1 um. 
     Referring next to  FIG. 5C  there is shown the presently disclosed PMR writer in a second recessed configuration (configuration 2) where the LS is recessed only in a region  43  within a central portion of the cross-track dimension and the lateral sides that extend out from that region are co-planar with the ABS plane. This region is shown in  FIG. 4C  as extending only partially in the cross-track direction (horizontal arrow) and partially in the down track direction (vertical arrow). The edges are beveled inward (proximally) as shown by the recess tilt angle θ in the side view of  FIG. 4C . The illustration here is indicative of a θ=0 tilt angle. We must point out that this configuration shows an entire portion of the LS recessed away from the ABS. We must not forget that we have the LET to serve as an additional portion of the LS that can be independently recessed away from the ABS by any amount as will be illustrated in  FIG. 5D  below. The illustration in  FIG. 5C  shows a configuration where the LET has been recessed along with the LS portion and the rectangular region shows a uniformly recessed situation. 
     Referring now to  FIG. 5D  there is shown the configuration of  FIG. 5C  with a difference being that a small LET region  50  is shown within the rectangular region where a portion of the LS  43  has been recessed but the LET has not been recessed by the same amount. The LET is shown as shaded to indicate that its recess into the plane of the figure is not by the same amount as that of the LS portion  43 . 
       FIG. 6  shows a head gimbal assembly (HGA)  200  that includes the slider-mounted present PMR writer  100  and a suspension  220  that elastically supports the PMR writer  100 . The suspension  220  has a spring-like load beam  230  made with a thin, corrosion-free elastic material like stainless steel. A flexure  231  is provided at a distal end of the load beam and a base-plate  240  is provided at the proximal end. The PMR writer  100  is attached to the load beam  230  at the flexure  231  which provides the PMR writer with the proper amount of freedom of motion. A gimbal part for maintaining the PMR writer at a proper level is provided in a portion of the flexure  231  to which the PMR writer  100  is mounted. 
     A member to which the HGA  200  is mounted to arm  260  is referred to as head arm assembly  220 . The arm  260  moves the PMR  100  in the cross-track direction (arrow) across the medium  14 . A hard disk, here shown, transparently, as being above the arm, is mounted on a spindle, but only the mounting hole is shown for clarity. One end of the arm  260  is mounted to a base plate (not shown). A coil  231  to be a part of a voice coil motor is mounted to the other end of the arm  260 . A bearing part  233  is provided to the intermediate portion of the arm  260 . The arm  260  is rotatably supported by a shaft  234  mounted to a bearing part  233 . The arm  260  and the voice coil motor that drives the arm  260  configure an actuator. 
     Referring next to  FIG. 7  and  FIG. 8 , there is shown a head stack assembly and a magnetic recording apparatus in which the PMR writer  100  is contained. The head stack assembly is an element to which the HGA  200  is mounted to arms of a carriage having a plurality of arms.  FIG. 7  is a side view of this assembly and  FIG. 8  is a plan view of the entire magnetic recording apparatus. 
     A head stack assembly  250  has a carriage  251  having a plurality of arms  260 . The HGA  200  is mounted to each arm  260  at intervals to be aligned in the vertical direction. A coil  231  (see  FIG. 6 ), which is to be a portion of a voice coil motor is mounted at the opposite portion of the arm  260  in the carriage  251 . The voice coil motor has a permanent magnet  263  arranged at an opposite location across the coil  231 . Two disks  14  are shown in side view mounted on a spindle motor  261 . 
     Referring finally to  FIG. 8 , the head stack assembly  250  is shown incorporated into a magnetic recording apparatus  290 . The magnetic recording apparatus  290  has a plurality of magnetic recording media  14  mounted on a spindle motor  261 . Each individual recording media  14  has two PMR elements  100  arranged opposite to each other across the magnetic recording media  14  (shown clearly in  FIG. 7 ). The head stack assembly  250  and the actuator (except for the PMR writer itself) act as a positioning device and support the PMR writers  100 . They also position the PMR writers correctly opposite the media surface in response to electronic signals. The PMR records information onto the surface of the magnetic media by means of the magnetic pole contained therein. 
     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 PMR writer with a leading edge shield that is recessed from an ABS in several configurations, while still forming and providing such a structure and its method of formation as defined by the appended claims.