Abstract:
A magnetic recording system includes a magnetic medium and a magnetic write head to write information on the magnetic medium. The magnetic write head includes a write pole having a downstream side that has a concave shaped portion when the write pole is viewed from an air bearing surface of the magnetic write head.

Description:
BACKGROUND 
     The present invention relates to magnetic data recording, and more particularly, to perpendicular magnetic data recording. 
     Perpendicular recording has been used to achieve higher recording densities. The National Storage Industry Consortium (SIC) believes that perpendicular recording will become necessary to achieve the densities above 100 Gbit/in 2 . 
     Writes for a perpendicular medium with a soft underlayer occur at a trailing (or downstream) edge of the write element. The curvature of the transitions is due to the rectangular shape of the trailing edge of the write element. Also, resolution loss between a write pole tip and the magnetic medium due to a physical spacing between them and saturation of corners of the write element can cause the curvature of the transitions. As widths of write tracks decrease, the resolution loss and the saturation of corners of the write element become larger contributors to the curvature. 
     As track density increases, edges of the track become a large part of the overall track width. The track edges are characterized by noise and imperfectly written transitions, in particular, the transitions with curvature across the track. Thus, it is important to match a read impulse shape, which is a line, with a written transition shape. 
     SUMMARY 
     In general, in one aspect, the invention is directed to a magnetic recording head that includes a write pole having a downstream side that has a concave shaped portion when the write pole is viewed from an air bearing surface of the magnetic recording head. 
     Embodiments of the invention may include one or more of the following features. The magnetic recording head may include a shield associated with the write pole. The shield may have an upstream side that has a convex shaped portion when the write pole shield is viewed from an air bearing surface of a slider upon which the magnetic recording head is mounted. 
     Particular implementations of the invention may provide one or more of the following advantages. Providing the downstream side of a write pole with a concave shape (as well as the upstream side of the a write pole shield, if employed, with a convex shape) increases a track width over which a written transition is straight. This serves to narrow the read pulse and increase the high frequency amplitude of the on-track read signal. It also increases the amplitude and resolution of the servo signal, and allows higher track densities for a given track width. 
     In general, in another aspect, the invention is directed to a write pole tip for a magnetic recording head. The write pole tip includes a downstream layer having a first saturation magnetization and an upstream layer comprising a tip body that has a second saturation magnetization. The downstream layer is wider than the upstream layer. 
     This aspect include one or more of the following features. The write pole tip may have a trapezoidal shape. The trapezoidal shape has a first width at one end and a second width, the first width being greater than the second width. The downstream layer may be at the first width and the upstream layer may be at the second width. A thickness of the downstream layer may be between 50 nm and 100 nm. At least one side of the write pole tip may be concave in shape. The tip body may include metal alloy. 
     In general, in another aspect, the invention is directed to a magnetic recording system. The magnetic recording system includes a magnetic medium and a magnetic write head to write information on the magnetic medium. The magnetic write head includes a downstream layer having a first saturation magnetization and an upstream layer comprising a tip body that has a second saturation magnetization. The downstream layer is wider than the upstream layer. 
     Other features and advantages of the invention will be apparent from the following detailed description, and from the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side view of a magnetic recording system including a recording head having a write pole and a medium on which the recording head records information. 
         FIG. 2A  is an Air Bearing Surface (ABS) view of a conventional rectangular write pole and write field contour generated by the conventional rectangular write pole. 
         FIG. 2B  is an ABS view of a write pole having a concave-shaped downstream side and write field contour generated by such write pole. 
         FIGS. 3A to 3C  depict stages of a process for fabricating the write pole structure shown in  FIG. 2B . 
         FIG. 4  is a side view of a magnetic recording system including a recording head having a shielded write pole and a medium on which the recording head records information. 
         FIG. 5A  is an ABS view of a conventional rectangular write pole and conventional write pole shield having a flat upstream side. 
         FIG. 5B  is an ABS view of a shielded write pole structure including a write pole having a concave-shaped downstream side and a write pole shield having a convex-shaped upstream side. 
         FIG. 6  is a depiction of a process for fabricating the shielded write pole structure shown in  FIG. 5B . 
         FIG. 7  shows a cross-track field profile for the deep gap field and write (or switching) fields of the write poles shown in  FIGS. 2A and 2B , respectively. 
         FIGS. 8A and 8B  show write track widths for write fields generated by the write poles shown in  FIGS. 2A and 2B , respectively. 
         FIG. 9  shows another embodiment of a write pole tip according to the invention. 
     
    
    
     Like reference numerals in different figures indicate like elements. 
     DETAILED DESCRIPTION 
     Referring to  FIG. 1 , a simplified magnetic recording system  10  includes a read/write head device  12  and a magnetic recording medium shown as a perpendicular recording medium  14 , e.g., a magnetic disk. The head device  12  includes a read portion  16  (“reader”) and a write portion (“writer”)  18 . The reader  16  includes a magnetoresistive sensor  19  located between two shields, shields  20  and  21 . The writer includes a top or write pole  22 . The shield  21  of the reader  16  also serves as a return write pole for the writer  18 . The medium  14  includes a recording layer  23  and a single soft magnetic layer  24 , also known as a soft underlayer (or “SUL”), which is formed on a substrate  25 . The recording layer  23  and the SUL  24  are separated by a non-magnetic spacer layer  26 . During a write operation, a coil  27  in the writer  18  energizes the write pole  22 , causing flux to flow primarily along a write field flux path  28 , returning to the return write pole  21 . 
       FIG. 2A  shows an ABS view of a conventional rectangular write pole embodiment of write pole  22 , indicated as write pole  20 ′, and a rounded contour  30  of a switching field generated by the write pole  20 ′. The rounded contour results in curved-shaped transitions, which limit the readback process as discussed above. That is, at higher densities, because of the curvature of the transitions, the reader  16  straddles transitions of opposite polarity, which cancel each other, thus degrading the quality of the readback signal. 
       FIG. 2B  shows an ABS view of an embodiment of the write pole  22  according to the present invention, indicated as write pole  20 ″, that has a concave-shaped downstream side  32 , and a somewhat straighter contour  34  of a switching field generated by the write pole  20 ″. One goal of the invention is to shape the downstream side so that the contour of the switching field is as close to a straight line as possible. 
       FIGS. 3A–3C  show processing stages used to produce write pole  20 ″ shown in  FIG. 2B . An ABS view of the head  12  is shown at the various stages of processing, indicated by reference numbers  36 ,  38  and  40 , in  FIGS. 3A ,  3 B and  3 C, respectively. Referring to  FIGS. 3A–3C , well-known processing techniques may be used to produce the reader  16  (from  FIG. 1 ), including undercoat  44 , bottom shield  46 , sensor  48 , insulative layer(s)  50 , top shield  52 , as well as insulation layer  54  disposed on the top shield  52 , and to produce a “pre-processed” write pole  56 , which may be trapezoidal in shape and have a thickness Th (e.g., 0.2 um). Referring to  FIG. 3A , to begin processing the write pole  56  for the concave shaped downstream side (from ABS perspective) discussed earlier with reference to  FIG. 2B , an aluminum oxide layer (Al 2 O 3 )is sputtered on the write pole  56  and insulation layer  54  (processing stage  60 ). This new layer  58  has a somewhat greater thickness than the thickness of the write pole  56  (that is, Th+ε), for example, if the write pole thickness is 0.2 um, the entire layer  58  could be ˜0.3 um. 
     Referring to  FIG. 3B , the surface of the layer  58  is processed using a chemical mechanical polishing process, which grinds back the surface using a chemical and mechanical polishing action to achieve a new, planarized surface  62  (processing stage  64 ). The chemical mechanical polish process uses particles and an abrasive in a carrier that is chemically active to help etch the surface and soften the surface for the mechanical action. The material used by the process is selected to remove only the Al 2 O 3 . For example, the carrier can be chosen to have a high pH so the carrier attacks (dissolves) the Al 2 O 3  material, but does not remove the magnetic pole material (which can be, for example, a magnetic alloy such as CoNiFe). 
     Referring to  FIG. 3C , to achieve the concave shape, a steep angle ion milling is performed (processing stage  66 ). The ion milling process uses in the chamber a gas such as O 2 , which hardens the Al 2 O 3 , making it difficult to remove the Al 2 O 3  relative to the magnetic pole material. As a result, a concave trench  68  is formed in the pole material, as the Al 2 O 3  sidewalls protect the pole edges where the pole material abuts the Al 2 O 3  but not the center. Thus, the center is etched out more readily, resulting in the concave shape as shown. 
     The parameters of the process may be profiled for different angles, etch times, and so forth, to optimize the concave shape to achieve the best (straightest) switching field contour and therefore the straightest write transition. Because the processing makes the write pole thinner, it may be necessary to design the write pole to be thicker to offset the effect of the additional processing. Once the concave shape has been achieved, a conventional thick overcoat layer of Al 2 O 3  is then deposited on the device as an encapsulant. Other techniques, such as focus ion beam milling (FIB) and electron bean lithography, can also be used to achieve the concave shape. 
     Referring to  FIG. 4 , a simplified magnetic recording system  70  includes a magnetic recording head (read/write head)  72  and a perpendicular magnetic recording medium  14 . The head  72  includes a read portion  16  (“reader”) and a write portion (“writer”)  74 . The writer  74  includes a top or write pole  22  and a write pole shield  76  spaced from the write pole  22  by a gap “G”. The write pole shield  76  serves to intercept downstream fringing flux emanating from the write pole  22 . An example of a shielded write pole can be found in U.S. Patent Re. 33,949, in the name of Mallary et al., incorporated herein by reference. 
     As shown in  FIG. 5A , the conventional rectangular write pole  122  generates a field in the presence of a conventional implementation of the shield  76 , indicated as  76 ′, that has a contour that is somewhat straighter in shape than it would be in the absence of the shield. That is, the shield imposes some degree of regularity to the field shape. Unfortunately, with smaller track densities and larger gaps, the curvature problem persists. A contour  80  represents a contour corresponding to a smaller gap G and contour  82  represents a contour corresponding to a larger gap G. It is possible to reduce the gap G, but a large gap is good for manufacturability as it is proportional to the throat (and stripe height of the MR sensor may be aligned with the throat). Also, if the gap G is too small, the shield may reduce the write field excessively. It may be desirable to design the gap G to be equal to the distance to the SUL (“D sul ”). 
     Thus, to optimize the curvature reduction for a shielded write pole structure, and as shown in an ABS view in  FIG. 5B , the write pole  123  having a concave-shaped downstream side  32  is used, as discussed earlier, along with an embodiment of the shield  76 , indicated as shield  76 ″, constructed to have a convex-shaped upstream side  84 . 
       FIG. 6  illustrates a process  90  for fabricating the shielded pole  76 ″ as shown in  FIG. 5B . Like the process illustrated in  FIGS. 3A–3C , an ABS view of the head at the relevant processing stages is shown, indicated by reference number  92 . It will be appreciated that the shield processing resumes where the concave shaped write pole processing left off, that is, after stage  66  (but prior to the aluminum oxide overcoat step). The process  90  includes sputtering a thin (e.g., 04 um) gap layer  93 , typically aluminum oxide (processing stage  94 ) and depositing the material for the shield  76 ″, typically a NiCoFe alloy material, e.g., by a plating process, onto the gap layer  93  (processing sage  96 ). The resulting gap and shield will have a shape  98  that conforms to the shape of write pole  123  ( FIG. 5B ); that is, the shape of the write pole  123  will be replicated in the subsequent gap and shield layers. Thus, from an ABS view, the upstream side of the shield has a convex shape, indicated by reference number  100 , while the downstream side of the write pole  123  has a concave shape. The convex shape is easy to achieve, as a planar shape would require further processing. In addition, the enhancement of the write field gradient provided by the shield  76 ″ is higher in the center than it would be if the upstream side of the shield  76 ″ were flat. The downstream side of the shield  76 ″ and the upstream side of the write pole  123  can have any shape. They need not be flat, as shown in the figures. 
       FIG. 7  shows the cross-track field profile for the deep gap field (at y=0) and write fields of the downstream side (trailing edge) of the write poles shown in  FIGS. 2A and 2B , respectively. The erase width is defined by a maximum width of the field under the write pole greater than the erase (or switching) field for the medium. For the write pole shown in  FIG. 2A , this occurs at y=0. For write poles with other shaped poles, for example, trapezoidal, the maximum width would occur elsewhere in the deep gap region, that is, wherever, the head is physically widest. The usable write track width is defined by a portion of the track that is written with enough resolution to be read by a read element, such as a magnetoresistive (“MR”) sensor or Giant MR (“GMR”) sensor. This is a part of the track at a given down track position “y” where the field amplitude exceeds the write field for the medium. As can be seen in  FIG. 7 , the write width is larger for the case of the write pole with a concave trailing edge. 
     Referring to  FIGS. 8A and 8B , the shaded area represents the width of the write track with an arbitrarily defined length in the down track (y) direction. The arbitrarily defined length is 4 nm (nanometers), for example.  FIG. 8A  shows a width of the write track of the write pole shown in  FIG. 2A  being 55 nm, and  FIG. 8B  shows a width of the write track of the concave-shaped write pole shown in  FIG. 2B  as being 70 nm. 
     Straightening the write field contour of the pole tip can be partially accomplished even with a flat downstream edge by providing a thin layer of magnetic material on this edge that has lower saturation magnetization, M sedge , than that of the pole tip body, M stip . Referring to  FIG. 9 , such a laminated pole tip  110  may have a trapezoidal shape to allow for track skew with a rotary positioner system. Pole tip  110  includes a thin downstream layer  112  with saturation magnetization M sedge , and upstream tip body (layer)  114  with saturation magnetization M stip . Ideally, M stip  should be as large as possible. Therefore, the tip body  114  could include a nearly balanced alloy of iron and cobalt such as Fe X Co 1-X  where 0.5&lt;x&lt;0.65. A third or fourth element might be included to improve permeability and resistance to corrosion. This region may also be as thick as possible to maximize write field consistent with the degree of bevel that forms the trapezoid and consistent with process limitations. For example, if the width  116  of the downstream edge  117  is 200 nm and the bevel angle ρ is 10 degrees, then the total pole thickness  118  cannot be greater than 567 nm without reducing the upstream edge  120  to zero width. 
     Process limitations would require a significant size for the upstream edge  120 . Therefore a typical pole tip thickness  118  would be about 400 nm. The thickness of the downstream layer  112  depends on M sedge , M stip , the degree of write field contour straightening required, the width  116  of the downstream edge, the distance between the pole tip  110  and the soft underlayer, and the required write field and its gradient. Optimization with typical values for these parameters would result in a desired thickness of the downstream layer of between 50 nm and 100 nm for M sedge , =1T and M stip , =2.35 T. 
     Of course the use of a laminated pole tip  110 , with M sedge , &lt;M stip , can be combined with the shielded pole writer  70 . One or both sides of tip  110  can also have a concave shape, such as that shown in  FIG. 2B , in order to reduce the required degree of concavity. 
     Individual features of the embodiments described herein can be combined in ways not specifically described to form new embodiments that are within the scope of the following claims. Thus, other embodiments are within the scope of the following claims.