Abstract:
As track densities increase, it becomes increasingly important, while writing in a given track, not to inadvertently write data in adjoining tracks. This problem has been overcome by limiting the width of material in the ABS plane to what it is at the write gap. The part of the lower pole that is wider than this is recessed back away from the ABS, thereby greatly reducing its magnetic influence on adjacent tracks. Four different embodiments of write heads that incorporate this notion are described together with a description of a general process for their manufacture.

Description:
This is a divisional application of U.S. patent application Ser. No. 10/706,381 filed on Nov. 12, 2003, which is herein incorporated by reference in its entirety, and assigned to a common assignee. 
    
    
     RELEVANT FIELD 
     The disclosed structure relates to the general field of magnetic write heads with particular reference to eliminating neighboring track erasure. 
     BACKGROUND 
     A typical write head structure for a magnetic disk system is schematically illustrated in  FIG. 1 . Its principal parts are lower pole  12  and upper pole  11  (commonly referred to as P 1  and P 2 , respectively. These are magnetically connected at one end and separated by a small non-magnetic layer  13  (the write gap) at the other end. The track width will be defined by the P 2  width at the gap. P 1  may be notched through a self aligned process, known as partial pole trim (PPT), to better define the written transitions. Coil  14  is located in the space enclosed by P 1  and P 2  and is the source of the magnetic field that is focused by the two pole pieces. All seen in the figure is a magnetic shield layer  16  which is electrically isolated from the lower pole by dielectric layer  15 . 
       FIG. 2  shows a variation on the basic design seen in  FIG. 1 . In this case a secondary upper pole  21  is ‘stitched’ in between  11  (P 2 ) and gap  13 . This is for ease of fabrication so that the track width definition can be done on relatively flatter topography. An additional feature, not present in the design of  FIG. 1 , is shallow trench  22  which is etched into lower pole  12 . Since trench  22  has sloping sides, the depth to which it is etched can be used to fine tune the length of lower pole  12  that is part of the write gap  13 . This is usually referred to as the throat. This allows for a further concentration of the available flux within the write gap. In the stitched pole design, the track width is defining part of pole  21  as well as the back gap connection  23  which are fabricated immediately following the deposition of write gap  13 . 
       FIG. 3  is an isometric view of part of  FIG. 1  or  FIG. 2  as seen when looking up from the magnetic track at the air bearing surface that passes over it (so-called ABS view). It is important to note that the surfaces of the upper pole ( 11  in  FIG. 1  or  21  in  FIG. 2 ), the gap  13 , and the lower pole  12 , are all coplanar. One consequence of this, the standard structure in use today, is the unintended erasure of adjacent tracks on the disk as narrower tracks and higher track densities are developed. Most improvements that have been proposed, such as increased PPT depth, smooth P  1  topography, and narrower gap all come with either process challenges or reduced on track writeablity performance. 
     As track densities increase, the read head extracts the recorded information from an ever decreasing narrow track. It becomes increasingly important not to affect the integrity of this narrow track of data. In the structure shown in  FIG. 3 , P 2  has magnetic material confined to the written track. P 1 , however, still includes material that extends outside the track width (TW) defining region. This may lead to unintended writing on an adjacent track and may therefore affect the data integrity of the system. 
     A routine search of the prior art was performed with the following references of interest being found: 
     U.S. Pat. No. 6,353,511 B1 (Shi et al.) shows a process for a improved Write head. U.S. Pat. No. 5,878,481 (Feng et al.) shows a pole trimming process for a write head. U.S. Pat. No. 5,843,521 (Ju et al.) and U.S. Pat. No. 5,802,700 (Chen et al.) are related patents. U.S. Pat. No. 5,652,687 (Chen et al.) shows a planarized write head process. 
     SUMMARY 
     It has been an object of at least one embodiment of the disclosed structure to provide a magnetic write head that does not write unintentionally onto data tracks located on either side of the track that is being written. 
     Another object of at least one embodiment of the disclosed structure has been that this be accomplished without a reduction in write field strength or track density. 
     Still another object of at least one embodiment of the disclosed structure has been to provide a process for the manufacture said write head. 
     A further object of at least one embodiment of the disclosed structure has been that said process not require significant modification of existing processes for the manufacture of write heads. 
     These objects have been achieved by limiting the width of material in the ABS plane to what it is at the write gap. The part of the lower pole that is wider than this is recessed away from the ABS, thereby greatly reducing its magnetic influence on adjacent tracks. Four different embodiments of write heads that incorporate this notion are described together with a description of a general process for their manufacture. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a basic read head design. 
         FIG. 2  shows the basic design of  FIG. 1  modified by use of a stitched upper pole. 
         FIG. 3  is the ABS view of  FIGS. 1 and 2  in isometric projection. 
         FIG. 4  shows the structure of  FIG. 1  modified according to the teachings of the disclosed structure. 
         FIG. 5  shows the structure of  FIG. 2  modified according to the teachings of the disclosed structure. 
         FIG. 6  illustrates a third embodiment of the disclosed structure. 
         FIG. 7  is an isometric view of a portion of a fourth embodiment. 
         FIGS. 8-12  illustrate successive steps in the manufacture of the disclosed structure. 
         FIG. 13  is a plan view of the disclosed structure. 
         FIG. 14  is an isometric view of part of a fourth embodiment of the disclosed structure. 
     
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The key novel feature of the disclosed structure is the restriction of the width of P 1  to TW for a distance such that there is no P 1  wider than the track width at the ABS. This is achieved by causing P 1  beyond this distance to be recessed away from the ABS, thereby greatly reducing its magnetic influence on the adjacent tracks. Thus, the amount of P 1  at the ABS should exceed the amount of P 1  that is recessed 
     1 st  Embodiment 
     Referring now to  FIG. 4 , we show there a structure that is similar to the one shown in  FIG. 1 , but modified in accordance with the teachings of the disclosed structure. As before, upper pole  11  and lower pole  12  enclose, between them, field coil  14 . The key novel feature is ledge  41 , which is between about 0.2 and 2 microns thick, of magnetic (high permeability) material that extends outwards, between about 0.1 and 2 microns, away from the main body of lower pole  12  and terminates at the ABS 30-30. The outer edge of ledge  41  at the ABS has the same width as, and is in alignment with, the outer edge of top pole  11  at the ABS so that write gap  13  lies between them and said widths define the track width TW. As a result, most of bottom pole  12  is set back some distance from the ABS and so has relatively little magnetic interaction with the disk surface.  FIG. 7  is an isometric view that illustrates the spatial relationships between top pole  11  and bottom poles  41  and  12 . 
     For purposes of simplification,  FIG. 4  has been drawn as though ledge  41  is a cantilever. In actuality, a layer of insulation is present below  41  to support it. Details of this support layer are provided later, in the section where we describe the process for manufacturing this structure. 
     2 nd  Embodiment 
       FIG. 5  shows a structure similar that seen in  FIG. 2 . As before, there is a general similarity to the first embodiment illustrated in  FIG. 4  with the addition of stitched secondary top pole  21  and shallow trench or depression  22  which has a depth between about 0.1 and 1 Angstroms. Note that primary lower magnetic pole  12  has a front end  12   f  that is recessed from the ABS 30-30 by a distance w, and has a back end  12   b  that is connected to upper magnetic pole  11  through the back gap connection  23 . Primary magnetic pole has a thickness t 1  at both ends  12   f ,  12   b  that is greater than a thickness t 2  below the depression in the top surface. The depression  22  is formed between end  12   f  and the back gap connection and has a back side  22   s  that is closer to the ABS than the back gap connection. The key departure is the addition to the structure of ledge  51  extending from end  12   f  to the ABS, which is analogous to ledge  41  of the first embodiment, and serves the same purpose.  FIG. 7  is an isometric view that illustrates the spatial relationships between top pole  21  and bottom poles  51  and  12  while  FIG. 13  is a plan view of this structure. 
     3 rd  Embodiment 
     This variation of the basic structure is sometimes preferred because certain parts, such as pole  11 , are easier to manufacture. By going to a somewhat thicker inter-pole connector  23  and using a single turn for field coil  23 , top pole  11  can be flat rather than humped, as in the previous two embodiments. The bottom pole in this case is composed of two layers,  62  and  12 , which, in prior art versions of this variant (not shown), would extend from bottom pole  12  all the way to write gap  13 . 
     As seen in  FIG. 6 , in the structure of the disclosed structure the secondary bottom pole is in two parts  62  and  63 . Part  62  extends upwards from bottom pole  12  but not all the way to write gap  13 . This leaves room for second part  63  which, in addition to extending the rest of the way up to the write gap, also extends laterally away from part  62  so as to be aligned with the ABS end of top pole  11 . As a result, the lower part of the secondary bottom pole and all of the main bottom pole  12  are set back from the ABS, thereby reducing their magnetic interaction with the write track. 
     4 th  Embodiment 
     This embodiment, illustrated in  FIG. 14 , entails still further modification of the three embodiments just discussed. In this embodiment shown from an ABS view, there is no recessing of the first lower magnetic pole portion  12   a  and the second lower magnetic pole portion  41 / 51 / 62 , 63 . First lower magnetic pole portion is a ledge with a height h 1  along the ABS while second lower magnetic pole portion is formed on layer  12   a  and extends to a height h 2  above a shared upper surface  12   s  of layer  12   a  and primary lower magnetic pole  12   b  along the z-axis in a down-track direction. An end of first lower magnetic pole portion  12   a , whose thickness (h 1 ) is between about 0.2 and 2 microns and whose width w 2  is between about 0.05 and 1 microns, and an end of the second lower magnetic pole portion remain coplanar with the ABS. The remainder  12   b  of the primary lower pole having a thickness from 0.5 to 3 microns is recessed from the ABS by a distance w of about 0.1 to 2 microns as in the previous embodiments. The amount that the second lower magnetic pole extends inwards from the ABS is between about 0.05 and 0.2 microns along the y-axis that is orthogonal to the ABS and in a direction toward a back end of the magnetic pole structure. Track width (TW) is shown along the upper magnetic pole  11 / 21  at the ABS in a cross-track direction. The second lower magnetic pole part is aligned below the upper magnetic pole and has an equivalent TW at the ABS while the first lower magnetic pole part has a width w 2  greater than TW. There are tapered surfaces  12   t   1 ,  12   t   2  on the primary lower magnetic pole that connect to upper surface  12   s  along opposite sides of first magnetic pole part  12   a  such that a recessed lower portion of layer  12   b  at an end facing the ABS has a cross-track width substantially greater than w 2 . This embodiment is unsuitable for extremely high track densities (greater than about 125,000 tracks per inch) but for lesser densities its advantage is manufacturability; the thickness and height of first lower magnetic pole portion  12   a  (the non-recessed part of P 1 ) and the depth of the partial pole trim ( 41 / 51 / 62 ,  63 ) do not need to be the same. 
     Manufacturing Process 
     Referring now to  FIG. 8 , the process to form the disclosed structure begins with the provision of substrate  15  on which is deposited, and then patterned, layer  12  of a high magnetic permeability material to form the primary lower pole. Next, as seen in  FIG. 9 , layer of insulating material  91  is deposited on substrate  15  as well as on primary lower pole  12 , making sure that its thickness exceeds that of  12 . 
     The structure is then planarized until all insulating material has been removed from over the primary lower pole so that the remaining insulation abuts, and extends away from, the primary pole. This is illustrated in  FIG. 10 . Second layer  110  of high magnetic permeability material is next deposited and patterned to form a secondary lower pole that covers primary pole  12  and extends over insulating layer  91  on one side so as to form ledge  112 . Optionally, an additional layer  114  of insulation may be introduced (in the same way as just described for  91 ) to fill in the part above  91  that is not covered by  110 . Since  110  is relatively thin, this step may be omitted without significant consequence. 
     In the case of the second embodiment ( FIG. 5 ), shallow trench  22  is formed at this time. For all embodiments, completion of the structure now proceeds along routine lines—field coil  14  is formed over, and insulated from, the lower poles following which the upper magnetic pole  11  is formed to overlie it. At one end the two poles are in magnetic contact with one another while at the other end they are by layer of non-magnetic material  13  to form the write gap whose width serves to define the track width TW. Finally, the ABS end of the structure is planarized as far as plane  115 , thereby determining how far ledge  112  extends out away from the main body of the lower pole.