Abstract:
A method of fabricating a single-pole perpendicular magnetic recording head to contain a bevel angle promotion layer that facilitates the fabrication of the bevel angle in a trapezoidal main pole. The bevel angle promotion layer is made of a non-magnetic material that is softer than the material (e.g., Al 2 O 3 ) that normally underlies the main pole. In one embodiment, the bevel angle promotion layer is formed between an end of the yoke and the air bearing surface (ABS), with the top surface of the bevel angle promotion layer being substantially coplanar wit the top surface of the yoke. In other embodiment the bevel angle promotion layer is integrated with a leading edge taper material, which is formed of a magnetic material, to broaden the magnetic flux path between the yoke and the main pole.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]     This application is a divisional of application Ser. No. 10/981,354, filed Nov. 4, 2004, now U.S. Pat. No. ______, which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION  
       [0002]     This invention relates to single-pole recording heads for disk drives and in particular to a structure and method for reducing cross-talk and improving the signal-to noise ratio in a head used for perpendicular recording on a magnetic disk  
       BACKGROUND  
       [0003]     In perpendicular magnetic recording the data is recorded on a magnetic disk in which the easy axis of magnetization is aligned perpendicular to the surface of the disk. The recording head, viewed from the air bearing surface, contains a relatively small main pole and a relatively large auxiliary pole.  
         [0004]     The recording head is normally mounted on a rotary arm which pivots about a stationary axis to move the head to various radial positions on the disk. This generates a skew angle θ between the main axis of the rotary arm and the tangential direction of the data tracks on the disk. This is illustrated schematically in  FIGS. 1A-1C . In  FIG. 1A  the skew angle θ is equal to zero, i.e., the main axis of rotary arm  2  is exactly parallel to the data track on disk  4  that underlies the recording head  3  at the end of rotary arm  2 . In  FIG. 1B , where the recording had  3  is located nearer to the center of disk  4 , the skew angle is equal to θ 1 . In  FIG. 1C , where recording head  3  is located nearer to the edge of disk  4 , the skew angle is equal to θ 2  (which would have a sign opposite to that of θ 1 ).  
         [0005]     The existence of a skew angle creates the problem illustrated in  FIG. 2A , which is a schematic top view of the main pole  5  over two data tracks T 1  and T 2 . The skew angle is θ 3 . Although recording head  5  is writing to track T 2 , it is evident that a corner of head  5  overlies track T 1 . A solution to this problem is to fabricate the recording head with a trapezoidal shape, as shown in  FIG. 2B . As shown, recording head  6  does not extend over track T 1  when the skew angle is equal to θ 3  because the sides of head  6  are canted by an angle α, giving head  6  a trapezoidal shape.  
         [0006]      FIG. 3  is general schematic view of a perpendicular recording head  10  taken from the air-bearing surface (ABS), showing a main pole  11 , an auxiliary pole  12 , a reading element  13  and a lower shield  14 . For clarity, the components shown in  FIG. 3  are not drawn to scale. The sides of main pole  11  are beveled by an angle α. It should be noted that this invention does not involve the structure of the auxiliary pole, reading element or lower shield. These components are well known and can be fabricated in accordance with known techniques.  
         [0007]      FIG. 4  is a view of recording head  10  taken through a cross section that is perpendicular to the ABS. Shown are the main pole  11  and the auxiliary pole  12 . Also shown are a yoke  15 , a back gap  16  and a coil  17 . The main pole  11 , auxiliary pole  12 , yoke  15  and back gap  16  are made of a magnetic metal such as NiFe. The coil  16  is made of an electrically conductive metal such as Cu. The supporting layers separating these components are made of a hard nonconductive material such as alumina (Al 2 O 3 ). In operation, an electrical signal through coil  17  generates a magnetic flux that flows through yoke  15  and main pole  11  in the direction of the ABS and from the head to a magnetic recording disk (not shown).  
         [0008]      FIGS. 5A and 5B  are views of main pole  11  from the ABS and show how the trapezoidal shape is normally fabricated. Initially, main pole  11  has a rectangular shape, as shown in  FIG. 5A . An ion milling process is normally used to bevel the sides of main pole  11 . As indicated by the arrows, the ion beam is directed to main pole  11  at an oblique angle so as to erode more material near the bottom of main pole  11 . To erode both sides of the main pole, the ion beam can be programmed to change the angle of incidence in sequence.  
         [0009]      FIG. 6  is a close-up view of the area designated A in  FIG. 4 , which is where most of the discussion herein is directed. The interface between the yoke  15  and the main pole  11  is shown, as well as the underlying and overlying alumina layers. The arrows denote the magnetic flux flowing from the yoke  15  to the main pole  11  and to the ABS.  
         [0010]     One of the difficulties that has been encountered is to get a large enough bevel angle α in the main pole to avoid the problems of cross talk and signal-to-noise (STN) degradation described above. Conventionally, the layer directly below the main pole is made of alumina, which is a very hard material. The presence of this underlying alumina layer acts as a hard mask from below and makes it difficult to get a large bevel angle with the ion milling process. This can happen in two ways. First, the alumina layer retards the material of the main pole from being removed without over-milling. Second, during the milling process the alumina may redeposit onto the surfaces of the main pole, slowing down the removal process even more.  
       SUMMARY  
       [0011]     According to this invention, a bevel angle promotion layer is formed beneath the layer of magnetic material that is to form the main pole. The main pole is not formed on a hard material such as Al 2 O 3 . The bevel angle promotion layer is formed of a non-magnetic material such as NiP, Rh, Ta, NiCr or Cd that is softer than Al 2 O 3 , (i.e., a material that is eroded more easily by ion milling than Al 2 O 3 ). With the main pole formed on this softer material, it is much easier to obtain the required bevel angle with an ion milling process, without the formation of the “fences” that result when the main pole rests on a hard material such as Al 2 O 3 .  
         [0012]     There are several embodiments within the scope of the invention. In a first embodiment, the bevel angle promotion layer is formed between an end of the yoke and the air bearing surface (ABS). A top surface of the bevel angle promotion layer is coplanar with a top surface of the yoke, and the bevel angle promotion layer has the same thickness as the yoke. The main pole overlaps the yoke, and the magnetic flux flows across an interface between the yoke and the main pole.  
         [0013]     In an second embodiment, the bevel angle promotion layer is integrated with a leading edge tape layer to broaden the path through which the magnetic flux may flow between the yoke and the main pole.  
         [0014]     The invention also includes methods of fabricating the embodiments of this invention.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]      FIGS. 1A-1C  illustrate how a skew angle is produced as a recording head mounted to a rotary arm sweeps across a magnetic disk.  
         [0016]      FIGS. 2A and 2B  illustrate how cross talk can be reduced and the signal-to-noise ratio improved by forming the main pole of a recording head in a trapezoidal shape.  
         [0017]      FIG. 3  is a schematic view from the ABS of a single pole type recording head having a trapezoidal main pole.  
         [0018]      FIG. 4  is view of the recording head of  FIG. 3  taken at a cross section perpendicular to the ABS.  
         [0019]      FIGS. 5A and 5B  illustrate conceptually the use of an ion milling process to form the beveled sides of a trapezoidal main pole.  
         [0020]      FIG. 6  is a cross-sectional view of a prior art recording head with no bevel angle promotion layer.  
         [0021]      FIG. 7  is a cross-sectional view of a single pole recording head with a promotion layer that overlaps the yoke.  
         [0022]      FIGS. 8A-8C  illustrate a process of fabricating the recording head shown in  FIG. 7 .  
         [0023]      FIGS. 9A and 9B  illustrate the formation of a “fence” in a head wherein the main pole directly overlies an Al 2 O 3  layer.  
         [0024]      FIG. 10  is a cross-sectional view of a single pole recording head with a bevel angle promotion layer that does not overlap the yoke so as to constrict the magnetic flux path.  
         [0025]      FIGS. 11A-11L  illustrate a process of fabricating the recording head shown in  FIG. 10 .  
         [0026]      FIG. 12  is a cross-sectional view of a recording head wherein a bevel angle promotion layer is integrated with a leading edge taper layer to broaden the magnetic flux path.  
         [0027]      FIGS. 13A-13G  illustrate a process of fabricating the recording head shown in  FIG. 12 .  
     
    
     DETAILED DESCRIPTION  
       [0028]     As described above, the presence of a hard alumina level directly beneath the main pole impedes the fabrication of a large bevel angle a using an ion milling process. One technique of overcoming this problem is to fabricate a relatively soft layer, which can be referred to as a “bevel angle promotion layer” or simply “promotion layer,” immediately below the main pole.  FIG. 7  illustrates a view similar to that of  FIG. 6  but with a promotion layer  20  underneath main pole  11 .  
         [0029]     The promotion layer  11  may be fabricated by the process illustrated in  FIGS. 8A-8C . Initially, the yoke  15  and underlying alumina layer are fabricated using known processes. Then, as shown in  FIG. 8A , a “lift off” photoresist layer  22  is deposited and patterned with an aperture overlying a portion of yoke  15 . A “lift” off photoresist layer is actually two photoresist layers which are patterned to produce the overhang shown in  FIG. 8A .  
         [0030]     Next, as shown in  FIG. 8B , promotion layer  20  is deposited on the structure. Promotion layer  20  could include NiP, Rh, Ta, NiCr or Cd, for example. Lift off photoresist layer  22  is then removed (along with the overlying portion of promotion layer  20 ), and main pole  11  is deposited. Main pole  11  could be made of NiFe. Afterward, the overlying alumina layer is deposited, and the structure is lapped or polished to the location of the ABS (shown in  FIGS. 8B and 8C ), producing the head shown in  FIG. 7 .  
         [0031]     One possible problem with this structure is illustrated in  FIG. 7 . Because the promotion layer  20  is made of a soft non-magnetic material, the overlap between promotion layer  20  and yoke  15  tends to reduce the area through which the magnetic flux must flow at the interface between yoke  15  and main pole  11 .  
         [0032]     Another possible problem is illustrated in  FIG. 9A . With a relatively thin promotion layer  20  the ion beam may still strike the alumina layer, causing atoms of alumina to become dislodged and forming “fences”  24  that extend upwards along the sides of main pole  11 . As the ion milling process continues, this can lead to a seriously deformed main pole, as shown in  FIG. 9B .  
         [0033]     These problems are overcome in the structure shown in  FIG. 10 . In this structure a thick promotion layer  26  is formed, having a top surface that is substantially coplanar with the top surface of the yoke  15 . Thus, promotion layer  26  does not overlap yoke  15 , and the flux flow across the interface between yoke  15  and main pole  11  is not restricted.  
         [0034]      FIGS. 11A-11J  illustrate a process that can be used to fabricate the structure of  FIG. 10 .  
         [0035]     The process to be described begins at the stage of the overall head fabrication process after the back gap  16  and an adjacent Al 2 O 3  layer  28  have been formed. This is shown in  FIG. 11A . The back gap  16  may be made of NiFe. The preceding stages of the process (e.g., the fabrication of the auxiliary pole and the coil) are conventional and will not be described here.  
         [0036]     Referring to  FIG. 11B , a NiP seed layer  30  is deposited on Al 2 O 3  layer  28  by chemical vapor deposition, sputtering or some other deposition technique to a thickness of 1000 Å, for example. If desired, the seed layer can be removing from the back gap  16  by ion milling.  
         [0037]     Next, as shown in  FIG. 11C , yoke  15 , typically made of NiFe, is plated onto back gap  16  and seed layer  30 , with an opening in the area where the ABS is to be formed. A photoresist layer (not shown) is deposited in the opening area to prevent NiFe from being plated in that area. After yoke  15  has been plated, the photoresist layer is removed. Yoke  15  merges with back gap  16  to form a path for the magnetic flux.  
         [0038]     As shown in  FIG. 11D , a photoresist layer  34  is deposited on yoke  15  and photoresist layer  34  is patterned to form an opening  36 , which overlies opening  32  and a portion of yoke  15 .  
         [0039]     As shown in  FIG. 11E , a NiP layer  38  is plated in opening  36  and on NiP seed layer. NiP layer  38  may be 5-7 μm thick, for example. Photoresist layer  34  is removed, as shown in  FIG. 11F .  
         [0040]     An Al 2 O 3  layer  40  is then deposited over the entire surface of the structure to fill areas not shown in the drawings, as shown in  FIG. 11G . The top surface of the structure is then polished by chemical-mechanical polishing (CMP) to a level below the top surface of yoke  15 , leaving the structure shown in  FIG. 11H .  
         [0041]     Next, as shown in  FIG. 11I , a NiFe layer  40  is deposited to form a structure which will become main pole  20 . NiFe layer  40  is then patterned to form a specified area of contact with yoke  15 , as shown in  FIG. 11J .  
         [0042]      FIGS. 11K and 11L  are views taken at the cross section labeled ABS in  FIG. 11I .  FIG. 11K  shows how NiFe layer  40  is initially patterned to the width of main pole  20 , and  FIG. 11L  shows how the sides of main pole  20  are beveled to a desired angle, using an ion milling process. Because layer  38  underneath main pole  20  is made of NiP, a relatively soft material as compared with Al 2 O 3 , a large angle can be formed, and there are no “fences” along the sides of main pole  20 .  
         [0043]     After the deposition of an Al 2 O 3  layer over and around main pole  20 , the structure is diced and polished along the cross section ABS to form the pole structure shown in  FIG. 10 .  
         [0044]     As described above, it is helpful to maximize the area of contact between the yoke and the main pole because this provides a broader path for the magnetic flux to flow between these elements. According to another aspect of this invention, the bevel angle promotion layer is integrated with a leading edge taper layer to increase the area of contact between the yoke and the main pole.  
         [0045]     A cross-sectional view of a main pole structure in accordance with this aspect of the invention is shown in  FIG. 12 . Main pole  20  overlies both a bevel angle promotion layer  50  and a leading edge taper layer  52 . Promotion layer  50  is formed of a relatively soft non-magnetic material such as NiP, Rh, Ta, NiCr or Cd. Leading edge taper layer  52  is formed of a magnetic material such as NiFe. The interface between promotion layer  50  and leading edge taper layer  52  is located between the end of yoke  15  and the ABS. As a result, the magnetic flux can flow through the portion of leading edge taper layer  52  that is located between the end of yoke  15  and the ABS.  
         [0046]      FIGS. 13A-13G  illustrate the steps of a process for fabricating the structure shown in  FIG. 12 . Initially, the main pole, coil, yoke and intervening Al 2 O 3  layers are formed in a conventional manner to arrive at the structure shown in  FIG. 13A . The top surface of yoke  15  and Al 2 O 3  layer  54  are coplanar.  
         [0047]     As shown in  FIG. 13B , promotion layer  50  is deposited by chemical vapor deposition, sputtering, or another full film deposition method to a thickness of 10-300 nm, for example, on top of yoke  15  and Al 2 O 3  layer  54 . Promotion layer  50  can be formed of Rh, for example.  
         [0048]     As shown in  FIG. 13C , a lift off photoresist layer  56  is deposited and patterned such that an edge of photoresist layer  56  is located over Al 2 O 3  layer  54  between the edge of yoke  15  and the plane of the ABS that is later to be formed.  
         [0049]     As shown in  FIG. 13D , the portion of promotion layer  50  that is left exposed by photoresist layer  56  is removed by ion milling, leaving an angled edge that overlies Al 2 O 3  layer  54 . The ion beam can be programmed to transition through a desired sequence of angles.  
         [0050]     Next, as shown in  FIG. 13E , the leading edge taper layer  52  is deposited. Leading edge taper layer  52  may be formed of NiFe. Because photoresist layer  56  is used as a mask both for the removal of a portion of promotion layer  50  and for the deposition of leading edge taper layer  52 , the edges of promotion layer  50  and lead edge taper layer  52  abut each other at a location above Al 2 O 3  layer  54 . The lateral location of the edge of photoresist layer  56  determines the location of the interface between leading edge taper layer  52  and promotion layer  50  and hence the amount of leading edge taper layer  52  that will be available as a path for the magnetic flux flowing from yoke  15 .  
         [0051]     Photoresist layer  56  is then removed by a lift-off process, yielding the structure shown in  FIG. 13F . The NiFe layer that will form the main pole  20  is deposited on top of leading edge taper layer  52  and promotion layer  50 . The main pole  20  is patterned and shaped by ion milling as described above in connection with  FIGS. 11K and 11L . The presence of the relatively soft promotion layer  50  in the area of the ABS allows the bevel angle a to be made larger than if the main pole  20  were located over a harder material such as Al 2 O 3 , for example. Thereafter an Al 2 O 3  layer is deposited over the main pole  20  and the structure is diced at the ABS (denoted by the dashed line in  FIG. 13G ) to produce the structure shown in  FIG. 12 . This unique structure allows two desirable objectives to be satisfied simultaneously: namely, the fabrication of a main pole having a trapezoidal shape with a large bevel angle and the creation of a broad path for the magnetic flux to flow between the yoke and the main pole.  
         [0052]     Although the present invention is illustrated in connection with specific embodiments for instructional purposes, the present invention is not limited thereto. Various adaptations and modifications may be made without departing from the scope of the invention. Therefore, the spirit and scope of the appended claims should not be limited to the foregoing description.