Abstract:
Insertion of a two part trailing shield between the write gap and the upper return pole of a magnetic write head reduces the sensitivity of the latter to increases in the current driving the field coils (beyond the required minimum). A key feature is careful control of the distance between the upper component of the write shield and the main pole. A process for manufacturing the structure is outlined.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to the general field perpendicular magnetic poles for magnetic recording with particular reference accidental writing on adjacent recording tracks. 
       BACKGROUND OF THE INVENTION 
       [0002]    Perpendicular magnetic recording (PMR) heads combined with double-layered media make it possible to further enhance the increase in recording density in hard disk drives (HDD). Additionally, a trailing shielded pole PMR head can be used to provide a large head field gradient which improves the write transition quality even more. 
         [0003]    Sometimes, however, a trailing shield may induce magnetic saturation of the media soft under layer (SUL) between the main-pole and the trailing shield, i.e. in the write-gap region, resulting in severe return field partial erasure (RFPE) of the write pattern. In addition, along the trailing shield edge there is a field of opposite polarity to the main pole which can spread in the cross-track direction. So it can be a cause of wide track erasure. These erasures become more severe in association with large write currents. Therefore, as write current increases in a conventional PMR head, the head field will also increase causing the magnetic write track width to become strongly dependent on the write current. Next track and far track erasures can become severe as well. 
         [0004]    A routine search of the prior art was performed with the following references of interest being found: 
         [0005]    In U.S. Pat. No. 7,221,539, Takano et al. (Headway) show a stitched shield  40  and main shield  55  similar to the first and second shields of the invention while U.S. Pat. No. 7,009,812 (Hsu et al.) discloses a two-part trailing shield. U.S. Pat. No. 4,656,546 (Mallory) teaches a large shield and a write pole tip with a small gap therebetween and U.S. Pat. No. 4,935,832 (Das et al) describes downstream pole portions that provide side shielding for the write pole. 
       SUMMARY OF THE INVENTION 
       [0006]    It has been an object of at least one embodiment of the present invention to provide a perpendicular magnetic write head that has low sensitivity to increases in the current driving the field coils beyond the required minimum. 
         [0007]    Another object of at least one embodiment of the present invention has been to enhance the field gradient across the write gap. 
         [0008]    Still another object of at least one embodiment of the present invention has been to suppress the formation of a fringing field as current to the field coils increases. 
         [0009]    A further object of at least one embodiment of the present invention has been to provide a process for the manufacture of said write head. 
         [0010]    These objects have been achieved by inserting a two-part trailing shield between the main pole and the upper return pole. By careful control of the distance between the upper trailing shield and the main pole, the head has been rendered insensitive to large increases in the write current beyond the minimum needed for writing. 
         [0011]    The trailing shield design disclosed in the present invention minimizes induced magnetic saturation of the media soft under layer in the write-gap region, thereby largely eliminating severe partial erasure of the write pattern as well as wide track erasure. Next track and far track erasures are also largely eliminated by this design. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]      FIGS. 1   a  and  1   b  illustrate the full read-write head with curved and planar upper return poles respectively. 
           [0013]      FIG. 2  is a close-up view of the upper and lower trailing shields. 
           [0014]      FIG. 3  shows the starting point for the process of the present invention 
           [0015]      FIG. 4  shows the hard mask that will define the trench for the main pole. 
           [0016]      FIGS. 5 and 6  are ABS and side views respectively of the main pole. 
           [0017]      FIG. 7  shows formation of the write-gap and the lower trailing shield. 
           [0018]      FIGS. 8 and 9  are side and ABS views, respectively, of the upper and lower trailing shields. 
           [0019]      FIG. 10  shows the completed write head. 
           [0020]      FIGS. 11   a  and  11   b  are plots of the y and x components, respectively, of the write field as a function of the write current 
           [0021]      FIG. 12  plots the effective width of the write field (in microns) as a function of the write current. 
           [0022]      FIG. 13  plots the effective maximum value of the fringe field at a distance of 0.2 microns off the active write track as a function of the write current (write field within the write track is 7,000 Oe). 
           [0023]      FIGS. 14 and 15  together illustrate why the claimed range for d is critical. 
           [0024]      FIGS. 16 and 17  are plots of the fringe field and the write field, respectively, as a function of distance from the track edge. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0025]      FIGS. 1   a  and  1   b  provide an overall view of the full write head of the present invention. Shown in both figures is main pole  16  and lower return pole  17 . Immediately above and below poles  16  and  17  are field coils  13  which are immersed in aluminum oxide, the upper coil being sealed in position by the upper return pole. The latter is element  11  in  FIG. 1   a  and element  12  in  FIG. 1   b.    
         [0026]    Trailing shields  14  and  15 , which are key novel features of the present invention, are in similar locations in both versions of the full write head, with write gap  25  being between lower shield  15  and main pole  16 , as can be seen in the enlarged view provided in  FIG. 2 . For the invention to perform as will be described below, it is critical that distance d (between the lower edge of the upper trailing shield and main pole  16 ) be precisely controlled to be at least 0.15 microns but no greater than 0.5 microns. It is also important that the width of the upper trailing shield be in a range of from 0.5 to 2.5 microns although a variation of up to about 0.1 microns in either direction is tolerable. 
         [0027]    Also shown in  FIG. 2  are recording medium  21  and high permeability (magnetically soft) under-layer  22 , the latter serving to provide the return path for flux from main pole  16  to upper return pole  11  by way of trailing shields  14  and  15 . 
         [0028]    We now provide a description of a process for forming the write head of the present invention, particularly the trailing shield structure: 
         [0029]    The process begins with the provision of a TMR or GMR read element  41  sandwiched between upper and lower shields  31  and  32 , respectively, as shown in  FIGS. 3 and 4 .  FIG. 3  is a side view in which field coil  33  can be seen while  FIG. 4  is an ABS view in which read element  41  can be seen. Also seen in both  FIGS. 3 and 4  is ruthenium layer  35  which will be used later as an etch stop layer.  FIG. 4  represents a later stage in the process than  FIG. 3  so it also shows alumina layer  44  which has been deposited onto ruthenium layer  35 . Next, a second ruthenium layer was deposited onto the surface of layer  44  where it was patterned to form hard mask  43  that included opening  42 . 
         [0030]    This was followed by the formation of trench  52  in the area defined by opening  42  and extending through layer  44  as far as etch stop layer  35 , as shown in  FIG. 5  (which is an ABS view). Then, trench  52  was overfilled with FeCoN and Chemical Mechanical Polishing (CMP) was used to remove all excess magnetic material, as well as the hard mask material, from the surface of layer  44 , thereby forming main pole  16  as can be seen in side view in  FIG. 6 . 
         [0031]    Referring now to  FIG. 7 , it can be seen that an alumina layer has been patterned to form small ledge  71  that will be used to define the write gap as well as to support lower trailing shield  15 .  FIG. 8  illustrates a critical process step, namely the formation of insulating ledge  81  which will be used to support upper trailing shield  14 . This step is critical in that the combined thickness of layers  71  and  81 , which determine the distance between the upper trailing shield and the main pole (distance d in  FIG. 2 ), must be at least 0.15 microns but no more than 0.5 microns. 
         [0032]      FIG. 9  is an ABS view of  FIG. 8   
         [0033]    Formation of the write head is completed with the formation of alumina layer  82  which covers lower return pole  17  so as to provide a substrate on which second set of field coils  93  can be formed, as illustrated in  FIG. 10 . 
       Results: 
       [0034]    The upper and lower parts of the trailing shield structure of the present invention serve as a larger head field gradient enhancer and as a main-pole flux controller, respectively. As a result, the write field and the field width level off despite further increases in the write current. This is shown in  FIGS. 11   a  and  11   b  which display the y and x components, respectively, of the write field as a function of the write current for the write head of the invention (both curved and planar return pole versions) as compared to a conventional read head (having no dual trailing shields). As can be seen, the invented head, particularly when a planar upper return pole is also used, shows virtually no field increase even though the write current has more than tripled in value. 
         [0035]    Another important feature of the invention is that the fringing field is suppressed (relative to prior art designs) especially at high write currents.  FIG. 12  plots the maximum width of the effective head field at 7 kOe (in microns) as a function of the write current. As can be seen, the field width of the invented write head (with planar return pole) does not grow larger than about 0.115 microns even when the write current is increased from about 40 mA to about 120 mA whereas for a write head of the prior art it increases to about 0.133 microns over the same write current range—a 20% increase over the present invention. 
         [0036]    Similarly,  FIG. 13  plots the maximum value of the effective head field at a distance of 0.2 microns off the active write track as a function of the write current (write field within the write track is 7,000 Oe). As can be seen, at a write current of 120 mA, the fringe field for the prior art design has increased to about 4,750 Oe whereas for the invented write head it has remained constant at about 3,500 Oe. 
         [0037]      FIGS. 14 and 15  taken together illustrate why the claimed range for d (distance between upper trailing shield and main pole) is critical for optimum operation of the present invention.  FIG. 14  shows that there is no advantage for d to exceed 0.5 microns while  FIG. 15  shows that the write field falls off very rapidly below 0.15 microns. 
         [0038]      FIG. 16  shows that the effective head field at 0.2 microns from the track edge decreases somewhat as L, the width of the upper trailing shield, increases from about 0.2 to about 1.75 microns while  FIG. 17  shows that the write field of about 9,000 Oe is essentially independent of L. 
         [0039]    Thus, the write head of the present invention offers several advantage over write heads of the prior art including reduced adjacent track erasure, reduced far tracks erasure, reduced return field partial erasure, and improved magnetic track width definition.