Abstract:
Prior art designs of single pole writers have been limited by premature saturation at the tip. This limits the head field that can be achieved without simultaneously widening the write profile. This problem has been solved by means of a vertical main pole whose thickness has its conventional value a short distance from the tip but that tapers down to a significantly reduced value as it approaches the tip. A process for manufacturing this tapered tip design is also presented.

Description:
This is a divisional application of U.S. patent application Ser. No. 10/818,577, filed on Apr. 6, 2004, now abandoned which is herein incorporated by reference in its entirety, and assigned to a common assignee. 

   FIELD OF THE INVENTION 
   The invention relates to the general field of magnetic disk systems with particular reference to perpendicular write poles and controlling flux therefrom. 
   BACKGROUND OF THE INVENTION 
   One of the key advantages of single-pole (SP) head/media, with a magnetically soft underlayer (SUL) and perpendicular recording system, is the capability of providing a larger write field (than that of a ring head) to enable writing into the relatively thick media with high anisotropy constant. The latter quality leads one to assume better thermal stability associated with perpendicular recording. However, this advantage is diminished as the dimension of the pole tip is reduced to increase the areal recording density [1]. So, the tradeoff between head writing field and thermal stability may still limit the achievable areal density for perpendicular recording. 
     FIG. 1  is a schematic representation of a typical single pole vertical recording system of the prior art. Seen there is single write pole  13  whose ABS (air bearing surface) moves parallel, and close to, the surface of recording medium  16 . The latter comprises an upper, high coercivity, layer (not shown) on a magnetically soft underlayer. Coils  12  generate magnetic flux in yoke  14  which passes through main pole  14  into tip  13  and then into media  16  (where a bit is written). The magnetic circuit is completed by flux that passes through the soft under layer and then back into return pole  15 . The space enclosed by the yoke and poles is normally filled with insulating material  17 . 
     FIG. 2  is a front view of the structure shown in  FIG. 1  when viewed along direction  18 . 
   An enlarged view of the write and return poles is shown in  FIG. 3 . In this prior art design, the main pole  13  is about 0.1 to 0.4 microns thick at the ABS  19 . The main pole is made of a high moment material, such as CoFe having a saturation magnetization, Bs, of about 2.4 T, but, in practice, this main pole does not saturate, except at the pole tip region. Thus the maximum write field in the media is mainly determined by the saturation level of the pole tip and the solid angle opened by the ABS of the pole tip. 
   To increase the write field, large W and t and small NH are preferred (as defined in  FIGS. 1 and 2 ). However, for ultra-high density recording, track width W is limited by the 
   track density requirement. To have good control of track width W, NH cannot be reduced to the extent desired due to the rounding effect of the photo mask used to pattern it. A small neck height also increases the side-fringing field and causes adjacent track erasure (ATE) [2]. 
   A large pole width t will result in head skew problems [3]. Thus better methods for compensating field loss at ultra-high recording densities are essential. The present invention discloses a novel structure for a perpendicular write head that overcomes these problems. 
   REFERENCES 
   
       
       (1) Z. Bai, and J.-G. Zhu, “Micromagnetics of Perpendicular Write Heads with Small Pole-Tip Dimensions”, J. Appl. Phys, vol. 91, 6833 (2001). 
       (2) J. Schare, L. Guan, J. G. Zhu, and M. Kryder, “Design Considerations for Single-Pole Type Write Heads”, IEEE Tran. Magn., May, 2003 
       (3) R. Wood, T. Sonobe, Z. Jin, and B. Wilson, “Perpendicular recording: the promise and the problems”, J. Magn. Magn. Mater., vol 235, 1 (2001) 
     
  
   A routine search of the prior art was performed with the following references of interest being found: 
   U.S. Pat. No. 5,600,519 (Heim et al) discloses a tapered main pole as does U.S. Pat. No. 5,173,821 (Maloney). 
   SUMMARY OF THE INVENTION 
   It has been an object of at least one embodiment of the present invention to provide a single pole vertical write head having both a large head field, as well as good spatial resolution. 
   Another object of at least one embodiment of the present invention has been to provide a process for manufacturing said vertical writer. 
   A further object of at least one embodiment of the present invention has been that said process introduce little or no changes to current processes for manufacturing vertical writers. 
   These objects have been achieved by means of a vertical main pole whose thickness has its conventional value a short distance from the tip but that tapers down to a significantly reduced value as it approaches the tip. Typically, the distance over which this tapering takes place is about 0.1 to 4 microns. In order to manufacture this structure, a trench is etched, using ion milling, partly into the yoke region and partly into the insulated coil well. Said trench has sides whose slope is carefully controlled through adjustment of the angle of incidence of the ion beam, this slope determining the afore-mentioned taper. After the trench has been just filled with a high moment layer, a second high moment layer is deposited to complete formation of the pole tip. After an appropriate lapping step to define the ABS, the process is complete. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a single vertical pole magnetic writer of the prior art. 
       FIG. 2  is a head-on view of the structure of  FIG. 1 . 
       FIG. 3  is a closer view of the pole tip portion of a vertical writer 
       FIG. 4  shows the starting point for the process of the present invention. 
       FIGS. 5 and 6  illustrate formation and filling of a trench with a high moment material. 
       FIG. 7  shows deposition of a second layer of high moment material over the afore-mentioned first layer. 
       FIG. 8  shows the final structure. 
       FIG. 9  compares the magnitude and spatial distribution of the head field in a device made according to the present invention with two prior art devices. 
       FIG. 10  is a cross-section of the write head, including an ABS level shield. 
       FIG. 11  is an ABS view of  FIG. 10  for a single trailing edge shield. 
       FIG. 12  is said ABS view for a shield that surrounds the main pole on three sides. 
       FIG. 13  is an example of a tapered main pole at a trailing edge combined with a trailing shield 
       FIGS. 14-20  illustrate the process for making the structure shown in  FIG. 13 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   We will disclose the present invention through a description of a process for its manufacture. This description will also serve to make clear the structure of the present invention. 
   Referring now to  FIG. 4 , the process of the present invention begins with the formation of return pole layer  15  on a substrate (not shown). Layer  15  is any of Ni, Fe, or Co, or their alloys and it is deposited to a thickness between about 0.5 and 5 microns. This is followed by the formation of magnetic yoke  14  that includes a well within which is coil  12  embedded in layer of insulation  17 . Yoke  14  is a material such as Ni, Fe, Co, or their alloys. 
   Now follows a key novel feature, namely the formation of trench  51 , as shown in  FIG. 5 . Ion beam milling is most commonly used to form said trench whose depth is typically between about 0.1 and 2 microns, this depth being controlled through adjustment of the ion beam&#39;s dose and duration. Walls  52  of trench  51  have sloping sides as shown in the figure. The sides of the trench slope at an angle between about 15 and 65 degrees from vertical, slope angle being controlled through adjustment of the ion beam&#39;s angle of incidence. 
   Trench  52  is then overfilled with layer  61  of a material capable of a magnetic moment of at least 1.8 T and is then planarized until insulation layer  17  is just exposed, as illustrated in  FIG. 6 . Layer  61  should have high B s  and is any of Ni, Fe, or Co, or their alloys. 
   Next, as seen in  FIG. 7 , layer  71  of a material capable of a magnetic moment of at least 2 T, is deposited. Layer  71  is any of Ni, Fe, or Co, or their alloys. This essentially completes formation of the magnetic write head which, as can be seen, now includes a tapered single vertical pole. All that remains to be done is to form air bearing surface  19  through planarizing in a plane normal to the upper surface of layer  71 . The final structure is seen in  FIG. 8 . 
     FIG. 9  compares calculated plots of the head field (in Tesla) as a function its downtrack position (in microns) for three cases: Curve  91  is a conventional straight pole design having t=0.2 microns. Curve  92  is a straight main pole having t=0.4 microns, while curve  93  is for a tapered main pole (present invention) (t 1 =t 2 =0.2 microns, and NH=0). These data make it clear that the head field can be increased by providing a thicker main pole (curve  92 ) but this comes with an accompanying problem that the head field could erase data on adjacent tracks when the head is skewed. On the other hand, a main pole designed according to the teachings of the present invention (curve  93 ) achieves a head field even larger than that of the thicker, but conventional, pole with less erasure problems for the same head skew angle because of smaller pole thickness at the ABS. 
   The concept of a tapered main pole is not limited to only single pole perpendicular writers, but is also applicable to a shielded pole type perpendicular write head, a cross-section of which is shown in  FIG. 10  with the shield being designated as element  25 . Shield designs may vary. For example, in  FIG. 11  we show an ABS view of shield  26  which is located on only one side (the trailing edge), while in  FIG. 12  we show shield  27  that surrounds the main pole on three sides (trailing edge and two sides in the cross-track). 
   In addition to the previously described tapered main pole structure at a leading edge, a main pole tapered at trailing edge  133 , at angle  134 , combined with trailing shield  135 , is disclosed here, as shown in  FIG. 13 . Note that the trailing shield is tapered to the same angle as the main pole, thereby maintaining a constant horizontal distance  131  therefrom. 
   The major process steps to make this trailing-edge-tapered main pole with trailing shield are illustrated in  FIGS. 14-20 .  FIG. 14  shows the starting point for manufacturing the writer once the reader structure has been completed. First, isolation  41  layer (usually Al 2 O 3 , between about 1 and 3 um thick) is deposited on the top reader shield  42 , followed by layer  43  of high Bs materials (Co, Fe and their alloys, Bs˜2.4 T, thickness about 0.2 to 2 um), which will eventually form the main pole. In  FIG. 15 , an etching process similar to that shown in  FIG. 5 , is applied to form trench  151 , whose slope angle defines the taper angle of the main pole. Subsequently, the process to define main pole track width is applied so the front geometry of the main pole (as in  FIG. 2 ) is formed. In  FIG. 16  non-magnetic layer  141  (usually Al 2 O 3 , 0.03 to 0.2 um thick) is deposited to serve as the gap between the trailing shield and main pole. In  FIG. 17 , trailing shield  135  (alloys of Co, Fe, Ni, Bs around 1.0-2.0 T) is deposited on top of gap layer  141 . In  FIG. 18 , coils  12  are made. Then the whole structure is filled with Al 2 O 3  and polished to expose the top surface of the trailing shield. In  FIG. 19 , the return pole (alloys of Co, Fe, Ni, Bs around 1.0-2.0 T, thickness=0.5-5.0 um) is deposited and connected with the trailing shield. Finally, in  FIG. 20 , lapping is applied to define the ABS of the head.