Abstract:
A process for reducing fringe field effects of a main write pole by shielding it on all four sides, with the regular return pole also serving as the leading edge shield, is described. The main pole may also be tapered and the leading edge and side shields may be magnetically connected to each other.

Description:
FIELD OF THE INVENTION 
   The invention relates to the general field of magnetic disk storage systems with particular reference to shielding perpendicular write heads. 
   BACKGROUND OF THE INVENTION 
   One of the key advantages of single-pole (SP) head/media, with a magnetically soft underlayer (SUL) and a perpendicular recording system, is the capability to provide 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. 
     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  11  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  11 . The space enclosed by the yoke and poles is normally filled with insulating material  17 . 
   The traditional single pole perpendicular writer with soft underlayer has two major problems—insufficient field gradient in the down track direction and adjacent track erasure (ATE) caused by side fringing fields. The second problem becomes even more severe when the neck height of the single pole is reduced so as to increase the write field, i.e. overwrite (OW) capability. 
   A shielded pole perpendicular writer has been proposed to improve field gradient and to reduce ATE [1]. Unfortunately, the presence of shields also reduces the perpendicular field component so a shielded pole head will generate insufficient write field, even taking into consideration the increased in-plane field. Proper design of a shield pole head should take both ATE improvement and OW performance into consideration. 
   A routine search of the prior art was performed with the following references of interest being found: 
   A tapered pole is described in U.S. Pat. No. 5,173,821 while Inamura describes a tapered pole portion at the tip in U.S. Pat. No. 5,995,343. In U.S. Pat. No. 5,600,519, Heim et al teach the use of a tapered pole tip to increase the head field and, in U.S. Pat. No. 4,935,832, Das et al. show side shields around the write pole. 
   REFERENCES: 
   
       
       [1] M. Mallary, A. Torabi, and M. Benakly “One terabit per square inch perpendicular recording conceptual design” IEEE Trans. Mag. 38 no. 4 1719-1724 July 2002. 
     
  
   SUMMARY OF THE INVENTION 
   It has been an object of at least one embodiment of the present invention to provide a method to improve the magnetic field distribution of a single pole magnetic write head. 
   Another object of at least one embodiment of the present invention has been that said improved write head have minimum adjacent track erasure. 
   These objects have been achieved by shielding the main write pole on all four sides, with the regular return pole also serving as the leading edge shield. Additionally, the main pole is tapered. Tapering has also been used in conventional designs but, without the additional shields disclosed by the present invention, tapered shields suffer from excess adjacent track erasure. Optionally, the leading edge and side shields may be magnetically connected as well. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  shows a typical single pole magnetic write head. 
       FIG. 2  is an ABS view of the four sided shielding structure of the invention. 
       FIG. 3  shows  FIG. 1  modified to include the features of the invention. 
       FIGS. 4-6  compare contours of constant field magnitude for several configurations. 
       FIG. 7  shows the enhancement due to the leading-edge tapered pole head. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring now to  FIG. 2  where the principal elements of the invention can be seen from an ABS view as leading shield  15  (which is connected to the return pole as shown in  FIG. 1 ), a trailing shield  21 , and two opposing side shields  22 . The main pole  19  (see  13  in  FIG. 1 ), sometimes also referred to as the write pole, is separated from shields by a different amount in each direction. Trailing shield  21 , separated from main pole with a gap GT, effects the sharp magnetic field gradient needed for high linear density applications. 
   The side shield  22 , separated from main pole  19  by a gap GS, prevent side-fringing magnetic fields from reaching the media and thereby reduce ATE. The leading shield  15 , separated from the main pole by a gap GL, blocks field leakage from the leading side and also bridges the return pole and the trailing/side shields to keep the magnetic potential of the trailing/side shield grounded. Optionally, the side and leading shields may be magnetically connected to one other through connectors  23 . Leading gap GL is usually larger than GT and GS, so that the field loss due to GL is negligible. Note that even though trailing and side shields are marked as different functional components in  FIG. 2 , they may be fabricated simultaneously during device processing. To minimize the field loss, the thicknesses of the trailing shield and side shields are kept small (typically between about 0.05 and 0.4 microns). 
     FIG. 3  shows a side view of the head structure. In order to compensate for the loss of magnetic fields due to leakage to the shields, the main pole is tapered, preferably at the leading side to maintain high trailing field gradients. The combination of tapered main pole and leading shield increases the head field and minimizes magnetic field spread at the leading edge. 
     FIGS. 4-6  compare contours of constant field magnitude for a single pole head ( FIG. 4 ), a single pole with trailing shield only ( FIG. 5 ), and the shielded pole head of the present invention ( FIG. 6 ). In all cases, the main pole had a 30 deg tapering angle. In the calculation, the following parameters were used: GT=50 nm, GS=100 nm, GL=300 nm. The spacing from head Air Bearing Surface (ABS) to soft underlayer was 50 nm. The thickness of trailing and side shield was about 0.1 microns while the thickness of the leading shield was about 0.3 microns. A large field gradient at the trailing edge that nevertheless confines the side-fringing field can be easily seen in the case of the structure of the present invention ( FIG. 6 ). Without the side shields, the tapered pole heads would have produced side-fringing magnetic fields that were too large, thus causing excessive ATE. 
     FIG. 7  illustrates the calculated magnetic field enhancement due to the leading-edge tapered pole head. At a tapering angle of 30 degrees (curve  72 ), the write field is increased by more than 1500 Oe compared to a pole having zero taper (curve  71 ). The corresponding shielded tapered head produces as much magnetic field as does a single pole head with only a trailing shield but without any taper. In the latter case, the taper could not be used in any case because of excessive ATE. In short, the proposed shielded tapered-pole head achieves an optimal design in the trade-off between maximum write fields and minimum fringing fields at the price of a slight increase in head processing complexity. 
   In order to fully facilitate reproduction of the invention by interested parties, the following enabling information is supplied: The return pole width is between about 10 and 50 microns. The distance between write pole and trailing shield is between about 0.02 and 0.2 microns. The trailing shield has a thickness between about 0.05 and 0.4 microns. The tapering of the write pole is at an angle of between about 15 and 65 degrees, relative to the vertical. The tapering of the write pole may begin at an edge that is closest to a trailing edge or it may begin at an edge that is closest to a leading edge. Each side shield has a width between about 0.2 and 5 microns. The distances between each of the side shields and the write pole is between about 0.02 and 0.2 microns. Each side shield is between about 0.05 and 5 microns from the leading shield. Each side shield has a thickness between about 0.05 and 0.4 microns. The return pole has a thickness between about 0.5 and 5 microns. The write pole length is between about 0.1 and 0.5 microns and the amount by which the side shield width exceeds the write pole length is up to about 0.2 microns.