# Patent

## Title
Method to reduce sensitivity of a perpendicular recording head to external fields

## Abstract

In a read-write head, the shields can serve as magnetic flux conductors for external fields, so that they direct a certain amount of flux into the recording medium. This problem has been overcome by the addition to the shields of a pair of tabs located at the edges closest to the ABS. These tabs serve to prevent flux concentrating at the edges so that horizontal fields at these edges are significantly reduced. Said tabs need to have aspect ratios of at least 2 and may be either triangular or rectangular in shape. Alternatively, the tabs may be omitted and, instead, outer portions of the shield's lower edge may be shaped so as to slope upwards away from the ABS.

## Background
This is a divisional application of U.S. patent application Ser. No. 11/117,672, filed on Apr. 28 2005, which is herein incorporated by reference in its entirety, and assigned to a common assignee.


RELATED PATENT APPLICATION
This application is related to Ser. No. 11/117,673, filed on Apr. 28 2005, which is herein incorporated by reference in its entirety, which is assigned to a common assignee as the instant application.
FIELD OF THE INVENTION
The invention relates to the general field of magnetic disk systems with particular reference to magnetic write heads for perpendicular designs and their sensitivity to external magnetic fields.
BACKGROUND OF THE INVENTION
As magnetic recording is pushed to higher areal densities, perpendicular recording may offer advantages in thermal stability over longitudinal recording, thus delaying arrival at the super-paramagnetic limit. Another advantage of perpendicular recording with single pole (SP) head and perpendicular media, with a soft underlayer (SUL), is the ability to produce a larger write field than that of a ring head to record on relatively thick media with high anisotropy constant.
A typical read-write unit is illustrated in FIG. 1. Seen there are yoke 11, write coil 12, return shield 14, and lower write shield 15. Writing is performed in the vertical direction by write pole 13 into soft underlayer and recording medium 16 (shown as a single layer) for the PMR (perpendicular magnetic recording) configuration shown here. Reading is performed by unit 19 which is typically a giant magneto-resistance (GMR) or a tunneling magnetic junction (TMJ) device.
The magnetic components of writer shield 14 as well as reader shields 17 and 18 can serve as magnetic flux conductors for external fields, so that they direct a certain amount of flux into soft underlayer and recording medium 16. When the flux density is large enough, unwanted writing or erasing can occur. Because of the magnetic softness of the shield materials, a small amount of external field can induce relatively large fields in the media and cause erasure of information on the media.
In most current PMR designs, shields 14, 17 and 18 have a strictly rectangular shape as seen in FIG. 2 which is a view of FIG. 1 along the direction of arrow 20. Due to the finite thickness and moment of the soft magnetic underlayer, flux distribution is not uniform over the surfaces of the shields. At the sharp corners and edges, the flux density can be much higher than that at the shield center. In general, data under a shield corner is usually erased first.
A routine search of the prior art was performed with the following references of interest being found:
In U.S. Pat. No. 6,757,141, Santini et al. disclose a flare on the bottom FM shaping layer and the top FM probe layer of the second pole piece where the flare point widens after the ABS. In U.S. Pat. No. 5,075,280, Pisharody et al. show surfaces of the pole portions chamfered to slope away from the plane of the recording medium. Pole shields are formed on the chamfered surfaces of the pole portion of the core.
Parker et al. teach a shield having an edge adjacent to the ABS in U.S. Patent Publication 2003/0227714 while Okada et al. describe a recessed shield to prevent leaking of the magnetic field in US Patent Publication 2003/0026039. Kuroda et al. show a shield formed to a required shape in US Patent Publication 2003/0021063 and Mori et al. teach patterning a shield layer to an appropriate size in US Patent Publication 2001/0017753.
SUMMARY OF THE INVENTION
It has been an object of at least one embodiment of the present invention to provide a magnetic read-write head.
Another object of at least one embodiment of the present invention has been that said read-write head be insensitive to the presence of external magnetic fields.
A further object of at least one embodiment of the present invention has been to provide a method for forming said read-write head.
These objects have been achieved by:

    1) The addition of a pair of tabs located at the edges closest to the ABS. Said tabs need to have an aspect ratio of at least 2 and may be either triangular, rectangular, other polygon in shape.
    2) Removal of sharp edges so as to create a shallow recess angle, said removed region needs to have an aspect ratio of at least 2.
    3) Any combination of (1) and (2)





BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a magnetic read-write head of the prior art.
FIG. 2 shows a read element shield of the prior art.
FIG. 3 shows a pair of triangular tabs appended to a shield.
FIG. 4 shows a pair of rectangular tabs appended to a shield.
FIG. 5 illustrates a recessed edge.
FIG. 6 illustrates a shield having both a tab and a recessed edge.
FIG. 7 shows plots for the structures seen in FIGS. 3 and 5.



DESCRIPTION OF THE PREFERRED EMBODIMENTS
The present invention solves the problem of excessive fields at shield edges by modifying their shape to include extra tabs or to create recessed edges at their lower (ABS) edges. In the case of extra tabs, the shape of these tabs may be either triangular (as in tabs 31 in FIG. 3) or rectangular (as in tabs 41 in FIG. 4). In the case of recessed edges, the angle of recessed edges is a constant, with respect to the ABS line (as shown in FIG. 5. Typically, the angle of the slope would be between about 8 to 20 degrees and outer portion 63 should constitute less than 30% of shield width. FIG. 6 shows yet another embodiment which is a combination of tabs (71) and recessed edge (73).
In FIG. 7, the magnetic field in the media under a constant external field of 200 Oe is plotted as a function of position along the shield for a conventional rectangular shield (curve 81), a shield with triangular tab (curve 82), and a shield with a recessed edge (curve 83). It is clear that the peak of the magnetic field occurs at the edge of the shield.
By introducing the tab, or a recessed edge, the concentration of flux at the edge is avoided and fields at the edges can be significantly reduced. In the calculation shown in FIG. 7, a length of L of 3 microns and a height H of 1 micron were used for the triangular tab (curve 82) and for the recessed edge (curve 83). In both cases, the erasing field at the outer edge of the tab or recessed edge is smaller than the field at the shield center. As already noted, for the tab or recessed edge to be effective, a larger valued of L/H is preferred.
To enable full reproduction of the invention, the following additional information is provided:

    
    
        Each tab has a length that is at least 2 times its height
        The height of each tab is between about 0.1 and 10 microns
        The length of each tab is between about 0.2 and 20 microns
        Each tab is made of the same material and thickness as its associated shield
        Each recessed edge has a slope angle between 5 and 20 degrees
        Each recessed edge has a recessed length of between about 0.2 and 20 microns.
        Suitable materials for the shield include Ni, Fe, Co alloys, such as NiFe, CoFeNi.
        Each shield has a height that is between about 10 and 50 microns
        Each shield has a thickness that is between about 0.5 and 5 microns

## Claims

1. A method to reduce sensitivity to external magnetic fields of a magnetic read-write head, comprising:
providing a perpendicular magnetic writer having an ABS, a magnetic read head having an ABS that is coplanar with said writer ABS, magnetic shields on opposing sides of said read head, one of said second magnetic shields being located between said perpendicular magnetic writer and said magnetic read head, all shields having lower horizontal edges that are parallel to said ABS, and opposing vertical edges that are normal to said ABS;
attaching to each shield a magnetically soft tab having a top edge that extends away from said vertical edge and, at said vertical edge, giving said tab a height that is less than that of its associated shield and a lower edge that begins as a coplanar extension of said lower horizontal edge; and
sloping part of said magnetically soft tab's lower edge upwards towards its outer edge, whereby flux concentration and horizontal magnetic fields are reduced at said shield's edges.

2. The method recited in claim 1 wherein said tab has a height that is between 0.1 and 10 microns.

3. The method recited in claim 1 wherein said associated shield has a height that is between 10 and 50 microns.

4. The method recited in claim 1 wherein the tab's lower edge slopes upward at an angle that is between 8 and 20 degrees.

5. A method to reduce sensitivity to external magnetic fields of a magnetic read-write head, comprising:
providing a perpendicular magnetic writer having a first ABS, a magnetic read head having an ABS that is coplanar with said first ABS, first and second magnetic shields on opposing sides of said read head, one of said magnetic shields being located between said perpendicular magnetic writer and said magnetic read head, all shields having lower horizontal edges that are parallel to said ABS, and opposing vertical edges that are normal to said ABS;
attaching to a first shield a magnetically soft tab having a top edge that extends away from said vertical edge and, at said vertical edge, giving said tab a height that is less than that of its associated shield and a lower edge that begins as a coplanar extension of said lower horizontal edge;
sloping part of said magnetically soft tab's lower edge upwards towards an outer edge; and
shaping the second shield's lower edge whereby it has a centrally located second ABS, that is narrower than said first ABS, and an outer portion that angles upwards from, and begins at, said second ABS towards said second shield's vertical edge.

6. The method recited in claim 5 wherein said tab has a height that is between 0.1 and 10 microns.

7. The method recited in claim 5 wherein said associated shield has a height that is between 10 and 50 microns.

8. The method recited in claim 5 wherein the tab's lower edge slopes upward at an angle that is between 8 and 20 degrees.