Abstract:
A magnetic write head for perpendicular magnetic recording, the write head having a magnetic write pole configured with a cross section as viewed from the ABS that has a trailing portion with substantially vertical side walls and a leading portion formed with a taper that becomes narrower as it extends toward the leading edge. The write pole provides for excellent write field strength by providing sufficient cross section near the trailing edge to avoid magnetic saturation of the pole tip. The parallel side walls of the trailing portion also provide for excellent track width control during manufacture of the write head. The tapered portion of the write head, which starts some distance away from the trailing edge, prevents skew related adjacent track writing when the actuator that holds the write head is at its innermost or outermost travel extensions.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention relates to perpendicular magnetic recording, and more particularly to a perpendicular magnetic write head having a novel write pole configured for improved write field and reduced skew related adjacent track interference.  
       BACKGROUND OF THE INVENTION  
       [0002]     At the heart of a computer is a magnetic disk drive that includes a magnetic disk, a slider where a magnetic head assembly including write and read heads is mounted, a suspension arm, and an actuator arm. When the magnetic disk rotates, air adjacent to the disk surface moves with it. This allows the slider to fly on an extremely thin cushion of air, generally referred to as an air bearing. When the slider flies on the air bearing, the actuator arm swings the suspension arm to place the magnetic head assembly over selected circular tracks on the rotating magnetic disk, where signal fields are written and read by the write and read heads, respectively. The write and read heads are connected to processing circuitry that operates according to a computer program to implement write and read functions.  
         [0003]     Typically magnetic disk drives have been longitudinal magnetic recording systems, wherein magnetic data is recorded as magnetic transitions formed longitudinally on a disk surface. The surface of the disk is magnetized in a direction along a track of data and then switched to the opposite direction, both directions being parallel with the surface of the disk and parallel with the direction of the data track.  
         [0004]     Data density requirements are fast approaching the physical limits, however. For example, increased data capacity requires decreased bit sizes, which in turn requires decreasing the grain size of the magnetic medium. As this grain size shrinks, the magnetic field required to write a bit of data increases proportionally. The ability to produce a magnetic field strong enough to write a bit of data using conventional longitudinal write head technologies is reaching its physical limit.  
         [0005]     One means for overcoming this physical limit has been to introduce perpendicular recording. In a perpendicular recording system, bits of data are recorded magnetically perpendicular to the plane of the surface of the disk. The magnetic disk may have a relatively high coercivity material at its surface and a relatively low coercivity material just beneath the surface. A write pole having a small cross section and very high flux emits a strong, concentrated magnetic field perpendicular to the surface of the disk. This magnetic field emitted from the write pole is sufficiently strong to overcome the high coercivity of the surface material and magnetize it in a direction perpendicular to its surface. This flux then flows through the relatively magnetically soft underlayer and returns to the surface of the disk at a location adjacent a return pole of the write element.  
         [0006]     The return pole of the write element has a cross section that is much larger than that of the write pole so that the flux through the disk at the location of the return pole (as well as the resulting magnetic field between the disk and return pole) is sufficiently spread out to render the flux too weak to overcome the coercivity of the disk surface material. In this way, the magnetization imparted by the write pole is not erased by the return pole.  
         [0007]     Efforts to minimize track width and bit size when using perpendicular recording have focused on the formation of the write pole since the write pole defines the track width. If the write pole is configured with a rectangular cross section, as viewed from the air bearing surface (ABS) problems with adjacent track interference arise. As those skilled in the art will recognize, skew occurs as an actuator arm swings the magnetic head to either extreme of its pivot range (ie. at the inner and outer portions of the disk). Such skew positions the head at an angle, which positions portions of the write pole outside of the desired track.  
         [0008]     One way to mitigate this skew related adjacent track interference is to form the write pole with a trapezoidal cross section as viewed from the ABS. Such a trapezoidal shape has the wider portion of the trapezoid at the trailing edge of the write pole where the bit is written. Unfortunately, such a trapezoidal configuration of the write pole restricts write field by reducing the amount of write pole material available for conducting magnetic flux, especially near the trailing edge where the bit is primarily written. This reduced write pole area, or footprint, of the pole tip at the ABS results in a reduced field at the media.  
         [0009]     Another problem that arises as a result of such trapezoidal configuration is that it seriously diminishes the ability to control trackwidth during manufacture of the write head. The trapezoidal write pole is constructed by an angled ion mill that removes material from the sides of the write pole, and since the sloped sides of the write pole extend all of the way to the trailing edge of the write pole, any variation of the sloped sides greatly affects the trackwidth of the write pole.  
         [0010]     Therefore, there is a strong felt need for a write pole design maximize write field at the media, especially at the trailing edge of the write pole, while also preventing skew related adjacent track interference. Such a write pole would preferably also allow for tight control of the track width of the write pole, since this is one of the most critical parameters in write head design.  
       SUMMARY OF THE INVENTION  
       [0011]     The present invention provides a magnetic write pole for perpendicular magnetic recording that is configured with a cross section as viewed from the ABS that has a trailing portion with substantially vertical side walls and a leading portion formed with a taper that becomes narrower as it extends toward the leading edge.  
         [0012]     The write pole exhibits excellent write field strength by providing sufficient cross section near the trailing edge of the write pole. The parallel side walls of the trailing portion also provide for excellent track width control during manufacture of the write head.  
         [0013]     The tapered portion of the write head, which starts some distance away from the trailing edge, prevents skew related adjacent track writing when the actuator that holds the write head is at its innermost or outermost travel extensions.  
         [0014]     The constant width portion of the write pole (trailing portion) may extend from the trailing edge to a distance D from the trailing edge. The leading portion may extend from the end of the trailing portion (the distance D from the trailing edge) all the way to the leading edge. The distance from the leading edge to the trailing edge of the write pole defines a length L and D can be, for example 1/10 to ½ L. The width of the leading edge can be 40% to 80% of the width of the trailing edge (ie. the width of the trailing portion).  
         [0015]     These and other advantages and features of the present invention will be apparent upon reading the following detailed description in conjunction with the Figures.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]     For a fuller understanding of the nature and advantages of this invention, as well as the preferred mode of use, reference should be made to the following detailed description read in conjunction with the accompanying drawings which are not to scale.  
         [0017]      FIG. 1  is a schematic view of a magnetic storage system in which the present invention might be embodied;  
         [0018]      FIG. 2  is a cross sectional view of a perpendicular magnetic write element according to an embodiment of the present invention;  
         [0019]      FIG. 3  is an ABS view, taken from line  3 - 3  of  FIG. 2 , illustrating a write pole according to an embodiment of the present invention;  
         [0020]      FIGS. 4-8  are ABS views of a write pole according to an embodiment of the invention, shown in various intermediate stages of manufacture in order to illustrate a method of manufacturing a write head according to an embodiment of the invention; and  
         [0021]      FIG. 9  is a top down view of a wafer illustrating an ion mill sweep.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]     The following description is the best embodiment presently contemplated for carrying out this invention. This description is made for the purpose of illustrating the general principles of this invention and is not meant to limit the inventive concepts claimed herein.  
         [0023]     Referring now to  FIG. 1 , there is shown a disk drive  100  embodying this invention. As shown in  FIG. 1 , at least one rotatable magnetic disk  112  is supported on a spindle  114  and rotated by a disk drive motor  118 . The magnetic recording on each disk is in the form of an annular pattern of concentric data tracks (not shown) on the magnetic disk  112 .  
         [0024]     At least one slider  113  is positioned near the magnetic disk  112 , each slider  113  supporting one or more magnetic head assemblies  121 . As the magnetic disk rotates, the slider  113  is moved radially in and out over the disk surface  122  so that the magnetic head assembly  121  may access different tracks of the magnetic disk where desired data are written. Each slider  113  is attached to an actuator arm  119  by way of a suspension  115 . The suspension  115  provides a slight spring force which biases slider  113  against the disk surface  122 . Each actuator arm  119  is attached to an actuator means  127 . The actuator means  127  as shown in  FIG. 1  may be a voice coil motor (VCM). The VCM comprises a coil movable within a fixed magnetic field, the direction and speed of the coil movements being controlled by the motor current signals supplied by controller  129 .  
         [0025]     During operation of the disk storage system, the rotation of the magnetic disk  112  generates an air bearing between the slider  113  and the disk surface  122  which exerts an upward force or lift on the slider. The air bearing thus counter-balances the slight spring force of suspension  115  and supports the slider  113  off and slightly above the disk surface by a small, substantially constant spacing during normal operation.  
         [0026]     The various components of the disk storage system are controlled in operation by control signals generated by control unit  129 , such as access control signals and internal clock signals. Typically, the control unit  129  comprises logic control circuits, storage means and a microprocessor. The control unit  129  generates control signals to control various system operations such as drive motor control signals on line  123  and head position and seek control signals on line  128 . The control signals on line  128  provide the desired current profiles to optimally move and position slider  113  to the desired data track on disk  112 . Write and read signals are communicated to and from write and read heads  121  by way of recording channel  125 .  
         [0027]     The above description of a typical magnetic disk storage system, and the accompanying illustration of  FIG. 1  are for representation purposes only. It should be apparent that disk storage systems may contain a large number of disks and actuators, and each actuator may support a number of sliders.  
         [0028]     With reference to  FIG. 2 , a side cross section of magnetic element  200  for perpendicular recording can be seen. The write head includes a write pole  202  formed upon a flux guide layer or shaping layer  204 . The write pole  202  and flux guide layer  204  are both constructed of magnetic materials. The write pole  202  is designed to contain a very large concentration of magnetic flux, and therefore, is preferably constructed of laminated layers (not shown) of high magnetic moment, high magnetic saturation (high Bsat) material such as CoFe. These magnetic layers are preferably separated by very thin layers of non-magnetic material such as chromium (Cr) and nickel chromium (CrNi) also not shown. The shaping layer  204  being much wider than the write pole (into the plane of the page) need not accommodate as high a magnetic flux concentration as the write pole  202  and can be constructed of for example NiFe or iron containing alloys.  
         [0029]     The write element  200  also includes a return pole  206  which is magnetically connected with the shaping layer  204  by a magnetic back gap layer  208 . The return pole and back gap layer can be constructed of a magnetic material such as for example NiFe iron containing alloys. An electrically conductive coil  210 , formed of for example Cu passes between the shaping layer  204  and the return pole, being insulated there from by non-magnetic, electrically insulating fill material  210 . Only a portion of the coil  210  is shown in  FIG. 2  and is shown in cross section. Although not shown, the coil would wrap around the back gap  208 . The non-magnetic, electrically non-conductive material  212  extends upward to separate the shaping layer  204  a desired distance from the ABS surface. As will be understood by those skilled in the art, the non-magnetic, electrically non-conductive fill material could be formed in several layers, and one or more chemical mechanical polishing processes may be performed between the deposition of each layer. In fact the fill  212  could be formed of layers of different materials such as for example, Al 2 O 3 , SiO 2  and photoresist.  
         [0030]     With reference now to  FIG. 3 , an ABS view of a portion of a write head  300 , includes a write pole  302  having a trailing edge  304 , and a leading edge  306 . As discussed above, the write pole can be constructed of a single layer of high saturation (high Bsat) magnetic material, such as CoFe, CoNiFe or CoFeX where X is a non-magnetic element, or some other magnetic material. However, the write pole is preferably constructed of as a lamination of layers of magnetic material separated by thin layers of non-magnetic material such as chromium (Cr), nickel chromium (CrNi), or some other non-magnetic material. The magnetic layers can be a high saturation (high Bsat) material such as described above. The write pole  302  is formed upon a substrate  308  that can be a non-magnetic, electrically insulating material such as alumina. Similarly, the write pole  302  can be surrounded by a non-magnetic, electrically insulating fill layer  310  such as alumina.  
         [0031]     The write pole is configured with first and second laterally opposed sides that are configured to define trailing region  312  having a substantially constant width, with substantially parallel laterally opposed sides, and a leading portion  314  having a tapered configuration (non-parallel sides), the width of the leading portion becoming increasingly narrower toward the leading edge  306 . In other words the leading portion has non-parallel sides that define a width that decreases with decreasing distance to the leading edge. The trailing portion (constant width portion)  312  extends a predetermined distance D 1  from the trailing edge  304  of the write pole. The remaining portion of the write pole  302  (tapered, or leading portion  314 ) extends a distance D 2  from the termination of the trailing portion  312  to the leading edge  306 . The write pole has a total length L, measured from the leading edge  306  to the trailing edge  304 .  
         [0032]     The length D 1  of the substantially constant width trailing portion  312  can be for example about 1/10 to ½ of the total length L. In other words D 1 /L can be 1/10 to ½. The width W 2  of the leading edge  306 , measured laterally from one side to the other at the trailing edge, can be about 40% to 80% of the width W 1  of the constant section  312  (ie. the width at the trailing edge  304 ). The configuration of the write pole  302  provides an optimal balance between avoiding skew related adjacent track writing, and also proving for strong write field near the trailing edge. Modeling has shown that the constant section  312  provides exceptional write field to the media, especially in the trailing region of the write pole  302 , as well as does a write pole having a full rectangular shape. The constant section also provides for exceptional track width control because the taper does not extend all of the way to the trailing edge  304 .  
         [0033]     The tapered portion  314  effectively prevents adjacent track writing due to skew.  
         [0034]     Modeling has shown that a write pole  302  having a tapered portion  314  that is removed from the trailing edge  304  prevents skew related adjacent track writing as well as does a write pole having a full trapezoidal shape (ie. where the taper extends all of the way to the trailing edge  304 ).  
         [0035]     It should be pointed out that, while a write pole according to the present invention has been described in terms of use in a simple single pole perpendicular write head, this write pole can just as easily be used in any number of other write head designs. For example, the write pole could be used in a write head having a trailing or wrap around magnetic shield. A trailing shield design can include a magnetic layer formed at or near the ABS and which is separated from the write pole by a desire gap distance. The trailing shield can cause a canting of the write field, which increases the speed at which the magnetic field can switch, thereby increasing writing speed and efficiency. Such a trailing shield can incorporate wrap around portions which extend along the sides of the write pole and prevent adjacent track writing, and possibly also stray field writing. A leading shield, formed adjacent to and separated from the leading edge of the write pole can also be employed.  
         [0036]     Another design in which a write pole according to the present invention can be used is a write head design wherein the write pole is disposed between a pair of return poles. In such a design, the write coil could be a helix which wraps around the write pole rather than a more commonly used pancake type write coil. Alternatively, a pair of pancake type write coils can be used with each coil being located between the write pole and its respective return pole, a so called “cusp” design. Various other write head designs may also become evident to those skilled in the art, and the novel write pole design of the present invention could be employed in those designs as well.  
         [0037]     With reference now to  FIGS. 4-8 , one possible method for constructing a write pole according to an embodiment of the invention is described. Other methods for constructing such a write pole may be effective as well. With particular reference to  FIG. 4 , a substrate  402  is provided. The substrate  402  may be or include, for example, a layer of alumina (Al 2 O 3 ) or some other non-magnetic, electrically insulating material. A layer of magnetic, electrically conductive write pole material  404  is deposited full film over the substrate  402 . As mentioned above, the write pole material can be a single layer of high saturation (high Bsat) material, such as CoFe, CoNiFe, CoFeX where X a non-magnetic element or some other material, or can be a lamination of layers of magnetic material separated by thin non-magnetic layers such as chromium (Cr), nickel chromium (CrNi) or some other non-magnetic material.  
         [0038]     With continued reference to  FIG. 4 , a mask structure  406  is deposited over the magnetic write pole material. Several mask structure can be used, but the mask structure  406  preferably includes a first hard mask layer  408  deposited over the write pole material layer  404 . The first hard mask may be a material that is resistant to chemical mechanical polishing (CMP stop layer) such as diamond like carbon (DLC) or could be some other material such as alumina or silicon oxide. An image transfer layer  410  is then deposited over the hard mask  408 . The image transfer layer is preferably a non-photoreactive material such as a soluble polyimide film such as DURIMIDE®. A layer of photosensitive mask material  412  such as photoresist is then deposited over the image transfer layer  410 .  
         [0039]     With reference now to  FIG. 5 , the photosensitive layer  412  is photolithographically patterned to form a photomask having a width to define a nominal track width. This width is a nominal width because a certain amount of write pole material will be consumed during ion milling as will be described in greater detail herein below. Therefore, the width of the photo mask  412  will be slightly larger than the final track width of the write pole. With reference now to  FIG. 6 , one or more reactive ion etch (RIE) processes  602  are performed to transfer the image of the photo mask  412  onto the underlying mask layers  410  and  408 .  
         [0040]     Then, with reference to  FIG. 7 , a first ion mill  702  is performed to form notches  704  by removing a desired amount of write pole material  404 . The first ion mill  702  is performed at a substantially vertical (normal) angle to form substantially vertical walls  706  in the notches  704 . This first, vertical ion mill can be performed at an angle of, for example, 15 to 45 degrees or about 30 degrees with respect to a normal to the surface of the write pole material  404 , and substrate  402 .  
         [0041]     With reference to  FIG. 8 , a second ion mill  802  is performed. The second ion mill  802  is performed at an angle with respect to normal, in order to form a tapered shape at the sides of write pole and to trim the write pole to a desired target track width. The second ion mill can be performed at an angle of, for example, 40 to 80 degrees or about 60 degrees with respect to normal, and is preferably performed until the substrate  402  has been reached.  
         [0042]     With reference to  FIG. 9  the first and second ion mills  702 ,  802  are preferably performed in a sweeping manner (as viewed from above) so that the ion mill rotates in a semi-circular sweep  903  about the axis of the wafer  902 . In this manner the ion mill sweeps about the third and fourth quadrants of the wafer, thereby directing the ion mill at both sides of the write pole. An entire rotation or 360 degree sweep is generally not performed in order to avoid shadowing from the flared portion  904  of the write pole  402 . The write pole is shown enlarged in order to more clearly illustrate the flare  904  of the write pole and its orientation relative to the sweep. However, it should be understood that the thousands of such write poles  402  would actually fit onto a single wafer.  
         [0043]     A small amount of the substrate  402  may be removed by the ion milling process  802 . It should be appreciated that certain clean up procedures may also be performed after one or both of the ion mills  702 ,  802  to remove re-deposited material from the sides of the write pole material  402 . This can be done by another sweeping ion mill. This third ion mill (not shown) can be performed at 50 to 90 degrees, or about 70 degrees with respect to normal.  
         [0044]     The angled second ion mill  802  forms tapered sides on a leading portion  804  of the write pole material  404 , leaving a trailing portion  806  formed with substantially desired side walls as desired. It will be appreciated, though, that a certain amount of material will be removed from both sides in the trailing portion. Therefore, the photo mask  412 , defined as described in  FIG. 5  should be constructed to have a width such that the final width of the write pole  404  in the trailing region (ie. distance between the laterally opposed sides in the trailing region) will define a desired track width for the write pole.  
         [0045]     The relatively vertical side walls ensure an accurately defined trackwidth, as compared with a purely trapezoidal write pole, because the width of the trailing portion is not as sensitive to material removal during the taper defining ion mill  802 . After the write pole  404  has been defined as described in  FIG. 8 , a layer of non-magnetic, electrically insulating material, such as alumina can be deposited, and a CMP or some other process can be used to remove any remaining mask structure  408 ,  410 . Another layer of non-magnetic material can be deposited over the trailing edge of the write pole to protect it from corrosion and other damage.  
         [0046]     It can be seen that during the various ion mill processes  702 ,  802  portions of the mask structure  406  are consumed. The image transfer layer ensures that sufficient mask material will remain to complete the ion milling and form the write pole  404 .  
         [0047]     While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.