Abstract:
A magnetic head structure for use in perpendicular magnetic recording. The magnetic head includes a magnetic write head having a return pole with a magnetic shunt structure extending from the back end opposite the ABS. The magnetic shunt structure prevents magnetic field from the write coil from reaching and affecting the read head. More specifically the shunt structure prevents magnetic field from the portion of the write coil beyond the back gap (as measured from the ABS) from magnetizing a magnetic shield of the read head. The shunt structure is also configured so as to avoid stray field writing. The size and shape of the shunt structure is therefore, limited to avoid attracting stray fields that might cause such stray field writing.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to perpendicular magnetic recording, and more particularly to a perpendicular write head structure that prevents the write head from interfering with the magnetoresistive read sensor. 
       BACKGROUND OF THE INVENTION 
       [0002]    The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm adjacent to a surface of the rotating magnetic disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions. 
         [0003]    Traditionally, magnetic writing has been performed longitudinally on a magnetic disk. A longitudinal write head used in such recording systems includes a coil layer embedded in an insulation layer, the insulation layer being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a magnetic field to fringe out at a write gap at the ABS for the purpose of writing the aforementioned magnetic impressions in tracks longitudinally on the moving media, such as in circular tracks on the aforementioned rotating disk. 
         [0004]    In recent read head designs a spin valve sensor, also referred to as a giant magnetoresistive (GMR) sensor, have been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer. 
         [0005]    The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layer are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos θ, where θ is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals. 
         [0006]    The spin valve sensor is located between first and second nonmagnetic electrically insulating read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head, a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers. 
         [0007]    The ever increasing demand for increased data rate and data capacity has lead a relentless push to develop completely new recording systems capable of meeting these demands. As a result, researchers have focused on the use of perpendicular magnetic recording systems. Such recording systems operate by recording data as localized magnetizations on a magnetic disk that are oriented perpendicular to the surface of the disk rather than longitudinally. A perpendicular magnetic recording disk includes a magnetically soft underlayer and a thin magnetically hard top layer. It is this top layer that remains magnetized after data has been written. The magnetically soft underlayer acts as a magnetic conduit for conducting magnetic flux back to a return pole. 
         [0008]    It turns out however, that magnetic disks suitable for perpendicular magnetic recording are susceptible to stray field writing. As a result, magnetic structures, such as those in the write head must be configured to prevent stray field writing. Structures such as shields and write poles must have a depth as measured from the ABS that is not too deep. This is to prevent the structure from acting as a magnetic antenna which might pick up stray fields and concentrate them at the disk, causing inadvertent writing. 
         [0009]    However, this lack of shielding has reduced the magnetic isolation between the writer and read sensor. Magnetic fields from the portion of the write coil that extends beyond the write pole can reach the read sensor and be read as a signal. Field from the writer is picked up by the reader shield, causing the shield&#39;s magnetization to flip. This causes an unacceptable amount of signal noise, making the recording system impractical. 
         [0010]    Therefore, there is a strong felt need for magnetic head design that can be used in magnetic recording while also preventing interference between the write head and the read sensor. Such a design should also prevent stray field writing to the disk. 
       SUMMARY OF THE INVENTION 
       [0011]    The present invention provides a write head structure for perpendicular magnetic recording that prevents magnetic field from the write head from reaching and affecting the read head. The write head includes a return pole having a front end near the air bearing surface (ABS), a back end opposite the front end and has a shunt structure that extends from the back end of the return pole. 
         [0012]    The shunt structure is configured to be large enough to prevent magnetic field from the write coil from reaching the read head, but is small enough not to cause stray field writing. With this in mind, the shunt structure can have a thickness (measured parallel with the ABS) that is less than the thickness of the return pole, and that is preferably not greater than ¾ of the return pole thickness. The shunt structure may have a thickness of 0.08-0.5 um and a height measured away from the ABS of 5-10 um. 
         [0013]    The shunt structure can be constructed of a magnetic material such as NiFe and can be advantageously easily incorporated into the build of the write head, with little or no additional expense. 
         [0014]    These and other features and advantages of the invention will be apparent upon reading of the following detailed description of preferred embodiments taken in conjunction with the Figures in which like reference numerals indicate like elements throughout. 
     
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0015]    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. 
           [0016]      FIG. 1  is a schematic illustration of a disk drive system in which the invention might be embodied; 
           [0017]      FIG. 2  is an ABS view of a slider illustrating the location of a magnetic head thereon; 
           [0018]      FIG. 3  is an enlarged cross sectional view taken from line  3 - 3  of  FIG. 2  illustrating write and read heads according to an embodiment of the invention; and 
           [0019]      FIG. 4  is an enlarged cross sectional view of read and write heads according to an alternate embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    The following description is of the best embodiments 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. 
         [0021]    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 annular patterns of concentric data tracks (not shown) on the magnetic disk  112 . 
         [0022]    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, slider  113  moves 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 . 
         [0023]    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 slider  113  off and slightly above the disk surface by a small, substantially constant spacing during normal operation. 
         [0024]    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 . 
         [0025]    With reference to  FIG. 2 , the orientation of the magnetic head  121  in a slider  113  can be seen in more detail.  FIG. 2  is an ABS view of the slider  113 , and as can be seen the magnetic head including an inductive write head and a read sensor, is located at a trailing edge of the slider. 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. 
         [0026]    With reference now to  FIG. 3 , a cross sectional view of a magnetic head  300  includes a read head  302  and a write head  304 . The read head  302  and write head  304  are separated by a non-magnetic, electrically insulating gap layer  306 , which may be, for example alumina (Al 2 O 3 ). The read and write heads  302 ,  304  have an air bearing surface (ABS) which is the surface to be disposed toward a magnetic medium (not shown in  FIG. 3 ) when in use. 
         [0027]    The read head  302  includes a magnetoresistive sensor  308 , such as a giant magnetoresistive sensor (GMR) or a tunnel valve. The sensor  308  is embedded in a non-magnetic, electrically insulating gap material  310 , which again can be alumina. First and second magnetic shields  312 ,  314 , constructed of a magnetic material such as NiFe are provided at either side (above and below) the sensor  308 . 
         [0028]    The write head  304  includes a return pole  316 , back gap layer  318 , shaping layer  320  and write pole  322 . The return pole  316 , back gap  318  and shaping layer  320  can be constructed of a magnetic material such as NiFe. The write pole  322  can be constructed of a high saturation (high Bsat) material, such as CoFe, but is preferably constructed as a lamination of layers of high Bsat material such as CoFe separated by thin non-magnetic layers such as. The return pole  316  is magnetically connected to the back gap layer  318  and the back gap is magnetically connected with the shaping layer  320 . The shaping layer  320  is magnetically connected with the write pole  322 . 
         [0029]    The magnetic head  300  has a trailing direction which up as viewed in  FIG. 3  and a leading direction which is down as viewed in  FIG. 3 . The terms leading and trailing refer to the direction of travel relative to a disk (not shown) over which the head  300  flies during use. Therefore, the return pole  316  has an ABS end  317  located at the ABS, a back end  319  opposite the ABS end, a trailing surface  321  that extends from the back end  319  to the ABS end  317  at the trailing edge of the return pole  316  and a leading surface  323  that extends from the back end  319  to the ABS end  317  at the leading edge of the write pole  316 . 
         [0030]    An electrically conductive write coil  324 , shown cross section in  FIG. 3 , passes between the shaping layer  322  and write pole  322  and the return pole  316 . The write coil  324  is what has been referred to as a pancake coil, because it has a flat shape, that extends out of and into the page as shown in  FIG. 3 . The coil  324  wraps around the back gap, so that it extends behind the write pole structure defined by the return pole  316 , back gap  318 , shaping layer  320  and write pole  322 . The write coil  324  is embedded in an insulation layer  326  that can be, for example alumina (Al 2 O 3 ). 
         [0031]    As discussed above in the Background of the Invention, a problem that has been experienced with prior art perpendicular heads is that magnetic field from the write coil  324  can be picked up by the read head shield  314 , which affects the sensor  308 . Magnetic fields from the portion of the coil  324  that pass over the return pole  316  are not as much of a problem, because the return pole  316  acts as a magnetic shield to absorb the field from this portion of the coil  324 . However, magnetic field  326  from portions of the coil located behind the back gap  318  can cause such interference. 
         [0032]    To ameliorate this problem, a magnetic shunt  328  is provided at the back of the pole structure. The shunt can be constructed of a magnetic material such as NiFe or some other material, and preferably extends from the back edge of the return pole, although the shunt  328  could extend from the back of the back gap as well. The shunt attracts and absorbs magnetic field from the write coil  324 . The shunt is located at a level in the head stack such that it is disposed between at least a portion of the coil and the read head  302 . 
         [0033]    The shunt  328  has a front end  325  where it connects with the return pole  316  (the end closest to the ABS) and a back end  327  opposite the front end (ie. furthest from the ABS). The shunt also has leading and trailing surfaces  329 ,  331  that extend from the back end to the front end. The shunt  328  has a thickness T measured parallel to the ABS in a down track direction and which can be defined as the distance between the leading and trailing surfaces  329 ,  331 , and has a length or height H measured perpendicular to the ABS as the distance from the front  325  end to the back end  327 . The shunt  328  can be of various thicknesses, but preferably has a thickness T that is smaller than the thickness of the return pole  316 . The shunt preferably has a thickness T that is no greater than ¾ the thickness of the return pole or that is 0.08 to 0.5 um. 
         [0034]    The shunt can have various heights H, but preferably has a height H that is large enough to prevent field from the coil  324  from affecting the read head  302 , but also small enough to avoid stray field writing. If the shunt  324  is too large it could act as a magnetic antenna to absorb stray magnetic fields which can collect at the ABS and cause inadvertent stray field writing to the magnetic medium. Therefore, the shunt preferably has a height H of 5 to 10 um, although the exact measurements depend upon the design requirements of a particular recording system and on the relative size of the write and read heads  302 ,  304 . 
         [0035]    To further prevent interference between the coil  324  and the read head  320 , the size of gap between the read and write heads  302 ,  304  can be increased. 
         [0036]    With reference now to  FIG. 4 , an alternate embodiment of the invention includes a shunt  402  that is separated from the return  316  pole by a gap  404 . In this embodiment of the invention, the shunt  406  can be constructed to have a thickness T that is as thick as the return pole  316 . The gap  404  allows the shunt  402  to be constructed thicker than in the previous embodiment while still avoiding stray field writing. If further protection against stray field writing is desired, the shunt  404  can be constructed with a thickness T that is thinner than that of the return pole  316 . Either of the shunt structures  328 ,  402  can be constructed by electroplating in the same masking and plating step as that used to construct the return pole  316 . However, making the shunt  402  the same thickness as the return pole  316  makes it much easier to plate the shunt  402  simultaneously with the return pole  316 . 
         [0037]    While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Other embodiments falling within the scope of the invention may also become apparent to those skilled in the art. Thus, the breadth and scope of the invention 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.