Abstract:
A perpendicular magnetic write head having a laminated trailing return pole structure that reduces magnetic eddy currents in the return pole for improved write head efficiency. The trailing magnetic return pole includes multiple magnetic layers. Each magnetic layer is separated from an adjacent magnetic layer of the return pole by a non-magnetic layer. The non-magnetic layer terminates at a region that is removed from the air bearing surface in order to allow contact between the magnetic layers at the ABS, thereby preventing stray magnetic fields from emitting from the magnetic layers of the write pole.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to magnetic write heads and more particularly to a write head having a laminated trailing return pole structure for improved performance. 
       BACKGROUND OF THE INVENTION 
       [0002]    The heart of a computer&#39;s long term memory is an assembly that is referred to as a magnetic hard disk drive. The magnetic hard 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 toward the surface of the disk, and when the disk rotates, air adjacent to the disk moves along with the surface of the disk. The slider flies over the surface of the disk on a cushion of this moving air. When the slider rides on the air bearing, the write and read heads are employed for writing magnetic transitions to and reading magnetic transitions 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]    The write head can include a coil that passes through a magnetic yoke that includes a write pole located between leading and trailing return poles. Current conducted to the coil layer induces a magnetic flux in the pole pieces which causes a write field to emit from the write pole for the purpose of writing a magnetic transition in tracks on the moving media, such as in circular tracks on the rotating disk. The write field passes through a magnetically soft under-layer of the magnetic media and returns to the return poles where it is sufficiently spread out and weak that it does not erase the previously recorded bit. 
         [0004]    In the quest for every increased data capacity and data rate, researchers have sought means for improving the performance of such magnetic write heads. Such an increase in performance can include maximizing the write field strength as well as minimizing the time necessary to switch the magnetic polarization of the poles of the magnetic write head (e.g. maximizing switching speed). 
       SUMMARY OF THE INVENTION 
       [0005]    The present invention provides a perpendicular magnetic write head having a laminated return pole structure for improved magnetic performance. The return pole includes magnetic layers that are each separated from one another by a non-magnetic layer that terminates at a location that is recessed from the air bearing surface, thereby allowing the magnetic layers to contact one another at the air bearing surface while being separated from one another in a region removed from the air bearing surface. 
         [0006]    The laminated structure of the return pole prevents eddy current formation, thereby improving the performance of the write head. If the non-magnetic lamination layers were allowed to extend all of the way to the air bearing surface a magnetic fringing field would extend from the ends of the magnetic layers in order to form a flux closure path between adjacent magnetic layers. This would then lead to stray field formation and inadvertent writing to the magnetic media. This is prevented by terminating the non-magnetic layers at a location, that is recessed from the air bearing surface. 
         [0007]    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 
         [0008]    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. 
           [0009]      FIG. 1  is a schematic illustration of a disk drive system in which the invention might be embodied; 
           [0010]      FIG. 2  is an ABS view of a slider, taken from line  2 - 2  of  FIG. 1 , illustrating the location of a magnetic head thereon; and 
           [0011]      FIG. 3  is a side cross sectional view of a magnetic write head according to an embodiment of the invention; and 
           [0012]      FIG. 4  is an enlarged cross sectional view of a magnetic write head according to an alternate embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0013]    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. 
         [0014]    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 . 
         [0015]    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  can 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 . 
         [0016]    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 a force 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. 
         [0017]    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 . 
         [0018]    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. 
         [0019]      FIG. 3  shows a magnetic write head  300  according to an embodiment of the invention. The write head includes a lower or leading magnetic return pole (P 1 )  302 , a write pole structure (P 2 )  306 , and an upper or trailing return pole structure (P 3 )  308 . The leading return pole  302  can be connected with the write pole structure by a magnetic back gap layer  310 . 
         [0020]    The write pole structure  306  can include a main write pole  312  that is located between first and second shaping layers  314 ,  316 . The main write pole  312  extends to the ABS, but the first and second shaping layers  314 ,  316  stop short of the ABS. The main write pole  312  can be separated from the first and second shaping layer  314 ,  316  by thin non-magnetic layers  318 ,  320 , which can be, for example, alumina. Alternatively, the non-magnetic layers  320 ,  318  could be eliminated so that the write pole  312  contacts both of the shaping layers  314 ,  316 . In addition, one of the shaping layers  314 ,  316  could be eliminated so that there is only one shaping layer. 
         [0021]    A trailing magnetic shield  322  may be provided to improve the field gradient of the write field emitted from the write pole  312 . The trailing magnetic shield  322  is separated from the trailing edge of the write pole  312  by a thin, non-magnetic trailing gap layer  324 . A non-magnetic fill layer  326  such as alumina may be provided to fill the space behind the trailing shield  322 . The trailing shield  322  is magnetically connected with the trailing return pole  308 . 
         [0022]    The write head  300  also includes a write coil  328 . The write coil  328  can be constructed of a non-magnetic, electrically conductive material such as Cu and can be constructed as a pair of pancake coils or as a helical coil. The lower portion of the write coil  328  is embedded in a lower insulation layer  330  that can be a material such as alumina. The upper portion of the write pole  328  is embedded in an upper insulation layer  332  that can be a material such as hard baked photoresist, or could be alumina like the lower insulation layer  330 . 
         [0023]    When an electrical current flows through the write coil, a magnetic field is induced around the turns of the write coil. This causes a magnetic flux to flow through the write pole structure  306 , resulting in a magnetic write field  334  being emitted from the tip of the write pole  312  in a direction that is substantially perpendicular to the ABS and to the surface of the media  112  and which locally magnetizes a hard magnetic layer  336  of the magnetic media  112 . The majority of the write field  334  then travels through a magnetically softer under-layer  338  and through an air gap between  344  and  322  to the trailing magnetic shield  322 . The flux return path continues with return pole  308 ,  340 ( a ),  340 ( b ),  320 ,  314 ,  322 . Therefore, reducing the flux return reluctance, such as  308 ,  340 ( a ),  340 ( b ) is beneficial in enhancing the writing switch time. 
         [0024]    At high data rate, the eddy current increases the flux reluctance of  308 ,  340 ( a ),  340 ( b ) significantly. One way to improve the performance of the write head  300  is to reduce the eddy current loss in the trailing return pole  308 ,  340 ( a ),  340 ( b ) such as by forming the majority of the return path with lamination such as  340 ( a ) and  340 ( b ). 
         [0025]    To this end, the trailing return pole  308  is constructed as a laminated structure having magnetic layers  340 ( a ),  340 ( b ) that are separated from one another by a thin layer of non-magnetic, dielectric material such as alumina  342 , which can be deposited by a process such as atomic layer deposition, chemical vapor deposition, sputter deposition or ion beam deposition. The magnetic layers  340 ( a ),  340 ( b ) can be constructed of a high Bsat material such as CoFe, NiFe, which is preferably formed by electroplating. 
         [0026]    A laminated pole structure can cause unintended writing to the magnetic media  112  if the pole  308  is laminated all of the way to the ABS. If the lamination structure were to extend all of the way to the ABS, a flux closure path would exist at the ABS forming a magnetic field at the ABS that has a component that is perpendicular to the surface of the magnetic media. This of course would be unacceptable. 
         [0027]    The present invention solves this problem by terminating the non-magnetic layer  342  at some point short of the ABS. Therefore, while the magnetic layers  340 ( a ),  340 ( b ) are separated from one another in regions removed from the ABS, they are in contact with one another near the ABS. 
         [0028]      FIG. 3  shows a laminated trailing return pole structure  308  that has only two magnetic layers  340 ( a ),  340 ( b ) and one non-magnetic lamination layer  342 . This is, however, by way of example only as there could be any number of laminations. However, the cost and complexity of constructing the write head  300  increases with increasing number of laminations. In another embodiment of the invention, as shown in  FIG. 4 , a write head  400  is shown having a trailing return pole  402  that has several laminations. In this embodiment the trailing return pole  402  has 4 magnetic layers  340 ( a ),  340 ( b ),  340 ( c ),  340 ( d ), although the return pole could have any number of magnetic layers  340  and non-magnetic layers  342 , such as three magnetic layers  340  or five or more magnetic layers  340 . Each magnetic layer  340  is separated from an adjacent magnetic layer (in a region removed from the ABS) by a non-magnetic layer  342 ( a ),  342 ( b ),  342 ( c ). As with the previously described embodiment, the non-magnetic layers  342 ( a ),  342 ( b ),  342 ( c ) terminate short of the ABS, so that magnetic layers  340 ( a - d ) contact one another in the region near the ABS. Again, this structure avoids forming magnetic fields at the ABS (which might write to the media) while still preventing the formation of eddy currents in the trailing return pole. 
         [0029]    In order to construct a write head according to the invention, a first magnetic layer ( 340 ( a ) of  FIG. 3  or  4 ) is formed by electroplating. An ion milling is then performed to remove the electroplating seed layer used to facilitate the electroplating process. Then, a thin non-magnetic layer such as alumina is deposited by a method such as sputtering, ion beam deposition, atomic vapor deposition or chemical vapor deposition. This non-magnetic layer is formed to terminate short of the ABS plane by either a liftoff process or by depositing the non-magnetic layer full film, forming a mask structure over the non-magnetic layer and then ion milling. Then, a second layer of magnetic material is formed by electroplating and another ion milling is performed to remove the seed layer that was used in the second electroplating process. This series of steps can be repeated as often as needed depending on the number of laminations desired. 
         [0030]    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.