Abstract:
A magnetic write head for perpendicular magnetic data recording having a trailing shield with a two step throat height. The trailing shield is formed over a non-magnetic bump that forms a notch in the leading edge of the trailing shield. This notch defines a first, smaller throat height closest to the write pole and a larger throat height away from the write pole. The smaller throat height near the write pole prevents excess magnetic flux from leaking to the write pole, thereby ensuring efficient strong write field. The larger trailing shield throat height away from the write pole prevents magnetic saturation oft the trailing shield and also greatly facilitates manufacturing avoiding problems related to variations and deviations in manufacturing processes used to define the trailing shield.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to perpendicular magnetic recording and more particularly to a magnetic write head having a bump structure that forms a trailing shield with a short throat height near the write pole and a larger throat height away from the write pole. 
       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 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 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 has traditionally included a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack 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 transitions in tracks 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, has been employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, 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]    In order to meet the ever increasing demand for improved data rate and data capacity, researchers have recently been focusing their efforts on the development of perpendicular recording systems. A traditional longitudinal recording system, such as one that incorporates the write head described above, stores data as magnetic bits oriented longitudinally along a track in the plane of the surface of the magnetic disk. This longitudinal data bit is recorded by a fringing field that forms between the pair of magnetic poles separated by a write gap. 
         [0007]    A perpendicular recording system, by contrast, records data as magnetizations oriented perpendicular to the plane of the magnetic disk. The magnetic disk has a magnetically soft underlayer covered by a thin magnetically hard top layer. The perpendicular write head has a write pole with a very small cross section and a return pole having a much larger cross section. A strong, highly concentrated magnetic field emits from the write pole in a direction perpendicular to the magnetic disk surface, magnetizing the magnetically hard top layer. The resulting magnetic flux then travels through the soft underlayer, returning to the return pole where it is sufficiently spread out and weak that it will not erase the signal recorded by the write pole when it passes back through the magnetically hard top layer on its way back to the return pole. 
         [0008]    Certain design parameters are important to efficient write head performance. However, as the write heads become ever smaller, it becomes ever more difficult to control these desired parameters. Therefore, there is a need for a structure and/or method of manufacture that can maximize these write head parameters even in very small write heads. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a write head for magnetic data recording. The write head includes a magnetic write pole and a magnetic trailing shield formed adjacent to a trailing edge of the write pole, the trailing shield being separated from the trailing edge of the write pole by a non-magnetic gap layer. The trailing shield including a notch that forms a first throat height in a region adjacent to the write pole and a second throat height, in a region away from the write pole, that is larger than the first throat height. The smaller throat height adjacent to the write pole prevents excessive flux loss to the trailing shield, thereby ensuring high write field. The larger throat height away from the write pole advantageously prevents saturation of the trailing shield in regions removed from the write pole, even when the trailing shield has nonmagnetic inclusions or impurities. This ensures that the trailing shield will not choke off magnetic flux (even in regions having such inclusions or impurities) and will not leak flux to the magnetic medium as a result of such non-magnetic impurities. 
         [0010]    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 
         [0011]    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. 
           [0012]      FIG. 1  is a schematic illustration of a disk drive system in which the invention might be embodied; 
           [0013]      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; 
           [0014]      FIG. 3  is a cross sectional view of a magnetic head, taken from line  3 - 3  of  FIG. 2  and rotated 90 degrees counterclockwise, of a magnetic write head according to an embodiment of the present invention; 
           [0015]      FIG. 4  is an enlarged view showing a portion of a trailing shield according to an embodiment of the invention; 
           [0016]      FIG. 5  is an enlarged view showing a portion of a trailing shield according to another embodiment of the invention; 
           [0017]      FIG. 6  is an enlarged view showing a portion of a trailing shield according to yet another embodiment of the invention; and 
           [0018]      FIG. 7  is a cross sectional view of a prior art trailing shield compared with a trailing shield according to an embodiment of the invention showing the affect of a non-magnetic inclusion on each. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0019]    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. 
         [0020]    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 . 
         [0021]    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 . 
         [0022]    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. 
         [0023]    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 . 
         [0024]    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. 
         [0025]    With reference now to  FIG. 3 , the invention can be embodied in a magnetic write head  302 . The magnetic head  302  can include a read head portion  304  and a write head portion  306 . The read head portion  304  can include a magnetoresistive sensor  308  such as a giant magnetoresistive sensor GMR, tunnel valve (TMR) etc. The magnetoresistive sensor  308  can be located between first and second magnetic shields  310 .  312 . 
         [0026]    The write head  306  includes a write pole  314 , having an end disposed toward an air bearing surface (ABS). The write head also includes a return pole  316 , which also has an end disposed toward the ABS. The return pole  316  is magnetically connected with a magnetic back gap  318 . The write pole  314  can be connected with a magnetic shaping layer  320  that is itself connected with the back gap  318 , so that tie write pole  314 , shaping layer  320  back (lap  318  and bottom return pole  316  are all magnetically connected with one another in a region removed from the ABS. The shaping layer  320 , back gap  318  and return pole  316  can be constructed of a magnetic material such as NiFe or CoFe. The write pole  320  is preferably constructed of a high magnetic moment, low coercivity magnetic material, and is more preferably constructed as a laminate of layers of magnetic material separated by thin layers of non-magnetic material. 
         [0027]    The write head  306  also includes an electrically conductive write coil  322 , shown in cross section in  FIG. 3 . The write coil can be constructed of, for example, CL and can be a pancake coil that wraps around the back gap  318  or can be a helical coil having upper and lower leads (as shown) disposed above and below the write pole  314  and shaping layer  320 . The upper and lower leads of the write coil  322  can each be formed upon an insulating layer  324  and surrounded by a coil insulation layer  326  and the upper leads can be connected with certain of the bottom leads in regions into and out of the plane of the page and, therefore, not shown in  FIG. 3 . 
         [0028]    During operation, a magnetic field from the write coil  322  causes a magnetic flux to flow through the shaping layer  320  and write pole  314 . This causes a magnetic write field  328  to emit from the write pole  314  at the ABS. This write field  328  passes through a thin magnetically hard top layer  330  of an adjacent magnetic medium  332 . The write field then travels through a magnetically soft under-layer  334  of the magnetic medium  332  before passing back to the return pole  316 . The write field emitted from the write pole  314  locally magnetizes the magnetically hard top layer  330 , thereby writing a bit of data. The return pole  316  has a cross section at the ABS that is much larger than that of the write pole  314  so that the write field  328  passing back to the return pole is sufficiently spread out that it does not erase the previously recorded bit. 
         [0029]    A magnetic pedestal  336  can be provided, and can be magnetically connected with the return pole  316  at the ABS end of the return pole  316 , extending toward, but not to the write pole  314 . The magnetic pedestal can act as a shield to prevent stray fields, such as from the write coil  332  from inadvertently writing to the magnetic medium  332 . 
         [0030]    With reference still to  FIG. 3 , the write head  306  includes a trailing magnetic shield. The presence of the trailing magnetic shield  338  increases the field gradient of the write field  328 , thereby increasing the speed with which the write head  306  can write data. The trailing shield  338  can be magnetically connected with the back portion of the write head  306  by a magnetic upper or trailing return pole  340  or could just be a floating design. 
         [0031]    The trailing shield  338  functions by attracting write field  338  toward it. There is, however, a fine balance between attracting enough magnetic field  338  toward the trailing shield to increase the write field gradient, and loosing too much field to the trailing shield  338  which would decrease the strength of the write field  328 . Several parameters affect the efficiency of the trailing shield  338  and must, therefore, be tightly controlled. 
         [0032]      FIG. 4  shows an enlarged view of a portion of the trailing shield  338 . As can be seen, the trailing shield  338  is separated from the write pole  314  by a non-magnetic trailing gap  324  having a thickness TG at the ABS. The trailing gap  324  and trailing shield  338  are adjacent to the trailing edge  325  of the write pole  314 . The term “trailing” refers to the direction of travel over the medium  332  ( FIG. 3 ). Therefore, the trailing shield  338  is separated from the trailing edge  325  of the write pole  314  by the trailing gap  324  having a thickness TG. The non-magnetic layer  324  separating the trailing shield  338  from the write pole  314  can be constructed of various non-magnetic materials, such as alumina, Rh, etc. This trailing gap thickness TG is one of the parameters that affects the performance of the trailing shield  338 . If the TG is too large, write field gradient will not be sufficiently increased. If TG is too small, then too much field will be lost to the trailing shield  338  and the write field will be too weak. 
         [0033]    Another parameter that greatly affects the performance of the trailing shield is the throat height of the trailing shield. The throat height is defined as the distance from the ABS to the back edge of the trailing shield opposite the ABS. As write heads become ever smaller, this trailing shield throat height must also become smaller. Write head sizes are reaching the point that, order for the trailing shield to function properly, it must be constructed with such a small throat height that it eventually become impractical and impossible to manufacture. For instance, the trailing shield throat height can become so small minor manufacturing variations (such as during lapping) could cause to trailing shield  338  to be completely removed in spots or to be so large that write field suffers. 
         [0034]    The present invention overcomes this problem by providing a hybrid trailing shield having one throat height TH 1  adjacent to the trailing gap  324  and another (larger) throat height TH 2  away from the trailing gap  324 . This hybrid trailing shield configuration is provided by forming the trailing shield  338  on a non-magnetic bump  342 . This non-magnetic bump  342  can be constructed of, for example, alumina or could be some other material. The bump  342  forms a notch  344  in the trailing shield  338  at a location adjacent to the write gap  324  and which extends toward the back edge of the trailing shield  338 . 
         [0035]    Therefore, the bump  342  and resulting notch  344  allow the trailing shield  338  to have a very small throat height TH 1  adjacent to the write pole  314  and trailing gap  324  where such small throat height is needed to avoid loosing too much write field to the trailing shield. The bump further allows the trailing shield  338  to have a larger throat height TH 2  away from the write pole  314  and trailing gap  324 , where Such larger throat height will not affect or cause such a loss of write field. The larger throat height TH 2  keeps the trailing shield  338  from becoming magnetically saturated, thereby improving the efficiency of the trailing shield  338  and the performance of the write head  306  ( FIG. 3 ). The larger throat height TH 2  also facilitates manufacture allowing existing manufacturing techniques to be employed with existing manufacturing variations. 
         [0036]    The presence of the bump  342  and notch  344  provides another important benefit as well. As can be seen in  FIG. 3 , the trailing shield  338  and second return pole  340  provide an additional return path for the field  328 . The larger trailing shield throat height TH 2  ( FIG. 4 ) provides a more efficient return path for the magnetic write field, thereby increasing the writer efficiency. The presence of the bump  342  and notch  344  allow this increase in writer efficiency while also maintaining the necessary smaller throat height TH 1  at the leading edge of the trailing shield  338  near the write pole  314  in order to ensure minimal loss of write field from tile write pole to the trailing shield  338 . 
         [0037]    With continued reference to  FIG. 4 , the non-magnetic bump  342  can be configured to form the trailing shield notch  344  with configuration that has an angled edge portion  346  and a substantially flat edge portion  348 . The angled edge  346  preferably forms an angle θ of 30-60 degrees with respect to the trailing gap. Alternatively, as shown in  FIG. 5 , a bump  502  and notch  504  can be configured have a rounded shape. Or, as shown in  FIG. 6 , a bump  602  and notch  604  can he configured to have a substantially rectangular shape. As shown in either of  FIGS. 4 ,  5  and  6 , the bump  342  and corresponding notch can have a height NT that is preferably 1-2 times or about 1.5 times the trailing shield gap TG. The NT is the height of the non-magnetic bump  342 ,  502 ,  504  as measured in a down-track direction, or vertically as shown in  FIGS. 3 ,  4 ,  5  and  6 . The trailing gap TG is the distance between the trailing shield  338  and the write pole  314 , also measured in a down-track direction. Therefore, the notch and bump height NT can be, for example, 20-100 nm or about 60 nm. Although angled, rounded and rectangular bump/notch configurations are shown in  FIGS. 4 ,  5  and  6 , this is by way of example only. Other bump/notch configurations are possible and would fall within the scope of the invention as well. Although various notch configurations are possible and would fall within the scope of the invention, the invention preferably uses an angle notch  344  such as that described with reference to  FIG. 4 . Such an angled notch provides a desired balance of manufacturability and optimal shield performance. 
         [0038]    The first throat height TH 1  is preferably about 0.5-1.5 times the shield gap TG. This ensures minimal flux leakage from the main pole to the shield. The second throat height TH 2  is larger, preferably about 3 times the shield gap TG. This larger throat height TH 2  minimizes the chance that a localized defect to the shield could cause an unwanted erasure of the medium. 
         [0039]    With reference now to  FIG. 7 , an important advantage of the novel hybrid trailing shield design can be better understood.  FIG. 7  shows a trailing shield  702  according to the prior art, as compared with a trailing shield  704  according to a possible embodiment of the invention. Because of irregularities in manufacturing magnetic heads at very small sizes, it is always possible that a defect  706  can be present in a trailing shield (either  702  or  704 . Such a defect  706  can take the form of an inclusion of non-magnetic (or less magnetic) material within the trailing shield. As magnetic flux  708  from the write pole  710  flows through the magnetic shield ( 702 ,  704 ), this flux  708  must pass around the non-magnetic inclusion  706 . 
         [0040]    While it is necessary to have short throat height at the write pole  710  in order to prevent the trailing shield ( 702 ,  704 ) from stealing too much flux  708  from the write pole  710  (and therefore reducing write field to the medium). The narrower throat height of the prior art trailing shield  702  away from write pole  710  does not allow the magnetic flux to flow freely around the non-magnetic inclusion  706 . As a result, the portions of the shield  702  adjacent to the inclusion  706  become saturated, causing magnetic flux/field  708  to leak from the shield  702  to inadvertently write to the magnetic medium  712 . 
         [0041]    However, as can be seen with respect to a trailing shield  704  according to an embodiment of the invention. The larger throat height way from the magnetic write pole  710  allows the magnetic flux  708  to travel around the defect (non-magnetic inclusion)  706  without saturating the trailing shield  704  and without leaking to and write to the adjacent magnetic medium. 
         [0042]    While various embodiments have been described, 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.