Abstract:
Electromagnetic transducers are disclosed having write poles with a leading edge that is smaller than a trailing edge, which can reduce erroneous writing for perpendicular recording systems. The write poles may have a trapezoidal shape when viewed from a direction of an associated medium. The write poles may be incorporated in heads or sliders that also contain read elements such as magnetoresistive sensors, and may be employed with information storage systems such as disk drives.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit under 35 U.S.C. §120 of, (and is a continuation of) U.S. patent application Ser. No. 09/933,508, filed Aug. 20, 2001, which is incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to electromagnetic transducers for information storage and retrieval systems, such as disk or tape drives. 
     FIG. 1 is a schematic top view of a disk drive storage system  20 , including a spinning disk  22  coated with a media layer  23  and a transducer  25  held by an arm  28  for storing and retrieving information on the media. Such a drive system  20  may have another transducer for storing and retrieving information on another media layer on an opposite side of the disk  22 , and may have additional disks and associated transducers, not shown. The transducer  25  may be attached to a slider that is held near a free end of the arm  28  by a gimbal structure. The transducer  25  writes and reads data on multiple concentric tracks of the disk  22  such as track  30 . To instead write and read data on another track  31  that is near a center  33  of the disk  22 , the arm is driven by an actuator, not shown, to move the transducer toward the center  33 . By sweeping the arm  28  over the surface of the disk  22 , as shown by arrow  35 , the transducer  25  can access the multiple data tracks. The orientation of the transducer, however, is skewed relative to tracks such as  30  and  31  disposed near outer and inner radiuses of the media layer. 
     Current commercially available disk drives store data in domains having magnetizations that are substantially parallel to tracks such as tracks  30  and  31 , which is sometimes called longitudinal recording. It has been predicted that such longitudinal magnetic storage will become unstable at normal operating conditions when the domains reach a minimal size, termed the superparamagnetic limit. In order to store the data at higher density, the drive system  20  may instead be designed to store data in domains that are substantially perpendicular to the disk  22  surface, which may be termed perpendicular recording. 
     FIG. 2 is a schematic side view of a prior art system for perpendicular recording, including a transducer  50  positioned in close proximity to a surface  55  of a disk  52  that is moving relative to the transducer in the direction of arrow  58 . The disk has a media layer  60  that has an easy axis of magnetization that is substantially perpendicular to the disk  22  surface. The disk also has a low-coercivity, high-permeability (“soft magnetic”) underlayer  62  that provides a path for magnetic flux, allowing the flux  64  written by the transducer to be directed substantially perpendicular to the disk surface. The transducer  50  includes a write pole  66  and a return pole  68  that are magnetically coupled by a magnetic layer  70  in the transducer and by the underlayer  60  to form a magnetic circuit, with the write pole  66  communicating a more concentrated flux  64  through the media  62  than the return pole  68 , for magnetizing the media adjacent the write pole. 
     FIG. 3 illustrates a prior art pattern of magnetization  70  of such a write pole  66  for a track such as track  30  where the transducer is skewed relative to the track. The write pole has a conventional rectangular area facing the media, which is reflected in the most recent magnetization  72 . Prior magnetizations written to the media, such as magnetization  71 , have edge effects or side writing  75  from the skew that may lead to errors in reading data. 
     SUMMARY OF THE INVENTION 
     In accordance with the present invention, write poles having a leading edge that is smaller than a trailing edge are disclosed, which can reduce erroneous writing for perpendicular recording systems. The write poles may have a trapezoidal shape when viewed from a direction of an associated media. The write poles may be incorporated in heads that also contain read elements such as magnetoresistive sensors, and may be employed with information storage systems such as disk drives. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a schematic top view of an information storage system including a spinning disk and an arm that sweeps a transducer over the disk surface to move between concentric tracks. 
     FIG. 2 is a prior art system for perpendicular recording, including a transducer with a write pole and a return pole and a media with a soft magnetic underlayer. 
     FIG. 3 is a prior art pattern of magnetization of the write pole of FIG. 2 for a track where the transducer is skewed relative to the track. 
     FIG. 4 is a media-facing view of a transducer in accordance with the present invention. 
     FIG. 5 is a cutaway schematic side view of the transducer of FIG. 4 in proximity to a relatively moving media. 
     FIG. 6 is a pattern of magnetization of the media of FIG. 5 by the transducer of FIG.  4  and FIG. 5 for a track where the transducer is skewed relative to the track. 
     FIG. 7 is a media-facing view of another embodiment of a transducer in accordance with the present invention. 
     FIG. 8 is a cutaway schematic side view of the transducer of FIG. 7 in proximity to the relatively moving media shown in FIG.  6 . 
     FIG. 9 is a cross-sectional view of some initial steps in a first method of forming a write pole tip having a trailing edge that is wider than a leading edge. 
     FIG. 10 is a cross-sectional view of some steps subsequent to the steps shown in FIG. 9 in the first method of forming a write pole tip having a trailing edge that is wider than a leading edge. 
     FIG. 11 is a cross-sectional view of some steps subsequent to the steps shown in FIG. 10 in the first method of forming a write pole tip having a trailing edge that is wider than a leading edge. 
     FIG. 12 is a cross-sectional view of some steps subsequent to the steps shown in FIG. 11 in the first method of forming a write pole tip having a trailing edge that is wider than a leading edge. 
     FIG. 13 is a cross-sectional view of some initial steps in a second method of forming a write pole tip having a trailing edge that is wider than a leading edge. 
     FIG. 14 is a cross-sectional view of some steps subsequent to the steps shown in FIG. 13 in the second method of forming a write pole tip having a trailing edge that is wider than a leading edge. 
     FIG. 15 is a cross-sectional view of some steps subsequent to the steps shown in FIG. 14 in the second method of forming a write pole tip having a trailing edge that is wider than a leading edge. 
     FIG. 16 is a cross-sectional view of some initial steps in a third method of forming a write pole tip having a trailing edge that is wider than a leading edge. 
     FIG. 17 is a cross-sectional view of some steps subsequent to the steps shown in FIG. 16 in the third method of forming a write pole tip having a trailing edge that is wider than a leading edge. 
     FIG. 18 is a cross-sectional view of some steps subsequent to the steps shown in FIG. 17 in the third method of forming a write pole tip having a trailing edge that is wider than a leading edge. 
     FIG. 19 is a top view of a media-facing surface of a slider having a transducer in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 4 depicts a media-facing view of a transducer  100  in accordance with the present invention, and FIG. 5 depicts a cutaway side view of that transducer  100  interacting with a relatively moving media  102 . The transducer  100  includes a write pole layer  105  with a write pole tip  108  that is magnetically exposed to the media  102 . The write pole tip  108  has a leading edge  110  that is smaller than a trailing edge  111 . The transducer  100  also contains a return pole layer  113  with a return pole tip  115  that is magnetically exposed to the media  102 . 
     The write pole layer  105  and the return pole layer  113  are made of soft magnetic materials, such as nickel-iron Permalloy (Ni 80 Fe 20 ). Optionally, the write pole layer  105  or a trailing layer of the write pole layer may be made of a high magnetic saturation (high B SAT ) material such as a predominantly-iron nickel-iron alloy (e.g., Ni 45 Fe 55 ). The write pole layer  105  and the return pole layer  113  are magnetically coupled in the transducer  100  by first and second soft magnetic coupling layers  117  and  118 . An electrically conductive coil layer  120  is provided for inducing a magnetic flux in the pole layers  105  and  113  and coupling layers  117  and  118 . 
     An optional magnetoresistive (MR) sensor  122  is disposed in the transducer  100  adjacent the write pole  108 . MR sensor  122  may be an anisotropic magnetoresistive (AMR) sensor, spin:valve (SV) sensor, spin tunneling (ST) sensor, giant magnetoresistive (GMR) sensor or other type of MR sensor. Although a MR sensor is shown, other sensors, such as magneto-optical sensors may instead be employed for reading magnetic fields from the media  102 . Alternatively, the write pole  105  may be used to sense magnetic fields from the media  102 , with the changing fields of the relatively moving media inducing a current in the coil  120  that is read as a signal. A soft magnetic shield layer  125  is disposed adjacent to the sensor  122 , the shield layer  125  and the write pole layer  105  shielding the MR sensor  122  from magnetic flux that is not located in a portion of the media adjacent to the sensor. A nonmagnetic protective coating, not shown, may be disposed on a media-facing surface  128  of the transducer, protecting the sensor  122  from damage and corrosion. Areas of the transducer  100  that are shown in FIG.  4  and FIG.  5  and that have not, for conciseness, been specifically labeled with element numbers, are made of nonferromagnetic and electrically nonconductive materials such as alumina (Al 2 O 3 ). 
     The media  102 , which may for example be a rigid disk, includes a media layer  130  and underlayer  133  disposed atop a self-supporting substrate  135 . A protective coating, not shown, may be disposed on a surface  138  of the media  102 , protecting the media layer  130  from damage and corrosion. The substrate  135  may be formed of glass, aluminum or other known materials. The underlayer  133  may be made of Permalloy or other soft magnetic materials. The media layer  130  may be formed of a stack of layers alternating between ferromagnetic (e.g., Co and Fe) and platinum group metal metals (e.g., Pt and Pd) for example, and may have an easy axis of magnetization substantially perpendicular to the media surface  138 . The media  102  is moving relative to the transducer in a direction indicated by arrow  139 . 
     To provide a more concentrated magnetic flux in a portion of the media  102  adjacent the write pole tip  108  than in a portion of the media adjacent the return pole tip  115 , the area of the return pole tip  115  may be substantially larger than that of the write pole tip  108 . Also, to provide a magnetic signal to the media  102  that does not bridge a gap between the write pole tip  108  and the return pole tip  115 , a distance between those pole tips may be substantially larger than that between the write pole tip  108  and the soft magnetic underlayer  133 , as factored by the coercivity of the media layer  130 . For current operating conditions, a sufficient magnetic signal is communicated between the media  102  and the write pole tip  108  provided that a distance D between the write pole tip  108  and the return pole tip  115  is greater than one micron. 
     FIG. 6 shows a pattern of magnetization  140  written in the media layer  130  by the write pole tip  108  on a track for which the transducer  100  is skewed relative to the track. The write pole tip  108  has a novel trapezoidal-shaped area facing the media  102 , which can be seen in the most recent magnetization  142 . Prior magnetizations written to the media, such as magnetization  141 , do not have edge effects or side writing the skew. As a result, errors in reading data can be substantially reduced. Note that prior magnetizations written to the media, such as magnetization  141 , also have a trapezoidal-shaped area. 
     FIG. 7 depicts a media-facing view of another transducer  200  in accordance with the present invention, and FIG. 8 depicts a cutaway side view of that transducer  200  interacting with the media  102 . The transducer  200  includes a write pole layer  205  with a write pole tip  208  that is magnetically exposed to the media  102 . The write pole tip  208  has a leading edge  210  that is smaller than a trailing edge  211 . The transducer  200  also contains a return pole layer  213  with a return pole tip  215  that is magnetically exposed to the media  102 . The write pole layer  205  and the return pole layer  213  are magnetically coupled in the transducer  200  by first and second soft magnetic coupling layers  217  and  218 . An electrically conductive coil layer  220  is provided for inducing a magnetic flux in the pole layers  205  and  213  and coupling layers  217  and  218 . The return pole tip  215  includes a pair of peninsulas  250  and  252  that extend in a trailing direction near the media facing surface  228 , and which may be formed at the same time as the coupling layer  217 . 
     An optional magnetoresistive (MR) or other sensor  222  is disposed in the transducer  200  adjacent the return pole layer  213 . Alternatively, the write pole  205  may be used to sense magnetic fields from the media  102 , with the changing fields of the relatively moving media inducing a current in the coil  220  that is read as a signal. A soft magnetic shield layer  225  is disposed adjacent to the sensor  222 , the shield layer  225  and the return pole layer  213  shielding the MR sensor  222  from magnetic flux that is not located in a portion of the media adjacent to the sensor. A nonmagnetic protective coating  240  is disposed on a media-facing surface  228  of the transducer, protecting the sensor  222  from damage and corrosion. Areas of the transducer  100  shown in FIG.  7  and FIG. 8 that have not, for conciseness, been labeled with element numbers, are made of nonmagnetic and electrically nonconductive materials, such as alumina. The transducer  200  may contact the media  102  during data communication, or may be spaced a minimal distance (e.g., less than 100 nanometers) from the media during reading or writing. 
     FIG. 9 shows some steps in a first method of forming a write pole tip having a trailing edge that is wider than a leading edge, such as write pole tip  108  or  208 . Although it is possible to form such a structure by focused ion beam (FIB) etching of the media-facing surface, FIB etching creates a trench around each pole tip and may leave some redeposited magnetic material near the pole tip. FIB etching is also limited in extent, so that the desired pole tip shape may extend for example less than a micron from the media-facing surface, which can result in fringe fields for perpendicular recording that defocus the magnetic pattern on the media. Moreover, FIB etching is performed individually on each pole tip, as opposed to essentially simultaneous production of many hundreds or thousands of pole tips on a wafer. 
     In FIG. 9, which shows a cross-section of a portion of a wafer substrate  300  and appended transducer layers near what will become a media-facing surface, a return pole layer  303  of Permalloy has been formed by electroplating atop conventional MR sensor layers  305  and a conventional Permalloy shield layer  308 . Electrically conductive lead layers  306  and  307  have been formed generally coplanar with sensor layers  305 , to provide electric current to the sensor layers. Return pole layer  303 , sensor and lead layers  305 - 307 , and shield layer  308  are separated by read gap layers  310  and  311 , which may be made of alumina or other nonferromagnetic and electrically nonconductive materials. Similar dielectric materials have been formed in layers  302  and  303  on either side of the return pole layer  303 . Additional dielectric spacer layers  313  and  315  have been formed coplanar to respective soft magnetic coupling layers, not shown in this figure. The dielectric layers having been formed by sputter or other deposition that overlaps the electroplated magnetic coupling layers, followed by chemical mechanical polishing (CMP) or otherwise smoothing each combined coupling and alumina layer to a planar surface. 
     To create a write pole tip having tapered sides, a nonferromagnetic and electrically nonconductive layer  320  is first formed, for example of alumina, on top of the surface of the dielectric layer  315  and the soft magnetic coupling layer that is not shown in this figure. Layer  320  is covered with a photoresist or other mask  322 , which is formed with an edge adjacent to where an edge of a write pole layer is desired. A directional dry etch, such as an ion beam etch (IBE) is then applied to create a sloping side  318  of dielectric layer  320  and to expose the soft magnetic coupling layer that is coplanar with dielectric layer  315 . The mask  322  is then removed, and a conductive seed layer is deposited onto the exposed magnetic coupling layer and dielectric layers  315  and  320 . 
     In FIG. 10, a soft magnetic write pole layer  325  has been electroplated atop the conductive seed layer, after which the seed layer and write pole layer  325  have been CMP or otherwise polished to remove the portion of pole layer  325  that was formed atop dielectric layer  320 . A side  328  of pole layer  325  that abuts dielectric layer  320  has a slope that is not perpendicular to the wafer  300  surface. This tapered side  328  will become a side of the write pole tip, with the slope causing a trailing edge of the pole tip to be larger than a leading edge of the pole tip. 
     In FIG. 11, a mask  330  has been created atop dielectric layer  320  and overlapping the write pole layer  325 , with a mask edge  335  defined near the side  328  of the write pole layer  325 . A dry etch such as an IBE is then applied in the direction of arrows  333  to create a sloping side  338  of write pole layer  325 , resulting in a trapezoidal shape of the pole layer  325  cross-section, which will become the trapezoidal pole tip. The directional etch may be at an angle of incidence Ø to the wafer  300  surface that is on an opposite side of a normal  323  to that surface than the IBE or other directional removal that created side  328 . 
     The angle of incidence Ø may also vary in order to achieve a desired undercut and slope of side  328 . For example, Ø may begin at an angle to perpendicular of less than 45° that initially causes material removed from pole layer  325  to be redeposited on edge  335 , slowing the rate of etching on that edge  335 . With a bottom portion of layer  325  being removed at a greater rate than a top portion of that layer, the desired undercut of side  338  is created. A larger angle Ø IBE may then be performed that removes redeposited material. The wafer can be set at a fixed tilt to create side  338  or the IBE can sweep between acute and obtuse directions to perpendicular. 
     FIG. 12 shows the write pole layer  325  that has been formed with a leading edge  340  that is smaller than a trailing edge  344 . After formation of the write pole layer  325  as described above, a layer  350  of nonferromagnetic and electrically nonconductive material is formed, for example, of alumina, creating a trailing edge  355  of the head. The layer  350  may be formed by sputtering or other directional deposition at an angle that sweeps over the wafer surface to avoid air pockets, or the layer  350  may be formed by an isotropic deposition, such as chemical vapor deposition (CVD). The wafer substrate  300  is then diced or otherwise divided into rows of individual heads each containing transducer layers similar to those shown in FIG. 12, including exposing the wafer and transducer layers along the cross-section shown in FIG. 12. A media-facing surface is then created from that exposed area, including polishing the surface, tailoring any media-facing relief and optionally coating the surface with a protective dielectric material, after which the individual heads are released from the row and integrated into storage systems. 
     FIG. 13 shows another method for making a transducer in accordance with the present invention. For conciseness, the elements described above with regard to previous figures are not described for FIG.  13 . In this example, creation of a write pole tip having tapered sides begins with formation of an electrically conductive seed layer  360  on the surface of the dielectric layer  315  and the soft magnetic coupling layer that is not shown in this figure. Atop the seed layer  361  a photoresist layer  360  has been patterned by photolithography to form an aperture  363  exposing the surface of the seed layer  360  atop the soft magnetic coupling layer. 
     The photoresist layer  361  is then baked, as shown in FIG. 14, to form sloping sides  366  and  367  that provide a tapered mold for forming the trailing pole tip. The baking may be at a temperature ranging between 70° C. and 120° C., and typically between 80° C. and 100° C., with the slope of the sides controlled by the temperature. A 95° C. bake for 15 minutes has proven effective. A soft magnetic write pole layer  370  is formed by electroplating atop the exposed portion of the seed layer  360 . 
     FIG. 15 shows the write pole layer  370  after the photoresist layer  361  has been chemically removed, and ion milling has removed the portion of the seed layer  360  that was covered by photoresist layer  361 . The write pole layer  370  has sloping sides  372  and  374  and a leading edge  376  that is smaller than a trailing edge  377 . A dielectric layer  380  has been formed that encases the write pole layer  370 . The layer  380  may be formed by sputtering or other directional deposition at an angle that sweeps over the wafer surface to avoid air pockets, or the layer  380  may be formed by an isotropic deposition, such as CVD. A MR or other sensor may now be formed on layer  380  for the case in which such a sensor was not formed previously. 
     FIG. 16 shows another method for making a transducer in accordance with the present invention. In this example, creation of a write pole tip having tapered sides begins with formation of a dielectric layer  400  on the surface of dielectric layer  315  and the soft magnetic coupling layer that is not shown in this figure. A photoresist layer  404  is then deposited and patterned to forman aperture  406  exposing the surface of the dielectric layer  400 . 
     A directional dry etch, such as IBE is then applied to create sloping sides  416  and  417  of dielectric layer  400  and to expose the soft magnetic coupling layer that is coplanar with dielectric layer  315 . The mask  322  is then removed, and an electrically conductive seed layer  420  is deposited onto the exposed magnetic coupling layer and dielectric layers  315  and  400 , as shown in FIG.  17 . 
     FIG. 18 shows that a soft magnetic write pole layer  422  has been electroplated onto the electrically conductive seed layer  420 , after which the wafer has been polished, and another dielectric layer  425  deposited. 
     FIG. 19 is a media-facing view of a head or slider  500  in accordance with the present invention. The head  500  has a leading end  502 , a trailing end  505 , and a media-facing surface  507 . The media-facing surface  507  has a U-shaped projection  510  and a trailing pad  511  containing transducer elements described above. At least part of the trailing pad  511  has been coated with a transparent protective coating such as diamond-like carbon (DLC), and the pad  511  may contact or be disposed in close proximity to a rapidly-moving media, not shown in this figure. Other known configurations for the media-facing surface may alternatively be employed. The transducer elements include a write pole tip  515  having a trapezoidal shape, a return pole tip  517 , a MR sensor  520  and a magnetic shield  522 . The slider  500  can be mechanically and electrically connected by conventional means to the arm  28  shown in FIG.  1 . 
     Although we have focused on teaching the preferred embodiments of an improved electromagnetic transducer, other embodiments and modifications of this invention will be apparent to persons of ordinary skill in the art in view of these teachings. Therefore, this invention is limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.