Abstract:
An inductive transducer having first and second magnetic pedestals disposed between first and second magnetic pole layers and adjacent to a media-facing surface, the pedestals separated by a submicron, nonmagnetic gap. The first pedestal extends less than the second pedestal from the media-facing surface, defining a short throat height. The second pedestal extends further to provide sufficient area for stitching to the second pole layer. The stitching and the thickness provided by the pedestals allow plural coil layers to be disposed between the pole layers, and the second pedestal, as well as other features, can be defined by high-resolution photolithography. The two coil layers have lower resistance, lower inductance and allow the pole layers to be shorter, improving performance. All or part of either or both of the pedestals may be formed of high magnetic saturation material, further enhancing performance.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to inductive electromagnetic transducers, which may for example be employed in information storage systems or measurement and testing systems. 
     An inductive head used for writing and/or reading magnetic information on a storage media such as a disk or tape includes electrically conductive coil windings encircled by a magnetic core including first and second pole layers. Portions of the pole layers adjacent the media are termed pole tips. The magnetic core is interrupted by a submicron nonmagnetic gap disposed between the pole tips to divert magnetic flux to the media during writing. To write to the media electric current is flowed through the coil, which produces magnetic flux in the core encircling the coil windings, the magnetic flux fringing across the nonmagnetic gap adjacent to the media so as to write bits of magnetic field information in tracks on the media. 
     The first pole layer may also serve as a magnetic shield layer for a magnetoresistive (MR) sensor that has been formed prior to the pole layers, the combined MR and inductive transducers termed a merged or piggyback head. Typically the first pole layer is substantially flat and the second pole layer is curved, as a part of the second pole layer is formed over the coil windings and insulation disposed between the pole layers, while another part nearly adjoins the first pole layer adjacent the gap. The second pole layer may also diverge from a flat plane by curving to meet the first pole layer in a region distal to the media-facing surface, sometimes termed the back gap region, although typically a nonmagnetic gap in the core does not exist at this location. 
     The curvature of the second pole layer from planar affects the performance of the head. An important parameter of the head is the throat height, which is the distance from the media-facing surface to where the first and second pole layers begin to diverge and be separated by more than the submicron nonmagnetic gap. Because less magnetic flux crosses the gap as the pole layers are further separated, a short throat height is desirable in obtaining a fringing field for writing to the media that is a significant fraction of the total flux crossing the gap. 
     In addition to the second pole layer being curved from planar, one or both pole layers may also have a tapered width in the pole tip area, to funnel flux through the pole tips. A place where the second pole layer begins to widen is sometimes termed a nose or flare point. The distance to the flare point from the media-facing surface, sometimes called the nose length, also affects the magnitude of the magnetic field produced to write information on the recording medium, due to decay of the magnetic flux as it travels down the length of the narrow second pole tip. Thus, shortening the distance of the flare point from the media-facing surface would also increase the flux reaching the recording media. 
     Unfortunately, the aforementioned design parameters require a tradeoff in the fabrication of the second pole tip. The second pole tip should be narrow and well-defined in order to produce narrow and well-defined written tracks on the rotating disk, but the slope of the second pole layer at the end of the throat height makes photolithography difficult. The second pole layer can be formed in two pieces to better define the pole tip; a flat pole tip layer and a curved yoke layer that are connected or stitched together. This solution, however, can actually require the throat height to be extended in order to have a sufficient stitched area for flux transfer between the second pole tip and the yoke. High-resolution photolithography, such as I-line or deep ultra violet (DUV) photolithography, may be useful for reducing feature sizes but has a more limited depth of focus that may exacerbate the problem of focusing on the sloped pole layer adjacent the throat. 
     In addition, several methods are known to form self-aligned pole tips. In one method, an ion beam etch (IBE) or other highly anisotropic process removes a portion of the second pole layer not protected by a mask, thereby creating the second pole tip, with the etching continued to similarly remove a portion of the first pole tip not covered by the second pole tip. The width of the pole tip layers are therefore matched, and walls of the pole tips are aligned, but the problem of accurately defining the second pole tip by photolithography for a short throat height remains. Other proposals include forming an electrically conductive gap layer, so that the second pole tip can be electroplated atop the first. A second pole tip directly plated on a conductive gap layer may have magnetic disadvantages and other difficulties, however, and so has not been widely employed. 
     SUMMARY 
     In accordance with the present invention, an inductive transducer is disclosed having first and second magnetic pedestals disposed between first and second magnetic pole layers adjacent to a media-facing surface, the pedestals separated by a submicron, nonmagnetic gap. The first pedestal extends less than the second pedestal from the media-facing surface and defines a short throat height. The second pedestal extends further to provide sufficient area for stitching to the second pole layer. The second pedestal is formed on a flat surface, allowing a high performance magnetic layer defined by high-resolution photolithography to adjoin the trailing edge of the gap. 
     The stitching and the thickness provided by the pedestals allow plural coil layers to be disposed between the pole layers, reducing the coil circumference compared to a conventional single layer coil having equivalent electromotive force. The plural coil layers have less resistance and inductance than the conventional single layer coil, and allow the pole layers to be shorter, all of which improve performance. All or part of either or both of the pedestals can also be formed of high magnetic saturation material, further enhancing performance. 
    
    
     BRIEF DESCRIPTION OF THE FIGURES 
     FIG. 1 is a cutaway cross-sectional view of a portion of an information storage system in accordance with one embodiment of the present invention. 
     FIG. 2 is a cutaway cross-sectional view of a portion of an information storage system in accordance with another embodiment of the present invention. 
     FIG. 3 is a cutaway cross-sectional view of a step in the fabrication of a transducer for the information storage system of FIG.  1 . 
     FIG. 4 is a cutaway cross-sectional view of another step in the fabrication of the transducer subsequent to that shown in FIG.  3 . 
     FIG. 5 is a cutaway cross-sectional view of another step in the fabrication of the transducer subsequent to that shown in FIG.  4 . 
     FIG. 6 is a cutaway cross-sectional view of another step in the fabrication of the transducer subsequent to that shown in FIG. 5, the cross-section of FIG. 6 being perpendicular to that of FIG.  5 . 
     FIG. 7 is a cutaway cross-sectional view of another step in the fabrication of the transducer subsequent to that shown in FIG. 6, the cross-section of FIG. 7 being perpendicular to that of FIG.  6  and parallel to that of FIG.  5 . 
     FIG. 8 is a cutaway cross-sectional view of another step in the fabrication of the transducer subsequent to that shown in FIG.  7 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 depicts a cutaway cross-section of a portion of an information storage system  20  in accordance with an embodiment of the present invention. A portion of an electromagnetic head including a merged inductive and MR transducer  22  is depicted in close proximity to a relatively moving media such as a spinning disk  25 . The transducer  22  is formed in a plurality of adjoining solid layers on a wafer substrate  28  that may remain affixed to the transducer  22 . A media-facing surface  33  of the solid body that includes the transducer  22  may be formed with a desired relief for fluid and solid interaction with the disk  25 , and the body may be termed a head or slider. 
     The disk  25  may be conventional and includes a self-supporting substrate  35 , an underlayer  34 , a media layer  37  and a protective overcoat  39 . The disk  25  is spinning in a direction indicated by arrow  31  and has a surface  32  adjacent the media-facing surface  33  of the head. 
     Atop the slider substrate  28  a first low-coercivity, high-permeability or “soft magnetic” shield layer  30  has been formed, for example of Permalloy (Ni 0.8 Fe 0.2 ) either directly or atop a seed layer, not shown. A first layer of nonmagnetic, electrically insulating material has been formed on the shield layer, followed by a magnetoresistive (MR) sensor  44 . The MR sensor can be any sensor that utilizes a change in resistance associated with a change in magnetic field to sense that field, which may be measured as a change in current or voltage across the sensor, including anisotropic magnetoresistive (AMR) sensors, spin-valve (SV) sensors, spin-dependent tunneling (SDT) sensors, giant magnetoresistive (GMR) sensors and colossal magnetoresistive (CMR) sensors. 
     A second layer of nonmagnetic, electrically insulating material has been formed between the MR sensor and a second soft magnetic shield layer, which also serves as a first pole layer  46  in this example of a merged head. The first and second layers of nonmagnetic, electrically insulating material are indicated together as region  40 . The MR sensor  44  may be electrically connected to the shield layers  30  and  46  in some embodiments, such as spin-dependent tunneling sensors. 
     A first electrically conductive coil layer  52  has first coil sections  55  that are separated from the first pole layer  46  by additional nonmagnetic, electrically insulating material  45 . A second electrically conductive coil layer  57  has second coil sections  59  that are separated from the first coil sections  55  by material  45 , but may be connected to first coil layer  52  in an interconnect not shown in this cross-section. For example, first coil layer  52  may spiral in a clockwise direction and second coil layer  57  may spiral in a counterclockwise direction with the center sections of the coils interconnected, so that current in coil sections  55  is parallel to current in coil sections  59 . Second coil sections  59  are isolated from a second soft magnetic pole layer  60 , the second pole layer coupled to the first pole layer  46  by a soft magnetic stud  62 . Additional coil layers may also be formed. A protective coating  80  is formed on a trailing edge  82  of the body, while another protective coating  88  is formed on the media-facing surface  33 . 
     Having two coil layers  52  and  57  as opposed to a single coil layer that is typical is advantageous for several reasons. First, the two coil layers have less resistance than a single coil layer. This is because the overall length of the coil is less for the case of two coil layers, as the circumference of the coil is reduced despite having the same number of coil sections encircled by the magnetic core. The shorter coil length reduces the resistive heat produced by the coil, reducing the possibility of protrusion of a pole tip that can occur due to expansion of material  45 , which typically includes baked photoresist. Since current commercially available disk drive heads “fly” at a separation of less than a microinch (about 25 nanometers) from a rigid disk that may be spinning at 10,000 revolutions per minute, even a small protrusion due to the resistive heating of those heads could cause a crash, and avoiding a crash may require increasing the separation of the sensor from the disk, decreasing the resolution. Second, the inductance of the two coil layers is reduced compared to that of a typical single coil layer. Inductance of a coil is a function of the area surrounded by the coil, and so the smaller circumference afforded by two coil layers reduces the inductance of that coil, despite having the same number of coil sections encircled by the magnetic core. Lower inductance allows higher frequency operation. Third, the inductance of the core is reduced due to the shorter pole layers afforded by the two coil layers. This also allows for higher frequency operation, which is important for higher storage density, higher recording rates and faster access times. 
     A first soft magnetic pedestal  66  is disposed adjacent the media-facing surface  33  and the first pole layer  46 . The first pedestal  66  may be made of high moment or saturation material (high Bs) to avoid saturation of the pedestal  66  during writing. High Bs materials currently have a saturation moment of at least 18 kG. For example, the first pedestal  66  may be made of sputtered, laminated high B S  material, such as laminated CoFeN having a moment B S  of about 24 kG. Alternative high B S  materials include FeXN, where X is an element selected from a group including Rh, Al, Ta, Zr and Ti, having a B S  of about 20 kG-22 kG. Other high B S  materials known or developed may alternatively be employed in first pedestal  66 . For the case in which first pedestal  66  is laminated, plural layers of high B S  material may be interspersed with at least one layer of lower B S  material or nonmagnetic material that is either electrically conductive or not electrically conductive. The first pedestal  66  may have a tapered base  67  that provides for increased flux transfer between pedestal  66  and pole layer  46 . 
     A second soft magnetic pedestal  68  is disposed adjacent the media-facing surface  33  and the second pole layer  60 , the second pedestal  68  separated from the first pedestal  66  by a submicron nonmagnetic gap  70 . A throat height TH is defined by the first pedestal  66 , allowing the throat height TH to be made small for high performance. The height TH may be less than a micron, for example. The second pedestal  68  extends further than the first pedestal  66  from the media-facing surface  33 , allowing the second pole layer  60  to overlap the second pedestal  68  in a relatively large area for transfer of flux between the pedestal  68  and pole layer  60 . Second pole layer  60  terminates further from the media-facing surface  33  than does second pedestal  68 , to reduce the possibility of writing to the media layer  37  with the second pole layer  60  instead of or in addition to the second pedestal  68 . All of or a layer  72  of the second pedestal  68  adjacent the gap  70  may be made of high B S  material to avoid saturation of the pedestal  68  during writing. Second pedestal  68  may also be made of plural layers of high B S  material with at least one interspersed layer of lower B S  material or nonmagnetic material that is either electrically conductive or not electrically conductive. 
     FIG. 2 depicts a cutaway cross-section of a portion of an information storage system  90  similar to that depicted in FIG. 1, but having a piggyback transducer including a spin-dependent tunneling sensor  94  with an electrically insulating tunnel barrier  96 . A first pole layer  98  is separated from second shield layer  46  in this piggyback embodiment by an electrically insulating layer  99 . Shields  30  and  46  can serve as or be connected to a conductive lead for the sensor  94 . Although FIG. 2 depicts a SDT sensor in a piggyback head and FIG. 1 depicts a SV sensor in a merged head, the converse combinations are also possible, as well as other head/sensor combinations. For example, a magnetic field sensor can be disposed closer than the inductive transducer to the trailing end. 
     FIG. 3 shows some initial steps in forming the transducer  22  of FIG.  1 . The transducer  22  is formed along with thousands of similar transducers, not shown, on the wafer substrate  28 , which may be made of AlTiC, Alumina, SiC or other known materials. Atop the wafer substrate  28  the first soft magnetic shield layer  30  is formed, for example by window frame plating, either directly on the substrate or atop a seed layer, not shown. An alumina or other dielectric layer, not shown, is then deposited and lapped to form a coplanar surface with the first shield layer  30 . 
     A first submicron read gap layer of nonmagnetic, electrically insulating material is formed on the shield layer, followed by MR sensor  44 . Although shown as a single element in this figure, the MR sensor may be composed of plural layers, and electrical leads for the MR sensor  44  may extend between the shields  30  and  46  toward and away from the viewer, as known in the art. A second submicron read gap layer of nonmagnetic, electrically insulating material is then formed between the MR sensor  44  and the shield/pole layer  46 . The first and second layers of nonmagnetic, electrically insulating material, as well as additional layers of such material, are indicated together as region  40 . 
     After lapping the shield/pole layer  46  and a dielectric layer that forms a flat surface with the shield/pole layer  46 , the first pedestal  66  is formed on the shield/pole layer  46 . In this example, first pedestal  66  is formed of a plurality of layers of sputtered, high B S  material, such as CoFeN or FeXN, where X is an element selected from a group including Rh, Al, Ta, Zr and Ti, interspersed with at least one layer of magnetic material such as Permalloy, conductive nonmagnetic material such as Cr or Ti, or dielectric material such as alumina or AlN. The layers forming first pedestal can each have a thickness in a range between a single atomic layer and a micron. A mask  100  is defined over the layers of material and the pedestal is then defined by an angled, rotating or sweeping IBE  105  or other anisotropic removal at an angle Ø to perpendicular  110  that may vary, the IBE producing tapered edges such as edge  67  and edge  112 . 
     Alternatively, first pedestal  66  can be formed of a single layer of sputtered, high B S  material, or can be formed of a sputtered layer, for example of Permalloy, upon which a high B S  material, for example Ni 0.45 Fe 0.55  is electroplated. In the latter case, the pedestal may be electroplated though an opening in a negative photoresist layer to form a tapered base, with a magnetic stud layer electroplated in another photoresist opening in the back gap region, after which the photoresist is chemically removed. In yet another embodiment, first pedestal  66  can be formed of seeding and plating material such as permalloy, after which a layer of high B S  material can be formed by sputtering or other vacuum techniques. 
     In FIG. 4 a dielectric filler layer  115  has been formed over and around the first pedestal  66  and then polished flat, by lapping or chemical-mechanical polishing (CMP). The write gap layer  70  is then deposited, for example of alumina or other non-ferromagnetic material sputtered to a thickness in a range between about 50 nanometers and 250 nanometers. A mask is formed over the gap layer  70  that leaves an aperture for forming a magnetic stud, and a removal step such as reactive ion etching (RIE) or IBE is performed that exposes shield/pole layer  46 . A first soft magnetic stud layer  118  is then formed by electroplating. Alternatively, for the case in which the stud  118  has been earlier electroplated, the stud layer  118  can be polished by CMP along with the pedestal and dielectric layer  115 . A mask can then be defined over the stud  118 , the mask being lifted off after deposit of the gap layer  70  to expose the stud layer  118 . 
     FIG. 5 shows that a layer  120  of high B S  material has been sputtered or otherwise deposited on the gap layer  70  and exposed stud layer  118  for creating a sharp magnetic pattern at an unsaturated edge of the second pedestal that adjoins the gap  70 . High B S  material having a favorable crystalline structure can be formed on the flat write gap surface, whereas formation of such material on a conventional curving yoke is problematic. An optional seed layer  122  may then formed of NiFe or CoNiFe over the high B S  layer  120  for the case in which it is beneficial for subsequent electroplating. A photoresist mask  125  is then defined that leaves openings for electroplating a pedestal layer  130  and second stud layer  133 , for example of NiFe. The mask  125  can be defined by high-resolution photolithography such as UV or deep UV with or without a tri-level image transfer technique. Alternatively, the second pedestal can be formed of a plurality of sputtered high B S  layers with other layers formed therebetween, as a single sputtered layer of high B S  material, or as a sputtered layer of high B S  material upon which another layer high of B S  material is electroplated. 
     FIG. 6 shows a cross-section that is perpendicular to that of FIG. 5, FIG. 6 viewed from a direction where the media will be located during later operation. An IBE, RIE, reactive ion beam etching (RIBE) or other highly directional removal process is performed, represented by arrows  140 , to remove the high B S  layer  120  and optional seed layer  122  not covered by electroplated layer  130 . This etching may also be used to trim edges of the first pedestal to match those of the second pedestal layers  120 ,  122  and  130 . Alternatively, a mask  144  may be formed on electroplated layer  130 , so that the first pedestal can be defined by directional etching about the mask  144 , again represented by arrows  140 , and a track width of the first pedestal matches that of the second pedestal. Also shown in the cross-sectional view of FIG. 6 are electrical leads  146  and  148  that provide electrical connections to MR sensor  44 . 
     FIG. 7 shows a cross-section of the partially formed transducer that is perpendicular to that of FIG.  6  and parallel to that of FIG.  5 . In FIG. 7, subsequent to the trimming depicted in FIG. 6, a conductive seed layer  150  of Cu, Au, Ag or the like has been sputter-deposited, after which a photoresist  152  has been deposited and spun to form a flat surface. The photoresist  152  can then be patterned into a mask having a spiral opening, and the coil layer  52  electroplated through the opening. Alternatively, a hard mask  155  made of SiO 2 , for example, has been patterned by another photoresist and etched in a spiral pattern, for example by RIE with CHF 3 , to expose the photoresist  152 , which is then etched, for example by RIE with O 2 , to expose the seed layer  150 . Coil layer  52  is then electroplated with similar materials as seed layer  150 , to form coil sections  55 . An interconnect that will provide electrical connection between the coil layers is then electroplated, while the other coil sections are covered with photoresist. The photoresist  152  is then chemically removed and then the portions of seed layer  150  that are not covered by the electroplated coil layer are removed, for example by IBE or wet etching, separating coil sections  55 . 
     In FIG. 8, a dielectric filler material  160 , such as alumina, baked photoresist or a combination of such materials, has been formed on and around the second pedestal  68 , coil sections  55  and magnetic stud layer  133 . For example, a minimal amount of cured photoresist may be used to fill the space between coil sections  55 , then covered by alumina that provides additional electrical insulation. The use of alumina instead of conventional baked photoresist as a filler material is advantageous in that alumina has a lower thermal expansion coefficient, reducing problems such as pole tip protrusion. The filler material  160  has been flattened by CMP to expose second pedestal  68 , stud layer  133  and the electrical interconnect. A conductive seed layer  166  has been deposited and then covered with a photoresist, which has been formed into a mask exposing the seed layer  166  in a spiral pattern through which the second coil layer has been electroplated. After removal of the photoresist mask and milling of the seed layer  166  that is not covered by the coil sections  59 , another layer of photoresist is patterned and cured about coil sections  59  to create sloping edges for the second pole layer  60 . 
     A magnetic seed layer  177  has been deposited, and another photoresist then applied and patterned so that electroplating of second pole layer  60  leaves an edge  180  that will be removed from the media-facing surface, and another edge  182  at the back gap region. The photoresist has been removed, and portions of the seed layer  177  that are not covered by second pole layer  60  have been milled away. Protective coating  80 , which may for example be sputtered of alumina, has been formed, after which the wafer will be diced into rows of transducers, for example along line  188 , which will be polished and prepared into the media-facing surface. 
     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.