Abstract:
A magnetic write head having a metal, non-magnetic write gap that extends only partially to the magnetic back gap, the remainder of the distance between the pole tip and the back gap being a magnetic material. The elimination of the seed layer reduces the amount of milling required to perform the desired notching needed to form a self aligned pedestal on the first pole and voids electrolytic corrosion of the back gap during plating.

Description:
FIELD OF THE INVENTION 
   The present invention relates to magnetic recording and more particularly to a method of manufacturing an inductive write head having a metal write gap layer. 
   BACKGROUND OF THE INVENTION 
   Computer systems generally utilize auxiliary memory storage devices having media on which data can be written and from which data can be read for later use. A direct access storage device (DASD) such as a disk drive incorporating a rotating magnetic disks is commonly used for storing data in magnetic form on the disk surfaces. Data is recorded on concentric, radially spaced tracks on the disk surfaces, and magnetic heads are used to write the data to and read the data from the tracks on the disk surfaces. 
   Data is written onto a disk by a write head that includes a magnetic yoke having a coil, passing there through. When current flows through the coil, a magnetic flux is induced in the yoke, which causes a magnetic field to fringe out at a write gap. It is this magnetic field that writes data, in the form of magnetic transitions, onto the disk. Currently, such heads are thin film magnetic heads, constructed using material deposition techniques such as sputtering and electroplating, along with photolithographic techniques that include the use of photoresist masks. 
   Examples of such heads include a first magnetic pole, formed of a material such as NiFe which might be plated onto a substrate after sputter depositing an electrically conductive seed layer. Thereafter a magnetic pedestal could be constructed at a portion of the pole intended as a pole tip and where a write gap is to be formed. The pedestal is generally in the form of a magnetically soft, high magnetic saturation (high Bsat) material, such as CoFe or Ni 55 Fe 45 . A high magnetic saturation material is desired because of its ability to concentrate magnetic flux into a small pole tip region for emitting a concentrated magnetic field therefrom. Opposite the pedestal, at a back end of the magnetic pole, a magnetic back gap can be formed. A back gap is the term generally used to describe a magnetic structure that magnetically connects first and second poles to form a completed magnetic yoke as will be described. Although the back gap is constructed of a magnetic material, it need not have as high a magnetic saturation as the pedestal, because it can be constructed to have a much larger cross sectional area. A coil can be formed over the first pole, between the pedestal and the back gap and can be electrically isolated from the pole and yoke by an insulation layer, which could be alumina (Al 2 O 3 ) or hard baked photoresist. A second pole formed over the first pole completes the magnetic yoke, being magnetically connected with the first pole by the write gap and being magnetically separated from the first pole and the pedestal by a thin layer of non-magnetic material called a write gap. 
   The write gap material has traditionally been constructed of a thin layer of non-magnetic dielectric material, which has usually been Alumina or SiO 2 . This thin layer of write gap material is generally deposited as a full film on a planarized surface consisting of the top of the pedestal, the top the coil insulation, the top of the back gap material, and the top of a layer of insulation in the field area. 
   In order to magnetically connect the second pole with the back gap material, an opening must be created in the write gap material over the back gap. Generally this has been done by spinning on a thin photoresist layer and applying photolithographic techniques to form a photoresist mask that has an opening at the back gap and covers all other areas. A material removal process such as wet etching or ion milling would then be performed to remove the portion of the write gap material over the back gap, exposing the back gap. 
   Some head designs require the formation of a P 2  pedestal in the pole tip area. This P 2  pedestal is formed directly over the first pedestal, but on top of the write gap. The two pedestal portions can be self aligned by using the upper P 2  pedestal as a mask, and then ion milling to notch into the first pole creating a self aligned pedestal directly under the upper pedestal. 
   However, since the write gap is generally constructed of a dielectric material such as alumina or SiO 2 , an electrically conductive seed layer must be deposited prior to plating the upper P 2  pedestal. Therefore, in order to form the desired notch in the first pole, the ion mill process must remove not only the desired magnetic material of the first pole, and the non-magnetic material of the write gap, but must also remove the seed layer from the write gap. This requires more extensive ion milling than would be necessary if the seed were not there. An undesirable byproduct of the ion mill process is that in addition to removing the desired write gap and lower pole material, it also undesirably consumes the upper pole pedestal. Therefore, the more extensive the ion mill is the more the upper pole pedestal will be consumed. The additional milling required to remove the seed layer, also means that additional upper pole material must be removed. 
   The presence of a seed layer on the write gap also degrades magnetic performance. In a most preferred arrangement, a magnetically soft high magnetic moment, high saturation (high Bsat) material would occupy the space closest to the write gap in the pole tip region. This is because this is the region where magnetic flux is most desirably concentrated in order to generate the strongest possible magnetic field at the write gap. However, the seed layer deposited on the write gap is not the most desirable, magnetically soft, high moment, high Bsat material, but is by necessity the material closest to the write gap. Therefore, the most desirable material (that which is plated over the seed layer) gets pushed up to a less desirable location. 
   Therefore, eliminating the need for a seed layer over the write gap would provide several advantages. One way to eliminate the need for such a seed would be to make use an electrically conductive write gap, such as a metal write gap. One possible material could be for example Rh. However, the use of such metallic write gap materials presents its own challenges. For example, the material removal process needed to remove the metal write gap material over the back gap area might be corrosive to the magnetic back gap material. Furthermore, once the back gap has been exposed, the large surface area of the metal write gap material combined with the much smaller area of the back gap creates a severe electrolytic reaction, with the back gap essentially becoming a sacrificial anode. When exposed to the plating bath during plating of the second pole, the back gap becomes severely corroded and full of voids. The voids in the back gap can even trap plating solution which can continue the corrosion even in the completed head leading to in situ failure of the head. 
   Therefore, there remains a strong felt need for a manufacturing process that will allow the use of a conductive metal write gap that will address the corrosion issues typically associated with such a metal write gaps. Such a method would preferably utilize existing manufacturing techniques and not result in inordinate extra manufacturing processes. 
   SUMMARY OF THE INVENTION 
   The present invention provides a magnetic write head having an electrically conductive metal write gap that extends only partially to a back gap of the write head. The remainder of the distance between the pole tip and the back gap can comprise a magnetic material. 
   The present invention provides the advantages of using a metal write gap, that is that no seed layer is required to plate magnetic structures there over. This allows the most desirable high magnetic moment, high Bsat material to be deposited directly on the write gap material where it is most needed. The elimination of the seed layer also reduces the amount of milling required to perform the desired notching needed to form a self aligned pedestal on the first pole. The present invention provides these benefits avoiding the electrolytic corrosion of the back gap during plating. This achieved by minimizing the amount of metal write gap material available for electrolytic reaction with the back gap. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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. 
       FIG. 1  is a schematic view illustrating a magnetic data storage system in which the present invention can be embodied; 
       FIG. 2  is a plan view taken from line  2 — 2  of  FIG. 1 , shown enlarged, magnetic write head of the present invention; 
       FIGS. 3–6 , are a cross sectional views illustrating various stages of development of a write head having a metal write gap and constructed using prior art manufacturing methods; 
       FIG. 7  is a cross sectional view of a magnetic write head according to an embodiment of the present invention; 
       FIGS. 8–12  are cross sectional views illustrating various stages of manufacture of a write head according to an embodiment of the present invention; and 
       FIG. 13  is a cross sectional view of an alternate embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The following description is the best embodiment 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. 
   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 an annular pattern of concentric data tracks (not shown) on the magnetic disk  112 . 
   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, the slider  113  is moved 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 . 
   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 the slider  113  off and slightly above the disk surface by a small, substantially constant spacing during normal operation. 
   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 . 
   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. 
   This invention provides a method of forming a write element. With reference to  FIG. 2 , a plan view of an exemplary write element  202 , can be seen in relation to a slider  113 . A coil  204 , passing through a magnetic yoke  206 , induces a magnetic flux in the yoke  206 . The magnetic flux in the yoke  206 , in turn causes a magnetic field to fringe out at the pole tip  208 . It is this fringing field  210  that writes magnetic signals onto a nearby magnetic medium. 
   As discussed above with reference to the Background of the Invention, it would be desirable to construct a magnetic write head using a conductive, metal write gap. However, attempts to construct such a metal write gap using processes similar to those used to construct dielectric write gaps have met with serious challenges, which can be better understood with reference to  FIGS. 3–6 . With reference to  FIG. 3 , a write head  300  in an intermediate stage of construction includes a first pole  302  having a first pedestal  304  in a pole tip region. A magnetic back gap  306  is provided on the first pole  302  at an end opposite the first pedestal  304 . A dielectric material  308  such as alumina Al 2 O 3  may be provided in the areas outside of the pole  302 . A magnetic coil  310  passes through the head  300  over the first pole  302 , between the first pedestal  304  and the back gap  306  and is insulated by an insulation layer  312 . An electrically conductive, non-magnetic write gap  314  could be provided on top of the insulation layer  312 , pedestal  304 , and back gap  306 . 
   With reference now to  FIG. 4 , a photoresist mask  402  could then be formed according to photolithographic methods familiar to those skilled in the art, leaving an opening over the back gap  306 . A material removal process  404 , such as for example, ion milling is performed to remove the uncovered portions of the write gap material. The photoresist mask  402  can then be removed, resulting in the structure shown in  FIG. 5 . 
   With reference to  FIG. 6 , a second magnetic pole  602 , can be plated onto the back gap  306 . Optionally a magnetic pedestal could be formed and a magnetic pole could be formed thereover. As can be seen, the back gap at this point is severely corroded and very little back gap material actually contacts the pole  602 . In the embodiment shown in  FIGS. 5 and 6 , about 5% or less of the area is CoFe and the rest is the metal write gap such as Rh. In the acidic plating solution, the Co becomes Co 2+ +2e − , and the hydrogen ions 2H + +2e −  become hydrogen gas H 2 , and as mentioned the corrosion of the back gap is greatly exacerbated by the large area of Rh write gap material and very small area of back gap material. 
   With reference now to  FIG. 7 , a magnetic write head  700  constructed according to an embodiment of the present invention achieves the benefits of an electrically conductive write gap  702 , while overcoming the corrosion problems described above with reference to  FIGS. 3–6 . The magnetic write head  700  includes a first pole  704  having a first magnetic pedestal P 1   706  formed there over at a pole tip region  708 , and a magnetic back gap  710  at an end opposite the pole tip  708 . A second pole  712  is formed over the first pole  704 , and is magnetically connected with the back gap  710  by a magnetic layer  714 . The second pole  712  is separated from the P 1  pedestal  706  by the write gap layer  702 . The first and second poles  712 , along with the back gap  710 , magnetic layer  714 , and P 1  pedestal  706  form a magnetic yoke, generally referred to as  715 . An electrically conductive coil  716 , only a portion of which is shown in cross section in  FIG. 7 , passes between the first and second poles  704 ,  712  between the P 1  pedestal  706  and back gap  710 . The coil is electrically isolated from the poles  704 ,  712 , pedestal  706  and back gap  710  by an insulation layer  718 , which could be for example alumina or hard baked photoresist. 
   With reference still to  FIG. 7 , the non-magnetic write gap layer  702  extends only partially beyond the P 1  pedestal. The remainder of the material beneath the second pole  712  is a magnetic material such as NiFe. As will be seen below, this greatly enhances manufacturability, avoiding corrosion of the back gap, while advantageously allowing the use of a metal write gap  702 . 
   With reference now to  FIG. 8 , the first magnetic pole  704  is provided. Fill material  802  such as alumina may be provided in the field areas. A magnetic layer  804 , which will become the P 1  pedestal  706 , is provided over the first pole  704 . The magnetic material is preferably a magnetically soft, high Bsat material such as laminated layers of NiFe or CoFe, and can be formed by electroplating. The back gap  710  is provided opposite the magnetic layer  804 , and can be formed in the same manufacturing step and of the same material as the as the magnetic layer  804 . A coil  716 , and surrounding insulation  718 , is formed by methods familiar to those skilled in the art, such as frame plating within a patterned hard baked photoresist or by damascene methods. 
   With continued reference to  FIG. 8 , the upper surface of the magnetic layer  804 , insulation  718 , and back gap  710  and field fill  802  are planarized by a process such as chemical mechanical polishing to create a smooth planar surface. A full film layer of non-magnetic, electrically conductive write gap material  806  such as Rh can then be deposited. Deposition of the Rh can be accomplished by sputter deposition. 
   With reference now to  FIG. 9 , a photoresist mask  902  is then formed over the region containing the magnetic layer  804  that will become the P 1  pedestal  706 . The photoresist mask  902  is preferably a bilayer photoresist, but could be a simple single layer mask. 
   Then, with reference to  FIG. 10  an ion mill  1002  can be performed to remove selected portions of the write gap material layer  806  that are not covered by the photoresist mask. Thereafter, with reference to  FIG. 11 , with the photoresist mask still in place, a layer of magnetic material  1102 , such as NiFe is deposited. The layer of magnetic material  1102  is preferably about the same thickness as the write gap material layer  806 , but can have a thickness plus or minus 50% that of the write gap material layer  806 . The magnetic layer  1102  can be deposited by sputter deposition. With reference to  FIG. 12 , the photoresist mask  902  can be removed and the second pole  712  can be formed by electroplating. It will be appreciated that, when the second pole  712  is being electroplated there is very little metal write gap material available and the majority of the surface area is covered by magnetic material  714 . This virtually eliminates the corrosion problem experienced by the method described with reference to  FIGS. 3–6 . 
   In fact the write gap material  702  preferably reaches less than 50 percent of the distance between the P 1  pole  706  and the back gap  710  the rest of the distance comprising the magnetic material  714 . More preferably, the write gap material  702  preferably reaches less than 20 percent of the distance to the back gap  710 , the rest of the distance comprising the magnetic material  714 . Similarly, the area of the write head  700  covered by the write gap material  702  is preferably less than 50% write gap material  702 , the remainder being magnetic material  714 . More preferably, the area of the write head consumed by the write gap material is less than 20% write gap material  702 , the remainder being the magnetic material  714 . 
   With continued reference to  FIG. 12 , after electroplating the second pole  712 , an ion milling operation  1200  can then be performed if desired, using the second pole  712  as a mask to self align the P 1  pedestal by notching according to method that will be familiar to those skilled in the art. It will be appreciated that the write gap  702  does not have a seed layer deposited thereon as would be necessary if the write gap had been constructed of a dielectric material. Therefore, the ion milling operation  1200  can be performed in a less invasive manner, removing less of the second pole  712  in the process than would be required if an additional seed layer had to be removed. A lapping operation  1202  can then be performed to up to an ABS location  1204  to form the head  700 . 
   With reference to  FIG. 13 , another embodiment of the invention includes a second coil layer  1302  and P 2  pedestal  1304 , and a second back gap pedestal  1305 . This embodiment can be constructed according to methods described above with the additional steps of plating the P 2  pedestal  1304  and forming the second coil  1302  and its surrounding insulation layer  1306 . The pedestal  1304  can then be used as a mask, to notch the P 1  pedestal  706  in a manner similar to that described above and with the same advantage of not requiring removal of additional seed layer material. In this embodiment, however, the magnetic material  714 , is preferably disposed substantially only between the back gap portions  710 ,  1305  in order to prevent shorting between the coils  716  and the magnetic yoke. 
   While various embodiments have been described above, it should be understood that they have been presented by way of example only, and not limitation. Thus, the breadth and scope of a preferred embodiment 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.