Abstract:
An inductive write element for use with a magnetic data recording and retrieval system is provided. The write element includes a magnetic yoke having an electrically conductive coil passing there through. The yoke is constructed of first and second magnetic poles, and performance of the write element is improved by the inclusion of a very thin pedestal of a high magnetic moment material on the first pole in the pole tip region. Further performance gains are realized by providing a tapered edge on the pedestal to facilitate magnetic flux flow through the pedestal.

Description:
FIELD OF THE INVENTION 
     This invention relates generally to magnetic disk storage systems, and more particularly to write heads having low height, high moment pedestals. 
     BACKGROUND OF THE INVENTION 
     Magnetic disk drives are used to store and retrieve data for digital electronic apparatus such as computers. In FIGS. 1A and 1B, a magnetic disk data storage system  10  of the prior art includes a sealed enclosure  12 , a disk drive motor  14 , one or more magnetic disks  16 , supported for rotation by a drive spindle  13  of motor  14 , and an actuator  18  including at least one arm  20 , the actuator being attached to an actuator spindle  21 . Suspensions  22  are coupled to the ends of the arms  20 , and each suspension supports at its distal end a read/write head or transducer  24 . The head  24  (which will be described in greater detail wit reference to FIGS. 2A and 2B) typically includes an inductive write element with a sensor read element As the motor  14  rotates the magnetic disk  16 , as indicated by the arrow R, an air bearing is formed under the transducer  24  causing it to lift slightly off the surface of the magnetic disk  16 , or, as is termed in the art, to “fly” above the magnet disk  16 . Alternatively, some transducers, known as contact heads, ride on the disk surface. Various magnetic “tracks” of information can be written to and/or read from the magnetic disk  16  as the actuator  18  causes the transducer  24  to pivot in a short arc. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art. 
     FIG. 2A shows the distal end of the head  24  having a write element  26 . The write element  26  is shown enlarged and with portions exposed for clarity. The write element  26  includes a magnetic yoke  28  having an electrically conductive coil  30  passing therethrough. 
     The write element  26  can be better understood with reference to FIG. 2B, which shows the write element  26  and an integral read element  32  in cross section. The head  24  includes a substrate  34  above which the read element  32  and the write element  26  are disposed. An edge of the read element  32  and of the write element  26  also define an air bearing surface ABS, in a plane  36 , which can be aligned to face the surface of the magnetic disk  16  (see FIGS.  1 A and  1 B). The read element  32  includes a first shield  38 , a second shield  40 , and a read sensor  42  that is located within a dielectric medium  44  between the first shield  38  and the second shield  40 . The most common type of read sensor  42  used in the read/write head  24  is the magnetoresistive (AMR or GMR) sensor, which is used to detect magnetic field signal changes in a magnetic medium by means of changes in the resistance of the read sensor imparted from the changing magnitude and direction of the magnetic field being sensed. 
     The write element  26  is typically an inductive write element that includes the second shield  40  (which functions as a first pole for the write element) and a second pole  46  disposed above the first pole  40 . Since the present invention focuses on the write element  26 , the second shield/first pole  40  will hereafter be referred to as the “first pole”. The first pole  40  and the second pole  46  contact one another at a backgap portion  48 , with these three elements collectively forming the yoke  28 . The combination of a first pole tip portion and a second pole tip portion near the ABS are sometimes referred to as the yoke tip portion  50 . A write gap  52  is formed between the first and second poles  40  and  46  in the yoke tip portion  50 . The write gap  52  is filled with a non-magnetic, electrically insulating material that forms a write gap material layer  54 . This non-magnetic material can be either integral with (as is shown here) or separate from a first insulation layer  56  that lies upon the first pole  40  and extends from the yoke tip portion  46  to the backgap portion  40 . The conductive coil  30 , shown in cross section, passes through the yoke  28 , sitting upon the write gap material  54 . A second insulation layer  58  covers the coil and electrically insulates it from the second pole  46 . 
     An inductive write head such as that shown in FIGS. 2A and 2B operates by passing a writing current through the conductive coil  30 . Because of the magnetic properties of the yoke  28 , a magnetic flux is induced in the first and second poles  40  and  46  by write currents passed through the coil  30 . The write gap  52  allows the magnetic flux to fringe out from the yoke  28  (thus forming a fringing gap field) and to cross a magnetic recording medium that is placed near the ABS. 
     With reference to FIG. 2C, a critical parameter of a magnetic write element is the trackwidth of the write element, which defines track density. For example, a narrower trackwidth can result in a higher magnetic recording density. The Width is defined by the geometries in the yoke tip portion at the ABS. In some newer designs a pedestal  60  is construed of a high magnetic moment material (high B sat ), having a width W 3 . The high B sat  pedestal promotes concentration of magnetic flux in the yoke tip region  50  of the write element  26 . As can be seen from this view, the first and second poles  40  and  46  can have different widths W 2  and W 1  respectively in the yoke tip portion  50 . The pedestal has a width W 3 , which in some implementations can have the same width as that of the second pole W 1 , as when the pedestal is created by a self aligning process. 
     With reference to FIG. 2B, the fringing gap field of the write element can be further affected by the positioning of the zero throat level ZT. ZT is defined as the distance from the ABS to the first divergence between the first and second pole, and it can be defined by either the first or second pole  40 ,  46  depending upon which has the shorter pole tip portion. If the first pole  40  includes a pedestal  60 , then ZT is usually defined by the pedestal depth. The pedestal provides a well defined ZT. In order to prevent flux leakage from the second pole  46  into the back portions of the first pole  40 , it is desirable to provide a zero throat level in a well defined plane which is parallel to the plane of the ABS. Thus, accurate definition of the trackwidth, and zero throat is critical during the fabrication of the write element. 
     The performance of the write element is further dependent upon the properties of the magnetic materials used in fabricating the poles of the write element. In order to achieve greater overwrite performance, magnetic materials having a high saturation magnetic flux density B sat  are preferred. A common material employed in forming the poles is high Fe content (55 at % Fe) NiFe alloy having a B sat  of about 16 kG. However, high Fe content NiFe alloy has a high magnetostriction constant λs (on the order of 10 −5 ) which causes undesirable domain formation in the poles. It is known that the domain wall motion in the writer is directly related to the increase in popcorn noise in the read element, especially when the motion occurs in the first pole, which also serves as a shield for the read element. 
     A reduction in popcorn noise in the read element can be achieved through the use of soft magnetic materials, (i.e. materials having a low magnetostriction constant) in the fabrication of the first pole  40 . However, such materials generally have limited B sat . In order to promote concentration of magnetic flux density in the yoke tip region, a high B sat  material is used to form the pedestal  60 . 
     The size and shape of the pedestal has dramatic affect on the flow of magnetic flux in the yoke tip region  50 . For example, the abrupt angle between the pedestal  60  and the rest of the first pole  40  inhibits flux flow and can lead to choking or saturation of flux. In addition, a thick pedestal (i.e. in the direction from the first pole  40  to the write gap  52 ) causes further choking of the flux and also leads to poorly defined signal pulses. Therefore, accurate control of pedestal size and shape is critical. Creating a pedestal which is sufficiently thin and also has a desirable shape has been limited by available manufacturing techniques. For example, existing manufacturing techniques which employ CMP can not be used to construct a pedestal with a tightly controlled thickness, thus limiting the pedestal to an overall minimum size. 
     Therefore, there remains a need for a process for manufacturing a desired thin pedestal. The process would necessarily allow tighter control of thickness than is possible with previous processes and would also allow the shape of the pedestal to be controlled to soften the angle of the transition between the pedestal and the rest of the first pole  40 . In addition, the process would allow the pedestal to be constructed of a high B sat  material, many of which materials must be sputter deposited. 
     SUMMARY OF THE INVENTION 
     The present invention provides a method for manufacturing a write element for use in a magnetic data recording system, the write element having a thin pedestal having a well controlled shape and size. A first pole is constructed of a soft magnetic material. A layer of high B sat  material is then deposited onto the magnetic material of the first pole. A bi-layer photoresist is patterned onto the layer of high B sat  material in a pattern corresponding to the desired pedestal shape. The high B sat  material layer is then etched, forming a pedestal with a tapered edge, by removing material from the region not covered by the bi-layer photoresist A first insulation layer is then deposited, and the bi-layer photoresist is subsequently lifted off. Thereafter, a layer of write gap material is deposited and an electrically conductive coil is formed on the write gap material. A second insulation layer is applied, and a second pole is formed so as to be electrically connected with the first pole. 
     The etching can be performed in such a manner that the edge of the pedestal can be a smoothly tapered. This advantageously promotes smooth flux flow through the pole tip region of the first pole. In addition, the process allows the high B sat  material to be sputter deposited. This is advantageous in that currently available high B sat  materials cannot be plated and must, therefore, be sputter deposited. 
     Another aspect of the invention is that it allows excellent control of pedestal thickness. One reason that the thickness of the pedestal can be tightly controlled is that chemical mechanical polishing is not required. CMP processes remove material in a manner which is difficult to accurately control, and therefore a relatively large tolerance in pedestal thickness would be required if such a process were used. 
     The bi-layer photoresist includes a first layer and a second layer that covers and extends beyond the edge of the first layer. The portion of the second layer extending beyond the first layer creates an overhang. When the first insulation layer is subsequently applied, the first insulation layer will form a smooth tapered edge terminating beneath the overhang. The termination point of the insulation layer can be controlled by the amount of overhang on the bi-layer photoresist or can also be controlled by the manner in which the first insulation layer is deposited. Although the deposited first insulation layer will cover the photoresist, the portion under the overhang will be accessible to chemicals for lifting off the photoresist. 
     For a fuller understanding of the nature and advantages of the present invention, reference should be made to the following detailed description taken together with the accompanying figures. 
     BRIEF DESCRIPTION OF THE FIGURES 
     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, with like reference numerals designating like elements. 
     FIG. 1A is a partial cross-sectional front elevation view of a magnetic data storage system of the background art; 
     FIG. 1B is a top plan view taken along line  1 B— 1 B of FIG. 1A; 
     FIG. 2A is a plan view of a read/write head of the background art, taken from  2 A— 2 A of FIG. 1B, shown enlarged; 
     FIG. 2B is a view taken from line  2 B— 2 B of FIG. 2A, shown enlarged; 
     FIG. 2C is a view taken from line  2 C— 2 C of FIG. 2B; 
     FIG. 3 is a cross sectional view similar to FIG. 2B showing a read/write head of the present invention; 
     FIG. 4 is a flow diagram of a process for producing a read/write head of the present invention; and 
     FIGS. 5-9 show the read write head of the present invention in various, intermediate stages of manufacture. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 3, the present invention is embodied in a combination read/write head, generally designated  61 , having merged read and write elements  62 ,  64 , construction of the read element having been previously discussed in the background of the invention with reference to FIGS. 1A through 2C. The write element  64  includes first and second magnetic poles  66 ,  68 , which join to form a magnetic yoke  70 . An electrically conductive coil  72  passes through the interior of the yoke  70 , and is electrically isolated therefrom. The first magnetic pole includes at its pole tip portion a pedestal  74  which will be described in greater detail below. 
     With continued reference to FIG. 3, the first pole  66  is primarily constructed of a soft magnetic material (i.e. low magnetorestriction). A pedestal  74  is formed on the first pole  66  at the pole tip region, constructed of a high B sat  material. The pedestal is very thin, preferably between 0.1 and 1.0 μm, and more preferably less than 0.5 μm. The pedestal has a smoothly tapered edge  76 . The smoothly tapered edge  76  facilitates the smooth flow of magnetic flux through the pole tip region of the first pole  66 . 
     A first insulation layer  78  covers the first pole  66 , and terminates at the pedestal  74 . The first insulation layer  78  preferably terminates in a smoothly tapered edge which ends near the apex of the tapered edge as shown in FIG.  3 . Depending upon design requirements, the tapered edge of the first insulation layer can be located at various locations relative to the pedestal  74 . For example, if desired, the first insulation layer  78  can be formed to terminate at the upper surface of the pedestal beyond the tapered edge  76 . Alternatively, if desired, the edge of the first insulation layer can be formed to end along the tapered edge  76  at a lower point away from the apex and toward the termination of the tapered edge  76 . The first insulation layer  78  is preferably formed of Al 2 O 3  which is sputter deposited. However, as will be appreciated by those skilled in the art, other dielectric materials can be used as well. 
     With continued reference to FIG. 3, a layer of write gap material  80  sits atop the first insulation layer  78  and the pedestal  74 . The write gap material is preferably constructed of silicon, but can also be constructed of other dielectric materials such as Al 2 O 3 . The electrically conductive coil  72  includes a plurality of winds, with a portion of each wind passing through the yoke  70 . The coil sits atop the write gap material layer  80 . The coil is preferably constructed of copper (Cu) and is manufactured according to a photolithographic process, which will be familiar to those skilled in the art. 
     With further reference to FIG. 3, a second insulation layer  81  covers the coil  72  and electrically insulates it from the yoke  70 . The second insulation layer  81  is preferably constructed of cured photoresist which is deposited by a pbotolithographic process and cured at a high temperature. the second pole  68  covers the second insulation layer  81  and electrically couples with the first pole  66  at a backgap region  82  to form the yoke  70 . 
     With reference to FIG. 4, a process  84  for constructing the write element  64  of the present invention will be described. The read element  62  having been partially constructed according to methods familiar to those skilled in the art, the process  84  begins with a step  86  of providing the first pole  66 . The first pole  66  is preferably formed of a nickel iron alloy NiFe by a plating process which will be familiar to those skilled in the art, but can also be deposited by sputtering and can be formed of another soft magnetic material. Then, in a step  88  a protective layer of alumina (Al 2 O 3 ) is sputter deposited to provide electrical insulation between S 1  and a read element interconnect (not shown). Then, in a step  90  vias (not shown) are provided for a set of read sensor leads (also not shown). The leads vias are formed by a wet etch process which will be familiar to those skilled in the art. Thereafter, in a step  92  a read element interconnect is formed (not shown). The interconnect is electroplated copper formed to about 1.0 to 1.5 μm, which is thinner than the final target thickness of the first pole  66  (FIG.  3 ). Thereafter, in a step  94  another layer of Al 2 O 3  is deposited and planarized using a chemical mechanical polishing process. This results in a layer of insulation  95  having a smooth upper surface (FIG.  3 ), which is flush with a smooth upper surface of the first pole  66 . The chemical mechanical polishing process preferably results in a first pole  66  that is 1.5-3 μm thick. 
     With continued reference to FIG. 4, in a step  96  a layer  120  of high B sat  material is deposited This layer is deposited as a thin film, which is preferably deposited onto the first pole  66  and insulation  95  either by sputtering or electroplating, as can be seen in FIG.  5 . In one embodiment of the invention, the high B sat  material is FeXN, wherein X is one or more of Rh, Ta or Al. This material can be either sputter deposited in a single layer or applied as a plurality of laminated films, and is preferably deposited to a thickness of 0.1-1.0 μm, or more preferably less than 0.5 μm. Thereafter, in a step  98 , a photolithography process is used to form a bi-layer photoresist  100  which can be more clearly understood with reference to FIG.  6 . The bi-layer photoresist is formed to pattern the pedestal  74 , and includes a bottom layer  112 , and an upper layer  114  which extends beyond the first layer forming an overhang  116 . Thereafter, in a step  118 , an ion milling process is performed to selectively remove unwanted high B sat  material, forming the pedestal  74  as can be seen with reference to FIG.  7 . The ion milling process is preferably performed so as to form a desirable sloped or tapered edge  76  on the pedestal  74 . 
     With continued reference to FIG. 4, in a step  122  a layer of Al 2 O 3    124  is deposited. With reference to FIG. 8 it will be appreciated that the Al 2 O 3  insulation layer  124  as deposited covers the first pole  66  and the bi-layer photoresist  100 . In addition, the insulation layer  124  partially covers the portion of the pedestal covered by the overhang  116  of the bi layer photoresist  100 . The insulation layer terminates in a smoothly tapered edge, and the location at which the insulation terminates can be controlled by controlling the amount of overhang of the bi-layer photoresist  100  and can also be controlled by the deposition process used to deposit the insulation layer. The location of the termination of the insulation layer can be controlled to within +/−0.25 μm of a predetermined target location relative to the tapered edge of the pedestal. The insulation layer preferably has an edge which terminates near the apex of the tapered edge of the pedestal, that is, at the point where the tapered edge meets the flat top of the pedestal. In addition, the insulation layer  124  preferably is formed to a height that is roughly the same as the height of the pedestal. 
     With reference still to FIG. 4, in a step  126  the bi-layer photoresist  100  is lifted off. This is accomplished by applying a solvent. However, as will be appreciated by those skilled in the art, solvents used to remove such a photoresist will not dissolve the AL 2 O 3 . The overhang  116  provided by the bi-layer photoresist  100  facilitates lifting off the photoresist  100 , by leaving a portion of the photoresist  100  uncovered by Al 2 O 3 . Thus, the overhang  116  allows solvent to enter and contact the photoresist in order to lift it off. 
     Thereafter, in a step  128 , a layer of write gap material  80  is deposited. Then, in a step  130 , a coil  72  is formed. The coil is preferably constructed of copper formed by a plating process which will be familiar to those skilled in the art. Subsequently, in a step  132  another insulation layer is deposited, thus forming the second insulation layer  81  discussed with reference to FIG.  3 . Then, in a step  134  the second pole  68  is formed. The second pole is constructed of magnetic material, such as for instance FeXN and can be formed by sputtering or plating as necessitated by the choice of material. 
     While the present invention has been particularly shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes in form and detail may be made without departing from the spirit, scope, and teaching of the invention. Accordingly, the disclosed invention is to be considered merely as illustrative and limited in scope only as specified in the appended claims.