Abstract:
A magnetoresistive head having improved overwrite performance and a small trackwidth. The magnetoresistive head having a magnetic yoke formed of first and second poles joined at a back gap region and having an opposite write gap region. A pedestal with a top portion constructed of a high saturation moment material is provided on the first pole, limited to the write gap region and spaced from the read element so as to prevent popcorn noise in read sensor. The high moment pedestal is raised above surrounding structure causing the second pole to define a very low apex angle in the write gap region.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to magnetic disk data storage systems, and more particularly to magnetic write transducers and methods of making same. 
     Magnetic disk drives are used to store and retrieve data for digital electronic apparatuses such as computers. In FIGS. 1A and 1B, a magnetic disk data storage systems  10  of the prior art includes a sealed enclosure  12 , a disk drive motor  14 , a magnetic disk  16 , supported for rotation by a drive spindle S 1  of motor  14 , an actuator  18  and an arm  20  attached to an actuator spindle S 2  of actuator  18 . A suspension  22  is coupled at one end to the arm  20 , and at its other end to a read/write head or transducer  24 . The transducer  24  (which will be described in greater detail with reference to FIG. 2A) 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 of the surface of the magnetic disk  16 , or, as it is termed in the art, to “fly” above the magnetic 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 as indicated by the arrows P. The design and manufacture of magnetic disk data storage systems is well known to those skilled in the art. 
     FIG. 2A depicts a magnetic read/write head  24  including a substrate  25  above which a read element  26  and a write element  28  are disposed. Edges of the read element  26  and write element  28  also define an air bearing surface ABS, in a plane  29 , which can be aligned to face the surface of the magnetic disk  16  (see FIGS.  1 A and  1 B). The read element  26  includes a first shield  30 , an intermediate layer  32 , which functions as a second shield, and a read sensor  34  that is located within a dielectric medium  35  between the first shield  30  and the second shield  32 . The most common type of read sensor  34  used in the read/write head  24  is the magnetoresistive (AMR or GMR) sensor which is used to detect magnetic field signals from a magnetic medium through changing resistance in the read sensor. 
     The write element  28  is typically an inductive write element which includes the intermediate layer  32 , which functions as a first pole, and a second pole  38  disposed above the first pole  32 . The first pole  32  and the second pole  38  are attached to each other by a backgap portion  40 , with these three elements collectively forming a yoke  41 . The combination of a first pole tip portion  43  and a second pole tip portion  45  near the ABS are sometimes referred to as the yoke tip portion  46 . A write gap  36  is formed between the first and second poles  32 ,  38  in the yoke tip portion  46 . The write gap  36  is filled with a non-magnetic electrically insulating material that forms a write gap material layer  37 . This non-magnetic material can be either integral with (as is shown here) or separate from a first insulation layer  47  that lies below the second yoke  38  and extends from the yoke tip portion  46  to the backgap portion  40 . 
     Also included in write element  28  is a conductive coil  48 , formed of multiple winds  49  which each have a wind height Hw. The coil  48  can be characterized by a dimension sometimes referred to as the wind pitch P, which is the distance from one coil wind front edge to the next coil wind front edge, as shown in FIG.  2 A. As is shown, the wind pitch P is defined by the sum of the wind thickness Tw and the separation between adjacent winds Sw. The conductive coil  48  is positioned within a coil insulation layer  50  that lies above the first insulation layer  47 . The first insulation layer  47  thereby electrically insulates the coil layer from the first pole  32 , while the coil insulation layer  50  electrically insulates the winds  49  from each other and from the second pole  38 . 
     The configuration of the conductive coil  48  can be better understood with reference to a plan view of the read/write head  24  shown in FIG. 2B taken along line  2 B— 2 B of FIG.  2 A. Because the conductive coil extends beyond the first and second poles, insulation may be needed beneath, as well as above, the conductive coil to electrically insulate the conductive coil from other structures. For example, as shown in FIG. 3, a view taken along line  3 — 3  of FIG. 2A, a buildup insulation layer  52  can be formed adjacent the first pole, and under the conductive coil layer  48 . As is well known to those skilled in the art, these elements operate to magnetically write data on a magnetic medium such as a magnetic disk  16  (see FIGS.  1 A and  1 B). 
     More specifically, an inductive write head such as that shown in FIGS. 2A-3 operates by passing a writing current through the conductive coil layer  48 . Because of the magnetic properties of the yoke  41 , a magnetic flux is induced in the first and second poles  32 ,  38  by write currents passed through the coil layer  48 . The write gap  36  allows the magnetic flux to fringe out from the yoke  41  (thus forming a fringing gap field) and to cross a magnetic recording medium that is placed near the ABS. A critical parameter of a magnetic write element is a trackwidth of the write element, which defines track density. For example, a narrower trackwidth can result in a higher magnetic recording density. The trackwidth is defined by geometries in the yoke tip portion  46  (see FIG. 2A) at the ABS. These geometries can be better understood with reference to FIG.  3 . As can be seen from this view, the first and second poles  32 ,  38  can have different widths W 1 , W 2  respectively in the yoke tip portion  46  (see FIG.  2 A). In the shown configuration, the trackwidth of the write element  28  is defined by the width W 2  of the second pole  38 . The gap field of the write element can be affected by the throat height TH, which is measured from the ABS to the zero throat ZT, as shown in FIG.  2 A. The strength of the gap field strongly affects the over writing performance of a recording head. Thus, accurate definition of the trackwidth and throat height is critical during the fabrication of the write element. 
     However, the control of trackwidth, and throat height can be limited by typical fabrication processes, an example of which is shown in the process diagram of FIG.  4 . The method  54  includes providing a first pole with first and second edges in operation  56 . This operation can include, for example, forming a plating dam, plating, and then removing the dam. In operation  58 , a write gap material layer is formed over the first pole. In particular, the write gap material layer is formed over an upper surface and the first and second edges of the first pole. Also, in operation  58 , a via is formed through the write gap material layer to the first pole in the backgap portion  40  (see FIG.  2 A). In the instance herein described, the write gap material layer extends above the first pole in the area between the yoke tip portion and the backgap portion, although in other cases the write gap material layer may not be above this area A buildup insulation layer is also formed in operation  60 , adjacent the first and second edges, with the write gap material layer between the first pole and the buildup insulation layer. The buildup insulation layer is typically formed by depositing (e.g., spinning) and patterning photoresistive material and then hard baking the remaining photoresistive material. Such processes often result in the height of the buildup insulation layer being non-uniform and different than the height of the write gap material layer, as is illustrated in FIGS. 2A and 3. 
     The method  54  also includes forming a first coil layer above the write gap material layer and the buildup insulation layer in operation  62 . This can include first depositing a seed layer above the first pole. Typically, photoresistive material can then be deposited and patterned. With the patterned photoresistive material in place, conductive material can be plated. With removal of the photoresistive material the remaining conductive material thereby forms the first coil layer. 
     In operation  64 , the method  54  further includes forming a coil insulation layer above the first coil layer that is formed in operation  62 . In addition, a second pole is formed above the coil insulation layer of operation  64 , in operation  66 . 
     Still another parameter of the write element is the stack height SH, the distance between the top surface of the first pole  32  and the top of the second pole  38 , as shown in FIG.  2 A. Of course, this height is affected by the thickness of the first insulation layer  47 , the thickness of the coil layer  48  and any other coil layers that might be included, and the height Hi of the coil insulation layer  50  and any other coil insulation layers that might be included. The stack height can be an indicator of the apex angle α, which partially characterizes the topology over which the second pole must be formed near the yoke tip portion. Typically, the reliability of the write element decreases as the apex angle α increases. This is due, at least in part, to the corresponding increased difficulty, particularly in the yoke tip portion  46 , of forming the second pole  38  over the higher topography of the stack. For example, the definition of the second pole width W, shown in FIG. 3, including photoresist deposition and etching, can be decreasingly reliable and precise with increasing topography. When demand for higher density writing capabilities drives yoke tip portions to have smaller widths W, this aspect of fabrication becomes increasingly problematic. 
     Also, with higher topography, when the second pole is formed, for example by sputtering or plating, the material properties of the second pole in the sloped region, adjacent the second pole tip region  45 , can be undesirable. Thus, this decreased reliability results in undesirable lower production yield. 
     Adding further challenges to the design of recording heads, newer high end disk drive units require the maintenance of high over write performance for heads operating with sub-micron pole tips recording on high coercivity media. “Over write” is the recording of a new higher frequency signal on top of an older lower frequency signal. In order to meet these requirements such heads must impart a very strong fringing field using a yoke having a very small track width to provide high density recording capability. One method of meeting these design challenges is to use a high saturation moment material in the yoke  41 , for example in the first pole  32 . Such high saturation moment materials can be used to construct an entire first pole  32  or can be used on a portion of the first pole by constructing pedestals, not shown, at the write gap portion  46  and back gap  40  of the yoke. 
     Using such a high saturation moment material in the yoke  41  of a write head presents several difficulties. First, the use of a high saturation moment material in the first pole, especially in the back gap region has been found to contributed to “popcorn noise”. Popcorn noise is the undesirable phenomenon which occurs when the magnetic domain boundary movement in the write element extends to the region of the read sensor. In such a case the read sensor will detect the magnetic signal as a spike or “pop”. The greater the amount of high saturation moment material in use in the first pole of the write element, the greater the domain boundary expansion will be, especially when the back gap is also constructed of such a material. 
     Another problem with using such high saturation moment materials is their inherent corrosivity. The high temperatures required to cure the coil insulation layer  50  cause such materials to corrode. This corrosion problem has prevented such material from being used in magnetoresistive heads. 
     Therefore there remains a need for a write head which can take advantage of the magnetic properties of high saturation moment materials while eliminating popcorn noise and overcoming the corrosion problems inherent in the use of such materials. Such a head would preferably have a very low apex angle so as to provide improved magnetic flux characteristics and tolerance control in the manufacture of the second pole. Also, such a head would provide the ability to tightly control track width as well as stack height and the tolerances of the second pole. 
     SUMMARY OF THE INVENTION 
     The present invention provides a magnetoresistive head which uses a high saturation moment material to impart a strong fringing field while not exhibiting popcorn noise in an adjacently located read sensor. The head includes first and second magnetic poles joined to form the yoke having a closed end and an open end. The poles define therebetween a yoke interior. A pedestal constructed of a high saturation moment material is connected with the first pole at the open end of the yoke. The head also includes an electrically conducting coil, a portion of which passes through the interior of the yoke. The coil is electrically isolated from the yoke. 
     More particularly, the head includes a read element and a write element, both of which are built upon a ceramic substrate. The read portion includes a first magnetic shield and a second magnetic shield located thereover and separated by a distance. The space between the shields is filled with a first non-magnetic dielectric material in which a read sensor is embedded. 
     The second shield of the read element serves as a portion of the first pole of the write element. The first pole also includes a write gap pedestal formed at the ABS side of the first pole, and a back gap pedestal formed at the back gap end of the first pole. The write gap pedestal and back gap pedestal have upper surfaces which are smooth, flat and coplanar. A second layer of non-magnetic, dielectric material covers the first pole, extending beyond the edges thereof and has a smooth flat upper surface which is flush with the upper surfaces of the write gap and back gap pedestals. 
     A pedestal constructed of the high saturation moment material extends upward from the write gap pedestal, having a width somewhat less than that of the write gap pedestal. A thin layer of non-magnetic, electrically insulating write gap material covers the high saturation moment pedestal as well as the other pedestals and the second dielectric layer. The electrically conductive coil sits atop the write gap material, and is in the form of a planar helix constructed of copper and having inner and an outer contacts disposed outside of the yoke. 
     A coil insulation layer covers the coil and is formed so that it does not cover the pedestals. The coil insulation layer is also formed with vias at the locations of the coil contacts. The coil insulation layer is cured to form gradually sloping edges, and due to the increased height of the high moment pedestal, has an especially gradual slope at the edge adjacent that pedestal. 
     The second pole is formed over the first pole and over the coil insulation layer. Since the coil insulation layer has an especially gradual slope at the high moment pedestal, the second pole can likewise be formed to define an especially low apex angle. This low apex angle improves the magnetic flux flow properties of the yoke and also allows the second pole to be constructed with increased precision. 
     Locating the high moment material only at the top portion of the first pole pedestal effectively separates the high moment material effect from the read element, thereby reducing popcorn noise. Furthermore, providing the high moment material only at the write gap region of the yoke where it is needed, further reduces popcorn noise. 
     These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following descriptions of the invention and a study of the several figures of the drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     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; 
     FIG. 1B is a top plan view taken along line  2 B— 2 B of FIG. 2A; 
     FIG. 2A is a cross-sectional view of a prior art read/write head of the magnetic disk drive assembly of FIGS. 1A and 1B; 
     FIG. 2B is a plan view taken along line  2 B— 2 B of FIG. 2A; 
     FIG. 3 is an ABS view taken along line  3 — 3  of FIG. 2A; 
     FIG. 4 is a process diagram of a method for forming a write element of the background art; 
     FIG. 5 is a cross sectional view of a read/write head of the present invention taken along line  5 — 5  of FIG. 1B shown expanded and rotated 110 degrees clockwise; 
     FIG. 6 is a cross sectional view taken along line  6 — 6  of FIG. 5; 
     FIG. 7 is a process diagram of a method of forming a write element of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     With reference to FIG. 5, the present invention is embodied in a combination read/write head, generally designated  500  including a read portion  502  and a write element  504 , all of which is built upon a ceramic substrate  506 . The read/write head  500  terminates at an end, the surface of which defines an air bearing surface (ABS). 
     The read portion  502  includes first and second shields  508  and  510  formed adjacent one another and separated by a distance. A first layer of dielectric material  512  is sandwiched between the first and second shield and a read sensor  513  is embedded within the dielectric layer at the end adjacent the ABS. The second shield  510  has a smooth planar upper surface  514 . The dielectric layer  512  extends beyond the end of the first and second shields  506  and  510  opposite the ABS and also extends beyond the edges of the shields, as can be seen more clearly with reference to FIG. 6, to rise to a level flush with the smooth upper surface  514  of the second shield  510 . 
     The write portion  504  of the read/write head  500  includes a yoke  515  having an open end adjacent the ABS and an opposite closed end. The yoke  515  includes a first pole  516  and a second pole  540  which define therebetween an interior through which passes a conductive coil  517  which is electrically isolated from the yoke  515 . 
     With continued reference to FIG. 5, the second shield  510  serves as a portion of the first pole  516  of the write element  504 . The first pole  516  also includes a write gap pedestal  518  which extends from the upper surface  514  of the second shield  510 . The write gap pedestal has a smooth planar upper surface  520 . Similarly, the first pole includes a back gap pedestal  522  which extends from the upper surface  514  of the second shield  510  at the end opposite the write gap pedestal. The back gap pedestal  522  has a smooth planar upper surface  524  which is coplanar with the upper surface  520  of the write gap pedestal  518 , the upper surfaces  520  and  524  together defining a plane  526 . While the shield  510 , write gap pedestal  518  and back gap pedestal  522  could be constructed of any suitable magnetic material, they are preferably constructed of Ni 80 Fe 20 . 
     A second layer of dielectric material  528  is covers the second shield  510  of the first pole  516  and also extends over the first dielectric layer  512  in the area beyond the first pole  516 . The second dielectric layer  528  has a smooth planar upper surface  530  which is flush with the upper surfaces  520  and  524  of the pedestals  518  and  522  across the plane  526 . While the dielectric layer  528  could be constructed of any suitable dielectric material, it is preferably constructed of Al 2 O 3 . 
     With reference to FIGS. 5 and 6, the first pole further includes a high saturation moment. (high moment) pedestal  532 . The high moment pedestal has a width which is relatively narrow compared with the write gap pedestal  518 , as can be seen more clearly with reference to FIG.  6 . The width of the high moment pedestal defines the track width (TW) of the w rite element  504 . The smooth surface of the write gap pedestal  518  allows the high moment pedestal to be constructed with high precision to define a very narrow track width which allows the write element  504  to write data with a higher density, as described in the background of the invention. While the high moment pedestal  532  could be constructed of any suitable high moment material it is preferably constructed of Ni 65 Fe 35 , Ni 55 Fe 45 , Ni 45 Fe 55 , CoZrCr or FeXN, where X stands for Rh, Al, Ta, etc. 
     With continued reference to FIGS. 5 and 6, a layer of non-magnetic, electrically insulating write gap material  534  covers the high moment pedestal  532 , second insulation layer  528 , and the exposed portion of the write gap pedestal  518 . The write gap material layer  534  can be formed of various non-magnetic, electrically insulating materials, however it is preferably formed of Alumina (Al 2 O 3 ) or alternatively of SiO 2 . The write gap material layer is formed so as not to cover the back gap pedestal. 
     Upon the write gap material, the coil  517  is formed. The coil is formed as an electrically conductive planar helix configured such that a portion thereof passes over the first pole  516  in the region between the write gap pedestal  518  and the back gap pedestal  522 . While the coil can consist of any suitable electrically conducting material, it is preferably constructed of copper, plated onto the write gap material. 
     With reference to FIG. 5, a coil insulation layer,  538  covers the coil and the dielectric layer. The coil insulation layer  538  does not cover the high moment pedestal  532  and does not cover the back gap pedestal  524 . In addition, vias are provided in the coil insulation layer to provide access to a pair of coil contacts, not shown. The coil insulation layer has gently sloping edges due to a curing procedure which will be discussed below. The edge of the coil insulation layer  538  adjacent the high moment pedestal  532  has a low slope due to the relatively high elevation of the high moment pedestal. 
     With the third coil insulation layer  538  deposited, a second pole  540  can be formed thereover. The second pole  540  contacts the write gap material  534  in the region of the high moment pedestal and also contacts the upper surface  524  of the back gap pedestal  522 . While the second pole could be formed of any suitable magnetic material, it is preferably constructed of Ni 45 Fe 55 , deposited by plating. 
     The low slope of the third dielectric layer  538  in the region of the high moment pedestal causes the second pole  540  to have a very low apex angle  542 . This is due to the fact that the dielectric layer does not have to rise very high above the high moment pedestal to cover the coil  517 . This reduced apex angle allows the second pole to be constructed with a smaller and more accurately controlled track width as discussed in the Background of the Invention. The reduced apex angle  542  also improves flux flow characteristics through the second pole  540 , leading to improved magnetic performance of the write element  504 . 
     In operation, the high moment pedestal  518  allows efficient concentration of magnetic flux in the write gap portion of the yoke  515 . This provides a significantly increased fringing field at the write gap, improving the overwrite characteristics of the write element  504  and beneficially allowing the write element to impart a signal on a high coercivity recording medium. The present invention eliminates popcorn noise in the read sensor  513  which would otherwise be caused by the use of such a high moment material. This is achieved by maintaining a sufficient distance between the high moment pedestal  532  and the read sensor  513 , as well as by limiting the high moment material only to a small portion of the first pole  516 . When constructing the high moment pedestal  532  of a high magnetostrictive material, the height of the pedestal must be limited to, for instance, between 1 and 2 times the thickness of the write gap, or limited to between 0.1 and 1 microns. More preferably the height is 1.5 times the thickness of the write gap or 0.5 microns. 
     With reference now to FIG. 7, a method  700  of forming a read write head of the present invention will be described. With the read element  502  having been already constructed according to methods of the background art, the method  700  begins with a step  702  of providing the second shield portion of the first pole  510 . The shield  510  can be constructed of several magnetic materials, but is preferably Ni 80 Fe 20 . Then in a step  704 , the write gap pedestal  518  and back gap pedestal  522  are formed. The pedestals  518  and  522  are also preferably constructed of Ni 80 Fe 20  and are formed by masking and plating. Subsequently, in a step  706  the second dielectric layer  528  is deposited over the shield  510  as well as the write gap and back gap pedestals  518  and  524 . In a step  708 , the dielectric layer  528  is polished using a chemical mechanical polishing process. The polishing is performed sufficiently to expose and planarize the top surfaces  520  and  524  of the pedestals  518  and  522  thereby creating the smooth planar surface  530  of the dielectric layer across plane  526 . Thereafter, in a step  710 , the high moment pedestal  532  is constructed on top of the write gap pedestal  518 . The high moment pedestal is preferably constructed of Ni 45 Fe 55  deposited by masking and plating. Alternatively, the high moment pedestal is constructed of CoZrCr or FeXN, where X represents Rh, Al, Ta, etc., deposited by a sputtering process. However, with either choice of materials, the smooth planar surface  520  generated on the write gap pedestal  518  by the chemical mechanical polishing (CMP) process of step  708  allows the high moment pedestal to be constructed with extremely high precision to define a very narrow track width. 
     Subsequently in a step  712  the write gap material  534  is deposited over the high moment pedestal  532  and over the dielectric layer  528 . The write gap material is locally removed at the location of the back gap pedestal  522  to expose the surface  524  of the back gap pedestal. This localized removal of the write gap material is performed by an etching process. Then, in a step  714 , the coil  517  is formed over the write gap material  534 . To form the coil,  517  a copper seed layer is first deposited over the write gap material  534 . Then the coil is masked and plated in the desired configuration. After plating the coil the seed layer is removed by etching. In a step  716 , the coil insulation layer is deposited. The coil insulation layer is preferably a spun photoresist. The photoresist is masked and exposed. The mask is then lifted off to remove the photoresist material from the high moment pedestal  532  and the back gap pedestal  522 . The photoresist is also masked and lifted off to provide vias for providing access to coil contacts, not shown. The photoresist is then cured. Finally, in a step  718 , the second pole  540  is formed. The second pole is preferably constructed can be constructed of a high magnetic moment material, preferably using Ni 45 Fe 55  which can be deposited by plating. 
     Curing the photoresist material of the coil insulation layer gives it a gently sloping edge which advantageously allows the second pole to be formed with a low apex angle  542 . However, the high moment material of the pedestal  532  is prone to corrosion at the high temperatures required to cure the photoresist. The present invention, however, solves this problem by covering the high moment pedestal  532  with the write gap material  534 . This effectively prevents such corrosion of the high moment pedestal. 
     Conducting the CMP process provides a smooth planar surface on which to build the second pole  540 . However such a process cannot be conducted after forming the high moment pedestal  532 , because doing so would render impossible an accurate control the height of the high moment pedestal. By conducting the CMP process before building the high moment pedestal, it is possible to realize the advantages of the CMP process when constructing the second pole  540  without affecting the height of the high moment pedestal. 
     From the above it will be appreciated that the present invention provides a read write head capable of providing sufficient flux field to provide high overwrite performance even with the use of high coersivity recording media. Further the present invention exhibits such high performance write characteristics while avoiding undesirable popcorn noise in the read sensor. While the invention has been described in terms of a preferred embodiment, other embodiments of the invention, including alternatives, modifications, permutations and equivalents of the embodiments described herein, will be apparent to those skilled in the art from consideration of the specification, study of the Figures, and practice of the invention. Therefore, the embodiments and preferred features described above should be considered exemplary, with the invention being defined by the appended claims, which therefore include all such alternatives, modifications, permutations and equivalents as fall within the true spirit and scope of the present invention.