Patent Publication Number: US-6221218-B1

Title: Method of forming an inductive write head for magnetic data storage media

Description:
This is a continuation-in-part of prior copending U.S. patent application No. 09/199,252, filed on Nov. 23, 1998, the disclosure of which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to magnetic disk data storage systems, and more particularly to inductive write heads for magnetic data storage media. 
     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 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  typically includes an inductive write element with a sensor read element (which will be described in greater detail with reference to FIG.  1 C). 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 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. 1C depicts a magnetic read/write head  24  including a write element  26  and a read element  28 . The edges of the write element  26  and read element  28  also define an air bearing surface ABS, in a plane  29 , which faces the surface of the magnetic disk  16  shown in FIG. 1A and 1B. 
     The read element  28  includes a first shield  36 , an intermediate layer  31 , which functions as a second shield, and a read sensor  40  that is located between the first shield  36  and the second shield  31  and suspended within a dielectric layer  37 . The most common type of read sensor  40  used in the read/write head  30  is the magnetoresistive sensor which is used to detect magnetic field signals from a magnetic medium through changing resistance in the read sensor. 
     The write element  26  is typically an inductive write element. The intermediate layer  31  is shared between the read element  28  and the write element  26 , forming a first pole of the write element  26 . With a second pole  32 , the first pole  31  forms a yoke  38 . A write gap  30  is formed between the first pole  31  and the second pole  32 . Specifically, the write gap  30  is located adjacent to a portion of the first pole and second pole which is sometimes referred to as the yoke tip region  33 . The write gap  30  is filled with a non-magnetic material  39 . Also included in write element  26 , is a conductive coil  34  that is positioned within a dielectric medium  35 . The conductive coil  34  of FIG. 1C is formed of a first coil C 1  and a second coil C 2 . 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 . 
     In FIG. 1D, a view taken along line  1 D— 1 D of FIG. 1C (i.e., perpendicular to the plane  29  and therefore perpendicular to the air bearing surface ABS) further illustrates the structure of the write element  28 . As can be seen from this perspective, a pole width W of the first pole  31  and second pole  32  in the yoke tip region  30  are substantially equal. A parameter of any write element is its trackwidth which affects its performance. In the configuration of FIG. 1D, the trackwidth is defined by the pole width W. 
     FIGS. 1E and 1F show two views of another prior art read/write head. The read element  28  of FIG. 1E is substantially the same as in the read/write head of FIG.  1 C. However, above and attached to the first pole  31 , is a first yoke pedestal Y 1 P in the yoke tip region  33 , abutting the ABS. In addition, a second yoke pedestal Y 2 P is disposed above and aligned with the first yoke pedestal Y 1 P. Further, the second yoke pedestal Y 2 P is adjacent to the second pole  32 . The write gap  30  is formed between the first and second yoke pedestals Y 1 P and Y 2 P. 
     The write element  26  of the prior art is shown in FIG. 1F as viewed along the line  1 F— 1 F of FIG.  1 E. Here it can be seen that the first and second yoke pedestals Y 1 P and Y 2 P have substantially equal pedestal widths Wp which are smaller than the pole width W of the first and second poles  31  and  32  in the yoke tip region  33 . In this configuration, the trackwidth of the write element  28  is defined by the width Wp. 
     An inductive write head such as those shown in FIGS. 1C-1F operates by inducing a magnetic flux in the first and second pole. This can be accomplished by passing a writing current through the conductive coil  34 . The write gap  30  allows the magnetic flux to fringe (thus forming a gap fringing field) and impinge upon a recording medium that is placed near the ABS. Thus, the strength of the gap field is a parameter of the write element performance. Other performance parameters include the non-linear transition shift (NLTS), which arises from interbit magnetostatic interactions that occur during the write process, and overwrite. 
     The amount of time that it takes the magnetic flux to be generated in the poles by the writing current (sometimes termed the “flux rise time”) is a critical parameter also, especially for high-speed write elements. In particular, the smaller the flux rise time, the faster the write element can record data on a magnetic media (i.e., a higher data rate). The extended flux rise time is an indicator of eddy current losses and head saturation in the write element. Thus, high data rate applications with large linear bit density and large track density can be accommodated by a writer having a large gap field and low eddy current loss. 
     It has been found that the yoke length YL of the second pole  32  influences the flux rise time, as is shown by the curves in the graph of FIG.  2 A. The corresponding impact of yoke length on data rate can be seen with reference to the curves of FIG.  2 B. As can be seen in FIGS. 2A and 2B, the flux rise time, and therefore data rate, of a typical second pole of 35% FeNi can be improved with lamination. However, such lamination can increase the fabrication process complexity, for example increasing cycle time as well as cost of fabrication. 
     It has also been found that materials with higher electrical resistivity ρ exhibit smaller flux rise times, which indicates that using such materials can reduce eddy current loss in a write element. Other material properties desired in a write material include high saturation magnetic flux density Bs, low saturation magnetostriction λs, and good corrosion resistance. 
     Materials that have been used to form the poles in write elements include NiFe, CoFe, CoNiFe, CoZrTa, and FeN. The saturation magnetic flux density, saturation magnetostriction λs, and corrosion resistance of these materials are listed in the table of FIG.  3 . Higher Fe concentration in NiFe alloy does enhance its saturation magnetic flux density Bs, but the magnetostriction λs of the resultant NiFe alloy increases rapidly. For example, Ni 45 Fe 55  has Bs and λs values of 15.5 kGauss and 20×10 −6 , respectively. In addition, the NiFe alloy family has low electrical resistivity which can inhibit high speed applications because of high eddy current losses. CoFe and CoNiFe also suffer from low electrical resistivity. Also, while Fe-based nitride films and their derivatives can have high Bs values when the nitrogenized films are in crystallized bcc phase, they require film lamination to overcome their low electrical resistivity for high data rate applications. As an additional option, CoZrTa, having a relatively large electrical resistivity, can be used. However, CoZrTa exhibits poor corrosion resistance and is therefore less desirable for write element pole use. For example, the corrosion resistance of CoZrTa is exemplified in the graphs of FIGS. 4A and 4B which show Tafel plots using 0.01 M NaCl and Na 2 SO 4  electrolytes, respectively. 
     Thus, what is desired is an improved write element design that can effectively operate at high speeds while significantly resisting corrosion. Further, such a write element that can write at high data densities is desired. 
     SUMMARY OF THE INVENTION 
     The present invention provides a write element and method for making the same that provides high write performance and significantly resists corrosion. Further, fabrication of the write element is inexpensive and entails low complexity. Specifically, a magnetic material formed of CoZrCr forms a second pole of a write element. Particular formulations of this material exhibit high resistivity which reduces eddy currents, thereby decreasing flux rise time and facilitating high speed data recording. More particularly, the write element can include a first pedestal and a second pedestal, the write element trackwidth being defined by the first pedestal width. This configuration facilitates high density recording. A write element having this configuration and incorporating the CoZrCr second pole provides high speed, high density magnetic data recording. 
     According to an embodiment of the present invention, a magnetic write element for use in high speed magnetic recording includes a first pole having a first pole tip, and a second pole having a second pole tip which defines a write gap with the first pole tip. The second pole is formed of a Co 100-a-b Zr a Cr b  compound, where “a” is in the range of about 2 atomic percent to about 18 atomic percent, and “b” is in the range of about 0.5 atomic percent to about 6 atomic percent. The magnetic write element also includes a conductive coil which lies between the first pole and the second pole. The write element with such a Co 100-a-b Zr a Cr b  compound results in a smaller flux rise time which supports high data rate and high density recording while minimizing corrosivity. 
     In another embodiment of the present invention, a magnetic device for high density magnetic recording includes a first pole having a first pole tip portion, and a first yoke pedestal, having a first width, connected to the first pole at the first pole tip portion. The magnetic device also includes a second pole, having a second pole tip portion, and a second yoke pedestal. The second pole is formed of a Co 100-a-b Zr a Cr b  compound, where “a” is in the range of about 2 atomic percent to about 18 atomic percent, and “b” is in the range of about 0.5 atomic percent to about 6 atomic percent. The second yoke pedestal is connected to the second pole at the second pole tip portion and aligned with the first yoke pedestal, and has a second width that is larger than the first width. Also, a write gap is formed between the first yoke pedestal and the second yoke pedestal, while a conductive coil is positioned between the first pole and the second. The use of such a compound in a write element so configured provides good high density recording performance while minimizing corrosivity. 
     In yet another embodiment of the present invention, a method for forming a write element, including forming a first pole, forming a first insulation layer over the first pole, forming a conductive coil layer over the first insulation layer, and covering said conductive coil layer with non-magnetic and electrically insulating material. The method also includes forming a second pole, over the non-magnetic and electrically insulating material, of a CoZrCr compound having a stoichiometric composition of Co 100-a-b Zr a Cr b , where “a” is in the range of about 2 atomic percent to about 18 atomic percent, and “b” is in the range of about 0.5 atomic percent to about 6 atomic percent. With such a method, a write element capable of high performance high density recording can be formed, which also exhibits low corrosivity. 
     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 drawing. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate 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 along line  1 B— 1 B of FIG. 1A; 
     FIG. 1C is a cross-sectional view of a prior art read/write head of the magnetic disk drive assembly of FIGS. 1A and 1B; 
     FIG. 1D is an end view taken along line  1 D— 1 D of FIG. 1C, of a prior art write element of the read/write head of FIG. 1C; 
     FIG. 1E is a cross-sectional view of another prior art read/write head of the magnetic disk drive assembly of FIGS. 1A and 1B; 
     FIG. 1F is an end view taken along line  1 F— 1 F of FIG. 1E, of a prior art write element of the read/write head of FIG. 1E; 
     FIG. 2A is a graph of the variation of flux rise time exhibited by prior art write elements with varying yoke length; 
     FIG. 2B is a graph of the variation of recorded data rate with varying yoke length, as exhibited with write elements of the prior art. 
     FIG. 3 is a table of various material characteristics of materials used in second poles of the prior art; 
     FIG. 4A is a graph illustrating the corrosion resistance of CoZrTa in NaCl electrolyte; 
     FIG. 4B is a graph illustrating the corrosion resistance of CoZrTa in NA 2  SO 4  electrolyte; 
     FIG. 5A is a graph of the variation of flux rise time with varying yoke length, exhibited by a write element in accordance with an embodiment of the present invention, in comparison with similar variations exhibited by prior art write elements; 
     FIG. 5B is a graph of the variation of recorded data rate with varying yoke length exhibited by a write element in accordance with an embodiment of the present invention, in comparison with similar variations exhibited by prior art write elements; 
     FIG. 6 is a table of various material characteristics of CoZrCr used in a second pole according to an embodiment of the present invention, in comparison with such characteristics of the prior art; 
     FIG. 7A is a graph illustrating the corrosion resistance of CoZrCr and CoZrTa in NaCl electrolyte; 
     FIG. 7B is a graph illustrating the corrosion resistance of CoZrCr and CoZrTa in Na 2 SO 4  electrolyte; 
     FIG. 8A is a cross-sectional view of a read/write head, according to an embodiment of the present invention; 
     FIG. 8B is an end view of the read/write head of FIG. 8A taken along line  8 B— 8 B of FIG. 8A; 
     FIG. 9 is a graph of the gap field versus write current exhibited by the write element of FIGS. 8A and 8B, according to an embodiment of the present invention; 
     FIG. 10 is a graph of the NLTS and overwrite characteristics versus write current of the write element of FIGS. 8A and 8B, according to an embodiment of the present invention; 
     FIG. 11 is a process diagram of a method for forming a read/write head, according to an embodiment of the present invention; 
     FIG. 12 is a process diagram of a method for forming a tip stitch pole in the method of FIG. 11, according to an embodiment of the present invention; 
     FIG. 13 is a process diagram of a method for forming a second pole in the method of FIG. 11, according to an embodiment of the present invention; and 
     FIG. 14 is a process diagram of a method for improving thermal stability of a write yoke, according to an embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 1-4 were discussed with reference to the prior art. An embodiment of the present invention includes the use of a CoZrCr compound exhibiting high electrical resistivity ρ which results in high speed recording capabilities when used in write element poles. The effect of an electrical resistivity ρ on the order of 90 μΩ-cm on flux rise time is shown in FIG. 5A for varying yoke length YL. As shown by the curves of FIG. 5A, the CoZrCr compound results in substantially shorter flux rise times than those with the 35% FeNi without lamination. In addition, the CoZrCr performance is better than or substantially similar to that with 35% FeNi with one layer lamination across a wide range of yoke lengths. The flux rise time responses are indicative of the data rate performance of the write element, as is demonstrated in FIG.  5 B. 
     FIG. 5B illustrates the data rate experienced with the CoZrCr compound, in comparison with 35% FeNi both with and without one layer lamination. Again, across substantially all yoke lengths, the CoZrCr compound produces higher data rates than the 35% FeNi without lamination. Also, the curves show the data rate of the CoZrCr compound as being substantially similar to or greater than that of the 35% FeNi with one layer lamination, for a wide range of yoke length. Because the performance of the CoZrCr compound relative to the laminated FeNi, and the inherent drawbacks of lamination, using the high resistivity CoZrCr is a more effective approach to improving flux rise time and data rate than implementing laminations in the yoke. 
     In addition to high electrical resistivity, the CoZrCr compound exhibits other characteristics that make it a particularly suitable material for use in the yoke of a write element. As shown in FIG.  6  and compared with other yoke materials, a Co 92.5 Zr 5.2 Cr 2.3  compound has a saturation field of about 13.5 kGauss, an electrical resistivity of about 90 to about 95, and a magnetostriction of about 3×10 −6 . In addition, the Co 92.5 Zr 5.2 Cr 2.3  compound has a good resistance to corrosion. This resistance to corrosion can be seen in FIGS. 7A and 7B, in comparison with the behavior of a CoZrTa compound. Specifically, FIGS. 7A and 7B show Tafel plots for films of the two compounds using a NaCl electrolyte and a Na 2 SO 4  electrolyte, respectively. As can be easily seen, the CoZrCr compound is significantly more corrosion resistant than is the CoZrTa compound tested. 
     In addition to the particular Co 92.5 Zr 5.2 Cr 2.3  compound, other stoichiometric compositions of CoZrCr can work well. For example, a composition of Co 100-a-b Zr a Cr b , where “a” is in the range of about 2 to about 18 atomic percent and “b” is in the range of about 0.5 to about 6 atomic percent, can be satisfactory for high speed data recording. More specifically, “a” in the range of about 4 to about 9 atomic percent and “b” in the range of about 1 to about 3 atomic percent, can work well. In addition to high electrical resistivity and good corrosion resistance, this compound further possesses a soft magnetic property, with coercivity Hc about equal to zero (i.e., with hard axis coercivity Hch and easy axis coercivity Hce less than about 0.2). 
     A write element configuration according to another embodiment of the present invention is illustrated in FIGS. 8A and 8B. FIG. 8A shows a cross-sectional view of a read/write head  50  incorporating a write element  52  having a particular geometry, formed over a read element  53 . The write element  50  includes a first pole  54 , a second pole  56 , and a conductive coil  58  that is embedded within a non-magnetic and electrically insulating material  60 . In addition, the write element  50  incorporates a first yoke pedestal (Y 1 P)  62  adjacent to the first pole  54  in the yoke tip region  64 . Further, a second yoke pedestal (Y 2 P)  66  is adjacent the second pole  56 , also in the yoke tip region  64 , and defines a write gap  68  between it and the first yoke pedestal  62 . The write gap  68  is filled with non-magnetic material  67 . Additionally, the Y 1 P  62 , Y 2 P  66 , and write gap  68  combine to form a tip stitch pole (TSP)  69 . The particular geometry of the write element  52  can be more easily understood with reference to FIG.  8 B. 
     FIG. 8B shows a partial end view of the write element  52  in the direction marked as  8 B— 8 B in FIG.  8 A. As can be seen from this view, the first yoke pedestal (Y 1 P)  62  is characterized by a first width W 1 , while the second yoke pedestal (Y 2 P)  66  is characterized by a second width W 2 . In the operation of such a write element, it is found that the trackwidth TW of the write element is substantially equal to the first width W 1  of the first yoke pedestal, and thus is a first yoke pedestal defined (Y 1 P-defined) write element. Thus, a smaller trackwidth can be defined while the second width W 2  of the second yoke pedestal Y 2 P can remain relatively similar to the width W of the second pole  56  to minimize flux leakage. 
     When this configuration is used in conjunction with a CoZrCr compound, the write element can produce a very large gap field, which is an important factor for high areal density applications in conjunction with high coercivity magnetic media, such as magnetic disk  16  of FIG.  1 A. For example, FIG. 9 shows a graph of gap field versus write current for the Co 92.5 Zr 5.2 Cr 2.3  compound. In addition, the use of this compound with the particular write element geometry shown in FIGS. 8A and 8B, at a high data rate of 500 Mb/s, results in the write performance shown by the curves of FIG.  10 . Specifically, the data of FIG. 10 pertains to a disk media having a high coercivity of about 4000 Oe and an Mrt of about 0.4 memu/cm 2 . This performance indicates that this material is a good candidate for high areal density recording in conjunction with high coercivity magnetic media. Further, because of its other material properties, such a write head is also particularly well suited to high speed data recording. 
     A method  80  for forming a read/write element according to yet another embodiment of the present invention, is shown by the process diagram of FIG.  11 . In operation  82 , a read element including a second shield is formed. The read element further includes a first shield and a read sensor, each component of the read element being formed of various materials and by various methods known to those skilled in the art. In operation  84 , a Y 1 P-defined tip stitch pole (TSP) is formed over the second shield which also performs as a first pole. The layers of the TSP can be formed using convention processes such as plating, sputtering, and various possible etching techniques. The formation of the Y 1 P-defined geometry is further discussed below with reference to FIG.  12 . 
     A first insulation layer is also formed over the first pole in operation  86 . This can be accomplished by sputter deposition of a non-magnetic and electrically insulating material over the first pole, and may further entail etching or planarizing of the non-magnetic and electrically insulating material. In operation  88 , overlying coil layers embedded and electrically isolated within insulation layers are successively formed over the first insulation layer. A second pole is formed in operation  90  over the overlying coil layers and over the Y 1 P-defined tip stitch pole. 
     FIG. 12 further outlines operation  84  of FIG.  11 . In operation  94  a first yoke pedestal (Y 1 P) is formed over the first pole, with a first width W 1 . The Y 1 P material can be made of the same material as used to form the first pole, such as Permalloy. A nonmagnetic gap material layer is deposited over the Y 1 P in operation  96 . Operation  84  also includes the formation, in operation  98 , of a second yoke pedestal over the gap material layer, with a second width W 2  that is larger than the first width W 1 . Alternatively, the width W 2  of the second yoke pedestal can be smaller than or equal to the width W 1  of the first yoke pedestal. 
     Operation  90  of the method in FIG. 11 is expanded upon in the process diagram of FIG.  13 . Specifically, operation  90  pertains to formation of the second pole through DC magnetron sputtering of CoZrCr or other high Bs and high resistivity materials. In operation  102 , the sputter deposition power is set at about 2.5 kW, while the gas (e.g., argon) pressure inside the deposition chamber is set at about 4 mTorr in operation  104 . Operation  106  includes setting the substrate bias at about 75V. Alternatively, the substrate bias can be less than about 75V. The alignment field to obtain magnetic anisotropy in the deposition film is set at about 80 Oe in operation  108 , and the target to wafer distance is set at about 5 inches. Under these conditions, CoZrCr is sputter deposited over the Y 1 P-defined tip stitch pole, coil layers, and insulation layers. With this deposition process, a Co 92.5 Zr 5.2 Cr 2.3 compound can be easily formed. This material then provides high areal density and high speed recording capability while resisting corrosion well. 
     Desirable write performance can be attained when the field-induced anisotropy Hk of the yoke materials is thermally stable. In some embodiments of the present invention, a CoZrCr field-induced anisotropy Hk that is set during deposition may not be desirably thermally stable. For example, sputter deposited CoZrCr that is amorphous can have a field-induced anisotropy Hk set during deposition by external field that is more thermally unstable than desired. In such embodiments, the field-induced anisotropy Hk can be made more thermally stable through subsequent operations. For example, method  120  can be used to twice annealed the CoZrCr, as illustrated in the process diagram of FIG.  14 . 
     As shown in FIG. 14, in operation  122  the CoZrCr can be first annealed in an easy axis direction of the CoZrCr. More specifically, this annealing can be performed with an external field of about 6000 Oe applied along the easy axis at about 225° C. for about two hours. Then, after cooling to between about 25° C. and 60° C., the CoZrCr can be annealed again in operation  124  with an external field of about 6000 Oe along the hard axis at about 225° C. for about two hours. With such a process the anisotropy Hk can change from about 14 to about 15 to about 5 Oe before the first anneal, before the second anneal, and after the second anneal, respectively. Likewise, the easy axis coercivity Hce can change from about 0.06 to about 0.09 to about 0.03 Oe. In addition, with this process, the hard axis coercivity Hch can change from about 0.12 to about 0.14 to about 0.08 Oe. As a result, the pole including CoZrCr has a sufficiently low anisotropy field Hk, and the anisotropy direction is substantially thermally stable. For example, CoZrCr subjected to such operations substantially does not rotate when subsequently annealed with a 6000 Oe external field at ≦225° C. 
     Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. Accordingly, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.