Abstract:
A high speed magnetic data writer containing a stitched pole tip that works in conjunction with the main pole is disclosed, together with a process for their manufacture. The material composition of each of these two sub-structures is slightly different; one sub-structure is optimized for high magnetic damping while the other sub-structure is optimized for high saturation magnetization.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to recording data on magnetic disks, with particular reference to the design and manufacture of devices capable of recording at rates in the gigabits per second range. 
       BACKGROUND OF THE INVENTION 
       [0002]    For today&#39;s high density magnetic recording, the recorded bits per inch (BPI) and the data rate for writing have both either already entered, or are rapidly approaching, the Giga range. It is essential that this increase in the data rate capability of writers not be accompanied by an increase in the bit error rate (BER). 
         [0003]    To enhance the data rate of a writer, its frequency response to the writing current has to be improved. During the writing process, magnetization will follow the Landau-Lifshitz-Gilbert equation: 
         [0000]    
       
         
           
             
               
                  
                 M 
               
               
                  
                 t 
               
             
             = 
             
               
                 
                   - 
                   γ 
                 
                  
                 
                     
                 
                  
                 M 
                 × 
                 
                   H 
                   eff 
                 
               
               + 
               
                 
                   α 
                   M 
                 
                  
                 M 
                 × 
                 
                   
                      
                     M 
                   
                   
                      
                     t 
                   
                 
               
             
           
         
       
     
         [0000]    where M is the magnetization, γ is the gyromagnetic coefficient, Heff is the field, including the applied field, the demagnetization field, and the anisotropic field. α is the Gilbert damping constant. The 1 st  term is the gyro motion of magnetization around the direction of Heff while the 2 nd  term is the damping term which will dissipate the energy of M motion and align the M along the direction of Heff. 
         [0004]    The value of α determines how fast M aligns with Heff, as illustrated schematically by the two examples shown in  FIGS. 1   a  and  1   b . In  FIG. 1   a  α is relatively small while in  FIG. 1   b  α is relatively large. This damping process is a major factor in determining the magnetic material&#39;s response time to the writing field. The damping constants of the high saturation magnetization (Ms) materials used in present day writers (Fe, Co, Ni alloys) is small, being in the range of from 0.002 to 0.02. 
         [0005]    Another issue facing today&#39;s high density writers is the accidental erasure of data due to the remnant magnetization of the write pole. To eliminate this problem, magnetic materials with good soft properties (small anisotropy field Hk) are needed. However, not all soft magnetic materials have an Ms value that is large enough to provide a high intensity writing field. 
       REFERENCES 
       [0000]    
       
         [1]W. Bailey et. al. IEEE Magn. 37, pp 1749, 2001 
         [2] J. Rantschler, et. al. JAP. 101, pp 033911, 2007
 
A routine search of the prior art was performed with the following references of interest being found:
 
       
     
         [0008]    U.S. Pat. No. 7,595,959 (Covington et al) teaches that damping may be increased by doping with rare earth or transition elements. Dopants include Os, Ir, and Pt. In U.S. Patent Application 2007/0171575, Lim et al. teach a damping control layer formed by doping rare earth or transition metals such as Os, Ru, Pt on the soft magnetic underlayer while Kong et al., in U.S. Patent Application 2009/0197119, disclose a soft magnetic layer having a low anisotropic field. 
       SUMMARY OF THE INVENTION 
       [0009]    It has been an object of at least one embodiment of the present invention to describe a high data rate magnetic writer 
         [0010]    Another object of at least one embodiment of the present invention has been to present a process for the manufacture of said high data rate magnetic writer. 
         [0011]    Still another object of at least one embodiment of the present invention has been to describe the composition of several key sub-structures within said high data rate magnetic writer. 
         [0012]    These objects have been achieved by utilizing magnetic materials with high damping constant as part or all of the writer&#39;s magnetic sub-structure. These materials are high moment Co, Fe, Ni alloys doped with a small percentage of rare earth and/or 3d-5d transition metals that will increase the damping constant significantly. 
         [0013]    An important feature of the invention is the provision of a stitched pole tip that works in conjunction with the main pole. The material composition of each of these two sub-structures is slightly different; one sub-structure is optimized for high magnetic damping while the other sub-structure is optimized for high saturation magnetization. This arrangement results in a device having both a high damping constant as well as a high saturation magnetization. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]      FIG. 1  compares magnetization motions for low ( 1   a ) and high ( 1   b ) values of the damping constant. 
           [0015]      FIG. 2  damping constant as a function of atomic percentage of the Rare Earth dopants Tb and Gd for a NiFe thin film (Ref.1) 
           [0016]      FIG. 3  Ms value as a function of Rare Earth element dopants Tb and Gd for a NiFe 
           [0017]      FIG. 4  damping constant as a function of atomic percentage of 3d-5d elements in a NiFe thin film (Ref.2) 
           [0018]      FIGS. 5   a - 9  Process steps for manufacturing the stitched main pole design 
           [0019]      FIGS. 10   a  and  10   b  Cross-sectional and bird&#39;s eye views, respectively, of a first embodiment of the invention. 
           [0020]      FIG. 11  Cross-sectional view of the full writer structure 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0021]    As illustrated in  FIG. 2 , the damping constant increases from a value of less than 0.1 to a value of 0.3 as the concentration of Tb dopant increases from 2% to about 17.5%. However, as shown by  FIG. 3 , although Ms, the saturation magnetization of the material, is essentially unchanged for Tb concentrations up to about 4%, Ms has been reduced by about 50% by the time the Tb concentration reaches about 17.5%. Thus a small amount of Tb doping will enhance the damping constant significantly without decreasing the saturation magnetization but, if further increases in α are to be achieved, the price is a correspondingly lower value of Ms. 
         [0022]    Note that the damping constant can also be increased by doping with a 3d-5d transition metal, as shown in  FIG. 4 , where the damping constant α z , at a doping concentration of x atomic %, was calculated from the following formula: 
         [0000]      α Z =α 0 +β Z   x.  
 
         [0000]      where 
         [0000]      α 0 =(8.0±0.5)×10 −3  
 
         [0000]    β z  values for various 3d-5d metals are as listed in  FIG. 4  where they are displayed in histogram format. 
         [0023]    The present invention discloses a writer design in which both high Ms and high α are achieved in the same unit. 
         [0024]    Referring now to  FIG. 5   a , we show there the starting point for the manufacture of a first embodiment of the invention. This initial structure includes lower field coil  54  that has been embedded within non-magnetic dielectric  55 . Cavity  51  has been formed in the top surface of  55  and its internal walls have been coated with layer  52  suitable for use as the write gap portion of the final structure. Note that one of these internal walls is not vertically oriented relative to the floor of cavity  51  but, rather, slopes upwards at an angle of about 30 degrees relative to, and away from, the floor. Note, too, the presence of leading shield  53  located between layer  55  and the underside of layer  52 . 
         [0025]      FIG. 5   b  is a bird&#39;s eye view of  FIG. 5   a  from a point located a short distance above  5   a . 
         [0026]    Next, as illustrated in  FIG. 6 , photoresist layer  61  is laid down and patterned to form a mask that covers all of layer  52  except about half the sloping portion of  52  that was described above. Next, in a key feature of the invention shown in  FIG. 7 , layer  71  is electrodeposited on the exposed portion of gap layer  52 . Although not shown, in practice, prior to initiating electroplating, a seed layer of conductive material is deposited (usually by sputtering) over the entire structure. Once layer  71  has reached the desired thickness (generally in a range of from 0.1 to 1 microns), electrodeposition is terminated and photoresist layer  61  is fully removed (as illustrated in  FIG. 8 ) thereby recreating cavity  51  seen earlier. 
         [0027]    The material used for layer  71 , in addition to being suitable for the formation of the pole tip, is characterized by possessing a high value of Ms (4πMs) (generally in a range of from 20 k to 24.5 k Oe, with a range of from 24.3 k to 24.5 k Oe being preferred), while the value of α in layer  71  is required to be at least 0.02. To achieve these properties, the composition of layer  71  was typically Fe30% Co70%. 
         [0028]    Turning next to  FIG. 9 , cavity  51  is first over-filled with material that, in addition to being suitable for the formation of the main pole, is characterized by possessing a high value of α (generally in a range of from 0.05 to 0.5, with a range of from 0.1 to 0.2 being preferred), while the value of Ms (4πMs) in layer  71  is required to be at least 19 k Oe. To achieve these properties, the composition of this layer was typically [Fe30% Co70%] 1-x Tb x  where x ranges from 0.01 to about 0.2. 
         [0029]    Note that, from  FIG. 9  on, the pole tip (formerly designated as layer  71 ) has been given the designation of region A while the main pole (filling former cavity  51 ) is now designated as region B. 
         [0030]    As illustrated in  FIG. 10   a , the structure is then planarized (typically through use of CMP) until the top surface of region A is exposed and the thickness of region A extends upwards from write gap  52  by an amount that is in a range of from 0.1 to 1.0 microns.  FIG. 10   b  is a bird&#39;s eye view looking down at region B (main pole) and showing the latter&#39;s relationship to region B (a stitched pole tip). 
         [0031]    The remaining parts of the device, including the top and write yokes and the upper field coil, are formed in the usual manner, thereby completing fabrication of the device. Provided the materials specified above were used, this device is able to record magnetic data at a rate of at least 1 GHz. 
       Additional Embodiments of the Invention 
       [0032]    In a second embodiment, the high-α material is used in other parts of the writer as well. The yoke for example. This is illustrated in  FIG. 11  where only top yoke  111  is explicitly shown. However, the top and/or the bottom (B) sections of the yoke could also have been formed in the same way (i.e. with high-α material). Also shown in  FIG. 11  are upper field coils  154  and background material  113  (such as Al 2 O 3 ). 
         [0033]    In a third embodiment, high-α material is used for some or all of the remaining parts of the writer structure, as shown in  FIG. 7 .