Abstract:
One of the major requirements for higher frequency extendability is to reduce yoke length and inductance in order to have fast saturation. This has been accomplished by using a design that provides a cavity in the lower pole piece inside which is located at least two coils, one on top of the other. A process for manufacturing the device is also described.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to the general field of magnetic write heads for data storage systems with particular reference to increasing the writing speed.  
         BACKGROUND OF THE INVENTION  
         [0002]    There are several design options available to make high data rate writers. One of the major requirements for higher frequency extendability is to reduce yoke length and inductance in order to have fast saturation. Given fast saturation during the writing process, one can have better overwrite and cold overwrite performance at higher frequency. Some designs for faster write heads have the planar writer with a short yoke length. However, one of the drawbacks of this design is the coil real estate utilization which creates either high DC coil resistance or requires a small number of coil turns.  
           [0003]    In FIG. 1 we show a typical write head of the prior art. Seen there is magnetic shield  11  which is separated from the lower magnetic pole by insulating layer  12 . The lower pole is made up of two parts—base  13  and upper portion  14  which is open so that it forms a cavity. In this cavity is housed magnetic coil  16  which is seated on shallow pedestal  15 . Insulating layers  17  and  18  cover the coil while insulating layer  19  serves to control throat height (see later). Non-magnetic gap layer  20  separates the lower coil structure from upper pole  21 .  
           [0004]    A routine search of the prior art was performed with the following references of interest being found:  
           [0005]    In U.S. Pat. No. 6,325,947 B1, Garfunkel et al. show a process for a head with a short yoke while Nakajima et al. show a process for a head in U.S. Pat. No. 6,317,280 B1. Santini shows a process for a head in U.S. Pat. No. 6,339,523 B1 and related patents are U.S. Pat. No. 6,333,830 B2 (Rose et al.) and U.S. Pat. No. 6,304,414 B1 (Crue, Jr. et al.).  
         SUMMARY OF THE INVENTION  
         [0006]    It has been an object of at least one embodiment of the present invention to provide a magnetic write head having fast saturation.  
           [0007]    Another object of at least one embodiment of the present invention has been that said write head occupy minimum real estate and have minimum electrical resistance.  
           [0008]    Still another object of at least one embodiment of the present invention has been to provide a process for manufacturing said write head.  
           [0009]    These objects have been achieved by forming a cavity in the lower pole piece and locating therein at least two coils, one on top of the other. A process for manufacturing the device is also described. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    [0010]FIG. 1 shows a typical write head of the prior art FIG. 2 shows the starting point for the process of the present invention.  
         [0011]    FIGS.  3 - 5  show steps leading to the formation of the lower coil and the cavity in which it is housed.  
         [0012]    [0012]FIG. 6 is a plan view of the cross-sectional view seen in FIG. 5.  
         [0013]    FIGS.  7 - 8  show steps leading to the formation of the upper coil and the cavity in which it is housed  
         [0014]    [0014]FIG. 9 shows the step for controlling the throat height of the device.  
         [0015]    [0015]FIG. 10 shows the addition of the non-magnetic gap layer.  
         [0016]    [0016]FIG. 11 shows the completed device. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0017]    The present invention is based on a two layer coil structure for a planar writer. This two layer structure design leads to low DC coil resistance relative to similar designs having a short yoke.  
         [0018]    A key feature is breaking the lower pole into two separate layers which allows the achievement of an optimized coil space for each coil. This two layer coil structure enables one to maintain the same planar writer structure but with better performance on fast saturation and lower DC coil resistance or better thermal pole tip protrusion.  
         [0019]    The process of the present invention begins, as shown in FIG. 2, with the deposition of layer  11  which will serve as the lower magnetic shield. It is between about 1 and 2 microns thick and is of a metal such as NiFe or CoNiFe. This is followed by layer  12 , between about 1,000 and 5,000 Angstroms thick, made of alumina, whose purpose is to separate the reader shield and the writer&#39;s bottom pole. Then, layer  13  (of the writer&#39;s bottom pole) is deposited onto layer  12  to a thickness between about 1 and 2 microns. It will serve as the lower magnetic pole of the writer.  
         [0020]    Referring now to FIG. 3, insulating layer  15  (of alumina or silica), between about 1,000 and 3,000 Angstroms thick, is deposited onto layer  13  and patterned to form a low pedestal. This is followed by the deposition of a seed layer, typically of copper, (not shown) which, after protection of the appropriate areas by photoresist (also not shown), is used as a base onto which to electrodeposit lower coil  16 . After removal of both the photoresist and the seed layer, the structure is as seen in FIG. 3.  
         [0021]    Next, as shown in FIG. 4, the upper section  14  of the lower pole is formed by electroplating. Insulating layer  17  is then formed of photoresist to a thickness that is between about 1 and 1.5 microns, and then selectively removed from above  14 , giving the structure the appearance seen in FIG. 4. Layer  17  is then hard baked to become a permanent insulating layer.  
         [0022]    The next step is the overfilling of the space above layer  17  with insulating layer  58  following which the structure is planarized (typically using CMP) so that the thickness of the upper portion of the lower pole (now shown as layer  24 ) is reduced, as can be seen in FIG. 5. The deposition is performed in two separate layers is to avoid void formation in layer  58 .  
         [0023]    [0023]FIG. 6 is a plan view of the structure whose cross-section we saw in FIG. 5.  
         [0024]    The process continues with the formation of upper coil  76  which is formed on the surface of layer  58  in a similar manner to that described above for lower coil  16 . Layers  76 ,  87  and  88  are formed using similar materials and thicknesses to layers  16 ,  17  and  58  respectively as shown in FIG. 7. This is followed, as before, by a planarization step whereby layer  74  is reduced in thickness, being now designated as  84  in FIG. 8.  
         [0025]    Referring next to FIG. 9, a shallow trench, between about 2,000 and 4,000 Angstroms deep, is etched into layer  88  as well as a small portion of the lower pole on one side of the structure only. This cavity is then overfilled with material  91  (such as alumina or silica) and the structure is then planarized, as shown in FIG. 9 until some of layer  84  begins to be removed. As a result, width  92  of the lower pole, on one side, is gradually decreased so that the throat height of the finished structure can be controlled.  
         [0026]    [0026]FIG. 10 shows the structure after the deposition of write gap layer  20 . In principle this could be any non-magnetic material but our preferred material for layer  20  has been ruthenium, deposited to a thickness between about 700 and 1,200 Angstroms. Note that layer  20  has been selectively removed from the one side of lower pole  84  to form a flux transmission area that will allows unimpeded passage of magnetic flux between the upper and lower magnetic poles.  
         [0027]    The process of the present invention concludes with the successive depositions of layers  110  and  112 , as illustrated in FIG. 11. Layer  110  is between about 1,000 and 3,000 Angstroms thick and is made of a material capable of sustaining a very high magnetic moment. Examples are CoFeN and CoFe, with CoFeN being preferred. The magnetic permeability of layer  110  was generally between about 700 and 1,000. The presence of layer  110  right above write gap  20  ensures a concentration of magnetic flux in the immediate vicinity of the latter. Layer  112  is of the same material as layers  13 ,  24 , and  84  and serves as the upper magnetic pole. It is between about 1 and 1.5 microns thick.