BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention relates to a high data rate magnetic write head and more particularly to a multi-layer stitched magnetic write head design. 
     (2) Description of the Related Art 
     Magnetic read heads, often referred to as inductive read heads, must be designed in such a way that the magnetic flux extends across the air bearing surface into the magnetic media as much as possible. A cross section view of a conventional magnetic read/write head is shown in FIG.  1 . As shown in FIG. 1 a magnetic sensor  16  is placed adjacent to the air bearing surface  30  of the head between a first ferromagnetic shield  10  and a second ferromagnetic shield  18  ferromagnetic shield. 
     The second ferromagnetic shield  18  also serves as the first pole piece  18  for the write portion of the head. A first non-magnetic gap layer  20  is formed on the first pole piece  18  and determines the gap  12  between the first pole piece  18  and the second pole piece  26  at the plane of the air bearing surface (ABS)  30 . A second non-magnetic gap layer  22  is formed on the first non-magnetic gap layer  20  beginning a first distance  32  away from the ABS plane  30 . The beginning of the second non-magnetic gap layer  22  defines the point where the gap  12  between the first pole piece  18  and the second pole piece  26  begins to widen. A layer of wiring  28 , imbedded in a layer of insulating material  24 , is formed on the second non-magnetic gap layer  20 . An additional insulation layer  25  may be used to provide a smoother surface on which to form the second pole piece  26 . The second pole piece is formed over the first non-magnetic gap layer, the second non-magnetic gap layer, and the additional insulation layer  25 . It is advantageous to have the first distance  32  as small as possible in order to have the optimum distribution of magnetic flux. 
     U.S. Pat. No. 5,805,391 to Chang et al. describes a write head with a recessed stitched yoke on a planar portion of an insulation layer defining the zero throat height, or the point where the gap between pole pieces begins to widen. A second pole piece if formed of two pole piece components stitched together, or placed in contact to reduce the non-magnetic gap between the two pole components to zero. 
     U.S. Pat. No. 5,802,700 to Chen et al. describes a method of making a planarized thin film magnetic write head with submicron trackwidth. 
     U.S. Pat. No. 5,878,481 to Feng et al. describes a pole trimming method of forming a magnetic transducer structure. 
     SUMMARY OF THE INVENTION 
     In the design of magnetic write heads for high track per inch or low trackwidth applications it is important to have the throat height as small as possible. The throat height is the distance from the ABS end of the poles to point where the non-magnetic gap between the poles begins to widen, reference number  32  in FIG. 1. A stitched pole design can be used to improve the throat height but it is also necessary to have a recessed yoke design. The recessed yoke design provides a separation between the second pole piece, reference number  26  in FIG. 1, and the air bearing surface at the point where the second pole piece curves to provide an increased non-magnetic gap width. 
     It is a principle objective of this invention to provide a magnetic write head having multi-layer stitched poles, a small throat height, a recessed yoke design, and a planar top surface. 
     It is another principle objective of this invention to provide a magnetic write head having multi-layer stitched poles, a small throat height, and a recessed yoke design. 
     These objectives are achieved by using a multi-layer stitched pole design. A non-magnetic gap layer is formed on a layer of ferromagnetic material. A first pole piece is then formed on the non-magnetic gap layer. A notch is formed in the first pole piece to define the throat height. A second pole piece, recessed from the first pole piece is then formed making contact with the first pole piece. A third pole piece, recessed from the second pole piece is formed making contact with the second pole piece. The first, second, and third pole pieces form a stitched pole since there are regions of zero non-magnetic gap between the first pole piece and the second pole piece and between the second pole piece and the third pole piece. The notch in the first pole piece defines the throat height, the recessed second and third pole pieces form a recessed yoke, and the structure can be made planar. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a cross section view of a conventional magnetic write head. 
     FIG. 2 shows a cross section view of a magnetic write head of this invention having a planarized top surface. 
     FIG. 3 shows a cross section view of a magnetic write head of this invention without a planarized top surface. 
     FIG. 4 shows a cross section view of a magnetic read head which can be combined with the magnetic write heads of this invention. 
     FIG. 5 shows a cross section view of a part of the magnetic write head of this invention after the first pole piece has been formed and the head planarized. 
     FIG. 6 shows a cross section view of a part of the magnetic write head of this invention after the second pole piece has been formed and the head planarized. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Refer now to FIGS. 2,  4 ,  5 , and  6  for a description of the preferred embodiment of the write head design of this invention. FIG. 2 shows a cross section view of a preferred embodiment of the magnetic write head of this invention. A layer of first ferromagnetic material  40  forms one of the pole pieces of the magnetic write head. Those skilled in the art will readily recognize that the magnetic write head can be combined with a read head, however only the write head will be described here. This layer of first ferromagnetic material  40  will also act as a magnetic shield for the case where a read head is combined with the write head. 
     FIG. 4 shows a magnetic read head which can be combined with the magnetic write head of this invention. The read head has a magnetic sensing element  16  between a first shield  40  and a second shield  10  which act as magnetic shields for the read head. The first and second shields are ferromagnetic material such as NiFe or permalloy. The first shield  40  is the layer of first ferromagnetic material  40  forming one of the pole pieces of the magnetic write head shown in FIG.  2 . The ferromagnetic material can be any soft ferromagnetic material such as NiFe or permalloy. 
     As shown in FIGS. 2 and 5 a gap layer of first non-magnetic dielectric material  42 , such as alumina, having a first end and a second end is formed on the layer of ferromagnetic material. The first end of the gap layer  42  lies on the air bearing surface (ABS) plane  30 . The gap layer  42  determines the non-magnetic gap width  12  at the air bearing surface end of the write head. The gap width  12  is between about 0.5 and 0.05 microns. The air bearing surface (ABS) plane  30  is shown as a dashed line in FIG. 2. A first pole piece  44  having a first end and a first notch  55  is formed on the gap layer  42  such that the first end of the first pole piece  44  is on the ABS plane  30 . The first notch  55  is a first distance  32  from the ABS plane  30 . The first distance  32  is also the throat height  32  of the write head and in this example is between about 0.5 and 3.0 microns. 
     A first back gap piece  52 , of ferromagnetic material, is formed on the layer of first ferromagnetic material  40  adjacent to the second end of the gap layer of non-magnetic dielectric material  42  at the back gap end  51  of the write head. The first back gap piece  52  makes contact with the layer of first ferromagnetic material  40  so that they are magnetically stitched together. The region  60  between the first pole piece  44  and the first back gap piece  52  has a first wiring layer  64  and is filled with a second non-magnetic dielectric material, in this example alumina. The second non-magnetic dielectric material also fills the first notch  55 . The formation of the write head at this stage is shown in FIG.  5 . FIG. 5 shows that the top surface  70  of the write head at this stage of fabrication is planar making subsequent fabrication steps easier. 
     As shown in FIGS. 2 and 6, a second pole piece  46  having a first end and a second notch  57  is formed on the planar layer having the first pole piece  44 , the first back gap piece  52 , and the layer of second non-magnetic dielectric with the imbedded first wiring layer  64 . The second pole piece  46  is typically formed of the same ferromagnetic material as the first pole piece  44 , in this example NiFe or permalloy. The first end of the second pole piece  46  is recessed a second distance  14  from the ABS plane  30 . In this example the second distance  14  is between about 0.5 and 2.0 microns. A portion of the second pole piece  46  contacts the first pole piece  44  so that the first pole piece  44  and the second pole piece  46  are magnetically stitched together. The second notch  57  further widens the non-magnetic gap between the stitched pole pieces and the layer of first ferromagnetic material  40 . 
     A second back gap piece  50 , of ferromagnetic material, is formed on the first back gap piece  52  and is in contact with the first back gap piece  52  so that the first back gap piece  52  and the second back gap piece  50  are magnetically stitched together. The region  58  between the second pole piece  46  and the second back gap piece  50  is filled with the second non-magnetic dielectric, such as alumina, and has a second wiring layer  62  formed therein. The second notch  57  is also filled with the second non-magnetic dielectric. The region  54  between the second pole piece  46  and the ABS plane  30  is also filled with the second non-magnetic dielectric. The formation of the write head at this stage is shown in FIG.  6 . FIG. 6 shows that the top surface  72  of the write head at this stage of fabrication is planar making subsequent fabrication steps easier. 
     As shown in FIG. 2, a third pole piece  48  having a first end and a second end is formed on the planar layer having the second pole piece  46 , the second back gap piece  50 , and the layer of second non-magnetic dielectric with the second imbedded wiring layer  62 . The third pole piece  48  is typically formed of the same ferromagnetic material as the first pole piece  44  and the second pole piece  46 , in this example NiFe or permalloy. The first end of the third pole piece  48  is recessed a third distance  15  from the ABS plane  30 . In this example the third distance  15  is between about 2.0 and 4.0 microns. A portion of the third pole piece  48  contacts the second pole piece  46  so that the second pole piece  46  and the third pole piece  48  are magnetically stitched together. Another portion of the third pole piece  48  contacts the second back gap piece  50  so that the third pole piece  48  and the second back gap piece  50  are magnetically stitched together. The region  56  between the first end of the third pole piece  48  and the ABS plane  30  is filled with the second non-magnetic dielectric so that the top surface  74  of the completed write head is planar. A cross section of the completed write head is shown in FIG.  2 . 
     Refer now to FIGS. 3,  4 ,  5 , and  6  for another preferred embodiment of the write head design of this invention. FIG. 3 shows a cross section view of this embodiment of the magnetic write head of this invention. A layer of first ferromagnetic material  40  forms one of the pole pieces of the magnetic write head. Those skilled in the art will readily recognize that the magnetic write head can be combined with a read head, however only the write head will be described here. This layer of first ferromagnetic material  40  will also act as a magnetic shield for the case where a read head is combined with the write head. 
     FIG. 4 shows a magnetic read head which can be combined with the magnetic write head of this invention. The read head has a magnetic sensing element  16  between a first shield  40  and a second shield  10  which act as magnetic shields for the read head. The first and second shields are ferromagnetic material such as NiFe or permalloy. The first shield  40  is the layer of first ferromagnetic material  40  forming one of the pole pieces of the magnetic write head shown in FIG.  3 . The ferromagnetic material can be any soft ferromagnetic material such as NiFe or permalloy. 
     As shown in FIGS. 3 and 5 a gap layer of first non-magnetic dielectric material  42 , such as alumina, having a first end and a second end is formed on the layer of ferromagnetic material. The first end of the gap layer  42  lies on the air bearing surface (ABS) plane  30 . The gap layer  42  determines the non-magnetic gap width  12  at the air bearing surface end of the write head. The gap width  12  is between about 0.05 and 0.5 microns. The air bearing surface (ABS) plane  30  is shown as a dashed line in FIG. 3. A first pole piece  44  having a first end and a first notch  55  is formed on the gap layer  42  such that the first end of the first pole piece  44  is on the ABS plane  30 . The first notch  55  is a first distance  32  from the ABS plane  30 . The first distance  32  is also the throat height  32  of the write head and in this example is between about 0.5 and 3.0 microns. 
     A first back gap piece  52 , of ferromagnetic material, is formed on the layer of first ferromagnetic material  40  adjacent to the second end of the gap layer of non-magnetic dielectric material  42  at the back gap end  51  of the write head. The first back gap piece  52  makes contact with the layer of first ferromagnetic material  40  so that they are magnetically stitched together. The region  60  between the first pole piece  44  and the first back gap piece  52  has a first wiring layer  64  and is filled with a second non-magnetic dielectric material, in this example alumina. The second non-magnetic dielectric material also fills the first notch  55 . The formation of the write head at this stage is shown in FIG.  5 . FIG. 5 shows that the top surface  70  of the write head at this stage of fabrication is planar making subsequent fabrication steps easier. 
     As shown in FIGS. 3 and 6, a second pole piece  46  having a first end and a second notch  57  is formed on the planar layer having the first pole piece  44 , the first back gap piece  52 , and the layer of second non-magnetic dielectric with the imbedded first wiring layer  64 . The second pole piece  46  is typically formed of the same ferromagnetic material as the first pole piece  44 , in this example NiFe or permalloy. The first end of the second pole piece  46  is recessed a second distance  14  from the ABS plane  30 . In this example the second distance  14  is between about 0.5 and 2.0 microns. A portion of the second pole piece  46  contacts the first pole piece  44  so that the first pole piece  44  and the second pole piece  46  are magnetically stitched together. The second notch  57  further widens the non-magnetic gap between the stitched pole pieces and the layer of first ferromagnetic material  40 . 
     A second back gap piece  50 , of ferromagnetic material, is formed on the first back gap piece  52  and is in contact with the first back gap piece  52  so that the first back gap piece  52  and the second back gap piece  50  are magnetically stitched together. The region  58  between the second pole piece  46  and the second back gap piece  50  is filled with the second non-magnetic dielectric, such as alumina, and has a second wiring layer  62  formed therein. The second notch  57  is also filled with the second non-magnetic dielectric. The region  54  between the second pole piece  46  and the ABS plane  30  is also filled with the second non-magnetic dielectric. The formation of the write head at this stage is shown in FIG.  6 . FIG. 6 shows that the top surface  72  of the write head at this stage of fabrication is planar making subsequent fabrication steps easier. 
     This write head at this point of the fabrication is exactly the same as the write head of the previous embodiment. Next, as shown in FIG. 3, a third pole piece  70  having a first end and a second end is formed on the planar layer having the second pole piece  46 , the second back gap piece  50 , and the layer of second non-magnetic dielectric with the second imbedded wiring layer  62 . The third pole piece  70  is typically formed of the same ferromagnetic material as the first pole piece  44  and the second pole piece  46 , in this example NiFe or permalloy. The first end of the third pole piece  70  is recessed a third distance  15  from the ABS plane  30 . In this example the third distance is between about 2.0 and 4.0 microns. A portion of the third pole piece  70  contacts the second pole piece  46  so that the second pole piece  46  and the third pole piece  70  are magnetically stitched together. Another portion of the third pole piece  70  contacts the second back gap piece  50  so that the third pole piece  70  and the second back gap piece  50  are magnetically stitched together. 
     The third pole piece  70  in this embodiment has an interior region  68  containing a third wiring layer  66 . The interior region  68  is filled with the second non-magnetic dielectric material. A cross section of the completed write head is shown in FIG.  3 . 
     While the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made without departing from the spirit and scope of the invention.
A design for a magnetic write head having multi-layer stitched poles, a small throat height, and a recessed yoke design is described. The write head is formed of a number of planar layers and in one embodiment the write head also has a planar top surface. In another embodiment the planarity of the top layer is disturbed in order to provide an additional wiring layer. The magnetic write head is formed on a layer of ferromagnetic material which can also be used as a shield layer for a read head combined with the write head. A first pole piece has a notch which defines the throat height of the write head. A second pole piece, recessed from the air bearing surface plane, is magnetically stitched to the first pole piece. A third pole piece, further recessed from the air bearing surface plane, is magnetically stitched to the second pole piece.