Abstract:
A magnetic head has an exchange isolated poletip located between a shield of an MR sensor and a write pole of an inductive sensor. The poletip is preferably made of high B s  material, allowing the flux that travels through the much larger pole layer to funnel through the poletip without saturation. The poletip is isolated from the shield layer in order to decouple the shield layer from unfavorable domain patterns that may occur in the poletip, which in turn reduces noise in the sensor, while the shield layer serves to complete the inductive circuit. Despite having a poletip isolated by nonmagnetic material, heads built according to this invention have demonstrated high overwrite as well as remarkably low noise.

Description:
TECHNICAL FIELD 
     The present invention relates to electromagnetic transducers such as may be employed in disk or tape storage systems. 
     BACKGROUND OF THE INVENTION 
     Electromagnetic transducers such as heads for disk or tape drives commonly include Permalloy (approximately Ni 80 Fe 20 ), which is formed in thin layers to create magnetic features. For example, an inductive head may have conductive coils that induce a magnetic flux in an adjacent Permalloy core, that flux employed to magnetize a portion or bit of an adjacent media. That same inductive head may read signals from the media by bringing the core near the magnetized media portion so that the flux from the media portion induces a flux in the core, the changing flux in the core inducing an electric current in the coils. Alternatively, instead of inductively sensing media fields, magnetoresistive (MR) sensors or merged heads that include MR sensors may have thin layers of materials that are used to read magnetic signals by sensing changes in electrical resistance of the MR sensor that are caused by such signals. 
     In order to store more information in smaller spaces, transducer elements have decreased in size for many years. One difficulty with this deceased size is that the amount of flux that needs to be transmitted may saturate elements such as magnetic pole layers, which becomes particularly troublesome when ends of the pole layers closest to the media, commonly termed poletips, are saturated. Magnetic saturation in this case limits the amount of flux that is transmitted through the poletips, limiting writing or reading of signals. Moreover, such saturation may blur that writing or reading, as the flux may be evenly dispersed over an entire poletip instead of being focused in a corner that has relatively high flux density. For these reasons the use of high magnetic moment (high B s ) materials in magnetic core elements has been known for many years to be desirable. For instance, iron is known to have a higher magnetic moment than nickel, so increasing the proportion of iron compared to nickel generally yields a higher moment alloy. While a number of other high-magnetic moment materials are known in the art, such as Sendust (Fe—Ni—Al) and CoZrTa, the use of predominantly-iron NiFe alloys, such as Ni 45 Fe 55 , has advantages including similarities to Permalloy that can facilitate forming high moment elements. 
     As noted in U.S. Pat. No. 5,606,478 to Chen et al., the use of high moment materials has been proposed for layers of magnetic cores located closest to a gap region separating the cores. Also noted by Chen et al. are some of the difficulties presented by these high moment materials, including challenges in forming desired elements and corrosion of the elements once formed. Chen et al. note that magnetostriction is another problem with Ni 45 Fe 55 , and teach the importance of constructing of heads having Permalloy material layers that counteract the effects of that magnetostriction. This balancing of positive and negative magnetostriction with plural NiFe alloys is also described in U.S. Pat. No. 5,874,010 to Tao et al. Anderson et al., in U.S. Pat. No. 4,589,042, also suggest that magnetostriction may be a problem with Ni 45 Fe 55 , and teach the use of high moment Ni 45 Fe 55  for poletip layers. 
     Another difficulty encountered with thin film inductive heads involves the shape of the pole layers near the poletips. The pole layers typically curve outward from the poletips in order to circumvent the coil and insulation layers sandwiched between the pole layers. This curvature between layers that are parallel in the vicinity of the recording gap can allow bleeding of the signal across the curving pole layers, diminishing fringing fields from the gap that are used to write on the media. Also problematic can be accurately defining the poletips, which may each be formed as part of a pole layer through a much thicker mask layer. An indefinite poletip width causes the track width of the head to be uncertain. To overcome these problems, U.S. Pat. No. 5,285,340 to Ju et al. and U.S. Pat. No. 5,452,164 to Cole et al. teach forming poletips in separate steps from forming pole layers, and stitching the poletips to the pole layers so that magnetic continuity is established between the intimately connected pole layers and poletips. 
     The combination of MR sensors with inductive heads introduces additional complications. Although the MR sensor may be unshielded, a pair of magnetically permeable shields usually sandwiches the sensor in order to restrict the magnetic fields reaching the sensor, essentially focusing the sensor. In one type of combined head, sometimes termed a piggyback head, the shields are separated from the inductive transducer by a layer of nonmagnetic material such as alumina (Al 2 O 3 ). An integrated head, on the other hand, uses the pole layers of the inductive transducer as shields for the MR sensor, which is formed in the recording gap in order to ensure that the sensor and inductive transducer are aligned with the same recording track of the medium despite any skewing of the head relative to such a track. Perhaps the most common type of head currently employed for hard disk drives is a merged head, in which one pole layer of the inductive transducer forms one shield of the sensor. 
     U.S. Pat. No. 5,850,325 to Miyauchi et al. teaches reducing the separation between the shield and pole layers of a piggyback head to a layer of nonmagnetic material that is thin enough to allow coupling between the shield and pole layers. With the exception of a recording gap, such an inductive transducer ensures a continuous magnetic circuit through the pole layers, since it is known that any feature that increases the reluctance associated with magnetic portions of the head decreases the efficiency of that head. Further discussion of the requirements and challenges of transducer technology can be found in  Magnetic Recording Technology , 2nd Edition, C. Denis Mee and Eric D. Daniel, Chapter 6, incorporated herein by reference. 
     SUMMARY OF THE INVENTION 
     The present invention provides a magnetic head that overcomes the challenges outlined above to provide superior performance. A magnetically isolated poletip is located between a shield of an MR sensor and a write pole of an inductive sensor. The poletip is preferably made of high B s  material, allowing the flux that travels through the much larger pole layer to funnel through the poletip without saturation. The poletip is isolated from the shield layer in order to decouple the shield layer from Barkhausen noise that may occur in the poletip, which in turn reduces noise in the sensor, while the shield layer serves to complete the inductive circuit. Despite having a poletip surrounded by nonmagnetic material, heads built according to this invention have demonstrated high overwrite as well as remarkably low noise. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cutaway cross-sectional view of a head including a transducer of the present invention. 
     FIG. 2 is a cutaway media-facing view of the head and transducer of FIG.  1 . 
     FIG. 3 is a cutaway media-facing view of a second embodiment of a head including a transducer of the present invention. 
     FIG. 4 is a cutaway cross-sectional view of a head including a transducer of the present invention interacting with an associated media. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring now to FIG. 1, a cross-sectional view of a portion of a head  20  of the present invention shows a magnetically isolated poletip  22 . A number of such heads are formed in a plurality of thin layers on wafer, which is then diced to form a number of individual heads that may include a portion of the wafer as a substrate  25 . The substrate may contain alumina, Al 2 O 3 TiC or other conventional materials. A first magnetically permeable shield layer  28  is shown disposed atop the substrate  25 , although a thin interlayer of alumina or the like may first be formed on the substrate. A read gap  30  composed of electrically insulative, nonmagnetic material such as Al 2 O 3  surrounds an MR sensor  33 . The MR sensor  33  may include a single layer of anisotropic magnetoresistive (AMR) material such as Permalloy, or the sensor may contain plural or multiple layers of sensor materials as is known to form a spin valve (SV) sensor, giant magnetoresistive (GMR) sensor, dual stripe magnetoresistive (DSMR) sensor or other known types of sensing mechanisms. 
     An electrically insulative, nonmagnetic layers  29  formed of material such as Al 2 O 3  surround shield layer  28 . Although the read gap  30  is shown as a single layer in this figure for conciseness, it may actually be formed of plural layers as is conventional. A second magnetically permeable shield layer  35  is disposed atop the read gap  30 , the second shield layer adjoining a magnetically permeable pedestal  37  distal to a media-facing surface  40  of the head  20 . Both the second magnetically permeable shield layer  35  and the magnetically permeable pedestal  37  may be formed of Permalloy or similar materials. Another electrically insulative, nonmagnetic layer  31  formed of material such as Al 2 O 3  surrounds shield layer  35 . 
     The magnetically isolated poletip  22  is separated from the shield layer  35  by a submicron layer of nonmagnetic material  44 . The nonmagnetic layer  44  may be formed of various nonmagentic materials such as alumina or various other oxides, tantalum (Ta), titanium (Ti) or other metals, silicon (S), carbon (C) or other elements. The insulative layer  44  should provide exchange decoupling between the poletip and the shield layer  35  and for that reason it is important that the layer does not permit coupling between the layers. On the other hand, the layer  44  should be thin enough to allow magnetic write signals to pass between the shield  35  and the poletip  22 . The exchange decoupling layer  44  effectively prevents domains from the poletip to influence the shield, yet allows magnetic write fields to pass through the layer  44 , filtering noise from signals. This shielding layer  44  allows the poletip  22  to contain high B s  materials, such as Ni 45 Fe 55 , FeN, FeRhN, FeTaN or FeAlN, that otherwise may be problematic. The thickness of layer  44  is preferably less than about 100 Å, in order to ensure that poletip  22  is not too isolated from shield  35 , and a 50 Å layer of Ta has proven particularly effective in this regard. 
     Between poletip  22  and pedestal  37  is a nonmagnetic, electrically insulating layer  48  which may be formed of alumina or other known materials. Adjoining insulating layer  48  is a conductive coil layer  50 , which may be formed of various highly conductive materials such as gold (Au) or copper (Cu). Although six windings are shown in this figure, more or less windings may be patterned in coil layer  50 . A recording gap layer  52  of nonmagnetic, electrically insulating material such as alumina adjoins the coil layer  50  and insulating layer  48 , and separates the poletip  22  from a write pole layer  55 . Another nonmagnetic, electrically insulating layer  57  formed with a material such as baked photoresist is disposed between the coil windings. A first protective layer  60  may be formed on the pole layer  55  on what will be a trailing end of head  20 , and a second protective layer  62  may be formed on the media-facing surface  40  after the wafer has been diced, the layers made of corrosion resistant, nonmagnetic materials. For the situation in which a corrosion resistant protective layer such as layer  62  is not formed, poletip  22  still has a nonmagnetic material such as air or perhaps lubricant adjoining its media-facing surface, so that the poletip is isolated from other magnetic materials. 
     FIG. 2 shows a view of the head  20  of FIG. 1 as it appears from the perspective of a associated media on which the head reads and writes, looking through any transparent protective layer that may be formed on the media-facing surface of the head. The isolation of poletip  22  from other magnetic elements such as shield layer  35  and write layer  55  is evident in this view of the head as it interacts with a disk or tape. A double recording gap is in effect provided by nonmagnetic layers  44  and  52 , however, this does not appear to interfere with writing signals to the media since layer  44  is typically much thinner than layer  52  and produces a much smaller fringing field than that adjacent gap layer  52 . Additionally, the desired recording gap layer  52  encounters the media after the isolation layer  44  and thus overwrites any magnetic pattern written on the media by layer  44 . Also apparent from this figure is that electrically insulating, nonmagnetic layer  48  surrounds pole layer  55 , whereas another electrically insulating, nonmagnetic layer  66  adjoins layers  44  and  48  and isolated pole  22 . During trimming of pole  22  it is important to avoid removing isolation layer  44 . 
     FIG. 3 shows another embodiment of the present invention including a portion of a head  70  as it appears from an associated media. For conciseness, those features or elements that are effectively the same as shown in FIG. 2 will not be reiterated here. Much as before, a nonconductive or highly resistive, nonmagnetic layer  72  is formed, preferably of Ta having a thickness less than about 100 Å and extending beyond an area adjacent a poletip. A magnetically permeable layer  74  such as Permalloy is then formed on the nonmagnetic layer. Both these layers  72  and  74  may be sputter-deposited, and are followed by a layer of high B s  material, preferably Ni 45 Fe 55 , which may be electroplated via window frame plating or other known techniques to form isolated poletip  77 , creating an island of magnetic material encircled by electrically insulating layers  86  and  88 . 
     A recording gap layer  76  of insulating, nonmagnetic material such as alumina is formed to a thickness that may be less than is conventional, preferably between about 1000 Å-2000 Å, to allow space in the recording gap for a nonmagnetic seed layer  80  such as chromium (Cr). The Cr seed layer  80  provides a favorable crystallographic template for sputtering or other epitaxial deposition of a high B s  and high permeability poletip layer  83  of Ni 45 Fe 55 . A thicker layer  85  of high B s  and high permeability Ni 45 Fe 55  is electroplated via window frame plating or other known techniques atop layer  83  to form the remainder of a trailing write pole, which is surrounded by nonmagnetic, electrically insulating layer  88 . A protective coating  90  is formed on the trailing pole layer  85  and insulating material  88  to create a trailing end for the head  70 . 
     FIG. 4 shows a head  100  of the present invention interacting with a media such as a rigid disk  200 . Much as described above, the head  100  of this embodiment has a substrate  105  and a magnetically permeable first shield  107 . A nonmagnetic first read gap layer  110  adjoins the shield  107  and an MR sensor  112 , the sensor preferably incorporating plural layers forming one of a variety of known sensing mechanisms. A nonmagnetic back gap layer  115  and a second read gap layer  117  surround the sensor  112  in this cross-sectional view. A second magnetically permeable shield layer  120  adjoins the second read gap layer, and a nonmagnetic, electrically insulating or highly resistive isolation layer  122  is disposed on the second shield adjacent a protective coating  123  that forms a media-facing surface  125  of the head  100 . The isolation layer  122  is preferably formed to a thickness of less than 100 Å, and extends from the media-facing surface  125  much further than the sensor  112 . A seed layer  127  of Permalloy or other magnetically permeable materials is formed on the isolation layer  122  adjacent the media-facing surface  125  and on the second shield layer  120  distal to the media-facing surface, the seed layer preferably formed by sputtering to a thickness in a range between about 500 Å and 1000 Å. 
     A magnetic poletip  130  is then formed, preferably of high B s  material such as Ni 45 Fe 55 , atop a portion of the seed layer closest to the media-facing surface. The poletip  130  may extend significantly less than the isolation layer from the media-facing surface. Although not shown in this cross-sectional drawing, the isolation layer also extends much further than the poletip  130  in a direction into and out of the plane of the drawing, the isolation layer preferably extending about as far as the seed layer  127  while the poletip extends only as far as a recording track width. A nonmagnetic, electrically insulating spacer layer  133  adjoins the poletip  130  distal to the media-facing surface  125 , and a conductive coil layer  135  and recording gap layer  138  are formed on the planar interface presented by the poletip and spacer. Another nonmagnetic, electrically insulating spacer layer  140  encircles the conductive coil layer  135  windings, and a write pole layer  144 , preferably formed of a magnetically permeable, high B s  material such as Ni 45 Fe 55 , is disposed on the recording gap layer  138  and spacer layer  140 . The coil layer  135  is disposed significantly further from the media-facing surface  125  than the termination of both poletip  130  and isolation layer  122 , affording a reduced apex angle to the write pole layer  144 . 
     The disk  200  includes a wafer substrate  202  that may be made of glass, SiC, aluminum, or any of a number of other materials known to be used for this purpose. The substrate may or may not be roughened or patterned, as is known in the art, and is covered with an underlayer  205  that may provide adhesion and a desired structure for a media layer  210  formed on the underlayer. The media layer  210  may be a conventional cobalt (Co) based alloy, which may include elements such as chromium (Cr), platinum (Pt) and tantalum (Ta), for instance. Although a single media layer  210  is shown for conciseness, layer  210  may actually represent several layers as is known, and may be designed for longitudinal or perpendicular data storage. The underlayer  205  may include Cr, nickel aluminum (NiAl), magnesium oxide (MgO) or other materials known in the art, and may be formed of more than one layer. Atop the media layer  210  a thin overcoat  212  is formed of a dense, hard material such as diamond-like carbon (DLC), tetrahedral amorphous carbon (ta-C), silicon carbide (SiC) or other materials. The disk  200  is spinning relative to the head  100  as shown by arrow  220 , at operating speeds that may range from 1000 RPM to over 10,000 RPM. Although the head is shown spaced from the disk in this figure, it is known that the head may alternatively contact the disk. 
     Although we have focused on teaching the preferred embodiment, other embodiments and modifications of this invention will be apparent to persons of ordinary skill in the art in view of these teachings. Therefore, this invention is to be limited only by the following claims, which include all such embodiments and modifications when viewed in conjunction with the above specification and accompanying drawings.