Patent Publication Number: US-9412400-B2

Title: Tunnel magnetoresistance read head with narrow shield-to-shield spacing

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 14/242,717, filed on Apr. 1, 2014, which is a divisional of and claims priority to U.S. patent application Ser. No. 13/538,650 filed on Jun. 29, 2012, issued as U.S. Pat. No. 8,711,528, which are hereby incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This invention relates to the field of disk read/write heads and more specifically, to tunnel magnetoresistance (TMR) read heads and method of fabricating the same. 
     BACKGROUND 
     Increasing magnetic recording density requires narrower-track widths and narrower shield-to-shield spacing on read heads. Current tunnel magnetoresistance (TMR) read heads comprise a pinned layer coupled to an antiferromagnet (AFM) layer. The TMR read heads further comprise a free layer separated from the pinned layer by a barrier layer. Current attempts to narrow the shield-to-shield spacing by removing the AFM layer have been unsuccessful because AFM-free TMR read heads are prevalently magnetically bi-directional 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not limitation, in the figures of the accompanying drawings in which: 
         FIG. 1  illustrates a read sensor having a tabbed antiferromagnet (AFM) layer and extended pinned layer. 
         FIGS. 2A-E  illustrate a process for manufacturing a read sensor having a tabbed AFM layer and extended pinned layer. 
         FIGS. 3A-E  illustrate a second process for manufacturing a read sensor having a tabbed AFM layer and extended pinned layer. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth, such as examples of specific layer compositions and properties, to provide a thorough understanding of various embodiment of the present invention. It will be apparent however, to one skilled in the art that these specific details need not be employed to practice various embodiments of the present invention. In other instances, well known components or methods have not been described in detail to avoid unnecessarily obscuring various embodiments of the present invention. 
     The terms “over,” “under,” “between,” and “on” as used herein refer to a relative position of one media layer with respect to other layers. As such, for example, one layer disposed over or under another layer may be directly in contact with the other layer or may have one or more intervening layers. Moreover, one layer disposed between two layers may be directly in contact with the two layers or may have one or more intervening layers. In contrast, a first layer “on” a second layer is in contact with that second layer. Additionally, the relative position of one layer with respect to other layers is provided assuming operations are performed relative to a substrate without consideration of the absolute orientation of the substrate. 
       FIG. 1  illustrates a tunnel magnetoresistance (TMR) read sensor having a tabbed AFM layer and an extended pinned layer. The read sensor has an air-bearing surface plane (ABS)  104  and a plurality of layers perpendicular to the ABS  104 . A shield layer  116  is disposed over a substrate. The shield layer  116  comprises NiFe or another conventional magnetic shield material for TMR read sensors. In some cases, the shield layer  116  is composed of a single shield material. In other cases, the shield layer  116  has a composite structure. For example, shield layer  116  may comprise on or more layers of NiFe, NiFe multilayers, CoFe, or Ru. A top shield  101  is disposed over the TMR read sensor layers. The top shield layer  101  may also comprise NiFe or other conventional material for TMR read sensors. For example, the top shield  101  may have a composition similar to the lower shield layer  116 . The shield-to-shield distance  117  is the distance between the first shield layer  116  and the top layer  101  at the ABS  104 . 
     A seed layer  115  is disposed on the shield layer  116 . The seed layer may comprise Ta, Ru, a Ta/Ru bilayer or other conventional seed layers. An antiferromagnetic layer  113  (AFM layer) is disposed over the shield layer  116  on the seed layer  115 . An antiferromagnet exchange biased pinned layer  114  (or “stitching layer”) is disposed over the AFM layer  113 . The AFM layer  113  and stitching layer  114  are recessed from the ABS  104  by a recess distance  112 . Because the AFM layer  113  and stitching layer  114  are recessed from the ABS, the layers do not contribute to the shield-to-shield distance  117 . In particular cases, the recess distance may be between 10 and 500 nm. 
     The AFM material layer  113  may comprise various antiferromagnetic materials, such as IrMn, PtMn, PdMn, NiMn, RhMn, or RhRuMn. IrMn is often used in TMR AFM layers because it provides a thinner AFM layer than other materials. Because the AFM layer  113  is recessed  112  from the ABS  104 , thicker AFM layers  113  may be employed than in conventional TMR sensors without increasing shield-to-shield distance  117 . Accordingly, other antiferromagnetic materials besides IrMn may be used without increasing shield-to-shield distance  117 . 
     The stitching layer  114  is magnetically pinned by the AFM layer  113  in a direction  120 . In the illustrated sensor, the stitching layer  114  comprises a layer of CoFe that provides a material transition between the AFM material layer  113  and the pinned layer  108 . In other cases, the stitching layer  114  comprises a tri-layer of a first layer of a soft magnetic material such as CoFe, a second layer of Ru, Cr, Ag, or Au, or other suitable non-magnetic material, and a third layer of the soft magnetic material, such as CoFe. The non-magnetic material may a thickness approximately equal to the first or second oscillatory peak of the exchange coupling between the two soft magnetic layer of the multilayer. These thicknesses increase the pinning strength provided by the layer  114 . For example, for a CoFe/Ru/CoFe multilayer stitching layer  114 , the Ru thickness is either approximately 4.3 Å for the first oscillatory peak or between approximately 7 and 8 Å for the second oscillatory peak. In some cases, the stitching layer  114  may be omitted without impacting the coupling between the AFM layer  113  and the pinned layer  108 . 
     A second pinned layer  108  is disposed on the antiferromagnet exchange biased pinned layer  114  along its area and on the seed layer  115  along the shield  116  contact area. The second pinned layer  108  has its magnetic direction fixed by the stitching layer  120 . The second pinned layer  108  extends from the ABS  104  to the rear edge of the first pinned layer  114 . The pinned layer  108  may comprise conventional pinned layer materials. For example, the pinned layer  108  may have a composite, multilayer structure including a first ferromagnetic layer  110 , a non-magnetic layer  109 , and a second ferromagnetic layer  107 . The ferromagnetic layers  110  and  107  pinned layer  108  may be composed of conventional ferromagnetic materials such as NiFe, CoFe, or CoNiFe. The non-magnetic layer  109  may be composed of conventional non-magnetic materials, such as Ru. In the illustrated sensor, the first and second ferromagnetic layers  107 ,  110  are in an anti-parallel configuration  118 ,  119 , which is fixed by the orientation  120  of the first pinned layer  114 . 
     The TMR read sensor further comprises a free layer  105  separated from the pinned layer  108  by a barrier layer  106  and separated from the top shield layer  101  by a capping layer  121 . The barrier layer  106 , the capping layer  121 , and free layer  105  extend from the ABS  104  to a stripe height distance  102 . In some cases, the recess distance  112  is greater than or equal to the stripe height distance  102 . In other cases, the recess distance  112  is less than the stripe height distance. The free layer  105  comprises a ferromagnetic material, such as NiFe, CoFe, or CoNiFe. The barrier layer comprises an insulating material, and may be selected to provide a seed layer for the free layer  105 . For example, MgO may be used as the barrier layer  106 . The capping layer  121  isolates the free layer  105  from the shield layer  101  and comprises a non-magnetic material, such as Ru, Ta, or a bilayer thereof. 
     A region of conventional insulating substrate material, such as AlOx  103  covers the rear portion of the pinned layer  108  and back of the stitching layer  114  and AFM layer  113 . Along with the free layer  105 , the material layer  103  provides a planar surface for a shield layer  101 . As discussed above, this may comprise NiFe or other conventional material for TMR read sensors. 
       FIGS. 2A-2E  illustrate a first process for making a TMR read head. 
     The first processing step is illustrated in  FIG. 2A . Here, a shield layer  203  is provided on a substrate. A seed layer for the TMR read sensor is deposited on the shield layer  203 . In some embodiments, the shield layer  203  may have a composite structure. For example, the shield layer  203  may comprise one or more alternating layers of magnetic shield material and seed layers. The layers of magnetic shield materials may comprise conventional shield materials, such as NiFe. The seed layers may comprise a material that mimic the crystal structure of the magnetic shield materials, such as a layer of CoFeB. Alternatively, the seed layer may comprise an amorphous structure that isolates the grain structure of alternating shield material layers. The TMR seed further comprises a seed layer or layers  202 ,  201  for the pinned layer. For example, a bilayer of tantalum  202  and ruthenium  201  may be provided as a seed for the pinned layer. As discussed below, a further process step involves cleaning the assembly by material, so the uppermost layer  201  of the seed layer is sufficiently thick so that a proper thickness remains after planarization. In a particular case, the Ta layer  202  may be 10 nm thick and the Ru layer  201  may be 60 nm thick. 
       FIG. 2B  illustrates a second process step of the first method for making a TMR read head. In this process step a layer of photoresist  206  is formed on the substrate assembly. The photoresist pattern  206  is configured for formation of a region for the AFM layer that is recessed from the ABS. 
       FIG. 2C  illustrates a third process step of the first method for making a TMR read head. Here, the substrate assembly is etched to form a region for the AFM and the AFM is deposited in the region. The step of etching comprises etching through the seed layers  201 ,  202  into the shield layer  203 . The depth of penetration into the shield layer is configured according to the desired height of the AFM layer. After deposition, the photoresist pattern  206  is removed. In the illustrated method, the AFM includes an AFM seed layer  210 ,  209 . The AFM seed layer  210 ,  209  comprises a bilayer of Ta  210  and Ru  209 . An AFM material layer  208  is deposited on the seed layer  209 ,  210 . Then, a soft magnetic stitching layer  207  is deposited on the AFM material layer  208 . Similar to the thickness of the upper seed layer  201 , the thickness for the stitching layer  207  is configured according to the amount of material removal to occur during the subsequent cleaning step. 
     In a particular case, the first seed layer may comprise 10 nm of Ta, the second seed layer may comprise 10 nm of Ru, the AFM material layer may comprise 80 nm of IrMn, and the stitching layer may comprise 100 nm of CoFe. In this case, the depth of penetration into the shield layer  203  is 130 nm. 
       FIG. 2D  illustrates a fourth process step of the first method for making a TMR read head. In this process step, the pinned layer, free layer, and attendant layers are deposited on the substrate assembly. First, the upper layers of the assembly are cleaned by removal of some of the material of the layers—for example, by sputter each clean removal of 50 nm of material. After cleaning, the first magnetic layer  211 , the non-magnetic layer  212 , and the second magnetic layer  213  are sequentially deposited. The seed layer  216  is then deposited on the second magnetic layer  213 . The free layer  215  is deposited on the seed layer  216 . Then, the capping layer  217  is deposited on the free layer. 
     In some cases, after the capping layer  217  is deposited, the assembly is magnetically annealed. Additionally, the manufacture of the assembly up to  FIG. 2C  may be performed in situ or ex situ with the completion of the assembly in  FIG. 2D . 
       FIG. 2E  illustrates a fifth process step of the first method for making the TMR read head. After the deposition of the head layers up to the capping layer  217 , conventional subsequent processing is performed on the assembly to define the stripe height and track width. During these subsequent processing steps, the free layer  215 , capping layer  217 , and seed layer  216  are etched to the proper profile for the track width and stripe height. A filling material  214 , such as AlOx is deposited on the substrate to provide a planar region for the upper shield layer  218 . Finally, the upper shield layer  218  is deposited on the substrate. 
       FIGS. 3A-3E  illustrate a second method for making a TMR read head. 
       FIG. 3A  illustrates a first process step of the second method of making a TMR read head. The second method begins by depositing the AFM layer on the shield  305 . Similar to  FIG. 2C , the AFM layer comprises a seed layer  304 ,  303 , such as a Ta/Ru bilayer, an AFM material layer  302  and a soft stitching layer  301 . The AFM layer is deposited with similar thicknesses as the AFM layer in  FIG. 2C . For example, in a particular case, the AFM film stack comprises 10 nm of Ta  304 , 10 nm of Ru  303 , 80 nm of IrMn, and 100 nm of CoFe. 
       FIG. 3B  illustrates a second process step of the second method of making a TMR read head. In this method, a photoresist pattern  306  is formed on the upper layer  301  of the AFM layer. The photoresist pattern  306  is configured to provide a region for formation of a TMR read head seed layer such that the remaining AFM layer is recessed from the ABS. 
       FIG. 3C  illustrates a third process step of the second method of making a TMR read head. In this step, the assembly is etched to a predetermined depth into the shield  305 . A layer of shield material  309  is deposited in the region to a thickness such that the shield material layer  309  is as thick as that in the second method. A TMR seed bi-layer  308 ,  307  is then deposited on the shield material layer  309 . In some cases, a seed layer, such as a CoFeB layer is deposited on the shield layer  309  prior to the deposition of the shield material layer  209 . As with the first method, the second seed layer  307  has a thickness configured for etch cleaning. 
     In a particular case, the TMR seed layer comprises 150 nm of NiFe, 10 nm of Ta and 60 nm of Ru. 
       FIG. 3D  illustrates a fourth process step of the second method of making a TMR read head. The fourth process step proceeds similarly to the fourth process step of the first method. Like the fourth process step of the first method, this process can be performed in situ or ex situ with the third process step. An etch cleaning step removes a certain thickness of material from the uppermost layers—for example, 50 nm. Next, a pinned layer comprising a first ferromagnetic layer  310  and a second ferromagnetic layer  312  sandwiching a non-magnetic layer  311  is deposited on the substrate assembly after cleaning. Afterwards, a seed layer  313 , free layer  315  and capping layer  134  are deposited on the pinned layer. In some cases, the assembly is then magnetically annealed. 
     As in the first method, after the capping layer  314  is deposited, the assembly may be magnetically annealed. Additionally, the manufacture of the assembly up to  FIG. 3C  may be performed in situ or ex situ with the completion of the assembly in  FIG. 3D . 
       FIG. 3E  illustrates a fifth process step of the second method of making a TMR read head. This process proceeds in a substantially similar manner as described above with respect to  FIG. 2E . After the track height and stripe width of the free layer  315  are defined, a filling material  316  is deposited to form a planar region with the capping layer  314  and a top shield layer  317  are deposited on layers  314  and  316 . 
     In the foregoing specification, embodiments of the invention have been described with reference to specific exemplary features thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and figures are, accordingly, to be regarded in an illustrative rather than a restrictive sense.