Abstract:
A current perpendicular-to-the-plane magnetoresistance (CPP-MR) read head includes a top shield and a bottom shield formed of magnetically shielding, electrically-conductive material. A multilayer magnetoresistance (MR) structure is disposed between the top shield and the bottom shield. The MR structure is in electrical contact with the top and bottom shields. A transverse magnetic field generating structure is adjacent the MR structure to transversely, magnetically bias the MR structure. The transverse magnetic field generating structure includes two permanent magnets on either side of the MR structure, and a T-shaped soft magnetic layer to direct magnetic flux from the magnets to the MR structure. In this manner, the read head provides a strong and uniform transverse magnetic bias to the MR structure.

Description:
This application claims the benefit of a provisional application, which was filed on Aug. 8, 2000 and assigned Provisional Application No. 60/223,694, which is hereby incorporated by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to giant magnetoresistance (“GMR”) transducers or read heads for reading magnetic signals from magnetic recording media, and more particularly, to current perpendicular-to-the-plane giant magnetoresistance (“CPP-GMR”) designs. While the invention finds particular application in conjunction with reading hard disk drives, the invention can be implemented with other magnetic storage media. Moreover, the invention can be implemented in other magnetic field detection devices as well as in other devices and environments. 
     2. Description of the Related Art 
     Giant magnetoresistance (GMR) was initially described by Baibich et al. in Physical Review Letters, Volume 61, No. 21, pp. 2472-2475 (1988), which is hereby incorporated by reference. GMR occurs when an application of an external field causes a variation in the relative orientation of the magnetizations of neighboring ferromagnetic layers. This in turn causes a change in the spin-dependent scattering of conduction electrons, thereby changing the electrical resistance of the structure. The discovery of GMR triggered a wide study of transport properties of magnetic multilayers. In most cases, the current flows-in-the plane of the layers, called CIP-MR. 
     Pratt et al. extended the GMR measurements to the case where the current flows perpendicular-to-the-plane, called CPP-MR as described in Pratt et al., Physical Review Letters, Volume 66, pp. 3060 (1991), which is hereby incorporated by reference. In general, the CPP-MR effect is several times larger than the CIP-MR effect. For MR read head applications, the CPP-MR element has to be dramatically scaled down (&lt;100 nm) because of the very small specific resistance of the MR element with the CPP configuration. 
     In both CIP-MR and CPP-MR, the application of an external field causes a variation in the relative orientation of the magnetizations of neighboring ferromagnetic layers. This in turn causes a change in the spin-dependent scattering of conduction electrons and thus the electrical resistance of the structure. Theoretically, the resistance for CPP multilayers with a unique type of magnetic layer varies approximately as R(θ)/R ap =1−a·cos 2 (θ/2), where R(θ) is the resistance in an external field, R ap  (ap refers to antiparallel) is the resistance at zero field, θ is the angle between the magnetization of successive or neighboring magnetic layers, and 0&lt;a&lt;1. Dauguet et al., Physical Review B, Volume 54, pp. 1083-87 (July 1996). Thus, the resistance versus magnetic field for a CPP multilayer is a typical parabolic curve. As a result, in order to apply CPP-MR for MR heads, a transverse magnetic bias to the CPP multilayer is required. 
     SUMMARY OF THE INVENTION 
     Accordingly, the present invention is directed to a CPP-MR read head with novel transverse magnetic bias that substantially obviates one or more of problems due to limitations and disadvantages of the related art. 
     Additional features and advantages of the invention will be set forth in the description which follows and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. 
     To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, a CPP-MR head includes a top shield and a bottom shield formed of magnetically shielding, electrically-conductive material. A multilayer magnetoresistance (MR) structure is disposed between the top shield and the bottom shield. The MR structure is in electrical contact with the top and bottom shields. A transverse magnetic field generating structure is adjacent the MR structure to transversely, magnetically bias the MR structure. 
     In another aspect of the present invention, a method of magnetically biasing a CPP-GMR read head is provided. The read head includes a multilayer GMR structure comprising a bilayer portion represented by [F/NM] n , where F represents a ferromagnetic material, NM represents a non-magnetic material, and n is an integer greater than or equal to 2 referring to the number of times the bilayer is repeated. The GMR structure is transversely magnetically biased using at least one magnet. Magnetic flux of the magnet is directed through the GMR structure using a soft magnetic layer. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiments of the invention and together with the description serve to explain the principle of the invention. 
     In the drawings: 
     FIG. 1 is a top schematic view of one embodiment of the CPP-MR head of the present invention; 
     FIG. 2 a  is a schematic cross-sectional view of the embodiment from an air bearing surface (ABS) or line A—A of FIG. 1; and 
     FIG. 2 b  is a schematic cross-sectional side view of the embodiment from a line B—B of FIG.  1 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. 
     FIG. 1 is a top schematic view of one embodiment of the present invention. A CPP-MR multilayer structure, pillar, or sensor  20  is placed in between two shields (bottom shield  10  and top shield  50 ). Preferably, the MR structure has a top surface area of less than or equal to 0.1×0.1 μm 2  and a thickness in a range of 10 nm to 100 nm. The shields may be any magnetically-shielding, electrically-conductive material such as NiFe, NiFeX (where X=Cr, Ta, Nb, Zr, and/or Mo), CoZrNb or CoZrTa. 
     Two permanent magnets  30   a  and  30   b  are disposed adjacent opposite side edges of the MR pillar  20 . A T-shape soft magnetic layer  40  is disposed such that a center portion or stem  42  is adjacent a back edge of the MR pillar  20  and two side portions  44  of the magnetic layer are connected to or are contiguous with the two magnets. Preferably, a length or height of the stem of the T-shape soft magnetic layer is less than 5 μm. The permanent magnets and soft magnetic layer provide a transverse magnetic bias field to the MR pillar. The arrangement of the permanent magnets and the soft magnetic layer desirably directs magnetic flux to the MR pillar. Preferably, the MR pillar is positioned symmetrically with respect to a width d, of the stem such that a center of the width of the stem and a center of a width of the MR pillar are in a line perpendicular to the line A—A. Further, preferably, a separation d 2  between the two permanent magnets is less than 5 μm. 
     An oxide layer (not shown) separates and electrically isolates the edges of the MR pillar from the two permanent magnets and the soft magnetic layer. In this embodiment, no ferromagnetic layer is located at a front edge of the CPP multilayer pillar  20 . The front edge of the CPP pillar as well as the front edges of the permanent magnets will be the site of an air-bearing surface (“ABS”), denoted by the dashed line A—A, after machining of the MR head. During operation, the ABS will face a magnetic recording medium. In this manner, magnetic flux from transitions recorded in the magnetic medium will be detected by the MR pillar. In an alternative embodiment, the front edge of the MR pillar can be recessed from the ABS and the flux brought to the recessed front edge of the pillar by means of a flux guide. 
     The two permanent magnets are initialized in a direction (as shown by arrows in FIG. 1) perpendicular or orthogonal to the ABS. Thus, the soft magnetic layer  40  brings the magnetic field from the two permanent magnets to the MR pillar  20  in a direction perpendicular to the ABS, called transverse magnetic bias. The operating point of the CPP-MR heads can be optimized by adjusting 1) the separation h 1  between the MR pillar and the front edge of the stem of the soft magnetic layer, and 2) the width d 1  of the stem of the soft magnetic layer located in between the two permanent magnets. 
     FIG. 2 a  is a cross-sectional front or ABS view of the embodiment shown in FIG.  1 . The two shields  10  and  50  are isolated from each other by an oxide  60  made of Al 2 O 3  or SiO 2 . The shields are electrically connected with the MR pillar  22  through two nonmagnetic metal gaps  21  and  23 . Thus, a sense current Is carried by the two shields flows through the MR pillar in a current perpendicular-to-the-plane configuration, as represented by an arrow in FIG. 2 extending through the pillar. The two permanent magnets  30   a  and  30   b  are embedded inside the oxide  60  and are disposed adjacent and opposite either side of the MR pillar. In order to achieve transverse magnetic bias, the permanent magnets are initialized perpendicular to the ABS. In an alternative embodiment, each of the permanent magnets are deposited on top of an underlayer  70  made of Cr, Ta, or CrTa. 
     In the preferred structure, the MR pillar includes a repeated bilayer portion represented by [F/NM] n , where F represents a ferromagnetic material, NM represents a non-magnetic material, such as a noble metal, and n refers to a bilayer number, which is an integer greater than or equal to 2. At zero magnetic field, neighboring F layers are antiferromagnetically coupled. The [F/NM] n  portion is deposited on top of a buffer layer such as Ta, NiCr, or NiFeCr. A thickness of the MR pillar is in the range of 10 nm to 100 nm, preferably less than 50 nm. Also, the ferromagnetic layer is made of Co or Co-based alloys such as CoFe, CoFeB, and NiFeCo, and the nonmagnetic layer is made of Cu, Ag, or Cu-based alloys. The metal gaps are made of Cu, Ag, Au, or α-Ta. The permanent magnets are selected from Co-αFe 2 O 3 , CoPt, CoCrPt, and CoCrTaPt. The soft magnetic layer is selected from NiFe, where NiFeX (X=Cr, Ta, Nb, Zr, and/or Mo), CoZrNb and CoZrTa. 
     FIG. 2 b  is a cross-sectional view along line B—B of FIG.  1 . The soft magnetic layer  40  embedded in oxides  60  is disposed in between the two shield  10  and  50 , and is separated from the MR structure with a separation h 1 . In an alternative embodiment, the soft magnetic layer is deposited on top of an underlayer  80  made of Ta, NiCr or NiFeCr. The soft magnetic layer is thicker than the GMR multilayer and the bottom part of the T-shape soft magnetic layer is wider than the GMR multilayer. The magnetic field from the permanent magnets is brought to the GMR multilayer by the soft magnetic layer in a direction represented by the arrows, which are perpendicular to the ABS, i.e., transverse magnetic bias. The strength of transverse magnetic bias to the GMR multilayer can be adjusted by adjusting 1) the separation h 1  between the GMR multilayer and the front edge of the stem of the T-shape soft magnetic layer, and/or 2) the material and the thickness of the soft magnetic layer and permanent magnets. The uniformity of the transverse magnetic bias to the GMR multilayer can be assured by patterning the soft magnetic layer such that the width d 1  of the stem is wider than a width of the MR head (and thus wider than a trackwidth of the magnetic recording medium with which the head will be used). 
     In developing and evaluating the invention, various tests were performed which will now be discussed. These tests show additional preferable features of the invention. First, the output, asymmetry, and signal-to-noise ratio SNR versus the separation h 1 , i.e., the distance between the GMR multilayer and the stem of the T-shape soft magnetic layer, was investigated. Each of Tables 1-1 to 1-3 below shows test results for heads designed for an areal density over 100 Gbit/in 2 . Further, each of Tables 1-1 to 1-3 shows the results using an MR pillar having length and width dimensions (as seen in the top view of FIG. 1) of 0.1×0.1 μm 2 , 0.08×0.08 μm 2 , and 0.06×0.06 μm 2 , respectively. The definitions of d 1 , d 2 , h 2 , t PM  and t SM  are denoted in FIG. 1, FIG. 2 a  and FIG. 2 b . Ref. CIP refers to a reference CIP MR structure. The MR multilayer pillar tested comprised a structure of NiCr3/[CoFe2.5/Cu2] 10  (where the stated thickness is in nm). As shown in the Tables, for the three different dimension heads, the output and asymmetry are good with h 1  of 0.6 μm or 1.0 μm. Thus, in the present invention, h 1  is preferably in the range of 0.05 μm to 2.0 μm, and more preferably in the range of 0.5 μm to 1.0 μm. 
     
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1-1 
               
             
             
               
                   
                   
               
               
                   
                 0.1 × 0.1 μm 2   
               
             
          
           
               
                   
                 h1 (μm) 
                 output (mV/μm) 
                 Asym (%) 
                 SNR (dB) 
               
               
                   
                   
               
             
          
           
               
                   
                 0.3 
                 11.6 
                 −4.7 
                 26.9 
               
               
                   
                 0.6 
                 12.9 
                 0.6 
                 28.6 
               
               
                   
                 1 
                 12.4 
                 0.9 
                 27.9 
               
               
                   
                 1.5 
                 13.5 
                 4.2 
                 29.4 
               
               
                   
                 Ref. CIP 
                 8.1 
                 0.7 
                 23.9 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1-2 
               
             
             
               
                   
                   
               
               
                   
                 0.08 × 0.08 μm 2   
               
             
          
           
               
                   
                 h1 (μm) 
                 output (mV/μm) 
                 Asym (%) 
                 SNR (dB) 
               
               
                   
                   
               
             
          
           
               
                   
                 0.3 
                 15.3 
                 −5.9 
                 27.2 
               
               
                   
                 0.6 
                 17.5 
                 0.5 
                 29.5 
               
               
                   
                 1 
                 16.9 
                 0.7 
                 23.9 
               
               
                   
                 1.5 
                 18.6 
                 3.5 
                 30.7 
               
               
                   
                 Ref. CIP 
                 10.5 
                 0.5 
                 24.5 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 1-3 
               
             
             
               
                   
                   
               
               
                   
                 0.06 × 0.06 μm 2   
               
             
          
           
               
                   
                 h1 (μm) 
                 output (mV/μm) 
                 Asym (%) 
                 SNR (dB) 
               
               
                   
                   
               
               
                   
                 0.3 
                 22.3 
                 −7.2   
                 28.2 
               
               
                   
                 0.6 
                 23.3 
                 0.9 
                 29.0 
               
               
                   
                 1 
                 23.7 
                 1.3 
                 29.3 
               
               
                   
                 1.5 
                 24.1 
                 3.2 
                 29.6 
               
               
                   
                 Ref. CIP 
                 — 
                 — 
                 — 
               
               
                   
                   
               
             
          
         
       
     
     Next, the output, asymmetry, and SNR versus the width d 1  of the stem of the soft magnetic layer was investigated. Each of Tables 2-1 to 2-3 below shows test results for heads designed for an areal density over 100 Gbit/in 2 . Further, each of Tables 2-1 to 2-3 shows the results using an MR pillar having length and width dimensions (as seen from top view of FIG. 1) of 0.1×0.1 μm 2 , 0.08×0.08 μm 2 , and 0.06×0.06 μm 2 , respectively. The definitions of d 1 , d 2 , h 2 , t PM  and t SM  are denoted in FIG. 1, FIG. 2 a  and FIG. 2 b . Ref. CIP refers to a reference CIP MR structure. The MR multilayer pillar tested comprised a structure of NiCr3/[CoFe2.5/Cu2] 10  (where the stated thickness is in nm). As shown in the Tables, the width d 1  of the stem of the soft magnetic layer is preferred to be at least 10 times of width of the MR pillar. 
     
       
         
               
               
             
               
               
               
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2-1 
               
             
             
               
                   
                   
               
               
                   
                 0.1 × 0.1 μm 2   
               
             
          
           
               
                   
                 d1 (μm) 
                 output (mV/μm) 
                 Asym (%) 
                 SNR (dB) 
               
               
                   
                   
               
             
          
           
               
                   
                 0.2 
                 10.7 
                 3.1 
                 25.7 
               
               
                   
                 0.5 
                 11.3 
                 1.7 
                 26.5 
               
               
                   
                 0.8 
                 12.2 
                 0.9 
                 27.7 
               
               
                   
                 1 
                 12.9 
                 0.6 
                 28.6 
               
               
                   
                 Ref. CIP 
                 8.1 
                 0.7 
                 23.9 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2-2 
               
             
             
               
                   
                   
               
               
                   
                 0.08 × 0.08 μm 2   
               
             
          
           
               
                   
                 d1 (μm) 
                 output (mV/μm) 
                 Asym (%) 
                 SNR (dB) 
               
               
                   
                   
               
               
                   
                 0.2 
                 16.0 
                 2.9 
                 27.9 
               
               
                   
                 0.5 
                 16.2 
                 1.3 
                 28.2 
               
               
                   
                 0.8 
                 16.9 
                 0.7 
                 28.9 
               
               
                   
                 1 
                 17.5 
                 0.5 
                 29.5 
               
               
                   
                 Ref. CIP 
                 10.5 
                 0.5 
                 24.5 
               
               
                   
                   
               
             
          
         
       
     
     
       
         
               
               
             
               
               
               
               
               
             
           
               
                   
                 TABLE 2-3 
               
             
             
               
                   
                   
               
               
                   
                 0.06 × 0.06 μm 2   
               
             
          
           
               
                   
                 d1 (μm) 
                 output (mV/μm) 
                 Asym (%) 
                 SNR (dB) 
               
               
                   
                   
               
               
                   
                 0.2 
                 23.6 
                 2.6 
                 29.2 
               
               
                   
                 0.5 
                 23.1 
                 0.7 
                 28.8 
               
               
                   
                 0.8 
                 22.7 
                 0.5 
                 28.5 
               
               
                   
                 1 
                 23.3 
                 0.9 
                 29.0 
               
               
                   
                 Ref. CIP 
                 — 
                 — 
                 — 
               
               
                   
                   
               
             
          
         
       
     
     It will be apparent to those skilled in the art that various modifications and variations can be made in the apparatus and method of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention cover the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.