Abstract:
A basic design is disclosed for bottom shield (S 1 ) and top shield (S 2 ) of the reader shields in a magnetic read-write head. The critical part of new design includes an antiferromagnetic film which pins an antiferromagnetically coupled trilayer (AFCT). The simplest embodiment for top shield, for example, would be a film sequence of FM/Ru/FM/AFM. This replaces the normal top shield design which typically comprises a ferromagnetic seed layer and a thicker plated ferromagnetic film. Processes for manufacturing these shields are also described.

Description:
[0001]    This application is related to HT06-041, filed on Aug. 2, 2007 as application Ser. No. 11/888,856, and herein incorporated, by reference, in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to the general field of magnetic read-write heads with particular reference to stabilizing their associated internal shields. 
       BACKGROUND OF THE INVENTION 
       [0003]    Magnetic read-write heads typically include two magnetic shields that are important for the reader part—the shield S 1  below the read sensor, also called the bottom shield, and shield S 2  immediately above the sensor, also called the top shield. Current typical thick film shield designs have several problems, including magnetic stability problems, increased spacing between reader and writer, and manufacturing and other issues. Changes in shield magnetic domain states can cause sensor signal changes; these are the so-called shield magnetic stability problems which may arise from applied external fields, media fields, internal write head related or thermal stresses, or even from statistical equilibrium state changes. A new shield design is disclosed that overcomes these problems. 
         [0004]    These, and other limitations of the prior art can be seen in the references that we review immediately below: 
         [0005]    U.S. Pat. No. 7,180,712 by Min Li et al. describes a laminated shield using Ru, but no AFM; it applies to MR heads, not TMR/CPP. Without the AFM layers, the shield may rotate or switch as a whole, as there is no single preferred orientation. The present invention applies to TMR/CPP and GMR/CPP devices. Min&#39;s patent also has undercoat limitations, which are not relevant for the present invention. 
         [0006]    U.S. Pat. No. 6,801,409 by Richard Michel et al. also applies to MR heads. It describes a non-laminated shield that employs an AFM to pin the shield. It is thus a single ferromagnetic(FM) layer, which is different from the present invention. In Michel&#39;s patent, the shield domain pattern is, ideally, stabilized and locked in by setting the AFM during an anneal; but as the shield is a monolayer it will have a large net moment, and is thus much harder to stabilize. There is no discussion of film thicknesses. 
         [0007]    U.S. Pat. No. 7,236,333 by Macken and Daclen applies to MR heads also. They employ an AFM pinned bilayer, but with ferromagnetic bilayer decoupled through a non-magnetic thick spacer layer. U.S. Patent Application 2007/0195467 (Gill) shows a second shield layer comprising a FM layer, an AFM layer, and a non-magnetic layer. 
         [0008]    U.S. Patent Application 2007/0139826 (Carey et al) discloses a shield with anisotropy achieved by use of textured surfaces. U.S. Pat. No. 6,496,335 (Gill) shows FM layers separated by spacer layers such as Ru as a shield, but does not include AFM layers as part of the system. Also, it claims a net moment for the FM layers, and applies to GMR/CPP heads. In U.S. Pat. No. 6,456,467, Mao et al. disclose “Laminated shields with antiparallel magnetizations”. This work does not include an AFM pinning layer. 
       SUMMARY OF THE INVENTION 
       [0009]    The shield design disclosed here can be applied to either or both S 1  and S 2 . The new design includes use of thin ferromagnetic films (FM) which are antiferromagnetically coupled (AFC) through Ru, and antiferromagnetically pinned through use of IrMn or similar layers (AFM). As an example, one of the preferred embodiments, for the case of the top shield, is a FM/Ru/FM/AFM multilayer system, where the FM are ferromagnetic layers (and may include sublayers), and Ru provides the antiferromagnetic coupling between the FM layers, and the AFM layer IrMn (or other antiferromagnetic layers) pins the rest of the system (FM/Ru/FM) and results in a preferred single orientation and direction for the shield magnetic domains. 
         [0010]    The use of 2 (or more) antiparallel FM layers allows large reductions (or elimination) of the shield net moment, and consequently allows much better pinning than can be achieved with only a single FM layer. If more the two FM layers are included, the system design is denoted as FM/Ru/FM( . . . /Ru/FM)/AFM, which altogether is referred to as the ‘SAF/AFM’ system. The FM/Ru/FM( . . . /Ru/FM) part is the synthetic antiferromagnet, or SAF. All layers are required in order to achieve stable robust magnetic domain control, with a single preferred magnetic orientation; neighboring FM layers will have opposing or antiparallel domain orientations, by virtue of the AFC coupling. 
         [0011]    Without the AFM layer, the system has multiple stable magnetic domain states. Without the Ru, for example by substituting some other non-AFC spacer, certain of the FM layers would not be stable. With only a single FM layer, the system net moment is high, shield edge demagnetizing field value and range will be very high, and the shield domain state will be difficult to stabilize. The multilayers of the SAF/AFM structure act together as a complete system which is the key part of the new stable shield design disclosed here; the SAF/AFM together with optional supplementary shielding, is called the ‘compound shield.’ This design allows reduction or optimization of read-gap-to-write-gap spacing, simplifies manufacturing, and eliminates some secondary constraints (on junction design) or penalties that burden the current unstable designs. 
         [0012]    It has been an object of at least one embodiment of the present invention to provide an improved shield for a magnetic read-write head. 
         [0013]    Another object of at least one embodiment of the present invention has been to provide a process for manufacturing said shield. 
         [0014]    Still another object of at least one embodiment of the present invention has been that the SAF/AFM part of the compound shield have a thickness less than 2500 Angstroms, without suffering any performance degradation. For the case of top shield S 2 , this thinner shield allows reduction of certain write-to-read spacing and other critical head parameters. 
         [0015]    A further object of at least one embodiment of the present invention has been to assure a reproducible shield magnetic domain orientation, a directional anisotropy, and a controlled response or rotation of the shield domains in an applied external field. 
         [0016]    These objects have been achieved by the use of a compound multilayer shield which may be used for either bottom (S 1 ) or top (S 2 ) shields of a TMR/CPP or GMR/CPP magnetic recording head. The same design applies even for heads that contain only a single shield, e.g. only a bottom shield, or only a top shield 
         [0017]    The basic design that we disclose for top shields is FM/Ru/FM/(optional additional Ru/FM)/AFM(with cap), and optional additional non-magnetic spacer and ferromagnetic shielding on top of AFM. The basic design for bottom shields is the inverse of the top shield, which is altogether [(Optional [Shielding)/(Non-magnetic Spacer)]/AFM/FM/Ru/FM. For top shield compound shields, the optional shielding on top of SAF/AFM is called the S 2   b  shield. The arrows in  FIG. 1  indicate a possible magnetization orientation for the FM layers near the sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1 . illustrates the structural features of a dual FM layer embodiment of the invention as applied to a top shield. The arrows indicate possible magnetization orientations of the upper and lower FM layers. 
           [0019]      FIG. 2  shows quasi-static transfer curves for samples with SAF/AFM pinned S 2 A. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]    In the description of the invention that follows we will provide details in terms of the top shield (S 2 ) system but it is to be understood that all these features may be applied with comparable effect to improve the bottom shield (S 1 ) system. For the top shield, the preferred embodiments are FM/Ru/FM/AFM or FM/Ru/FM/Ru/FM/AFM (3 FM layer version). 
         [0021]    A thermal anneal at between approx. 150 and 280° C. is preformed at some step after deposition, to set the pinning layer orientation, and establish the intended domain orientation for the FM layers; the anneal can be performed with or without an externally applied field, depending on design optimization considerations. 
         [0022]    The use of 3 FM layers, as opposed to 2 FM layers, results in opposite magnetic domain orientation for the FM layer closest to the sensor (for field anneal in a fixed direction). Because either orientation may be desirable depending on other aspects of the design, both 2 and 3 FM layer designs are among the preferred embodiments. 
         [0023]    As a certain amount of unbalance in the FM layers may be desirable, e.g. having the FM layer adjacent the sensor have a slightly higher moment than the other FM layer (for dual FM design), to assure specific rotation with applied external field. 
         [0024]    A multilayer stabilized shield is disclosed. An important feature is that it eliminates the shield state changes that result in sensor performance changes in TMR/CPP and GMR/CPP magnetic recording heads. Stabilizing the shield in particular will further enable reduction of thermal protrusion by thinning of the shield, enable relaxation of junction design constraints (currently hypersensitive to topology), and enable further the read gap. A specific example of new S 2  design (SAF/AFM) would be NiFe(500 Å)/CoFe(˜20 Å)/Ru(7 Å)/CoFe(˜20 Å)/NiFe(500 Å)/IrMn(70 Å), made using an all dry process. A schematic of this is given in  FIG. 1  Other specific examples are NiFe(500 Å)/CoFe(˜20 Å)/Ru(7 Å)/CoFe(˜20 Å)/NiFe 500 Å)/CoFe (˜20 Å)/IrMn(70 Å) or NiFe(500 Å)/Ru(7 Å)/NiFe(500 Å)/CoFe(˜20 Å)/IrMn(70 Å) which differ in pinning and coupling due to the CoFe sublayers in FM layers. 
         [0025]    Other permutations are recited in the claims below. 
         [0026]    There are several improvements in head design that the disclosed shields achieve: 
         [0027]    a. Stabilizes shield to minimize amp/asym/noise problems arising from shield magnetic state changes 
         [0028]    b. Facilitates use of much thinner shields than are currently employed, thus improving protrusion issues 
         [0029]    c. Makes possible the reduction or elimination of S 2   b , in which case S 2  is an all dry process. 
         [0030]    d. Enables thinner read gaps. 
         [0031]    e. With a stable S 2 , constraints on topology are relaxed making feasible thicker Hard Bias and other junction designs. 
         [0032]    f. With a thinner S 2 , a reduction of read-gap to write-gap separation becomes possible 
         [0033]    g. With a stable shields, constraints on the shield shapes are relaxed. 
         [0034]    Referring now to  FIG. 1 , we describe below a process for the manufacture of the present invention. This process description will also serve to describe the structure of the invention. 
         [0035]    After forming TMR/CPP or GMR/CPP stack  11 , on bottom shield S 1 , in the usual way, isolation layer  12  is deposited onto sidewalls  13  as well as onto the upper surface of S 1 , while leaving stack  11 &#39;s top surface uncovered. Longitudinal bias/cap layer  14  is then deposited onto isolation layer  12 , following which conducting spacer layer  15  is deposited onto longitudinal bias layer  14  as well as onto the top surface of stack  11 . These steps are not part of the invention but rather the sensor that the invented shield provides shielding for. No constraints are made for spacer layer  15  thickness, meaning the disclosure covers the range of thickness down to 0 Angstroms. 
         [0036]    Next, on top of conducting spacer layer  15 , is deposition of the first FM layer, which comprises ferromagnetic layer S 2   a - 1  and optional ferromagnetic sublayer layer  16 . On top of this is deposited the Ru antiferromagnetic coupling (AFC) layer  17 , and a second FM layer; similarly, this second FM layer comprises optional ferromagnetic sublayer layer  18  followed by S 2   a - 2 . The sublayers enhance the antiparallel exchange strength mediated by the Ru, while S 2   a - 1  and S 2   a - 2  provide the majority of the shielding. For this drawing, S 2   a - 1  &amp;  16  &amp;  17  &amp;  18  &amp; S 2   a - 2  comprise the SAF (synthetic antiferromagnet). The FM sublayers each comprise one or more materials selected from the group consisting of NiFe, FeSiAI, FeN, CoFe, CoNiFe, CoFeB, and CoZrNb. 
         [0037]    Typically the thicknesses of these ferromagnetic layers are between 70 and 2000 Angstroms. In a given SAF, the FM layers may have approximately the same thickness, for a zero net moment design, or as a matter of design choice, may have a thickness difference of up to about 30%, thereby causing the SAF to have an intentional unbalanced magnetic moment, whereby specific domain rotation in an applied external field is assured. 
         [0038]    As a matter of designer&#39;s choice, one or more additional Ru/FM layers may now be formed on S 2   a   2 . 
         [0039]    The process continues with the deposition of pinning AFM layer  19 . The latter is made up of one or more layers selected from the group consisting of NiMn, FeMn, PtMn, IrMn, PtPdMn, and NiO. Note that the FM layer adjacent the AFM layer may be made along with a special sublayer, to improve the exchange coupling between this FM and the AFM layers. A second capping layer  20  can now be deposited onto pinning AFM layer  19  to stabilize the AFM layer. As a final option and additional design choice prior to the conclusion of the process of the invention, supplementary shield layers such as S 2   b  may be formed on spacer layer  21 ; these may be needed for additional spacing and shielding. 
         [0040]    An important advantage of the structure of the present invention is that the various layers that comprise it may be kept to a minimum thickness; The SAF/AFM structure combined thickness can be less than 0.25 microns, and as thin as approx. 200 Angstroms. 
         [0041]    To complete manufacture of the full read-write head, the writer substructure (which is not shown here) will now be formed using spacer layer  21  as its substrate, or supplementary shield S 2   b  may serve this purpose as a matter of design choice. Whether or not one opts to include S 2   b  may depend on the stability of the SAF/AFM structure, and the amount of isolation, including thermal isolation, that is needed between the writer and the reader. 
         [0042]    The films of the current invention can be patterned into any shield shape (shape from plan view), including those of invention HT06-041 (incorporated herein by reference earlier). The shapes of invention HT06-041 can further optimize their behavior in the presence of repeated initialization fields, and include trapezoids, modified trapezoids, assisted trapezoids, hexagons, irregular octagons, notched quadrilaterals, and trapezoids modified to have reduced contact with the ABS (air bearing surface). 
         [0043]    Using any of these shapes will not reduce the advantages that are incurred when the process and structure disclosed in the present invention are employed. Nor will there be any loss in the effectiveness of the present invention if the various shields within a given head have shapes that differ one from another. 
         [0044]    Referring now to  FIG. 2 , we show there a series of quasi-static transfer curves for samples with SAF/AFM pinned S 2 A, as a way of demonstrating their good performance. These samples all had thick (plated) S 1  and S 2   b  layers while their S 2   a  design was of the form FM/Ru/Fm/AFM.