Abstract:
A magnetic head includes a substrate and a data transducer positioned upon the substrate. The data transducer includes a reader comprised of a top shield and a bottom shield characterized by at least one of the shields including a layer for compensating a thermally-caused expansion of the reader.

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S)  
       [0001]    This application claims priority from provisional application No. 60/397,634 filed Jul. 22, 2002, for “MULTILAYER MAGNETIC SHIELDS WITH COMPENSATED THERMAL PROTRUSION” by Ladislav Rudolf Pust, Mark Thomas Kief, Ibro Tabakovic, James F. Dolejsi, and Vee Sochivy Kong. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    The present invention relates generally to the field of magnetic data storage and retrieval systems. In particular, the present invention relates to a thin film transducing head having improved performance due to a reduced thermal pole tip protrusion.  
           [0003]    In a magnetic data storage and retrieval system, a thin film transducing head typically includes a transducer, a substrate upon which the transducer is built, and an overcoat deposited over the transducer. The transducer, which typically includes a writer portion for recording magnetically-encoded information on a magnetic media and a reader portion for retrieving that magnetically-encoded information from the magnetic media, is formed of multiple layers successively stacked upon the substrate. The volume of the transducer is typically much smaller than both the volume of the substrate and the volume of the overcoat.  
           [0004]    The layers of the transducer, which include both metallic and insulating layers, all have different mechanical and chemical properties than the substrate. These differences in properties affect several aspects of the transducer. First, the layers of the transducing head will be lapped at different rates. Thus, when an air bearing surface (ABS) of the transducing head is lapped during its fabrication, different amounts of the layers will be removed, resulting in the transducing head having an uneven ABS. Commonly, a greater amount of the metallic layers of the transducer will be removed during the lapping process than will be removed from the substrate. Thus, the lapping process results in a pole-tip recession (PTR) of the metallic layers of the transducer with respect to the substrate. The PTR of a particular layer is defined as the distance between the air bearing surface of the substrate and the air bearing surface of that layer.  
           [0005]    The differing mechanical and chemical properties of the substrate and transducer layers affect the air bearing surface during operation of the transducing head. As the magnetic data storage and retrieval system is operated, the transducing head is subjected to increased temperatures within the magnetic data storage and retrieval system. In addition, a temperature of the transducing head itself, or a part thereof, may be significantly higher than the temperature within the magnetic data storage and retrieval system due to heat dissipation caused by electrical currents in the transducer.  
           [0006]    The coefficient of thermal expansion (CTE) of materials used in forming the substrate is typically much smaller than the CTE of materials used in forming the metallic layers of the transducer. Due to the large CTE of the transducer&#39;s metallic layers, those layers tend to expand a greater amount in response to high temperatures than the substrate. Thus, when the transducing head is subjected to high operating temperatures, the metallic layers tend to protrude closer to the magnetic disc than the substrate, thereby affecting the PTR of the transducer. This change in PTR caused by temperature is referred to as the Thermal PTR (TPTR).  
           [0007]    During operation of the magnetic data storage and retrieval system, the transducing head is positioned in close proximity to the magnetic media. The distance between the transducer and the media is preferably small enough to allow for writing to and reading from the magnetic media with a large areal density, and great enough to prevent contact between the magnetic media and the transducing head. Performance of the transducer depends primarily upon the distance between the media and the transducing head.  
           [0008]    To keep the distance between the transducing head and the magnetic media constant, PTR should not change significantly with temperature. If TPTR is large, then the spacing between the transducer and the media will change significantly with temperature, thereby requiring that the low temperature fly height be enough to accommodate the higher operating temperatures. On the other hand, if TPTR is close to zero, the low temperature fly height can be reduced.  
           [0009]    In typical transducing heads, the magnetic shields are made of Permalloy, in particular a NiFe alloy with a composition close to 20% Fe-80% Ni. Permalloy is nearly ideal shielding material with very high permability and nearly zero magnetostriction. However, Permalloy has a large CTE, between 12 and 13×10 −6 /° C. Large thermal expansion of the shields, in comparison to the AlTiC substrate, is a major contributor to TPTR. Without drastic reduction of TPTR, disc drives with such transducing heads cannot operate at areal density around and above 100 Gb/inch 2 . Other prior art solutions for reducing the shield contribution to TPTR include (a) using a smaller shield, (b) using a thinner shield, or (c) manufacturing the shield with another magnetic material having a low CTE, such as 45/55 NiFe. These known solutions only partially reduce TPTR and oftentimes result in transducing heads having deteriorated magnetic performance.  
           [0010]    The present invention is a transducing head structure that reduces the TPTR of magnetic shields when the transducing head is operated at high temperatures.  
         BRIEF SUMMARY OF THE INVENTION  
         [0011]    The present invention relates to a magnetic head having a substrate and a data transducer positioned upon the substrate. The data transducer includes a reader comprised of a top shield and a bottom shield characterized by at least one of the shields including a layer for compensating a thermally-caused expansion of the reader. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    [0012]FIG. 1 is a partial cross-sectional view of a transducing head in accord with the present invention.  
         [0013]    [0013]FIG. 2 is a schematic cross-sectional view of the transducing head in accord with the present invention.  
         [0014]    [0014]FIG. 3 is a schematic cross-sectional view of another embodiment of a transducing head in accord with the present invention.  
         [0015]    [0015]FIG. 4 is a schematic cross-sectional view of another embodiment of a transducing head in accord with the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0016]    [0016]FIG. 1 is a partial cross-sectional view of a transducing head  10  in accord with the present invention. The cross-section of FIG. 1 is taken substantially normal to an air bearing surface (ABS) of transducing head  10 . Transducing head includes a substrate  12 , a basecoat  14 , a reader  16 , a writer  18 , an insulating layer  20  and an overcoat  22 . Reader  16  includes a bottom shield structure  24 , a read element  26 , a read gap  28 , and a top shield structure  30 . Writer  18  includes a bottom pole  32 , a shared pole extension  34 , a back via  36 , a conductive coil  38 , a coil insulator  40 , and a top pole  42 . A shared pole  44  is formed by the combination of top shield structure  30  and bottom pole  32 .  
         [0017]    Basecoat  14  is deposited on substrate  12 . Reader  16  and writer  18  are each multi-layered devices, which are stacked upon basecoat  14  adjacent the ABS of transducing head  10 . As shown in FIG. 1, reader  16  is formed on basecoat  14 , and writer  18  is stacked on reader  16  in a piggyback configuration (in which layers are not shared between the two elements). In other embodiments not illustrated, reader  16  and writer  18  may be arranged in a merged-head configuration (in which layers are shared between the two elements) and/or writer  18  may be formed on basecoat  14  (with reader  16  being formed on writer  18 ). Co-planarly positioned with the layers of reader  16  and writer  18 , and opposite the ABS of transducing head  10 , is insulating layer  20 . Overcoat  22  is formed upon writer  18  and insulating layer  20 .  
         [0018]    Substrate  12  is typically formed of a material such as AlTiC, TiC, Si, SiC, Al 2 O 3 , or other composite materials formed of combinations of these materials. Of these materials, AlTiC and TiC have relatively large coefficients of thermal expansion (CTE), typically in the range of about 6.6×10 −6 /° C. to about 8.3×10 −6 /° C., while silicon has a lower CTE, in the range of about 2.0×10 −6 /° C. to about 3.0×10 −6 /° C.  
         [0019]    Basecoat  14  is formed on substrate  12  in transducing head  10  shown in FIG. 1, although other embodiments may have basecoat  14  formed in an alternative location. Basecoat  14  is generally formed of an insulating material, such as Al 2 O 3 , AlN, SiO 2 , Si 3 N 4 , or SiO 0-2 N 0-1.5 . Generally the insulating material for basecoat  14  is selected to most closely match the chemical and mechanical properties of the material used as substrate  12 . For example, an Al 2 O 3  basecoat is commonly used in conjunction with an AlTiC substrate, since the two materials have similar CTE.  
         [0020]    Reader  16  is formed on basecoat  14 , and includes bottom shield structure  24 , read element  26 , read gap  28 , and top shield structure  30 . Bottom shield structure  24  is a multi-layered structure comprised of a compensation layer  46 , a non-magnetic spacer  48 , and a bottom shield  50 . Compensation layer  46  is formed upon basecoat  14  and bottom shield  50  is formed adjacent read gap  28 . Non-magnetic spacer  48  is positioned between compensation layer  46  and bottom shield  50 . The multi-layered bottom shield structure  24  is manufactured in a one-step plating or sputtering process.  
         [0021]    Top shield structure  30  is spaced apart from the bottom shield structure  24  by read gap  28 . Top shield structure  30  is a multi-layered structure comprised of a compensation layer  52 , a non-magnetic spacer  54 , and a top shield  56 . Top shield  56  is positioned adjacent read gap  28  and non-magnetic spacer  54  separates top shield  56  from compensation layer  52 . Compensation layer  52  is formed upon non-magnetic spacer  54  of top shield structure  30 . The multi-layered top shield structure  30  is manufactured in a one-step plating or sputtering process.  
         [0022]    Bottom and top shields  50  and  56  are formed of Permalloy, and in particular a NiFe alloy with a compensation close to 20% Fe-80% Ni. Such a metallic alloy typically has a large CTE. For example, Ni 79 Fe 21  has a CTE of about 12.2×10 −6 /° C. Permalloy exhibits large permeability and low coercivity needed for shields.  
         [0023]    Compensation layers  46  and  52  are formed of a material having a low CTE, such as Invar, a NiFe alloy with a composition close to 35% Fe-65% Ni. Preferably, compensation layers  46  and  52  are made of a low CTE material having a CTE between about 1×10 −6 /° C. to about 2.5×10 −6 /° C., and most importantly less than the CTE of the shields.  
         [0024]    Non-magnetic spacers  48  and  54  function to magnetically separate each shield ( 50  and  56 ) from its respective compensation layer ( 46  and  52 ) to ensure better magnetic performance of shields  50  and  56 . Although the material forming compensation layers  46 ,  52  has a low CTE, it is also a magnetic material. Thus, non-magnetic spacers  48 ,  54 , separate shields  50 ,  56  and compensation layers  46 ,  52  to protect shields  50 ,  56  from magnetic noise. First spacer  48  is positioned between bottom shield  50  and first compensation layer  46 , and second spacer  54  is positioned between top shield  56  and second compensation layer  52 . Furthermore, spacers  48 ,  54  are positioned adjacent the ABS. Spacers  48 ,  54  are formed of a non-magnetic material, such as NiPd, CuNi, NiP, Cr, or Alumina.  
         [0025]    Read gap  28  is defined on the ABS between terminating ends of bottom shield  50  and top shield  56 . Read element  26  is positioned in read gap  28  adjacent the ABS. Read gap  28  insulates read element  26  from bottom shield  50  and top shield  56 . Read element  26  may be any variety of different types of read elements, such as an anisotropic magnetoresistive (MR) read element or a giant magnetoresistive (GMR) read element. In operation, magnetic flux from a surface of a magnetic media causes rotation of a magnetization vector of MR read element  26 , which in turn causes a change in electrical resistivity of MR read element  26 . The change in resistivity of read element  26  can be detected by passing a current through read element  26  and measuring a voltage across read element  26 .  
         [0026]    Writer  18  is formed on reader  16 , and includes bottom pole  32 , shared pole extension  34 , back via  36 , conductive coil  38 , coil insulator  40 , and top pole  42 . Bottom pole  32  is formed on top shield structure  30 . Shared pole extension  34  and back via  36  are formed on bottom pole  32 , with shared pole extension  34  being positioned adjacent the ABS and back via  36  being spaced away from the ABS. A write gap  58  is defined on the ABS between shared pole extension  34  and top pole  42 . Top pole  42  is formed over shared pole extension  34  and extends from the ABS to back via  36 . Conductive coil  38  is positioned in coil insulator  40  between bottom pole  32  and top pole  42 , wrapping around back via  36 , such that the flow of electrical current through conductive coil  38  generates a magnetic field across write gap  58 .  
         [0027]    Transducing head  10  is a piggyback configuration in which top shield structure  30  of reader  16  and bottom pole  32  of writer  18  are made of separate layers. Although not illustrated, transducing head  10  may also be arranged in a merged-head configuration in which shared pole  44  serves as top shield structure  30  for reader  16  and bottom pole  32  for writer  18 , or in a merged-head configuration in which reader  16  is built upon writer  18 .  
         [0028]    Each of bottom shield  50 , top shield  56 , bottom pole  32 , shared pole extension  34 , back via  36 , and top pole  42  are formed of metallic materials. Preferably, each of these components is formed of an alloy primarily composed of Fe, Ni, and/or Co. Bottom and top shields  50 ,  56  are preferably formed of Permalloy, a NiFe alloy having a composition of about 20% Fe-80% Ni. Such metallic alloys typicallyhave large CTE&#39;s. For example Ni 79 Fe 21  has a CTE of about 12.2×10 −6 /° C.  
         [0029]    Read gap  28  is generally formed of an insulating material such as Al 2 O 3 . Coil  38  is generally formed of an electrically-conductive metal such as copper, gold, or silver. Most commonly used is copper, which has a CTE of about 16.5×10 −6 /° C. Coil insulator  40  is generally formed from a cured photoresist having a large CTE, or from other insulating materials, such as AlN, SiO 2 , and Si 3 N 4 .  
         [0030]    Not shown in FIG. 1 are electrical leads and contacts to read element  26  and coil  38 . The electrical leads and contacts are typically formed of metals, such as gold, tantalum, or metallic alloys.  
         [0031]    Insulating layer  20  is positioned in-plane with layers of reader  16  and writer  18  of transducing head  10 , opposite the ABS. Insulating layer  20  is preferably formed of an insulating material, such as Al 2 O 3 , AlN, SiO 2 , Si 3 N 4 , and SiO 0-2 N 0-1.5 .  
         [0032]    Overcoat  22  is formed over top pole  42  in the embodiment shown in FIG. 1, and generally is formed over writer  18 . Overcoat  22  is typically formed of an insulating material, such as Al 2 O 3 , AlN, SiO 2 , Si 3 N 4 , and SiO 0-2 N 0-1.5 .  
         [0033]    In the embodiment of the present invention shown in FIG. 1, two compensation layers are utilized. Compensation layer  46  is located on top of basecoat  14  and beneath first non-magnetic spacer  48 , and compensation layer  52  is located on top of second non-magnetic spacer  54  and beneath bottom pole  32 . Compensation layers  46 ,  52  have a thickness no greater than 90% of a thickness of the respective bottom or top shield. The thickness of bottom and top shields  50 ,  56  is between about 0.2 micron and about 2.5 microns.  
         [0034]    Compensation layer  46  is formed between basecoat  14  and first spacer  48 . Compensation layer  52  is formed between second spacer  54  and writer  18 . Compensation layers  46 ,  52  are formed of a low CTE compensation material, which has a CTE between about 1.0×10 −6 /° C. and about 2.5×10 −6 /° C. Preferably, compensation layers  46 ,  52  are formed of a NiFe alloy having a composition of 35% Fe-65% Ni. However, many other low CTE materials may be used as compensation layers  46  and  52 , such as, but not limited to, element or alloy metals, dielectric, and semiconductor materials having a CTE between about 1.0×10 −6 /° C. and about 2.5×10 −6 /° C. Examples of such materials that may be used are W, Mo, Cr, Si, Ta, Zr, Hf, Os, Ge, Re, Ru, Ce, B, Ir, NiFe, TiW, silicon oxides, silicon nitrides, and silicon oxide nitrides.  
         [0035]    Bottom shield structure  24  and top shield structure  30  are each formed in a single step and mask during fabrication of transducing head  10 , such as by plating or sputtering.  
         [0036]    The layers of transducing head  10  all have differing mechanical and chemical properties, and in particular the layers of bottom shield structure  24  and top shield structure  30 . Due to these differing properties, the layers of transducing head  10  will be lapped at different rates. Thus, the lapping of the ABS of transducing head  10  during fabrication results in transducing head  10  having an uneven ABS, as seen in FIG. 1. Commonly, a greater amount of the metallic layers of transducing head  10  will be removed during the lapping process than will be removed from substrate  12 , resulting in a pole tip recession (PTR) of the metallic layers with respect to substrate  12 . The PTR of a particular layer is defined as the distance between the ABS of substrate  12  and the ABS of that layer. A gap  60  of the present invention transducing head  10  is defined as the distance between the ABS of substrate  12  and an ABS  62  of shield structures  24  and  30 .  
         [0037]    The differing mechanical and chemical properties of the layers of transducing head  10  further affect the ABS of transducing head  10  during operation. The CTE of materials used in forming substrate  12  is typically much smaller than the CTE of the materials used in forming the metallic layers of transducing head  10 , in particular bottom shield  50  and top shield  56 . Due to the larger CTE of the metallic layers, those layers tend to expand a greater amount than substrate  12 . Thus, when transducing head  10  is subjected to a high operating temperature, the metallic layers protrude closer to the magnetic disc than substrate  12 , thereby affecting the PTR of the metallic layers of transducing head  10 . This change is PTR caused by the temperatures referred to as the Thermal PTR (TPTR).  
         [0038]    The present invention addresses the problem of TPTR by using multi-layered bottom shield structure  24  and multi-layered top shield structure  30 . Compensation layers  46  and  52  formed in each shield structure compensate for the high CTE of the metallic layers of transducing head  10 . Generally, compensation layers  46 ,  52  are located close to high CTE materials that are the large TPTR contributing factors of shields  50 ,  56 . Compensation layers  46 ,  52  extend substantially perpendicular to and rearward from the ABS of transducing head  10  and lie substantially parallel to shields  50 ,  56  of transducing head  10 . Relative to substrate  12 , the low CTE materials of compensation layers  46 ,  52  recess as the operating temperature rises and protrude as the operating temperature drops, exactly opposite to the high CTE materials that are sources of TPTR found in magnetic shield structures  24 ,  30 . The present invention multi-layered shield structures  24 ,  30  maintain the size of gap  60  at high operating temperatures and prevent TPTR of shield structures  24 ,  30  by canceling and compensating for shields  50 ,  56  contribution to TPTR. Furthermore, use of low CTE layers  46 ,  52  in the magnetic sheilds does not impact performance of transducing head  10 .  
         [0039]    [0039]FIG. 2 is a schematic cross-sectional view of transducing head  10  in accord with the present invention. Shown in FIG. 2 is reader  16  and a portion of writer  18 , in particular bottom pole  32  and shared pole extension  34 . Bottom shield structure  24  is comprised of first compensation layer  46 , first non-magnetic spacer  48 , and bottom shield  50 . In the embodiment shown in FIG. 2, first compensation layer  46  is formed upon a bottom shield seed layer  64 . Bottom shield seed layer  64  is a conductive surface used for plating bottom shield  50 . Bottom shield seed layer  64  is not required to achieve reduced TPTR and such layer may be omitted depending upon the process of manufacturing bottom shield structure  24 .  
         [0040]    First non-magnetic spacer  48  separates compensation layer  46  and bottom shield  50  to ensure better magnetic performance of bottom shield  50 . Furthermore, first non-magnetic spacer  48  shields bottom shield  50  from magnetic noise from first compensation layer  46 . Similar reduced TPTR can be achieved when there is no spacer layer in bottom shield structure  24 .  
         [0041]    Top shield structure  30  is spaced apart from bottom shield structure  24  by read gap  28 . Top shield structure  30  is comprised of top shield  56 , second non-magnetic spacer  54 , and second compensation layer  52 . Bottom pole  32  is formed upon top shield structure  30 . Bottom shield  50  of bottom shield structure  24  and top shield  56  of top shield structure  30  both lie adjacent to read gap  28 . Second spacer  54  separates top shield  56  from second compensation layer  52  to ensure better magnetic performance of reader  16 . For example, the material commonly used as compensation layers  46 ,  52  has a low CTE, but is also magnetic material. Non-magnetic spacers  48 ,  54  between shields  50 ,  56  and respective compensation layers  46 ,  52  protect shields  50 ,  56  from magnetic noise from compensation layers  48 ,  54 .  
         [0042]    Generally, compensation layers  46 ,  52  are positioned and located close to high CTE layers of magnetic shield structures  24 ,  30 , which are the TPTR contributing features of transducing head  10 . By appropriately selecting the material and size of the compensation layer, the compensation layer will counterbalance and compensate for the larger CTE of the metallic layers of shield structures  24 ,  30 . Compensation layers  46 ,  52  maintain the TPTR close to zero, thereby enabling fly height of transducing head  10  with respect to a readable/writeable media to remain low and enhance the performance of transducing head  10 . At high operating temperatures, compensation layers  46 ,  52  recess relative to substrate  12 , pulling back nearby protruding metallic layers of shields  50 ,  56 . As the operating temperature drops, compensation layers  46 ,  52  protrude relative to the high CTE material and reduce recession.  
         [0043]    [0043]FIG. 3 is a schematic cross-sectional view of another embodiment of reader  16  of transducing head  10  in accord with the present invention. In the embodiment shown in FIG. 3, bottom shield structure  24  includes a compensation layer  66  to reduce TPTR whereas top shield structure  30  is comprised of only a top shield  68 . Bottom shield structure  24  is comprised of compensation layer  66 , a non-magnetic spacer  70 , and a bottom shield  72 . Writer  18  of transducing head  10 , and in particular bottom pole  32  and shared pole extension  34 , is formed upon top shield  68  of reader  16 .  
         [0044]    [0044]FIG. 4 is a schematic cross-sectional view of another embodiment of transducing head  10  in accord with the present invention. In the embodiment shown in FIG. 4, top shield structure  30  includes a compensation layer  74  to reduce TPTR, whereas bottom shield structure  24  is comprised of only a bottom shield  76 . Top shield structure  30  includes a top shield  78 , a non-magnetic spacer  80 , and compensation layer  74 . Writer  18  of transducing head  10 , and in particular bottom pole  32  and shared pole extension  34 , is formed upon top shield  68  of reader  16 .  
         [0045]    As illustrated by the embodiments shown in FIGS. 3 &amp; 4, the low CTE compensation layers may be used adjacent to either the bottom shield or the top shield and still result in a large TPTR reduction within reader  16 .  
         [0046]    The present invention reduces thermal pole-tip protrusion and recession in a transducing head, and in particular the magnetic shields of a reader in the transducing head. The present invention is a multi-layered magnetic shield used as a bottom shield and/or a top shield within a reader of the transducing head. Each magnetic shield structure is comprised of a magnetic shield and a compensation layer. Preferably, the shield and the compensation layer are separated by a non-magnetic spacer. The compensation layer is formed of a low CTE material, such as Invar, which recesses as the temperature rises and protrudes as the temperature drops, relative to a substrate of the transducing head. Low TPTR enables continuous reduction of head disc spacing, which is critical with high recording areal density. The compensation layers counter-balance the thermal protrusion effects of the metallic layers of the magnetic shields to prevent increased TPTR of the transducing head and maintain fly height.  
         [0047]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.