Patent Publication Number: US-2007121245-A1

Title: Thin film magnetic head having recording coil and method of forming recording coil

Description:
This application claims the benefit of Japanese Patent Application No. 2005-345729 filed Nov. 30, 2005, which is hereby incorporated by reference.  
     BACKGROUND  
      1. Field  
      The present embodiments relate to a thin film magnetic head having a recording coil and a method of forming the recording coil.  
      2. Related Art  
      Generally, a recording element unit of a thin film magnetic head includes a core formed of a magnetic material. A recording coil generates a recording magnetic field in the core. A magnetic gap is formed at a front end of the core.  
      The thin film magnetic head records magnetic information on a recording medium by a leakage magnetic field that is generated from the core with the magnetic gap interposed therebetween at a surface that faces the recording medium. In this thin film magnetic head, the recording coil is generally formed by a frame-plating method. A frame, which divides a coil forming area, is formed on a plating base film by using, for example, photoresist, and the recording coil is formed in the frame by plating. The frame is removed. The plating base film remaining between pitches of the recording coil is removed by milling. In this way, the recording coil is formed (for example, see JP-A-2002-133611).  
      In the related art, as shown in  FIG. 8A , in a cross section of the recording coil C right after the plating in a coil width direction, the recording coil C has a top surface that has a convex shape, and has a thickness d 3  at both end portions thereof that is smaller than a thickness d 4  at a central portion thereof (d 3 &lt;d 4 ). As described above, after the coil is formed, the milling process is performed to remove the plating base film. By this milling process, both end portions of the top surface of the recording coil C are cut.  
      As shown in  FIG. 8B , the finally obtained recording coil C has both end portions C 1  of the top surface thereof which are excessively cut. As a result, a cross-sectional area of the recording coil C is reduced below a design value, which causes an increase in electric resistance of the recording coil C. When the electric resistance of the recording coil C increases, the recording element unit is likely to be expanded by heat radiating from the recording coil C and protrude toward the recording medium. The protrusion may damage the recording medium, or the thin film magnetic head itself may be damaged.  
     SUMMARY  
      The present embodiments may obviate one or more of the drawbacks inherent in the related art. For example, in one embodiment, a thin film magnetic head having a recording coil has a reduced coil resistance.  
      In one embodiment, a method ensures a cross-sectional area of a recording coil by forming both end portions of the recording coil to be thicker than the central portion thereof by plating, such that a top surface of the recording coil in a completed state is flat or has a concave shape. Both end portions of the top surface of the recording coil are likely to be cut by a milling process (i.e., a process of removing an unnecessary plating base film) that is performed after the coil is formed.  
      According to one embodiment, a thin film magnetic head includes a recording coil that applies a recording magnetic field to a core formed of a magnetic material. The recording coil has a thickness at both end portions thereof that is larger than that at a central portion thereof in a cross section in a coil width direction perpendicular to a coil extending direction.  
      In one embodiment, a top surface of the recording coil has a concave shape such that both end portions of the recording coil in the coil width direction are higher than the central portion thereof. The recording coil may be formed of a nonmagnetic metal plating film that is grown by plating on the metal base film.  
      In one embodiment, a method of forming a recording coil of a thin film magnetic head includes the recording coil that applies a recording magnetic field to a core formed of a magnetic material. The method includes forming a plating base film for forming a coil, forming frames, which divide a coil forming area, on the plating base film, etching the plating base film exposed between the frames, and re-attaching etching rebounds of the plating base film to a frame side wall, forming the recording coil by plating on the area divided by the frames, and removing the frames and the plating base film that is exposed between pitches of the recording coil.  
      In one embodiment, the plating base film that is not covered by the frame is etched by reactive ion etching or milling. The plating base film may be re-attached partially to a frame side wall, more specifically, from a lower side of the frame side wall. The plating base film may be attached to the frame side wall even though a pitch interval of the coil is smaller.  
      In one embodiment, since the recording coil has end portions in the coil width direction that are thicker than the central portion by plating, it is possible to sufficiently achieve a cross-sectional area of the coil in a complete state even though both end portions of the upper surface of the recording coil is cut in the milling process after the plating is formed. Accordingly, a thin film magnetic head that has a recording coil and a method of forming a recording coil that are capable of reducing coil resistance are obtained. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a partial longitudinal sectional view of one embodiment of a laminated structure of a thin film magnetic head;  
       FIG. 2  is a partially enlarged sectional view of one embodiment of a lower coil of  FIG. 1 ;  
       FIG. 3  is a cross-sectional view of one embodiment of a process of forming the lower coil;  
       FIG. 4  is a cross-sectional view of one embodiment of a process of forming the lower coil;  
       FIG. 5  is a cross-sectional view of one embodiment of a process of forming the lower coil;  
       FIG. 6  is a cross-sectional view of one embodiment of a process of forming the lower coil;  
       FIG. 7  is a cross-sectional view of one embodiment of a process of forming the lower coil;  
       FIG. 8A  is a cross-sectional view that illustrates a recording coil right after being formed by plating according to the related art; and  
       FIG. 8B  is a view that illustrates a recording coil (complete state) that is formed by using a method according to the related art. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       FIG. 1  is a partial longitudinal view that illustrates a laminated structure of a thin film magnetic head according to one embodiment. In  FIG. 1 , an X direction is defined as a track width direction, a Y direction is defined as a height direction, and a Z direction is defined as a lamination direction of respective layers that forms a thin film magnetic head.  
      The thin film magnetic head H is a perpendicular magnetic head that performs a recording operation by applying a perpendicular magnetic field φ to a recording medium M, and magnetizing a hard film Ma of the recording medium M in a perpendicular direction. The recording medium M includes the hard film Ma that has a high residual magnetization and located at the side of the surface of the recording medium, and a soft film Mb that has a high magnetic permeability and located closer to an inner side of the recording medium than the hard film Ma. The recording medium M has, for example, a disc shape, and rotates around the center of the disc that serves as a center of a rotary axis.  
      The thin film magnetic head H has, on an end surface  101   b  at a trailing side of a slider  101 , a nonmagnetic insulating layer  102 , a recording element unit W, and a surface protective layer  103  that covers the recording element unit W.  
      In one embodiment, the slider  101  is formed of a nonmagnetic material, for example, Al 2 O 3 .TiC. A medium-facing surface  101   a  of the slider  101  faces the recording medium M. When the recording medium M rotates, the slider  101  floats above the surface of the recording medium M because of an airflow generated along the surface of the recording medium M. The slider  101  may slide on the recording medium M. The nonmagnetic insulating layer  102  and the surface protective layer  103  are formed of an inorganic material, for example, Al 2 O 3  or SiO 2 .  
      The recording element unit W includes a main magnetic pole layer (a core)  110 , an auxiliary magnetic pole layer  115 , a magnetic gap layer  113  interposed between the main magnetic pole layer  110  and the auxiliary magnetic pole layer  115  at a surface F that faces the recording medium. A recording coil applies a recording magnetic field to the main magnetic pole layer  110  and the auxiliary magnetic pole layer  115 .  
      The main magnetic pole layer  110  and the auxiliary magnetic pole layer  115  are formed of a ferromagnetic material, for example, Ni—Fe, Co—Fe, or Ni—Fe—Co, which has a high saturated magnetic flux density. The main magnetic pole layer  110  has a predetermined length extending from the facing surface F in the Y direction (the height direction) shown in the drawing, and the size of a front end surface  110   a , which is exposed to the facing surface F, in the X direction (the track width direction) show in the drawing, is defined as the track width. An insulating material layer  111  formed of a material, for example, Al 2 O 3 , SiO 2 , or Al—Si—O, is formed at both sides of the main magnetic pole layer  110  in the X direction and a rear side of the main magnetic pole layer  110  in the Y direction.  
      The magnetic gap layer  113  is formed of a nonmagnetic insulating material, for example, alumina or SiO 2 . The magnetic gap layer  113  is formed on the main magnetic pole layer  110  and the insulating material layer  111 . The auxiliary magnetic pole layer  115  faces the main magnetic pole layer  110  with a gap G interposed therebetween at a front end surface  115   a  that is exposed to the facing surface F.  
      The auxiliary magnetic pole layer  115  is coupled with the main magnetic pole layer  110  by a coupling portion  115   b  that is located closer to the inside in the height direction than the front end surface  115   a . A height determining layer  114  formed of an inorganic or organic material is formed at the location of the magnetic gap layer  113  which is spaced from the facing surface F by a predetermined distance. On the basis of the distance from the facing surface F to a front end edge of the height determining layer  114 , the throat height of the thin film magnetic head H is determined.  
      The recording coil includes a lower coil  121  that is formed on the nonmagnetic insulating layer  102  with a coil insulating base film  120  interposed therebetween. An upper coil  124  is formed on the magnetic gap layer  113  with a coil insulating base film  123  interposed therebetween. End portions of the lower coil  121  and the upper coil  124  are electrically connected to each other in the track width direction. The lower coil  121  and the upper coil  124  wind around the main magnetic pole layer  110  to thereby form a solenoid coil. Coil insulating layers  122  and  125  formed of an inorganic insulating material, for example, Al 2 O 3 , or an organic insulating material, for example, a resist, are formed around the lower coil  121  and the upper coil  124 , respectively. Top surfaces of the coil insulating layers  122  and  125  are planarized, and the main magnetic pole layer  110  and the auxiliary magnetic pole layer  115  are formed on these flat surfaces, respectively.  
      The lower coil  121  includes plating base films  121   a  and  121   a   1 ′, which are formed of a nonmagnetic metal material, for example, Cu, Au, or the like. A metal plating layer  121   b  grown from the plating base films  121   a  and  121   a ′ by plating uses one nonmagnetic metal material or two or more nonmagnetic metal materials selected from a group comprising of, for example, Au, Cu, Al, or Ni.  
      Similar to the lower coil  121 , the upper coil  124  includes plating base films  124   a  and  124   a ′, which are formed of a nonmagnetic metal material, for example, Cu, Au, or the like, and a metal plating layer  124   b  grown from the plating base films  124   a  and  124   a ′ by plating that uses one nonmagnetic metal material or two or more nonmagnetic metal materials selected from the group comprising of Au, Cu, Al, or Ni.  
       FIG. 2  is an enlarged sectional view that illustrates the lower coil  121 . As shown in  FIG. 2 , the lower coil  121  has a thickness d 2  at both end portions thereof that is larger than a thickness d 1  at a central portion thereof (d 2 &gt;d 1 ) in a cross section (i.e., a cross section shown in  FIG. 2 ) in a coil width direction (Y direction in  FIG. 2 ) perpendicular to a coil extending direction (X direction in  FIG. 2 ). For example, a bottom surface  121   c  of the lower coil  121  (i.e., a lower surface of the plating base film  121   a ) is a flat surface, and a top surface  121   d  of the lower coil  121  (i.e., a top surface of the metal plating layer  121   b ) has a concave shape where both end portions thereof in the coil width direction are higher than the central portion thereof.  
      In one embodiment, when both end portions in the coil width direction protrude further than the central portion, it is possible to achieve a large cross-sectional area of the coil and reduce coil resistance, as compared with when the both end portions in the coil width direction are flat or are depressed more than the central portion thereof (shown by dotted lines in  FIG. 2 ).  
      The lower coil  121  has no problem in generating a recording magnetic field despite both of the protruding end portions in the coil width direction. The lower coil  121  and the upper coil  124  have the same shape. Even though the upper coil  124  is not described in detail, the upper coil  124  has both end portions that have a thickness larger than a central portion thereof in a cross section (a cross section shown in  FIG. 2 ) in the coil width direction perpendicular to the coil extending direction (a longitudinal direction).  
      A method of forming a coil according to one embodiment will now be described with reference to FIGS.  3  to  7 . FIGS.  3  to  7  illustrate processes of forming the lower coil  121 . In one embodiment, since the lower coil  121  and the upper coil  124  are formed to have the same shape according to the same process order, the processes of forming the lower coil  121  will be described hereinafter.  
      First, as shown in  FIG. 3 , the plating base film  121   a  is formed on the coil insulating base film  120 . The frames  131  that divide a coil-forming area are formed on the plating base film  121   a . The plating base film  121   a  is formed of a nonmagnetic metal material, for example, Cu or Au, and the frame  131  is formed of resist.  
      As shown in  FIG. 4 , etching is performed as a process prior to plating. In the etching, the plating base film  121   a  exposed between the frames  131  is cut by about 30 to 300 Å by means of reactive ion etching (RIE) or milling that uses, for example, an Ar ion. When the plating base film  121   a  is etched, since the frame  131  is located most adjacent to both sides of the plating base film  121   a , rebounds from the plating base film  121   a  are attached to a frame side wall  131   a.    
      As shown in  FIG. 5 , a side plating base film  121   a ′ is formed at the frame side wall  131   a . The rebounds of the plating base film  121   a  are likely to be sequentially attached to the frame side wall  131   a  from a lower side of the frame side wall  131   a . As an amount of etching of the plating base film  121   a  increases, the side plating base film  121   a   1  is expanded toward an upper side of the frame side wall  131   a . A range (area and height) in which the side plating base film  121   a ′ is formed can be controlled by the amount of etching of the plating base film  121   a.    
      The lower coil  121  is formed by plating in the area divided by the frame  131 . For example, the metal plating layer  121   b , which is formed of one nonmagnetic metal material or two or more nonmagnetic metal materials selected from the group comprising of, for example, Au, Cu, Al, or Ni, is grown by plating on the plating base film  121   a , which becomes a coil bottom layer, and the side plating base film  121   a ′ located at the side.  
      As shown in  FIG. 6 , as the lower coil  121  is formed by growing the metal plating layer  121   b  simultaneously from both the plating base film  121   a  and the side plating base films  121   a ′ by plating, the lower coil  121  has a thickness at both end portions in the coil width direction that is larger than that at a central portion thereof. In this embodiment, a bottom surface  121   c  of the lower coil  121  (a bottom surface of the plating base film  121   a ) is a flat surface, and a top surface  121   d  of the lower coil  121  (a top surface of the metal plating layer  121   b ) has a gentle concave shape where both end portions thereof are higher than the central portion thereof. A shape in section of the lower coil  121  is determined according to the amount of etching of the plating base film  121   a  that is performed in the previous process. For example, when the amount of etching of the plating base film  121   a  increases, the side plating base film  121   a ′ formed at the frame side wall  131   a  increases. A difference in thickness (d 1 −d 2 ) between both end portions of the lower coil  121  in the coil width direction and the central portion thereof increases.  
      In contrast, when the amount of etching of the plating base film  121   a  decreases, the side plating base film  121   a ′ formed at the frame side wall  131   a  decreases. Therefore, the difference in thickness (d 1 −d 2 ) between both end portions of the lower coil  121  in the coil width direction and the central portion thereof decreases.  
      After the lower coil  121  is formed, as shown in  FIG. 7 , the frame  131  is removed. The remaining plating base film  121   a  existing between pitches of the lower coils  121  is removed by milling. In this milling process, the lower coil  121  is cut at the same time as removing the plating base film  121   a , and especially, both end portions of the lower coil  121  in the coil width direction are largely cut. However, as described above, since the lower coil  121  is formed such that the thickness d 1  at both end portions in the coil width direction is greater than the thickness d 2  at the central portion thereof, the sectional area of the lower coil  121  is sufficiently achieved even though the milling process is performed.  
      In one embodiment, the lower coil  121  is completed. The upper coil  124  can be formed by the same process as the process of forming the lower coil  121 .  
      The lower coil  121  and the upper coil  124  that are formed in this embodiment can sufficiently achieve the sectional area in the coil width direction even though the milling process is performed after being formed by plating, because the thickness d 2  at both end portions in the coil width direction is greater than the thickness d 1  at the central portion. In this embodiment, it is possible to appropriately suppress the coil resistance, and the recording element unit W is not likely to be expanded to form a protrusion toward the recording medium. When the recording coil (the lower coil and the upper coil) C is plated to have a uniform thickness by using a method according to the related art, if the milling process of removing the plating base film is performed after being formed by plating, as shown in  FIG. 8B , both end portions C 1  of the recording coil C in the coil width direction are excessively cut. Therefore, it may be impossible to avoid an increase in the coil resistance due to a sharp reduction in the sectional area of the coil after the milling process.  
      In addition, in this embodiment, since a portion of the plating base film  121   a  is re-attached to the frame side wall  131   a  to thereby form the side plating base film  121   a ′ by etching (RIE or milling), even though a pitch interval of the coils formed is smaller, it is possible to re-attach the plating base film to the frame side wall  131   a  from the lower side of the frame side wall  131   a.    
      A thin film magnetic head that includes a solenoid-shaped recording coil C that has the lower coil  121  and the upper coil  124  has been described. However, the present embodiments can be applied to a thin film magnetic head of a longitudinal recording type. The shape of the recording coil is not limited to a specific shape. For example, the recording coil may have a spiral shape in which the recording coil is wound around a coupling portion of the auxiliary magnetic pole layer in parallel to a surface of an auxiliary magnetic pole layer. The recording coil may be a single layer coil or a multilayer coil that has at least two layers.  
      Various embodiments described herein can be used alone or in combination with one another. The forgoing detailed description has described only a few of the many possible implementations of the present invention. For this reason, this detailed description is intended by way of illustration, and not by way of limitation. It is only the following claims, including all equivalents that are intended to define the scope of this invention.