Abstract:
A thin-film magnetic head includes a thin-film magnetic circuit that contains a coil conductor with at least one surface. The coil conductor includes a plurality of grooves for reducing electrical resistance of the coil conductor due to skin effect. The grooves are formed on the at least one surface of the coil conductor to run along axis of the coil conductor.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to a thin-film magnetic head with an inductive transducer element for magnetically recording information into a magnetic medium such as a hard disk or a floppy disk, and to a manufacturing method of the thin-film magnetic head.  
         DESCRIPTION OF THE RELATED ART  
         [0002]    Two thin-film magnetic pole layers and a thin-film coil conductor basically constitute an inductive transducer element of such thin-film magnetic head. ABS (Air Bearing Surface) side ends of the respective magnetic pole layers are opposed with each other via a magnetic gap layer and rear portions of the magnetic pole layers are in contact with each other to form a magnetic yoke. The coil conductor is wound around the yoke.  
           [0003]    The conventional coil conductors used in such inductive transducer element have been fabricated to have a smooth profile of straight line parts or of straight line parts and partially curved parts in cross section as shown in FIG. 1.  
           [0004]    In case that the coil conductor has such smooth surface, the higher frequency range of the write current, the larger resistance value of the coil conductor due to the skin effect. Larger resistance value of the coil conductor causes not only high heating value and high power consumption but also difficulty in designing and in fabricating a head amplifier. Recently, the write current frequency of the thin-film magnetic head has been requested to more heighten in order to realize higher density magnetic recording. Thus, increase of the resistance value of the coil conductor due to the skin effect has become serious problem.  
         SUMMARY OF THE INVENTION  
         [0005]    It is therefore an object of the present invention to provide a thin-film magnetic head and a manufacturing method of the head that can adapt to high-density recording and has a coil conductor with a lower electrical resistance.  
           [0006]    Another object of the present invention is to provide a manufacturing method of a thin-film magnetic head that can form a coil conductor with a lower electrical resistance without introducing any additional process.  
           [0007]    According to the present invention, a thin-film magnetic head includes a thin-film magnetic circuit that contains a coil conductor with at least one surface. The coil conductor includes a plurality of grooves for reducing electrical resistance of the coil conductor due to skin effect. The grooves are formed on the at least one surface of the coil conductor to run along axis of the coil conductor.  
           [0008]    Since a plurality of grooves for reducing electrical resistance of the coil conductor due to skin effect are formed on the surface of the coil conductor to run along axis of the coil conductor, namely along the direction of write current flowing, increasing in resistance due to the skin effect can be suppressed even if the write current frequency more heightens. As a result, the magnetic head can be prevented from heating and high power consumption. In addition, thanks to very low resistance value of the coil conductor, design and fabrication of a head amplifier become very easy.  
           [0009]    It is preferred that the coil conductor has side faces, and that the plurality of grooves for reducing electrical resistance due to the skin effect are formed on the side faces.  
           [0010]    It is also preferred that the plurality of grooves for reducing electrical resistance due to the skin effect are many grooves with many projections and depressions.  
           [0011]    The plurality of grooves for reducing electrical resistance due to the skin effect may have pitches of about 0.05-0.2 μm, and/or may have a depth of about 0.01-0.1 μm.  
           [0012]    According to the present invention, furthermore, a manufacturing method of a thin-film magnetic head with a thin-film magnetic circuit which contains a coil conductor, includes a step of forming a resist layer, a step of exposing the formed resist layer by applying a monochromatic light via a mask with a predetermined pattern, a step of developing the exposed resist layer without performing a post exposure baking (PEB) process, and a step of plating the coil conductor by using the developed resist layer.  
           [0013]    Also, a manufacturing method of a thin-film magnetic head according to the present invention has a step of forming a lower magnetic pole layer, a step of depositing a magnetic gap layer on the lower magnetic pole layer, a step of forming a coil conductor with at least one surface above the magnetic gap layer, and a step of forming an upper magnetic pole layer above the magnetic gap layer. The coil conductor forming step includes a step of forming a low resistance layer on the magnetic gap layer, a step of forming a resist layer on the low resistance layer, a step of exposing the formed resist layer by applying a monochromatic light via a mask with a predetermined pattern, a step of developing the exposed resist layer without performing a post exposure baking (PEB) process, a step of plating the coil conductor by using the developed resist layer, and a step of, thereafter, removing the resist layer.  
           [0014]    The resist layer is exposed by a monochrome light and then developed without performing the PEB process. Thus, a plurality of grooves with many projections and depressions are formed on inner walls of resist trenches of the resist layer. Then, by executing frame plating using the resist layer, the coil conductor is formed with both side faces having the many grooves with many projections and depressions along its axis. Since no PEB process is needed, a more simple manufacturing process can provide the coil conductor with a lower resistance.  
           [0015]    It is preferred that the exposing step includes a step of exposing the formed resist layer by applying a monochromatic light via a mask with a predetermined pattern to make resist trenches with a plurality of grooves on inner walls of the resist trenches.  
           [0016]    It is also preferred that the plurality of grooves are many grooves with many projections and depressions  
           [0017]    The plurality of grooves may have pitches of about 0.05-0.2 μm, and/or may have a depth of about 0.01-0.1 μm.  
           [0018]    Further objects and advantages of the present invention will be apparent from the following description of the preferred embodiments of the invention as illustrated in the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]    [0019]FIG. 1 schematically illustrates sections of various examples of the coil conductors of the conventional inductive transducer elements;  
         [0020]    [0020]FIG. 2 is a sectional view schematically illustrating a part of a thin-film magnetic head as a preferred embodiment according to the present invention;  
         [0021]    [0021]FIG. 3 is an oblique view schematically illustrating a partial shape of a coil conductor in the embodiment shown in FIG. 2; and  
         [0022]    [0022]FIGS. 4 a  to  4   g  illustrate manufacturing processes of the coil conductor in the embodiment shown in FIG. 2.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0023]    [0023]FIG. 2 schematically illustrates a partial structure of a thin-film magnetic head as a preferred embodiment according to the present invention by a cross section of a plane passing through a track center of the magnetic head, and FIG. 3 schematically illustrates a partial shape of the coil conductor shown in FIG. 2. The thin-film magnetic head in this embodiment is a recording head with an inductive transducer element only. However, the present invention can be of course adapted to a composite type thin-film magnetic head with both inductive recording element and a magnetoresistive effect (MR) reproducing element which are integrated together.  
         [0024]    In FIG. 2, reference numeral  20  denotes a substrate,  21  an insulation layer deposited on the substrate  20 ,  22  a lower magnetic pole layer formed on the insulation layer  21 ,  23  a recording gap layer made of insulation material,  24  an upper magnetic pole layer,  25  a coil conductor,  26  an insulation layer surrounding the coil conductor  25 , and  27  a protection layer, respectively. The coil conductor  25  may be formed in two-layered structure as shown in FIG. 2, in three-layered structure or in a single layer structure.  
         [0025]    The coil conductor  25  is shaped, as shown in FIG. 3, so that its both side faces have many grooves  25   a  with many projections and depressions along its axis, namely along the direction of write current flowing I. Each of the grooves  25   a  has a pitch of about 0.05-0.2 μm, and a depth of about 0.01-0.1 μm.  
         [0026]    By forming such many grooves  25   a  on the surface of the coil conductor  25 , a surface area of the conductor extremely increases without varying coil width or coil pitch. Thus, increasing in resistance due to the skin effect can be suppressed even if the write current frequency more heightens. As a result, the magnetic head can be prevented from heating and high power consumption. In addition, thanks to very low resistance value of the coil conductor  25 , design and fabrication of a head amplifier become very easy.  
         [0027]    [0027]FIGS. 4 a  to  4   g  illustrate manufacturing processes using a frame plating method, of the coil conductor  25  in the embodiment shown in FIG. 2. These figures are shown by a cross section of a plane passing through a track center of the magnetic head.  
         [0028]    On the insulation layer  26  shown in FIG. 4 a , a low resistance layer  40  made of preferably material of the same component as that of the coil conductor  25  to be plated such as Cu is deposited in a thickness of about 10-500 nm, as shown in FIG. 4 b    
         [0029]    Then, as shown in FIG. 4 c , a resist layer  41  is coated on the low resistance layer  40 . The resist layer  41  should be formed to have a thickness lager than that of a layer to be plated. Then, a predetermined pattern of a mask  42  is transferred to the resist layer  41  by an exposure process of a monochromatic light  43  of Hg-i line for example, and developed without performing a post exposure baking (PEB) process. Because of monochromatic light exposure, interference between the incident light and the reflected light from the bottom of the resist layer  41  (top surface of the low resistance layer  40 ) will be occur causing a standing wave at exposed pattern portions of the resist layer  41  (inner walls of resist trenches) to generate. Thus, as shown in FIG. 4 d , the inner wall of each resist trench of the resist layer  41 ′ have many grooves  41 ′ a  with many projections and depressions. In the conventional processes, such grooves were removed to make the inner walls of the resist trench smooth by the PEB process. However, according to the present invention, the exposed resist layer  41 ′ is developed without executing the PEB process to remain the many grooves  41 ′ a.    
         [0030]    Thereafter, as shown in FIG. 4 e , conductive material such as Cu is plated to fabricate the coil conductor  25  by using thus patterned resist frame  41 ′ as a mold. Thus, the many projections and depressions or the many grooves  41 ′ a  formed on the inner walls of the resist trench of the resist layer  41 ′ are transferred on the side faces of the coil conductor  25 . By appropriately selecting the wave length of the exposure light, resist material and low resistance layer material, each of the grooves  25   a  will have a pitch of about 0.05-0.2 μm, and a depth of about 0.01-0.1 μm.  
         [0031]    After that, the resist layer  41 ′ is removed by using organic solution for example as shown in FIG. 4 f.    
         [0032]    Then, as shown in FIG. 4 g , the low resistance layer  40  except for regions which are covered by thus formed coil conductor  25  is removed by a dry etching such as ion milling or RIE (reactive ion etching) or by an wet etching.  
         [0033]    As will be understood from the above-description, according to the present invention, the resist layer  41  is exposed by the monochrome light and then developed without performing the PEB. Thus, many grooves  41 ′ a  with many projections and depressions are formed on the inner walls of the resist frame  41 ′. Then, by executing the frame plating using the resist frame  41 ′, the coil conductor  25  is formed with both side faces having the many grooves  25   a  with many projections and depressions along its axis. Since no PEB process is needed, a more simple manufacturing process can provide a coil conductor with a lower resistance.  
         [0034]    Many widely different embodiments of the present invention may be constructed without departing from the spirit and scope of the present invention. It should be understood that the present invention is not limited to the specific embodiments described in the specification, except as defined in the appended claims.