Abstract:
A magnetic head includes a dielectric member, a coil and a heat conductor. The dielectric member has an obverse surface held in facing relation to a data storage disk. The coil generates a required magnetic field. The coil is provided in the dielectric member or in the obverse surface of the dielectric member. The heat conductor absorbs heat generated by the coil. The heat conductor has a heat conductivity which is higher than that of the dielectric member. The heat conductor has a surface which is at least partially irregular.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The present invention relates to a magnetic head used for writing data to or reading data from a magneto-optical disk or a magnetic disk. The term “magnetic head” used in this specification refers to any type of data-writing/reading head provided with a magnetic field generating coil. Thus, for example, the “magnetic head” may refer to a magneto-optical head.  
           [0003]    2. Description of the Related Art  
           [0004]    When an electric current passes through the coil of a magnetic head for generation of a magnetic field, the coil is heated up. As the temperature of a coil increases, the electric resistance of the coil also increases. Thus, to generate an appropriately strong magnetic field with the coil heated up to a higher temperature, the power supply to the coil needs to be increased. However, with a large power supply, the coil may be overheated, thereby damaging the coil itself and/or the surrounding components of the magnetic head. Further, the large power supply may cause “electromigration” in the coil. As a result, the conductive element of the coil may become thinner or even break due to the growth of a void (in the conductive element) resulting from the electromigration.  
           [0005]    Since the heat generation in the coil can lead to the damaging of the coil, an appropriate countermeasure should be provided. One solution is suggested in JP-A-8-235556 which discloses a magnetic head as shown in FIG. 14. This conventional magnetic head includes a slider  91  supported by a suspension  90  in facing relation to a data storage disk D. The slider  91  is provided with a coil  92  for generating a magnetic field. In its bottom surface (facing the disk D), the slider  91  is formed several grooves  93  each of which extends generally in the track direction of the disk D.  
           [0006]    With the above arrangements, the slider  91  is caused to float over the disk D in rotation, and the air flowing between the slider  91  and the disk D passes through the grooves  93 . The passing air takes away some heat from the slider  91 .  
           [0007]    While the conventional magnetic head is functional in many respects, it still has some drawbacks in terms of prevention of the temperature rise in the coil  92 .  
           [0008]    Specifically, the slider  91  is typically made of a synthetic resin, which is not an excellent heat conductor. In addition, the coil  92  is enclosed by a dielectric protection coating made of e.g. silicon oxide which is not an excellent heat conductor, either. Thus, while the exposed surface of the slider  91  is cooled by the high-speed air flow, the temperature of the heated coil may not significantly decrease due to the existence of the materials of low heat conductivity.  
           [0009]    Further, though the conventional slider  91  is provided with the grooves  93  for enlarging the heat-dissipating area, each groove  93  has merely a simple, straight configuration whose width is constant over the entire length of the groove. Thus, the passing air may fail to contact with the entire wall surface of the groove  93 , and therefore cannot take away a sufficient amount of heat from the slider  91 .  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention has been proposed under the circumstances described above. It is, therefore, an object of the present invention to provide a magnetic head which is capable of efficiently preventing the temperature rise in the coil.  
           [0011]    According to a first aspect of the present invention, there is provided a magnetic head comprising: a dielectric member including an obverse surface facing a data storage disk; a coil that generates a magnetic field and is held in engagement with the dielectric member; and a heat conductor that takes heat generated by the coil and has a heat conductivity higher than a heat conductivity of the dielectric member. The heat conductor includes an irregular surface.  
           [0012]    Preferably, the irregular surface may be exposed from the obverse surface of the dielectric member.  
           [0013]    According to a second aspect of the present invention, there is provided a magnetic head comprising: a dielectric member including an obverse surface facing a data storage disk; a coil that generates a magnetic field and is held in engagement with the dielectric member; and a heat conductor that is provided in the dielectric member and includes a first portion and a second portion. The first portion is positioned opposite to the disk with respect to the coil, while the second portion is exposed from the obverse surface of the dielectric member. The heat conductor has a heat conductivity higher than the heat conductivity of the dielectric member.  
           [0014]    According to a third aspect of the present invention, there is provided a magnetic head comprising: a coil for generating a magnetic field; and a surface that faces a data storage disk and is formed with a plurality of grooves for allowing air to pass when the disk is rotated. Each groove includes an inlet end for entry of the passing air and an outlet end for exit of the passing air. Each groove becomes narrower from the inlet end to the outlet end.  
           [0015]    According to a fourth aspect of the present invention, there is provided a magnetic head comprising: a coil for generating a magnetic field; and a surface facing a data storage disk. This surface includes an irregular portion provided with a plurality of projections spaced from each other in a track direction and a tracking direction of the disk.  
           [0016]    Other features and advantages of the present invention will become clearer from the detailed description given below with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]    [0017]FIG. 1 is a sectional view showing the basic structure of a magnetic head according to a first embodiment of the present invention;  
         [0018]    [0018]FIG. 2 is a sectional view showing the principal portion of the magnetic head of FIG. 1;  
         [0019]    [0019]FIG. 3 is a plan view as seen in the direction of arrows III-III in FIG. 2;  
         [0020]    FIGS.  4 A˜ 4 E illustrate a process for making a heat conductive layer;  
         [0021]    [0021]FIG. 5 is a plan view showing a modified irregularity arrangement of the heat conductive layer shown in FIG. 3;  
         [0022]    [0022]FIG. 6 is a plan view showing another modified irregularity arrangement of the heat conductive layer shown in FIG. 3;  
         [0023]    [0023]FIG. 7 is a sectional view showing the basic structure of a magnetic head according to a second embodiment of the present invention;  
         [0024]    [0024]FIG. 8 is a sectional view showing the basic structure of a magnetic head according to a third embodiment of the present invention;  
         [0025]    [0025]FIG. 9 is a sectional view showing the basic structure of a magnetic head according to a fourth embodiment of the present invention;  
         [0026]    [0026]FIG. 10 is a sectional view showing the basic structure of a magnetic head according to a fifth embodiment of the present invention;  
         [0027]    [0027]FIG. 11 is a sectional view showing the basic structure of a magnetic head according to a sixth embodiment of the present invention;  
         [0028]    [0028]FIG. 12 is a plan view showing the surface configuration of the dielectric layer of the magnetic head shown in FIG. 11;  
         [0029]    [0029]FIG. 13 is a plan view showing a modified irregularity arrangement of the dielectric layer of the magnetic head shown in FIG. 11; and  
         [0030]    [0030]FIG. 14 shows a conventional magnetic head and some cooperating components. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]    Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings.  
         [0032]    [0032]FIGS. 1 through 3 illustrate a magnetic head H according to a first embodiment of the present invention. As clearly shown in FIG. 1, the magnetic head H of this embodiment includes a lens holder  10 , two objective lenses  11   a,    11   b  held by the lens holder  10 , a coil  2  for generating a magnetic field, a dielectric layer  3  for covering the coil  2  and a pair of heat conductive layers  4 .  
         [0033]    The lens holder  10  is carried by a carriage  50 , to be placed under a magneto-optical disk D. Specifically, the lens holder  10  is mounted to the carriage  50  via supporting means movable in the tracking direction, or radially, of the disk D that is indicated by the arrows Tg. Thus, the lens holder  10  is also movable in the direction Tg. Further, the lens holder  10  is movable in the focusing direction indicated by the arrows Fc by an electromagnetic driving means  19 . The magneto-optical disk D can be rotated at high speed about the axis C (phantom line) by a spindle motor (not shown). The disk D includes a recording layer  88  provided on a disk surface facing the lens holder  10  (See FIG. 2). Alternatively, the recording layer  88  may be provided on the other side of the disk D. This arrangement, however, may be disadvantageous in that the distance between the recording layer  88  and the coil  2  becomes large, thereby causing a greater loss of the magnetic force. Further, when a laser beam passes through the substrate of the magneto-optical disk D, the laser beam may be adversely affected by the deflection of the substrate. In view of these disadvantages, it is preferable that the recording layer  88  is so arranged as to face the magneto-optical disk D, as in the illustrated embodiment. As shown in FIG. 2, the recording layer  88  is protected by a transparent insulating film  89 .  
         [0034]    The carriage  50  is movable in the tracking direction Tg by e.g. a voice coil motor (not shown). Seek operation is performed by moving the carriage  50 , thereby causing the lens holder  10  to be positioned close to an intended track (target track).  
         [0035]    As shown in FIG. 1, a mirror  51  is mounted on the carriage  50  for directing horizontal laser beams upward. The laser beams are emitted from a stationary optical unit (not shown) consisting of a laser diode, a collimating lens, etc. The upward reflected beams pass through the objective lenses  11   a  and  11   b,  thereby converging to form a laser spot on the recording layer  88 .  
         [0036]    The stationary optical unit is provided with a beam splitter and a photo detector. After the upward laser beams are reflected on the recording layer  88 , the reflection light is detected by the photo detector. The tracking control and the focus control can be performed by moving the lens holder  10  in an appropriate direction. However, it is also possible to perform the tracking control by changing the inclination angle of the mirror  51 , whereby the traveling path of the reflected light is changed in the tracking direction.  
         [0037]    As shown in FIG. 2, the coil  2  is formed on a transparent substrate  60  to which the objective lens  11   b  is attached. The substrate  60  may be rectangular and made of the same glass material as that of the objective lens  11   b.  The substrate  60  is closely bonded to the objective lens  11   b  so that there is no gap between them. According to the present invention, instead of forming the coil  2  on the substrate  60 , the coil  2  may be directly provided on the objective lens  11   b  without using the substrate  60 .  
         [0038]    The coil  2  may be formed by patterning a metal film formed of e.g. copper. The coil  2  has a two-layer structure consisting of first and second spiral elements  20   a  and  20   b.  As shown in FIG. 2, the coil  2  has a central axis L 1  coinciding with the axis L 2  of the objective lens  11   b,  so that the laser beam, having passed through the objective lens  11   b,  is not obstructed by the coil  2 . As shown in FIG. 3, the spiral elements  20   a,    20   b  are connected to conductive leads which extend up to an edge (side surface) of the dielectric layer  3  or substrate  60 . There, the leads are connected to terminals  20   c  and  20   d  provided for power supply to the coil  2 . As shown in FIG. 2, a magnetic layer  61 , made of permalloy for example, is provided below the coil  2 . The magnetic layer  61  causes the magnetic field generated by the coil  2  to be applied efficiently to the disk D.  
         [0039]    The dielectric layer  3  may be made of a light-permeable dielectric material such as aluminum oxide or silicon oxide. The dielectric layer  3  is formed on the substrate  60  to cover the magnetic layer  61  and the coil  2 . The dielectric layer  3  consists of a plurality of dielectric films integrally laminated on each other. The dielectric films may be formed simultaneously with the magnetic layer  61  and the coil  2 . Preferably, the dielectric layer  3  has a refractive index which is equal (or substantially equal) to that of the substrate  60  or objective lens  11   b.    
         [0040]    The heat conductive layers  4  are formed of a metal (copper for example) whose heat conductivity is higher than that of the dielectric layer  3 . In the illustrated embodiment, the heat conductive layers  4  serve as a heat sink for the dissipation of the raised temperature of the coil  2 , while also serving as a component of a sensor to measure the distance between the disk D and the head H based on the detection of electrostatic capacity. Specifically, the electrostatic capacity between the heat conductive layers  4  and the recording layer  88  varies with the distance between the layers  4  and  88 . For example, when the distance increases, the electrostatic capacity decreases. This implies that the distance between the disk D and the head H can be determined based on the value of the electrostatic capacity. The data of the detected distance between the disk D and the head H is utilized for improving the precision of the focus control.  
         [0041]    The heat conductive layers  4 , which are exposed from the dielectric layer  3 , are held in close facing relation to the disk D. As seen from FIG. 3, the heat conductive layers  4  are formed over the obverse surface  30  of the dielectric layer  3  in a manner avoiding the coil  2 . The two heat conductive layers  4  are separated from each other by a clearance extending radially of the coil  2 . The sign S indicates the width of the clearance. The separation serves to prevent the generation of unduly strong induced currents in the layers  4  when a high-frequency current is applied to the coil  2  for writing data to the disk D by magnetic field modulation. As a result, it is possible to prevent the magnetic field generated by the coil  2  from being unacceptably weakened by the magnetic field generated by the induced currents in the layers  4 .  
         [0042]    The heat conductive layers  4  have a non-flat obverse surface facing the magneto-optical disk D. Specifically, the obverse surface is formed with a plurality of grooves  40  (conversely, a plurality of projections  41 ). Each of the grooves  40  extends in the track direction indicated by the arrow Tc. The width of the groove  40  is not constant over the length thereof. Specifically, in the embodiment shown in FIG. 3 wherein the disk D rotates counterclockwise (see the arrow N 1 ), each groove  40  has a greater width Sa at its upstream end  42   a  and a smaller width Sb at its downstream end  42   b.  The groove  40  tapers regularly from the upstream end  42   a  to the downstream end  42   b . In other words, the longitudinal side surfaces  43   a  defining the groove  40  are nonparallel to each other, but come closer to each other as proceeding from the upstream end  42   a  to the downstream end  42   b.    
         [0043]    The heat conductive layers  4  may be made by a process shown in FIGS.  4 A˜ 4 E.  
         [0044]    First, as shown in FIG. 4A, a copper base layer  49   a  is formed on a dielectric substrate  3   a  by sputtering or vapor deposition for example. Then, as shown in FIG. 4B, a first resist mask  69   a  is formed on the copper base layer  49   a.  The mask  69   a  may be made by forming a resist layer on the copper base layer  49   a  and then subjecting the resist layer to light exposure and development. After the mask  69   a  is provided, an additional copper layer  49   b  is formed (by plating for example) on such portions of the copper base layer  49   a  that are not covered by the mask  69   a.  Then, as shown in FIG. 4C, a second resist mask  69   b  is formed on the first resist mask  69   a  and the additional copper layer  49   b.  The second mask  69   b  is provided with a plurality of slits on the additional copper layer  49   b.  These slits are filled up with copper material  49   c.  Then, as shown in FIG. 4D, the first and the second resist masks  69   a,    69   b  are removed. Then, unnecessary portions of the copper base layer  49   a  are removed by ion milling for example. As a result, a heat conductive layer  4  as shown in FIG. 4E is obtained.  
         [0045]    The function of the magnetic head H will now be described. For writing data to a magneto-optical disk D by the magnetic field modulation, a laser beam is shone on a target track in the recording layer  88 . In this operation, the relevant magnetic material in the recording layer  88  is heated up to a Curie temperature. At the same time, a high-frequency current is applied to the coil  2  to change the direction of the magnetic flux of the magnetic field. In this way, the direction of magnetization of the magnetic material constituting the recording layer  88  is controlled. During this data writing operation, the heat generated by the coil  2  is partly transferred through the dielectric layer  3  to the heat conductive layers  4 , to be dissipated into the surrounding air. Since each of the heat conductive layers  4  has a high heat conductivity and has an irregular exposed surface (which means a large heat conduction area), unwanted heat can be efficiently dissipated through the heat conductive layer  4 .  
         [0046]    In the illustrated embodiment, the rotation of the magneto-optical disk D gives rise to high-velocity air flow between the disk D and the heat conductive layer  4 , whereby the heat conductive layer  4  is positively cooled. As indicated by the arrow N 2  in FIG. 3, the surrounding air flows into the grooves  40  at their wider end  42   a,  going to the smaller end  42   b.  Since each groove  40  tapers from the wider end  42   a  to the smaller end  42   b,  as described above, the high-velocity cooling air comes into sufficient contact with the longitudinal side surfaces  43   a  of the groove  40 . As a result, the heat conductive layer  4  is cooled more effectively than is conventionally possible.  
         [0047]    The efficient heat dissipation through the heat conductive layers  4  satisfactorily suppresses the temperature rise in the coil  2 . Thus, it is possible to prevent the occurrence of the electromigration in the coil  2 . Further, the restricted temperature rise in the coil  2  leads to prevention of an increase in the electric resistance of the coil  2 . Therefore, it is possible to prevent the increase of power consumption and hence an additional temperature rise in the coil  2  caused by the increased power consumption.  
         [0048]    In the above embodiment, the heat conductive layers  4  serve for two purposes, that is, as a heat sink for cooling the coil  2  and as a component of a sensor for detecting the distance between the disk D and the magnetic head H. This is advantageous to reducing the number of parts needed to compose the magnetic head H. Accordingly, the head H can be produced more readily and with reduced manufacturing cost.  
         [0049]    [0049]FIGS. 5 and 6 show possible modifications of the heat conductive layer arrangement shown in FIG. 3.  
         [0050]    By the arrangement shown in FIG. 5, the heat conductive layers  4  are provided with a plurality of projections  44  having a rectangular cross section. The projections  44  are regularly spaced from each other in the tracking direction Tg and the track direction Tc. In other words, the projections  44  are arranged in a matrix. With such a structure, the matrix arrangement of the projections  44  increases the surface area of the heat conductive layer  4 , which is advantageous to ensuring effective cooling of the coil  2 . Further, when the air flows between the disk D and the heat conductive layer  4  upon rotation of the magneto-optical disk D, the high-velocity air hits against the projections  44 , as indicated by the arrows n 1 . This enhances the cooling effect for the coil  2 .  
         [0051]    By the arrangement shown in FIG. 6, the heat conductive layer  4  is provided with a plurality of non-tapering grooves  45  having a constant width. Each of the grooves  45  is defined by a pair of longitudinal side surfaces  45   a  extending parallel to each other. This arrangement may lessen the cooling effect for the layer  4  (and hence the coil  2 ) as compared to the arrangements shown in FIG. 3 or  5 . However, the straight groove arrangement of FIG. 6 is still effective for cooling the coil  2  as compared to a case where no grooves or projections are formed in the layer  4 .  
         [0052]    [0052]FIG. 7 shows the principal structure of a magnetic head according to a second embodiment of the present invention. In the second embodiment, heat conductive layers  4 A are embedded in the dielectric layer  3  so that they are not exposed from the upper surface  30  of the dielectric layer  3 . Generally, the layers  4 A are disposed below the coil  2  to be located at a lower position than the coil  2 . The layers  4 A are a better heat conductor than the dielectric layer  3 . The layers  4 A are made of a magnetic material and perform the same function as the magnetic layer  61  of the first embodiment (see FIG. 2). The heat conductive layers  4 A are formed over a relatively large area of the obverse surface of the substrate  60 . The upper surface of the heat conductive layer  4 A is formed with a plurality of projections  48   a  or grooves  48   b.    
         [0053]    The heat conductive layers  4 A are provided with an enlarged surface area due to the non-flat upper surface. Also, the layers  4 A are made to have a higher heat conductivity than the dielectric layer  3 . Thus, unwanted heat generated at the coil  2  can be effectively dissipated through the conductive layers  4 A.  
         [0054]    [0054]FIG. 8 shows the principal structure of a magnetic head according to a third embodiment of the present invention. In this embodiment, the magnetic head includes a heat conductor  4 B consisting of a first element  46   a  and a second element  46   b.  The first element  46   a,  which is thinner than the second element  46   b,  is held in contact with the substrate  60 . The second element  46   b  is held in contact with the first element  46   a  on its bottom side, while on its upper side, the second element  46   b  is exposed from the dielectric layer  3  to face the disk D. The first and the second elements  46   a,    46   b  are both better heat conductor than the dielectric layer  3 . The first element  46   a  is made of a magnetic material and performs the same function as the magnetic layer  61  shown in FIG. 2. The first element  46   a  extends under and adjacent to the coil  2 .  
         [0055]    With this structure, the heat which is generated by the coil  2  and conducted toward the substrate  60  can be absorbed by the first element  46   a,  then conducted to the second element  46   b,  and finally dissipated into the air via the exposed surface of the second element  46   b.  In this manner, the unwanted heat which would otherwise be trapped inside the dielectric layer  3  can be positively dissipated into the air via the heat conductor  4 B.  
         [0056]    [0056]FIG. 9 shows the principal structure of a magnetic head according to a fourth embodiment of the present invention. In this embodiment, a pair of heat conductors  4 C is provided in the dielectric layer  3 . Each heat conductor  4 C consists of a first or lower element  47   a,  a second or upper element  47   b  and a third or intermediate element  47   c.  The first element  47   a,  made of a magnetic material, is disposed below the coil  2  and adjacent to the substrate  60 . The second element  47   b  has an obverse surface exposed from the dielectric layer  3 . The third element  47   c  connects the first element  47   a  to the second element  47   b.  The second element  47   b  may be larger than the first element  47   a.    
         [0057]    With this structure, the heat generated by the coil  2  is effectively dissipated into the surrounding air via the heat conductor  4 C.  
         [0058]    [0058]FIG. 10 shows the principal structure of a magnetic head according to a fifth embodiment of the present invention. The magnetic head of this embodiment is basically the same as the magnetic head of the fourth embodiment (FIG. 9) except that the heat conductor  4 D includes a second element  47   b  whose obverse surface (exposed surface) is formed with a plurality of projections  47   b  for increasing the heat dissipating area. The projections  47   b  may be the same as those shown in FIG. 3, 5 or  6 .  
         [0059]    [0059]FIGS. 11 and 12 show the principal structure of a magnetic head according to a sixth embodiment of the present invention. In this embodiment, the dielectric layer  3  has a non-flat obverse surface  30  which is entirely irregular except for the portion for passing the laser beam. The obverse surface  30  may have the same configuration as that of the irregular surface of the heat conductive layer  4  shown in FIG. 3 or  5 . Specifically, as shown in FIG. 12, the obverse surface  30  of the dielectric layer  3  may be formed with a plurality of grooves  39  (or a plurality of projections  38 ). The width of each groove  39  is defined by two wall surfaces  39   a  which gradually come closer to each other as proceeding in the air flow direction indicated by arrows N 5 .  
         [0060]    The irregularity of the exposed surface  30  of the dielectric layer  3  maybe provided by the matrix arrangement of projections  37  shown in FIG. 13. As illustrated, each projection  37  has a rectangular cross section. This matrix arrangement is similar to that of the heat conductive layer  4  shown in FIG. 5 and can enjoy the same advantages.  
         [0061]    The present invention being thus described, it is obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the present invention, and all such modifications as would be obvious to those skilled in the art are intended to be included within the scope of the following claims.