Abstract:
A magnetic head is provided with a substrate and a magnetic field generating coil formed on the substrate. The substrate has a principal surface facing a storage disk and divided into an inner area and an outer area surrounding the inner region. The magnetic head also includes a dielectric layer enclosing the coil and facing the storage disk. The dielectric layer is formed in the inner area of the principal surface of the substrate but not in the outer area. As tilting, the storage disk comes into contact with the dielectric layer, thereby being prevented from bumping into the outer area of the principal surface of the substrate.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the invention  
           [0002]    The present invention relates to a magnetic head used in a data writing/reading apparatus for writing data to or reading from a recording medium such as a magnetic disk or a magneto-optical disk. In this specification, a “magnetic head” is defined as any type of writing/reading head provided with a magnetic field generating coil. By this definition, a magneto-optical head may simply be referred to as “magnetic head.” The present invention also relates to a data writing/reading apparatus incorporating such a magnetic head.  
           [0003]    2. Description of the Related Art  
           [0004]    [0004]FIG. 7 shows a conventional magnetic head including a substrate  93  and a coil  92  formed on the substrate  93 . The coil  92  is entirely enclosed by a transparent dielectric layer  94  that has a uniform thickness and covers entirely the upper surface of the substrate  93 . Below the substrate  93  are provided a diametrically larger objective lens  91   a  and a diametrically smaller objective lens  91   b.  After being emitted from an unillustrated light source, laser beams are converged by the two objective lenses  91   a,    91   b  and pass through the substrate  93  and the dielectric layer  94 , to form a beam spot on the recording layer of the disk D. For performing data recording by magnetic field modulation, the magnetic field generated by the coil  92  is applied to the recording layer at the point where the beam spot is produced. For focus control, the magnetic head is supported by an actuator (not shown) so that it can be moved closer to or away from the disk D.  
           [0005]    While the conventional magnetic head is advantageous in that the dielectric layer  94  of the uniform thickness protects the coil  92  from external mechanical damage, it has the following drawback.  
           [0006]    Typically the magneto-optical disk D includes a thin substrate upon which a recording layer is formed. Due to this rather weak supporting structure, the disk D is liable to warp, thereby coming into contact with the edge  94   a  of the dielectric layer  94 . Even if the disk D itself is not warped, it may tilt, as shown by the single-dot chain lines in FIG. 7, due to unsteady rotation of a spindle supporting the disk D. In this instance again, the disk D may come into contact with the edge  94   a  of the dielectric layer  94 .  
           [0007]    Unfavorably, the disk D may be damaged by the contact with the dielectric layer  94 . Further, the actuator, which is coupled to the magnetic head, may also be damaged since a rather strong moment M can be exerted on the magnetic head when the disk D bumps into the dielectric layer  94 .  
         SUMMARY OF THE INVENTION  
         [0008]    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 arranged to reduce a moment produced by the contact between the recoding medium and the magnetic head. Another object of the present invention is to provide a data writing/reading apparatus incorporating such a magnetic head.  
           [0009]    According to a first aspect of the present invention, there is provided a magnetic head that is provided with: a coil for generating a magnetic field applied to a recoding medium; a substrate having a principal surface facing the recording medium, the principal surface including an inner region and an outer region surrounding the inner region; and a contact member facing the recording medium, the contact member coming into contact with the recording medium when the recoding medium tilts. The contact member is disposed only within the inner region of the principal surface so as to prevent the tilting recoding medium from coming into contact with the outer region of the principal surface.  
           [0010]    Preferably, the contact member may be a dielectric layer formed on the substrate to enclose the coil.  
           [0011]    Preferably, the dielectric layer may include a marginal portion spaced from the outer edge of the substrate toward the center of the substrate. This marginal portion comes into contact with the tilting recording medium.  
           [0012]    Preferably, the dielectric layer may consist of a lower sub-layer and an upper sub-layer formed on an inner region of the lower sub-layer. In this instance, the upper sub-layer may include a marginal portion that comes into contact with the tilting recoding medium.  
           [0013]    Preferably, the coil may include a first conductive spiral and a second conductive spiral, wherein the first conductive spiral is arranged within the upper sub-layer, while the second conductive spiral is arranged within the lower sub-layer.  
           [0014]    Preferably, the marginal portion of the dielectric layer may be rounded or chamfered so that the recoding medium is not damage by the contact with the dielectric layer.  
           [0015]    Preferably, the contact member may be coated with a lubricant for preventing the recoding medium from being damaged by the contact member.  
           [0016]    According to a second aspect of the present invention, there is provided a magnetic head that is provided with: a substrate including a principal surface facing a recoding medium; a magnetic field generating coil formed on the principal surface of the substrate and comprising a first conductor and a second conductor that is located closer to the recoding medium than the first conductor is; and a dielectric layer formed on the principal surface of the substrate and enclosing the coil. The second conductor is smaller in outer diameter than the first conductor. The dielectric layer has a stepped configuration. Specifically, the dielectric layer includes a first portion enclosing the first conductor of the coil and a second portion enclosing the second conductor of the coil. The second portion of the dielectric layer is smaller in size than the first portion thereof.  
           [0017]    Preferably, the magnetic head may further include a first cooling metal ring that surrounds the first conductor of the coil and a second cooling metal ring that surrounds the second conductor of the coil. The second cooling metal ring is smaller in diameter than the first cooling metal ring.  
           [0018]    Preferably, the magnetic head may further include an objective lens arranged on the opposite side to the principal surface of the substrate for convergence of light beams emitted from a light source. The converged light beams pass through the substrate and the dielectric layer to travel toward the recoding medium.  
           [0019]    Preferably, the magnetic head may further include an antireflection layer facing the recoding medium, wherein the antireflection layer is arranged within a recess formed in the dielectric layer. The light beams converged by the objective lens pass through the antireflection layer and travel toward the recoding medium.  
           [0020]    Preferably, the substrate is supported by an actuator so as to be moved closer to and away from the recoding medium by the actuator.  
           [0021]    Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0022]    [0022]FIG. 1 shows the principal components of a data writing/reading apparatus incorporating a magnetic head according to the present invention;  
         [0023]    [0023]FIG. 2 is a sectional view showing the details of the magnetic head of the present invention;  
         [0024]    [0024]FIG. 3 is a perspective view showing the magnetic head of the present invention;  
         [0025]    [0025]FIGS. 4A and 4B show a rounded or chamfered edge of the dielectric layer of the magnetic head of the present invention;  
         [0026]    [0026]FIGS. 5A and 5B illustrate how the magnetic head of the present invention is produced;  
         [0027]    [0027]FIG. 6 illustrates how a tilting magneto-optical disk comes into contact with a model magnetic head; and  
         [0028]    [0028]FIG. 7 shows a conventional magnetic head and a magneto-optical disk tilting above the magnetic head. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.  
         [0030]    [0030]FIG. 1 shows the principal components of a data writing/reading apparatus A incorporating a magnetic head according to the present invention. Precisely, the magnetic head H of the illustrated embodiment is a magneto-optical head, so that the apparatus A can write data to a magneto-optical disk D and read it from the disk.  
         [0031]    The magnetic head H, supported by a carriage  20  via an actuator  10 , includes a lens holder  11  to which two objective lenses  5   a,    5   b  are fixed. The lens holder  11  is moved by the actuator  10  in the focus direction Fs and the tracking direction Tg (the radial direction of the disk D).  
         [0032]    The magneto-optical disk D can be rotated at high speed about the axis C by a spindle motor  90 . As shown in FIG. 2, the disk D includes a base plate  98  upon which a recording layer  99  and a transparent coating layer  97  for protection of the recording layer  99  are formed. The two layers  99 ,  97  are provided on the lower side of the base plate  98 . Correspondingly, the magnetic head H is disposed under the disk D and held in direct facing relation to the recording layer  99 . With this arrangement, it is possible to reduce aberration observed in forming a beam spot on the recording layer  99  due to the thickness variation of the transparent coating layer  97 .  
         [0033]    As shown in FIG. 1, a slant mirror  23  is provided on the carriage  20  for reflecting upward the laser beams from a stationary optical unit  4 . The optical unit  4  is provided with a laser diode  40 , a collimator lens  41 , a beam splitter  42 , a beam expander  43 , and a galvano-mirror  44 . The laser beams emitted from the laser diode  40  are collimated by the lens  41 . Then, the laser beams pass through the beam splitter  42  and the beam expander  43 , and are reflected on the galvano-mirror  44  toward the slant mirror  23 . The upward beams reflected on the mirror  23  are converged by the objective lenses  5   a,    5   b  to form a beam spot on the recording layer  99  of the disk D. The converged beams are reflected on the recoding layer  99  to retrace the previous path. Finally, the laser beams are split by the beam splitter  42  and detected by an optical detector  45 .  
         [0034]    The beam expander  43  incorporates two lenses  43   a,    43   b  for reducing the effective diameter of the laser beam. The reduced effective diameter allows the size reduction of the objective lenses  5   a,    5   b,  which contributes to the overall weight reduction of the magnetic head H. With smaller inertia, the magnetic head H can be moved swiftly upon application of an external force. The carriage  20 , arranged under the disk D, is movable in the tracking direction Tg for performing a required seek action. In place of the carriage  20 , use may be made of a swing arm to move radially of the disk D with the magnetic head H attached to the arm.  
         [0035]    The magnetic head H includes a transparent substrate  6 , a magnetic layer  80 , a coil  3 , a dielectric layer  7 , a pair of cooling metal layers  81  and a reflection preventing layer (antireflection layer)  82 , as shown in FIG. 2, in addition to the objective lenses  5   a,    5   b  mentioned above.  
         [0036]    The substrate  6  is attached to the top of the lens holder  11  to support the magnetic layer  80 , the coil  3 , the dielectric layer  7 , etc. The transparent substrate  6  may be made of glass. The flat lens surface  50  of the objective lens  5   b  is attached to the bottom surface of the substrate  6 . The dielectric layer  7  may be made of transparent alumina. In this arrangement, the objective lens  5   b,  the substrate  6  and the dielectric layer  7  are combined to serve as a single lens.  
         [0037]    The magnetic layer  80  is provide for enabling effective application of the magnetic field of the coil  3  to the beam spot region on the disk D. The magnetic layer  80  may be made of a Ni—Fe alloy, Co-based amorphous alloy, Fe—Al—Si alloy, a combination of Fe—C alloy and Ni—Fe alloy, Fe—Ta—N alloy, or Mn—Zn ferrite. The magnetic layer  80  may have a thickness of 8 μm and is formed with a center hole  80   a  for allowing the passage of the laser beams. The hole  80   a  is filled with the dielectric layer  7 .  
         [0038]    The coil  3  may be made by patterning a metal layer, for example. The metal layer (typically copper layer) may be formed by a conventional plating technique. The illustrated coil  3  has a two-layer structure, consisting of an upper conductive spiral  30   a  and a lower conductive spiral  30   b  connected to the upper spiral  30   a.  Electric current passes through the two spirals  30   a,    30   b  in the same direction. The axis L of the coil  3  is aligned with the axis of the lens  5   a  and the axis of the lens  5   b.  To supply the coil  3  with power from outside of the dielectric layer  7 , power lines (not shown) are provided to extend from a side portion of the dielectric layer  7  to the coil  3 . As shown in FIG. 2, the center of the coil  3  is filled with the dielectric layer  7 . This portion (light transmitting portion), designated by the reference numeral  31 , should be as small as possible to reduce the inductance of the coil  3 , but not too small to pass the laser beam.  
         [0039]    The cooling layers  81 , made in a form of a ring, are provided for preventing the coil  3  from being overheated. As seen from FIG. 2, the upper cooling layer  81  surrounds the upper conductive spiral  30   a,  while the lower cooling layer  81  surrounds the lower conductive spiral  30   b.  The upper spiral  30   a  is diametrically smaller than the lower spiral  30   b.  Correspondingly, the upper cooling layer  81  is made diametrically smaller than the lower cooling layer  81 . For achieving the required cooling effect, the cooling layers  81  are made of a material having a higher thermal conductivity than the dielectric layer  7 . In the illustrated embodiment, the cooling layers  81  and the coil  3  are made of the same material, so that they can be formed in the same process.  
         [0040]    The dielectric layer  7 , formed on the substrate  6 , encloses the magnetic layer  80 , the coil  3  and the cooling layers  81 . As shown in FIGS. 2 and 3, the dielectric layer  7  includes a lower portion  70   a  having a thickness of h2 and an upper portion  70   b  having a thickness of h1. The upper portion  70   b  is diametrically smaller than the lower portion  70   a.  Thus, the circumferential part  70   a ′ of the lower portion  70   a  protrudes laterally from the upper portion  70   b.    
         [0041]    Referring to FIG. 3, the substrate  6  is rectangular, while the upper and the lower portions  70   b,    70   a  of the dielectric layer  7  are circular and concentric (the common axis is designated by L). The circular lower portion  70   a  is smaller in area than the rectangular substrate  6 , whereby a marginal area  6   a  of the substrate  6  is exposed. As shown in FIGS. 4A and 4B, the edge of the marginal area  70   b ′ of the upper portion  70   b  may preferably be rounded or chamfered. This rounded or chamfered edge may preferably be coated with a lubricant (fluoric resin, for example). The technical significance of these features will be described later.  
         [0042]    Referring to FIG. 2, the upper surface  73   a  of the dielectric layer  7  faces the disk D with an air layer intervening. The upper surface  73   a  is formed with a circular recess  73   b  the axis of which coincides with the axis L. The diameter of the recess  73   b  is larger than a laser beam diameter that is measured when the beam passes through the bottom of the recess  73   b.    
         [0043]    The reflection preventing layer  82 , arranged in the recess  73   b,  allows the passage of the laser beam. The layer  82  may be made of silicon oxide, tungsten oxide, magnesium fluoride, or silicon nitride. In the illustrated example, the layer  82  has a single layer structure. Alternatively, the layer  82  may have a multi-layer structure including two or more sub-layers made of different materials as mentioned above. The thickness of the layer  82  should be smaller than the depth of the recess  73   b  so that the layer  82  does not protrude beyond the upper surface  73   a  of the dielectric layer  7 .  
         [0044]    The magnetic head H described above may be produced in the following manner.  
         [0045]    Referring to FIG. 5A, a mother substrate  6 A is prepared, which is large enough to produce a prescribed number of rectangular substrates  6  (see FIG. 3, for example). Correspondingly to the substrates  6  to be produced, the mother substrate  6 A is provided with the same number of “magnetic head construction sites.” 
         [0046]    In each construction site, a magnetic layer  80 , conductive spirals  30   a - 30   b,  cooling layers  81  and a dielectric layer  7  are formed, as shown in FIG. 5A, together with an assembly of dummy metal layers  89  to be removed later. In the figure, the above-mentioned reflection preventing layer  82  and recess  73   b  are omitted.  
         [0047]    The dielectric layer  7  is composed of several sub-layers  7   a  that are stacked one upon another, as in the dummy metal layers  89 . As seen from FIG. 5A, the sub-layers  7   a  of the dielectric layer  7  and the dummy metal layers  89  are complementary to each other on the mother substrate  6 A. This structure may be built in several ways. For instance, the magnetic layer  80  and the lowermost dummy metal layer  89   a  are formed of the same material. Then, the lowermost sub-layer  7   a  is formed to cover the exposed surface of the mother substrate  6 A where no magnetic layers and no dummy metal layers are provided. Then, the second lowermost dummy metal layer  89  is formed on the first lowermost dummy metal layer  89   a.  The material to form the second dummy layer  89  may or may not be the same as that of the first dummy layer  89   a.  Then, the second lowermost sub-layer  7   a  is formed over the magnetic layer  80  and the first lowermost sub-layer  7   a.  Thus, the magnetic layer  80  is entirely enclosed by the dielectric material. The remaining steps necessary to complete the structure shown in FIG. 5A are apparent to the person skilled in the art, and therefore the explanation of them are omitted.  
         [0048]    Referring to FIG. 5B, after the desired structure is completed, the dummy metal layers  89  are removed by etching, for example. Thus, the voids S are produced on the mother substrate  6 A. By this etching, the magnetic layer  80 , the spirals  30   a,    30   b  and the cooling layers  81  are not removed since they are enclosed by the dielectric layer  7 .  
         [0049]    Finally, the mother substrate  6 A is divided into rectangular pieces to provide a number of identical products as shown in FIG. 3. The features of the thus produced magnetic head H will now be described below.  
         [0050]    The data writing to the disk D may be performed by magnetic field modulation, for example. According to this method, laser beams are converged by the objective lenses  5   a,    5   b  to produce a beam spot on the recording layer  99  of the disk D, thereby heating the recoding layer  99  up to the prescribed temperature near the Curie temperature. In this state, the magnetic field generated by the coil  3  is applied to the recoding layer  99 . In this manner, the direction of the magnetization in the recording layer  99  is controlled, whereby desired data is written to the disk D.  
         [0051]    During the data writing operation, the disk D may be tilted, as in the case of the prior art. However, in the present embodiment, arrangements are made such that the tilting disk D comes into contact with the upper marginal portion  70   b ′ of the dielectric layer  7 , but not with the lower marginal portion  70   a ′ nor the edge  6   a  of the substrate  6  (see the single-dot chain lines in FIG. 2). As seen from FIG. 2, the contact marginal portion  70   b ′ is located closer to the center of the magnetic head H than the lower marginal portion  70   a ′ and the edge  6   a  are. Therefore, upon contacting with the disk D being tilted, the magnetic head H receives a relatively small moment than when the lower marginal portion  70   a ′ of the dielectric layer  7  or the edge  6   a  of the substrate  6  would come into contact with the tilting disk D. Accordingly, it is possible to prevent the actuator  10  supporting the head H from being damaged.  
         [0052]    [0052]FIG. 6 illustrates a simulation conducted to show how a magneto-optical disk D being tilted comes into contact with a model magnetic head He that resembles the magnetic head H of the present invention.  
         [0053]    When the disk D is tilted by an angle θ, as shown in FIG. 6, and comes into contact with the marginal portion  70   b ′ of the dielectric layer  7 , an equation d1=2×WD/tanθ holds, where d1 is the diameter of the upper circular portion  70   b  of the dielectric layer  7 , and WD is the working distance between the disk D and the dielectric layer  7 .  
         [0054]    When the disk D also comes into contact with the marginal portion  70   a ′ of the lower circular portion  70   a  of the layer  7 , another equation d2=2×(WD+h1)/tanθ holds, where d2 is the diameter of the lower portion  70   a.  Therefore, to prevent the lower marginal portion  70   a ′ from contacting with the tilted disk D (with the inclination angle θ), the diameter of the lower portion  70   a  is set to be smaller than 2×(WD+h1)/tanθ.  
         [0055]    Likewise, when the disk D comes into contact with the edge  6   a  of the substrate  6 , an equation d3=2×(WD+h1+h2)/tanθ holds, where d3 is the maximum length of the substrate  6 . Therefore to prevent the edge  6   a  from contacting with the tilted disk D (with the inclination angle θ), the maximum length of the substrate  6  is set to be smaller than 2×(WD+h1+h2)/tanθ.  
         [0056]    As previously described, the magnetic head H of the present invention is moved in the focus direction Fs by the actuator  10 . With such an arrangement, the distance between the head H and the disk D is set to be relatively large (about 30 μm for example) in comparison with a slider type magnetic head designed to float over the rotating disk by the intervening air flow. This value (i.e. 30 μm), however, should not be put into the parameter WD of the aboveobtained equations for determining the diameter d2 or the maximum length d3, since the magnetic head H, moved by the actuator  10 , may actually come closer to the disk D. In light of this, to be on the safer side, the input value for the WD should be 7 μm, for example. The inclination angle θ may be in a range of 10-20 mrad, for example.  
         [0057]    In the present embodiment, the upper portion  70   b  of the dielectric layer  7  is circular, as seen from FIG. 3. This round edge arrangement is advantageous to preventing the tilted disk D from being damaged upon contacting with the upper portion  70   b  of the dielectric layer  7 . To provide more secure damage prevention, the edge of the marginal portion  70   b ′ may be rounded or chamfered, as shown in FIGS. 4A and 4B, and further be coated with a fluoric lubricant.  
         [0058]    In the magnetic head H, the laser beam emitted from the light source passes through the objective lenses  5   a - 5   b,  the dielectric layer  7  and the reflection preventing layer  82  to travel toward the recording layer  99 . The refraction index of the reflection preventing layer  82  is lower than that of the dielectric layer  7  but higher than that of the air. Advantageously, this reduces the reflection of the laser beam passing through the interface between the dielectric layer  7  and the reflection preventing layer  82  and the interface between the reflection preventing layer  82  and the air. As a result, the recording layer  99  is effectively irradiated by the laser beam.  
         [0059]    The reflection preventing layer  82  is unprotrudingly received in the recess  73   b  of the dielectric layer  7 , so that it does not damage the disk D even when the disk D comes close to the dielectric layer  7 . Further, the reflection preventing layer  82  is firmly fitted into the recess  73   b.  This prevents the layer  82  from unduly coming off the dielectric layer  7  when the tilting disk D bumps into the magnetic head H.  
         [0060]    The present invention is not limited to the specific features depicted in the drawings. For instance, the coil  3  may have only a single conductive spiral or more than two conductive spirals. Similarly, the dielectric layer  7  may have only a single sub-layer or more than two sub-layers. Further, the dielectric layer  7  may be provided, on its upper surface  73   a,  with a circular projection that can be brought into contact with the disk D. This contact projection may or may not be made of a dielectric material.  
         [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.