Patent Publication Number: US-RE46121-E

Title: Magnetic head and head gimbal assembly maintaining stable flying height in a disk drive

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2012-165003, filed Jul. 25, 2012, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments described herein relate generally to a magnetic head used in a disk drive, such as a magnetic disk drive, a head gimbal assembly provided with the head, and the disk drive. 
     BACKGROUND 
     A disk drive, such as a magnetic disk drive, comprises a magnetic disk for use as a recording medium, a spindle motor, a magnetic head, and a carriage assembly. The magnetic disk is disposed in a case. The spindle motor supports and rotates the magnetic disk. The magnetic head reads data from and writes data to the magnetic disk. The carriage assembly supports the head for movement relative to the magnetic disk. The magnetic head comprises a slider mounted on a suspension of the carriage assembly and a head section on the slider. The head section comprises a recording element for writing and a reproduction element for reading. 
     The head slider comprises a bearing surface (air-bearing surface or ABS) opposed to a recording surface of the magnetic disk. The head slider is subjected to a predetermined head load produced by the suspension and directed to a magnetic recording layer of the magnetic disk. When the magnetic disk drive is operating, an airflow is produced between the rotating disk and head slider, and the ABS of the slider is subjected to a force (positive pressure) that causes the slider to fly relative to the recording surface of the disk, based on the principle of air lubrication. The head slider is caused to fly over the recording surface of the magnetic disk, with a gap therebetween, by balancing this flying force with the head load. 
     In recent years, to meet the demand for greater recording density, increasing importance has been attached to reduction of head flying height and flying-height control in a low-height area, and development of technologies for dynamically controlling the head flying height has advanced rapidly. Presently, the flying gap between a magnetic disk and the head slider of a magnetic head in the vicinity of a read/write element is 10 nm or less. Further, for read/write operations, the gap between the read/write element and the magnetic disk is reduced to approximately several nanometers by additionally using a dynamic flying height (DFH) technology in which the magnetic spacing is controlled by dynamically adjusting the projection of the read/write element. 
     As a result, certain problems have become apparent. For example, a lubricant applied to the disk surface is transferred to the ABS of the head slider flying above the magnetic disk, the magnetic spacing is increased, and the flying performance of the head slider is made unstable. 
     The lubricant transferred to the ABS of the head slider of the magnetic head is moved onto the air-outflow end surface of the head slider by the airflow and accumulates there. If the transferred lubricant accumulates excessively, the flying height of the head slider becomes unstable. Thereupon, a high-fly write (HFW) problem occurs in which the recording and reproduction signals become unstable. Further, there is a problem wherein the reproduction signals vary when the magnetic disk drive is started up, since the lubricant diffuses and returns to the read/write element portion on the ABS side while the magnetic head is in an unloaded state with the disk drive off. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING 
         FIG. 1  is a plan view showing an HDD according to an embodiment; 
         FIG. 2  is an enlarged side view showing a magnetic head section of the HDD; 
         FIG. 3  is a perspective view showing the ABS side of a head slider of the magnetic head; 
         FIG. 4  is a plan view showing the ABS side of the head slider; 
         FIG. 5  is a diagram showing the relationship between the rate of change of the flying pitch of a head slider without second groove surfaces and the ratio of the width d of each first groove surface to the overall width D of the slider; 
         FIG. 6  is a diagram showing the relationship between the rate of change of the flying pitch of a head slider comprising first and second groove surfaces and the ratio of the width d of each first groove surface to the overall width D of the slider; and 
         FIG. 7  is a diagram showing differences between the rates of flying pitch change shown in  FIGS. 5 and 6 . 
     
    
    
     DETAILED DESCRIPTION 
     Various embodiments will be described hereinafter with reference to the accompanying drawings. In general, according to one embodiment, a magnetic head comprises: a head slider comprising a bearing surface opposed to a surface of a recording medium, and an inflow end portion and an outflow end portion for an airflow produced between the recording medium surface and the bearing surface; and a recording element and a reproduction element in the outflow end portion of the head slider. The bearing surface comprises a leading step at the inflow end portion, a skirt portion located at the inflow end portion and extending transversely relative to the head slider, a leading pad on the leading step and comprising a junction extending, at a transversely central portion thereof, to the skirt portion, first groove surfaces disposed individually on the opposite sides of the junction and being continuous with a downstream central portion of the skirt portion, second groove surfaces disposed on an upstream side of the first groove surfaces and formed deeper than the first groove surfaces, and negative-pressure grooves disposed individually on the transversely opposite sides of the first groove surfaces between the second groove surfaces and the skirt portion and formed deeper than the second groove surfaces. 
     An embodiment in which a disk drive is applied to a hard disk drive (HDD) will now be described in detail with reference to the accompanying drawings. 
       FIG. 1  shows the internal structure of the HDD with the top cover of its housing removed, and  FIG. 2  shows a flying magnetic head. As shown in  FIG. 1 , the HDD comprises a housing  10 . The housing  10  comprises a case  12  in the form of an open-topped rectangular box and a top cover (not shown), which is attached to the case by screws so as to close the top opening of the case. 
     The case  12  of the housing  10  carries therein a magnetic disk  16  for use as a recording medium, and a mechanical unit. The mechanical unit comprises a spindle motor  18 , a plurality (for example, two) of magnetic heads  40 , a carriage assembly  22 , and a voice coil motor (VCM)  24 . The spindle motor  18  supports and rotates the magnetic disk  16 . The magnetic heads  40  record and reproduce data on and from the magnetic disk. The carriage assembly  22  supports the heads  40  for movement relative to the disk  16 . The VCM  24  pivots and positions the carriage assembly  22 . Further, a ramp loading mechanism  25 , a board unit  21 , etc., are arranged in the case  12 . The ramp loading mechanism  25  holds the magnetic heads  40  in a position off the magnetic disk when the heads are moved to the outermost periphery of the magnetic disk. Electronic components, such as a preamplifier, a head IC, etc., are mounted on the board unit  21 . 
     A control circuit board (not shown) is attached to the outer surface of the bottom of the case  12  by screws. This circuit board controls the operations of the spindle motor  18 , VCM  24 , and magnetic heads  40  through the board unit  21 . 
     As shown in  FIGS. 1 and 2 , the magnetic disk  16  comprises a substrate  19  formed of a nonmagnetic disk with a diameter of, for example, about 2.5 inches (63.5 mm). A magnetic recording layer  20  is laminated on each surface of the substrate  19 , a protective film (not shown) is formed on the recording layer  20 , and in addition, a lubricant (for example, oil or an organic liquid)  23  is applied to a thickness of about 1 nm on the uppermost layer. 
     The magnetic disk  16  is fitted on a hub (not shown) of the spindle motor  18  and secured to the hub by a clamp spring  17 . Thus, the magnetic disk  16  is supported parallel to the bottom of the case  12 . The magnetic disk  16  is rotated in the direction of arrow B at a predetermined speed, for example, 5,400 or 7,200 rpm, by the spindle motor  18 . 
     The carriage assembly  22  comprises a bearing unit  26  secured to the bottom of the case  12  and a plurality of arms  32  extending from the bearing unit. These arms  32  are located parallel to the surfaces of the magnetic disk  16  with predetermined spaces therebetween and extend in the same direction from the bearing unit  26 . The carriage assembly  22  comprises elastically deformable suspensions  38  each in the form of an elongated plate. Each suspension  38  is formed of a plate spring, the proximal end of which is secured to the distal end of its corresponding arm  32  by spot welding or adhesive bonding and extends from the arm. Each suspension  38  may be integrally formed with its corresponding arm  32 . 
     As shown in  FIG. 2 , each magnetic head  40  comprises a substantially cuboid head slider  42  and read/write head section  44  on the slider and is secured to a gimbal  41  on the distal end portion of the suspension  38 . Each suspension  38  is formed with a dimple or substantially hemispheric protrusion  37  projecting on the magnetic head side in this case. The protrusion  37  is located at that position on the suspension  38  which faces the head mounting portion of the gimbal  41 , that is, the central portion of the magnetic head  40 . The protrusion  37  abuts a substantially central portion of a flat surface of the head slider  42  with the gimbal  41  between them. The gimbal  41  is pressed against the protrusion  37  by its own elasticity. Thus, the magnetic head  40  and the head mounting portion of the gimbal  41  can be displaced in the pitch and roll directions or vertically around the protrusion  37 . Further, the magnetic head  40  is subjected to a predetermined head load L produced by the spring force of the suspension  38  and directed to the surface of the magnetic disk  16 . 
     The suspension  38 , gimbal  41 , magnetic head  40 , and arm  32  constitute a head gimbal assembly. The head gimbal assembly need not always comprise the arm  32 . 
     As shown in  FIG. 1 , the carriage assembly  22  comprises a supporting frame  46  extending from the bearing unit  26  on the opposite side to the arms  32 . This supporting frame supports a voice coil  47  that constitutes part of the VCM  24 . The supporting frame  46  is a plastic structure integrally formed on the voice coil  47 . The voice coil  47  is located between a pair of yokes secured to the case  12 . Thus, the voice coil, along with the yokes and a magnet (not shown) secured to one of the yokes, constitutes the VCM  24 . If the voice coil  47  is energized, the carriage assembly  22  pivots around the bearing unit  26 , whereupon each magnetic head  40  is moved to and positioned over a desired track on the magnetic disk  16 . 
     The ramp loading mechanism  25  comprises a ramp  51  and tabs  48 . The ramp  51  is disposed on the bottom of the case  12  and located outside the magnetic disk  16 . The tabs  48  extend individually from the respective distal ends of the suspensions  38 . As the carriage assembly  22  pivots to a retracted position outside the disk  16 , each of the tabs  48  engages with a ramp surface formed on the ramp  51  and is then pushed up the ramp surface, whereupon the magnetic heads  40  are unloaded. 
     The structure of one of the magnetic heads  40  will now be described in detail.  FIG. 3  is a perspective view showing the head slider  42  of the magnetic head, and  FIG. 4  is a plan view of the head slider. 
     As shown in  FIGS. 3 and 4 , each magnetic head  40  is constructed as a flying head, which comprises the head slider  42  and read/write head section  44 . The head slider  42  is formed of, for example, a sintered body containing alumina and titanium carbide (AlTic or Al 2 O 3 —TiC). The slider  42  has a substantially cuboid structure as a whole, and comprises a rectangular air-bearing surface (ABS)  43 , inflow end surface  42 a, outflow end surface  42 b, and a pair of side surfaces  42 c. The ABS  43  is opposed to a surface of the magnetic disk  16 . The inflow and outflow end surfaces  42 a and  42 b extend perpendicular to the ABS. The side surfaces  42 c extend perpendicular to the ABS between the end surfaces  42 a and  42 b. The head section  44  is formed of thin films arranged on the outflow end of the slider body  45 . 
     The longitudinal direction of the ABS  43  is assumed to be a first direction X, and the transverse direction perpendicular thereto to be a second direction Y. The head slider  42  is a so-called femtoslider having a length L of 1.25 mm or less, for example, 0.85 mm, in the first direction X and a width W of 1.0 mm or less, for example, 0.7 mm, in the second direction Y. 
     The head slider  42  is caused to fly by the airflow C ( FIG. 2 ) produced between the disk surface and the ABS  43  as the magnetic disk  16  rotates. When the HDD is operating, the ABS  43  of the slider  42  is opposed to the disk surface with a gap therebetween. The direction of airflow C is coincident with the direction of rotation B of the disk  16 . The slider  42  is located on the surface of the disk  16  in such a manner that the first direction X of the ABS  43  is substantially coincident with the direction of airflow C. 
     As shown in  FIGS. 3 and 4 , a band-shaped negative-pressure groove (first negative-pressure groove)  50  extending throughout the length in the second direction Y is formed substantially in the central portion of the ABS  43 . If the head slider  42  is, for example, 0.23 mm thick, the depth of the groove  50  is 800 to 1,500 nm, for example, 1,500 nm. The negative-pressure groove  50  serves to produce a negative pressure on the central portion of the ABS  43  at every feasible yaw angle for the HDD. 
     An elongated skirt portion  72  is formed at the inflow end of the ABS  43  and extends substantially throughout the length of the head slider  42  in the second direction Y. A substantially rectangular leading step  52  is formed on the downstream side of the skirt portion  72  and extends substantially throughout the length of the head slider  42  in the second direction Y. The skirt portion  72  and leading step  52  project from the bottom surface of the negative-pressure groove  50  and are located on the inflow side of the groove  50  with respect to the airflow C. 
     In order to maintain the pitch angle of the magnetic head  40 , a leading pad  53  that supports the head slider  42  by means of an air film is formed projecting from the leading step  52 . The leading pad  53  and skirt portion  72  are formed flush with each other. The leading pad  53  is formed in an M-shape, which opens in a plurality of positions toward the inflow side. The leading pad  53  comprises a junction  53 b that extends along the central axis C at its transversely central portion to the central portion of the skirt portion  72 , that is, connects with the central portion of the skirt portion. 
     At the inflow end portion of the head slider  42 , first groove surfaces  74  are formed on the transversely opposite sides of the junction  53 b and on the upstream side of the leading pad  53 . The first groove surfaces  74  are continuous with the downstream central portion of the skirt portion  72 . Second groove surfaces  76  deeper than the first groove surfaces  74  are formed on the upstream side of the first groove surfaces. Further, negative-pressure grooves (second negative-pressure grooves)  78  are disposed on the transversely opposite sides of the first groove surfaces  74  between the second groove surfaces  76  and skirt portion  72 . The negative-pressure grooves  78  are deeper than the second groove surfaces  76  and, for example, as deep as the negative-pressure groove (first negative-pressure groove)  50 . 
     If the overall width of the head slider  42  and the width of each of the first groove surfaces (connection steps)  74  on the transversely opposite sides of the junction  53 b, in the second direction Y, are D and d, respectively, as shown in  FIG. 4 , d is about 30% of D. 
     An optimal value is given for the width d of each first groove surface  74  to be formed. The optimal value stated herein indicates the “maximum width within a range in which the flying pitch attitude of the head slider can be maintained”. The width d of each first groove surface  74  should be as large as possible in order to prevent cohesion of the organic liquid. It is believed, however, that if width d is too large, the rate of airflow becomes insufficient as the low-clearance area increases. Therefore, a positive pressure on the leading end side of the head slider is reduced, so that it is difficult to maintain the flying pitch attitude of the slider. The first groove surfaces (connection steps)  74  and second groove surfaces (intermediate steps)  76  are provided according to the present embodiment. As shown in  FIGS. 5 to 7 , moreover, the width d of each first groove surface  74  is restricted to about 5 to 30% of the overall width D of the head slider  42 . Even if width d is increased, therefore, a necessary positive pressure can be produced to suppress degradation in the flying pitch attitude. 
       FIG. 5  shows the results of an analysis of a head slider without the second groove surfaces (intermediate steps)  76 . In  FIG. 5 , the abscissa and ordinate represent the ratio of the width d of each first groove surface to the overall width D of the head slider and the rate of change of the flying pitch relative to a basic model, respectively. The basic model stated herein is a magnetic head designed so that the overall width D of its head slider and the width d of each first groove surface are 700 and 150 μm, respectively. The flying pitch of this basic model is assumed to be 100%. Further, the rate of pitch change is analyzed for five radial positions on the magnetic disk. The results are shown comparatively. 
       FIG. 6  shows the results of an analysis of a head slider comprising the first groove surfaces  74  and second groove surfaces (intermediate steps)  76 . In  FIG. 6 , the abscissa and ordinate represent the ratio of the width d of each first groove surface to the overall width D of the head slider and the rate of change of the flying pitch relative to a basic model, respectively. The flying pitch of this basic model, which is similar to the foregoing one, is assumed to be 100%. 
       FIG. 7  shows differences in the rate of flying pitch change obtained by subtracting the rate of flying pitch change shown in  FIG. 5  from that shown in  FIG. 6 , that is, differences in the rate of flying pitch change between the cases of head sliders with and without the second groove surfaces  76 . 
     Even if the width d of each first groove surface  74  is increased, a necessary positive pressure can be produced to suppress degradation in the flying pitch attitude by restricting width d to about 5 to 30% of the overall width D of the head slider  42 , as shown in  FIGS. 5 to 7 . It is indicated, moreover, that the second groove surfaces  76  serve to reduce the rate of pitch change, thereby maintaining a more reliable flying pitch attitude. 
     As shown in  FIGS. 3 and 4 , on the other hand, a negative-pressure cavity  54 , a recess, is formed ranging from a substantially central portion of the ABS  43  to the outflow end side. The negative-pressure cavity  54  is located on the outflow end side of the negative-pressure groove  50  and opens toward an outflow end surface  42 b of the head slider  42 . The negative-pressure cavity  54  is shallower than the negative-pressure groove  50 , that is, it is formed in a position higher than the bottom surface of the groove  50 . 
     A rib-shaped intermediate step  56  and a pair of side steps  58  are formed on the ABS  43  such that they surround the negative-pressure cavity  54 . The intermediate step  56  is located between the negative-pressure groove  50  and negative-pressure cavity  54  and extends in the second direction Y between the opposite side edges of the ABS  43 . The intermediate step  56  projects from the bottom surface of the negative-pressure cavity  54  and is located on the inflow side of the cavity  54  with respect to the airflow C. 
     The pair of side steps  58  are formed individually along the side edges of the ABS  43  and extend from the intermediate step  56  toward the outflow end of the ABS  43 . These side steps  58  project from the bottom surface of the negative-pressure cavity  54 . 
     The intermediate step  56  and side steps  58  are substantially U-shaped as a whole, closed upstream and open downstream. The steps  56  and  58  define the negative-pressure cavity  54 . 
     As shown in  FIGS. 3 and 4 , the head slider  42  comprises a trailing step  62  formed on the outflow end portion of the ABS  43  with respect to the airflow C. The trailing step  62  projects from the bottom surface of the negative-pressure cavity  54  so that it is flush with the leading step  52 . The trailing step  62  is located substantially in the center of the ABS  43  with respect to the second direction Y. A trailing pad  63  that supports the head slider  42  by means of an air film is formed projecting from the upper surface of the trailing step  62 . 
     The trailing pad  63  is kept at an inflow-side gap away from the outflow end surface of the trailing step  62  or the outflow end surface  42 b of the head slider  42  in this case. The trailing pad  63  is formed flush with the leading pad  53 , intermediate step  56 , and side steps  58 , which define the uppermost surface of the head slider  42  that constitutes the ABS  43 . The trailing step  62  and trailing pad  63  constitute a second pressure generating unit. 
     The head section  44  of the magnetic head  40  comprises a recording element  65  and reproduction element  66  for recording data on and reproducing data from the magnetic disk  16 . These elements  65  and  66  are embedded in the downstream end portion of the head slider  42  with respect to the direction of airflow C or in the trailing step  62  in this case. The respective distal end portions of the elements  65  and  66  are exposed in the ABS  43  in a position corresponding to the trailing pad  63 . 
     The ABS  43  of the head slider  42  comprises a pair of elongated center rails  68  extending in the first direction X from the intermediate step  56  to the trailing step  62 . The center rails  68  are located individually on the opposite sides of the central axis C of the head slider  42  and face each other across a gap in the second direction Y. The center rails  68  are formed so that its height above the bottom surface of the negative-pressure cavity  54  is the same as those of the intermediate step  56  and trailing pad  63 . A guide groove  70  that guides the airflow to the trailing step  62  and trailing pad  63  is formed between the pair of center rails  68 . The guide groove  70  is formed along the central axis C and extends through the negative-pressure groove  50  to the leading step  52 . 
     In the present embodiment, the ABS  43 , including the surface of the trailing pad  63  in which the respective distal ends of the recording and reproduction elements  65  and  66  are exposed, is formed so that its arithmetic surface roughness is greater than the surface roughness of other portions of the head slider  42 , for example, the upper surface of the trailing step  62  and the bottom surface of the negative-pressure cavity  54  in this case. 
     According to the HDD constructed in this manner, each magnetic head  40  is caused to fly by the airflow C produced between the disk surface and the ABS  43  as the magnetic disk  16  rotates. When the HDD is operating, therefore, the ABS  43  of the slider  42  is always opposed to the disk surface with a gap therebetween. The magnetic head  40  flies with the recording and reproduction elements  65  and  66  of the head section  44  inclined to be closest to the surface of the disk  16 . 
     In general, a strong airflow is produced above the ABS  43  of the head slider  42  while the magnetic head  40  is running above the magnetic disk  16 , so that any adhering organic liquid (magnetic disk lubricant or the like) flows and does not easily accumulate. However, the airflow above the bottom surface of each negative-pressure groove  78  formed between the skirt portion  72  and leading step  52  at the inflow end portion of the head slider  42  is relatively weak, so that the liquid easily accumulates there. The accumulated liquid on the bottom surface of the negative-pressure groove  78  diffuses and forms a film on the ABS  43  when the magnetic head  40  is unloaded and retracted from above the magnetic disk  16 . Thereupon, the flying height of the head  40  increases by a margin equivalent to the thickness of the formed film at the time of loading (drive startup), so that the read/write properties are degraded. According to the present embodiment described above, therefore, the first and second groove surfaces  74  and  76  are disposed between the leading pad  53  and skirt portion  72 , so that the organic liquid can be prevented from cohering in the negative-pressure grooves  78 . Further, the width d of each first groove surface  74  adjacent to the central portion of the skirt portion  72  is restricted to about 5 to 30% of the overall width D of the head slider  42 . Even if width d is increased, therefore, a necessary positive pressure can be produced to suppress degradation in the flying pitch attitude of the slider  42 . 
     According to the present embodiment, as described above, there can be obtained a magnetic head, head gimbal assembly, and magnetic disk drive with improved reliability, in which the flying height cannot be easily changed if a liquid, such as a lubricant, adheres to the head and which can perform stable recording and reproduction. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the inventions. Indeed, the novel embodiments described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the embodiments described herein may be made without departing from the spirit of the inventions. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the inventions. 
     For example, this invention is not limited to femtosliders and may also be applied to picosliders, pemtosliders, or other larger sliders. The shapes, sizes, etc., of the trailing step, trailing pad, and other parts of the head slider may be changed if necessary. The number of magnetic disks used in the disk drive is not limited to one and may be increased as required.