Abstract:
A method and apparatus for controlling lubrication in hard disk drives. Hard disk drives often include lubrication on the disks to protect the disks from incidental contact with the head slider. Embodiments of the invention include lubrication control surfaces or dams on the air bearing surface (ABS) of the head slider. The dams redirect air flow on the ABS and/or redirects excess lubrication that migrates from the disk to the head slider. By redirecting excess lubrication, the lubrication control dams remove and/or store the lubrication and avoid failure that may occur as a result of the lubrication interfering with the ABS or the read/write elements of the head.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     Embodiments of the invention generally relate to the field of hard disk drives. More specifically, embodiments of the invention relate methods and apparatus to control lubrication migration on head sliders in hard disk drives. 
     2. Description of the Related Art 
     Hard disk drives are used in many computer system operations. In fact, many computing systems operate with some type of hard disk drive to store the most basic computing information, e.g., the boot operation, the operating system, the applications, etc. In general, the hard disk drive is a device, which may or may not be removable, but without which, some computing systems may not operate. 
     One basic hard disk drive model was developed approximately 40 years ago and in some ways resembles a phonograph type apparatus. For instance, the hard drive model includes a storage disk or hard disk that spins at a standard rotational speed. An actuator arm or slider is utilized to reach out over the disk. The arm has a magnetic read/write transducer or head for reading/writing information to or from a location on the disk. The complete assembly, e.g., the arm and head, is called a head gimbal assembly (HGA). The assembly consisting of the disks, HGAs, spindle, housing, and the other parts internal to the housing is called the head disk assembly, or HDA. 
     In operation, the hard disk is rotated at a set speed via a spindle motor assembly having a central drive hub. Additionally, there are channels or tracks spaced at known intervals across the disk. Most current embodiments arrange the signal regions in concentric circular tracks, but other designs, such as spirals or irregular closed or open paths are possible and useful. When a request for a read of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head reads the information from the disk. In the same manner, when a request for a write of a specific portion or track is received, the hard disk aligns the head, via the arm, over the specific track location and the head writes the information to the disk. Refinements of the disk and the head have provided reductions in the size of the hard disk drive. For example, the original hard disk drive had a disk diameter of 24 inches. Modern hard disk drives are much smaller and include disk diameters of less than 2.5 inches. 
     The ever increasing need for data storage has led some disk drive makers to steadily increase the amount of data stored on a drive. Mechanical considerations, radiated audible noise limits, power requirements, and other factors limit the number of disks that can be economically combined in a single drive. Thus, disk drive technology has generally focused on increasing the amount of data stored on each disk surface by positioning the heads more closely to the media surface. However, care must be taken to avoid unintended contact between the head components and the moving media surface. 
     Typically, the heads are lightly spring loaded, with the spring tension perpendicular to the media surface plane and directed against the media surface. An air bearing separates the head and media surfaces as follows: As the media moves relative to the head, air is dragged by the disk surface through specifically designed channels in the surface of the head adjacent to the media surface. The surface of the head and the channels contained therein, collectively referred to as the air-bearing surface (ABS), are designed to generate regions of increased air pressure in between the ABS and media surface that forces the head away from direct contact with the media surface, in effect causing the head to fly above the media surface. The separation of the head ABS and media surface, commonly called fly height, is a complex phenomenon primarily a function of air density, the spring preload, the relative speed between the head and media surface, and the pattern of channels present on the head air bearing surface adjacent to the media surface. It is well known to those familiar with head-disk interface design that a particular head-disk combination will not fly precisely at the desired separation. Variances in mechanical tolerances, spring tensions, and other factors result in a nearly normal statistical fly-height population distribution generally centered about the mean fly height. Furthermore, the head and its mounting gimbal are subject to mechanical tolerances, aerodynamic forces, and inertial forces that can cause it to deviate from the desired attitude with respect to the media surface, (e.g. static and dynamic pitch and roll). This can move some areas of the air bearing surface closer or further from the media surface. 
     SUMMARY OF THE INVENTION 
     Accordingly, what is needed is an air bearing surface (ABS) design that will continue to function reliably at ultra-low fly heights, even in the presence of lubrication contamination. 
     In one embodiment the invention is a method of controlling lubrication migration on a head slider of a hard disk drive the head slider having a leading edge, two side edges, a trailing edge and an air bearing surface (ABS) wherein the leading edge, two side edges and the trailing edge define a perimeter of the ABS. The method includes: providing a trailing pad on the ABS, wherein the trailing pad is adjacent to the trailing edge; providing a front pad on the ABS, wherein the front pad is adjacent the leading edge; providing a laterally extending channel disposed between the trailing pad and the front pad; and providing a laterally extending dam disposed between the laterally extending channel and the front pad, the laterally extending dam defined by a top surface and one or more side walls, wherein the laterally extending dam is sized and positioned to perform at least one of redirecting air flow on the ABS, redirecting lubrication flow and storing lubrication; wherein a floor of the laterally extending channel defines a reference level and the front pad and the trailing pad are at a first height above the reference level. 
     In another embodiment, the invention is a head slider of a hard disk drive. The head slider includes: a leading edge; two side edges; a trailing edge; and an air bearing surface (ABS), the leading edge, two side edges and the trailing edge defining a perimeter of the ABS. The ABS has: a trailing pad adjacent to the trailing edge; a front pad adjacent to the leading edge; a laterally extending channel disposed between the trailing pad and the front pad; and a laterally extending dam disposed between the laterally extending channel and the front pad, the laterally extending dam defined by a top surface and one or more side walls; wherein the laterally extending dam is sized and positioned to perform at least one of redirecting air flow on the ABS, redirecting lubrication flow and storing lubrication, a floor of the laterally extending channel is at a reference level and the front pad and the trailing pad are at a first height above the reference level. 
     In a further embodiment, the invention is a hard disk drive including a disk, the disk including lubrication thereon, and a head slider. The head slider includes: a leading edge; two side edges; a trailing edge; and an air bearing surface (ABS), the leading edge, two side edges and the trailing edge defining a perimeter of the ABS. The ABS has: a trailing pad adjacent to the trailing edge; a front pad adjacent to the leading edge; a laterally extending channel disposed between the trailing pad and the front pad; and a laterally extending dam disposed between the laterally extending channel and the front pad, the laterally extending dam defined by a top surface and one or more side walls; wherein the laterally extending dam is sized and positioned to perform at least one of redirecting air flow on the ABS, redirecting lubrication flow and storing lubrication, a floor of the laterally extending channel is at a reference level and the front pad and the trailing pad are at a first height above the reference level. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments. 
         FIG. 1  shows an exemplary disk drive having a magnetic disk, and a head slider mounted on an actuator, according to embodiments of the invention. 
         FIG. 2  is a side view of the head slider and magnetic disk of the disk drive of  FIG. 1 , according to embodiments of the invention. 
         FIG. 3  is a plan view of the bottom of head slider of  FIGS. 1 and 2 , showing the air bearing surface (ABS) of the head slider, according to embodiments of the invention. 
         FIG. 4  is a plan view of the bottom of head slider of  FIGS. 1 and 2 , showing the air bearing surface (ABS) of the head slider, including a raised surface, according to embodiments of the invention. 
         FIG. 5  is an enlarged cross section of a portion of the head slider of  FIG. 4  taken through line  5 - 5 . 
     
    
    
     DETAILED DESCRIPTION 
     In the following, reference is made to embodiments of the invention. However, it should be understood that the invention is not limited to specific described embodiments. Instead, any combination of the following features and elements, whether related to different embodiments or not, is contemplated to implement and practice the invention. Furthermore, although embodiments of the invention may achieve advantages over other possible solutions and/or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the invention. Thus, the following aspects, features, embodiments and advantages are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim(s). Likewise, reference to “the invention” shall not be construed as a generalization of any inventive subject matter disclosed herein and shall not be considered to be an element or limitation of the appended claims except where explicitly recited in a claim(s). 
     As was noted above, fly height may vary for any number of reasons. Reducing the fly-height, while advantageously increasing the signal-to-noise ratio of the recovered signal, can undesirably lead to reduced disk drive reliability. Such reliability reduction can occur in the presence of particulate or lubrication contamination. Particulate contamination can include wear particles from drive components and/or airborne contaminates from the ambient surroundings. Lubrication contamination can occur from the protective lubrication on the disk surface migrating to the head slider surfaces. Such lubrication contaminants can accumulate on the air bearing surface. The buildup of lubrication contaminants can disrupt air flow, thus causing the head to fly higher or lower than desired, or at a different orientation relative to the media surface than desired. The lubrication buildup can also bridge the narrow fly height gap. This can lead to fouling and contact between the head and media. The resulting contact can generate more lubrication migration to the head slider, which can further exacerbate contamination. This can lead to drive failure that can occur rapidly by this mode. 
     Lubrication that is picked up on the head slider&#39;s ABS, will travel toward the trailing edge of the head slider, due to the air shear stress present while the head slider is “flying” over the disk surface. Further, lubrication that is deposited on the trailing edge, may migrate back onto the ABS. Often, the read/write head is on a pad that is near the trailing edge. Thus, lubrication buildup may collect near the read/write head transducer elements. Many components of the transducer elements have significant ferromagnetic properties. Thus, the magnetic sensitivity of a drive read element can be distorted and reduced, which can lead to lowered signal to noise ratios and drive failure. In an optical drive, lubrication can distort and/or occlude the optical path, which can result in poor performance. 
     Embodiments of the invention provide lubrication control methods and apparatus for head sliders in hard disk drives. One embodiment provides an air bearing surface (ABS) having one or more raised surfaces for redirecting air flow, redirecting lubrication flow and storing or trapping excess lubrication on the ABS. Therefore, embodiments of the invention allow the ABS to be effectively positioned in reference to the disk surface without (or with relatively less) lubrication buildup on the ABS. Fouling, head-disk contact, reduced transducer signal-to-noise ratio, and other detrimental outcomes of lubrication buildup are deterred with one or more recesses according to embodiments of the invention. 
       FIG. 1  shows one embodiment of a magnetic hard disk drive  10  that includes a housing  12  within which a magnetic disk  14  is fixed to a spindle motor (SPM) by a clamp. The SPM drives the magnetic disk  14  to spin at a certain speed. A head slider  18  accesses a recording area of the magnetic disk  14 . The head slider  18  has a head element section and a slider to which the head element section is fixed. The head slider  18  is provided with a fly-height control which adjusts the flying height of the head above the magnetic disk  14 . An actuator  16  carries the head slider  18 . In  FIG. 1 , the actuator  16  is pivotally held by a pivot shaft, and is pivoted around the pivot shaft by the drive force of a voice coil motor (VCM)  17  as a drive mechanism. The actuator  16  is pivoted in a radial direction of the magnetic disk  14  to move the head slider  18  to a desired position. Due to the viscosity of air between the spinning magnetic disk  14  and the head slider&#39;s air bearing surface (ABS) facing the magnetic disk  14 , a pressure acts on the head slider  18 . The head slider  18  flies low above the magnetic disk  14  as a result of this pressure balancing between the air and the force applied by the actuator  16  toward the magnetic disk  14 . In some embodiments, the head slider  18  may have raised areas or portions (such as pads) that actually contact disk  14 , as opposed to the slider head “flying” over the disk  14 . In some embodiments, the disk drive  10  may include a ramp  19 , where the head slider  18  is parked when the disk drive  10  is not in operation and disk  14  is not rotating. 
       FIG. 2  is a side view of the head slider  18  and the magnetic disk  14  of  FIG. 1 . Magnetic disk  14  is moving in the direction of arrow A, and causes airflow in the same direction. This airflow flows over the air bearing surface (ABS)  21  of the head slider  18  and produces the lifting pressure described above. In one embodiment, head slider  18  includes raised areas such as front pad  22  and trailing pad  24 , and recessed areas such as transverse or lateral channel  23 . The recessed areas, lateral channel  23  in this embodiment, are those surfaces of the ABS furthest from the disk  14 , and include a floor that defines a reference level of the ABS as described below. Trailing pad  24 , in one embodiment is located adjacent to and centered relative to, the trailing edge  26  of the head slider  18 , may further include the read/write head that writes and reads data to and from magnetic disk  14 . Front pad  22 , in one embodiment is located adjacent to and centered relative to, the leading edge ( 39  in  FIG. 3 ) of the head slider  18 . Disk  14  has a lubricant  28  on its upper surface to protect the disk  14  from contact with the head slider  18  and/or other components of the disk drive. In operation, lubricant  28  may migrate onto head slider  18 . Lubricant on forward portions of the head slider  18 , such as that labeled  28 ′, will migrate toward the trailing edge  26  of the head slider  18  as it is acted upon by the air flowing over the ABS of the head slider  18 . The lubricant will collect on different areas of the ABS including in the lateral channel  23  as shown by lubricant  28 ″. The lubricant  28 ″ in the lateral channel  23  of head slider  18  may flow onto trailing pad  24  and interfere with the read and write elements or other functional portions of the read/write head. 
       FIG. 3  shows one embodiment of the bottom of head slider  18  of  FIGS. 1 and 2 , from the air bearing surface (ABS) of the head slider. The head slider  18  includes a leading edge  39 , a trailing edge  26  and side edges  35  and  37 , that define the perimeter of the ABS. The ABS includes first recessed surfaces  23  having a floor at a reference level, which in some embodiments are those surfaces at the furthest distance from disk  14  (as seen in  FIG. 2 ). Second surfaces  32  are at a first height above the recessed surfaces  23  (reference level) and are closer to the disk  14 . Third, raised surfaces are at a second height above the first height, such as front pad  22  and trailing pad  24 . In some embodiments, surfaces  34  are included at a height in between the first and second height. In the embodiment as shown in  FIGS. 3 and 4 , the first recessed surfaces  23  form a laterally extending channel from one side  35  of the head slider  18  to the other side  37  of the head slider  18 . The laterally extending channel  23  includes a front surface  38  where it meets the second surfaces  32 . 
     Those raised surfaces at the highest, second height, (closest to the disk) such as front pad  22  and trailing pad  24  act as air-support surfaces. In some embodiments, other air support surfaces at the second height are included such as side pads  36 . Also in the embodiment shown in  FIGS. 3 and 4  arms connect the trailing pad  24  and the side pads  36 . Both arms include a longitudinally extending portion  33  and a laterally extending portion  31 . It should be understood that the arrangement of surfaces as shown in  FIGS. 3 and 4 , is only one particular arrangement of raised and recessed surfaces that may be present on the ABS of a head slider, and should not be considered limiting in terms of the invention, and is only provided here as an example. As air flows over the ABS surface, there are certain areas that act as gathering points for lubrication that is picked-up from the disk  14  (see  FIG. 2 ). If too much lubricant is collected in these areas, the lubricant may affect the read and write elements or other functional portions of the read/write head (not shown) that are, in one embodiment of the invention, mounted on trailing pad  24 . 
       FIG. 4  shows another embodiment of the bottom of head slider  18 ′ of  FIGS. 1 and 2 , from the air bearing surface (ABS) of the head slider. As described with reference to the head slider embodiment of  FIG. 3 , the ABS in  FIG. 4  includes first recessed surfaces  23  at a reference level which in some embodiments are those surfaces at the furthest distance from disk  14  (as seen in  FIG. 2 ). Second surfaces  32  are at a first height above the recessed surfaces  23  (reference level) and are closer to the disk  14 . Third raised surfaces are at a second height above the first height, such as front pad  22  and trailing pad  24 . In some embodiments, surfaces  34  are included at a height in between the first and second height. In the embodiment as shown in  FIGS. 3 and 4 , the first recessed surfaces  23  form a laterally extending channel from one side  35  of the head slider  18  to the other side  37  of the head slider  18 . Those raised surfaces at the highest, second height, (closest to the disk) such as front pad  22  and trailing pad  24  act as air-support surfaces. In some embodiments, other air support surfaces at the second height are included such as side pads  36 . Also in the embodiment shown in  FIGS. 3 and 4  arms connect the trailing pad  24  and the side pads  36 . Both arms include a longitudinally extending portion  33  and a laterally extending portion  31 . 
     As shown in  FIG. 4 , head slider  18 ′ includes one embodiment of a raised surface that is sized and positioned to redirect air flow, redirect lubrication flow and store or trap excess lubrication on the ABS, in the form of a laterally extending dam  40 . Lubrication that is picked-up from the disk  14 , may collect on various areas of the ABS, and as previously described, may migrate back onto pad  24  such that the lubricant may affect the read and write elements or other functional portions of the read/write head. The provision of the laterally extending dam  40  may mitigate this detrimental result in that the laterally extending dam  40  directs the airflow (shown as arrows B), to the side  37  of the head slider  18 ′. The arrows B are also indicative of lubrication flow in front of the laterally extending dam  40 . The laterally extending dam  40  directs the lubrication off of the ABS surface and prevents the lubrication from flowing back and forth through the region. 
     In the embodiment of  FIG. 4 , the laterally extending dam  40  is an elongated raised region having a first elongated side  44  adjacent the laterally extending channel  23 , a second elongated side  42  facing the front pad, and two sides  46 ,  48  adjacent to the side edges  35 ,  37 , respectively. The side edge  35  faces the outer edge of disk  14 , while the side edge  37  faces the center of disk  14 , (see  FIG. 1 ). The dam  40  has a width w and extends laterally within a distance d of the side edges  35  and  37  of the head slider  18 ′. The width of the laterally extending dam  40  is between about 2 μm and about 100 μm. The width may vary along the length of the laterally extending dam  40 , or, alternatively may be constant along the length of the laterally extending dam  40 . The distance d from the side edges  35  and  37  of the head slider  18 ′ to the laterally extending dam  40  is between about 0 μm (aligned with the side edge) and about 650 μm. The distance between one side edge and the laterally extending dam  40  and the other side edge, may be the same, or alternatively the laterally extending dam  40  may extend closer to one side than the other. 
     Illustratively,  FIG. 4  shows the dam  40  as being curved; however, in some embodiments, the dam  40  may be straight. Further, in some embodiments the dam  40  may be parallel to the leading edge  39  and the trailing edge  26 , while in other embodiments the dam  40  is slanted with respect to the leading edge  39  and the trailing edge  26 . In the embodiment of  FIG. 4 , the first elongated side  44  of the dam is aligned with the front surface  38  of the laterally extending channel  23 . In other embodiments, the first elongated side  44  may be closer to the leading edge  39  than the front surface  38  of the laterally extending channel  23 , such that a strip of second surfaces  32  at the second height may extend between the first elongated side  44  and the front surface  38  of the laterally extending channel  23 , as described below with respect to  FIG. 5 . 
       FIG. 5  is a cross-sectional view through line  5 - 5  of  FIG. 4 , showing the relative heights (not to scale) of the different surfaces of the ABS. The heights are described with respect to the first recessed surfaces  23  (the laterally extending channel) that are at a reference level (furthest distance from disk  14  as seen in  FIG. 2 ). The second surfaces  32  are at a first height closer to the disk  14  and above the reference level by a distance d 1 . In one embodiment, d 1  is between about 10 μm and about 20 μm. In some embodiments, third, raised surfaces are at a second height d 4  above the reference level, such as front pad  22  and trailing pad  24 . The second height being above the first height. In one embodiment, d 4  is between about 10 μm and about 20 μm. In some embodiments, surfaces  34  are included at a height d 2 , that is in between the first and second height. In one embodiment, d 2  is between about 10 μm and about 20 μm. In the embodiment as shown in  FIGS. 3 and 4 , the first recessed surfaces  23  form a laterally extending channel from one side  35  of the head slider  18  to the other side  37  of the head slider  18 . Those raised surfaces at the highest, second height, (closest to the disk) such as front pad  22  and trailing pad  24  act as air-support surfaces. In some embodiments, other air support surfaces at the second height are included, such as side pads  36 . Also in the embodiment shown in  FIGS. 3 and 4  arms connect the trailing pad  24  and the side pads  36 . Both arms include a longitudinally extending portion  33  and a laterally extending portion  31 . 
     Also shown in  FIG. 5 , is the relative height of the dam  40 . The dam  40  includes a top surface  50  that is at a height d 3  above the first recessed surfaces  23 . In one embodiment, d 3  is between about 10 μm and about 20 μm. The sidewalls of the dam extend from the second height d 1  to the top surface  50 . In some embodiments, the top surface  50  is relatively flat, while in other embodiments, the height d 3  of the top surface may vary along the width of the dam  40 , the length of the dam  40 , or both. In the embodiment shown in  FIG. 5 , the first elongated side  44  of the dam  40  is closer to the leading edge  39  than the front surface  38  of the laterally extending channel  23 , such that a strip of second surfaces  32 ′ at the second height extends between the first elongated side  44  and the front surface  38  of the laterally extending channel  23 . The distance between the first elongated side  44  of the dam  40  and the front surface  38  of the laterally extending channel  23 , in one embodiment is between about 0 μm (when they are aligned) and about 200 μm. In other embodiments, as shown in  FIG. 4 , the first elongated side  44  of the dam  40  and the front surface  38  of the laterally extending channel  23  are aligned with one another. While the figures show the sides  42 ,  44 ,  46  and  48  of the dam  40  as being orthogonal to the top surface  50 , in other embodiments, the sides may be slanted or curved. 
     While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.