Abstract:
An air bearing design enables a slider to fly at a higher fly height when the rotational speed of the disk is reduced to about one-third of its operational velocity. In addition, the slider has a flat profile as it scans the disk surface at a low fly height sigma, and low fly height loss during track seek and high altitude operation. This design also provides write protrusion compensation and thereby mitigates spacing losses due to the write current swelling of the write element protrusion. The leading region of the rear pad of the air bearing is mildly concave. This design produces unexpected results by compressing incoming air flow in such a way that, even under two very different velocities, good air bearing lift is generated while compensating for write element protrusion.

Description:
BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates in general to an improved air bearing design for disk drive sliders and, in particular, to a system, method, and apparatus for a slider air bearing design for improved multiple velocity fly height performance and write element protrusion compensation. 
     2. Description of the Related Art 
     Data access and storage systems typically comprise one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. The hard disks themselves are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, one to six disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm). 
     An HDD also utilizes an actuator assembly. The actuator moves magnetic read/write heads to the desired location on the rotating disk so as to write information to or read data from that location. Within most HDDs, the magnetic read/write head is mounted on a slider. A slider generally serves to mechanically support the head and any electrical connections between the head and the rest of the disk drive system. The slider is typically composed of various shaped pads to glide over moving air in order to maintain a uniform distance from the surface of the rotating disk, thereby preventing the head from undesirably contacting the disk. 
     Typically, a slider is formed with a set of shaped pads lying over its surface closest to the disk and called the air bearing surface (ABS) along with cavities of various depths surrounding the aforementioned pads and called etched cavities that enable the slider to fly at a constant height close to the disk during operation of the disk drive. A slider is associated with each side of each platter and flies just over the platter&#39;s surface. Each slider is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid actuator arm that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single movable unit having either a linear bearing or a rotary pivotal bearing system. 
     The head and arm assembly is linearly or pivotally moved utilizing a magnet/coil structure that is often called a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting with its spindle, actuator VCM, and internal filtration system is then enclosed with a cover and seal assembly to ensure that no contaminants can enter and adversely affect the reliability of the slider flying over the disk. 
     In some disk drive systems, the slider performance must satisfy seemingly contradictory requirements. One requirement is that the slider must actually fly at a higher fly height when the rotational speed of the disk is reduced to about one-third of the disk drive operating velocity. In one application, the need for this lower velocity arises during the writing of a servo pattern. For example, if the product velocity is about 10,000 rpm and the product fly height is about 10 nm, the servo writing velocity is about 3,780 rpm and the minimum fly height at the outer diameter of the slider is about 11 nm. 
     In addition to the dual velocity requirement, the slider must provide a flat profile as it scans the disk surface from the inner diameter (ID) to the outer diameter (OD). This flat profile requirement includes a minimum variation in the fly height from part-to-part due to manufacturing tolerances (low fly height sigma), low fly height loss during track seek, and low fly height loss during operation of the disk drive at high altitudes above sea level geographical regions. 
     A third requirement for these types of sliders is to be able to compensate for write protrusion. At high data writing rates, significant heat is created within the magnetic head. The heat causes material expansion within the magnetic head and slider, which in turn makes regions of the air bearing surface to protrude away from their nominal surface toward the magnetic disk. This protrusion substantially reduces the clearance at the protrusion location, and increases the likelihood of solid contact between the slider air bearing surface and the disk surface. The swelling of the write element reduces the fly height by a significant fraction of the original spacing and therefore creates spacing losses between the slider and the disk. 
     There have been many attempts to address these requirements in the prior art. Conventional methods vary the air bearing surface structure and include the use of multiple etch depths, shaping of the pads, and shifting the suspension pivot location. Typically, the front end of the rear air bearing pad is made convex or bullet-shaped so as to avoid trapping particles during operation. Alternatively, very deep pockets such as U-shaped designs having an aspect ratio (i.e., depth to width ratio) of 2.0 or greater. Although each of these prior art solutions are workable to some degree, an improved slider air bearing design that more thoroughly satisfies all of the previously described requirements would be desirable. 
     SUMMARY OF THE INVENTION 
     One embodiment of a system, method, and apparatus constructed in accordance with the present invention comprises a slider air bearing design for improved multiple velocity fly height performance, flat profile performance, and write element protrusion compensation. The air bearing design enables the slider to fly at a higher fly height when the rotational speed of the disk is reduced to about one-third of its operational velocity. In addition, the slider has a flat profile as it scans the disk surface from ID to the OD, with a low fly height sigma, low fly height loss during track seek, and low fly height loss during operation at high altitudes. The present invention also provides write protrusion compensation and thereby mitigates spacing losses due to the swelling of the write element protrusion with write current. 
     One feature of the air bearing design is the shape of the rear pad along with the etch depths. The leading region of the rear pad is mildly concave, having an aspect ratio (i.e., depth to width ratio) of approximately 0.1 to 0.8. This design produces unexpected results by compressing incoming air flow in such a way that, even under two very different velocities, good air bearing lift is generated. The mild concavity also serves to make the read pad region sensitive to write protrusion growth by producing needed extra lift force that compensates for the clearance reduction caused by the write element protrusion. 
     The foregoing and other objects and advantages of the present invention will be apparent  to those skilled in the art, in view of the following detailed description of the present invention, taken in conjunction with the appended claims and the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       So that the manner in which the features and advantages of the invention, as well as others which will become apparent are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only an embodiment of the invention and therefore are not to be considered limiting of its scope as the invention may admit to other equally effective embodiments. 
         FIG. 1  is a simplified plan view of one embodiment of a disk drive constructed in accordance with the present invention. 
         FIG. 2  is an isometric view of a slider air bearing surface constructed in accordance with the present invention that is used in conjunction with the disk drive of  FIG. 1 . 
         FIG. 3  is a two-dimensional plot of the x-y coordinates of the features of the slider air bearing surface of  FIG. 2 . 
         FIG. 4  depicts plots of the operation of the slider of  FIGS. 2 and 3  at various velocities and altitudes. 
         FIG. 5  illustrates the write protrusion compensation of the slider of  FIGS. 2 and 3 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to  FIG. 1 , a schematic drawing of one embodiment of an information storage system comprising a magnetic hard disk file or drive  111  for a computer system is shown. Drive  111  has an outer housing or base  113  containing a plurality of stacked, parallel magnetic disks  115  (one shown) which are closely spaced apart. Disks  115  are rotated by a spindle motor assembly having a central drive hub assembly  117 . An actuator  121  comprises a plurality of parallel actuator arms  125  (one shown) in the form of a comb that is pivotally mounted to base  113  about a pivot assembly  123 . A controller  119  is also mounted to base  113  for selectively moving the comb of arms  125  relative to disks  115 . 
     In the embodiment shown, each arm  125  has extending from it at least one cantilevered load beam and suspension  127 . A magnetic read/write transducer or head is mounted on a slider  129  and secured to a flexure that is flexibly mounted to each suspension  127 . The read/write heads magnetically read data from and/or magnetically write data to disks  115 . The level of integration called the head gimbal assembly is head and the slider  129 , which are mounted on suspension  127 . The slider  129  is usually bonded to the end of suspension  127 . The head is typically pico size (approximately 1250×1000×300 microns) and formed from ceramic or intermetallic materials. The head also may be nano size (approximately 850×700×230 microns) and is pre-loaded against the surface of disk  115  (in the range two to ten grams) by suspension  127 . 
     Suspensions  127  have a spring-like quality which biases or urges the air bearing surface of the slider  129  against the disk  115  to enable the creation of the air bearing film between the slider  129  and disk surface. A voice coil  133  housed within a conventional voice coil motor magnet assembly  134  (top pole not shown) is also mounted to arms  125  opposite the head gimbal assemblies. Movement of the actuator  121  (indicated by arrow  135 ) by controller  119  moves the head gimbal assemblies radially across tracks on the disks  115  until the heads settle on their respective target tracks. The head gimbal assemblies operate in a conventional manner and always move in unison with one another, unless drive  111  uses multiple independent actuators (not shown) wherein the arms can move independently of one another. 
     Referring now to  FIGS. 2 and 3 , detailed views of one embodiment of the air bearing surface (ABS)  140  of slider  129  are shown. One suggested embodiment of the x-y coordinates of the features on ABS  140  are shown in  FIG. 3 . Slider  129  is shown in a pico-size format, and ABS  140  has features that are formed at, for example, two etch depths: shallow (e.g., 0.18 micron) features, and deeper (e.g., 1.7 micron—the sum of 0.18 micron and 1.52 micron) features. By way of example, the gram load may comprise 2 grams and the load pivot is located at the center (intersection of axes  171 ,  173 ) of the slider  129 . 
     ABS  140  has a leading edge  141 , a trailing edge  143 , a pair of lateral edges  145 ,  147  extending therebetween, and a generally planar base surface  149  defined between the boundaries of edges  141 ,  143 ,  145 ,  147 . In the version shown, lateral edge  145  is closest to the inner diameter of the disk  115  ( FIG. 1 ), and lateral edge  147  is closest to the outer diameter edge of disk  115 . 
     ABS  140  has a generally U-shaped leading edge pad  151  that is aligned with the leading edge  141 . The “arms”  153 ,  155  of leading edge pad  151  extend rearward from leading edge  141  alongside but slightly offset from lateral edges  145 ,  147 . Two generally trapezoidal intermediate pads  161 ,  163  are formed on top of leading edge pad  151  near leading edge  141 . Again, one embodiment of the precise locations, shapes, and sizes of these features are illustrated in  FIG. 3 . 
     Adjacent to the trailing edge  143 , ABS  140  includes three trailing edge pads  165 ,  167 , and  169 . Trailing edge pads  165 ,  169  are very similar and are located adjacent to opposite corners of the trailing edge  143 . Trailing edge pads  165 ,  169  are generally tapered, streamlined shapes and the smallest of all of the pads on ABS  140 . Trailing edge pad  167  is located between trailing edge pads  165 ,  169  along a longitudinal axis  171  that bisects ABS  140  from side to side. A lateral axis  173  is perpendicular to longitudinal axis  171 , and bisects the ABS  140  from front to back. Trailing edge pad  167  is much larger than trailing edge pads  165 ,  169 , and actually abuts the trailing edge  143 . 
     One additional pad  175  is located on top of trailing edge pad  167  and is important for providing the desired performance for slider  129 . Pad  175  is generally U-shaped and mildly concave along its leading edge. The leading edge of pad  175  has an aspect ratio in the range of approximately 0.1 to 0.8. As shown in  FIG. 3 , the aspect ratio is defined as the depth  177  of the concave leading edge of pad  175  over the width  179  of the concave leading edge of pad  175 . To summarize, pads  161 ,  163 , and  175  are formed at the shallow etch depth, and pads  151 ,  165 ,  167 , and  169  are formed at the deep etch depth. 
     Examples of the improved performance of ABS  140  are depicted in  FIGS. 4 and 5 .  FIG. 4  illustrates plots of the operation of the slider  129  at various velocities and altitudes showing, on the vertical axis, fly height, and, on the horizontal axis, radius distance from a center of the disk  115  ( FIG. 1 ) going from the ID (left side) to the OD (right side). For example, plot  181  depicts the performance of ABS  140  while disk  115  is rotating at a normal product velocity of about 10,000 rpm at sea level. Plot  183  depicts the performance of ABS  140  while disk  115  is rotating at a servo writing velocity of about 3,800 rpm at sea level. Plot  185  depicts the performance of ABS  140  while disk  115  is rotating at a product velocity of 10,000 rpm, but at an altitude of 10,000 feet above sea level. These plots illustrate that ABS  140  can actually maintain slider  129  at a higher fly height at a lower speed than when it is operating at high speed at high altitude. 
       FIG. 5  illustrates the write protrusion compensation of the ABS  140  on slider  129 . When write current is sent to the write element in slider  129 , the write element has a tendency to swell by a small but nonetheless significant amount (e.g., a few nanometers), thereby reducing the spacing (fly height) between the slider  129  and the surface of disk  115 . The present invention compensates for this “write protrusion” and thereby mitigates spacing losses due to the swelling of the write element. For example, plot  189  shows the loss in fly height if no compensation existed. Plot  189  illustrates that every 1 nm of protrusion growth directly results in a 1 nm loss of fly height. However, plot  187  depicts the performance of ABS  140  on slider  129 , where a 1 nm protrusion growth results in less than a 1 nm loss of fly height. This is a performance improvement of approximately 25% over the prior art. 
     The present invention further comprises a method of improving multiple velocity fly height performance, flat profile performance, and write element protrusion compensation of a disk drive slider. One embodiment of the method comprises providing a disk drive  111 ; rotating a media disk  115  in the disk drive  111  at a media disk velocity of x rpm, and flying the slider  129  at a fly height of a nm relative to the media disk  115 ; and then rotating the media disk  115  at a servo writing velocity of y rpm (y&lt;x) for writing a servo pattern, and flying the slider  129  at a fly height of b nm (b&gt;a). 
     The method may comprise operating the disk drive  111  at a media disk velocity of about 10,000 rpm and a fly height is about 10 nm, and then a servo writing velocity of about 3,780 rpm at a fly height of about 11 nm. The method also may comprise performing the media disk velocity at an altitude of about 10,000 feet, and performing the servo writing velocity at an altitude of about sea level. The method may further comprise operating the disk drive  111  at sea level at the media disk velocity such that the fly height of the slider  129  is greater than the fly height of the slider  129  at the servo writing velocity at sea level. 
     Moreover, the method may further comprise sending write current to a write element in the slider  129  to swell the write element and thereby reducing the fly height between the slider  129  and the media disk  115 , but compensating for the reduction in fly height with an air bearing surface of the slider  129 . In addition, the method may comprises scanning the media disk  115  in a flat profile with the slider  129  from ID to OD, with a low fly height sigma, low fly height loss during track seek, and low fly height loss during operation at high altitudes. 
     The present invention has several advantages, including the ability to improve multiple velocity fly height performance, flat profile performance, and write element protrusion compensation. The air bearing design enables the slider to fly at a higher fly height when the rotational speed of the disk is reduced. In addition, the slider has a flat profile as it scans the disk surface from ID to the OD, with a low fly height sigma, low fly height loss during track seek, and low fly height loss during operation at high altitudes. The present invention also provides write protrusion compensation and thereby mitigates spacing losses due to the swelling of the write element protrusion with write current. 
     While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention.