Abstract:
An air bearing slider includes an asymmetric taper for control of pressurization and suction force formation. The asymmetric taper is disposed on an edge of a slider to accommodate for the speed differential across the disc radial direction, thereby improving take-off performance, reducing sensitivity to skew angle and altitude variation, and reducing the severity of impacts during ramp loading and unloading. A leading taper intersecting a leading surface and air bearing surface of the slider is asymmetric about a longitudinal, bisecting plane of the slider. In another embodiment, side taper intersecting a side surface and air bearing surface of the slider is asymmetric about a latitudinal, bisecting plane of the slider. In another embodiment, rail taper intersecting a rail recess surface and air bearing surface of the slider is asymmetric about a longitudinal, rail-bisecting plane.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application claims priority from provisional U.S. patent application Ser. No. 60/237,960, filed on Oct. 4, 2000 for “Asymmetric Taper Air Bearing” by Catalin Serpe, Weimin Qian, and Mary Hipwell. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an air bearing slider for use in a data storage device such as a disc drive. More particularly, it relates to an air bearing slider which allows for control of pressurization and suction force formation. 
     Air bearing sliders have been extensively used in magnetic disc drives to appropriately position a transducing head above a rotating disc. In a disc drive, each transducer “flies” just a few nanometers above a rotating disc surface. The transducer is mounted in a slider assembly which has a contoured surface which faces the disc surface. An air bearing force is produced by pressurization of the air as it flows between the disc and slider and is a consequence of the slider contour and relative motion of the two surfaces. The air force prevents unintentional contact between the transducer and the disc. The air bearing also provides a very narrow clearance between the slider transducer and the rotating disc. This allows a high density of magnetic data to be transferred and reduces wear and damage. 
     In most high capacity storage applications, when the disc is at rest, the air bearing slider is in contact with the disc. During operation, the disc rotates at high speeds, which generates a wind of air immediately adjacent to the flat surface of the disc. This wind acts upon a lower air bearing surface of the slider and generates a lift force directing the slider away from the disc and against a load beam causing the slider to fly at an ultra-low height above the disc. 
     In negative pressure sliders, the wind also acts upon a portion of the air bearing surface of the slider to generate a suction force. The suction force counteracts the lift force by pulling the slider back toward the surface of the disc. A slider is typically mounted on a gimbal and load beam assembly which biases the slider toward the rotating disc, providing a pre-load force opposite to the lift force acting on the air bearing surface of the slider. For the slider to maintain the ultralow flying height above the surface of the disc, the lift force must be balanced with the pre-load and suction forces. 
     As disc storage systems are designed for greater and greater storage capacities, the density of concentric data tracks on discs is increasing (that is, the size of data tracks and radial spacing between data tracks is decreasing), requiring that the air bearing gap between the transducing head carried by the slider and the rotating disc be reduced. One aspect of achieving higher data storage densities in discs is operating the air bearing slider at ultra-low flying heights. 
     However, shrinking the air bearing gap and operating the slider at ultra-low flying heights has become a source of intermittent contact between the transducing head and the disc. Furthermore, when a disc drive is subjected to a mechanical shock of sufficient amplitude, the slider may overcome the biasing preload force of the load beam assembly and further lift away from or off the disc. Damage to the disc may occur when the slider returns to the disc and impacts the disc under the biasing force of the load beam. Such contact can result in catastrophic head-disc interface failure. Damage to the disc may include lost or corrupted data or, in a fatal disc crash, render the disc drive inoperable. Contact resulting in catastrophic failure is more likely to occur in ultra-low flying height systems. Additionally, intermittent contact induces vibrations detrimental to the reading and writing capabilities of the transducing head. 
     For the disc drive to function properly, the slider must maintain the proper fly height and provide adequate contact stiffness to assure that the slider does not contact the disc during operation. Also, the air bearing slider must have enhanced take-off performance at start up to limit contact between the slider and the disc. Such contact would cause damage to the slider during take-off and landing of the slider. 
     Air bearing sliders typically possess three primary degrees of movement, which are vertical motion, pitch, and roll rotation. The movement is relative to the gimbal and load beam associated with three applied forces upon the slider defined as pre-load, suction, and lift force. Steady state fly attitude for the slider is achieved when the three applied forces balance each other. A typical air bearing slider has a taper or step at its leading edge to provide for fast pressure buildup during takeoff of the slider from a resting position to a flying altitude above the disc. Air bearing sliders have a trailing edge at which thin film transducers are deposited. Typically, the air bearing surface includes longitudinal rails or pads extending from the leading edge taper toward the trailing edge. The rail design determines the pressure generated by the slider. The pressure distribution underneath the slider determines the flying characteristics, including flying height and pitch and roll of the slider relative to a rotating magnetic disc. Other characteristics that are affected by the configuration of the air bearing surface of a slider are takeoff velocity, air bearing stiffness, and track seek performance. 
     Flying height is one of the most critical parameters of magnetic recording. As the average flying height of the slider decreases, the transducer achieves greater resolution between the individual data bit locations on the disc. Therefore, it is desirable to have the transducers fly as close to the disc as possible. Flying height is preferably uniform regardless of variable flying conditions, such as tangential velocity variation from inside to outside tracks, lateral slider movement during seek operations, and air bearing skew angles. 
     The amount of lift of a slider having parallel rails depends upon relative speed of the slider to the rotating magnetic disc. Normally, the amount of lift increases as the relative speed increases. With movement in a circular pattern, the outside rail of the slider necessarily travels at a higher speed relative to the disc than the inside rail of the slider. 
     BRIEF SUMMARY OF THE INVENTION 
     This invention provides control of pressurization and/or suction force formation in air bearing sliders so that the slider flies with controlled roll. An asymmetric taper is disposed on the edge(s) of a slider. The asymmetric taper helps accommodate for the speed differential across the disc radial direction, thereby improving take-off performance, reducing sensitivity to skew angle and altitude variation, and reducing the severity of impacts during ramp loading and unloading. 
     In one aspect, a leading taper intersecting a leading surface and air bearing surface of the slider is asymmetric about a longitudinal, bisecting plane of the slider. In another aspect, a side taper intersecting a side surface and air bearing surface of the slider is asymmetric about a latitudinal, bisecting plane of the slider. In a third aspect, a rail taper intersecting a rail recess surface and air bearing surface of the slider is asymmetric about a longitudinal, rail-bisecting plane. 
     The asymmetric taper can be disposed so as to provide increased pressurization on the side of the slider with the lowest air flow velocity (e.g. the inner rail) for faster take off and increased stability of the air bearing. Alternatively, the increased pressurization can be directed toward the outer rail in ramp load / unload operation such that contact between the slider and the disc is avoided or reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a top perspective view of a disc drive. 
     FIG. 2 is a perspective view of a slider embodying the present invention. 
     FIG. 3 is a perspective view of another slider embodying the present invention. 
     FIG. 4 is a perspective view of a wafer from which a plurality of sliders is produced. 
     FIG. 5 is a perspective view of a slider bar showing a plurality of slider units embodying the present invention during an intermediate formation step. 
     FIG. 6 is a perspective view of one embodiment of an individual slider of a slider bar as shown in FIG. 5, during an intermediate formation step. 
     FIG. 7 is a perspective view of a second embodiment of an individual slider of a slider bar as shown in FIG. 5, during an intermediate formation step. 
     FIG. 8 is a perspective view of a third embodiment of an individual slider of a slider bar as shown in FIG. 5, during an intermediate formation step. 
     FIG. 9 is a perspective view of a fourth embodiment of an individual slider of a slider bar as shown in FIG. 5, during an intermediate formation step. 
     FIG. 10 is a perspective view of a fifth embodiment of a slider embodying the present invention. 
     FIG. 11 is a perspective view of a sixth embodiment of a slider embodying the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIG. 1 shows a top perspective view of a disc drive  12 , which includes a voice coil motor (VCM)  13 , actuator arm  14 , suspension  16 , flexure  18 , slider  20 , head mounting block  22 , and disc  24 . Slider  20  is connected to the distal end of suspension  16  by flexure  18 . Suspension  16  is connected to actuator arm  14  at head mounting block  22 . Actuator arm  14  is coupled to VCM  13 . As shown on the right side of FIG. 1, disc  24  has a multiplicity of tracks  26  and rotates about axis  28 . 
     During operation of disc drive  12 , rotation of disc  24  generates air movement which is encountered by slider  20 . This air movement acts to keep slider  20  aloft a small distance above the surface of disc  24 , allowing slider  20  to fly above the surface of disc  24 . VCM  13  is selectively operated to move actuator arm  14  around axis  30 , thereby moving suspension  16  and positioning the transducing head (not shown) carried by slider  20  over tracks  26  of disc  24 . Proper positioning of the transducing head is necessary for reading and writing data on concentric tracks  26  of disc  24 . 
     FIG. 2 is a perspective view of a slider  20  embodying the present invention. Slider  20  is inverted to show air bearing surface  32 . The amount of lifting across the width of slider  20  can be controlled by employing a structure in which an asymmetrical taper is disposed on slider  20  such that the taper is asymmetric about a longitudinal, bisecting plane of slider  20 . 
     In a preferred embodiment, slider  20  includes air bearing surface  32 , inner side rail  34 , outer side rail  36 , cross rail  38 , recessed region or cavity  40 , leading surface  42 , taper surface  44 , leading edge  46 , and trailing edge  48 . Air bearing surface  32  is disposed on the disc opposing surface of slider  20  and comprises inner side rail  34  and outer side rail  36 , which are connected by cross rail  38 . The three rails  34 ,  36 , and  38  enclose cavity  40 , which defines a subambient pressure zone or negative pressure region. 
     Slider  20  includes leading surface  42 , which resides at the front end of slider  20  when slider  20  is in motion relative to a magnetic disc (not shown). Leading surface  42  is substantially perpendicular to air bearing surface  32 . Asymmetric leading taper surface  44  intersects air bearing surface  32  and leading surface  42 . In this embodiment, taper surface  44  is disposed across the entire width of slider  20 . 
     In this example, planar taper surface  44  is wider and deeper on the side of inner rail  34  than outer rail  36 . Thus, air flows more rapidly under inner rail  34  than outer rail  36 , as compared to a symmetrical taper. Increased air flow under inner rail  34  causes increased pressurization and increased lift, particularly during take off. Asymmetric taper  44  thereby compensates for the difference in tangential speed between inner rail  34  and outer rail  36  by providing a counteractive difference in air mass flow. This results in correcting roll angle across the width of slider  20 . As shown in FIG. 2, the wider side of taper  44  is nearly twice as wide as the narrower side of taper  44 . Additionally, taper  44  is shown about evenly angled, i.e., at about 45°, with respect to air bearing surface  32  and with respect to leading surface  42 . This is illustrative only. In practice, the asymmetry of taper  44  may be more or less pronounced. The angle of taper  44  can also vary. Precise determinations may depend on such factors as the speed, height, and pitch of flight, and the contours of air bearing surface  32 . 
     Because taper  44  intersects leading surface  42 , its effect on air pressurization of air bearing surface  32  is more significant during take-off than during flight. Before take-off, air bearing surface  32  rests on a magnetic recording disc. During take-off, air is directed between air bearing surface  32  and the disc. The air flows under taper surface  44  and across air bearing surface  32 . Taper surface  44  helps to create a lifting force which assists in achieving a fast take-off. During flight, air pressurization is caused primarily by side rails  34  and  36  and cavity  40 ; the influence of asymmetric taper  44  is still present, but is much less significant. 
     FIG. 3 is a perspective view of another embodiment of slider  20 . In this embodiment of a catamaran-type slider, cross rail  18  is eliminated, and the taper surface  44  comprises inner taper surface  44 A and outer taper surface  44 B. The area of inner taper surface  44 A is greater than that of outer taper surface  44 B. This results in more rapid air flow over inner rail  34  than outer rail  36 , thereby overcoming the difference in tangential speed between the two rails and resulting in a roll correction. 
     As can be appreciated, air bearing surface  32  may have many features which will affect the flow of air besides taper surface  44 , such as the shape, position, and size of side rails  34  and  36 , the configuration of cavity  40 , the presence or absence of members such as a cross rail or center rail, and other features. However, this discussion will focus on the effect of asymmetric taper surface  44  compared to a symmetric taper surface, assuming the other features of air bearing surface  32  are the same. 
     FIGS. 4 and 5 represent an exemplary method of forming an asymmetric taper air leaving slider of the present invention. FIG. 4 is a perspective view of a wafer  50  from which a plurality of sliders  20  is produced. Wafer  50  may be formed of an electrically-conductive, ceramic material such as Al 2 O 3 -TiC, AlTiC, TiC, Si, SiC, ZrO 2  or other composite materials formed of combinations of these materials. Optionally, a plurality of parallel grooves  52  and a plurality of parallel, orthogonally positioned grooves  54  may be formed on wafer  50 . Grooves  52  and  54  prevent chipping that may occur during cutting of wafer  50  into bars  56  and individual sliders  20 . After fabrication of transducers thereon, wafer  50  is severed along grooves  52  to form slider bars  56 . 
     FIG. 5 shows slider bar  56  including a plurality of slider units  20  embodying the present invention during an intermediate formation step. One of the cut surfaces of each bar  56  is lapped to form air bearing surface  32 . This lapping process, in combination with photolithographic material removal, may result in side rails  34  and  36 , cross rail  38 , and cavity  40 , as shown in FIG.  2 . Bar  56  may be processed to dispose asymmetric taper surface  44 , which intersects leading surface  42  and air bearing surface  32 , on each slider  20  before the sliders  20  of bar  56  are cut apart from each other along grooves  54 . Alternatively, and especially for more complex taper configurations, sliders  20  may be cut from bar  56  along grooves  54  prior to the fashioning of taper  44  on each individual slider  20 . Taper surface  44  may be formed by known processes, such as by machining, chemical or focused ion beam etching, or lithographic techniques. The particular technique may be chosen depending on the geometry of the desired taper. For example, very simple planar tapers are easily machined, while complex multiregional tapers are more precisely etched. 
     FIG. 6 shows an individual slider  20  of FIG. 5, during an intermediate formation step. FIG. 6 shows longitudinal bisecting plane  58 . As illustrated, taper surface  44  is substantially angled with respect to, but is not perpendicular to, air bearing surface  32 . Taper surface  44  is asymmetric about longitudinal, bisecting plane  58 . Taper surface  44  is not perpendicular to longitudinal, bisecting plane  58 . Excess material may be removed from the central portion of air bearing surface  32  of slider  20 , so that the remaining portions form rails, resulting in either the structure shown in FIG. 1 or FIG.  2 . Rails  34 ,  36 , and  38  may be formed on slider  20  before, simultaneously as, or after taper  44  is disposed on slider  20 . 
     FIG. 7 represents a second embodiment of an individual slider  20  during an intermediate formation step. In this embodiment, taper surface  60  is nonplanar. Taper surface  60  is defined by contour lines as follows. Non-linear intersection  62  is formed between taper surface  60  and leading surface  42 . Linear intersection  63  joins taper surface  60  and one side of slider  20 . Non-linear intersection  64  connects taper surface  60  and air bearing surface  32 . Linear intersection  65  links taper surface  60  and the other side of slider  20 . 
     Usually, slider  20  will be oriented on a disc so that wider side  66  of taper surface  60  is on the inside of the disc (i.e., toward the axis of rotation of the disc), and narrower side  68  is on the outside of the disc. This orientation will help to equilibrate the fly height across the width of slider  20 , resulting in correction of roll angle, as discussed with respect to FIG.  1 . In this example, taper surface  60  curves back, away from leading surface  42 . As slider  20  moves across the radius of a magnetic disc, the air flow under slider  20  does not generally flow straight from leading edge  42  back to trailing edge  48 . Usually, the air flows at an angle with respect to longitudinal bisecting plane  58 . As slider  20  moves across the radius of a magnetic disc, the air flow direction changes as the skew angle between slider  20  and the disc changes. Because taper surface  60  curves back, it presents a surface upon which the air may impinge, even though the air flow may be skewed on either side of longitudinal bisecting plane  58  of slider  20 . Thus, taper surface  60  affects the pressurization of air flowing between air bearing surface  32  and a magnetic disc. 
     FIG. 8 shows a third embodiment of an individual slider  20  during an intermediate formation step. In this embodiment, taper surface  70  is nonplanar. This embodiment includes linear intersection  72  between taper surface  70  and leading surface  22 . Linear intersection  74  forms the interface between taper surface  70  and air bearing surface  32 . Non-linear intersection  76  is disposed between taper surface  70  and a side of slider  20 . Non-linear intersection  78  is formed between taper surface  70  and the other side of slider  20 . In this particular example, intersection  76  comprises a convex curve and intersection  78  comprises a concave curve. However, intersections  76  and  78  may comprise any nonlinear lines corresponding to a nonplanar taper surface  70 . In this particular example, air pressurization will be higher on the side of slider  20  near convex curve  76  as compared to the side near concave curve  78 . This is expected because of the relative sizes of taper surface  70  in each region, as well as the aerodynamic qualities of the surfaces involved. 
     FIG. 9 represents a fourth embodiment of an individual slider  20  during an intermediate formation step. In this embodiment, taper surface  80  comprises a multiregional nonplanar surface including region  82 , region  84 , and region  86 . Each region  82 ,  84 , and  86  has a surface orientation different from that of an adjacent region. Region  82  is bound by linear intersections  88 ,  90 , and  92 ; and nonlinear intersection  94 . Region  84  is bound by linear intersections  90 ,  96 ,  98 , and  100 . Region  86  is bound by linear intersections  98 ,  102 ,  104 , and  106 . While taper surface  80  is almost symmetric about longitudinal bisecting plane  58 , a difference in air pressurization is achieved by the side of slider  20  near line  104  as compared to the side of slider  20  near convex curve  94 . 
     In general, any taper surface resulting in any combination of linear and non-linear intersections and any combination of planar and non-planar regions may be used, so long as taper surface is asymmetric with respect to a longitudinal, bisecting plane  58  of slider  20 . The benefit of asymmetry on a leading taper of slider  20  is most significant during take-off, and less so during flight. A variety of different configurations may be used, depending on such factors as the shape and location of air bearing rails and other characteristics. A primary consideration in designing an asymmetric taper for a particular application is the need to increase or decrease air pressurization under certain parts of air bearing surface  32  of slider  20 . This need may arise, for example, because of roll or other defects in take-off or flight. 
     FIG. 10 represents a fifth embodiment of a slider  20  embodying the present invention. In this embodiment, side taper surface  108  intersecting air bearing surface  32  and side surface  110  is asymmetric about latitudinal bisecting plane  112 . FIG. 10 also shows asymmetric leading taper surface  114 , which forms a smooth intersection between side taper surface  108 , leading surface  42 , and leading taper  116 . An asymmetric taper on a side rail is most influential during flight, and less so during take-off. Side taper  108  allows more air to flow under inner rail  34  than outer rail  36 . The asymmetric taper about latitudinal plane  112  also contributes to a higher air flow mass near the leading portion of taper  108 , as compared to the trailing portion of taper  108 . This feature can be used to correct twisting, pulling, or other forces which slider  20  may encounter. 
     FIG. 11 represents a sixth embodiment of a slider  20  embodying the present invention. In this embodiment, longitudinal plane  115  bisects inner rail  116 . Inner rail  116  includes rail recess  118 , which is of uniform depth along the length of slider  20 . Asymmetric taper  120  intersects rail recess  118  and air bearing surface  122 . Asymmetric taper  120  is not perpendicular to air bearing surface  122 . Taper surface  120  is asymmetric about longitudinal, rail-bisecting plane  114 . Taper surface  120  is not perpendicular to longitudinal, rail-bisecting plane  114 . Taper surface  120  has a similar effect on air pressurization as taper  44  of FIG.  2 . However, because taper  120  is smaller, its effect is smaller. Additionally, because taper  120  is disposed on side rail  116  rather than on leading surface  42 , its effect is more significant during flight than during take-off. 
     All the embodiments of the present invention can be generally described as follows. Slider  20  comprises air bearing surface  32  and a second surface which is substantially perpendicular or substantially parallel to air bearing surface  32 . The second surface may be, for example, leading surface  42  in FIGS. 2,  3 ,  6 ,  7 ,  8 , or  9 ; side surface  110  in FIG. 10; or recessed surface  118  in FIG. 11. A taper surface intersects the air bearing surface at a first contour of intersection, which may be, for example, intersection  126  of FIG. 6; intersection  64  of FIG. 7; intersection  74  of FIG. 8; the sum of intersections  88 ,  96 , and  102  of FIG. 9; intersection  126  of FIG. 10; or intersection  128  of FIG.  11 . The taper surface intersects the second surface at a second contour of intersection, for example, leading edge  46  of FIG. 6; intersection  62  of FIG. 7; intersection  72  of FIG. 8; the sum of intersections  92 ,  100 , and  106  of FIG. 9; intersection  130  of FIG. 10; or intersection  132  of FIG.  11 . The taper surface is asymmetric about a plane containing the midpoint of the first contour of intersection and the midpoint of the second contour of intersection. In many cases, that plane will correspond to the slider or rail bisecting planes shown in FIGS. 6,  10 , and  11 . Generally, the taper surface is not perpendicular or parallel to the air bearing surface; and the taper surface is not perpendicular or parallel to the second surface. 
     While the principles of this invention have been described in connection with specific embodiments, it should be understood clearly that these descriptions are made only by way of example and are not intended to limit the scope of the invention. Workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. 
     For example, while very simple examples have been illustrated for ease of discussion of the principles of this invention, it is contemplated that the invention can be incorporated into different or more complex slider configurations. Also, multiple asymmetric tapers may be disposed on a single slider. Moreover, while catamaran type sliders arc depicted, the invention could be used with center pad style and other style sliders. References to more complex air bearing surface designs can be found, for example, in the following patents, which are assigned to Seagate and fully incorporated by reference: U.S. Pat. No. 5,062,017 to Strom et al. entitled “Hour-glass disk head slider,” U.S. Pat. No. 5,343,343 to Chapin entitled “Air bearing slider with relieved rail ends,” and U.S. Pat. No. 6,134,083 to Warmka entitled “Self-loading head slider having angled leading rails and non-divergent notched cavity dam.”