Abstract:
A disc storage system includes a rotating disc and a transducer. The transducer is carried on a slider which is supported by an armature. The armature is used to move the slider radially across the disc surface whereby information may be read from or written to the disc surface of the transducer. The slider includes an air bearing surface which faces the disc surface. As the disc rotates, the air bearing surface causes the slider to “fly” over the disc surface. Pads are provided on the air bearing surface to improve operational characteristics of the system.

Description:
The present invention claims priority to Provisional Application Serial No. 60/051,043, filed Jun. 27, 1997; Provisional Application Serial No. 60/051,044, filed Jun. 27, 1997; Provisional Application Serial No. 60/054,313, filed Jul. 31, 1997; Provisional Application Serial No. 60/055,899, filed Aug. 15, 1997; Provisional Application Serial No. 60/064,949, filed Nov. 7, 1997; Provisional Application Serial No. 60/064,785, filed Nov. 10, 1997; Provisional Application Serial No. 60/064,789, filed Nov. 10, 1997; Provisional Application Serial No. 60/064,791, filed Nov. 10, 1997; Provisional Application Serial No. 60/067,590, filed Dec. 5, 1997; and Provisional Application Serial No. 60/074,968, filed Feb. 17, 1998 and also claims priority to U.S. Pat. No. 5,870,251, issued Feb. 9, 1999, and entitled “TAPERLESS/CROWN FREE/AIR BEARING DESIGN”. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to disc storage systems for storing information. More specifically, the present invention relates to sliders used in such systems. 
     Disc drives are used for storing information, typically as magnetically encoded data, and more recently as optically encoded data, on a disc surface. A transducing head is carried on a air-bearing slider that rides on a bearing of air above the disc surface as the disc rotates at high speed. In another technique, the slider contacts the disc surface with no air bearing interface such as is shown in U.S. Pat. Nos. 5,453,315 and 5,490,027. The head is then positioned radially over the disc to read back or write at a desired location. Benefits associated with an air bearing design are lost in such “contact” sliders. 
     In an air bearing design, the air bearing provides an interface between the slider and the disc which prevents damage to the disc over the life of the system, provides damping if the disc drive system undergoes shock due to external vibrations. The air bearing is also used to provide a desired spacing between the transducing element and the disc surface. A bias force is applied to the slider by a flexure armature in a direction toward the disc surface. This bias force is counteracted by lifting forces from the air bearing until an equilibrium is reached. The slider will contact the disc surface if the rotating speed of the disc is insufficient to cause the slider to “fly.” This contact typically occurs during start up or shut down of the disc. If the slider contacts a region of the disc which carries data, the data may be lost and the disc permanently damaged. 
     In many disc drive systems, a lubricant is applied to the disc surface to reduce damage to the head and the disc surface during starting and stopping. Air or gas also acts as a lubricant. However, a phenomenon known as “stiction,” which is caused by static friction and viscous shear forces, causes the slider to stick to the disc surface after periods of non use. The lubricant exasterbates the stiction problem. The stiction can damage the head or the disc when the slider is freed from the disc surface. Additionally, the spindle motor used to rotate the disc must provide sufficient torque to overcome the stiction. 
     One technique used to overcome the problem associated with stiction is to provide texturing to at least a portion of the disc surface. However, this reduces the effective recording area of the disc. Additionally, various attempts have been made to provide texturing on the air bearing surface of the slider. For example, U.S. Pat. Nos. 5,079,657 and 5,162,073 describes a technique for forming recesses in a slider surface. Another technique which is described in U.S. Pat. No. 5,418,667 includes providing large pads which provide a pitch to the slider to allow air flow between the air bearing surface and the disc. 
     SUMMARY OF THE INVENTION 
     A disc storage system includes a rotating disc and a transducer. The transducer is carried on a slider which is supported by an armature. The armature is used to move the slider radially across the disc surface whereby information may be read from or written to the disc surface of the transducer. The slider includes an air bearing surface which faces the disc surface. As the disc rotates, the air bearing surface causes the slider to “fly” over the disc surface. Pads are provided on the air bearing surface to improve operational characteristics of the system. For example, the pads may be used to reduce the stiction or improve flying characteristics. Further, one aspect of the present invention includes techniques for fabrication of such pads. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified diagram of a storage disc system in accordance with the present invention. 
     FIG. 2A is a graph of stiction as a function of height of landing pads of various sizes. 
     FIG. 2B is a graph of stiction as a function of lubrication thickness. 
     FIGS. 3A-3D are side cross-sectional views of steps in a process in accordance with one embodiment of the present invention for forming landing pads. 
     FIG. 3E is a bottom plan view of a slider including landing pads made in accordance with the steps of  3 A- 3 D. 
     FIG. 3F is a side view of a mask in accordance with one embodiment of the invention. 
     FIG. 3G is a side plan view of a landing pad formed using the mask of FIG.  3 F. 
     FIG. 3H is a side view of a mask in accordance with one embodiment of the invention. 
     FIG. 3I is a side plan view of a landing pad formed using the mask of FIG.  3 H. 
     FIG. 4A is a bottom of a slider in accordance with another embodiment of the present invention. 
     FIG. 4B is a side cross-sectional view of a rail of the slider of FIG.  4 A. 
     FIG. 4C is a side plan view of a rail of a slider in accordance with another embodiment of the present invention. 
     FIG. 5A is a bottom plan view of a slider in accordance with another embodiment of the present invention. 
     FIG. 5B is a bottom plan view of a slider in accordance with another embodiment of the present invention. 
     FIG. 6A is a bottom plan view of a slider in accordance with another embodiment of the present invention. 
     FIG. 6B is a bottom plan view of a slider in accordance with another embodiment of the present invention. 
     FIG. 6C is a bottom plan view of a slider in accordance with another embodiment of the present invention. 
     FIG. 6D is a side plan view of a slider in accordance with another embodiment of the present invention. 
     FIG. 6E is a side plan view of a slider in accordance with another embodiment of the present invention. 
     FIG. 7A is a bottom plan view of a slider in accordance with another embodiment of the invention including kick pads. 
     FIG. 7B is a side plan view of the slider of FIG.  7 A. 
     FIGS. 8A,  8 B and  8 C are side cross-sectional views of pads in accordance with embodiments of the invention. 
     FIG. 8D is a side plan view of a slider having an air bearing surface formed in accordance with the embodiments of FIGS. 8A-8C. 
     FIG. 9A is a side plan view of a slider in accordance with one embodiment of the invention shown relative to a medium surface. 
     FIG. 9B is a graph of stiction versus belly clearance for a slider. 
     FIG. 9C is a bottom plan view of a slider in accordance with another embodiment of the invention. 
     FIG. 10 is a bottom plan view of a slider in accordance with another embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a top view of a disc drive  10  including a slider in accordance with the present invention. Disc drive  10  includes a magnetic disc  12  mounted for rotational movement about and axis defined by spindle  14  within housing  16 . Disc drive  10  also includes an actuator  18  mounted to a base plate  20  of housing  16  and pivotally moveable relative to disc  14  about axis  22 . A cover  24  covers a portion of actuator  18 . Drive controller  26  is coupled to actuator  18 . In the preferred embodiment, drive controller  26  is either mountable within disc drive  10 , or is located outside of disc drive  10  with suitable connection to actuator  18 . Actuator  18 , includes an actuator arm assembly  28 , a rigid support member  30 , and a head gimbal assembly  32 . Head gimbal assembly  32  includes a load beam or flexure arm  34  coupled to rigid member  30 , and a slider  36  coupled by a gimbal (not shown) to load beam  34 . Slider  36  operates in accordance with the embodiments set forth herein and supports a transducer for reading information from and encoding information on disc  12 . 
     During operation, drive controller  26  receives position information indicating a portion of disc  12  to be accessed. Drive controller  26  receives the position information from an operator, from a host computer, or from another suitable controller. Based on the position information, drive controller  26  provides a position signal to actuator  18 . The position signal causes actuator  18  to pivot about axis  22 . This, in turn, causes actuator  18  to pivot about axis  22 . This, in turn, causes slider  36  (and consequently the transducer mounted on slider  36 ) to move radially over the surface of disc  12  in a generally arcuaic path indicated by arrow  38 . Drive controller  26  and actuator  18  operate in a known closed loop, negative feedback manner so that the transducer carried by slider  36  is positioned over the desired portion of disc  12 . Once the transducer is appropriately positioned, drive controller  26  then executes a desired read or write operation. 
     Recording density can be increased by reducing the fly height of slider  36 . Close proximity of slider  36  with disc  12  allows greater accuracy in reading and writing information onto disc  12 . 
     Stiction and fly/stiction are two major phenomena that impair the use of ultra-low flying recording heads to increase recording areal density. The solution to these problems has been to generate, in a controlled fashion, some asperities, or texture, on the media surface to reduce the area of contact at the head-media interface. The presence of these asperities on the media surface, although they can be confined to only within a small dedicated zone (i.e., a “landing zone”), enhances the chance of head-media contact during operation and thereby sets the limit to the true attainment of ultra-low flying. In most cases, due to the shape of the asperity, the nature of contact is called Hertzian contact, in which elastic deformation can occur locally. Consequently, the number of asperities on the media surface to support the head cannot be arbitrarily reduced, otherwise the interface will collapse leading to excessive stiction. In addition, this type of contact is prone to collapsing when an excessive amount of liquid lubricants are present in the interface. For example, the lubricant applied on the media to prevent wear during head-disc contact, as well as other outgassing materials from various drive components, may accumulate on the heads, and transfer to the interface thereby leading to excessive fly/stiction. 
     One aspect of the invention includes modeling the stiction to provide a desired texturing to the air bearing surface, as opposed to the medium surface. If the tip of the asperity in contact can be described as semi-spherical, a stiction model has predicted that head-disc interface could become unstable when the asperity density becomes too small or lube thickness too high. One stiction model is described in an article in  J. Appl. Phys . 78, 4206 (1995) by J. Gui and B. Marchon. However, if the shape of asperity is a column or a step, the elastic deformation does not occur locally. This “non-Hertzian” contact has a much higher rigidity in comparison to a spherical type of contact. Consequently, the number of contacting points at the interface may be reduced to control stiction without worrying about the possibility that the interface may collapse. Under this contact condition, fly/stiction will not occur, and stiction is mainly a function of the contacting area (or bearing area), which can be modelled rather readily. A stiction model can be used to predict stiction level as a function of texture geometries. 
     Texture features may be placed on either media or sliders. However, if this kind of texture is put on a media surface, the density of these texture features still has to meet a minimum requirement imposed by the fact that if the texture features are too far apart, the slider could fall in between the texture features and directly contact the smooth media surface, leading to high stiction. One aspect of the invention that can ensure the contacts between sliders and a disc are always made on texture is to put these texture features on the sliders. Kasamatsu et. al. from Fujitsu has reported low stiction from smooth disks using heads that had small pads on the sliders in the article at  IEEE Trans. Magn . 31, 2961 (1995). 
     The present invention includes small column-like texture features, i.e., landing pads, on the rails of a flying head to control stiction. For example, four such pads may be used. Sliders with such landing pads can be used on substantially smooth discs. The size and height of these landing pads must be controlled such that the pads can effectively reduce stiction during take-off yet provide enough clearance to prevent interference during normal flying. The following equations can be used to calculate the size and height of the pads based on the stiction requirement of a drive design:              S   =     μ                 Ea                     H   -   h     H               Eq   .              1                       2      γ                 A     h            d   -       (     h   /   α     )       1   /   3           h   -       (     h   /   α     )       1   /   3             +       2      γ                 a     h     +   W     =     aE          H   -   h     H               Eq   .              2                                
     where S is stiction, μ is coefficient of friction, E is the Young&#39;s modulus, a is the total surface area of all pads, H is the pad height, h is the head-disc separation at contact, W is the head pre-load, A is the air bearing surface area, and α is a constant defined by (12πγ/A H ) where γis the surface tension and A H  is the Hamaker constant. 
     FIG. 2A is a graph of stiction as a function of the heights of the landing pads of various sizes. These curves are generated from above two equations. Based on these curves, if one chooses the total area of landing pads to be between about 0.002 to 0.003 mm 2 , and height to be about 300 Å, stiction is between about 2 to 3 gram-force, which is well within current disc drive design requirement. 
     FIG. 2B shows stiction as a function of lubrication thickness for both landing pad design and a laser zone texture media design. As lube thickness increases, stiction increases. However, stiction increases much more rapidly in the case of the laser zone textured media, eventually stiction diverges at still higher lube thickness. This interface instability is the fundamental cause of fly/stiction. In the case the landing pad texture, on the other hand, stiction exhibits a well defined linear relationship with lube thickness. It does not diverge as lube thickness continues to increase. In other words, the fly/stiction problem does not occur for landing pad texture. 
     The modeling technique set forth herein may be used with other aspects of the present invention. The shape, density and placement of the pads may be modified as desired. Further, the pads may be formed using any appropriate technique. Such formation techniques are not limited to those specifically set forth herein. 
     One aspect of the present invention includes various techniques for forming landing pads. FIG. 3A is a cross-sectional view of one embodiment of a slider  110  in an area on which landing pads are to be formed on surface  112 . The slider body is coated with a vacuum compatible negative photoresist and the resist  114  is patterned as shown in FIG.  3 B. Next, a landing pad material is deposited anisotropically, typically using an ion beam to deposit, for example, diamond-like carbon (DLC) to form DLC layer  116 . The photoresist  114  and its overcoat of DLC are removed using any appropriate technique such as sodium bicarbonate blasting followed by a cleaning step such as a deionized water rinse and a dry to form pad  118  as shown in the cross section of FIG.  3 D. 
     This process offers a number of advantages over other techniques. For example, using this embodiment the edges of pad  118  are automatically deposited such that they blend smoothly into the slider body surface. This advantages arises from the “penumbral” shadowing of the anisotropic deposition process. Further, the landing pad material can be deposited over a previously deposited protective layer of the same material. This provides some protection from corrosion and electrostatic discharge (ESD) hazard to sensitive material used in the magnetic transducer early in the fabrication process. No additional adhesion layer, such as silicon, is required. The mechanical removal process makes any deviations which result from a landing pad material adhesion failure immediately and obviously detectable thereby providing improved reliability. This technique is also less expensive than reactive ion etching techniques and the pad can be deposited relatively quickly. The increased speed provides improved manufacturability and reduced costs by minimizing work in process. The process is also compatible with current techniques used for processing arrays of slider bars as they are lapped to their final surface finish. This is less expensive than attempting to deposit pads on individual sliders. Further, the process is compatible with materials that are difficult or impossible to remove from the substrate using etching or milling processes. Such materials include hard materials such as cathodic arc diamond films. FIG. 3E is a bottom plan view of slider  110  showing four pads  118  carried on rails  120 . Using a four to eight pad design such as shown in FIG. 3E, in one preferred embodiment of the invention the pads have a area of between about 100 μm 2  to about 12,000 μm 2 . The pads may provide any shape such as square or elliptical with an aspect ratio of about 2 to 1. Any other shape may be used such as round, tear drop, etc. 
     One aspect of the present invention includes controlling the angle of deposition relative to the plane of the substrate to form a desired surface on the landing pad. FIG. 3F shows one embodiment in which mask  114  has a thickness of 2.6 μm and a width of 5 μm. The ion beam  126  used for deposition is angled such that there is a 2.2 μm shadow. The substrate is rotated during deposition such that a convex contacting surface  122  as shown in FIG. 3G is formed on pad  118 . FIG. 3I shows a concave contacting surface  124  on pad  118 . Such a concave surface may be formed using the mask  114  shown in FIG. 3H having a thickness of 4.8 μm and a width of 5 μm. This provides the 4 μm shadow which, as the substrate rotates, causes the contact area of the pad  118  to have the concave shape. Such concave or convex shapes are particularly advantageous because the reduce the size of the contact area. Further, such shapes may have desirable hydrodynamic properties. 
     The above processing steps may be used to form any of the pads set forth herein, or other pads which are not explicitly set forth herein, as desired. The particular shape, height, placement and density of the pads may be in accordance with any particular design to achieve desired slider characteristics. 
     The present invention includes a novel technique for creating pads on the air bearing surface. As used herein, the term “pad” includes the structure formed by forming grooves in the air bearing surface of the slider. In one aspect of the invention, such pads or grooves are created using a laser beam, such as a pulsed continuous laser, at preferred locations along the air bearing surface. The dimensions of the features may be adjusted by varying the laser power, the pulse duration, the laser wavelength, etc. Instead of using diamond-like carbon, in this aspect of the invention the contact surface is the same as the slider, for example, AlTiC. This reduces the concern of wear of the DLC due to repeated landings and take offs. Further, the real area of contact between the disc and the head is reduced in comparison to “feet” type bumps in that the contact area is a line contact rather than an area contact. Further still, application of such a laser is easily integrated into current manufacturing techniques which use a laser to form the crown on a slider. 
     Diamond-like carbon is not considered advantageous for the formation of the pads in all embodiments of the invention. For example, DLC tends to wear with time and requires additional processing steps. 
     In another aspect of the invention, pads or feet are formed of AlTiC. For example, such feet may be formed through the application of a photoresist at selected locations on the slider followed by a subsequent etch such as an extended etch milling process. The photoresist is then removed revealing raised areas in the AlTiC slider body. For example, in FIG. 3B, ion milling may be applied to slider  110  thereby removing exposed portions of slider  110 . 
     These techniques may be used to form pads of any shape, position, density, or other desired characteristics whether or not specifically set forth in the present disclosure. 
     FIG. 4A is a bottom plan view of a slider  150  in accordance with another embodiment of the present invention. Slider  150  includes rails  152  carrying pads  154 . Furthermore, in accordance with one aspect of the present invention, depressions or recesses  156  are formed on rails  152 . FIG. 4B is a cross-sectional view of rail  152  taken along the line labeled  4 B— 4 B shown in FIG.  4 A and shows a cross-sectional view of recesses  156 . 
     The invention as set forth in FIGS. 4A and 4B is particularly advantageous because depressions  156  produce a hydrodynamic effect providing additional lift. Furthermore, as illustrated in FIG. 4C which is a side plan view of rail  152 , rail  152  typically includes a curvature between the leading and trailing edges. This curvature is referred to as a crown and may be on the order of 20 nm. Curvature along the outer rail and inner rail is referred to as camber and is on the order of 8 nm. If pads  154  have a height of 20 to 30 nm, the crown of rail  152  may be sufficient to interfere and cause contact to occur to the center region  160  of slider  152  and the disc surface. Recesses  156  provide additional lift to prevent such contact. 
     This aspect of the present invention is particularly advantageous because it does not require additional protrusions yet provides increased hydrodynamic effects during flying. This allows the slider to achieve a lower flying height by decreasing the air bearing effect. This “micro-hydrodynamic” effect improves flying characteristics when the slider transitions from a stationary position to a sliding position and vice versa. Recesses  156  may be optimized both in size, depth and shape. Recesses  156 ′ in FIG. 4A show four example shapes which may be used for recesses  156 . Similarly, recesses  156  and  156 ″ shown in FIG. 4B are various examples of cross-sectional shapes. The specifications for recesses  156  may be optimized by modeling using, for example, Reynold&#39;s Equation and/or by performing experiments. In some embodiments, it may be possible to eliminate the crown on the rails  152 . However, in another aspect of the invention, additional pads  162  may be added near the center line on the rail  152  as shown in FIG.  4 C. Pad  162  may hit a height which is less than the height of pads  154 . In one embodiment, the height of pads  154  should be slightly larger than the tallest asperity present in the media, typically around 10 nm for a very smooth media in which the roughness Ra is about 1 nm. 
     Furthermore, recesses  156  can be designed to provide additional damping to the air bearing for load/unload applications in which the quick formation of an air bearing between the slider and the disc is critical. Such air bearing damping is very advantageous for establishing the air bearing. The recesses  156  may also be used to provide additional damping should slider  150  contact an asperity on the disc surface. One aspect of the invention includes an air bearing surface including such recesses but without the use of landing pads. This is particularly advantageous for load/unload as there are no zero speed/stiction issues. Thus the recesses provide additional damping and reduced flying characteristics. 
     Another aspect of the present invention may be employed with pads in accordance with other aspects of the invention, or other pads which are not specifically set forth herein. Further, the recesses may be of any desired shape, form, depth, density to achieve desired air bearing characteristics. 
     In another aspect of the present invention, rails  200  of slider  202  as shown in FIG. 5A includes a large plurality of pads  204  formed thereon. This configuration of the invention is particularly advantageous. With the present invention, numerous small pads are fashioned over a majority of the air bearing surface of the slider. As discussed above, the head to disc spacing during the read and write operations is critical to recording densities. Therefore, the textured pads  204  stop at a position which is spaced apart from the trailing edge  208  of the slider  202  and the transducer  210 . 
     By placing numerous pads  204  across a relative large area, the interface between the slider  202  and the disc surface is less sensitive to changes in the crown or flatness of the slider. Further, the use of numerous pads  204  is advantageous because it provides improved reliability as a single defective pad will not cause a catastrophic failure. Further still, this aspect of the present invention provides a head/disc interface which may be studied based upon studies performed on head/disc interfaces in which the disc surface is textured and the slider is smooth. 
     During take-off, slider  202  tends to rock back and forth, and/or side to side. The use of multiple pads  204  allows the load to be distributed over numerous pads, even during this rocking motion. The pads  204  are also relatively easy to align with the air bearing surfaces during manufacture. Further, the use of numerous pads to provide a fully textured air bearing surface provides reduced friction and stiction relative to a design with four pads. 
     Experiments conducted in accordance with the present invention showed that the fully textured configuration provided an average dwell stiction of about 5 grams whereas a design using four pads yielded a dwell stiction of about 15 grams. In one preferred embodiment for the fully textured air bearing surface, the pads have a height of between about 100 and about 1000 Å, an area of between about 10 and 100 μm 2 , a density of about 1 pad per about 100 μm 2  to about 10,000 μm 2 . The pads may be distributed across anywhere from about 10% to about 100% of the air bearing surface, in one preferred embodiment, the full texturing is confined to an area in about the middle ⅔ of the rails. Further still, in some designs it may be desirable to have pads positioned differently on an inner rail of the slider versus an outer rail. For example, the relationship between pads on the rails may be such that pads on one rail are closer to a leading edge while pads on the other rail are closer to a trailing edge. However, these parameters may be adjusted as appropriate based upon the particular configuration and desired specifications. 
     FIG. 5B is a bottom plan view of slider  202  showing rails  200  with various configurations for pads  204 . As shown in FIG. 5B, pads  204  may by circular ( 204 A), rectangular ( 204 B), angled rectangles ( 204 C), squares ( 204 D), etc. the shape and placement of pads  204  may be predefined using masking techniques or may be random. 
     FIG. 6A is a bottom plan view of a slider  230  having rails  232  in accordance with another embodiment. Rails  232  carry pads having heights which vary with position. In this example of the invention, pads  234  have a height which is different than pads  236 . Varying the height of the pads can be used to further reduce fly stiction and dwell stiction. In the present example, pads  236  have a greatest height which is greater than about 200 Å and pads  234  have a lowest height which is about 200 Å. The greater height of pads  200  improves the margin for stiction and wear of the pads. Further, the lower height pads  234  help avoid contact between the trailing edge  238  of slider  230  and the disc during operation. Furthermore, as illustrated in FIG. 6A the location of the pads can be randomized. Such randomization reduces the chance that the pads will contact the disc along the same track during repeated operation. This reduces unbalanced wear on the disc surface. 
     In another aspect of the invention, the area of the pads can be varied either randomly or as a function of position. FIG. 6B is a bottom plan view of slider  240  having rails  242  carrying pads  244  and  246 . As illustrated in FIG. 6B pads  244  which are near the leading edge  248  of slider  240  provide a larger area in comparison to pads  246 . This configuration is advantageous because pads near the leading edge  248  of slider  240  tend to experience increased wear and stress relative to pads closer to the trailing edge. The large front pads  244  exhibit improved wear behavior and are less likely to be broken during operation. 
     FIG. 6C is a bottom plan view of a slider  250  in accordance with another embodiment having rails  252 . Rails  252  include pads  254  and  256 . Preferably, there are a plurality of pads  256  positioned near the crowned portion of a crowned rail  252 . Pads  256  may be of number, density, height and shape, etc. as desired to reduce contact between the crowned portion of rails  252  in the medium. 
     FIG. 6D is a side view of a slider  260  in accordance with another embodiment shown relative to storage disc  262 . In the embodiment of FIG. 6D, pads  264  positioned near the leading edge  266  of slider  260  have a height which is greater than pads  268  positioned closer to the trailing edge. Pads  264  extend from the leading edge to the mid section of slider  260 . This is particularly advantageous for heads in which the leading edge may experience increased wear in comparison to the trailing edge due to a negative pitch of the slider during initial operation. 
     Pads  268  may be formed using a second mask, or other technique set forth herein, for example, and disposed with a height to avoid contact with medium  262  during normal operation. Further, pads  264  reduce stiction during normal operation and are capable of absorbing any contact or wear should the slider  260  pitch forward. 
     FIG. 6E is a side view of a slider  270  shown flying over disc  262  in accordance with another embodiment. Slider  270  includes bumps  272  in accordance with the present invention. In the embodiment of FIG. 6F, bumps  272  have are tallest near the leading edge  274  of the slider which is progressively shorter in a direction toward the trailing edge  276 . This may be a relatively continuous change or may be through a series of steps. The geometry may be obtained through an desirable technique. For example, through the use of shadowing during the deposition and formation processes. 
     Another aspect of the present invention includes the recognition that placement of pads on the air bearing surface may be used to optimize performance. 
     For example, placing pads closer to the trailing edge of the slider can improve contact start/stop (CSS) performance because the slider is less likely to tip backwards thereby contacting the trailing edge of the air bearing surface which would lead to stiction with the polished media. However, slider flyability is improved by moving the rear pads toward the leading edge of the slider. Placing the rear pads near the leading edge of the slider reduces the likelihood that the pads will contact the media surface due to changes in altitude, roll sensitivity and access fly height losses. 
     The present invention also provides a technique to overcome the tradeoff between CSS and flyability performance. FIG. 7A is a bottom plan view and FIG. 7B is a side plan view of slider  300  in accordance with another embodiment of the invention. Slider  300  includes rails  302  and pads  304 . Further, slider  300  includes kick pads  306  positioned behind pads  304 , closer to trailing edge  308  of slider  300 . Kick pads  306  prevent slider  300  from tipping during operation in a manner which would cause the trailing edge of slider  300  to contact the medium surface. This will avoid a high stiction orientation during operation. Further, kick pads  306  allow pads  304  to be placed closer to the leading edge of slider  300  thereby improving flyability of slider  300 . Preferably, kick pads  306  have a height which is less than the height of pads  304  such that pads  306  do not contact the media surface during normal flying. The design of pads  304  and  306  is preferably such that they may be easily integrated into the manufacturing process and have size, shape and positioning to achieve the desired flying and start/stop characteristics for a particular slider, media, lubrication, speed, etc. The kick pads  306  may be of appropriate size, shape or density as desired. 
     One aspect of the use of pads on sliders in accordance with the present invention is that the pads may become smooth as the surface is worn over time. This tends to reduce the compatibility of the pads with a very smooth media surface. The smooth pad may increase the dynamic friction. 
     One aspect of the invention includes texturing the pads to thereby provide a rough surface on the pad to further reduce contact area and thereby reduce friction. The texturing may be in accordance with any technique. However, one technique which may be integrated in a diamond-like carbon pad is through the introduction of small particles, such as silicon dioxide, slightly below the diamond-like carbon. For example, the smallest particles may be 3 to about 20 nm below the DLC. The total thickness is in one embodiment, between about 30 nm and about 50 nm. The texture may be applied directly to the air bearing surface, (for example, using a mask to form a pad) on a DLC pad, on adhesion layer, or in multiple layers of particles and DLC. Such particles may provide a height of between about 0.1 micro inches to about 10 micro inches. 
     FIG. 8A is a side cross-sectional view of a rail  320  of an air bearing surface carrying a pad  322 . Pads  322  include particles  324 , such as silicon dioxide, coated with a DLC layer  326 . As illustrated in FIG. 8A, the particles  324  provide a texturing to the surface of the DLC layer  326 . 
     FIG. 8B is a cross-sectional view of an air bearing surface  328  of a rail  328  in accordance with another embodiment in which a pad  330  is formed on an intermediary layer  332  which carries particles  324  and DLC layer  326  thereon. Intermediary layer  332  may, for example, comprise a DLC layer or an adhesion layer with particles  324  deposited thereon. 
     FIG. 8C is a cross-sectional view of a pad  338  in accordance with another embodiment deposited on the air bearing surface  340  of a rail. Pad  338  is formed using any desired number of multiple layers of particles  342  and DLC layers  344 . This provides multiple layers of texturing which may be exposed as head  338  wears over extended use. 
     The particles may be deposited on the air bearing surface or landing pads to provide desired texturing. The DLC, or other layer, is applied to encapsulate the texture into the substrate. This layer also preferably provides a good tribological material. Tall structures may be obtained using multiple layers. FIG. 8D is a side plan view of a slider  350  including air bearing surfaces  352  which are formed using a texturing technique in accordance with this aspect of the invention in which a plurality of small particles are injected into layers of material during fabrication. 
     As set forth herein, pads on sliders in accordance with the present invention allow the slider to fly closer to the medium and thereby provide higher areal recording density. Further, the need for zone texture on the medium is eliminated. FIG. 9A is a side plan view of a rail  370  of a slider in accordance with one embodiment of the present invention. Rail  370  includes a crown in which the middle portion  372  of the rail is closer to the medium  374  in comparison to end portions  376 . This four pad design (two pads on each rail) may, in some embodiments, be susceptible to high stiction because of the interface between crown portion  372  and medium  374 . As illustrated in FIG. 9A, the minimum separation distance between the air bearing surface of rail  370  and the surface of medium  374  is defined by the clearance at crown portion  372  rather than by the height of pads  378 . As the crown may be substantial, especially in 50% slider designs in which the clearance between crown portion  372  can be significantly smaller than the height of pads  378 . Thus, a large menisci is formed between crown portion  372  and medium  374  which leads to relatively large stiction. For example, FIG. 9B is an example of stiction versus belly clearance (i.e., crown clearance) for a 50% slider design having four pads  378 . The data from FIG. 9B is the three second dwell stiction for sliders having four pads with a 15 Å lubricant film having a medium molecular weight. The variations in the belly heights for the five different heads plotted are caused by variations in the crown while the pad height was roughly constant at about 1.3 to 1.4 μinches. As illustrated in FIG. 9B, there is a strong correlation between stiction and belly clearance. In particular, a low belly clearance (i.e., highly crowned) slider exhibits very high stiction whereas heads with greater clearance provide significantly less stiction. Since the height of pads  378 , and in particular the height of the rear pad, is constrained by the requirement that when the head is flying over medium  374  the trailing edge of the slider which carries the transducer must be positioned very close to the disc surface, this stiction represents a critical issue in four pad designs having crowned rails. 
     FIG. 9C is a bottom plan view of a slider  390  in accordance with another embodiment. Slider  390  includes rails  392  extending from a leading edge  394  to a trailing edge  396 . Slider  390  further includes outer edge pads  398  and middle pads  400 . The addition of middle pads  400  cause the effective crown between adjacent pads to be reduced by a factor of 4 in comparison to the four pad designs shown in FIG.  9 A. Consequently, the clearance problems shown in FIG. 9B are mitigated. 
     In another aspect of the present invention, the problem associated with crown can be eliminated by leaving the slider uncrowned and using only four pads. The four pads lift the slider air bearing surface off of the medium when the head is at rest such that a crown is not necessary for take-off. With such a zero crown design, the separation between the air bearing surface and the medium surface is determined by the pad height and the stiction problem illustrated in FIGS. 9A and 9B is eliminated. In another embodiment, a slight crown is provided such that the clearance is sufficiently great to provide the desired stiction reduction. For example, using the data given in FIG. 9B, if the crown is less than 0.2 μinches, the disc to air bearing surface separation will be determined primarily by the pad height. 
     In another aspect of the present invention, it has been recognized that various portions of a slider are subjected to contact with the disc surface during take off. During the initial phase of take off, the middle portion (i.e., “belly”) of the slider contacts the medium. As the velocity increases, the leading edge of the slider contacts the medium because the slider tips forward. Finally, after take off, formation of the air bearing causes the slider to tip in the opposite direction leading to contact with the trailing edge. Thus, different portions of the slider are in contact with the medium surface during different take off periods. In one experiment, contact start/stop testing was performed on an air bearing surface in accordance with embodiments set forth herein having DLC pads on a highly polished medium surface. It was discovered that the pads located at the leading edge of the air bearing were broken due to high adhesive forces experienced during take off by the leading edge. However, pads located in the middle portion of the slider and near the trailing edge were not broken and were not substantially worn. 
     FIG. 10 is a bottom plan view of a slider  420  in accordance with another embodiment. Slider  420  includes leading edge  422  and trailing edge  424  having a center island  426  carried thereon. Rails  428  extend along either side of the slider  420 . As illustrated in FIG. 10, the rails of slider  420  are divided generally into three sections, a leading section  430 , a mid section  432  and a trailing section  434 . Leading section  430  carries pads  436  having a relatively large diameter (or area) to provide additional strength and reduce the likelihood of breakage. Similarly, trailing section  434  also carries large size pads  438  to provide additional strength and reduce the possibility of breakage. Mid section  432  carries smaller pads  440  which provide a smaller cross-sectional area which may be optimized to reduce stiction and improve flyability. The increased size of pads  438  also reduces the amount of wear should prolonged contact with media occur during operation. 
     The pads  436 , 438 , 440  shown in FIG. 10 may be fabricated using a single masking operation. However, should differing pads be desired, multiple masks may be provided. For example, the leading edge pads may be made higher such that they may sustain more wear without allowing the slider substrate to contact the medium surface which would substantially increase stiction. 
     Although the present invention has been described with reference to preferred embodiments, 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. In general, the pads may be placed along any protruding portion of the air bearing surface such as the side rails, a center rail, a center island, etc. In general, the present invention includes all of the various sizes, shapes, heights, placings, configurations, densities, etc. of the pads set forth herein. Such pads may be made in accordance with any of the processes set forth herein or may be fabricated using other processes as desired. Similarly, the specific process herein are not limited to fabrication of those pads which have been specifically set forth herein. The invention may be used with any type of transducing element including inductive, magnetoresistive and optical elements. In general, in these designs the pads only contact the disc surface during CSS and do not contact the disc surface during normal flying.