Slider having air bearing surface which includes pads for disk storage system

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.

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.

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:
 ##EQU1##
 where S is stiction, .mu. is coefficient of friction, E is the Young'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 .alpha. is a constant defined by
 (12.pi..gamma./A.sub.H) where .gamma.is the surface tension and A.sub.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.sup.2, and height to be about
 300 .ANG., 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. 3B. 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. 3D.
 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 .mu.m.sup.2 to about 12,000 .mu.m.sup.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 .mu.m and a width of 5 .mu.m. The ion beam 126 used
 for deposition is angled such that there is a 2.2 .mu.m 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 .mu.m
 and a width of 5 .mu.m. This provides the 4 .mu.m 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
 4B--4B shown in FIG. 4A 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'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. 4C. 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 .ANG., an area of between about 10 and 100 .mu.m.sup.2, a density of
 about 1 pad per about 100 .mu.m.sup.2 to about 10,000 .mu.m.sup.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 2/3 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
 (204A), rectangular (204B), angled rectangles (204C), squares (204D), 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 .ANG. and pads 234 have a lowest height which is about 200
 .ANG.. 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 .ANG. 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 .mu.inches.
 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. 9A. 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 .mu.inches,
 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.