Abstract:
The present invention is directed towards air-bearing sliders that are used in disk drives. The invention involves pitching a slider so that the leading portion of the slider is closer to the disk than the trailing portion of the slider. The negative pitch reduces the sensitivity of the slider to ambient air pressure, radial position, and to data accessing over the disk. When used in combination with a reverse-flow disk drive, negatively pitched sliders facilitate the routing of traces to the head.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to air-bearing sliders used in disk drives. In particular, it relates to air-bearing sliders that are negatively pitched relative to the disk.  
         BACKGROUND OF THE INVENTION  
         [0002]    Disk drives are data storage devices that are routinely used with computers and other data processors. In a disk drive, the transducer element, commonly referred to as the head, reads and/or writes data from a spinning data-storage medium, or disk. The head is typically formed as part of an air bearing slider that is fixed to a suspension. The suspension helps to damp vibrations and keep the slider and its head steady. With reference to FIG. 1, the suspension  230  is attached to an actuator arm  210 . The entire head-carrying assembly  200  is deployed to a desired position radial position over the disk  100 . The slider and head are not shown in FIG. 1 because they would typically be disposed on the disk-facing side of the suspension  230  near the distal end  204  of the head-carrying assembly  200 . With the disk  100  spinning in the direction indicated by  120 , a flow  125  is induced adjacent to the disk  100 .  
           [0003]    One of the challenges of disk-drive design is to maintain the head at a very precise location that is preferably a very small fixed distance above the disk. Variations in the height of the head from the disk increase the probability of read/write errors. An exceptional design would hold the head at a fixed height above the disk over a large range of conditions. Modern disk-drive design attempts to achieve this goal in part by tailoring the details of the slider. As the disk spins, the air adjacent to the disk is induced to rotate substantially with the disk, as is shown in FIG. 1. Only the flow deflected by the head-carrying assembly  200  and the flow near the outside diameter of the disk  100  deviate much from the substantially solid-body rotation of the flow. The slider flies in the induced flow. The aerodynamic forces generated on the slider are balanced by the suspension to which the slider is attached. A balance between the design aerodynamic forces on the slider and the restoring elastic forces imposed by the suspension is required to maintain the slider, and hence the head, at the desired fly height. However, as the head-to-disk spacing reduces further in the near future, the slider may contact with disk asperities or the disk surface itself. In such circumstances the force balance is more complex and must include the aerodynamics forces generated on the slider, the elastic forces imposed on the slider by the suspension, and the contact and frictional forces imposed on the slider by the disk contacts and friction. In addition, during data accessing, the slider is quickly moved radially by the action of the actuator. This imposes a radial inertial force to the slider and is balanced by forces generated by changing the flying attitude of the slider. To design a slider that minimizes this data accessing fly height variation is challenging.  
           [0004]    All currently used sliders are designed so that in the induced flow, the leading portion of the slider is lifted away from the disk slightly more than the trailing portion of the slider. This type of slider has positive pitch. In a slider with positive pitch, the head is located in the trailing portion of the slider, i.e., in that portion of the slider that is closest to the disk. For disk drives with conventional flow, wiring is simplified with the location of the head in the trailing portion of the slider.  
         SUMMARY OF THE INVENTION  
         [0005]    The current invention explores a new paradigm for the design of sliders used in disk drives. Rather than continuing to design sliders with positive pitch, the current invention includes sliders that are designed to fly with negative pitch. Such designs are typified by having at least one point in the leading portion of the slider closer to the disk than any point in the trailing portion of the slider when the slider is flying in the flow induced by the spinning disk.  
           [0006]    Another way to imagine a negatively pitched slider is to consider a ray from a first point in the trailing portion of the slider through a second point in the leading portion of the slider. The first and second points are chosen such that in the absence of flow, the ray would be parallel to the disk, but in the presence of flow, the ray intersects the plane of the disk surface. This occurs if the flow tilts or pitches the trailing portion further from the disk than the leading portion.  
           [0007]    Tests indicate unexpected benefits from the use of the negatively pitched slider. The negatively pitched slider has reduced fly height sensitivity to ambient pressure variations and to radial location over the disk. In addition, during data accessing, the negatively pitched slider experiences a reduced drop in fly height relative to a positively pitched slider. Therefore, flying a slider such that a point on the slider closest to the disk is located on the leading portion of the slider is useful for achieving reduced head altitude sensitivity to ambient pressure and radial position, and reduced fly height variation during data accessing.  
           [0008]    Because the head is usually located near the point of closest approach to the spinning disk, most embodiments of a negatively pitched slider will have the head coupled to a head pad in the leading portion of the slider. Although having the head in the leading portion of the slider complicates the wiring in disk drives with conventional flow, it simplifies the wiring in reverse-flow disk drives. Large reductions in head vibration and fly height variation have been observed when a negatively pitched slider is used in combination with reverse flow.  
           [0009]    Additional features and advantages of the invention will be set forth in part in the description that follows, and in part will be obvious from the description, or may be learned by practice of the invention. Various embodiments of the invention do not necessarily include all of the stated features or achieve all of the stated advantages. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The accompanying drawings illustrate a complete embodiment of the invention according to the best modes so far devised for the practical application of the principles thereof, and in which:  
         [0011]    [0011]FIG. 1 shows a disk drive with conventional flow.  
         [0012]    [0012]FIG. 2A shows a simplified slider over a disk.  
         [0013]    [0013]FIG. 2B shows that the simplified slider is negatively pitched in the presence of flow.  
         [0014]    [0014]FIG. 3 shows a perspective view of a preferred embodiment of a negatively pitched slider.  
         [0015]    [0015]FIG. 4 shows a perspective view of another preferred embodiment.  
         [0016]    [0016]FIG. 5 shows a disk drive with reverse flow.  
         [0017]    [0017]FIG. 6A shows a plan view of a slider and a suspension. The view is from the disk.  
         [0018]    [0018]FIG. 6B shows a cross section of the slider and suspension of FIG. 6A.  
         [0019]    [0019]FIG. 7A shows a portion of a flexure with traces for a negatively pitched slider in a conventional-flow configuration.  
         [0020]    [0020]FIG. 7B shows a portion of a flexure with traces for a negatively pitched slider in a reverse-flow configuration. 
     
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS  
       [0021]    Referring now to the drawings, where similar elements are numbered the same, FIGS. 2A and 2B depict an embodiment of a very simplified slider  400  that has negative pitch in the presence of flow  125 . FIG. 2A illustrates the orientation of the slider  400  relative to the disk  100  without flow. FIG. 2B illustrates the orientation of the slider  400  relative to the disk  100  with flow  125 .  
         [0022]    The slider  400  has a leading portion  410  and a trailing portion  420 . The leading portion  410  is upstream of the trailing portion  420  in the presence of the flow  125 . For exactness, every part of the slider  400  can be considered as being disposed in either the leading portion  410  or the trailing portion  420 .  
         [0023]    The direction of the flow  125  relative to the slider  400  varies slightly with the slider&#39;s position over the disk  100 . Therefore, the slider leading  410  and trailing  420  portions are to be determined for the case in which the slider  400  is located at the midpoint of the design range of use of the head  220  supported in the slider  400 . For instance, if the head  220  in the slider  400  were designed to operate from the disk inner diameter to the disk outer diameter, then the midpoint would be halfway between the disk inner and outer diameters. The parking position and other positions that the slider  400  may occupy when the head  220  is not in use should not be used in the computation of the midpoint.  
         [0024]    To eliminate uncertainty in the use of the term “upstream,” a body A is defined to be upstream of a body B if the time required for a flow disturbance generated at body A to be observed at body B is less than the time required for a flow disturbance generated at body B to be observed at body A. This definition is intended to reduce to the usual meaning of upstream in the case of bodies at rest in a uniform linear flow.  
         [0025]    In preferred embodiments of the invention, the slider  400  includes a base  450 , a head pad  465  that projects from the base in the leading portion  410  of the slider  400 , and a head  220  that is coupled to the head pad  465 . Although in most preferred embodiments the head  220  is an integral part of the slider  400 , the invention also includes embodiments in which the head  220  is more loosely coupled with the head pad  465 . The head pad  465  is a projection from the base  450  that supports the head  220 . The head pad  465  typically includes leads for electrically coupling the head  220  with traces or conduction leads outside of the slider  400 .  
         [0026]    In prior art sliders, the head pad is located in the trailing portion of the slider. In the most preferred embodiments of the invention, not only does the head pad  465  project from the base  450  in the leading portion  410  of the slider  400 , but the head pad  465  is disposed in approximately the most upstream portion of the slider  400 .  
         [0027]    In preferred embodiments of the invention the base  450  of the slider  400  has a disk-facing side  415  that faces the disk  100 . At least one projection projects from the disk-facing side  415  of the base  450 . In FIGS. 2A and 2B, the head pad  465  is the only projection. In alternate embodiments other projections are included either with, or in place of the head pad  465 . The base  450  and the projections are arranged such that in the presence of the flow  125 , at least one point in the leading portion  410  of the slider  400  is closer to the disk  100  than any point in the trailing portion  420  of the slider  400 . This is clearly the case in FIG. 2B, in which the flow  125  is included. In the most preferred embodiments, the most upstream position on the slider  400  is closer to the disk  100  than any point in the trailing portion  420  of the slider  400 .  
         [0028]    Preferred embodiments of the negatively pitched slider can also be described with the use of a ray  560  that extends from a first point  540  in the trailing portion  420  of the slider  400  through a second point  550  in the leading portion  410  of the slider  400 . The points are selected such that in the absence of flow, the ray  560  is parallel to the disk plane  115  that is defined by the surface of the disk  100  as shown in FIG. 2A. Although FIG. 2A shows the ray  560  as substantially parallel to the base  450 , this condition is not necessary. The orientation of the ray  560  relative to features in the slider  400  can vary greatly with different embodiments. In the presence of flow  125 , as shown in FIG. 2B, the ray  560  intersects the disk plane  115 .  
         [0029]    The angle of the pitch of the slider  400  relative to the disk  100  shown in FIG. 2B is sufficiently steep for the ray  560  to intersect the disk  100  itself. Preferred embodiments have pitch angles ranging from tens to hundreds of microradians, approximately a few hundredths of a degree. Therefore the intersection of the ray  560  with the disk plane  115  that is defined by the surface of the disk  100  is likely to occur at a radial position outside that encompassed by the physical disk  100 .  
         [0030]    A preferred embodiment of a slider  400  designed for negative pitch is illustrated in FIG. 3. The slider  400  includes multiple projections that emerge from the base  450 . These projections are arranged such that in the presence of flow from left to right the slider  400  pitches so that the downstream portion  420  becomes relatively further from the disk  100  than the upstream portion  410 .  
         [0031]    The particular embodiment shown in FIG. 3 is designed with the outer-diameter side  440  at the top of the figure and the inner-diameter side  430  at the bottom of the figure. The inner-diameter side  430  will be closer to the center of the disk. The asymmetry between the inner-diameter side  430  and the outer-diameter side  440  alleviates problems associated with the nonuniform flow environment. Without accounting for the influence of the slider  400  and its associated head-carrying assembly, the flow induced by the disk is substantially in solid body rotation. Therefore the flow speed at the inner-diameter side  430  of the slider  400  is somewhat slower than that at the outer-diameter side  440 . The asymmetric design accounts for these different flow speeds and flow directions when the slider  400  is placed at the different radial positions.  
         [0032]    The preferred embodiment shown in FIG. 3 includes a head pad  465  in the leading portion  410  and two trailing high-pressure pads  470  in the trailing portion  420 . A trailing-portion outflow region  520  between the two trailing high-pressure pads  470  allows flow to escape the confines of the slider  400 . Although not necessary in all embodiments, the relatively large size of the trailing-portion high-pressure pads  470  is useful for lifting the trailing portion  420  of the slider  400  more than the leading portion  410 . The term “pad” as used herein is intended to include the surface of the described projection, as well as its underlying structure down to the base  450 .  
         [0033]    [0033]FIG. 3 also shows leading-portion compression pads  480  in the leading portion  410  of the slider  400 . In addition, trailing-portion compression pads  530  are located just upstream of the trailing-portion high-pressure pads  470 . Compression pads do not project as far from the base  450  as their adjacent high-pressure pads. Although not required, compression pads are generally intended to compress the flow just upstream an adjacent high-pressure pad.  
         [0034]    In FIG. 3, the leading-portion compression pads  480  and the trailing-portion compression pads  530  are each shown with a slanted portion to smoothly compress the flow. An alternative embodiment, shown in FIG. 4, is similar in many respects to that shown in FIG. 3, except that the compression pads do not include a slanted portion. The designer makes the decision to use or not use a slanted portion, or even a curved portion of the compression pads after consideration of many factors, including performance and production costs.  
         [0035]    The embodiments shown in FIGS. 3 and 4 also include high-pressure nose pads  490  adjacent to the leading-portion compression pads  480 . The high-pressure nose pads  490 , the trailing-portion high-pressure pads  470 , and the head  220  supported by the head pad  465  are all preferably about the same height above the base  450 . These projections typically experience the highest pressures.  
         [0036]    The preferred embodiment shown in either FIG. 3 or  4  includes an inner-diameter rail  500  disposed nearto the inner-diameter side  430  of the slider  400  and an outer-diameter rail  510  disposed nearto the outer-diameter side  440  of the slider  400 . As shown in the figures, the inner-diameter rail  500  joins with the inner-diameter segment  482  of the leading-portion compression pad  480  and the outer-diameter rail  510  joins with the outer-diameter segment  484  of the leading-portion compression pad  480 . The joined projections form a partial enclosure. Inside the enclosure the exposed base  450  of the slider  400  experiences subambient pressure. The rails and the compression ramps typically extend approximately the same distance from the base  450 . Of course, if slanted portions of compression ramps are included, they will have variable height about the base  450 .  
         [0037]    Negatively pitched sliders may include any or all of the various projections described above in any combination that satisfies the design objectives. In addition, although current manufacturing considerations strongly favor sliders with rectangular planforms, a negatively pitched slider with some other planform shape, such as a circle, oval, or ellipse are also considered part of the invention. Similarly, although the slider base  450  has been shown as flat in the preferred embodiments, a contoured base  450  would also be considered as part of the invention.  
         [0038]    In the most preferred embodiments the slider is made from an aluminum-titanate ceramic substrate. The head is typically encapsulated in alumina. Other appropriate materials may be used for either the head or the slider.  
         [0039]    The most preferred embodiments are manufactured in a manner similar to that used for a pico slider. In a typical production process of a pico slider the head layers are deposited to a thickness of about 0.035 mm on a wafer that is about 1.21 mm thick. The total wafer thickness plus head now equals about 1.25 mm, which corresponds to the slider length. The wafers are diced into rows, turned on their sides, mounted in carriers and etched. The etching leaves elevated structures, which form the various pads, rails and other projections that emerge from the base. Although particular embodiments can vary greatly in the etch depths for each projection, in a typical preferred embodiment, the head and the high-pressure pads have approximately equivalent heights from the base and are not etched. Also in a typical preferred embodiment, the compression pads and rails are made with a shallow etch of about 0.2 to 0.3 microns and the base is reached with a deep etch that typically ranges from about 1 to 3 microns. Final dicing produces finished sliders.  
         [0040]    A negatively pitched slider has been found to achieve reduced head altitude sensitivity to ambient pressure and radial position over a spinning disk. This is accomplished by flying a slider in the induced flow produced over the spinning disk such that a point on the slider closest to the disk is located in on the leading portion of the slider. The reduced altitude sensitivity is achieved both for conventional-flow disk drives, as shown in FIG. 1, and reverse-flow disk drives, as shown in FIG. 5. In the conventional-flow disk drive, the disk  100  is spinning in a direction  120  so that, relative to the induced flow  125 , the slider is downstream of the actuator arm  210 . In the reverse-flow disk drive the disk  100  is spinning in a direction  120  so that, relative to the induced flow  125 , the slider is upstream of the actuator arm  210 . For a given conventional-flow disk drive, a reverse-flow disk drive is obtained by either spinning the disk in the opposite direction or by reorienting the head-carrying assembly. Both approaches are equivalent.  
         [0041]    To better appreciate the use of a negatively pitched slider in a disk drive, consider both the conventional-flow disk drive of FIG. 1 and the reverse-flow disk drive of FIG. 5. In both cases, the disk drive includes a disk  100  that spins, in a spinning direction  120 , thereby inducing a flow  125  that rotates substantially with the disk  100 . The disk drive also includes a head-carrying assembly  200  deployable adjacent to the disk  100 . The head-carrying assembly  200  has an actuator arm  210 , a suspension  230  attached to the actuator arm  210 , and a slider (not shown in FIGS. 1 and 5, because it would be obscured by the suspension  230 .)  
         [0042]    [0042]FIG. 6A shows a plan view of a slider  400  fixed to an embodiment of a suspension  230 . The view is of the disk-facing side of the suspension  230 . FIG. 6B shows a cross-section view of the suspension  230  and slider  400  shown in FIG. 6A. Note that the slider  400  has a leading portion  410  and a trailing portion  420 . The leading portion  410  is upstream of the trailing portion  420  in the presence of flow. The relative positions of the leading  410  and trailing  420  portions in FIGS. 6A and 6B correspond to the conventional-flow disk drive shown in FIG. 1, wherein the slider is disposed downstream of the actuator arm  210 . For the reverse-flow disk drive shown in FIG. 5, wherein the slider is disposed upstream of the actuator arm  210 , the leading  410  and trailing  420  portions of the slider  400  would be reversed from that shown in FIGS. 6A and 6B.  
         [0043]    For either the conventional-flow disk drive or the reverse-flow disk drive, in the presence of flow, embodiments of the negatively pitched slider have at least one point in the leading portion  410  of the slider  400  closer to the disk  100  than any point in the trailing portion  420  of the slider  400 .  
         [0044]    The reverse-flow orientation is preferred when using a negatively pitched slider. With reference to FIGS. 6A and 6B, a suspension  230  typically includes a load beam  300  that would be attached to the actuator arm, and a flexure  350  that is mounted to the load beam  300 . The flexure  350  includes flexure legs  390  that support a gimbaled region  370  to which the slider  400  is fixed. Typically an adhesive process fixes the slider  400  to the gimbaled region  370  of the suspension  230 . In alternate embodiments, appropriate other methods for fixing the slider  400  to the gimbaled region  370  may be used. The gimbaled region  370  allows the slider  400  to pitch and roll in response to surface nonuniformities as it flies over the disk. The flexure legs  390  provide a restoring force that counteracts the slider  400  motions. Preferably, the suspension  230  and slider  400  are designed so that the proper resiliency of the gimbaled region  370  is maintained in all operating conditions. This has implications for the routing of traces, or conduction leads to the head.  
         [0045]    Referring to FIG. 7A, because the flexure  350  is metallic in most embodiments, the traces  600  are not bonded directly to the flexure  350 . Instead, an insulator  610 , (typically a polyimide layer) is bonded to the flexure  350  and the traces  600  are laid thereon. To reduce any influence of the traces  600  and the insulator  610  on the flexibility of the gimbaled region  370 , the traces  600  are often routed alongside the flexure legs  390  to the distal end  380  of the gimbaled region  370 . The use of a negatively pitched slider with a conventional-flow disk drive means that the leading portion of the slider ( 410  in FIGS. 6A and 6B) is near the proximal end  375  of the gimbaled region  370 . The head is usually disposed in the leading portion of a negatively pitched slider. Hence, in this configuration preferably the traces  600  are routed from the distal end  380  of the gimbaled region  370  to the proximal end  375  of the gimbaled region  370  where they connect to mounting pads  620 . The mounting pads  620  are then soldered to appropriate terminals on the slider.  
         [0046]    With reference to FIG. 7B, if a negatively pitched slider is used in a reverse-flow disk drive, the routing of the traces  600  becomes simpler. In a reverse-flow disk drive, the leading portion of the slider would be located near the distal end  380  of the gimbaled region  370 . Because the head would typically be located in the leading portion of the slider, the electrical connections to the slider can be made near the distal end  380  of the gimbaled region  370 . In addition to simplifying the routing of the traces  600 , the gimbaled region  370  can be made narrower because it no longer supports traces  600  extending from its distal end  380  to its proximal end  375 . The combination of a reverse-flow disk drive with negatively pitched sliders greatly reduces head vibrations. When used in combination, the routing of the traces is no more difficult than a conventional-flow disk drive with positively pitched sliders.  
         [0047]    The above description and drawings are only illustrative of preferred embodiments, and the present invention is not intended to be limited thereto. Any modification of the present invention that comes within the spirit and scope of the following claims is considered part of the present invention.