Abstract:
A slider utilizes a triple-etch, high pitch-stiffness side rail ABS design. The slider is characterized by a relatively deep shallow recession at its leading edge, which maximizes the cavity area while at the same time increases the pitch angle to achieve DLC pad clearance as required by smooth media ABS designs. The slider ABS has a shallower recession at the trailing edge, which provides low gram-load sensitivity and low flying standard deviation. The slider ABS further presents a decreased sensitivity in response to altitude variations.

Description:
FIELD OF THE INVENTION 
     The present invention relates in general to data storage systems such as disk drives, and it particularly relates to a thin film read/write head for use in such data storage systems. More specifically, the present invention discloses a new slider design utilizing a high-pitch stiffness air bearing design for smooth media drive applications. 
     BACKGROUND OF THE INVENTION 
     In a conventional magnetic storage system, a thin film magnetic head includes an inductive read/write element mounted on a slider. The magnetic head is coupled to a rotary actuator magnet and a voice coil assembly by a suspension and an actuator arm positioned over a surface of a spinning magnetic disk. 
     In operation, a lift force is generated by the aerodynamic interaction between the magnetic head and the spinning magnetic disk. The lift force is opposed by equal and opposite spring forces applied by the suspension such that a predetermined flying height is maintained over a full radial stroke of the rotary actuator assembly above the surface of the spinning magnetic disk. 
     The flying height is defined as the spacing between the surface of the spinning magnetic disk and the lowest point of the slider assembly. One objective of the design of magnetic read/write heads is to obtain a very small flying height between the read/write element and the disk surface. By maintaining a flying height close to the disk, it is possible to record short wavelength or high frequency signals, thereby achieving high density and high storage data recording capacity. 
     A problem with flying the slider close to the disk surface is that when there is any variation of slider flying height, the possibility of physical interference between the slider and the disk may result in reliability problems and head crashes. Therefore, one objective of the slider design is to maintain a substantially constant flying height close to the disk surface, while minimizing flying height variations when operating the disk drive in a different environment, since variations in head-to-disk spacing may adversely affect signal amplitude and resolution, and may possibly cause head crashes. 
     An important consideration in slider design for controlling the aerodynamic interaction between the magnetic head and the spinning magnetic disk thereunder, is the air bearing surface. Sliders used in disk drives typically have a leading edge, and a trailing edge at which thin film read/write heads are typically deposited. Generally, sliders have tapered portions at the leading edge and longitudinal side rails that extend from the tapers to the trailing edge. 
     The tapers may be shaped and of such length as to provide fast pressure buildup during takeoff of the slider from a rest position to a flying height relative to the disk with controlled pitch. The dimensions and shapes of the tapers and side rails are instrumental in determining the flying characteristics of the head. The side rail design determines the pressure generated at the ABS of the slider. In effect, the pressure distribution on the ABS contributes to the flying characteristics of the slider that include flying height, pitch, and roll of the read/write head relative to the rotating magnetic disk. 
     A conventional magnetic medium, such as a magnetic recording disk, includes a landing zone, which is defined as an annulus area of a width of about 0.5 cm (0.2 in) located at the inner radius of the magnetic disk. The landing zone is made of a non-magnetic material, as its function is not for data recording but is to provide a surface upon which the slider comes to rest in between track seeks during a read/write operation. The surface of the landing zone is typically designed to have a certain degree of roughness so as to prevent stiction between the slider and the disk, and to enable a fast take-off of the slider. 
     As the continuing trend toward high capacity storage applications currently prevails in this industry, smooth media applications have emerged. A smooth medium disk is characterized by a finely polished surface in its entirety from the outer radius to the inner radius of the disk without a landing zone. The reduced surface roughness allows for lower fly heights, which results in increased data compared to conventional media disks. 
     The increasing use of smooth media applications, however, poses a technical difficulty with a conventional ABS slider. Because of the low surface roughness of the smooth media disk, the stiction force may increase substantially, thereby preventing the conventional slider from taking off rapidly and smoothly from the surface of the smooth media disk. 
     To address this problem, sliders have been designed with a dual-etch ABS incorporating Diamond Like Carbon (DLC) pads. In order to maintain a proper trailing edge DLC pad clearance, the slider is required to possess a pitch angle relative to the surface of the disk. The pitch angle is the angle between the planar surface of the media disk and the longitudinal axis of the slider or the arm assembly to which the slider is secured. Because the DLC pads protrude from the surface of the ABS on the slider, it is usually difficult to achieve the clearance between the DLC pads and the surface of the disk. 
     Without a proper clearance, the DLC pads can come in contact with the surface of the disk, thereby causing physical wear of the disk surface. One conventional method of achieving this clearance is by increasing the leading edge ABS area to raise the pitch angle. Nevertheless, this approach is not entirely satisfactory because the reduction in the leading edge ABS area usually accompanies a lower overall stiffness which can adversely affect the flying characteristics of the slider. Yet, another method of achieving the same objective is to have a relatively deep shallow recession. It, too, fails to provide a desirable solution for achieving the clearance because, in so designed, the gram-load sensitivity and the flying standard deviation of the slider are degraded. 
     Still another concern arises with the conventional dual-etch ABS slider design. When smooth media disk drives that incorporate rotating smooth media disks and read/write heads with dual-etch ABS sliders are used at relative high altitudes such as 10,000 ft above the sea level, for example, the less air density and ambient pressure adversely affect the slider aerodynamic characteristics which contribute to the flying performance of the dual-etch ABS sliders. Specifically, in the dual-etch ABS slider design, the cavity area is be reduced in order to raise the pitch angle. 
     Since the lift force is proportional to the cavity area and the ambient pressure, the dual-etch ABS sliders experience a significant reduction in lift at high altitude. Consequently, the flying height of the dual-etch ABS slider substantially decreases from the design flying height, thereby causing the slider to move closer to the surface of the rotating magnetic disk. Hence, this poses a significant concern with a physical interference between the read/write head and the rotating disk that may lead to a head crash or excessive wear of the magnetic disk surface, and thus rendering the disk drive less reliable. 
     It is thus recognized in light of the above concerns, that there is an unfulfilled need for an improvement in the ABS slider design for smooth media applications. Preferably, the new slider design should provide a necessary DLC pad clearance as required for smooth media applications, without adversely affecting the slider performance characteristics such as ABS stiffness and gram-load sensitivity. Furthermore, the new slider design should exhibit an improved altitude sensitivity. 
     SUMMARY OF THE INVENTION 
     It is a feature of the present invention to provide a new ABS slider design for use with smooth media applications. The new slider utilizes a triple-etch, high pitch-stiffness side rail ABS design incorporating the following features: 
     1. A relatively deep shallow recession at the leading edge of the slider, which maximizes the cavity area while at the same time increases the pitch angle to achieve the DLC pad clearance as required by smooth media ABS designs. 
     2. A shallower recession at the trailing edge of the slider, which provides low gram-load sensitivity and low flying standard deviation. 
     3. A decreased sensitivity in response to altitude variations. 
     The foregoing and other features of the present invention are realized by a slider having a generally rectangularly shaped ABS that is bounded by a leading edge, a trailing edge, and two sides. A shallow step region having the shape of the letter “C” is formed on the ABS. 
     The shallow step region is formed by etching the ABS to a depth of approximately 0.25 μm relative to a reference datum. In contrast to the dual-etch ABS slider, the shallow step region of the present ABS design has a greater depth than that of the conventional shallow step region. This greater depth provides the necessary high pitch angle as required to maximize the clearance between DLC pads and the disk. 
     An ABS region adjoins the shallow step region. The area of the present ABS region is generally smaller than that of the ABS region of a conventional dual-etch ABS slider, thereby making it less susceptible to camber and crown sensitivities due to the respective curvatures in the axial direction from the leading edge to the trailing edge, and in the transverse direction from side to side of the ABS. The reduced camber and crown sensitivities of the ABS region enhance the flying height performance of the triple-etch high pitch-stiffness slider. 
     A cavity region adjoins the ABS region and has a generally polygonal shape that is formed by etching to a depth that ranges between approximately 50 μm and 80 μm relative to the reference datum of the ABS. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The features of the present invention and the manner of attaining them will become apparent, and the invention itself will be understood by reference to the following description and the accompanying drawings, wherein: 
     FIG. 1 is a fragmentary perspective view of a data storage system utilizing a read/write head of a conventional design or of the present invention; 
     FIG. 2 is a perspective view of a head gimbal assembly comprised of a suspension, and a slider to which the read/write head of FIG. 1 is secured, for use in a head stack assembly; 
     FIG. 3 is a bottom view of a conventional dual-etch ABS slider; 
     FIG. 4 is a cross-sectional view of the conventional slider of FIG. 3, taken along section A—A thereof; 
     FIG. 5 is a graphical illustration of the pitch angle and DLC pads of the slider of FIGS. 3 and 4; 
     FIG. 6 is a bottom view of a triple-etch high pitch-stiffness ABS slider according to the present invention; and 
     FIG. 7 is a cross-sectional view of the slider of FIG. 6, taken along section B—B; and 
     FIG. 8 is a graphical illustration of the pitch angle and DLC pads of the slider of FIGS.  6  and  7 . 
    
    
     Similar numerals in the drawings refer to similar elements. It should be understood that the sizes of the different components in the figures might not in exact proportion, and are shown for visual clarity and for the purpose of explanation. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 illustrates a disk drive  10  comprised of a head stack assembly  12  and a stack of spaced apart smooth media magnetic data storage disks or smooth media  14  that are rotatable about a common shaft  15 . The head stack assembly  12  is rotatable about an actuator axis  16  in the direction of the arrow C. The head stack assembly  12  includes a number of actuator arms, only three of which  18 A,  18 B,  18 C are illustrated, which extend into spacings between the disks  14 . 
     The head stack assembly  12  further includes an E-shaped block  19  and a magnetic rotor  20  attached to the block  19  in a position diametrically opposite to the actuator arms  18 A,  18 B,  18 C. The rotor  20  cooperates with a stator (not shown) for rotating in an arc about the actuator axis  16 . Energizing a coil of the rotor  20  with a direct current in one polarity or the reverse polarity causes the head stack assembly  12 , including the actuator arms  18 A,  18 B,  18 C, to rotate about the actuator axis  16  in a direction substantially radial to the disks  14 . 
     A head gimbal assembly (HGA)  28  is secured to each of the actuator arms, for instance  18 A. With reference to FIG. 2, the HGA  28  is comprised of a suspension  33  and a read/write head  35 . The suspension  33  includes a resilient load beam  36  and a flexure  40  to which the head  35  is secured. 
     The head  35  is formed of either a slider  47  that is secured to the free end of the load beam  36  by means of the flexure  40 , and a read/write element  50  that is supported by the slider  47 . The read/write element  50  is mounted at the trailing edge  55  of the slider  47  so that its forwardmost tip is generally flush with the ABS  60  of the slider  47 . 
     In order to appreciate the novelty and advantages of the present invention, a conventional dual-etch ABS slider design will now be described with reference to FIGS. 3,  4 , and  5 . FIGS. 3 and 4 illustrate a patterned ABS  60  of a dual-etch ABS slider having a leading edge  62  and a trailing edge  64 . The ABS  60  typically has a rectangular shape and is bounded by the leading edge  62 , the trailing edge  64 , and the two sides  66  and  68 . A topology of varying depths is formed on the ABS  60 . 
     The topology includes a shallow step region  70  that has the shape of the letter “C”. The step region  70  is comprised of a leading edge area  72  and two side rails  80 ,  82 . The step region  70  is generally bounded by the leading edge  62  and a segmented edge  74 . Notches  76  and  78  at formed at two corners of the leading edge area  72 . 
     The side rails  80 ,  82  extend from the leading edge  62  and are slightly recessed inwardly from the slider sides  66  and  68 , respectively. The step region  70  is formed by etching the slider ABS to a depth ranging from approximately 0.1 μm to 0.3 μm relative to a reference datum  122  (FIG. 4) of the ABS  60 . 
     An ABS region  84  adjoins the shallow step region  70  along the segmented edge  74  and the inner edges  86  and  88  of the side rails  80  and  82  that are common to both the shallow step region  70  and the ABS region  84 . The ABS region  84  is generally formed of a horseshoe shape having three identifiable areas. A leading edge ABS area  90  having the largest footprint, is generally bounded by the segmented edge  74  and another segmented edge  92 . 
     A first side rail ABS area  94  is generally disposed along the side  66  of the ABS  60  and extends from the leading edge ABS area  90  to a notch  96 . A second side rail ABS area  98  having the smallest footprint is generally disposed along the side  68  of the ABS  60  and extends from the leading edge ABS area  90 . The top surface of the ABS region  84  defines the reference datum height  122  for the ABS  60  (FIG.  4 ). 
     A cavity region  100  adjoins the central region  84  along a segmented edge  92  and inner edges  102  and  104  of side rails  94 ,  98 , respectively. The cavity region  100  has a generally polygonal shape, extends from the segmented edge  92  to the slider trailing edge  64 , and is formed by etching the slider ABS to a depth ranging between approximately 1 μm to 3 μm relative to the reference datum  122  (FIG.  4 ). 
     Two oppositely disposed islands  106  and  108  are formed near the corners of the ABS  60 , adjacent to the trailing edge  64 . Each of these islands  106  and  108  includes a respectively small shallow step region ( 110  and  112 , respectively), and a small ABS region ( 114  and  116 , respectively). The shallow step regions  110  and  112  are formed by etching the ABS  60  to the same depth as that of the shallow step region  70 . 
     A plurality of posts are positioned at various locations throughout the ABS  60 . With reference to FIG. 3, the ABS  60  is shown to have seven posts  118 A- 118 G. With reference to FIG. 4, the posts  118 A,  118 C have a generally cylindrical shape, and protrude outwardly from the bottom of either the shallow step region  70  (post  118 C), or from the cavity region  100  (post  118 A). 
     FIG. 4 illustrates only two DLC pads  120 A,  120 C that are secured to the tips of the posts  118 A,  118 C, respectively. Other DLC pads (not shown) are secured to the remaining posts  118 B and  118 D- 118 G. The posts  118 A,  118 C raise the DLC pads  120 A,  120 C, respectively, to a height, such that the DLC pads  120 A,  120 C are raised above the reference datum  122 . 
     When the slider is in a rest position on a smooth medium disk  14 , the DLC pads, such as the illustrated DLC pads  120 A,  120 C, come into contact with the disk  14 , and provide a support to the ABS  60 , thereby preventing the ABS region  70 , and the plateaus such as  84  and  116 , from making contact with the surface of the disk  14 . 
     FIG. 5 illustrates the concerns associated with the conventional slider design of FIGS. 3 and 4. An exemplary DLC pad  120 A is shown to extend beyond the reference datum  122  of the ABS  60 , at a low pitch angle  124 . However, relative to the disk surface, the DLC pad  120 A is lower than the lowest point  126  of the slider ABS  60 . This poses a possibility of a physical contact between the DLC pads  120 A and the surface of the disk  14 , in the event the aerodynamic lift force is not optimal. Such a physical contact would cause physical wear of the disk  14  and the DLC pads, and thus presents a reliability problem for the magnetic disk drive  10 . 
     In order to reduce this contact possibility, the DLC pads  120 A should be above the lowest point  126  of the slider ABS  60 , relative to the disk  14 . This can be achieved by increasing the pitch angle  124  sufficiently so that the DLC pads (i.e.,  120 A) are situated above the lowest point  126 . 
     One approach for increasing the pitch angle  124  is to make the shallow step region  70  deeper. However, when the depth of the shallow region  70  increases, the gram-load sensitivity also increases and adversely affects the performance of the slider. 
     Alternatively, the pitch angle  124  can be increased by increasing the leading edge ABS area  90  of the ABS region  84 . However, an increase in the leading edge ABS area  90  is typically accompanied by a reduction in the area of the cavity region  100 . This also poses a problem with the stiffness of the slider. 
     The cavity region  100  is designed to generate a subambient pressure due to the aerodynamic interaction between the ABS  60  of the slider and the surface of the spinning disk  14 . This subambient pressure creates a suction force that effectively augments the structural stiffness of the slider to produce the desired flying height. When the area of the cavity region  100  is reduced, the aerodynamically induced stiffness of the slider also decreases and causes large standard deviations in the fly heights of a population of sliders, thereby further exacerbating the slider reliability problem. Moreover, the reduction in the size of the cavity region  100  leads to an increase in the fly height sensitivity of the ABS altitude changes. 
     It is therefore recognized that what is needed is a new design that provides a high pitch angle  124  for maximizing the DLC pad (i.e.,  120 A) clearance and a larger area of the cavity region  100  for improving the altitude sensitivity, without increasing the gram-load sensitivity, or reducing the overall stiffness of the slider. 
     To this end, a new high pitch-stiffness ABS slider design for smooth media drive applications in accordance with the present invention is proposed. This new design is also referred to herein as a triple-etch high pitch-stiffness ABS slider design. 
     FIGS. 6 and 7 show a slider  47  having a ABS  260  that is patterned according to the present invention. The ABS  260  has a generally rectangular shape that is bounded by a leading edge  262 , a trailing edge  264 , and two sides  266 ,  268 . 
     A shallow step region  270  having the shape of the letter “C” is formed on the ABS  260 . The step region is formed of three areas: a leading edge area  272  and two side rails  280 ,  282 . The leading edge area  272  is generally bounded by the leading edge  262  and a segmented edge  274 . 
     Notches  276 ,  278  are formed at the corners of the leading edge area  272 . The side rails  280 ,  282  extend from the leading edge  262  and are slightly recessed inwardly from the sides  266 ,  268 . 
     The shallow step region  270  is formed by etching the ABS  260  to a depth of approximately 0.25 μm relative to a reference datum  322  of the ABS  260  (FIG.  7 ). In contrast to the dual-etch ABS slider of FIGS. 3 and 4, the shallow step region  270  has a greater depth than that of the shallow step region  70 . This greater depth provides the necessary high pitch angle  124  as required to maximize the clearance between DLC pads and the disk  14 . 
     An ABS region  284  adjoins the shallow step region  270  along the segmented edge  274  and the inner edges  286  and  288  of the side rails  280  and  282 , respectively. The ABS region  284  is generally formed of a horseshoe shape having three identifiable areas: a leading edge ABS area  290 , a first side rail ABS area  294 , and a second side rail ABS area  298 . 
     The leading edge ABS area  290  has a relatively large footprint and is generally bounded by the segmented edge  274  and another segmented edge  292 . The first side rail ABS area  294  is generally disposed along the side  266  of the ABS  260  and extends from the leading edge ABS area  290  to a notch  296 . The second side rail ABS area  298  has a smaller footprint and is generally disposed along the side  268  of the ABS  260  and extends from the leading edge ABS area  290 . 
     The bottom surface that contains the highest point of the ABS region  284  defines the reference datum height  322  for the ABS  260 . The area of the ABS region  284  is generally smaller than that of the ABS region  84  of the conventional dual-etch ABS slider (FIGS. 3,  4 ), thereby making it less susceptible to camber and crown sensitivities due to the respective curvatures in the axial direction from the leading edge  262  to the trailing edge  264 , and in the transverse direction from side  266  to side  268  of the ABS  260 . The reduced camber and crown sensitivities of the ABS region  28 . 4  enhance the flying height performance of the triple-etch high pitch-stiffness slider  47 . 
     A cavity region  300  adjoins the ABS region  284  along the triply segmented edge  292  and the inner edges  302  and  304  of the side rail ABS areas  294  and  298 . The cavity region  300  has a generally polygonal shape that substantially occupies the remaining area of the ABS  260 . The cavity region  300  extends from the segmented edge  292  to the trailing edge  264 , and is formed by etching to a depth that ranges between approximately 50 μm and 80 μm relative to the reference datum  322  of the ABS  260 . 
     In contrast to the conventional dual-etch ABS slider of FIGS. 3 and 4, the area of the cavity region  300  of the triple-etch high pitch-stiffness ABS slider  47  of the present invention is greater than that of the cavity region  100 . This increase in area of the cavity region  300  gives the ABS  260  more suction force developed thereon for the same amount of pitch angle  124  (FIG.  5 ), thereby substantially increasing the aerodynamically induced stiffness of the slider  47 . 
     The resulting stiffness increase provides a significant enhancement in the high-altitude performance of the disk drive  10  that employs the triple-etch high-stiffness ABS slider  47  due to the greater suction force afforded by the larger cavity region  300  in the presence of a decrease in the ambient pressure at high altitudes. It is expected that the triple-etch high pitch-stiffness ABS slider  47  of the present invention will show a marked improvement in the altitude loss parameter on the order of 20% to 30% at an altitude of 10,000 ft above sea level, relative to the conventional dual-etch ABS slider. 
     Another added benefit resulting from having a larger area of the cavity region  300  is the reduction in the pitch variation. 
     Two oppositely disposed islands  306  and  308  are formed at the corners of the ABS  260  adjacent to the trailing edge  264 . Each of the islands  306  and  308  includes, respectively, a small shallow step region  310 ,  312 , and a small ABS region  314 ,  316 . In a preferred embodiment, the shallow step region  310  is formed by etching to the same depth as that of the shallow step region  270 , that is approximately 10 μm, and the shallow step region  312  is formed by etching to a depth of approximately 4.5 μm relative to the reference datum  322  of the ABS  260 . 
     In conjunction with the shallow step region  270 , the triple-step configuration of the triple-etch high-stiffness ABS slider  47  effectively separates the pitch angle  124  requirement from the stiffness and gram-load sensitivities. The pitch angle  124  requirement is accomplished by the increased depth of the shallow step region  270 , while the reduced depth of the shallow step region  312  provides sufficient pressurization at the trailing edge  264  to reduce the gram-load sensitivity. Alternatively, the shallow step region  310  could have the same depth as that of the shallow step region  312  without substantially departing from the teaching of the present invention. 
     A plurality of posts that are similar in design and construction to posts  18 A- 18 G (FIG. 4) are positioned at various locations throughout the ABS  260 . With reference to FIG. 6, the ABS  260  is shown to have five posts  318 A- 318 E (it being understood that a different number of posts may be selected). 
     With reference to FIG. 7, the posts  318 A- 318 E have a generally cylindrical shape that protrude outwardly from bottom of either the shallow step region  70  or the cavity region  300 . DLC pads  320 A- 320 G are secured to the tips of the posts  318 A- 318 E, respectively. 
     When the slider  47  is in a rest position on the smooth media disk  14 , the DLC pads  320 A- 320 G come into contact with the smooth media disk  14  and provide a support to the ABS  260 , thus preventing the ABS region  270  from making contact with the surface of the disk  14  which would have caused a damage to the read/write element  50 . 
     Furthermore, the DLC pads  320 A- 320 G enable the slider  47  to take off rapidly for performing a track seek operation. The DLC pads  320 A- 320 G are secured to the posts  318 A- 318 E. 
     Thus, and as illustrated in FIG. 8, with an increased pitch angle  124 , the DLC pads  320 A- 320 G are above the lowest point  126  of the slider  47  relative to the surface of the disk  14 , achieving the objective of maximizing the DLC pad clearance. 
     It should be understood that the geometry, compositions, and dimensions of the elements described herein can be modified within the scope of the invention and are not intended to be the exclusive; rather, they can be modified within the scope of the invention. Other modifications can be made when implementing the invention for a particular environment.