Abstract:
One embodiment of a recording head for a disk drive with a load/unload mechanism has an air bearing on one surface. The air bearing comprises a patterned set of three air bearing pads, and at least one deep pocket. The three air bearing pads are spaced apart from each other by the deep pocket, with the largest of the air bearing pads located on the leading edge, and the other pads on the trailing edge. The air bearing pads have unique geometry one of the trailing corners of the air bearing is free of all the air bearing pads. This configuration gives the air bearing superior performance characteristics over prior art designs with load/unload mechanisms, particularly in regard to contact with the disk during loading and unloading sequences.

Description:
[0001]    The present patent application is related to the following concurrently filed and co-pending patent applications: Attorney Docket No. SJO9000028US1, entitled,  Magnetic Disk Drive with Offset Load/Unload Tab;  and Attorney Docket No. SJO920000152US1, entitled,  Offset Limiter for Reducing Potential of Disk Damage During Unload Sequence in Load/Unload Disk Drive,  which are incorporated herein by reference.  
         BACKGROUND OF THE INVENTION  
         [0002]    1. Technical Field  
           [0003]    The present invention relates in general to an improved disk drive, and in particular to an improved air bearing design for a transducer in a disk drive.  
           [0004]    2. Description of the Related Art  
           [0005]    Generally, a data access and storage system consists of one or more storage devices that store data on magnetic or optical storage media. For example, a magnetic storage device is known as a direct access storage device (DASD) or a hard disk drive (HDD) and includes one or more disks and a disk controller to manage local operations concerning the disks. Disks are rigid platters that are usually made of aluminum alloy or a mixture of glass and ceramic, and are covered with a magnetic coating. Typically, two or three disks are stacked vertically on a common spindle that is turned by a disk drive motor at several thousand revolutions per minute (rpm).  
           [0006]    The only other moving part within a typical HDD is the head stack assembly. Within most HDDs, one magnetic read/write head or slider is associated with each side of each platter and flies just above the platter&#39;s surface. Each read/write head is mounted on a suspension to form a head gimbal assembly (HGA). The HGA is then attached to a semi-rigid arm apparatus that supports the entire head flying unit. Several semi-rigid arms may be combined to form a single armature unit.  
           [0007]    Each read/write head scans the surface of a disk during a “read” or “write” operation. The head and arm assembly is moved utilizing an actuator that is often a voice coil motor (VCM). The stator of a VCM is mounted to a base plate or casting on which the spindle is also mounted. The base casting is in turn mounted to a frame via a compliant suspension. When current is fed to the motor, the VCM develops force or torque that is substantially proportional to the applied current. The arm acceleration is therefore substantially proportional to the magnitude of the current. As the read/write head approaches a desired track, a reverse polarity signal is applied to the actuator, causing the signal to act as a brake, and ideally causing the read/write head to stop directly over the desired track.  
           [0008]    To successfully achieve file performance, the read/write head must fly steadily at a given fly height over the disk with minimal variations. Since the variations in fly height are dependent on the various sensitivities of the fly height to the process parameters as well as the variability of the parameters, a state-of-the-art air bearing surface (ABS) design technology and tight process control are mandatory to minimize such variations. Common dominant process parameters affecting fly height include head-gimbal assembly moments, crown and etch depths.  
           [0009]    In the prior art, the disk and carbon overcoat on the slider are subject to extensive wear during start/stop cycles. Recent designs have employed load/unload technology to reduce this problem, where a ramp is provided for each slider/suspension assembly at the inner or outer diameter of the disk where the slider is parked. However, during the loading/unloading sequence, the sliders may still contact the disks. In order to read or write data in the load/unload zone (near the outer radial edges of the disks), the inner diameter corners/edges of the slider must not contact the disk surface. Even for systems that do not write data in the load/unload zone, it is desirable to avoid the inner diameter edges of the slider contacting the disk surface since the slider will need to fly over this zone. Thus, further improvements for disk drive components are needed to enhance performance and reduce the potential for data erasure.  
         SUMMARY OF THE INVENTION  
         [0010]    One embodiment of a recording head for a disk drive with a load/unload mechanism has an air bearing on one surface. The air bearing suitably comprises a patterned set of three air bearing pads, and at least one etch surface. The three air bearing pads are spaced apart from each other, with two of the air bearing pads located on the leading edge, and the other pad on the trailing edge. The air bearing also has an offset pad at one of the trailing corners of the air bearing surface. This configuration gives the air bearing superior performance characteristics over prior art designs with load/unload mechanisms, particularly in regard to contact with the disk during loading and unloading sequences.  
           [0011]    The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]    So that the manner in which the features, advantages and objects of the invention, as well as others which will become apparent, are attained and can be understood in more detail, more particular description of the invention briefly summarized above may be had by reference to the embodiment thereof which is illustrated in the appended drawings, which drawings form a part of this specification. It is to be noted, however, that the drawings illustrate only a preferred embodiment of the invention and is therefore not to be considered limiting of its scope as the invention may admit to other equally effective embodiments.  
         [0013]    [0013]FIG. 1 is a schematic isometric drawing of a disk drive showing a disk and an actuator with a slider assembly having a read/write head or transducer.  
         [0014]    [0014]FIG. 2 is an enlarged isometric view of one embodiment of a head on the slider assembly of FIG. 1 and is constructed in accordance with the present invention.  
         [0015]    [0015]FIG. 3 is a schematic isometric drawing of the head of FIG. 2 inverted on a lower side of the disk of FIG. 1.  
         [0016]    [0016]FIG. 4 is a bottom isometric view of the head of FIG. 2 showing an air bearing surface.  
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0017]    Referring to FIG. 1, a disk drive  11  for reading and writing information to the surface of a rotating, magnetic disk  13  having a large plurality of tracks is shown. Disk  13  is mounted on spindle  14 , which is attached to a motor (not shown) that is operable to rotate disk  13 . Drive  11  comprises an actuator  15  with a movable arm  17  and a suspension  19  on one end. Arm  17  and disk  13  move in the directions indicated by arrows  21 ,  23 , respectively. Arm  17  provides the seek motion when changing tracks on disk  13 . A load/unload mechanism, such as ramp  25 , is located adjacent to disk  13  for engaging actuator  15 .  
         [0018]    As shown in FIG. 2, a slider, transducer, or flying head  31  having a read/write element is bonded to the end of suspension  19 . In the embodiment shown, head  31  is pico size (approximately 1250×1000×300 microns) and formed from ceramic or intermetallic materials. Head  31  also may be nano size (approximately 2050×1600×450 microns), or femto size (approximately 850×700×230 microns). Head  31  is pre-loaded against the surface of disk  13  (preferably in the range two to ten grams) by suspension  19 .  
         [0019]    As shown in FIGS. 3 and 4, the air bearing  35  of head  31  comprises a patterned set of stepped elements, such as air bearing surface (ABS) pads  50 ,  51 ,  52 , an offset ABS pad  38 , which can have a height at the ABS surface (same height as the ABS pads) or below the ABS surface, shallow etch surfaces  37  and  53 , and one irregularly-shaped, deep etch pocket  39 . For reference purposes, a longitudinal direction is defined from left to right (FIG. 4), and a lateral direction is defined from top to bottom. Pocket  39  is manufactured using standard etching techniques such as reactive ion etching (RIE) and ion milling (IM), for example. Common etch depths range from about 0.1 to 5 microns. The ABS pads  50 ,  51 ,  52 , or portions of the air bearing  35  that have not been etched, are also known as air bearing surfaces (ABS). In the embodiment shown, head  31  has three ABS pads  50 ,  51 ,  52 , shallow etch surfaces  53 ,  37  (which are approximately 100 to 200 nm beneath the ABS pads), and one continuous but very irregular, deep etch pocket  39  (approximately 1.60 microns beneath the ABS pads) that extends to portions of the leading edge  40 , lateral edges  41 ,  42 , and trailing edge  43 . Lateral edges  41 ,  42  also represent the inner and outer radial directions, respectively, of disk  13 . The trailing edge  43  of air bearing  35  is defined by the rear edge of pocket  39 , and the rear edges of surface  37 . Each of the ABS are asymmetrical in both the longitudinal and lateral directions.  
         [0020]    In a very general sense, pocket  39  has a U-type shape with thin strips extending between lateral edges  41  and  42 . Leading etch surface  53  is generally C-shaped, having a rectangular main body and thin, elongated, trailing portions that are adjacent to lateral edges  41 ,  42 , respectively.  
         [0021]    Offset pad  38  is preferably smaller in surface area than shallow etch surfaces  53 ,  37 , but is located at or adjacent to the corner defined by the intersection of lateral edge  41  and trailing edge  43 . Note that the corner defined by the intersection of lateral edge  42  and trailing edge  43  has no offset pad, but only pocket  39 , as all the ABS pads are spaced apart from the corner. In the preferred embodiment, head  31  is pico size. It should be apparent that the shape, location and etching depths of the various elements on air bearing  35  may be varied and are not necessarily limited to the slider size nor dimensions suggested above.  
         [0022]    There are several important parameters-that measure the performance of head  31 . Fly height is the separation between a point on the ABS and disk  13 , such as the center of the trailing edge  43  of air bearing  35  and the surface of disk  13 . Pitch is the tilting of the flying slider in the longitudinal direction with respect to the plane of the disk  13 . Roll is the tilting of the flying slider in the transversal direction with respect to the plane of the disk  13 . Fly height, pitch, and roll are all dependent on parameters like ambient pressure, temperature, air viscosity, linear velocity (product of radius from center of disk  13  and disk angular velocity or rpm), skew angle (angle between the longitudinal axis of head  31  and the tangent to the current radius from the center of disk  13 ), pre-load (the force applied by suspension  19 ), suspension moments (moments applied in the pitch and roll directions by suspension  19 ), slider flatness, and the design of air bearing  35  itself (described in the previous paragraphs). The design of head  31  targets a low velocity and low skew dependent, fly height profile that remains flat across the radius of disk  13 . The spacing between head  31  and disk  13  is completely described by fly height, together with its pitch and roll.  
         [0023]    The performance of head  31  may also be measured in terms of sensitivities. The sensitivities of head  31  describe its change in fly height, pitch, or roll when another parameter that affects the fly height changes by one unit. For example, “sensitivity to pre-load” measures the decrease in fly height when the pre-load force is increased by one gram. “Sensitivity to slider flatness” is also an important parameter. The surfaces  51 ,  52 ,  53  of air bearing  35  are not perfectly flat since head  31  exhibits a longitudinal curvature or crown, a transversal curvature or camber, and a cross curvature or twist. Among these features, crown has the greatest effect on fly height.  
         [0024]    In general, the parameters that affect fly height are associated with the suspension  19  (pre-load, location of the dimple with respect to the slider, and static attitudes in the pitch and roll directions), head  31  (flatness and size of ABS  51 ,  52 ,  53 , etch depths, mask alignment, and rail width), and operating conditions (ambient temperature, pressure, viscosity, and velocity). It is desirable for head  31  to have low sensitivities since that implies that the departure of fly height from its desired target is small. Each parameter affecting fly height is described statistically by its mean and standard deviation. A tight distribution of values for a parameter around their mean implies that the spread or standard deviation is small.  
         [0025]    For example, “fly height sigma” is a statistical estimator of the fly height variation of a group of heads  31 . This parameter is proportional to the standard deviation of other parameters that affect fly height, and to the sensitivities of the design of air bearing  35 . Thus, by designing head  31  to possess low sensitivities, and by ensuring that the manufacturing process is very repeatable, a tight distribution of fly heights is realized.  
         [0026]    There are also a number of specific requirements for head  31  that must be met. Since disk  13  is not perfectly flat and exhibits waviness or curvature that affects fly height, it is desirable that head  31  responds consistently to changes in the curvature of disk  13 . There are at least two disk curvatures of interest. One is in the tangential direction is related to the crown of the slider. Another is in the radial direction and is related to the camber of the slider. Because of the magnitude of the radial curvature near the rim of the disk (also called roll-off or ski jump), it is important for the head  31  to feature a low transversal curvature sensitivity. The flatness sensitivity of head  31  is important in this respect.  
         [0027]    Another requirement for head  31  is low fly height and roll sigmas. The variability in fly height of head  31  must be consistent. In particular, the roll standard deviation must be small since it is the spacing between the trailing edge  43  of head  31  and disk  13  that controls the fly height. If trailing edge  43  is perfectly parallel to disk  13 , the clearance is uniform. Any amount of roll creates an uneven clearance between the head  31  and disk  13 .  
         [0028]    As a related requirement, head  31  must have good load/unload performance. During operation, head  31  is loaded onto a spinning disk  13  and must establish its supportive air bearing to avoid contact with disk  13 . Ideally, there will be no exposure to contact during the load/unload sequences. However, physical contact with disk  13  is almost inevitable and can be a disturbing event on the fly height as it causes head  31  to lose support and cause damage to the disk  13 .  
         [0029]    Therefore, a robust and stable response to loading and unloading processes is provided by the absence of an ABS at the corner defined by the outer diameter lateral edge  42  and trailing edge  43  of head  31 . During the unloading sequence, the presence of offset pad  38  and the lack of a similar structure in the other trailing corner of air bearing  35 , slightly skews head  31  such that the probability of slider/disk contact with the inner diameter edge is reduced and contact with the outer diameter edge is increased. Offset pad  38  essentially forces head  31  to roll during load processes so that the likelihood of contacting disk  13  is much higher on the outer diameter side of head  31 . Similarly (during unloading), pad  38  acts to bias the contact region to the outer diameter side of the slider. During the unloading sequence, the slider is lifted up away from the disk leading edge first. As the leading edge is pulled, pad  38  resists motion toward the disk surface due to pressurization at the pad. However, the outer diameter corner of the slider has less resistance since it does not have a pad similar to pad  38 . This asymmetry causes the slider to roll during unloading processes so that the likelihood of contacting the disk  13  is much higher on the outer diameter side of head  31 .  
         [0030]    While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes without departing from the scope of the invention. For example, if the slider/suspension assembly is parked at the inner diameter of the disk, the present invention may be implemented by locating the air bearing pads away from the corner of the air bearing defined by its inner radial edge and trailing edge.