Abstract:
A method of controlling clearance in a disk drive, including the steps of: mounting a recording head having at least one heating element at a first distance from a top surface of the disk; measuring a first passive fly height between the top surface of the disk and a bottom surface of the head; applying a first quantity of energy to the heating element(s) to permanently deform the head and change the distance between the top surface of the disk and a bottom surface of the head to a second passive fly height that is less than the first passive fly height; and applying a second quantity of energy to the heating element(s) to temporarily deform the head and change the distance between the top surface of the disk and a bottom surface of the head to an operational clearance distance that is less than the second passive fly height.

Description:
BACKGROUND 
     Hard disk drive (HDD) systems typically include one or more data storage disks with concentric tracks containing information. A transducing head carried by a slider is used to read from and write to a data track on a disk, wherein each slider has an air bearing surface that is supportable by a cushion of air generated by one of the rotating disks. The slider is carried by an arm assembly that includes an actuator arm and a suspension assembly, which can include a separate gimbal structure or can integrally form a gimbal. 
     In more particularity, many disk drives include a transducer that “flies” only a few nanometers above a rotating disk surface. The transducer is mounted in a slider assembly which has a contoured surface. When the disk is at rest, the air bearing slider is in contact with the disk. During operation, the disk rotates at high speed, and an air bearing force is produced by pressurization of the air as it flows between the disk and slider. This air force acts upon a lower air bearing surface of the slider and generates a lift force directing the slider away from the disk and against a load beam causing the slider to fly at an ultra-low height above the disk. Thus, the air force prevents unintentional contact between the transducer and the disk and also provides a very narrow clearance between the slider transducer and the rotating disk. This allows a high density of magnetic data to be transferred and reduces wear and damage. The height at which the read/write head of a slider is positioned above a rotating disk when no reading or writing is taking place is known as the passive fly height, which height is decreased to an operational clearance when reading and/or writing is taking place 
     Because the demand for disk storage systems with large storage capacities is increasing, the density of concentric data tracks on disks is increasing, which in turn requires that the air bearing gap between the transducing head and the rotating disk be reduced to even lower flying heights. During operation of the magnetic data storage and retrieval system, the transducing head is positioned in close proximity to the magnetic media. A distance between the transducer and the media is preferably small enough to allow for writing to and reading from a magnetic medium having a large a real density, and great enough to prevent contact between the magnetic media and the transducer. As the average flying height of the slider decreases, the transducer achieves greater resolution between the individual data bit locations on the disk. Therefore, operational flying height is one of the most critical parameters of magnetic recording. 
     Part to part variation in manufacturing processes can cause a distribution in fly height for a given head-disk interface design. Many factors impose restrictions on passive fly heights that can be achieved, including changes in ambient conditions, manufacturing and processing variations in the components, and maximum temperature limits of the head itself. In particular, the passive fly height distribution has a maximum limit for high flying heads due to degraded head reliability caused by the high temperatures generated by heat actuators of the head that are activated to modify the head to achieve a desired operational clearance. This limit constrains the allowed design space and can reduce factory yields because heads with too high of a passive fly height are not usable and are generally scrapped, which can greatly reduce yields. Thus, a need exists for an air bearing slider design which is adjustable to achieve a constant, ultra-low transducer flying height, despite certain mechanical limitations. 
     SUMMARY 
     In accordance with aspects of the invention, a heating source is provided to permanently deform a magnetic recording head to provide a one-time passive fly height adjustment. This controlled adjustment is designed to be local to the transducer region of the head and will bring high flying heads to passive clearance levels that are in a more desirable range and therefore have desired operating temperatures. 
     The heating source of the invention can be an existing element that is present in the head, such as a heating actuator, or can instead be a dedicated heating source. The operational parameters of the heating actuator or heating source, such as the time and the applied power, are controllable to adjust the amount of head deformation or protrusion and thus the fly height correction applied to a specific head. This correction can be applied off disk or on disk. In either case, the heating source and region to be deformed are designed so that sufficient temperatures are achieved to provide the desired shape change. The amount and profile of shape change desired for a given head can be determined by assessing contact powers or clearance measurements on an electrical tester, for example. In a case where the head is being adjusted while on a tester prior to placing it on a disk drive, the head can be immediately checked to confirm that the head has been properly adjusted to a desired operating temperature. If the head has operational heater powers that are too high, for example, the head can be adjusted while still on the tester. 
     In one aspect of the invention, a method is provided for controlling clearance in a disk drive between a disk and a magnetic recording head of a slider, the method including the steps of: mounting the head at a first distance from a top surface of the disk, wherein the head has at least one heating element. The steps further include measuring a first passive fly height between the top surface of the disk and a bottom surface of the head; applying a first quantity of energy to the at least one heating element to permanently deform the head and change the distance between the top surface of the disk and a bottom surface of the head to a second passive fly height that is less than the first passive fly height; and applying a second quantity of energy to the at least one heating element to temporarily deform the head and change the distance between the top surface of the disk and a bottom surface of the head to an operational clearance distance that is less than the second passive fly height. The first quantity of energy can be the same or different from the second quantity of energy applied to the head. The heating elements and quantity thereof can vary, wherein the head can include two heating elements, can comprise at least one heating element integrated into a transducer region of the head, can comprise a heat actuator or laser, and/or can be externally positioned relative to the transducer region of the head. 
     These and various other features and advantages will be apparent from a reading of the following detailed description. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will be further explained with reference to the appended Figures, wherein like structure is referred to by like numerals throughout the several views, and wherein: 
         FIG. 1  is a perspective view of an exemplary hard disk drive (HDD) system; 
         FIG. 2  is a perspective view of an exploded head stack assembly of the type that can be used in an HDD system, such as the system illustrated in  FIG. 1 ; 
         FIG. 3  is a schematic side view of an embodiment of a read/write head with an internally located heating source, in accordance with the invention; 
         FIG. 4  is a schematic side view of an embodiment of a read/write head with an externally located heating source, in accordance with the invention; 
         FIG. 5  is a flow chart depicting an embodiment of a series of steps that are performed in accordance with the invention to provide a desired deformation of a read/write head; 
         FIG. 6  is a schematic side view of a read/write head positioned at an initial passive fly height distance from a disk; 
         FIG. 7  is a schematic side view of the read/write head of  FIG. 6  after the application of a controlled amount of heat to the reader/writer area of the head; to provide controlled deformation thereof; and 
         FIG. 8  is a schematic side view of the read/write head of  FIG. 7  as positioned at a decreased passive fly height distance from a disk. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to the Figures, wherein the components are labeled with like numerals throughout the several Figures, and initially to  FIG. 1 , an exemplary configuration of a typical hard disk drive (HDD) system  20  is illustrated. The HDD system generally includes at least one magnetic storage disk  22  configured to rotate about an axis  24 , an actuation motor  26  (e.g., a voice coil motor), an actuator arm  28 , a suspension assembly  30  that includes a load beam, and a slider  32  carrying a transducing or read/write head (not shown). Slider  32  is supported by suspension assembly  30 , which in turn is supported by actuator arm  28 . Together, actuator arm  28 , suspension assembly  30  and slider  32  form a head stack assembly (HSA). Actuation motor  26  is configured to pivot actuator arm  28  about an axis  34 , in order to sweep suspension  30  and slider  32  in an arc across a surface of rotating disk  22  with slider  32  “sliding” or “flying” across disk  22  on a cushion of air, often referred to as an air bearing. The read/write head carried by slider  32  can be positioned relative to selected concentric data tracks  36  of disk  22  by a piezoelectric microactuator, not seen in  FIG. 1 . A stack of co-rotating disks  22  can be provided with additional actuator arms  28 , suspension assemblies  30 , and sliders  32  that carry read/write heads for reading and writing at top and bottom surfaces of each disk  22  in the stack. 
     In order to better illustrate sliders and associated components of the type discussed herein relative to the invention,  FIG. 2  provides an exploded, perspective view of a typical head stack assembly (HSA)  40  of  FIG. 1 , which includes a load beam  42 , actuator arm  28 , and a base plate  44  with an upwardly projecting boss tower  46 . In the illustrated embodiment, HSA  40  includes a flexure piece  50  to which slider  32  (which includes a transducing or read/write head) is mountable. Flexure  50  may be attached to load beam  42  by any conventional mechanism or may be integral with load beam  42 . In some embodiments, load beam  42 , flexure  50  and slider  32  can be referred to as a head suspension assembly. Load beam  42  includes a mounting region  52  at a proximal end, a rigid region  54  adjacent to the distal end of the load beam  42 , and a spring region  56  between the mounting region  52  and rigid region  54 . An aperture  60  is extends through the mounting region  52 . Spring region  56  is relatively resilient and provides a downward bias force at the distal tip of load beam  42  for holding the slider  32  with read/write head near a spinning disk in opposition to an upward force created by the air bearing over the disk. HSA  40  is typically coupled to actuation motor  26  of the type illustrated in  FIG. 1 , for example, via actuator arm  28  that is attached to mounting region  52  of load beam  42 . 
     The read/write heads described above are carried by a slider that is used to read from and write to a data track on a disk. The slider is carried by an arm assembly that includes an actuator arm and a suspension assembly, which can include a separate gimbal structure or can integrally form a gimbal. In a typical process, an array of sliders are formed on a common substrate or an AlTiC wafer which is then sliced to produce bars, with a row of sliders in a side-by-side pattern on each bar. The bars (which can be referred to as row bars) are then subjected to a series of processes to form individual sliders, including lapping, cleaning, formation of air-bearing surfaces (ABS), and dicing. 
     Referring now to  FIG. 3 , a schematic side view of a read/write head  100  is illustrated, which generally includes reader/writer  102  and a heating source  104  that is internal or integrated into the head  100  to provide an initial, one-time clearance adjustment. The integrated heating source  104  can be a dedicated element that is provided specifically for the adjustments of the present invention, or can be an existing heating element that is integrated into the head  100  for other purposes, such as actuation. The heating source  104  can provide heat via joule heating, for example. 
     The integrated heating source  104  of the head  100  is positioned in a location so that the material from which the head  100  is made can expand sufficiently and in a controlled manner to provide a desired clearance adjustment (i.e., reduce the clearance between the head and an adjacent disk), but also so that it does not damage temperature sensitive elements of the head  100 . The heating source  104  is sized, shaped, positioned, and otherwise configured so that when it is heated to a certain temperature for a specific period of time, a change in the profile of the read/write head will be accomplished in a predictable and repeatable manner 
       FIG. 4  is a schematic view of a read/write head  120 , which includes a reader/writer  122  and a heating source  124  that is positioned external to the head  120  itself. The heating source  124  is in communication with an absorber element  126  that is positioned in a particular location of the head  120  to provide a desired head deformation. Heating source  124  can be permanently attached to the head  120 , or can instead be removably attached to the head  120 . One exemplary heating source  124  is a laser that provides controlled energy to the head  120  to cause the desired deformation of the head  120 . In particular, the laser can be focused through the material of the head  120  (e.g., alumina) to a feature positioned in a particular area inside the head  120  or on its exterior surface. 
     Although examples of an integrated heating source  104  and an external heating source  124  are described briefly above, it is understood that the heating source can include a wide variety of heating elements, and that any heating source that can heat a predetermined area of the read/write head to a desired temperature can be used to cause controlled deformation of the head. In addition, it is understood that a read/write head can include single or multiple heating sources made of the same or different materials to provide a desired deformation profile. It is further understood that if multiple heating sources are provided, they can either be internal to the read/write head, external to the read/write head, or a combination of internal and external heating sources. 
     In accordance with the invention, the desired area or areas to be deformed of a read/write head are precisely calculated so that when the heating of that area occurs, the head can deform to match a predicted profile. In addition, each area to be deformed is made of a material that can predictably deform in response to a certain quantity and duration of heat provided from the heating source. For one example, the material of the head itself can be used to provide the head deformation, such as alumina. Alternatively, a specially designed or selected block of material can be incorporated into the head to allow for the desired deformation. The added block of material can be designed to provide the a desired deformation in the transducer region of the head to create the clearance adjustment. The material chosen can be selected based on the desired performance and ease of implementation in the head design. 
     The deformable material of the invention is generally provided to be permanently or semi-permanently deformed, although permanent deformation will be preferred in certain aspects of the invention. Such permanent deformations can be considered to be plastic deformations in that the material will retain its deformed configuration after removal of heat or other activation energy. 
     Further in accordance with the invention, deformation of a read/write head will depend on the applied heating power and the time the power is applied. An empirically derived relation between these two inputs and the desired clearance change will be determined for a given head design, as is illustrated in the flow chart  140  of  FIG. 5 . This flow chart  140  illustrates an exemplary procedure for determining a relationship between heating source operation and the deformation that causes a decrease in contact power or clearance. The flow chart is for a fixed heating source, but a similar procedure can be used for determining the length of time the heating source will be applied to achieve a desired head deformation. 
     As discussed below relative to the flow chart  140  of  FIG. 5 , the relationship between deformation of a particular head and applied power can be determined on an electrical or a mechanical tester by applying increasing amounts of power from a heating source for a given length of time. In between heat power steps, the head is loaded onto the disk and the contact power or clearance is measured. This procedure produces a transfer function between the decrease in contact power or clearance and the amount of heating power applied to the head. The transfer function between the length of time the heating power is applied and the clearance change is determined in a similar way. This can be performed using a fixed heater power and increasing the time the power is applied. If the maximum temperature provided by the head source is not exceeded during operation, measurements of off disk head shape is shown to not change with repeated heating source cycling. After this procedure, the clearance change as a function of both heating source power and duration will have been determined. 
     The particular steps provided in an exemplary procedure of the invention are depicted in the flow chart  140 , which starts with step  142  of loading a head with particular characteristics onto a disk, and measuring the initial contact power. The next step  144  is unloading the head, and then applying an desired amount of heat to the head (step  146 ) that may be needed to achieve a certain amount of deformation of the head and the corresponding adjustment of the clearance. The head can then be loaded onto a disk to simulate an actual loaded disk in operation (step  148 ), and the contact power is measured. If the desired contact power or clearance is achieved (step  150 ), the head is unloaded (step  152 ) and the adjustment is complete. If the desired amount of contact power or clearance is not achieved, the head can then be unloaded again (step  144 ), and an incremental amount of power is again applied to the head (step  146 ). The head is loaded onto a disk again to simulate a loaded disk in operation, and the contact power is measured. The process can be repeated until the desired contact power or clearance is achieved. 
     Once the relationship between heat applied and corresponding deformation for a particular head design is determined, this relationship can be applied to individual heads that have contact powers or clearances that are measured to be too high, as is illustrated in  FIGS. 6-8 , for example. For such a head, a predetermined amount of heating power (as determined by the above method, for example) is applied to bring contact power or clearance down to an acceptable level. Because the adjustment can be performed on the tester, the clearance adjustment can be immediately verified. If desired, the adjustment can be done incrementally. In this case, a series of smaller adjustments can be performed to bring head to the desired passive clearance. 
     Referring to  FIG. 6 , an exemplary read/write head  180  is illustrated, which is positioned relative to a disk  184  (also referred to as “on-disk”) with a reader/writer  182  being located at a distance  186  from the disk  184  that is equivalent to a representative initial passive fly height. In this position, the contact power is measured to determine the adjustment that may be required to reposition the reader/writer  182  at the desired distance from the disk  184 . A certain quantity of power can then be applied to a heating source  190  of the read/write head  180  to provide the desired deformation to adjust the clearance, wherein the heating source can be an integrated or external heating source, as discussed above.  FIG. 7  illustrates the deformed head  180 , in which the reader/writer  182  has been permanently deformed by the heat that was applied by the heating source  190  in such a way that the reader/writer  182  will be closer to the disk  184  than in  FIG. 6 . The read/write head  180  is then positioned above disk  184  and the clearance between the reader/writer  182  and the disk  184  is measured, which will be a reduced passive fly height distance  188  than the initial passive fly height distance prior to the application of heat, as is schematically illustrated in  FIG. 8 . 
     Although  FIGS. 6-8  illustrate a situation where the clearance adjustment is performed off-disk, it is understood that the adjustments can instead be made when the reader/writer is on-disk. That is, the head will not be unloaded as in  FIG. 7 , but instead will remain positioned with the reader/writer spaced slightly from the top surface of the disk during the process of applying heat via the heating source to cause the desired deformation. 
     After the deformation of the read/write head is complete, a functional passive fly height for the head will be established. At this point, the head can be used in a disk drive in such a way that heat or other activation energy can be applied to move the head from a passive fly height to an operational fly height so that reading and writing operations can take place. 
     The present invention has now been described with reference to several embodiments thereof. The foregoing detailed description and examples have been given for clarity of understanding only. No unnecessary limitations are to be understood therefrom. It will be apparent to those skilled in the art that many changes can be made in the embodiments described without departing from the scope of the invention. The implementations described above and other implementations are within the scope of the following claims.