Abstract:
Systems and methods are provided for burnishing a recording head in-situ in a magnetic recording disk drive. The burnishing process generates a tribocurrent, which is electricity generated by the rubbing of dissimilar materials. Different materials exhibit widely different tribocurrent characteristics while in sliding contact. The tribocurrent thus acts as an indicator of the particular materials of the recording head making contact with the magnetic recording media during different stages of the burnishing process. The tribocurrent is thus monitored to determine when it reaches a threshold value. The threshold value indicates that the burnishing has exposed a particular material of the recording head. Thus, the burnishing process may be stopped upon the tribocurrent reaching the threshold value so that the read sensor of the recording head is not burnished and inadvertently damaged.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The invention is related to the field of magnetic recording disk drive systems and, in particular, to burnishing a recording head to reduce the topography of the recording head. 
         [0003]    2. Statement of the Problem 
         [0004]    Magnetic hard disk drive systems typically include a magnetic disk, a recording head having write and read elements, a suspension arm, and an actuator arm. As the magnetic recording media is rotated, air adjacent to the disk surface moves with the disk. This allows the recording head (also referred to as a slider) to fly on an extremely thin cushion of air, generally referred to as an air bearing. When the recording head flies on the air bearing, the actuator arm swings the suspension arm to place the recording head over selected circular tracks on the rotating magnetic recording media where signal fields are written to and read by the write and read elements, respectively. The write and read elements are connected to processing circuitry that operates according to a computer program to implement write and read functions. 
         [0005]    Recording head flying height is one of the key elements of the density of magnetic recording drives. The closer a recording head flies above the magnetic recording media, the higher density recording that can be utilized. Typically, the recording head and the recording media are each covered with a layer of overcoat material, such as carbon. The thickness of the carbon overcoat region on the head is presently approximately 2 nm, and the thickness of the media overcoat layer is presently approximately 3.8 nm to 4 nm. On top of the disk overcoat layers is a layer of lubricant material, typically 1 nm in thickness. These layers are typically deposited with an uneven topography. Thus, the media and recording head roughness limit how close the recording head can safely fly over the disk with an adequate clearance margin. Further, because of differences in lapping rates during manufacturing, the read sensor is typically recessed from the air-bearing surface (ABS), further increasing the magnetic spacing between the read sensor and the magnetic recording media. 
         [0006]    One technique utilized to reduce the recording head roughness and recording head overcoat is to burnish the recording head surface in the region around the read sensor and the write pole in a controlled manner to remove a few nanometers of material, as described in “A novel wear-in-pad approach to minimizing spacing at the head/disk interface”, Singh, G. P.; Knigge, B. E.; Payne, R.; Run-Han Wang; Mate, C. M.; Arnett, P. C.; Davis, C.; Nayak, V.; Xiao Wu; Schouterden, K.; Baumgart, P., IEEE Transactions on Magnetics, Volume 40, Issue 4, Part 2, July 2004 Page(s): 3148-3152. The material removed typically comprises the carbon overcoat region of the recording head. Burnishing may be performed in-situ in the magnetic recording disk drive using a burnishing pad fabricated on the magnetic recording media. The recording head is burnished against the burnishing pad in a special process after the assembly of the drive until the recording head can safely clear the surface of the magnetic recording media. However, if the burnishing process proceeds into the read sensor material, then the read back signal is degraded due to thermal and mechanical stress imposed on the read sensor by the burnishing process. Thus, it is a problem for accurately determining when to stop the burnishing process such that wear does not proceed into the read sensor material. 
       SUMMARY OF THE SOLUTION 
       [0007]    Embodiments of the invention solve the above and other related problems with systems and methods for burnishing a recording head in-situ in a magnetic recording disk drive. The burnishing process generates a tribocurrent, which is electricity generated by the rubbing of dissimilar materials. Different materials can exhibit widely different tribocurrent characteristics while in sliding contact. The tribocurrent can thus act as an indicator of the particular materials of the recording head making contact with the magnetic recording media during different stages of the burnishing process. 
         [0008]    By identifying the materials contacting the magnetic recording media at any particular stage of the process, the burnishing process may be stopped prior to wearing the material comprising the read element. For example, because the read sensor is often recessed from the ABS, the carbon overcoat layer covering portions of the recording head on the side regions of the read sensor will wear away prior to portions of the carbon overcoat layer covering the read sensor. This will expose material of the recording head (e.g., insulation material) on side regions of the read sensor, causing a change in the tribocurrent generated by the burnishing process: Advantageously, the burnishing process can be stopped prior to wearing the read sensor and affecting its subsequent read back performance. 
         [0009]    One embodiment of the invention comprises a method for burnishing a recording head in-situ in a magnetic recording disk drive. The method comprises initiating contact between the recording head and a magnetic recording media of the magnetic recording disk drive and identifying an initial value of a tribocurrent of the recording head during the contact between the recording head and the magnetic recording media. The method further comprises monitoring the tribocurrent to detect a change in the initial value of the tribocurrent indicating that the burnishing has exposed a particular material of the recording head, and stopping the contact between the recording head and the magnetic recording media responsive to determining that the particular material of the recording head is exposed. 
         [0010]    A second embodiment of the invention comprises a system for burnishing a recording head. The system comprises a magnetic recording disk drive including a recording head and a magnetic recording media. The system further comprises a burnishing control module adapted to initiate contact between the recording head and the magnetic recording media and adapted to identify an initial value of a tribocurrent of the recording head during the contact between the recording head and the magnetic recording media. The burnishing control module is further adapted to monitor the tribocurrent to detect a change in the initial value of the tribocurrent indicating that the contact has exposed a particular material of the recording head, and adapted to stop the contact between the recording head and the magnetic recording media responsive to determining that the particular material of the recording head is exposed. 
         [0011]    Another embodiment of the invention comprises another method for burnishing a recording head in-situ in a magnetic recording disk drive. The method comprises burnishing the recording head against a magnetic recording media of the magnetic recording disk drive and monitoring a tribocurrent in the recording head generated by the burnishing to determine whether the tribocurrent has reached a threshold value. The method further comprises stopping the burnishing responsive to determining that the tribocurrent has reached the threshold value. 
         [0012]    The invention may include other exemplary embodiments described below. 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0013]    The same reference number represents the same element or same type of element on all drawings. 
           [0014]      FIG. 1  illustrates a magnetic recording disk drive in an exemplary embodiment of the invention. 
           [0015]      FIG. 2  illustrates the recording head of  FIG. 1  in an exemplary embodiment of the invention. 
           [0016]      FIG. 3  illustrates a flow chart of a method for burnishing a recording head in-situ in a magnetic recording disk drive in an exemplary embodiment of the invention. 
           [0017]      FIG. 4  illustrates the recording head of  FIG. 1  during initiation of the burnishing process in an exemplary embodiment of the invention. 
           [0018]      FIG. 5  illustrates a magnetic recording disk drive after burnishing has exposed insulation material in an exemplary embodiment of the invention. 
           [0019]      FIG. 6  illustrates a side view of the recording head of  FIG. 1  prior to the burnishing process in an exemplary embodiment of the invention. 
           [0020]      FIG. 7  illustrates a side view of the recording head of  FIG. 1  after completion of the method of  FIG. 3  in an exemplary embodiment of the invention. 
           [0021]      FIG. 8  illustrates a flow chart of another method for burnishing a recording head in-situ in a magnetic recording disk drive in an exemplary embodiment of the invention. 
           [0022]      FIG. 9  illustrates a graph of a tribocurrent measured during a burnishing process in an exemplary embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]      FIGS. 1-9  and the following description depict specific exemplary embodiments of the invention to teach those skilled in the art how to make and use the invention. For the purpose of teaching inventive principles, some conventional aspects of the invention have been simplified or omitted. Those skilled in the art will appreciate variations from these embodiments that fall within the scope of the invention. Those skilled in the art will appreciate that the features described below can be combined in various ways to form multiple variations of the invention. As a result, the invention is not limited to the specific embodiments described below, but only by the claims and their equivalents. 
         [0024]      FIG. 1  illustrates a magnetic recording disk drive  100  in an exemplary embodiment of the invention. Magnetic recording disk drive  100  includes a spindle  102 , a magnetic recording media  104 , a motor controller  106 , an actuator  108 , an actuator arm  110 , a suspension arm  112 , and a recording head  114 . Spindle  102  supports and rotates a magnetic recording media  104  in the direction indicated by the arrow. A spindle motor (not shown) rotates spindle  102  according to control signals from motor controller  106 . Recording head  114  is supported by suspension arm  112  and actuator arm  110 . Actuator arm  110  is connected to actuator  108  that is configured to rotate in order to position recording head  114  over a desired track of magnetic recording media  104 . 
         [0025]    When magnetic recording media  104  rotates, air generated by the rotation of magnetic recording media  104  causes an air bearing surface (ABS) of recording head  114  to ride on a cushion of air a particular height above magnetic recording media  104 . The height depends on the shape of the ABS. As recording head  114  rides on the cushion of air, actuator  108  moves actuator arm  110  to position a read element (not shown) and a write element (not shown) in recording head  114  over selected tracks of magnetic recording media  104 . 
         [0026]    Magnetic recording media  104  may optionally comprise a burnishing pad  116 , which comprises one or more tracks of magnetic recording media  104 . Recording head  114  may make contact with a surface of magnetic recording media  104  (or burnishing pad  116 ) to polish the surface of recording head  114  and reduce the topography of recording head  114 . Magnetic recording disk drive  100  further comprises a burnishing control module  118 . Burnishing control module  118  controls and monitors an in-situ burnishing process of magnetic recording disk drive  100 . Burnishing control module  118  may be electrically coupled to suspension arm  112  or elements of recording head  114  (e.g., a read sensor or write pole) to monitor a tribocurrent generated by the burnishing process. 
         [0027]    While burnishing control module  118  is illustrated within magnetic recording disk drive  100 , it will be appreciated that burnishing control module  118  may be implemented as a device external to magnetic recording disk drive  100 . Thus, suspension arm  112  or recording head  114  may be electrically coupled to an output line (not shown) that carries a tribocurrent signal to an external burnishing control module for monitoring of the burnishing process. Magnetic recording disk drive  100  may include other devices, components, or systems not shown in  FIG. 1 . For instance, a plurality of magnetic disks, actuators, actuator arms, suspension arms, and recording heads may be used. 
         [0028]      FIG. 2  illustrates recording head  114  in an exemplary embodiment of the invention. The view of recording head  114  is of the ABS side of recording head  114 . Recording head  114  has a cross rail  202 , two side rails  204 - 205 , and a center rail  206  on the ABS side. The rails on recording head  114  illustrate just one embodiment, and the configuration of the ABS side of recording head  114  may take on any desired form. Recording head  114  also includes a write element  210  and a read sensor  212  on a trailing edge  214  of recording head  114 . 
         [0029]      FIG. 3  illustrates a flow chart of a method  300  for burnishing a recording head in-situ in a magnetic recording disk drive in an exemplary embodiment of the invention. The steps of method  300  will be discussed in reference to magnetic recording disk drive  100  of  FIGS. 1-2  and  4 - 7 . The steps of method  300  are not all inclusive, and may include other steps now shown for the sake of brevity. 
         [0030]    In step  302 , burnishing control module  118  initiates contact between recording head  114  (see  FIG. 1 ) and magnetic recording media  104  of magnetic recording disk drive  100 . Particularly, recording head  114  may make direct contact with a recordable surface of magnetic recording media  118 . Alternatively, contact may be initiated between recording head  114  and a burnishing pad  116  of magnetic recording media  104 .  FIG. 4  illustrates recording head  114  of  FIG. 1  during initiation of the burnishing process in an exemplary embodiment of the invention. Contact is initiated by positioning recording head  114  over magnetic recording media  104 , and adjusting a height of recording head  114  such that a bottom surface of recording head  114  becomes engaged with a surface of magnetic recording media  104 . Initially, an overcoat layer structure  402  (see  FIG. 4 ) will make contact with magnetic recording media  104  and will begin to wear away. 
         [0031]    In step  304 , burnishing control module  118  (see  FIG. 1 ) identifies an initial value of a tribocurrent of recording head  114  during contact between recording head  114  and magnetic recording media  104 . As recording head  114  makes contact with magnetic recording media  104  (or burnishing pad  116 ), a tribocurrent is generated which flows through recording head  114 . The initial value of the tribocurrent identifies the initial layer of material being burnished (e.g., overcoat layer structure  402  (see  FIG. 4 )). For example, overcoat layer structure  402  may comprise a carbon material. When overcoat layer structure  402  is worn away on portions of recording head  114 , another layer of material (e.g., insulation material  404 ) will be exposed to magnetic recording media  104 . For example, insulation material  404  may comprise alumina. Because insulation material  404  is a different material than overcoat layer structure  402 , insulation material  404  will generate a different tribocurrent while in contact with magnetic recording media  116 , and thus, the transition between burnishing of overcoat layer structure  402  and insulation material  404  can be identified. 
         [0032]    Overcoat layer structure  402  may also comprise multiple layers, such as a carbon overcoat layer and a silicon adhesion layer. Wearing of the silicon adhesion layer generates a different tribocurrent than wearing of the carbon layer. Thus, the transition between wearing of the silicon and wearing of the carbon can be identified based on the generated tribocurrent. Overcoat layer structure  402  may additionally comprise other layers, such as an overcoat material that has a very characteristic tribocurrent (e.g., very high with respect to the carbon overcoat layer) that is much easier to detect than the typical overcoat layers (e.g., silicon and carbon). On exemplary overcoat material with this characteristic includes glass. 
         [0033]    In step  306 , burnishing control module  118  (see  FIG. 1 ) monitors the tribocurrent to detect a change in the initial value of the tribocurrent. This change in the tribocurrent indicates that the burnishing has exposed a particular material of recording head  114 . In this case, burnishing has exposed insulation material  404  on side regions of read sensor  212 .  FIG. 5  illustrates magnetic recording disk drive  100  after burnishing has exposed insulation material  404  in an exemplary embodiment of the invention. 
         [0034]    In step  308 , burnishing control module  118  (see  FIG. 1 ) stops contact between recording head  114  (see  FIG. 1 ) and magnetic recording media  104  responsive to determining that a particular material (e.g., insulation material  404  of  FIG. 4 ) of recording head  114  is exposed. Burnishing control module  118  may instruct motor controller  106  to raise a height of recording head  114  so that recording head  114  is not contacting magnetic recording media  104 . Based on the change in the tribocurrent, burnishing control module  118  stops the burnishing process when insulation material  404  is exposed. Because read sensor  212  is recessed from an ABS of recording head  114 , portions of carbon overcoat layer structure  402  will remain over read sensor  212 . 
         [0035]    Alternatively, the burnishing process may be stopped when a silicon adhesion layer of overcoat layer structure  402  is exposed or removed by burnishing. If a special high tribocurrent material is utilized in overcoat layer structure  402 , then the burnishing process may be stopped once this material is exposed or removed by burnishing. 
         [0036]      FIG. 6  illustrates a side view of recording head  114  of  FIG. 1  prior to the burnishing process in an exemplary embodiment of the invention.  FIG. 7  illustrates a side view of recording head  114  of  FIG. 1  after completion of step  306  (see  FIG. 3 ) in an exemplary embodiment of the invention. There is a height difference due to the removal of portions of carbon overcoat layer structure  402 . Because of the lower clearance, recording head  114  can fly at a lower height over magnetic recording media  104 . Thus, read sensor  212  is closer to magnetic recording media  104  for reading data recorded on magnetic recording media  104 . Additionally, because there is a small amount of carbon overcoat layer structure  402  remaining on read sensor  212 , read sensor  212  is not actually worn by the burnishing process. Advantageously, the burnishing process of  FIG. 3  decreases the magnetic spacing of recording head  114  (i.e., the distance between read sensor  212  and magnetic recording media  104 ) without wearing read sensor  212 . Thus, the burnishing process does not negatively impact the subsequent performance of read sensor  212 . 
         [0037]    There are different techniques for monitoring a tribocurrent to determine when to stop a burnishing process. Once such process determines whether the tribocurrent crosses a specified threshold value. The threshold value indicates a change in the material wearing against magnetic recording media  104  (see  FIG. 1 ). 
         [0038]      FIG. 8  illustrates a flow chart of another method  800  for burnishing a recording head in-situ in a magnetic recording disk drive in an exemplary embodiment of the invention. The steps of method  800  will be discussed in reference to magnetic recording disk drive  100  of  FIGS. 1-2  and  4 - 5 . The steps of method  800  are not all inclusive, and may include other steps now shown for the sake of brevity. 
         [0039]    In step  802  (see  FIG. 8 ), burnishing control module  118  (see  FIG. 1 ) burnishes recording head  114  against magnetic recording media  104 . The burnishing process may be initiated as described in step  302  of  FIG. 3 . 
         [0040]    In step  804  (see  FIG. 8 ), burnishing control module  118  monitors a tribocurrent in the recording head generated by the burnishing process to determine whether the tribocurrent has reached a threshold value. The threshold value may define a particular tribocurrent occurring when a specific type of material is contacting magnetic recording media  104 . 
         [0041]      FIG. 9  illustrates a graph of a tribocurrent measured during a burnishing process in an exemplary embodiment of the invention. The tribocurrent has a relatively steady value from 0 seconds to 30 seconds. At approximately 30 seconds, the tribocurrent begins to decrease significantly. Because most of carbon overcoat layer structure  402  (see  FIG. 4 ) has worn away from the surface of recording head  114 , the tribocurrent shows a change in polarity and a significant decrease at the transition point when insulation material  404  begins to wear against magnetic recording media  104  instead of carbon overcoat layer structure  402 . Thus, the change in polarity and the sharp decrease in the tribocurrent represent an indication that burnishing has removed carbon overcoat layer structure  402  (see  FIG. 4 ) and exposed insulation material  404 . 
         [0042]    In step  806  (see  FIG. 8 ), burnishing control module  118  (see  FIG. 1 ) stops the burnishing process responsive to determining that the tribocurrent has reached the threshold value. For example, burnishing control module  118  may stop the burnishing process when the tribocurrent falls below a threshold of −3 nA (representing the transition between burnishing of carbon overcoat layer structure  402  (see  FIG. 4 ) and insulation material  404 ). Further burnishing past the selected threshold may completely remove carbon overcoat layer structure  402 , thus exposing read sensor  212  to wear against magnetic recording media  104 . Thus, the threshold value of the tribocurrent may represent a burnishing threshold in which additional burnishing may damage read sensor  212  (see  FIG. 2 ). 
         [0043]    In one embodiment, identification of the threshold may comprise monitoring a derivative of the tribocurrent (e.g., a first derivative). When the first derivative of the tribocurrent is zero, a maximum or minimum of the tribocurrent occurs at that particular value. It is typical for a tribocurrent to reach a maximum or minimum value during the burnishing process near the transition point between materials. This maximum or minimum value can thus be used as an indicator of the transition point between two materials of recording head  114  (see  FIG. 1 ) making contact with magnetic recording media  104 . 
         [0044]    Referring back to  FIG. 9 , the tribocurrent begins to rise between 20 and 30 seconds, reaching a maximum before trailing off and changing polarity. By monitoring the first derivative of the tribocurrent, burnishing control module  118  determines when a maximum value of the tribocurrent occurs. This maximum value of the tribocurrent is one indication that carbon overcoat layer structure  402  (see  FIG. 4 ) on side regions of read sensor  212  will soon be worn away exposing insulation material  404 . Thus, if it is desirable to stop the burnishing process while carbon overcoat layer structure  402  remains across the surface of recording head  114 , then the burnishing process may be stopped at this maximum or minimum value of the value of the tribocurrent. 
         [0045]    Although specific embodiments were described herein, the scope of the invention is not limited to those specific embodiments. The scope of the invention is defined by the following claims and any equivalents thereof.