Abstract:
This application discloses a hard disk drive and a disk employing Discrete Tracks each including a land with a groove at a first depth with sectors of each track separated by servo pattern wedges with a variable second land and a variable second groove possessing widths and a second depth for the grooves differing from the first widths and depth of the groove of the sectors. The second depth optimizes the stability of the flying height of a slider over both sectors and servo pattern wedges, removing the possibility of added vibrational modes adversely affecting the slider&#39;s normal operations of reading, writing and flying above the disk surface. This also discloses the disks and their manufacture of disk surfaces with these sector zones and servo pattern wedges.

Description:
TECHNICAL FIELD 
     This invention relates to the disk surface of a Discrete Track Media (DTM) disk in a hard disk drive and the reduction of fluctuations in the flying height of a slider over a track on a rotating disk surface. 
     BACKGROUND OF THE INVENTION 
     At present, there is no hard disk drive in production that uses a Discrete Track Media disk surface, and consequently, the problem this invention addresses is not yet well known in the prior art. With that said, it is well known that anything that causes fluctuations in the flying height of a slider above a rotating disk surface induces noise and that noise tends to reduce the reliability of the hard disk drive. 
     SUMMARY OF THE INVENTION 
     Discrete Track Media (DTM) disk surfaces may partition a disk surface into sector zones between servo pattern wedges with each track including sectors in the sector zones and servo patterns in the servo pattern wedges. Each track in its sectors may include a land above of a groove at a first depth. The radial width of the land and the groove may be close to constant within manufacturing tolerances. The servo patterns may have varying widths to their lands and grooves, known hereafter as the second lands and the second grooves, or completely different patterns of data not in a track format. A problem may arise when the ratio of the average width of the second lands and the second grooves varies from the ratio of the lands and grooves. If the second depth from the second land to the second groove is the same as the first depth, the air bearing pressure of a slider flying over the servo pattern may fluctuate compared to the sector, adversely affecting flying height stability thereby injecting noise into the operation of the hard disk drive. 
     Embodiments of the invention include a hard disk drive comprising a disk base, a spindle motor mounted on the disk base and to rotate at least one disk to create at least one rotating disk surface, and a head stack assembly pivotably coupled to the disk base to position at least one slider at a flying height over the rotating disk surface where the second depth differs from the first depth. The difference may be at least two nanometers. 
     Embodiments of the invention include the disk with this disk surface and the method of manufacturing the disk including two process steps, one to create the grooves at the first depth and the second to create the second grooves at the second depth. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows an example of an embodiment of the invention as a hard disk drive including a disk base to which a spindle motor is mounted with at least one disk rotatably coupled to the spindle motor to create a rotating disk surface. A head stack assembly is configured to pivot on the disk base to position at least one slider to access a track on the rotating disk surface. 
         FIG. 2A  shows a perspective view of the voice coil motor, its head stack assembly and the one or more head gimbal assemblies coupled to the one or more actuator arms of  FIG. 1 . 
         FIG. 2B  shows a side view of some details of a head gimbal assembly positioning the slider over the rotating disk surface near the track. The slider includes an air bearing surface that interacts with the airflow induced by the disk surface rotating to form an air bearing that floats the slider at a flying height above that surface. 
         FIG. 3  shows the disk surface comprised of at least two sector zones and at least two servo pattern wedges with a servo pattern wedge between each of the sectors of the track from  FIG. 1 . In a Discrete Track Media (DTM) disk as shown in  FIGS. 4 and 5 , the disk surface is usually not planar. 
         FIG. 4  shows the radial cross section of the disk taken through the A-A line in  FIG. 3 , showing that each of the tracks includes a land and a groove at a first depth D 1  with the groove having a first width of W 1  and the land having a second width of W 2 . 
         FIG. 5  shows a circumferential cross section of the disk for the track over the servo pattern wedge, known herein as the servo pattern, with a second depth D 2  for the second grooves from the second lands. The second depth differs from the first depth to preferably minimize changes in the flying height of the slider passing over the servo pattern wedge from the flying height over the sectors without vertical micro-actuation. The circumferential cross section may be locally perpendicular to the radial cross section of  FIG. 4 . 
       And  FIG. 6  shows a top view of part of the disk surface with the sectors having the land and the groove of the tracks running circumferentially, approximated here as horizontal strips, whereas the servo patterns have the second lands and the second grooves vary in a radial pattern, leading to considering the third width W 3  of the second grooves of  FIG. 5  being based upon what is needed to generate the correct servo pattern for the recording system. Similarly, the fourth width W 4  may be determined similarly for the second lands  54 . 
     
    
    
     DETAILED DESCRIPTION 
     This invention relates to the disk surface of a Discrete Track Media (DTM) disk in a hard disk drive and the reduction of fluctuations in the flying height of a slider over a track on a rotating disk surface. Discrete Track Media (DTM) disk surfaces may partition a disk surface into data sector zones between servo pattern wedges with each track including sectors in the data sector zones and servo patterns in the servo pattern wedges as shown in  FIG. 3 . Each track in its sectors may include a land above a groove of a first depth as shown in  FIG. 4 . The radial width of the land and the groove may be close to constant within manufacturing tolerances. The servo patterns may well have varying widths to their lands and grooves, known hereafter as the second lands and the second grooves as shown in  FIG. 5 . A problem may arise when the orientation and the ratio of the average width of the second lands and the second grooves varies from that of the lands and grooves as shown in  FIG. 6 . Due to abrupt changes in orientation and the width of lands and grooves in the servo pattern area, if the second depth from the second land to the second groove is the same as the first depth, the air bearing pressure of a slider flying over the servo pattern may fluctuate compared to the sector. This dynamic fluctuation adversely affects flying height stability, thereby injecting noise into the operation of the hard disk drive. 
     Referring to the drawings more particularly by reference numbers,  FIG. 1  shows an example of an embodiment of the invention as a hard disk drive  10  including a disk base  2  to which a spindle motor  11  is mounted with at least one disk  8  rotatably coupled to the spindle motor to create a rotating disk surface  6 . A voice coil motor  36  includes a head stack assembly  12  pivotably mounted by an actuator pivot  30  to the disk base, responsive to its voice coil  32  interacting with a fixed magnetic assembly  34  mounted on the disk base and coupled through an actuator arm to a head gimbal assembly  28  configured to position at least one slider  20  to access data stored in a track  14  on the rotating disk surface. The hard disk drive includes an assembled circuit board also mounted on the disk base opposite the spindle motor and the voice coil motor. A disk cover  4  is mounted on the disk base to encapsulate all of the shown components except the assembled circuit board. 
     The hard disk drive  10  preferably accesses the data arranged in tracks  14  on the rotating disk surface  6  by controlling the spindle motor  14  to rotate the disks  8 . The tracks may be configured as concentric circles or as a tightly packed spiral. The voice coil motor  36  stimulates the voice coil  32  with a time varying electrical signal to magnetically interact with the fixed magnet assembly  34  causing the head stack assembly  12  to pivot about the actuator pivot  30  moving the head gimbal assembly  28  to position the slider  20  near the track. In many embodiments, a micro-actuator assembly coupled to the slider may be further stimulated to further control the position of the slider. A vertical micro-actuator either in the micro-actuator assembly, or preferably in the slider, may be stimulated to alter the flying height of the slider over the rotating disk surface. 
       FIG. 2A  shows a perspective view of the voice coil motor  36 , its head stack assembly  12  and the one or more head gimbal assemblies  28  coupled to the one or more actuator arms  40  of  FIG. 1 . The head stack assembly is configured to pivot about the actuator pivot  30 . 
       FIG. 2B  shows a side view of some details of the head gimbal assembly  28  of the previous Figures, in particular the head gimbal assembly couples the actuator arm  40  to the slider  20  to aid in positioning the slider over the rotating disk surface  6  near a track  14 . The slider includes an air bearing surface  18  configured to face the rotating disk surface  6  while the slider is accessing data. The air bearing surface, the rotating disk surface and the airflow induced by the disk surface rotating interact to form an air bearing that floats the slider at a flying height  22  above the disk surface. 
     The slider  20  may use a perpendicular or longitudinal recording approach to accessing data of the track  14  on the rotating disk surface  6  and may employ a magneto-resistive effect or a tunneling effect to read the data. The slider may include a vertical and/or horizontal micro-actuator or the flexure finger may include a vertical and/or horizontal micro-actuator. Either approach to vertical and/or horizontal micro-actuation may employ a thermal-mechanical effect, a piezoelectric effect, and/or an electro-static effect. The vertical actuator may be used to alter the flying height  22 . This application will refer to the vertical actuator being active as pushing the slider toward the rotating disk surface, which will be referred to as vertical actuation of the slider over the rotating disk surface. 
       FIG. 3  shows the disk surface  6  comprised of at least two sector zones  40  between adjacent servo pattern wedges  46  with each of the tracks  14  including a sector  42  in each of the sector zones and a servo pattern  48  in each of the servo pattern wedges. In a Discrete Track Media (DTM) disk  8  as shown in  FIGS. 4 and 5 , the disk surface may not be planar. The two basic operations involved with accessing data in the track, seeking the track and following the track for data access are both affected by the DTM disk format discussed in  FIGS. 4 to 6 . The servo pattern wedges  46  can extend radially from a servo wedge inner edge  41  to a servo wedge outer edge  43 . 
       FIG. 4  shows the radial cross section of the disk taken through the A-A line in  FIG. 3 , showing that each of the tracks  14  includes a land  50  and a groove  52  at a first depth D 1  with the groove having a first width of W 1  and the land having a second width of W 2 . 
       FIG. 5  shows a circumferential cross section of the disk at a servo pattern  48  for the track  14  in the servo pattern wedge  46 , with a second depth D 2  for the second grooves  56  from the second lands  54  that minimizes changes in the flying height  22  of the slider  20  passing over the servo pattern wedge from the flying height over the sectors  42 . The circumferential cross section is locally perpendicular to the radial cross section of  FIG. 4 . 
     As shown in the top view of part of the disk surface  6  in  FIG. 6 , the sectors  42  have the lands  50  and the grooves  52  of the tracks  14  running circumferentially, approximated here as horizontal strips, whereas the servo pattern wedge  46  finds the second lands  54  and the second grooves  56  forming a varying radial pattern, leading to considering the third width W 3  of the second grooves of  FIG. 5  being based upon what is needed to generate the correct servo pattern for the recording system. Similarly, the fourth width W 4  may be determined similarly for the second lands  54 . The second lands  54  can be formed radially in the sector pattern wedge  46  and contiguously between the servo wedge inner edge  41  of  FIG. 3  and the servo wedge outer edge  43  of  FIG. 3 . 
     The lands  50  and the second lands  54  may be at the same elevation above the soft under layer  609  and the substrate  58 , as indicated in  FIGS. 4 and 5  to within a small tolerance, possibly within one or two nanometers across the disk surface  6 . Further, the first depth D 1  may be at least two nanometers. It may be greater than ten nanometers, possibly greater than twenty nanometers, and further possibly greater than thirty nanometers. The second depth D 2  differs from the first depth by at least two nanometers. It may be less than seventy percent of the first depth, possibly further less than fifty percent of the second depth. In other embodiments, the second depth may be larger than the first depth. 
     Seeking the track  14  may include turning off vertical actuation to reduce the force acting on the slider  20  to maximize the flying height  22 . As the slider passes the sectors  42  and the servo patterns  48 , the first depth D 1  and the second depth D 2  are optimized to minimize fluctuations in the flying height, thereby minimizing the probability of unwanted contact with the disk surface  6 . 
     Following the track  14  may include turning off vertical actuation of the slider  20  over the servo pattern  48  while turning on vertical actuation over the sector  42 . Minimizing the pressure fluctuations of the air bearing may limit mechanical vibration resonances thereby aiding the access of the data of the track. 
     Embodiments of the invention include the disk  8  with this disk surface  6  and the manufacturing of the disk surface including two process steps, one to create the grooves  52  at the first depth D 1  and the second to create the second grooves  56  at the second depth D 2 . The first width W 1  plus the second width W 2  may approximate the track  14  pitch, which may be not more than one hundred nanometers. 
     In some embodiments of the invention, the first depth D 1  may be greater than the second depth D 2 . The process step making the second grooves  56  at the second depth may occur before the step making the first grooves  52  at the first depth. Alternatively, the first depth D 1  may be less than the second depth D 2 . Similarly, making the first grooves  52  may occur before the second grooves  56 . 
     The preceding embodiments provide examples of the invention, and are not meant to constrain the scope of the following claims.