Abstract:
Magnetic recording disks and associated fabrication methods are described for utilizing polymer structures in planarized magnetic media. A polymer fill material is deposited on the disk and a removal process is performed on the fill material to planarize the disk. In some embodiments, the fill material is deposited subsequent to bonding a lubrication layer to a protective layer on the disk. In other embodiments, the fill material is bonded directly to a protective layer on the disk.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention is related to the field of magnetic disks, and in particular, to planarizing patterned magnetic disks utilizing polymer structures. 
       BACKGROUND 
       [0002]    Many computer systems use magnetic disk drives for mass storage of information. Magnetic disk drives typically include one or more sliders having a read head and a write head. An actuator/suspension arm holds the slider above the surface of a magnetic disk. When the disk rotates, an air flow generated by the rotation of the disk causes an air bearing surface (ABS) side of the slider to fly to a particular height above the disk. As the slider flies on the air bearing, a voice coil motor (VCM) moves the actuator/suspension arm to position the read/write head over selected tracks of the disk. The read/write head may then read data from or write data to the tracks of the disk. 
         [0003]    A conventional disk includes data fields where the actual data is stored. In the data fields, the magnetic surface of the disk is divided into small magnetic regions, each of which is used to encode a single binary bit of information. The magnetic regions include a few dozen magnetic grains forming a magnetic dipole, which generates a highly localized magnetic field. The write head magnetizes a magnetic region by generating a strong local magnetic field to store a bit of data within the magnetic region during a write process. The read head senses the magnetic dipole of the magnetic region to read the bit of data during a read process. 
         [0004]    As the areal bit density of the disk increases, the super-paramagnetic effect causes reliability problems for magnetic data storage. The super-paramagnetic effect occurs when the magnetic regions on the disk become so tiny that ambient temperature can reverse the orientation of their magnetic dipole. The result is that the bit is reversed and the data encoded by the bit is corrupted. 
         [0005]    One solution to the problems posed by the super-paramagnetic effect is to pattern the disk. A patterned disk is created as an ordered array of discrete magnetic lands between grooves with some depth and with each land capable of storing an individual bit. 
         [0006]    One consequence of using unplanarized patterned disks is that the depth created when patterning the disk causes a disturbance in the spacing between the read/write heads and the surface of the disk. This problem arises as, when the slider flies over the disk with the desired clearance between the head and land areas, the presence of unfilled grooves results in increasing the mean flying height, which leads to a larger modulation of the clearance between the read/write heads and the surface of the disk than for smooth disks. This modulation of the clearance and magnetic spacing degrades the quality of reading data from or writing data to the disk. To planarize these disks a fill material may be deposited within the grooves of the patterned disk to reduce the variations in depth between the top of the lands and the bottom of the grooves. However, known polymer fill materials may be inadequate due to shrinkage and recession in the grooves, which may ultimately render the disk poorly planarized. 
       SUMMARY 
       [0007]    Embodiments provided herein include depositing a perfluoropolyether polymer fill material on a patterned magnetic disk and performing a removal process on the fill material to planarize the disk. In some embodiments, the fill material is a perfluoropolyether backbone coupled to a cross-linkable end and/or side group with a urethane linkage, which provides exceptional planarization results on patterned media. In these embodiments, the fill material is bonded directly to a protective layer on the disk. In other embodiments, the fill material is deposited subsequent to bonding a lubrication layer to a protective layer on the disk. 
         [0008]    One embodiment comprises a method of fabricating a patterned magnetic recording disk. According to the method, a fill material is deposited on the magnetic recording disk. In one embodiment, the fill material is a polymer comprising a perfluoropolyether backbone coupled to a cross-linkable end and/or side group using a urethane linkage. In another embodiment, the fill material is a perfluoropolyether backbone coupled to non-cross-linkable functional groups. A removal process is performed on the fill material to planarize the magnetic recording disk. In some embodiments, a protective layer is deposited on a patterned magnetic recording layer of the magnetic recording disk. A lubrication layer is deposited on the protective layer, and bonded to the protective layer. The fill material is deposited on the lubrication layer. 
         [0009]    Another embodiment comprises an alternate method of fabricating a patterned magnetic recording disk. According to the method, a protective layer is deposited on a patterned magnetic recording layer of the disk. A fill material is deposited on the protective layer. The fill material is a polymer comprising a perfluoropolyether backbone coupled to a cross-linkable end and/or side group using a urethane linkage. The fill material is bonded to the protective layer. A removal process is performed on the fill material to planarize the magnetic disk. In some embodiments, a lubrication layer is deposited on the magnetic recording disk and bonded to the fill material. Other exemplary embodiments may be described below: 
     
    
     
       DESCRIPTION OF THE DRAWINGS 
         [0010]    Some embodiments of the present invention are now described, by way of example only, and with reference to the accompanying drawings. The same reference number represents the same element or the same type of element on all drawings. 
           [0011]      FIG. 1  is a flow chart illustrating a method of fabricating a patterned magnetic disk in an exemplary embodiment. 
           [0012]      FIG. 2  is a cross-sectional view illustrating the disk after depositing a protective layer on a patterned magnetic recording layer according to an optional step of the method of  FIG. 1 . 
           [0013]      FIG. 3  is a cross-sectional view illustrating the disk after depositing and bonding a lubrication layer on the protective layer according to optional steps of the method of  FIG. 1 . 
           [0014]      FIG. 4  is a cross-sectional view illustrating the disk after depositing a fill material on the lubrication layer according to a step of the method of  FIG. 1 . 
           [0015]      FIG. 5  is a cross-sectional view illustrating the disk after performing a removal process on the fill material according to a step of the method of  FIG. 1 . 
           [0016]      FIG. 6  is a flow chart illustrating an alternate method of fabricating a patterned magnetic recording disk in an exemplary embodiment. 
           [0017]      FIG. 7  is a cross-sectional view illustrating the disk after depositing a protective layer on a patterned magnetic recording layer according to a step of the method of  FIG. 6 . 
           [0018]      FIG. 8  is a cross-sectional view illustrating the disk after depositing and bonding a fill material on the protective layer according to steps of the method of  FIG. 6 . 
           [0019]      FIG. 9  is a cross-sectional view illustrating the disk after removing excess fill material according to an optional step of the method of  FIG. 6 . 
           [0020]      FIG. 10  is a cross-sectional view illustrating the disk after performing a removal process on the fill material according to an optional step of the method of  FIG. 6 . 
           [0021]      FIG. 11  is a cross-sectional view illustrating the disk after depositing a lubrication layer on the disk according to an optional step of the method of  FIG. 6 . 
           [0022]      FIG. 12  is a flow chart illustrating an alternate method of fabricating a patterned magnetic recording disk in an exemplary embodiment. 
           [0023]      FIG. 13  is a cross-sectional view illustrating the disk after depositing a protective layer on a patterned magnetic recording layer according to a step of the method of  FIG. 12 . 
           [0024]      FIG. 14  is a cross-sectional view illustrating the disk after depositing and bonding a lubrication layer on the protective layer according to steps of the method of  FIG. 12 . 
           [0025]      FIG. 15  is a cross-sectional view illustrating the disk after depositing a fill material on the lubrication layer according to a step of the method of  FIG. 12 . 
           [0026]      FIG. 16  is a cross-sectional view illustrating the disk after removing excess fill material according to a step of the method of  FIG. 12 . 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0027]    The figures and the following description illustrate specific exemplary embodiments of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements that, although not explicitly described or shown herein, embody the principles of the invention and are included within the scope of the invention. Furthermore, any examples described herein are intended to aid in understanding the principles of the invention, and are to be construed as being without limitation to such specifically recited examples and conditions. As a result, the invention is not limited to the specific embodiments or examples described below, but by the claims and their equivalents. 
         [0028]      FIG. 1  is a flow chart illustrating a method  100  of fabrication a patterned magnetic recording disk in an exemplary embodiment. The steps of the flow charts provided herein are not all inclusive and other steps, not shown, may be included. Further, the steps may be performed in an alternative order. 
         [0029]    Step  102  is an optional step for method  100 , which comprises depositing a protective layer on a patterned magnetic recording layer.  FIG. 2  is a cross-sectional view illustrating a patterned magnetic recording disk  202  after depositing a protective layer  204  on a patterned magnetic recording layer  206 . Protective layer  204  may include Diamond Like Carbon (DLC) or other protective layers, which act to protect a relatively soft magnetic recording layer  206  from damage. In this example, magnetic recording layer  206  is patterned on disk  202 . Thus,  FIG. 2  illustrates grooves  208  and lands  210  formed on disk  202  after a patterning process is performed on disk  202 . When a patterning process is performed, grooves  208  may be created having a depth of up to about 20 nanometers into disk  202 , as shown by depth  212 . A variation between the top of lands  210  and the bottom of groves  208  as shown by depth  212  may modulate the clearance between read/write heads (not shown) and the surface of rotating disk  202 , which degrades the quality of reading data from or writing data to disk  202 . 
         [0030]    Step  104  of  FIG. 1  is an optional step for method  100 , which comprises depositing a lubrication layer on protective layer  204 .  FIG. 3  is a cross-sectional view illustrating disk  202  after depositing a lubrication layer  302  on protective layer  204 . Lubrication layer  302  acts to lubricate a slider (not shown) when the slider contacts the surface of disk  202  (e.g., when disk  202  is not rotating). Lubrication layer  302  may have a thickness of between about 0.5 nanometers and 2 nanometers. In some embodiments, lubrication layer  302  may comprise a non cross-linkable perfluoropolyether (PFPE) polymer. PFPE polymers are a class of materials that include a PFPE backbone coupled with functional end groups (and possibly functional side groups). In some cases, the end groups (or side groups) are cross-linkable by exposing the polymer to radiation, such as Ultra-Violet (UV) radiation. When a cross linkable polymer is exposed to UV, the end groups (or side groups) interconnect or cross-link. In other cases, the end groups (or side groups) are not cross-linkable. Thus, exposing the polymer to UV wavelengths typically used for cross-linking may have little effect on the fill polymers without cross-linkable groups. In some embodiments, depositing lubrication layer  302  is performed by dip coating disk  202 . 
         [0031]    Step  106  of  FIG. 1  is an optional step for method  100 , which comprises bonding lubrication layer  302  to protective layer  204 . The bonding process may comprise exposing disk  202  to UV wavelengths that result in scission of the PFPE chains within the lubricant layer  302  to create radicals that react with the protective layer  204 . Further, the bonding process may comprise exposing disk  202  to a thermal heating process to react the functional groups of lubrication layer  302  to protective layer  204 . The bonding process does not cross-link the polymer, but rather forms strong covalent bonds between lubrication layer  302  and protective layer  204 . Step  106  is performed to prevent the removal of lubrication layer  302  from lands  210  in subsequent processing steps, discussed below. Further, performing step  106  to bond lubrication layer  302  to protective layer  204  makes it easier to remove fill material  402  from the lands  210  prior to an optional bonding step. 
         [0032]    Step  108  comprises depositing a fill material on lubrication layer  302 .  FIG. 4  is a cross-sectional view illustrating disk  202  after depositing fill material  402  on lubrication layer  302 . Fill material  402  comprises a polymer with a PFPE backbone, cross-linkable end groups (or side groups), and a urethane linkage between the PFPE backbone and the end (or side) groups. In some embodiments, the end groups (or side groups) may include di-acrylate or methyl-acrylate. Fill material  402  is deposited to overfill grooves  208  and cover lands  210  as illustrated in  FIG. 4 . In the embodiment described herein, the chemical structure of fill material  402  may be: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    where the length of the PFPE backbone may vary such that the overall molecular weight of the polymer is between about 1,000 and 10,000 atomic mass units. 
         [0033]    The urethane block is typically formed by reacting isocyanato ethyl methacrylate with the PFPE as a means of attaching the acrylate group to the polymer. The acrylate group can be made to undergo free radical polymerization with acrylate groups on adjacent polymer chains to form a cross-linked network or attachment to a media surface (e.g., lubricant layer  302 ) when exposed to UV. One advantage to adding the urethane block is that the polarity of the polymer, hence the compatibility with disk coatings, can be adjusted though the composition of the urethane block. Further compatibility can be achieved by using the appropriate acrylate subsistent R, where R is part of the chemical structure comprising 
         [0000]    
       
                 
         
             
             
         
       
     
         [0000]    and where R is chosen from a group including H and CH 3  or other linear alkyl and/or aryl groups. 
         [0034]    Another advantage to these types of PFPE-urethane-acrylate polymers is that the density after cross-linking, hence the modulus of fill material  402 , can be controlled by the molecular weight of the polyether and the number of initial hydroxyl end groups per chain. Decreasing the polyol molecular weight or increasing the hydroxyl functionality of the starting polylol (e.g., 2, 4 . . . ) increases the cross-linked modulus and decreases the elongation at break and durability. In the embodiment described herein, the step of depositing fill material  402  may comprise dip coating disk  202 . 
         [0035]    Step  110  of  FIG. 1  comprises performing a removal process on fill material  402  to planarize disk  202 .  FIG. 5  is a cross-sectional view illustrating disk  202  after performing the removal process. The removal process is used to remove fill material  402  from lands  210  between grooves  208  (e.g., to a residual thickness on lands  210  less than about 0.5 nanometers). Enough of fill material  402  is removed from grooves  208  in the removal process to render the remaining fill material  402  in grooves  208  essentially co-planar with the top of lubrication layer  302 , as shown in  FIG. 5 . Typically, the top of the remaining fill material  402  in grooves  208  protrudes less than about 1 nanometer above the surface of lubrication layer  302 , and recesses less than about 3 nanometers below the surface of lubrication layer  302 . In the embodiment described herein, a mechanical process is used to remove the excess material from disk  202 . 
         [0036]    Step  112  of  FIG. 1  is an optional step for method  100 , which comprises bonding the remaining fill material  402  to lubrication layer  302 . Disk  202  may be exposed to UV so that the end groups (or side groups) react, cross-linking the remaining fill material  402 . Some of the end groups (or side groups) may also react with lubrication layer  302  and protective layer  204 , bonding the remaining fill material  408  to the sides of grove areas  208 . An abrasive mechanical process (e.g., a chemical mechanical polishing process) or an ion based process (e.g., plasma etch) may then be performed on disk  202  to remove fill material  402  that may remain in lands  210 . 
         [0037]      FIG. 6  is a flow chart illustrating an alternate method  600  of fabricating a patterned magnetic recording disk in an exemplary embodiment. While method  100  previously described depositing a fill material on a lubrication layer bonded to a disk, method  600  will describe depositing a lubrication layer on a fill material bonded to a disk. 
         [0038]    Step  602  comprises depositing a protective layer on a patterned magnetic recording layer.  FIG. 7  is a cross-sectional view illustrating a patterned magnetic recording disk  702  after depositing a protective layer  704  on a patterned magnetic recording layer  706 .  FIG. 7  illustrates grooves  708  and lands  710 , which may be formed after patterning disk  702 . Step  604  of  FIG. 6  comprises depositing a PFPE urethane acrylate polymer with cross-linkable end groups (or side groups) similar to the polymer discussed with regard to step  108  of method  100 .  FIG. 8  is a cross-sectional view illustrating disk  702  after depositing fill material  802  on protective layer  704 . 
         [0039]    Step  606  comprises performing an optional removal process to remove excess fill material  802  before bonding fill material  802  to protective layer  704 . In some embodiments, excess fill material  802  is removed in step  606  before bonding fill material  802  to protective layer  704 . In other embodiments, excess fill material  802  is removed after bonding fill material  802  to protective layer  704 .  FIG. 9  is a cross-sectional view illustrating disk  702  after excess of fill material  802  is optionally removed in step  606 . After removing the excess fill material  802 , fill material  802  may have a thickness  902  of between about 0 and 3 nanometers on lands  710 . This may result in fill material  802  in lands  710  being essentially co-planar with fill material  802  in grooves  708  as shown in  FIG. 9 . 
         [0040]    Step  608  of  FIG. 6  comprises bonding remaining fill material  802  to protective layer  704 . Disk  702  may be exposed to UV, which cross-links fill material  802 . Some of the end groups (or side groups) also react with protective layer  704 , bonding the remaining fill material  802  to the sides of grooves  708 , and the top of lands  710 . 
         [0041]    Step  610  comprises performing an optional removal process to remove excess fill material  802  after bonding fill material  802  to protective layer  704 . As discussed with regard to step  606  above, removing excess fill material  802  may occur before step  608  or after step  608 . Further, step  610  may be performed by an ion bombardment process applied to disk  702 .  FIG. 10  is a cross-sectional view illustrating disk  702  after excess of fill material  802  is optionally removed in step  610 . 
         [0042]    Step  612  of  FIG. 6  comprises depositing an optional lubrication layer on disk  702 , which covers fill material  802  in grooves  708 , and covers protective layer  704  on lands  710 .  FIG. 11  is a cross-sectional view illustrating disk  702  after lubrication layer  1102  is optionally deposited on disk  702 . Lubrication layer  1102  may be deposited to a thickness of between about 0.5 nanometers and 2 nanometers, and may comprise non-cross linkable polymer similar to the polymer discussed with regard to step  104  of method  100 . 
         [0043]    Step  614  of  FIG. 6  is an optional step for method  600 , which comprises bonding a portion of lubrication layer  1102  to disk  702  when step  612  occurs. Bonding lubrication layer  1102  may comprise exposing disk  702  to UV or a thermal heating process. The bonding process does not cross-link the lubricant, but rather forms strong covalent bonds between lubrication layer  1102  and protective layer  704 , and also between lubrication layer  1102  and fill material  802 . Bonding lubrication layer  1102  to disk  702  may reduce the loss of lubrication layer  1102 . Typically, step  614  is controlled so that some of lubrication layer  1102  remains un-bonded, which helps maintain durability of disk  702 . 
         [0044]      FIG. 12  is a flow chart illustrating an alternate method  1200  of fabricating a patterned magnetic recording disk in an exemplary embodiment. While method  100  previously described a fabrication process whereby the top surface of fill material  402  is substantially co-planar with the top surface of lubrication layer  302  (See  FIG. 5 ), method  1200  will describe fabricating a disk such that a fill material remains on a lubrication layer after a removal process is performed on the fill material to planarize the disk. Further, the fill material of method  1200  comprises a PFPE backbone coupled with non cross-linkable functional groups. 
         [0045]    Step  1202  of  FIG. 12  comprises depositing a protective layer on a patterned magnetic recording layer.  FIG. 13  is a cross-sectional view illustrating a patterned magnetic recording disk  1302  after depositing a protective layer  1304  on a patterned magnetic recording layer  1306 .  FIG. 13  also illustrates grooves  1308  and lands  1310  formed on disk  1302  after a patterning process is performed on disk  1302 . 
         [0046]    Step  1204  of  FIG. 12  comprises depositing a lubrication layer on protective layer  1304 .  FIG. 14  is a cross-sectional view illustrating disk  1302  after depositing a lubrication layer  1402  on protective layer  1304 . Lubrication layer  1402  may comprise a non-cross linkable polymer similar to the polymer discussed with regard to step  104  of method  100  (See  FIG. 1 ). 
         [0047]    Step  1206  of  FIG. 12  comprises bonding lubrication layer  1402  to protective layer  1304 . Bonding lubrication layer  1402  may be performed in a manner similar to step  106  of method  100 . 
         [0048]    Step  1208  of  FIG. 12  comprises depositing a fill material on lubrication layer  1402 .  FIG. 15  is a cross-sectional view illustrating disk  1302  after depositing fill material  1502  on lubrication layer  302 . Fill material  1502  may comprise a non cross-linkable PFPE polymer called Demnum-Tetraol having a chemical structure of: 
         [0000]    
       
                 
         
             
             
         
       
     
         [0049]    Fill material  1502  is considered a “free” PFPE polymer in this embodiment because fill material  1502  may not be bonded to lubricant layer  1402 . Thus, fill material  1502  may readily be removed from disk  1302  by rinsing disk  1302  with a solvent. 
         [0050]    Step  1210  comprises performing a process to remove an excess of fill material  1502  to planarize disk  1302 .  FIG. 16  is a cross-sectional view illustrating disk  1302  after performing the removal process. The removal process is used to planarize fill material  1502  in lands  1310  and grooves  1308  such that a residual thickness  1602  on lands  1310  less than about 1 nanometer. In  FIG. 16 , fill material  1502  covers the underlying lubrication layer  1402  and forms a continuous planar surface on disk  1302 . In  FIG. 16 , fill material  1502  remains mobile on disk  1302 , enabling fill material  1502  to flow out onto lands  1310  and replenish loss of lubrication due to occasional head to disk contact. 
         [0051]    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.