Abstract:
A perpendicular magnetic recording (PMR) media including a non-magnetic or superparamagnetic grain isolation magnetic anisotropy layer (GIMAL) to provide a template for initially well-isolated small grain microstructure as well as improvement of K u  in core grains of a magnetic recording layer. The GIMAL composition may be adjusted to have lattice parameters similar to a bottom magnetic recording layer and to provide a buffer for reducing interface strains caused by lattice mismatch between the bottom magnetic recording layer and an underlying layer.

Description:
TECHNICAL FIELD 
     This invention relates to the field of disk drives and more specifically, to perpendicular agnetic recording media with high permeability grain boundaries. 
     BACKGROUND 
     Magnetic recording media has begun to incorporate perpendicular magnetic recording (PMR) technology in an effort to increase areal density and has recently demonstrated densities of 612 Gbits/in 2 . Generally, PMR media may be partitioned into three functional regions: a soft magnetic underlayer (SUL), a nonmagnetic intermediate layer (interlayer) and a magnetic recording layer (RL). Well-isolated smaller grains of higher magnetic anisotropy constant (K u ) for a bottom magnetic recording layer can reduce media noise to achieve these higher areal densities. Enhanced grain isolation in a bottom magnetic recording layer of a PMR media structure, for example, can provide a smaller magnetic cluster size and narrow the size distribution. 
     It has been determined experimentally that the interlayer thickness of recording media shows a strong correlation with receiver overwrite. Since 2000, constant efforts have been made by media companies and the magnetic recording community on reducing the interlayer thickness. Today the thickness of interlayers (e.g., containing Ru) can be reduced to around 10-15 nm from a previous level of around 30-40 nm. Nevertheless, experimental data also shows that a further reduction of Ru interlayer thickness may also have a negative impact on bit error rate (BER) performance due to the resultant c-axis dispersion in recording layers. Since 2005, numerous attempts have unsuccessfully been made to fabricate interlayers with either high permeability or ultra-thin Ru thickness. 
     The interlayer has several key functionalities, including introducing the magnetic layer&#39;s vertical crystal growth or textural growth so as to tightly control the sigma of the magnetic grains&#39; c-axis distribution, thereby leading to a narrow switching field distribution. Additionally, the grain size and surface morphology of the interlayer directly dictates the grain size and the grain decoupling in the recording layer. Moreover, the interlayer thickness directly impacts the head/media separation. It is well known that Ru has the same crystal structure and very similar crystal lattice parameters as CoCrPtX alloy. The use of an Ru interlayer with sufficient thickness (e.g., &gt;10 nm) may lead to a narrow c-axis distribution and a better controlling of its dome shape surface morphology. 
     In cases where the interlayer is very thin or the grain size is small, it may be impossible to obtain a very small c-axis dispersion of magnetic grains in the recording layer. Since 2005, there have been various attempts to make a multi-layer interlayer by adopting a laminated magnetic or non-magnetic interlayer structure (e.g., a CoCr(10 nm)/Ru(4.5 nm) and CoPt or CoIr(6 nm)/Ru(5 nm) stack), in order to reduce the effective thickness of the interlayer while achieving similar c-axis dispersion. 
     In view of the above, it is a challenging task to drastically reduce Ru thickness (or to replace Ru) without increasing the switching field distribution of the recording layer. More particularly, it is extremely difficult to maintain a narrow c-axis dispersion in a small grain size setting without employing a Ru interlayer having sufficient thickness. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention is illustrated by way of example, and not limitation, in the figures of the accompanying drawings in which: 
         FIG. 1  is a cross-sectional view showing a perpendicular magnetic media structure having a granular intermediate layer design in accordance with an embodiment of the invention; 
         FIG. 2  is a cross-sectional illustration depicting the perpendicular magnetic media structure of  FIG. 1 ; 
         FIG. 3  is a cross-sectional high resolution view of the perpendicular magnetic media structures of  FIG. 1 ; 
         FIG. 4  is a planar view of the granular intermediate layer of the perpendicular magnetic media structure of  FIG. 1 ; 
         FIG. 5  illustrates a method of manufacturing a perpendicular magnetic media structure in accordance with an embodiment of the present invention; and 
         FIG. 6  illustrates a disk drive including a perpendicular magnetic recording disk in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     In the following description, numerous specific details are set forth such as examples of specific, components, processes, etc. to provide a thorough understanding of various embodiment of the present invention. It will be apparent, however, to one skilled in the art that these specific details need not be employed to practice various embodiments of the present invention. In other instances, well known components or methods have not been described in detail to avoid unnecessarily obscuring various embodiments of the present invention. 
     The terms “over,” “under,” “between,” and “on” as used herein refer to a relative position of one media layer with respect to other layers. As such, for example, one layer disposed over or under another layer may be directly in contact with the other layer or may have one or more intervening layers. Moreover, one layer disposed between two layers may be directly in contact with the two layers or may have one or more intervening layers. In contrast, a first layer “on” a second layer is in contact with that second layer. Additionally, the relative position of one layer with respect to other layers is provided assuming operations are performed relative to a substrate without consideration of the absolute orientation of the substrate. 
     Some embodiments of the present invention are directed toward a perpendicular magnetic recording media having a soft magnetic underlayer (SUL), an intermediate layer (IL) disposed over the soft magnetic layer (wherein the IL includes a granular Ru structure separated by high permeability magnetic grain boundaries), and a magnetic recording layer (RL) disposed over the intermediate layer. The high permeability magnetic grain boundaries allow the IL to have a smaller effective magnetic thickness than that of a pure Ru IL having an equivalent thickness, while maintaining a limited c-axis dispersion provided by the physical thickness of the Ru grains. The intermediate layer may also be referred to herein as the “interlayer.” 
     In some embodiments, the IL includes an effective magnetic thickness of between approximately 5 nm and 10 nm. In other embodiments, the IL includes an effective magnetic thickness of less than approximately 5 nm. Additionally, in some cases the IL includes an Ru grain size of between approximately 4 nm and 10 nm. In other cases, the IL includes an Ru grain size of between approximately 5 nm and 6 nm. The IL may comprise a grain boundary thickness of between approximately 1 nm and 1.5 nm. By way pf example, the grain boundaries may be formed by co-sputtering of targets or sputtering using a composite target. In certain embodiments, the SUL includes a thin layer of Ru embedded therein having a thickness between approximately 0.8 nm and 1.2 nm. 
     Further embodiments of the invention are directed toward a media drive, comprising a head having a magneto-resistive read element, and a perpendicular magnetic recording media operatively coupled to the head. The perpendicular magnetic recording media comprises an SUL, an IL disposed over the SUL, wherein the ILyer includes a granular Ru structure separated by high permeability magnetic grain boundaries, and a magnetic RL disposed over the IL. 
     Additional embodiments of the invention are directed toward a method comprising depositing an SUL over a substrate, depositing an IL over the SUL (the IL having a granular Ru structure separated by high permeability magnetic grain boundaries), and depositing a magnetic RL over the IL. 
       FIG. 1  is a cross-sectional view of a PMR media structure  100  including a non-magnetic intermediate layer (interlayer)  120  disposed between a soft magnetic underlayer SUL  110  and a magnetic recording layer (RL)  150 , in accordance with an embodiment of the present invention. It will be appreciated by those of ordinary skill in the art that the layers discussed herein may be formed on both sides of substrate  101  to form a double-sided magnetic recording disk. However, only the layers on a single side of substrate  101  are shown for ease of illustration. Alternatively, a single sided perpendicular magnetic recording disk may be formed. 
     The embodiment of  FIG. 1  features an interlayer  120  having a reduced effective magnetic thickness, while the Ru thickness is kept at a normal level in order to maintain the narrow c-axis dispersion in the media recording layer. As used herein, the term “effective magnetic thickness,” t eff , is the physical thickness of the interlayer with average volumetric magnetization M S  (Int), normalized to the magnetization of the soft magnetic underlayer M S  (SUL), such that 
               t   eff     =       t   ⁡     (     1   -       M   S   Int       M   S   SUL         )       .           
The average volumetric magnetization of the interlayer  120  is the total magnetic moment of the interlayer stack structure, divided by its total volume.
 
     The proposed approach for reducing the effective magnetic thickness of the interlayer  120  may enable an effective IL thickness as low as 2-3 nm. As set forth above, the IL  120  may comprise an effective magnetic thickness of between 5 nm and 10 nm. In other configurations, the IL  120  includes an effective magnetic thickness of less than 5 nm. It should be noted that the current industry standard for effective magnetic thickness is approximately 15-20 nm. 
     As depicted in  FIG. 1 , the PMR media structure  100  further includes substrate  101 . Substrate  101  may comprise, for example, a glass, a metal, and/or a metal alloy material. In a particular embodiment, the substrate  101  is disk-shaped or annular. Glass substrates that may be used include, for example, a silica containing glass such as borosilicate glass and aluminosilicate glass. Metal and metal alloy substrates that may be used include, for example, aluminum (Al) and aluminum magnesium (AlMg) substrates, respectively. In an alternative embodiment, other substrate materials such as polymers and ceramics may be used. Substrate  101  may also be plated with a nickel phosphorous (NiP) layer (not shown). The substrate surface (or the plated NiP surface) may be polished and/or textured. Substrates and seed layers are known in the art and accordingly a more detailed discussion is not provided. 
     Disposed over the substrate  101  is an SUL  110 . Generally, the SUL  110  may include any materials known in the art. In one exemplary embodiment, the SUL  110  includes a synthetic antiferromagnet (SAF) structure comprising two soft ferromagnetic layers (e.g., CoTaZr or CoFeTaZr, etc.) antiferromagnetically coupled with one another across a spacer layer (e.g., Ru, Re, Rh, Ir) disposed there between. A seed layer  115  is disposed over the SUL  110 , and the interlayer  120  is disposed over the seed layer  115 . Alternative embodiments do not feature the use of a seed layer between the SUL  110  and the interlayer  120 . 
     As depicted in  FIG. 1 , the magnetic recording layer  150 , including one or more layers, is disposed over the interlayer  120 . The magnetic recording layer  150  may be any suitable thickness, with an exemplary thickness between 5 nm and 20 nm. 
     Completing the magnetic media structure depicted in  FIG. 1 , one or more layers may be formed on top of the magnetic recording layer  150 . For example, an overcoat (OC) may be applied on top of the top magnetic recording layer to meet tribological requirements such as contact-start-stop (CSS) performance and corrosion protection. Predominant materials for the overcoat layer are carbon-based materials, such as hydrogenated or nitrogenated carbon to form a carbon over coat (COC)  160 . A lubricant may be placed (e.g., by dip coating, spin coating, etc.) on top of the overcoat layer to further improve tribological performance. Exemplary lubricants include perfluoropolyether or phosphazene lubricant. 
       FIG. 2  is a cross-sectional view of the interlayer  120  and SUL  110  of the PMR media structure  100  of  FIG. 1 . In particular, the Ru intermediate layer  120  includes magnetic grain boundaries  210  and has an ultra-thin effective magnetic thickness. The grain core consists of the hcp Ru and the grain boundaries are made from magnetic materials having high permeability. In some embodiments, the IL  120  includes an Ru grain size of between approximately 4 nm and 10 nm. In other embodiments, the IL  120  includes an Ru grain size of between approximately 5 nm and 6 nm. The grain boundary thickness may be between approximately 1 nm and 1.5 nm, while the Ru layer thickness may be about 15 nm. The grain boundaries may be formed by a co-sputtering process using CoPt, CoIr, CoCr, CoRu, CoO, NiO, Eu Ru 2 O 7 , or Fe 2 O 3 . In the illustrated embodiment, the SUL includes a thin layer of Ru embedded therein having a thickness between approximately 0.8 nm and 1.2 nm. 
     With further reference to  FIG. 2 , the composite intermediate layer  120  for PMR media may be formed using a co-sputtering process, wherein the grain boundaries  210  comprise magnetic materials with high permeability, thereby providing the non-resistance path for magnetic flux path for the writing process. The illustrated vertically laminated IL  120  with magnetic grain boundaries  210  can achieve ultra-thin effective magnetic thickness, ultra-small c-axis dispersion, and ultra-small grain size. By tailing both the grain size and the thickness of the grain boundaries  210 , both very good c-axis dispersion and very small magnetic flux path for the writing process may be achieved. 
       FIG. 3  is a cross-sectional high resolution view of the perpendicular magnetic media structure  100  of  FIG. 1 , showing the recording layer  150  disposed on top of the composite Ru interlayer  120  disposed on top of the SUL  110 .  FIG. 4  is a planar view of the granular Ru intermediate layer  120  of the perpendicular magnetic media structure  100  of  FIG. 1 , wherein the Ru IL  120  includes high permeability grain boundaries  210  (e.g., CoRu or Coir). 
       FIG. 5  illustrates one embodiment of a method  500  of manufacturing perpendicular magnetic recording disk  100  having a media structure such as described herein. A substrate  101  is generated, or otherwise provided, at operation  510 . The generation of a substrate for a magnetic recording disk is known in the art; accordingly a detailed discussion is not provided. In one embodiment, the substrate  101  may be plated (e.g., with NiP) and may also be polished and/or textured prior to subsequent deposition of layers. 
     In operation  520 , the SUL  110  is deposited over substrate  101 . Operation  530  comprises the deposition of the seed layer  115  on the SUL  110 . In operation  540 , the IL  120  is deposited over the seed layer  115 . At operation  550 , the magnetic recording layer  150  is deposited on the IL  120 . In particular embodiments, deposition of the recording layer  150  may include depositing a bottom magnetic recording layer on the IL  120  and depositing one or more capping layers over the bottom magnetic recording layer. In an embodiment, the magnetic recording layer  150  is deposited with a reactive sputtering process where oxygen (O 2 ) is introduced into the sputtering chamber. The amount of O 2  provided during deposition may vary depending on the target alloy composition, thickness of the magnetic recording layer and deposition system configuration, etc 
     In operation  550 , the sputter target alloy composition may be any capable of achieving the compositions described elsewhere herein for the magnetic recording layer  150 . Operation  560  completes the method  500  with a deposition of a protection layer, such as the COC  160 . 
     The deposition of each of the SUL  110 , seed layer  115 , IL  120 , recording layer  150  and the protection layer can be accomplished by a variety of methods well known in the art, for example, electroless plating, sputtering (e.g., static or in-line), chemical vapor deposition (CVD), ion-beam deposition (IBD), etc. Static sputter systems are available from manufacturers such as Intevac Inc. of Santa Clara, Calif. and Canon-Anelva Corp. of Japan. With in-line sputtering systems, disk substrates are loaded on a pallet that passes through a series of deposition chambers the deposit films successively on substrates. In-line sputtering systems are available from manufacturers such as Ulvac Corp. of Japan. 
       FIG. 6  illustrates a disk drive having disk  100 . Disk drive  600  may include one or more disks  100  to store datum. Disk  100  resides on a spindle assembly  660  that is mounted to drive housing  680 . Data may be stored along tracks in the magnetic recording layer of disk  100 . The reading and writing of data is accomplished with head  650  that has both read and write elements. The write element is used to alter the properties of the perpendicular magnetic recording layer of disk  100 . In one embodiment, head  650  may have a magneto-resistive (MR) and, in particular, a giant magneto-resistive (GMR) read element and an inductive write element. In an alternative embodiment, head  650  may be another type of head, for example, an inductive read/write head or a Hall effect head. A spindle motor (not shown) rotates spindle assembly  660  and, thereby, disk  100  to position head  650  at a particular location along a desired disk track. The position of head  650  relative to disk  100  may be controlled by position control circuitry  670 . The use of disk  100  fabricated in the manners discussed above may improve the performance of the perpendicular magnetic recording layer of disk  100 . 
     In the foregoing specification, embodiments of the invention have been described with reference to specific exemplary features thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the appended claims. The specification and figures are, accordingly, to be regarded in an illustrative rather than a restrictive sense.