Patent Publication Number: US-2010110584-A1

Title: Dual oxide recording sublayers in perpendicular recording media

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to perpendicular magnetic recording media, including continuous and patterned recording media, and more particularly to apparatus and methods for using oxides in sublayers of the recording layer. 
     2. Description of the Related Art 
     Hard-disk drives provide data storage for data processing systems in computers and servers, and are becoming increasingly pervasive in media players, digital recorders, and other personal devices. Advances in hard-disk drive technology have made it possible for a user to store an immense amount of digital information on an increasingly small disk, and to selectively retrieve and alter portions of such information almost instantaneously. Particularly, recent developments have simplified hard-disk drive manufacture while yielding increased track densities, thus promoting increased data storage capabilities at reduced costs. 
     In a hard-disk drive, rotating high precision media including an aluminum or glass disk that is coated on both sides with thin films designed to store information in the form of magnetic patterns. Electromagnetic read/write heads suspended or floating only fractions of micro inches above the disk are used to either record information onto the thin film media, or read information from it. 
     A read/write head may write information to the disk by creating an electromagnetic field to orient a cluster of magnetic grains, known as a bit, in one direction or the other. In longitudinal magnetic recording media applications, a magnetic recording layer has a magnetic c-axis (or easy axis) parallel to the disk plane. As the Hard-Drive industry is transitioning to perpendicular recording technology, adjustments are being made to adapt the disk media so that the magnetic easy axis (crystallographic c-axis) of the cobalt alloy recording layers grow perpendicular to the disk plane. Hexagonal Close Packed (HCP) cobalt alloys are typically used as a magnetic recording layer for perpendicular recording. Most media manufacturers now rely on a cobalt alloy with the incorporation of an oxide segregant to promote the formation of small and uniform grains. 
     To read information, magnetic patterns detected by the read/write head are converted into a series of pulses which are sent to the logic circuits to be converted to binary data and processed by the rest of the system. To write information, a write element located on the read/write head generates a magnetic write field that travels vertically through the magnetic recording layer and returns to the write element through a soft underlayer. In this manner, the write element magnetizes vertical regions, or bits, in the magnetic recording layer. Because of the easy axis orientation, each of these bits has a magnetization that points in a direction substantially perpendicular to the media surface. To increase the capacity of disk drives, manufacturers are continually striving to reduce the size of bits and the grains that comprise the bits. 
     The ability of individual magnetic grains to be magnetized in one direction or the other, however, poses problems where grains are extremely small. The superparamagnetic effect results when the product of a grain&#39;s volume (V) and its anisotropy energy (K u ) fall below a certain value such that the magnetization of that grain may flip spontaneously due to thermal excitations. Where this occurs, data stored on the disk is corrupted. Thus, while it is desirable to make smaller grains to support higher density recording with less noise, grain miniaturization is inherently limited by the superparamagnetic effect. To maintain thermal stability of the magnetic grains, material with high K u  may be used for the magnetic layer. However, material with a high K u  requires a stronger magnetic field to reverse the magnetic moment. Thus, the ability of the write head to write on magnetic material may be reduced where the magnetic layer has a high K u  value. 
     The perpendicular magnetic recording medium is generally formed with a substrate, a soft magnetic underlayer (SUL), an interlayer, an exchange break layer, a perpendicular magnetic recording layer, and a protective layer for protecting the surface of the perpendicular magnetic recording layer. The performance of the recording layer is important for efficient recording. 
     Accordingly, a need exists for a practical, attainable apparatus, system, and method for improving the perpendicular magnetic recording layer. Beneficially, such an apparatus, system and method would increase the recording performance of the system. Such apparatuses, systems and methods are disclosed and claimed herein. Further, the perpendicular magnetic recording layers should be able to resist corrosion. 
     SUMMARY OF THE INVENTION 
     The present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by currently available apparatus, systems and methods. Accordingly, the present invention has been developed to provide apparatus, system and methods for improving the performance of the perpendicular magnetic recording layer. 
     Embodiment in accordance with the invention for a recording medium for perpendicular recording applications includes a soft magnetic underlayer deposited on a nonmagnetic substrate and a perpendicular magnetic recording layer deposited below an overcoat layer. Further, an exchange break layer is generally located between the soft magnetic underlayer and the perpendicular magnetic recording layer. The perpendicular recording layer includes a plurality of sublayers. 
     In certain embodiments, the magnetic recording layer consists of two sublayers: one oxide sublayer and one non-oxide sublayer. In other embodiments, a non-oxide sublayer or an exchange control sublayer is added to the two sublayers of the magnetic recording layer. In still another embodiment, both a non-oxide sublayer and an exchange control sublayer are added to the two sublayers of the magnetic recording layer. 
     In a specific embodiment, a bottom sublayer of the two oxide sublayers includes two segregants. These segregants are Ta and B. Ta can be added to this bottom sublayer in amounts between 1 at. % and 5 at. % and preferably between 2 at. % and 3 at. %. B can be added to this bottom sublayer in amounts between 4 at. % and 10 at. % and preferably between 5 at. % and 7 at. %. Together, the Ta and B concentration in this bottom sublayer can be between 5 at. % and 15 at. % and preferably between 7 at. % and 10 at. %. The use of Ta as a segregant in a magnetic recording sublayer is advantageous because it promotes Cr segregation at the magnetic grain boundaries. The further addition of B reduces grain size and enhances grain boundary segregation by forming of a CrB alloy at the grain boundaries. 
     In another specific embodiment, a bottom sublayer of the two oxide sublayers includes two segregants. These segregants are Ta 2 O 5  and SiO 2 . Ta 2 O 5  can be added to this bottom sublayer in amounts between 0.5 molecular % and 3 molecular % and preferably between 1 molecular % and 1.5 molecular %. SiO 2  can be added to this bottom sublayer in amounts between 2 molecular % and 10 molecular % and preferably between 4 molecular % and 8 molecular %. Together, the Ta 2 O 5  and SiO 2  concentration in this bottom sublayer can be between 2.5 molecular % and 13 molecular % and preferably between 4 molecular % and 10 molecular %. The use of dual Ta 2 O 5  and SiO 2  enhances intergranular decoupling in the magnetic layer at relatively low total segregant content for better magnetic and corrosion properties. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In order that the advantages of the invention will be readily understood, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments that are illustrated in the appended drawings. Understanding that these drawings depict only typical embodiments of the invention and are not therefore to be considered to be limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings, in which: 
         FIG. 1  is a schematic of a hard-disk drive; 
         FIG. 2  is a cross-section view of the layers of a perpendicular recording media in accordance with one embodiment of the present invention; 
         FIG. 3  is a view of one embodiment of a perpendicular recording media including a detailed view of the sublayers of the magnetic recording layer; 
         FIG. 4  is a view of a second embodiment of a perpendicular recording media including a detailed view of the sublayers of the magnetic recording layer; 
         FIG. 5  is a view of a third embodiment of a perpendicular recording media including a detailed view of the sublayers of the magnetic recording layer; 
         FIG. 6  is a graph of the relation between EBL thickness and jitter for three different experimental media; 
         FIG. 7  is a graph of overcoat thickness versus anodic current at 1V of an experimental media; and 
         FIGS. 8   a  and  8   b  are diagrams of two media structures. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference throughout this specification to “one embodiment,” “an embodiment,” or similar language means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases “in one embodiment,” “in an embodiment,” and similar language throughout this specification may, but do not necessarily, all refer to the same embodiment. 
     Furthermore, the described features, structures, or characteristics of the invention may be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are disclosed to provide a thorough understanding of embodiments of the present invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth. In other instances, well-known structures, materials, or operations are not shown or described in detail to avoid obscuring aspects of the invention. 
     Referring now to  FIG. 1 , a diagram of a conventional hard-disk drive assembly  100  is shown. A hard-disk drive assembly  100  generally comprises a plurality of hard disks comprising a perpendicular magnetic recording media  102 , rotated at high speeds by a spindle motor (not shown) during operation. The perpendicular magnetic recording media  102  will be more fully described herein. Concentric data tracks  104  formed on either or both disk surfaces receive and store magnetic information. 
     A read/write head  110  may be moved across the disk surface by an actuator assembly  106 , allowing the head  110  to read or write magnetic data to a particular track  104 . The actuator assembly  106  may pivot on a pivot  114 . The actuator assembly  106  may form part of a closed loop feedback system, known as servo control, which dynamically positions the read/write head  110  to compensate for thermal expansion of the perpendicular magnetic recording media  102  as well as vibrations and other disturbances. Also involved in the servo control system is a complex computational algorithm executed by a microprocessor, digital signal processor, or analog signal processor  116  that receives data address information from an associated computer, converts it to a location on the perpendicular magnetic recording media  102 , and moves the read/write head  110  accordingly. 
     Specifically, read/write heads  110  periodically reference servo patterns recorded on the disk to ensure accurate head  110  positioning. Servo patterns may be used to ensure a read/write head  110  follows a particular track accurately, and to control and monitor transition of the head  110  from one track  104  to another. Upon referencing a servo pattern, the read/write head  110  obtains head position information that enables the control circuitry  116  to subsequently re-align the head  110  to correct any detected error. 
     Servo patterns may be contained in engineered servo sectors  112  embedded within a plurality of data tracks  104  to allow frequent sampling of the servo patterns for optimum disk drive performance. In a typical perpendicular magnetic recording media  102 , embedded servo sectors  112  extend substantially radially from the perpendicular magnetic recording media  102  center, like spokes from the center of a wheel. Unlike spokes however, servo sectors  112  form a subtly arc-shaped path calibrated to substantially match the range of motion of the read/write head  110 . 
       FIG. 2  is a cross-sectional view of a typical perpendicular magnetic recording media  102 . The layers shown in  FIG. 2  may be deposited on a substrate  202  or on an adhesion layer  204  previously deposited on the substrate  202 . The layers may include a soft underlayer (SUL)  206  an exchange break layer  208  (EBL), a perpendicular magnetic recording layer  210  and an overcoat  212 . The perpendicular magnetic recording media  102  may include other layers not shown in  FIG. 2 . Similarly, one skilled in the art will recognize that some of the layers illustrated in  FIG. 2  may be omitted in certain embodiments. 
     The platter or substrate  202  may comprise an AlMg or glass platter which provides a rigid support structure upon which the recording media is deposited. In certain embodiments ion beam deposition or magnetron sputtering may be utilized to deposit the various layers comprising the perpendicular magnetic recording media  102 . 
     In one embodiment, the first layer deposited on substrate  202  is an adhesion layer  204 . The adhesion layer  204  may comprise an AlTi layer to aid in the adhesion of subsequent layers. In certain embodiments the adhesion layer  204  may be omitted and a soft underlayer  206  may be deposited directly on the substrate  202 . The material comprising the soft underlayer  206  is a soft, magnetic alloy. In certain embodiments the material comprising the soft underlayer  206  may be CoFeTaZr. 
     The soft underlayer  206  may also be formed as an antiferromagnetic structure. A coupling layer may be disposed between two the soft underlayers to antiferromagnetically couple the two soft underlayers. The antiferromagnetic structure may be used to reduce magnetic signals originating from the soft underlayers where such signals are undesirable in the perpendicular magnetic recording media  102 . 
     Above the soft underlayer  206  an exchange break layer  208  may be added. The exchange break layer helps to prevent the soft underlayer  206  from magnetically coupling to the magnetic recording layer  210 . 
     The magnetic recording medium  102  also includes a magnetic recording layer above the exchange break layer  210 , to store data. The magnetic recording layer  210  may include thin films with a plurality of magnetic grains, each grain having a magnetic easy axis substantially perpendicular to the media surface. This allows the grains to be vertically magnetized. The magnetic grains may comprise a magnetic material such as CoPt or CoPtCr or CoPtCrB. To maintain a highly segregated magnetic layer, one or more segregants may be added to the magnetic material. 
     Above the magnetic recording layer  210  is a protective layer  212 . The protective layer is generally made of a carbon bilayer, the bottom layer being CHx and the top layer being CNx. The protective layer both mechanically protects the magnetic recording layer  210  as well as prevents corrosion of the magnetic recording layer  210 . 
     The magnetic recording layer  210  can be configured in many different arrangements.  FIGS. 3-5  describe three possible arrangement of the magnetic recording layer  210 .  FIG. 3  shows a media with magnetic recording layer  210  having two sublayers  302  and  308 . The bottom sublayer  302  includes an oxide while the top sublayer  308  does not include an oxide. In addition, various layers can be introduced between sublayer  302  and sublayer  308  to improve the performance of the media. Sublayer  308  is generally a CoPtCr alloy. 
       FIG. 4  describes a second possible arrangement for magnetic recording layer  210 . In this arrangement, an exchange control layer (ECL)  306  is placed between the oxide sublayer  302  and the non-oxide sublayer  308  of the magnetic recording layer  210 . The ECL  306  may be formed of Co alloys including Ru, Cr, Pt and/or B. The ECL  306  provides for a reduction of interfacial exchange coupling strength between the oxide sublayer  302  and the non-oxide sublayer  308 . 
       FIG. 5  describes a third possible arrangement for the magnetic recording layer  210 . In this arrangement, a second oxide sublayer  304  is located between ECL  306  and oxide sublayer  302 . The advantage of the second oxide layer is to enhance corrosion resistance and to adjust magnetic and recording properties of the PMR media. 
     Oxide sublayer  302  may be made of an alloy of CoPtCrTa 2 O 5 B 2 O 3  or CoPrCrTa 2 O 5 SiO 2 . Both of these materials are advantageous as oxide sublayer  302 . 
     In an embodiment of the media having an oxide sublayer  302  made of an alloy of CoPtCrTa 2 O 5 B 2 O 3 , specific amounts of Ta and B can be advantageous. Ta can be added to this bottom oxide sublayer  302  in amounts between 1 at. % and 5 at. % and preferably between 2 at. % and 3 at. %. B can be added to this bottom oxide sublayer  302  in amounts between 4 at. % and 10 at. % and preferably between 5 at. % and 7 at. %. Together, the Ta and B concentration in this bottom sublayer can be between 5 at. % and 15 at. % and preferably between 7 at. % and 10 at. %. Generally, the concentrations in the bottom oxide sublayer  302  of Pt will be around from 14-20 at. % and of Cr will be around 12-25 at. %. Generally, the remainder of the bottom oxide sublayer will be Co, however, other materials may be added to the alloy as well. Further, the bottom oxide sublayer  302  with Ta and B has a thickness between 6 and 16 nm. 
     An advantage of using a CoPtCrTa 2 O 5 B 2 O 3  alloy as a bottom oxide sublayer  302  is that it allows for a thinner EBL  208 .  FIG. 6  shows the relation between EBL thickness and jitter for the three different media configured as described in  FIG. 3 . The first media  601  has a bottom oxide sublayer  302  of Ta and B. The second media  602  includes a segregant with an alloy of CoPtCrSiO 2  as the bottom sublayer  302  and has no non-oxide layer  308 . The third media  603  includes and alloy of CoPtCrSiO 2  as the bottom sublayer  302  and has no non-oxide layer  308 . As can be seen from the graph, the first media  601  has superior jitter performance. Further, the jitter performance increases as the EBL  208  is thinned. Therefore, it is possible to use an EBL of 13 nm, or even smaller with this embodiment. Since the EBL is generally made from an expensive material, Ru, it is beneficial to be able to incorporate a thinner Ru EBL into magnetic media. 
     A second advantage of using a CoPtCrTa 2 O 5 B 2 O 3  alloy as a bottom oxide sublayer  302  is that it allows for a thin protective layer  212 .  FIG. 7  is a graph of overcoat thickness versus anodic current at 1V. This test is used to determine the susceptibility of the media to corrosion. As can be seen from the graph, the media becomes far less susceptible to corrosion with an overcoat of only 17 angstroms, whereas a media with a bottom oxide sublayer  302  of CoPtCrTa 2 O 5  will need a 25 A of overcoat in order to achieve the same degree of protection. Since thinner overcoats tend to provide better recording and readback performance, it is preferable that the overcoat be less than 25 angstroms or even 20 angstroms. 
     In an embodiment of the media having an oxide sublayer  302  made of an alloy of CoPtCrTaOSiO. Ta 2 O 5  can be added to this-bottom oxide sublayer  302  in amounts between 0.5 molecular % and 3 molecular % and preferably between 1 molecular % and 1.5 molecular %. SiO 2  can be added to this bottom oxide sublayer  302  in amounts between 2 molecular % and 10 molecular % and preferably between 4 molecular % and 8 molecular %. Together, the Ta 2 O 5  and SiO 2  concentration in this bottom oxide sublayer  302  can be between 2.5 molecular % and 13 molecular % and preferably between 4 molecular % and 10 molecular %. The thickness of oxide sublayer  302  is preferably between 6.75 nm and 7.5 nm and generally between 4 nm and 15 nm. 
     An advantage of using oxide sublayer  302  made of an alloy of CoPtCrTa 2 O 5 SiO 2  is that it improves 2TS0NR, 2TSNR, OW, T50 and jitter. Two media, media  1  and media  2 , similar in construction to those of  FIG. 5  were tested. The difference between the two media was Ta being added as a second oxide to the oxide sublayer  302  of the second media.  FIG. 8   a  is a diagram of media  1  and  FIG. 8   b  is a diagram of media  2 . Table 1 below shows the results of testing the-two media showing the superiority of the dual oxide media. 
     
       
         
           
               
               
               
               
               
               
             
               
                   
                 TABLE 1 
               
               
                   
                   
               
               
                   
                 2TS0NR 
                 2TSNR 
                 OW 
                 T50 
                 Jitter 
               
               
                   
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
               
               
               
            
               
                   
                 Media 1 
                 29.5 
                 22.0 
                 32.6 
                 32.3 
                 2.32 
               
               
                   
                 Media 2 
                 29.9 
                 22.5 
                 35.0 
                 30.8 
                 2.26 
               
               
                   
                   
               
            
           
         
       
     
     The media is manufactured in a sputtering device with several chambers. In each chamber, one or more of the layers is sputtered one on top of the other over a substrate. The chambers include at least one sputter target with the elements of the layer that is to be sputtered. In addition, the chambers include gases, such as oxygen, that can affect the composition of the sputtered layers. Lastly, the pressures in the chambers can be altered to affect the composition and properties of the various sputtered layers. 
     As an example, a substrate is sent into a first sputter chamber. In this first sputter chamber, an adhesion layer of AlTi is sputtered onto the substrate. The substrate is then passed to a second sputter chamber where a SUL layer of CoZrFeTa is sputtered onto the substrate. Next, the substrate is passed to a third sputter chamber where a EBL layer of Ru is sputtered onto the substrate. The substrate is then passed to successive sputter chambers to sputter the various sublayers of the magnetic recording layer and then the carbon overcoat layer. Lastly, lubricant is added to the substrate generally through a dipping process. 
     The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.