Abstract:
Perpendicular magnetic recording media and methods of fabricating perpendicular magnetic recording media are described. The perpendicular magnetic recording medium of one embodiment includes a soft magnetic underlayer (SUL), an interlayer, and a perpendicular magnetic recording layer. The interlayer comprises a layer formed from a first material (e.g., NiWCr) having a face-centered-cubic (FCC) structure, a layer formed from a second material (e.g., Cr) having a body-centered-cubic (BCC) structure, and a layer formed from a third material (e.g., Ru) having a hexagonal-close-packed (HCP) structure.

Description:
RELATED APPLICATIONS 
     This patent application is a continuation-in-part of a co-pending patent application having the Ser. No. 11/681,693, which was filed on Mar. 2, 2007, and is incorporated by reference as if fully provided herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is related to the field of magnetic disk drive systems and, in particular, to a perpendicular magnetic recording medium having an interlayer formed from multiple layers. More particularly, the interlayer is formed from a layer of FCC material (e.g., NiWCr), a layer of BCC material (e.g., Cr), and a layer of HCP material (e.g., Ru). 
     2. Statement of the Problem 
     One type of recording medium presently used in magnetic recording/reproducing apparatuses is a longitudinal magnetic recording medium. A longitudinal magnetic recording medium includes a magnetic recording layer having an easy axis of magnetization parallel to the substrate. The easy axis of magnetization is the crystalline axis that is aligned along the lowest energy direction for the magnetic moment. Another type of recording medium is a perpendicular magnetic recording medium. A perpendicular magnetic recording medium includes a magnetic recording layer having an easy axis of magnetization oriented substantially perpendicular to the substrate. Hexagonal-close-packed (HCP) Co-alloys are typically used as the magnetic recording layer for both longitudinal and perpendicular recording. The easy axis of magnetization for these materials lies along the c-axis or &lt;0001&gt; direction. 
     The perpendicular magnetic recording medium is generally formed with the following layers on a substrate, a soft magnetic underlayer (SUL), an interlayer, a perpendicular magnetic recording layer, and a protective layer for protecting the surface of the perpendicular magnetic recording layer. The soft magnetic underlayer (SUL) serves to concentrate a magnetic flux emitted from a main pole of a write head and to serve as a flux return path back to a return pole of the write head during recording on the magnetic recording layer. The interlayer serves to control the size of magnetic crystal grains and the orientation of the magnetic crystal grains in the magnetic recording layer. The interlayer also serves to magnetically de-couple the SUL and the magnetic recording layer. 
     The interlayer may be formed from a single layer of material, such as a layer of Ru that has an HCP structure. The interlayer may alternatively be formed from multiple layers. For example, a common interlayer comprises a layer of Ru formed on a seed layer, such as Ta, NiFe, NiW, etc. The seed layer is commonly formed from a face-centered-cubic (FCC) material with the layer of Ru (having the HCP structure) formed on the FCC material. One particular interlayer comprises a seed layer of NiW or another Ni-based alloy, a first layer of Ru deposited at a lower pressure, and a second layer of Ru deposited at a higher pressure. 
     One problem with many present interlayers for perpendicular magnetic recording media is that they include significant amounts of Ru, which is an HCP material. The thickness of Ru in a common interlayer can reach 200 Å or more. As the cost of Ru and other HCP materials increases, the cost of fabricating perpendicular magnetic recording media unfortunately also increases. 
     SUMMARY OF THE SOLUTION 
     Embodiments of the invention solve the above and other related problems with an interlayer of a perpendicular magnetic recording medium that includes less Ru (or other HCP material) than present interlayers. The interlayer as provided herein is formed from multiple layers including a layer formed from a face-centered-cubic (FCC) material (e.g., NiWCr), a layer formed from a body-centered-cubic (BCC) material (e.g., Cr), and a layer formed from a hexagonal-close-packed (HCP) material (e.g., Ru). The BCC material advantageously replaces some of the HCP material in the interlayer without affecting performance. Because the BCC material has a lower cost than the HCP material, such as Ru, perpendicular magnetic recording media may be fabricated at a lower cost without degrading performance. The addition of some BCC materials, such as Cr, may also help with corrosion resistance in the media. 
     One embodiment comprises an interlayer of perpendicular magnetic recording media. The interlayer includes a first layer formed from a first material having a FCC structure. The interlayer also includes a second layer formed from a second material having a BCC structure. The interlayer also includes a third layer formed from a third material having a HCP structure. The BCC material in the interlayer replaces some of the HCP material without degrading performance. At the same time, the BCC material, such as Cr, is less expensive than an HCP material, such as Ru, which allows for more cost effective fabrication of perpendicular magnetic recording media. 
     In another embodiment, a perpendicular magnetic recording medium includes, among other layers, a soft magnetic underlayer (SUL), an interlayer, and a perpendicular magnetic recording layer. The interlayer includes a FCC layer, a BCC layer, and a HCP layer. In one particular example of the interlayer, the FCC layer is formed from a Ni-based material (e.g., NiWCr), the BCC layer is formed from a Cr-based material (e.g., Cr), and the HCP layer is formed from a Ru-based material (e.g., Ru). 
     The invention may include other exemplary embodiments described below, such as associated methods of fabricating perpendicular magnetic recording media. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       The same reference number represents the same element or same type of element on all drawings. 
         FIG. 1  illustrates a magnetic disk drive system in an exemplary embodiment. 
         FIG. 2  is a cross-sectional view of one exemplary embodiment of a perpendicular magnetic recording medium. 
         FIG. 3  is a cross-sectional view illustrating one exemplary embodiment of an interlayer. 
         FIG. 4  is a cross-sectional view illustrating another exemplary embodiment of an interlayer. 
         FIG. 5  is a cross-sectional view illustrating another exemplary embodiment of an interlayer. 
         FIG. 6  is a flow chart illustrating one exemplary method of fabricating a perpendicular magnetic recording medium. 
         FIG. 7  is a flow chart illustrating another exemplary method of fabricating a perpendicular magnetic recording medium. 
         FIG. 8  is a graph illustrating the performance of a perpendicular magnetic recording medium using an interlayer as provided herein. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1-8  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. 
       FIG. 1  illustrates a magnetic disk drive system  100  in an exemplary embodiment of the invention. Magnetic disk drive system  100  includes a spindle  102 , a perpendicular magnetic recording medium  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 perpendicular magnetic recording medium  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 perpendicular magnetic recording medium  104 . Magnetic disk drive system  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. 
     When perpendicular magnetic recording medium  104  rotates, an air flow generated by the rotation of magnetic disk  104  causes an air bearing surface (ABS) of recording head  114  to ride on a cushion of air at a particular height above magnetic disk  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 perpendicular magnetic recording medium  104 . 
     The perpendicular magnetic recording medium  104  is shown as a disk in  FIG. 1 . However, a perpendicular magnetic recording medium as discussed can take on other forms in other embodiments. 
       FIG. 2  is a cross-sectional view illustrating one exemplary embodiment of perpendicular magnetic recording medium  104 . Perpendicular magnetic recording medium  104  includes a soft magnetic underlayer (SUL)  205 , an interlayer  210 , and a perpendicular magnetic recording layer  215 . The layers shown in  FIG. 2  may be deposited on a substrate (not shown) or on multiple other layers (not shown) previously deposited on a substrate. Perpendicular magnetic recording medium  104  may include other layers not shown in  FIG. 2 , such as a cap layer, an overcoat layer, etc. For instance, a cap layer may be formed on perpendicular magnetic recording layer  215  from a material such as CoPtCrB. An overcoat layer may be formed on the cap layer to protect perpendicular magnetic recording layer  215  against damage if the recording head happens to contact the perpendicular magnetic recording medium  104 . 
     SUL  205  acts in conjunction with the write head to increase the perpendicular field magnitude and improve the field gradient generated by the write head passing over the perpendicular magnetic recording medium  104 . SUL  205  may be formed from CoFeTaZr or another type of material. Interlayer  210  controls the orientation and grain diameter of perpendicular magnetic recording layer  215 , and also acts to de-couple SUL  205  and perpendicular magnetic recording layer  215 . Perpendicular magnetic recording layer  215  comprises one or more materials that have an easy axis of magnetization oriented substantially perpendicular to the substrate. Perpendicular magnetic recording layer  215  is typically formed from a Co-alloy and may contain elements such as Cr and Pt as well as oxides such as SiO 2 . One example of perpendicular magnetic recording layer  215  comprises CoPtCr—SiOx. 
     In this embodiment, interlayer  210  is formed from multiple layers of material having different crystallographic structures.  FIG. 3  is a cross-sectional view illustrating one exemplary embodiment of interlayer  210 . In  FIG. 3 , interlayer  210  includes a first layer  301  formed from a material having a FCC structure, such as a FCC(111) structure. The material forming the first layer  301  may be a Ni-based material having the FCC structure, examples of which are NiW, NiCr, NiWCr, NiFeCr, and NiFeW. A Ni-based material means any material solely or partially formed from Ni. The first layer  301  may have a thickness of about 5-10 nanometers. 
     Interlayer  210  also includes a second layer  302  formed from a material having a BCC structure, such as a BCC(110) structure. The material forming the second layer  302  may be a Cr-based material having the BCC structure, examples of which are Cr, CrMo, CrV, CrTi, CrW, CrMoB, CrMoC, CrMoSe, CrTi, CrV, and MoCr. A Cr-based material means any material solely or partially formed from Cr. The second layer  302  may have a thickness of about 3-15 nanometers. 
     Interlayer  210  also includes a third layer  303  formed from a material having a HCP structure, such as a HCP(00.2) structure. The material forming the third layer  303  may be a Ru-based material having the HCP structure, examples of which are Ru, RuCr, and RuTi. A Ru-based material means any material solely or partially formed from Ru. The third layer  303  may have a thickness of about 3-15 nanometers. The terms “first”, “second”, and “third” are used to distinguish between layers of different material, and are not necessarily indicative of a particular order of the layers. Also, interlayer  210  may include more layers than those illustrated in  FIG. 3 . 
     The second layer  302  of BCC material may be multi-layer itself.  FIG. 4  is a cross-sectional view illustrating another exemplary embodiment of interlayer  210 . In  FIG. 4 , the second layer  302  of  FIG. 3  is formed from two layers of BCC material. The first layer  401  of BCC material may serve as a crystallographic enhancement layer. As an example, the first layer  401  may comprise a layer of Cr or a Cr alloy (CrX) having a low concentration of a doping element (X), such as Mo, Ti, V, W, Ta, Mn, or another element. The atomic percentage of the doping element (X) in the Cr alloy may be between about 5 to 30%. 
     The second layer  402  of BCC material may serve as a grain size control layer. As an example, the second layer  402  may comprise a layer of a Cr alloy (CrX or CrXY) having a higher concentration of a doping element. For instance, the Cr alloy (CrX) may have a doping element (X), such as Mo, Ti, V, W, Ta, Mn, or another element. The Cr alloy (CrXY) may additionally have the doping element (Y), such as B, Si, O, N, or another element. The atomic percentage of the doping element (X) in the Cr alloy may be between about 5 to 30%, and the atomic percentage of the doping element (Y) in the Cr alloy may be between about 5 to 10%. The second layer  302  may include more layers of BCC material in other embodiments. 
     Interlayer  210  may comprise other layers than those shown in  FIGS. 3-4 .  FIG. 5  is a cross-sectional view illustrating another exemplary embodiment of interlayer  210 . In  FIG. 5 , interlayer  210  includes the first layer  301  formed from a material having a FCC structure. Interlayer  210  also includes the second layer  302  formed from a material having a BCC structure. Interlayer  210  also includes the third layer  303  formed from a material having a HCP structure. These layers resemble the layers illustrated in  FIG. 3 . However in  FIG. 5 , interlayer  210  also includes a fourth layer  504  formed from a material having an HCP structure. The fourth layer  504  is formed between the first layer  301  (the FCC layer) and the second layer  302  (the BCC layer). The material forming the fourth layer  504  may be a Ru-based material having the HCP structure, examples of which are Ru, RuCr, and RuTi. Although four layers are shown in  FIG. 5 , interlayer  210  may comprise more or less than four layers in other embodiments. 
     For the embodiments shown in  FIGS. 3-5 , interlayer  210  includes a layer of BCC material that replaces some of the HCP material used in many other interlayers. For instance, assume that a prior interlayer includes 200 Å of HCP material, such as Ru. According to the embodiments herein, some of the 200 Å of HCP material will be replaced with BCC material, such as Cr. For instance, interlayer  210  may include 90 Å of BCC material and 110 Å of HCP material. The thickness of the interlayer  210  does not change, but the amount of HCP material used is almost cut in half. The reduction in HCP material causes a corresponding reduction in cost of fabrication for the perpendicular magnetic recording medium  104  due to the higher cost of the HCP material. 
     The BCC material works well in interlayer  210  as the lattice of the BCC material matches well with both of the FCC material and the HCP material. With the BCC material replacing some of the HCP material in interlayer  210 , interlayer  210  still effectively controls the size of magnetic crystal grains and the orientation of the magnetic crystal grains in perpendicular magnetic recording layer  215 . Interlayer  210  also effectively serves to magnetically de-couple SUL  205  and perpendicular magnetic recording layer  215 . If a BCC material such as Cr is used in interlayer  210 , perpendicular magnetic recording medium  104  will also exhibit a higher resistance to corrosion. 
       FIGS. 6-7  illustrate possible methods of fabricating the perpendicular magnetic recording medium  104 .  FIG. 6  is a flow chart illustrating one exemplary method  600  of fabricating perpendicular magnetic recording medium  104 . In step  602 , SUL  205  is formed (see  FIG. 3 ) such as by depositing material for SUL  205  on a nonmagnetic substrate or on other layers previously deposited. In step  604 , a first layer  301  of interlayer  210  is formed (see  FIG. 3 ). The first layer  301  is formed from a material having a FCC structure, such as a Ni-based material. In step  606 , a second layer  302  of interlayer  210  is formed (see  FIG. 3 ). The second layer  302  is formed from a material having a BCC structure, such as a Cr-based material. In step  608 , a third layer  303  of interlayer  210  is formed (see  FIG. 3 ). The third layer  303  is formed from a material having a HCP structure, such as a Ru-based material. In step  610 , perpendicular magnetic recording layer  215  is formed (see  FIG. 2 ) such as by depositing material for perpendicular magnetic recording layer  215 . The material for perpendicular magnetic recording layer  215  may comprise CoPtCr—SiOx or another material. Method  600  forms the perpendicular magnetic recording medium  104  illustrated in  FIG. 3 . There may be other layers of material deposited than those described in method  600 . 
     To form the perpendicular magnetic recording medium  104  illustrated in  FIG. 4 , step  606  of method  600  would include two steps of depositing BCC material. The first step may comprise forming a layer of BCC material that serves as a crystallographic enhancement layer. The second step may comprise forming another layer of BCC material that serves as a grain size control layer. Exemplary compositions of these layers of BCC material are provided above. 
       FIG. 7  is a flow chart of another exemplary method  700  of fabricating perpendicular magnetic recording medium  104 . Method  700  is substantially similar to method  700  in forming SUL  205 , a first layer  301  (FCC material) of interlayer  210 , a second layer  302  (BCC material) of interlayer  210 , a third layer  303  (HCP material) of interlayer  210 , and perpendicular magnetic recording layer  215  (see  FIG. 5 ). Method  700  includes the additional step  702  where a fourth layer  504  of interlayer  210  is formed (see  FIG. 5 ). The fourth layer  404  is formed from a material having a HCP structure, such as a Ru-based material. Method  700  forms the perpendicular magnetic recording medium  104  illustrated in  FIG. 5 . There may be other layers of material deposited than those described in method  700 . 
       FIG. 8  is a graph illustrating the performance of a perpendicular magnetic recording medium using the interlayer  210  provided herein. Assume for this example that interlayer  210  includes a first layer  301  of NiW (FCC structure), a second layer  302  of Cr (BCC structure), and a third layer  303  of Ru (HCP structure). Graph  800  in  FIG. 8  illustrates the coercivity of the interlayer for different thicknesses of NiW and Cr. A coercivity measurement indicates the quality of the magnetic layer growth in the perpendicular direction. A high coercivity (Hc) represents a good crystalline orientation. 
     As a reference point, graph  800  illustrates the coercivity of a typical interlayer formed from NiW(70)/Ru(90)/Ru(90) (a FCC/HCP interlayer), where the thicknesses referred to are in Angstroms. The coercivity of this reference point is about 4900 Oe. Graph  800  also illustrates data points  802  for NiW(x)/Cr(90)/Ru(110) (a FCC/BCC/HCP interlayer). As x increases above about 20 Å, the coercivity raises above 4900 Oe. At about 70 Å, the coercivity is about 5300 Oe. This indicates that the FCC/BCC/HCP interlayer provides a good crystalline orientation even better than the FCC/HCP interlayer traditionally used. 
     Graph  800  also illustrates data points  804  for NiW(52)/Cr(x)/Ru(110). As x increases above about 20 Å, the coercivity raises above 4900 Oe again. At about 70 Å, the coercivity is between 5200 and 5300 Oe. This again indicates that the FCC/BCC/HCP interlayer provides a good crystalline orientation even better than the FCC/HCP interlayer traditionally used. 
     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.