# Patent

## Title
Systems and methods for providing capping layers for heat assisted magnetic recording media

## Abstract

Aspects of the present invention are directed to heat assisted magnetic recording (HAMR) media with a CoCrPtB based capping layer design that is capable of reducing switching field distribution and boosting signal-to-noise ratio of HAMR media. In one embodiment of the invention, a recording medium for heat assisted magnetic recording (HAMR) includes a substrate, a magnetic recording layer on the substrate, and a capping layer on and directly in contact with the magnetic recording layer. The capping layer includes CoCrPtB.

## Background
CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority to and the benefit of U.S. Provisional Application No. 61/819,520, filed on May 3, 2013, titled “CAP LAYER FOR HEAT ASSISTED MAGNETIC RECORDING MEDIA,” the entire content of which is incorporated herein by reference.


FIELD
Aspects of the present invention relate to magnetic recording media, and more specifically to systems and methods for providing capping layers for heat assisted magnetic recording media.
BACKGROUND
Heat-assisted magnetic recording (HAMR) is a technology that magnetically records data on recording media using thermal assistance. HAMR can utilize high-stability magnetic compounds that can store single bits in a small area. To achieve areal density greater than one terabit per square inch (Tb/in2) for next generation hard drives, FePt based alloys (e.g., L10 FePt) have been widely investigated because of their desirably high magnetocrystalline anisotropy. The performance of such magnetic media can be characterized by a number of parameters. For example, signal-to-noise ratio (SNR) is an important parameter for measuring recording performance of magnetic media and conventional media often have insufficient SNR. Therefore, it is desirable to develop new approaches to improve SNR of HAMR magnetic recording media.



BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a top schematic view of a disk drive configured for heat assisted magnetic recording (HAMR) and including a magnetic recording medium with a capping layer configured to improve signal-to-noise ratio (SNR) of the medium in accordance with one embodiment of the invention.
FIG. 2 is a side cross sectional schematic view of selected components of the HAMR system of FIG. 1 including the magnetic recording medium with the capping layer configured to improve SNR of the medium in accordance with one embodiment of the invention.
FIG. 3 illustrates a heat assisted magnetic recording (HAMR) media stack with a capping layer configured to improve SNR of the HAMR media stack in accordance with an embodiment of the present invention.
FIG. 4 is a graph showing hysteresis loops of HAMR media with and without a capping layer, respectively, in accordance with an embodiment of the present invention.
FIG. 5 is a graph showing the calculation of the switching field distribution (SFD) of HAMR media based on a hysteresis loop.
FIGS. 6a, 6b, and 6c are graphs comparing performance of HAMR media with and without a capping layer in accordance with an embodiment of the present invention.
FIG. 7 are cross-section transmission electron microscopy (TEM) images of HAMR media with a capping layer in accordance with an embodiment and without a capping layer.
FIG. 8 are images illustrating a fast Fourier transform (FFT) analysis of the capping layer structure of FIG. 4.
FIG. 9 is a flowchart illustrating a method for fabricating HAMR media with a capping layer in accordance with an embodiment of the present invention.



DETAILED DESCRIPTION
Signal-to-noise ratio (SNR) of heat assisted magnetic recording (HAMR) media may be improved through the design and material selection of magnetic layer, seed layer, heat sink, etc. One of the effective approaches for increasing SNR is to reduce the switching field distribution (SFD) of the magnetic layer. Aspects of the present invention are directed to a HAMR media design with improved SNR by introducing a capping layer (or cap layer). However, the present invention is not limited to HAMR technology only. Aspects of the present invention may be applied to other types of magnetic recording media. In various embodiments, the introduction of a suitable capping layer results in a desirable decrease in the magnetic switching field and corresponding increase in the SNR for the HAMR media.
FIG. 1 is a top schematic view of a disk drive 100 configured for heat assisted magnetic recording (HAMR) and including a magnetic recording medium 102 with a capping layer configured to improve SNR of the medium 102 in accordance with one embodiment of the invention. The laser (not visible in FIG. 1 but see FIG. 2) is positioned with a head/slider 108. Disk drive 100 may include one or more disks/media 102 to store data. Disk/media 102 resides on a spindle assembly 104 that is mounted to drive housing 106. Data may be stored along tracks in the magnetic recording layer of disk 102. The reading and writing of data is accomplished with the head 108 that may have both read and write elements. The write element is used to alter the properties of the magnetic recording layer of disk 102 and thereby write information thereto. In one embodiment, head 108 may have magneto-resistive (MR), or giant magneto-resistive (GMR) elements. In an alternative embodiment, head 108 may be another type of head, for example, an inductive read/write head or a Hall effect head.
In operation, a spindle motor (not shown) rotates the spindle assembly 104, and thereby rotates disk 102 to position head 108 at a particular location along a desired disk track. The position of head 108 relative to disk 102 may be controlled by position control circuitry 110.
FIG. 2 is a side cross sectional schematic view of selected components of the HAMR system of FIG. 1 including the magnetic medium 102 with the capping layer configured to improve SNR of the medium 102 in accordance with one embodiment of the invention. The HAMR system components also include a sub-mount attached to a top surface of the slider. The laser is attached to the sub-mount, and possibly to the slider. The slider includes the write element and the read element positioned along an air bearing surface (ABS) of the slider for writing information to, and reading information from, respectively, the media 102.
In operation, the laser is configured to direct light energy to a waveguide in the slider which directs the light to an NFT near the air bearing surface (e.g., bottom surface in FIG. 2) of the slider. Upon receiving the light from the laser via the waveguide, the NFT generates localized heat energy that heats a portion of the media 102 near the write element and the read element.
FIG. 3 illustrates a HAMR medium 300 that includes a capping layer for improving SNR in accordance with an embodiment of the present invention. The HAMR medium 300 includes a stacked structure with a bottom layer substrate 302, an adhesion layer 304 on the substrate 302, an intermediate layer 306 on the adhesion layer 304, a magnetic recording layer 308 on the intermediate layer 306, a capping layer 310 on the magnetic recording layer 308, an overcoat layer 312 on the capping layer 310, and a lubricant layer 314 on the overcoat layer 312.
In an embodiment, the magnetic recording layer 308 may be a FePt based recording layer. For example, the magnetic recording layer 308 may include FePt or any suitable FePt alloys (e.g., L10 FePt). In an embodiment, the capping layer 310 may include a thin layer of CoCrPtB based material or alloy. In an embodiment, the capping layer 310 may include Co at about 40 to 80 atomic percent, Cr at about 0 to 35 atomic percent, Pt at about 0 to 30 atomic percent, and B at about 0 to 15 atomic percent. In another embodiment, the capping layer 310 may include Co at about 55 to 65 atomic percent, Cr at about 10 to 20 atomic percent, Pt at about 15 to 25 atomic percent, and B at about 5 to 15 atomic percent. In an embodiment, the capping layer 310 may have a thickness of less than about 2 nm. In an embodiment, the capping layer 310 may have a thickness of about 0.3 nm to 1.5 nm. In an embodiment, the capping layer 310 may have a half-crystalline structure. In an embodiment, the capping layer 310 may be directly on and in contact with the magnetic recording layer 108.
The addition of the capping layer 310 can increase SNR of the magnetic recording layer 308 by reducing the SFD of the HAMR medium. To further improve the recording performance of the HAMR medium 300, especially media SNR, various suitable media designs and material selections may be used. In one embodiment, the substrate 302 may include a material selected from the group consisting of an Al alloy, NiP plated Al, glass, glass ceramic, and combinations thereof. In one embodiment, the adhesion layer 304 may include a material selected from the group consisting of CrTi, CrTa, NiTa, CoCrTaZr, CoFeZrBCr, CoTaZr, CoFeTaZr, CoCrWTaZr, CoCrMoTaZr, CoZrWMo and combinations thereof. In one embodiment, the intermediate layer 306 may include Cr, Mo, Ru, W, CuZr, MoCu, AgPd, CrRu, CrV, CrW, CrMo, CrNd, NiAl, NiTa, CrTiX, CrTaX, NiTaX, CoCrTaZrX, CoFeZrBCrX, CoTaZrX, CoFeTaZrX, CoCrWTaZrX, CoCrMoTaZrX, CoZrWMoX, and combinations thereof, wherein X is selected from the group consisting of SiO2 and ZrO2. In one embodiment, the overcoat layer 312 may include diamond-like-carbon (DLC). In one embodiment, the lubricant layer 314 may include polymer based material. The HAMR medium 300 with the above-described CoCrPtB based capping layer shows a desirable reduction of SFD as compared to a reference HAMR medium without such a capping layer.
FIG. 4 is a graph showing hysteresis loops of a HAMR medium (e.g., HAMR medium 300) with a CoCrPtB based capping layer and a HAMR medium without a capping layer. The loops 402 correspond to a HAMR medium with a CoCrPtB capping layer and the loops 404 correspond to a reference HAMR medium without a capping layer. As shown in FIG. 4, the HAMR medium with the capping layer (402) has an SFD of about 16.1 percent, and the reference HAMR medium (404) has an SFD of about 21.7 percent. That is equal to a significant reduction of about 5.6 percent in SFD. FIG. 5 is a graph showing the calculation of the SFD of HAMR media based on a hysteresis loop. Referring the FIG. 5, SFD can be calculated according to Equation (1).




  
    
      
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In an embodiment, the HAMR medium 300 does not include a soft magnetic underlayer. In another embodiment, the HAMR medium 300 may include a soft magnetic underlayer between the magnetic recording layer 308 and the adhesion layer 304. With a soft magnetic underlayer, the recording performance of the HAMR medium in terms of signal-to-DC-noise ratio may be improved. However, the soft magnetic underlayer also acts as a thermal barrier, and may cause noise increase in the HAMR medium, thereby decreasing SNR. For example, in one embodiment, the soft magnetic underlayer may be positioned below a MgO growth layer for the magnetic recording layer 308, where the MgO growth layer is positioned just below the magnetic recording layer 308. In an embodiment, the capping layer 310 may include less than 5 atomic percent of Ta. In an embodiment, the capping layer 310 does not include Ta.
FIGS. 6a, 6b, and 6c illustrate the improvement on various characteristics of an exemplary HAMR medium (e.g., the HAMR medium 300) with a capping layer resulted from the reduction of SFD as compared to a reference HAMR medium without a capping layer. The HAMR medium with the capping layer shows (1) in FIG. 6a, a boost of SNR (wsSNRinit) of about 0.4 dB, (2) in FIG. 6b, an increase of signal-to-DC-noise ratio (SNRdc) of about 0.4 dB, and, (3) in FIG. 6c, a decrease of jitter by about 0.26 nm.
FIG. 7 illustrates a cross-section transmission electron microscopy (TEM) image 700 of a HAMR medium with a capping layer in accordance with an embodiment and a cross-section TEM image 702 of a reference HAMR medium without a capping layer.
FIG. 8 are images illustrating a fast Fourier transform (FFT) analysis of a capping layer structure of the HAMR medium with a capping layer. Here, the capping layer has a semi-crystalline structure 800. As shown in FIGS. 7 and 8, the HAMR medium with the capping layer may be slightly thicker, and the structure of the CoCrPtB capping layer has a semi-crystalline structure.
The HAMR media stack disclosed above in reference to FIGS. 3 to 8 may be manufactured in current PMR and HAMR equipment. For example, the HAMR media 300 may be fabricated in a single sputtering process using an Anelva 3040/50 multi-chamber sputtering tool. In this embodiment, the sputter time for the extra capping layer is less than about one quarter of the process time for conventional techniques and should have no substantial impact on the productivity for media fabrication. Aspects of the present invention may be implemented in an HAMR hard disk drive including such HAMR media.
FIG. 9 is a flowchart illustrating a method 900 for fabricating HAMR media with a capping layer configured to reduce SNR of the HAMR media in accordance with an embodiment of the present invention. In one embodiment, the method 900 may be used to fabricate the HAMR medium 300. In block 902, a suitable substrate for HAMR media is formed or provided. The substrate may be the substrate 302. In block 904, a magnetic recording layer is formed on the substrate. The magnetic recording layer may be the magnetic recording layer 308. In block 906, a capping layer is formed on and directly in contact with the magnetic recording layer. The capping layer may be the capping layer 310. In this embodiment, the capping layer includes CoCrPtB or a CoCrPtB alloy.
It is to be understood that the specific order or hierarchy of steps in the methods disclosed is an illustration of exemplary processes. Based upon design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not meant to be limited to the specific order or hierarchy presented unless specifically recited therein.
In several embodiments, the deposition of layers can be performed using a variety of deposition sub-processes, including, but not limited to physical vapor deposition (PVD), sputter deposition and ion beam deposition, and chemical vapor deposition (CVD) including plasma enhanced chemical vapor deposition (PECVD), low pressure chemical vapor deposition (LPCVD) and atomic layer chemical vapor deposition (ALCVD). In other embodiments, other suitable deposition techniques known in the art may also be used.
It shall be appreciated by those skilled in the art in view of the present disclosure that although various exemplary fabrication methods are discussed herein with reference to magnetic recording disks or wafers containing magnetic heads, the methods, with or without some modifications, may be used for fabricating other types of recording disks, for example, optical recording disks such as a compact disc (CD) and a digital-versatile-disk (DVD), or magneto-optical recording disks, or ferroelectric data storage devices.
While the above description contains many specific embodiments of the invention, these should not be construed as limitations on the scope of the invention, but rather as examples of specific embodiments thereof. Accordingly, the scope of the invention should be determined not by the embodiments illustrated, but by the appended claims and their equivalents.
The various features and processes described above may be used independently of one another, or may be combined in various ways. All possible combinations and sub-combinations are intended to fall within the scope of this disclosure. In addition, certain method, event, state or process blocks may be omitted in some implementations. The methods and processes described herein are also not limited to any particular sequence, and the blocks or states relating thereto can be performed in other sequences that are appropriate. For example, described tasks or events may be performed in an order other than that specifically disclosed, or multiple may be combined in a single block or state. The example tasks or events may be performed in serial, in parallel, or in some other suitable manner. Tasks or events may be added to or removed from the disclosed example embodiments. The example systems and components described herein may be configured differently than described. For example, elements may be added to, removed from, or rearranged compared to the disclosed example embodiments.

## Claims

1. A heat assisted magnetic recording (HAMR) medium comprising:
a substrate;
a magnetic recording layer on the substrate; and
a capping layer on and directly in contact with the magnetic recording layer,
wherein the capping layer comprises CoCrPtB and has a half-crystalline structure formed by a single sputtering process.

2. The HAMR medium of claim 1, wherein the magnetic recording layer comprises FePt or FePt based alloys.

3. The HAMR medium of claim 1, wherein the capping layer is configured to reduce switching field distribution of the magnetic recording layer.

4. A heat assisted magnetic recording (HAMR) medium comprising:
a substrate;
a magnetic recording layer on the substrate; and
a capping layer on and directly in contact with the magnetic recording layer,
wherein the capping layer comprises CoCrPtB, and
wherein the capping layer comprises Co at about 40 to 80 atomic percent, Cr at about 0 to 35 atomic percent, Pt at about 0 to 30 atomic percent, and B at about 0 to 15 atomic percent.

5. The HAMR medium of claim 1, wherein the capping layer has a thickness less than about 2 nm.

6. The HAMR medium of claim 5, wherein the capping layer has a thickness between about 0.3 nm and about 1.5 nm.

7. The HAMR medium of claim 1, wherein the HAMR medium does not comprise a soft magnetic underlayer.

8. The HAMR medium of claim 1, wherein the capping layer comprises less than 5 atomic percent of Ta.

9. The HAMR medium of claim 8, wherein the capping layer does not comprise Ta.

10. The HAMR medium of claim 1, further comprising
an adhesion layer on the substrate;
an intermediate layer on the adhesion layer, wherein the adhesion layer and the intermediate layer are below the magnetic recording layer;
an overcoat on the capping layer; and
a lubricant layer on the overcoat.

11. A hard disk drive comprising the HAMR medium of claim 1.

12. A method of fabricating a heat assisted magnetic recording (HAMR) medium, the method comprising:
forming a substrate;
forming a magnetic recording layer on the substrate; and
forming a capping layer on and directly in contact with the magnetic recording layer,
wherein the capping layer comprises CoCrPtB and has a half-crystalline structure.

13. The method of claim 12, further comprising forming the capping layer by a single sputtering process.

14. The method of claim 12, wherein the magnetic recording layer comprises FePt or FePt based alloys.

15. The method of claim 12, wherein the capping layer is configured to reduce switching field distribution of the magnetic recording layer.

16. A method of fabricating a heat assisted magnetic recording (HAMR) medium, the method comprising:
forming a substrate;
forming a magnetic recording layer on the substrate; and
forming a capping layer on and directly in contact with the magnetic recording layer,
wherein the capping layer comprises CoCrPtB, and
wherein the capping layer comprises Co at about 40 to 80 atomic percent, Cr at about 0 to 35 atomic percent, Pt at about 0 to 30 atomic percent, and B at about 0 to 15 atomic percent.

17. The method of claim 12, wherein the capping layer has a thickness less than about 2 nm.

18. The method of claim 17, wherein the capping layer has a thickness between about 0.3 nm and about 1.5 nm.

19. The method of claim 12, wherein the HAMR medium does not comprise a soft magnetic underlayer.

20. The method of claim 12, wherein the capping layer comprises less than 5 atomic percent of Ta.

21. The method of claim 20, wherein the capping layer does not comprise Ta.

22. The method of claim 12, further comprising
forming an adhesion layer on the substrate;
forming an intermediate layer on the adhesion layer, wherein the adhesion layer and the intermediate layer are below the magnetic recording layer;
forming an overcoat on the capping layer; and
forming a lubricant layer on the overcoat.