Systems and methods for providing thermal barrier bilayers for heat assisted magnetic recording media

Description

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to and the benefit of U.S. Provisional Application No. 61/820,583, filed on May 7, 2013, entitled, “SYSTEMS AND METHODS FOR PROVIDING TRANSPARENT THERMAL BARRIER LAYERS FOR HEAT ASSISTED MAGNETIC RECORDING MEDIA”, the entire content of which is incorporated herein by reference.

FIELD

The present invention relates generally to magnetic media disks for magnetic recording, and more specifically to systems and methods for providing thermal barrier bilayers for heat assisted magnetic recording (HAMR) media.

BACKGROUND

Energy/Heat Assisted Magnetic Recording (EAMR/HAMR) systems can potentially increase the areal density of information recorded magnetically on various media. For example, to achieve magnetic information storage levels beyond 1 terabit per inch squared, smaller grain size (e.g., less than 6 nm) media may be required. Such designs can demand higher Ku materials for a recording layer to sustain thermal stability, such as L10 ordered FePt alloys. Due to high anisotropy, FePt media is not writable with conventional recording heads. Therefore, either exchange coupled composite media structure or heat-assisted magnetic recording (HAMR) are generally needed. HAMR media generally includes a magnetic recording layer and a heat sink positioned beneath the magnetic recording layer. To facilitate efficient HAMR, including the use of minimal laser power to achieve heat assisted writing and reading of information on the media, it is necessary to dissipate heat and/or light energy from the magnetic recording layer. Typically, this is achieved to a certain degree by the heat sink layer. However, conventional heat sink layers may not adequately dissipate heat and/or light energy from the magnetic recording layer.

To address this problem and a more specific problem of lateral heat spreading from the heat sink, U.S. Pat. No. 7,869,162 describes HAMR media including a thermal resistor layer added between the heat sink and recording layer. However, the HAMR media with this thermal resistor layer has limited efficiency and may not adequately dissipate heat and/or light energy from the magnetic recording layer in many applications. Accordingly, an improved HAMR media structure that addresses these shortcomings is needed.

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 medium with a thermal barrier bilayer 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 medium with the thermal barrier bilayer in accordance with one embodiment of the invention.

FIG. 3 is side cross sectional view of a HAMR medium having a thermal barrier bilayer that includes a first thermal barrier layer under an amorphous underlayer (AUL) in accordance with one embodiment of the invention.

FIG. 4 is side cross sectional transmission electron microscope (TEM) view of a HAMR medium including a thermal barrier bilayer between the recording layer and the heat sink layer in accordance with one embodiment of the invention.

FIG. 5 is a flowchart of a process for manufacturing a HAMR medium including a thermal barrier bilayer in accordance with one embodiment of the invention.

FIGS. 6a, 6b, and 6c illustrate coercive field (Hc), full width half maximum (FWHM), and surface roughness (Ra) measurements, respectively, versus AUL thickness for a comparative HAMR medium without a thermal barrier bilayer (Control) compared against a HAMR medium with a thermal barrier bilayer in accordance with one embodiment of the invention.

FIGS. 7a, 7b, and 7c illustrate laser current, weighted sum signal to noise ratio (wsSNR), and jitter measurements, respectively, versus AUL thickness for a comparative HAMR medium without a thermal barrier bilayer (Control) compared against a HAMR medium with a thermal barrier bilayer in accordance with one embodiment of the invention.

DETAILED DESCRIPTION

Some comparative thermal designs for heat assisted magnetic recording (HAMR) media include a recording layer made of FePt, a thermal barrier layer and a heat sink. For example, one such comparative media design utilizes Ru or Mo as a heat sink, and an amorphous under-layer (AUL) as a thermal barrier layer. In order to minimize surface roughness (Ra) or waviness caused by the heat sink, the AUL layer generally has to be thicker than about 25 nanometers (nm). However, the relatively thick AUL not only degrades on-track thermal gradient, but also absorbs a significant portion of incoming light from the near field transducer (NFT) of a HAMR system.

While not bound by any particular theory, optimizing thermal barrier layer and heat sink thicknesses and thermal properties can ensure the highest thermal gradient per laser power that a magnetic head could sustain. An ideal heat sink layer can have as high as possible thermal conductivity (κ) and an ideal thermal barrier layer can have as low as possible κ. The latter ensures that a barrier layer should be relatively thin and lateral heat diffusion in the thermal barrier layer is minimal. Another aspect of the thermal barrier layer is the associated optical properties. As observed experimentally, the recording layer could generally absorb only a portion of light coming from a nearby NFT, and therefore, a significant portion of incoming NFT and waveguide light could be absorbed in the thermal barrier layer depending on its properties. The latter absorption effect would degrade both on-track and off-track media recording performance, especially if side lobes from the waveguide are present. On the contrary, if barrier layer is transparent, light is coupled more directly to the heat sink and the associated energy is quickly dissipated. Accordingly, the thermal barrier bilayers described herein can address both lowering the thermal conductivity of the thermal barrier layer, and, when the first thermal barrier layer is transparent, coupling light from the NFT directly to the heat sink for rapid dissipation.

Another comparative design utilizes an AUL as a thermal barrier layer in between a growth layer of MgO and a heat sink of Mo. While not bound by any particular theory, in EAMR or HAMR systems including a thermal barrier layer between the growth layer and the heat sink layer, the heat sink and interlayer (e.g., AUL) serve mutually competitive purposes. More specifically, the steady state temperature profile is controlled by inter-layer (thermal resistance) and heat sink heat conductivity/thickness (lateral dissipation). The heat sink ensures fast cooling rate to achieve a high gradient, small thermal spot and avoid adjacent track erasure. However, the interlayer (e.g., AUL in this case) degrades the gradient, but limits laser power to reach Curie temperature (TC).

To minimize the above described disadvantages, a new HAMR media structure is proposed that includes a thermal barrier bilayer including first thermal barrier layer and an AUL on the first thermal barrier layer, where the first thermal barrier layer is composed of one or more materials having a relatively low thermal conductivity such that the thermal conductivity of the first thermal barrier layer is less than the thermal conductivity of the amorphous underlayer. The thermal barrier bilayer can efficiently dissipate both heat and light from a nearby HAMR light source (e.g., laser) and can also reduce the media surface roughness typically caused by the heat sink. Since heat and light are efficiently dissipated, the associated HAMR laser power may be controlled and reduced.

In one embodiment, the first thermal barrier layer of the thermal barrier bilayer is substantially (e.g., about) transparent. The transparent feature enables the thermal barrier bilayer to substantially conduct laser light to the heat sink and thereby allow the heat sink to efficiently dissipate the laser light from the nearby HAMR laser. In some embodiments, the first thermal barrier layer (e.g., lower layer) of the thermal barrier bilayer is made of carbon and deposited using chemical vapor deposition (CVD) or sputter deposition. In one such case, with the appropriately selected materials, the first thermal barrier layer has lower thermal conductivity (about 1 watt per meter Kelvin or W/mK) than the AUL (about 10 W/mK), is transparent, and is capable of reducing Ra or waviness caused by the heat sink.

In one embodiment of the new HAMR media with the thermal barrier bilayer, it is proposed to partially substitute a portion of the AUL with a transparent CVD carbon layer, or another suitable material. As an amorphous material, the AUL has relatively low thermal conductivity (κ of about 10 W/mK), but the κ of the CVD layer is significantly lower (about 1 W/mK, as measured in a pump probe test). In some embodiments, the carbon first thermal barrier layer can be deposited using sputtering instead of CVD. In general, the deposition can be performed using a bias voltage applied to the media substrate to improve deposition. In one embodiment, the heat sink layer a can have an experimental thermal conductivity value of about 50 to 100 W/mK, and possibly nominal values of 70 and 100 W/mK.

The AUL can also be deposited with a high bias voltage (e.g., 300V) which can effectively reduce the roughness (Ra) caused by the heat sink. In some of the comparative designs, a 25 nm thick AUL is generally capable to reduce the surface roughness to an acceptable level. However, a thinner AUL (less than 25 nm) shows degradation in performance due to waviness.

The terms “above,” “below,” and “between” as used herein refer to a relative position of one layer with respect to other layers. As such, one layer deposited or disposed above or below another layer may be directly in contact with the other layer or may have one or more intervening layers. Moreover, one layer deposited or disposed between layers may be directly in contact with the layers or may have one or more intervening layers.

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, 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.

FIG. 1 is a top schematic view of a disk drive 100 configured for heat assisted magnetic recording (HAMR) and including a magnetic medium 102 with a thermal barrier bilayer 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 104 may have magneto-resistive (MR), or giant magneto-resistive (GMR) elements. In an alternative embodiment, head 104 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 104 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 thermal barrier bilayer (not visible in FIG. 2 but see FIG. 3) 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 a NFT near the air bearing surface (e.g., bottom surface) 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. FIGS. 1 and 2 illustrate a specific embodiment of a HAMR system. In other embodiments, the new media with the thermal barrier bilayer can be used in other suitable HAMR systems.

FIG. 3 is side cross sectional view of a HAMR medium 200 having a thermal barrier bilayer that includes a first thermal barrier layer (208) under an amorphous underlayer (AUL, 210) in accordance with one embodiment of the invention. The medium 200 has a stacked structure with a glass substrate 202 at a bottom/base layer, an adhesion layer 204 on the glass substrate 202, a heat sink layer 206 on the adhesion layer 204, the first thermal barrier layer 208 on the heat sink layer 206, the AUL 210 on the first thermal barrier layer 208, a growth layer 212 on the AUL 210, a magnetic recording layer 214 on the growth layer 212, and a carbon overcoat layer 216 on the magnetic recording layer 214. The first thermal barrier layer 208 and the AUL 210 make up the thermal barrier bilayer. In some embodiments, the adhesion layer 204, growth layer 212, and carbon overcoat 216 can be omitted from the medium structure.

In several embodiments, the thermal conductivity of the first thermal barrier layer 208 is less than the thermal conductivity of the AUL 210. As a result, the overall thermal conductivity of the thermal barrier bilayer is substantially reduced as compared to a medium having only the AUL. In some embodiments, the thermal conductivity of the first thermal barrier layer is in a range of about 5 percent to about 25 percent of the thermal conductivity of the AUL. In one such embodiment, the thermal conductivity of the first thermal barrier layer is about 10 percent of the thermal conductivity of the AUL.

In several embodiments, the first thermal barrier layer 208 is made of one or materials that are substantially (e.g., about) transparent. For example, in one embodiment, the first thermal barrier layer is at least 50 percent transparent at a common wavelength of light applied to the media (e.g., at a wavelength of about 800 nm). In some embodiments, the first thermal barrier layer is made of at least one material that is different from one material of the amorphous underlayer. In several embodiments, the first thermal barrier layer includes an amorphous material, such as amorphous carbon or another suitable amorphous material.

In several embodiments, the thermal barrier bilayer is configured to (e.g., the materials for the first thermal barrier layer are selected to) facilitate a heat transfer from the magnetic recording layer to the heat sink layer, and impede a heat transfer from the heat sink layer to the magnetic recording layer. In a number of embodiments, the first thermal barrier layer is deposited using a deposition sub-process involving application of a bias voltage (e.g., about 300 volts or another suitable voltage) to the substrate. For example, in one such embodiment, the deposition sub-process is a chemical vapor deposition (CVD) sub-process or a sputter deposition sub-process. In one such embodiment, the first thermal barrier layer includes CVD deposited amorphous carbon.

In several embodiments, the AUL can include one or more materials such as CrTiX, CrTaX, NiTaX, CoCrTaZrX, CoFeZrBCrX, CoTaZrX, CoFeTaZrX, CoCrWTaZrX, CoCrMoTaZrX, CoZrWMoX, combinations thereof, and/or other suitable materials known in the art, where X can be SiO2 and/or ZrO2.

In one embodiment, the substrate can be made of one or more materials such as an Al alloy, NiP plated Al, glass, glass ceramic, and/or combinations thereof. In one embodiment, the adhesion layer can includes one or more materials such as CrTi, CrTa, NiTa, CoCrTaZr, CoFeZrBCr, CoTaZr, CoFeTaZr, CoCrWTaZr, CoCrMoTaZr, CoZrWMo, combinations thereof, and/or other suitable materials known in the art.

In one embodiment, the heat sink layer can be made of one or more materials such as Ag, Al, Au, Cu, Cr, Mo, Ru, W, CuZr, MoCu, AgPd, CrRu, CrV, CrW, CrMo, CrNd, NiAl, NiTa, combinations thereof, and/or other suitable materials known in the art.

In one embodiment, the first thermal barrier layer can be made of one or more materials such as C, Al2O3, SiO2, WO3, Ta2O5, Nb2O5, ZrO2, SiN, NiP, TiN, combinations thereof, and/or other suitable materials known in the art.

In one embodiment, the growth layer can be made of one or more materials such as Cr, Mo, NiAl, MgO, TiC, TiN, Ag, CrMo, Pt, Pd, Ru, combinations thereof, and/or other suitable materials known in the art.

In one embodiment, the magnetic recording layer can be made of one or more materials such as FePt, CoPt, combinations thereof, and/or other suitable materials known in the art.

FIG. 4 is side cross sectional transmission electron microscope (TEM) view of a HAMR medium including a thermal barrier bilayer (CVD, AUL) between the recording layer (FePt) and the heat sink layer (Mo) in accordance with one embodiment of the invention. As illustrated, the thermal barrier bilayer which includes the first thermal barrier layer or CVD layer also effectively smoothens the Ra from the heat sink. In one aspect, it was determined that the AUL could not be completely eliminated due to adhesion problems between the growth layer of MgO and the CVD deposited first thermal barrier layer of amorphous carbon. The carbon overcoat layer is designated as COC.

FIG. 5 is a flowchart of a process 300 for manufacturing a HAMR medium including a thermal barrier bilayer in accordance with one embodiment of the invention. In particular embodiments, the process 300 can be used to manufacture the HAMR magnetic media of FIG. 3, FIG. 2, or FIG. 1. The process first provides a substrate in block 302. The process then provides a heat sink layer on the substrate in block 304. The process then provides a thermal barrier bilayer on the heat sink layer by providing a first thermal barrier layer on the heat sink layer, and providing an amorphous underlayer on the first thermal barrier layer in block 306. The process then provides a magnetic recording layer on the amorphous underlayer, where a thermal conductivity of the first thermal barrier layer is less than a thermal conductivity of the amorphous underlayer in block 308.

In a number of embodiments, the process can manufacture the layers of the HAMR medium with any of the numerous variations described above for the embodiments of FIGS. 1, 2, and 3. For example, in one such case, the process can also provide an adhesion layer between the substrate and the heat sink layer, a growth layer between the amorphous underlayer and the magnetic recording layer, and an overcoat layer on the magnetic recording layer. In several embodiments, the layers can include the materials as are described above.

In some embodiments, the process provides the first thermal barrier layer on the heat sink layer by applying a bias voltage to the substrate, and depositing the first thermal barrier layer on the heat sink layer using a deposition sub-process. In one such case, the deposition sub-process can be a chemical vapor deposition sub-process and/or a sputter deposition sub-process.

In one embodiment, the process can perform the sequence of actions in a different order. In another embodiment, the process can skip one or more of the actions. In other embodiments, one or more of the actions are performed simultaneously. In some embodiments, additional actions can be performed.

FIGS. 6a, 6b, and 6c illustrate coercive field (Hc), full width half maximum (FWHM), and surface roughness (Ra) measurements, respectively, versus AUL thickness for a comparative HAMR medium without a thermal barrier bilayer (Control) compared against a HAMR medium with a thermal barrier bilayer in accordance with one embodiment of the invention. The comparative HAMR medium without a thermal barrier bilayer (Control) can have a relatively thick AUL as compared to the new HAMR medium with the thermal barrier bilayer (e.g., 6 nm CVD amorphous carbon for first thermal barrier layer and 8 nm AUL of CoZiWMo). One can see that the performance measurements for the new HAMR medium with the thermal barrier bilayer with the combined 6 nm CVD and roughly 8 nm AUL thickness show roughly matching Hc, and substantially lower FWHM and Ra as compared to the control HAMR medium without the thermal barrier bilayer. The coercive field (Hc) is measured in Oersteds, the full width half maximum (FWHM) is measured in degrees, and the surface roughness (Ra) is measured in Angstroms.

FIGS. 7a, 7b, and 7c illustrate laser current, weighted sum signal to noise ratio (wsSNR), and jitter measurements, respectively, versus AUL thickness for a comparative HAMR medium without a thermal barrier bilayer (Control) compared against a HAMR medium with a thermal barrier bilayer in accordance with one embodiment of the invention. The comparative HAMR medium without a thermal barrier bilayer (Control) can have a relatively thick AUL as compared to the new HAMR medium with the thermal barrier bilayer (e.g., 6 nm CVD amorphous carbon for first thermal barrier layer and 8 nm AUL of CoZiWMo). One can see that at combined 6 nm CVD and roughly 8 nm AUL thickness, the performance measurements for the new HAMR medium with the thermal barrier bilayer shows about 14% laser current/power reduction, about 0.3 dB wsSNR improvement, and about matching jitter as compared to the control HAMR medium without the thermal barrier bilayer. The laser current is measured in milliamps or mA, the weighted sum signal to noise (wsSNR) is measured in decibels or dB, and the jitter is measured in nm.

In several embodiments, the HAMR media with the thermal barrier bilayer can significantly enhance technology capability towards implementation of various HAMR designs. For example, in some embodiments, the HAMR media with the thermal barrier bilayer has low thermal conductivity (about 1 W/mK) and effectively smoothens Ra/waviness from heat sink. In addition, laser power can be reduced by about 14% and the improved design does not increase costs for media fabrication processes. In some embodiments, and while not bound by any particular theory, it can be non-intuitive to add a layer such as the first thermal barrier layer between the AUL and the heat sink layer using a deposition process such as CVD or sputtering while applying a bias voltage since these radio frequency (RF) processes may generate a number of particles which can interfere with the formation of the AUL and consequently the growth layer, which is often formed of MgO. If the AUL and growth layer are improperly formed, the recording layer and media as a whole may exhibit performance problems.

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.

For example, in several embodiments, the deposition of such 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.

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.