Patent Application
20080220290
This application is based upon and claims the benefits of the priority from the prior Japanese Patent Application No. 2007-000566 filed on Jan. 5, 2007, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a large-capacity magnetic recording medium which is suitably used for a hard disk drive widely used as an external storage device for a computer, a household video recording device and the like and which is capable of achieving high density recording, and to an effective low cost manufacturing method for manufacturing the recording medium.
2. Description of the Related Art
Recent technical innovation in the IT industry has promoted extensive research and development for large capacity, high-speed, low cost magnetic recording media. To realize such media it is inevitable to increase the recording density of the magnetic recording medium, and patterned magnetic recording media (patterned media) have been proposed in which the magnetic film in the magnetic recording medium is not formed as a continuous film but formed as a patterned film having dots, bars or pillars of the order of nanometers to thereby obtain a single domain structure rather than a complex domain.
In the above patterned media, a pattern of submicron order needs to be formed over the entire surface of the magnetic disk with high accuracy and at low costs. For example, a patterned medium prepared by filling nanoholes of anodized aluminum with magnetic metal is known to offer an ordered array of nanoholes by forming a pattern of concaves that serves as a nanohole source on a surface of an aluminum layer before it is anodized (see Japanese Patent Application Laid-Open (JP-A) No. 10-121292).
Further, the present inventors have accomplished forming a one-dimensional array of nanoholes along the circumferential of a magnetic disk by forming a pattern of groove rather than concave (see JP-A No. 2005-305634).
Methods of forming such patterns are of two types: direct write methods that form patterns in each magnetic disk, including EB writing method and various lithography techniques; and imprint methods in which a mold (also referred to as “stamper”) is fabricated from a lithography pattern followed by transfer of the pattern formed on the mold onto a disk. In terms of productively, the latter is more advantageous.
For the manufacture of patterned media using nanoholes described above, available imprint methods are imprint methods shown in
The method shown in
A method which is expected to solve such a problem inherent to the hard imprint method is a “soft imprint method” shown in
The hard imprint method and soft imprint method both have the following inherent problem. Each method conducts pattern transfer after deposition of the aluminum layer. When sputtering or vapor deposition is used for deposition, however, the crystal grain size increases as layer formation proceeds, thereby generating asperities over the surface of the aluminum layer to which a pattern is to be transferred, whereby accurate transfer of a nanoscale pattern is made difficult.
As a third method of forming the pattern in the anodized alumina-nanoholes, a method shown in
The method shown in
The method shown in
With the methods shown in
Accordingly, the current situation is that a manufacturing method for a large capacity and high density recording-enabled magnetic recording medium, capable of solving abovementioned problem inherent to the imprint method, achieving high pattern transfer accuracy, transferring a pattern that can serve as a source for forming anodized alumina-nanoholes with high precision, and realizing high productivity, and techniques related to the manufacturing method have not yet been provided.
An object of the present invention is to solve the above problem inherent to the related arts and to provide a low cost manufacturing method for a magnetic recording medium, which method is capable of transferring a pattern that can serve as a source for anodized alumina-nanoholes with high precision and realizing high productivity, and a large-capacity magnetic recording medium which is suitably used in a hard disk drive widely used as an external storage device for a computer, a household video recording device and the like and which is capable of achieving high density recording.
The means to solve the foregoing problems are described in attached claims.
More specifically, the method of the present invention for manufacturing a magnetic recording medium includes: forming a metallic layer on a concavo-convex pattern formed on a surface of a mold; bonding a substrate using an adhesive to a surface of the metallic layer on the side opposite to the mold; separating the mold from the metallic layer; forming, through nanohole formation treatment, a porous layer in which a plurality of nanoholes are formed to orient in a direction substantially perpendicular to a substrate plane by using as a nanohole source a concavo-convex pattern which has been formed by transferring the concavo-convex pattern in the mold to the metallic layer; and charging a magnetic material inside the nanoholes.
In the metallic layer formation step a metallic layer is deposited onto the concavo-convex pattern of a mold. In the substrate bonding step a substrate is bonded to a surface of the deposited metallic layer on the side opposite to the mold by use of an adhesive. Thereafter, in the mold separation step, the mold is separated from the metallic layer. In this way the concavo-convex pattern of the mold is transferred to the metallic layer with high accuracy, forming a high-resolution concavo-convex pattern on a surface of the metallic layer. In the subsequent porous film formation step, nanohole formation treatment is conducted to form a porous layer in which a plurality of nanoholes is formed that are oriented in a direction substantially perpendicular to a surface plane at positions corresponding to the concavo-convex pattern. In the magnetic material charging step the nanoholes are filled with magnetic material. In this way a magnetic recording medium is manufactured efficiently and inexpensively that is capable of high-density recording for large storage capacity.
The magnetic recording medium of the present invention includes: a substrate; an adhesive layer over the substrate; and a porous layer over the adhesive layer, wherein the porous layer comprises a plurality of nanoholes that are oriented in a direction substantially perpendicular to a plane of the substrate, and wherein the nanoholes comprise therein a magnetic material.
The magnetic recording medium of the present invention has a porous film with a plurality of nanoholes formed therein over a substrate, with an adhesive layer interposed between the porous film and the substrate, wherein the nanoholes are generated using as a nanohole source a concavo-convex pattern transferred with high accuracy from a mold, and are filled with magnetic material as well. Accordingly, the magnetic recording medium is capable of high-density recording for large storage capacity and is of very high quality, and thus is suitable for instance for hard disk devices used as external storage devices for computers and house-hold video recorders.
A magnetic recording medium manufacturing method according to the present invention includes at least a metallic layer formation step, a substrate bonding step, a mold separation step, a porous layer formation step, and a magnetic material charging step and preferably further includes a soft magnetic underlayer formation step and a polishing step. Further, the method includes, if necessary, an electrode layer formation step, a protective layer formation step, and the like.
The metallic layer formation step is a step in which a metallic layer is formed on a concavo-convex pattern of a mold.
The mold is not especially limited as long as it has a concavo-convex pattern on the surface thereof and materials thereof can appropriately be selected according to the purpose; preferably used materials include: silicon, silicon oxide film and a combination thereof in view of the fact that they are most widely used as materials for manufacturing fine structures in the semiconductor field; silicon carbide for its high durability in continuous use; and Ni which is used in the forming of optical disks. The mold can be used a plurality of times.
The concavo-convex pattern in the mold is preferably one corresponding to a pattern of arrangement of formed nanoholes, that is, one having land portions (convex portions) and groove portions (concave portions) that respectively correspond to the concave portions and convex portions that may serve as a nanohole source.
The shape of the land portion is not especially limited and can appropriately be selected according to the purpose but is preferably a line shape and, therefore, the concavo-convex pattern in the mold is preferably a line pattern in which the land portions and groove portions are alternately arranged.
When the concavo-convex pattern in the mold is transferred to the metallic layer, a concavo-convex pattern (or nanohole source) is formed in which concave lines (concave portions) and convex lines (convex portions) are alternately arranged. After that, when nanohole formation treatment (e.g., anodizing) is carried out, nanoholes can be formed at constant intervals only in the concave portions, whereby a porous layer on which the nanoholes are linearly arranged is formed.
The cross-sectional shape of the land portion (convex line) in the direction perpendicular to the longitudinal direction thereof is not especially limited and can appropriately be selected according to the purpose. Examples of the cross-sectional shape of the land portion include a quadrangle, V-shape, and semicircular shape.
The land portions (convex lines) are preferably arranged in a concentric or helical manner. In the case where a recording medium is used for a hard disk, the land portions are preferably arranged in a concentric manner in terms of accessibility; while in the case where a recording medium is used for a video disk, the land portions are preferably arranged in a helical manner because of advantage in continuous reproduction. In the case where the land portions are arranged in a concentric or helical manner, it is possible to arrange nanoholes to be formed in a concentric or helical manner correspondingly.
The height of the land portion in the concavo-convex pattern is not especially limited and can appropriately be selected according to the purpose but is preferably 5 nm or more and, more preferably, is 10 nm to 100 nm.
When the height of the land portion is less than 5 nm, fixation of the positions of nanohole sources are likely to be poor, which may in turn result in less regular arrangement of resulting nanoholes.
The material for the metallic layer can be any suitable material selected according to the purpose, such as elementary metals, as well as oxides, nitrides and alloys of such metals. Alumina (aluminum oxide) and aluminum can be taken as examples. Among them, especially preferred is aluminum.
The metallic layer can be formed using a known method. For example, sputtering or vapor deposition is preferably used.
Further, the metallic layer can be formed under any suitable condition according to the purpose.
In the case of sputtering, a sputtering target made of any of the metallic materials can be employed. The sputtering target used herein preferably has a high purity, and when the metallic material is aluminum, it preferably has a purity of 99.990% or more.
The metallic layer formation step preferably includes, prior to deposition of the metallic layer, applying a releasing agent on the concavo-convex pattern of the mold. This makes it easy to remove the mold from the metallic layer in the mold separation step to be described later.
The releasing agent is not particularly limited and may be suitably selected from various surface treating agents according to the purpose. Among them, fluorine-containing surface treating agents and silane coupling agents are preferably used.
Examples of the fluorine containing surface treating agent include, for example, “Novec EGC-1720” manufactured by Sumitomo 3M Ltd. Examples of the silane coupling agents include, for example, “Optool DSX” manufactured by Daikin Industries Ltd.
With the above steps, the metallic layer is formed on the concavo-convex pattern in the mold.
The soft magnetic underlayer formation step is a step in which a soft magnetic underlayer is formed on the metallic layer.
The soft magnetic underlayer can be formed using a known method. For example, formation of the soft magnetic underlayer may be conducted by means of vacuum film deposition such as sputtering or vapor deposition, electrodeposition, or electroless deposition.
With the soft magnetic underlayer formation step, the soft magnetic underlayer having a desired thickness is formed on the metallic layer.
If necessary, a metallic layer may be formed on the soft magnetic underlayer for the purpose of ensuring mechanical strength.
The electrode layer formation step is a step in which an electrode layer is formed between the metallic layer and soft magnetic underlayer.
The electrode layer can be formed using a known method. For example, sputtering or vapor deposition is preferably used. Further, the electrode layer can be formed under any suitable condition according to the purpose.
The electrode layer formed by the electrode layer formation step serves as an electrode in the formation of at least one of a soft magnetic layer, nonmagnetic layer and ferromagnetic layer by electrodeposition.
The substrate boding step is a step in which a substrate is bonded by adhesive to the surface of the metallic layer on the side opposite to the mold (in the case where the soft magnetic layer is formed or both the soft magnetic layer and metallic layer for mechanical strength are formed on the metallic layer, the substrate is bonded to the outermost surface of these layers on the side opposite to the mold).
The substrate can have any suitable shape, structure and size and be made of any suitable material according to the purpose. The substrate preferably has a disk shape when the magnetic recording medium is a magnetic disk such as hard disk. It can have a single layer structure or a multilayer structure. Examples of the material include glass, aluminum, silicon, and quartz.
Preferable examples of the substrate include a glass substrate, aluminum substrate, and silicon substrate as a magnetic disk substrate.
The substrate can be suitably prepared or is available as a commercial product.
The adhesive is not particularly limited and may be suitably selected according to the purpose, but preferably used adhesives include epoxy resin-based adhesives for their high bonding strength; low-hardening contraction type adhesives for their low hardening contraction ratios; modified silicone resin-based adhesives in view of the fact that they exhibit a high capability of bonding together materials having different thermal expansion coefficients; and cyanoacrylate-based adhesives in view of the fact that they set in a shot time. These adhesives can be used singly or in combination.
The epoxy resin adhesive is generally a two-component type. Preferable examples thereof include “Bond—white for repairing enameled products” and “Bond E-set” manufactured by Konishi Co., Ltd., “EP007” manufactured by Cemedine Co., Ltd., and “EPICLON EXA-4850 series” manufactured by Dainippon Ink & Chemicals Incorporated.
As the low-hardening contraction type adhesive, “EPICLON EXA-4850-150” manufactured by Dainippon Ink & Chemicals Incorporated. using TETA (TriEhylene TetraAmine) as hardening agent is preferable because of its flexibility, rigidity, and low hardening contraction ratio of 0.6%.
Preferable examples of the modified silicone resin adhesives include “Bond MOS7” manufactured by Konishi Co., Ltd., and “PM series” manufactured by Cemedine Co., Ltd.
A preferable example of the cyanoacrylate adhesive is “Bond Aron Alpha—impact resistance—for professional use” manufactured by Konishi Co., Ltd.
With the above steps, the substrate is bonded by the adhesive to the surface of the metallic layer on the side opposite to the mold. As a result, the metallic layer (in the case where the soft magnetic layer is formed or both the soft magnetic layer and metallic layer for mechanical strength are formed on the metallic layer, the metallic layer includes these layers) and substrate are laminated in this order on the concavo-convex pattern in the mold.
The mold separation step is a step in which the mold is separated from the metallic layer after the substrate bonding step.
The method of separating the mold from the metallic layer is not especially limited and any suitable method can be employed according to the purpose; for example, a separating method of making a cut in the end of the interface between the mold and metallic layer with a knife edge is used. However, a Ni stamper is generally used as the mold and, therefore, it is actually very difficult to separate nickel having a submicron structure from aluminum (the metallic layer) at their interface. That is, with the separation method using a knife edge, wrinkles may occur over the surface of the aluminum layer (metallic layer) due to non-uniform stress applied upon separation, as shown in
Thus, the mold separation step is preferably carried out using a push-up mechanism. More specifically, the push-up mechanism is used to push up the inner peripheral edge of the substrate having an opening in its center from the mold side. In this case, as shown in
The push-up mechanism can have any suitable configuration as long as it has a function of pushing up the substrate (the magnetic disk substrate) having an opening in its center at its inner peripheral edge from the mold to thereby separate the mold from the metallic layer. For example, as shown in
As the separation method using the push-up mechanism, there has been proposed, in a duplication technique of an optical disk using a photopolymer method, a method of separating a glass substrate that is bonded to a stamper (mold) with a photopolymer (see Re-published Patent WO2003/083854). This method aims at separating the photopolymer from the stamper at their interface, but differs from the mold separation step in the magnetic recording medium manufacturing method according to the present invention, and thus this patent literature fails to disclose separation of the mold from the metallic layer at their interface (metal-metal interface).
Hereinafter, an example of a method of manufacturing a bonded article composed of the substrate and metallic layer (aluminum layer) through the above metallic layer formation step, substrate bonding step, and mold separation step will be described with reference to the drawings.
As shown in
Subsequently, a unillustrated releasing agent is applied over the concavo-convex pattern P1 in the mold 12 and, as shown in
Subsequently, when the mold 12 is separated from the aluminum layer 13 as shown in
Further, after obtaining the bonded article composed of the substrate and the metallic layer having on its surface the concavo-convex pattern (i.e., after the mold separation step and before the porous layer formation step to be described later) through the above steps, the metallic layer that has been formed on the mold by the metallic layer formation step may be bonded to the surface of the substrate on the side opposite to the bonding surface to the metallic layer, followed by separation of the mold from the metallic layer. In this case, both the front and back sides of the substrate become available, whereby a double-sided recordable magnetic disk can be manufactured.
Hereinafter, a procedure of the metallic layer formation step, substrate bonding step, and mold separation step in the case where the two sides of the substrate are made available will be described with reference to the drawings.
First, the mold 12 for A-side is used to produce the bonded article 16 composed of the substrate 15, aluminum layer 13, and soft magnetic underlayer 14 (and further a unillustrated metallic layer for increased mechanical strength) shown in
Meanwhile, a mold for B-side is used to previously produce a structure in which a metallic layer has been formed on the mold for B-side through the metallic layer formation step. More specifically, as shown in
Then, the surface of the substrate 15 of the bonded article shown in
Subsequently, when the mold 32 for B-side is separated from the aluminum layer 13 formed on the mold 32 for B-side, the concavo-convex pattern P1 in the mold 32 for B-side is transferred with accuracy to the surface of the aluminum layer 13, whereby a concavo-convex pattern P2 that can serve as a nanohole source is formed (mold separation step, see
With the above steps, the aluminum layers 13 each having the concavo-convex pattern P2 are formed on both the front and back sides of the substrate 15. After the porous layer formation step and magnetic material charging step are carried out using the obtained structure, a double-sided recordable magnetic disk can be obtained.
In both the case of a single-sided structure and a double-sided structure, the metallic layer formation step, substrate bonding step, and mold separation step are preferably carried out for a plurality of substrates in a collective manner. In this case, it is possible to obtain a plurality of bonded articles each composed of the substrate and metallic layer at the same time, thereby increasing productivity.
Hereinafter, a procedure of the collective processing in the case where a single-sided structure is obtained will be described with reference to the drawings.
First, as shown in
The porous layer formation step is a step in which a porous layer is formed by performing nanohole formation treatment. The porous layer includes a plurality of nanoholes that are oriented in a direction substantially perpendicular to a plane of the substrate and that are formed by using as a nanohole source the concavo-convex pattern formed on the metallic layer through the transfer processing of the concavo-convex pattern in the mold.
The nanohole forming treatment can be any suitable treatment according to the purpose; examples include anodizing and etching. Among them, anodizing is particularly preferred since it can form a plurality of uniform nanoholes in the metallic layer at substantially equal intervals in a direction substantially perpendicular to a plane of the substrate.
The anodizing can be carried out by electrolyzing and etching the metallic layer in an aqueous solution of sulfuric acid, phosphoric acid or oxalic acid using an electrode contacting the metallic layer as an anode. The soft magnetic underlayer or the electrode layer can be used as the electrode.
The anodizing can be carried out at any suitable voltage but preferably at such a voltage satisfying the following relationship: interval (pitch) between adjacent rows of nanoholes (nm)/A (nm/V), (wherein A=1.0 to 4.0).
When the anodizing is carried out at a voltage satisfying the above equation, the nanoholes are advantageously arranged in the rows of concave portions in the concavo-convex pattern which has been formed through the transfer processing of the concavo-convex pattern in the mold.
When the substrate has a disk-shape, the nanoholes (fine pores) formed by the above nanohole formation treatment are arranged so as to extend in a direction substantially perpendicular to a free surface (plane) of the disk-shaped substrate.
The nanoholes may be through holes penetrating the nanohole structure or may be pits or convex portions not penetrating the porous layer. The nanoholes are preferably through holes penetrating the porous layer when the porous layer is used in the magnetic recording medium.
The nanoholes can be arranged in any suitable arrangement according to the purpose, bur are preferably arranged either a concentric manner or a helical manner when the nanohole structure is used in the magnetic recording medium such as a hard disk or video disk. In particular, they are preferably arranged in a concentric manner in the use for hard disks in view of accessibility, and are preferably arranged in a helical manner in the use for video disks for advantage in continuous reproduction.
In the case where the nanohole structure is used in the magnetic recording medium such as a hard disk, the nanoholes in adjacent nanohole rows are preferably arranged in a radial direction. The resulting magnetic recording medium is capable of high density, high speed recording without increasing a write current of the magnetic head, exhibits excellent and uniform properties such as overwrite properties, avoids crosstalk and crosswrite and is of very high quality.
The nanoholes can have openings with any suitable diameter according to the purpose. When the nanohole structure is used in the magnetic recording medium such as a hard disk, the diameter of opening is preferably such that the ferromagnetic layer becomes a single domain structure and is preferably 100 nm or less, more preferably 30 nm or less for realizing high density recording, and even more preferably 5 nm to 20 nm.
If the nanoholes have openings with a diameter exceeding 100 nm, in a magnetic recording medium, it results in failure to achieve a single domain structure in the magnetic recording medium, which is achieved by utilizing the above porous layer.
The nanoholes can have any suitable aspect ratio, i.e., the ratio of the depth to the diameter of opening. A high aspect ratio is preferable for higher anisotropy in dimensions and for higher coercive force of the magnetic recording medium. When the porous layer is used in a magnetic recording medium such as a hard disk, the aspect ratio is preferably 2 or more and more preferably 3 to 15.
An aspect ratio of less than 2 may invite insufficient coercive force of the magnetic recording medium.
The porous layer can have any suitable thickness according to the purpose. When the porous layer is used in the magnetic recording medium, the thickness is preferably 500 nm or less, more preferably 300 nm or less and even more preferably 20 nm to 200 nm.
If the porous layer having a thickness exceeding 500 nm is used in the magnetic recording medium, high-density information recording may not be achieved even if the magnetic recording medium further includes the soft magnetic underlayer. Thus, the porous layer must be polished to reduce its thickness and this requires time and costs, leading to poor quality.
The conditions the type, concentration, and temperature of an electrolyte and the time period for anodizing are not specifically limited and can be selected according to the number, size and aspect ratio of the target nanoholes. For example, the electrolyte is preferably a diluted phosphoric acid solution at intervals (pitches) of adjacent rows of nanoholes of 150 nm to 500 nm, is preferably a diluted oxalic acid solution at pitches of 80 nm to 200 nm, and is preferably a diluted sulfuric acid solution at a pitch of 10 nm to 150 nm. In any case, the aspect ratio of the nanoholes can be controlled by immersing the anodized metallic layer in, for example, a phosphoric acid solution to thereby increase the diameter of the nanoholes such as alumina pores.
When the porous layer formation step is carried out by the anodizing, a plurality of nanoholes can be formed in the metallic layer. However, a barrier layer may be formed at the bottom of the nanoholes in some cases. The barrier layer can be easily separated according to a known etching procedure using a known etchant such as phosphoric acid. Thus, a plurality of the nanoholes can be formed in the metallic layer so as to extend in a direction substantially perpendicular to the substrate surface and to expose the soft magnetic underlayer or the substrate from the bottom thereof.
The porous layer formation step forms the porous layer on or above the substrate or the soft magnetic underlayer.
The magnetic material charging step is a step in which a magnetic material is charged into the nanoholes formed in the porous layer.
The magnetic material charging step includes at least a ferromagnetic layer formation step for charging the ferromagnetic material into the nanoholes. The magnetic material charging step may include, if necessary, a soft magnetic layer formation step for charging the soft magnetic material into the nanoholes and a nonmagnetic layer formation step for forming a nonmagnetic layer (interlayer) between the ferromagnetic layer and soft magnetic layer.
The ferromagnetic layer formation step is a step in which a ferromagnetic layer is formed inside the nanoholes (or on or above the soft magnetic layer or the nonmagnetic layer, if formed in the nanoholes).
The ferromagnetic layer can be formed, for example, by depositing or charging the material for the ferromagnetic layer such as Fe, Co, Ni, FeCo, FeNi, CoNi, CoNiP, FePt, CoPt, or NiPt, inside the nanoholes typically by electrodeposition.
The electrodeposition can be carried out according to any suitable procedure under any suitable conditions according to the purpose. It is preferably carried out by applying a voltage to a solution containing one or more of the materials for the ferromagnetic layer using the soft magnetic underlayer or the electrode layer (seed layer) as an electrode and precipitating or depositing the material inside the nanoholes.
As a result of the ferromagnetic layer formation step, the ferromagnetic layer is formed inside the nanoholes in the porous layer.
The soft magnetic layer formation step is a step in which a soft magnetic layer is formed inside the nanoholes.
The soft magnetic layer can be formed, for example, by depositing or charging the material for the soft magnetic layer such as NiFe, FeSiAl, FeC, FeCoB, FeCoNiB, or CoZrNb, inside the nanoholes typically by electrodeposition.
The electrodeposition can be carried out according to any suitable procedure under any suitable conditions according to the purpose. It is preferably carried out by applying a voltage to a solution containing one or more of the materials for the soft magnetic layer using the soft magnetic underlayer or the electrode layer as an electrode and precipitating or depositing the material on the electrode.
As a result of the soft magnetic layer formation step, the soft magnetic layer is formed on or above the substrate, the soft magnetic underlayer or the electrode layer inside the nanoholes in the porous layer.
The nonmagnetic layer formation step is a step in which a nonmagnetic layer is formed on the soft magnetic layer.
The nonmagnetic layer can be formed, for example, by depositing or charging the material for nonmagnetic layer on the soft magnetic layer inside the nanoholes typically by electrodeposition.
The material for the nonmagnetic layer can be any suitable one selected from known materials such as Cu, Al, Cr, Pt, W, Nb, Ru, Ta and Ti. These materials can be used alone or in combination.
The electrodeposition can be carried out according to any suitable procedure under any suitable conditions according to the purpose. It is preferably carried out by applying a voltage to a solution containing one or more of the materials for the nonmagnetic layer using the soft magnetic underlayer or the electrode layer as an electrode and precipitating or depositing the material inside the nanoholes.
As a result of the nonmagnetic layer formation step, the nonmagnetic layer is formed on the soft magnetic layer or the like inside the nanoholes in the porous layer.
The polishing step is a step in which a surface of the porous layer is polished and flattened after the magnetic material charging step.
In the polishing step, the surface of nanohole structure can be polished according to any suitable known procedure. A suitable example thereof includes a CMP (Chemical Mechanical Polishing) process.
By flattening the surface of the magnetic recording medium in the polishing step, the magnetic head such as a vertical magnetic recording head can stably float to thereby realize high-density recording with good reliability.
Hereinafter, an example of a magnetic recording medium manufacturing method according to the present invention applied in the case where both sides of the substrate are used will be described with reference to the drawings.
In the same manner as described above, the mold 12 for A-side is used to produce the bonded article 16 composed of the substrate 15, aluminum layer 13, and soft magnetic underlayer 14 (and further a unillustrated metallic layer for increased mechanical strength) shown in
Meanwhile, as shown in
Then, the surface of the substrate 15 of the bonded article shown in
Subsequently, the mold separation step is carried out to remove the mold 32 for B-side from the aluminum layer 13 formed on the mold 32 for B-side (see
By applying the nanohole formation treatment (anodizing) to the aluminum layers 13 each having the concavo-convex pattern P2 formed on both the front and back sides of the substrate 15, a plurality of nanoholes 17A are formed in the direction substantially perpendicular to a plane of the substrate 15 using the concavo-convex pattern P2, whereby porous layers 17 are formed (porous layer formation step, see
Subsequently, in the magnetic material charging step, electrodeposition is carried out to charge a magnetic material 18 inside the nanoholes 17A (see
After the surfaces of the porous layers 17 in which the magnetic material 18 is charged inside the nanoholes 17A are flattened through the polishing step, protective films 19 are applied over the porous layers 17 followed by application of lubricant. As a result, a double-sided magnetic disk according to the present invention is obtained (see
The magnetic recording medium manufacturing method of the present invention is capable of providing a low cost, large capacity, and high density recording-enabled magnetic recording medium, achieving high pattern transfer accuracy, transferring a pattern that can serve as a source for forming anodized alumina-nanoholes with high precision, and realizing high productivity. Therefore, it is possible to manufacture a magnetic recording medium according to the present invention to be described below can be manufactured in an effective manner and at low cost.
The magnetic recording medium according to the present invention includes a substrate and a porous layer on the substrate through an adhesive layer and may further include other layers selected according to necessity.
The substrate can have any suitable shape, structure and size and can be formed of any suitable material according to the purpose. The details thereof are as described above. Preferable examples of the substrate include a glass substrate, aluminum substrate, and silicon substrate.
The adhesive layer has a function of bonding the substrate and porous layer together.
The material of the adhesive layer is not particularly limited and may be suitably selected according to the purpose, but the abovementioned adhesive are preferably used. Specific examples thereof include epoxy resin-based adhesives, low-hardening contraction type adhesives, modified silicone resin-based adhesive, and cyanoacrylate adhesives.
The porous layer includes a plurality of nanoholes which are formed in the direction substantially perpendicular to the substrate surface. The details thereof are as described above.
The porous layer can have any suitable thickness according to the purpose. The thickness thereof is preferably 500 nm or less, and more preferably 5 nm to 200 nm.
If the thickness exceeds 500 nm, it may become difficult to charge the magnetic material into the nanoholes.
The nanoholes in the porous layer may be through holes penetrating the porous layer or be pits or concave portions not penetrating the porous layer. The nanoholes are preferably through holes penetrating the porous layer in consideration of a case where another magnetic layer is formed under the magnetic layer obtained by charging the magnetic material into the nanoholes.
The porous layer preferably has, at constant intervals, rows of nanoholes each including a plurality of nanoholes regularly spaced.
The interval between adjacent rows of nanoholes can be any suitable interval. When the nanohole structure is used in the magnetic recording medium such as a hard disk, the interval is preferably from 5 nm to 500 nm and more preferably from 10 nm to 200 nm.
If the interval is less than 5 nm, the nanoholes may be difficult to form. If it exceeds 500 nm, it may become difficult to arrange the nanoholes regularly.
The ratio (interval/width) of the interval between adjacent rows of nanoholes to the width of a row of nanoholes can be any suitable ratio and is preferably from 1.1 to 1.9 and more preferably from 1.2 to 1.8.
The ratio (interval/width) less than 1.1 may invite fused adjacent nanoholes and fail to provide separated nanoholes. A ratio exceeding 1.9 may invite formation of nanoholes in extra portions other than rows of groove portions in anodizing.
The rows of nanoholes can each have any suitable width according to the purpose. When the nanohole structure is used in the magnetic recording medium such as a hard disk, the width is preferably from 5 nm to 450 nm and more preferably from 8 nm to 200 nm.
If the rows of nanoholes have a width less than 5 nm, the nanoholes may be difficult to form. If it exceeds 450 nm, it may become difficult to arrange the nanoholes regularly.
The nanoholes are preferably arranged in one of a concentric manner and a helical manner when the substrate has a disk-shape. In particular, they are preferably arranged in a concentric manner in the use for hard disks in terms of accessibility, and are preferably arranged in a helical manner in the use for video disks because of advantage in continuous reproduction.
Further, the nanoholes in adjacent nanohole rows are preferably arranged in a radial direction. The resulting magnetic recording medium enables recording of information at high density and high speed with a large storage capacity without increasing a write current of the magnetic head, exhibits satisfactory and uniform properties such as overwrite properties, avoids crosstalk and crosswrite and is of very high quality.
The nanoholes can have openings with any suitable diameter according to the purpose. When the nanohole structure is used in the magnetic recording medium such as a hard disk, the diameter of opening is preferably such that the ferromagnetic layer becomes a single domain structure and is preferably 200 nm or less, and, more preferably, 5 nm to 100 nm.
If the nanoholes have openings with a diameter exceeding 200 nm, a hard disk having a single domain structure may not be obtained.
The nanoholes can have any suitable aspect ratio, i.e., a ratio of the depth to the diameter of opening, according to the purpose. A high aspect ratio is preferable for higher anisotropy in dimensions and for higher coercive force of the magnetic recording medium, and, for example, the aspect ratio is preferably 2 or more and more preferably 3 to 15.
An aspect of ratio less than 2 may lead to insufficient coercive force of the magnetic recording medium.
The nanoholes are preferably filled with a magnetic material to form a magnetic layer inside thereof.
The magnetic layer can be any suitable one according to the purpose and may be, for example, a ferromagnetic layer and a soft magnetic layer. In the present invention, it is sufficient to form at least the ferromagnetic layer inside the nanoholes. If necessary, the soft magnetic layer may be formed between the substrate and ferromagnetic layer. Further, if necessary, a nonmagnetic layer (interlayer) may be formed between the ferromagnetic layer and soft magnetic layer.
The ferromagnetic layer functions as a recording layer in the magnetic recording medium.
The ferromagnetic layer can be formed from any known suitable material according to the purpose, such as Fe, Co, Ni, FeCo, FeNi, CoNi, CoNiP, FePt, CoPt and NiPt. These materials can be used singly or in combination.
The ferromagnetic layer can be any suitable layer formed from the material as a perpendicularly magnetized film. Suitable examples thereof are one having an Ll0 ordered structure with the C axis oriented in a direction perpendicular to the substrate plane, and one having a fcc structure or bcc structure with the C axis oriented in a direction perpendicular to the substrate plane.
The ferromagnetic layer can have any suitable thickness that does not adversely affect the advantages of the present invention and can be set depending on, for example, the linear recording density. The thickness is preferably (1) equal to or less than the thickness of the soft magnetic layer; (2) one-thirds to three times the minimum bit length determined by the linear recording density used in the recording; or (3) equal to or less than the total thickness of the soft magnetic layer and the soft magnetic underlayer. It is generally preferably from about 5 nm to about 100 nm and, more preferably, from about 5 nm to 50 nm. It is preferably 50 nm or less (around 20 nm) in magnetic recording at a linear recording density of 1,500 kBPI at a target density of 1 Tb/in2.
The thickness of the “ferromagnetic layer” means a total of the thickness of individual ferromagnetic layers when the ferromagnetic layer has plural continuous layers or plural separated layers, for example, in the case where the ferromagnetic layer is partitioned by one or more intermediate layers such as nonmagnetic layers and constitutes discontinuous separated ferromagnetic layers. The thickness of the “soft magnetic layer” means a total thickness of individual soft magnetic layers when the soft magnetic layer has plural continuous layers or plural separated layers, for example, in the case where the soft magnetic layer is partitioned by one or more intermediate layers such as nonmagnetic layers and constitutes discontinuous soft magnetic layers. The “total thickness of the soft magnetic layer and the soft magnetic underlayer” means a total of individual soft magnetic layers and soft magnetic underlayers when at least one of the soft magnetic layer and the soft magnetic underlayer has plural continuous layers or plural separated layers, for example, in the case where the soft magnetic layer or the soft magnetic underlayer is partitioned by one or more intermediate layers such as nonmagnetic layers and constitutes discontinuous soft magnetic (under) layers.
According to the magnetic recording medium of the present invention having the ferromagnetic layer and soft magnetic layer, the distance between a single pole head and the soft magnetic layer in magnetic recording can be less than the thickness of the porous layer and substantially equal to the thickness of the ferromagnetic layer. Thus, the convergence of a magnetic flux from the single pole head and the optimum properties for magnetic recording and reproduction at a recording density in practice can be controlled only by controlling the thickness of the ferromagnetic layer, regardless of the thickness of the porous layer. Consequently, the magnetic recording medium exhibits significantly increased write efficiency, requires a decreased write current and has markedly improved overwrite properties compared with conventional equivalents.
The ferromagnetic layer can be formed by means of any known suitable method such as electrodeposition.
The soft magnetic layer can be formed from any known suitable material according to the purpose, such as NiFe, FeSiAl, FeC, FeCoB, FeCoNiB and CoZrNb. These materials can be used singly or in combination.
The soft magnetic layer can have any suitable thickness that does not adversely affect the advantages of the present invention and is selected according to the depth of nanoholes in the porous layer and the thickness of the ferromagnetic layer. For example, (1) the soft magnetic layer has a thickness greater the thickness of the ferromagnetic layer, or (2) the total thickness of the soft magnetic layer and the soft magnetic underlayer may be greater than the thickness of the ferromagnetic layer.
The soft magnetic layer advantageously serves to effectively converge a magnetic flux from the magnetic head in magnetic recording to the ferromagnetic layer to thereby increase the vertical component of magnetic field of the magnetic head. The soft magnetic layer and the soft magnetic underlayer preferably constitute a magnetic circuit of a recording magnetic field supplied from the magnetic head.
The soft magnetic layer preferably has an axis of easy magnetization in a direction substantially perpendicular to the substrate plane. Thus, in magnetic recording using a vertical magnetic recording head, the convergence of a magnetic flux from the vertical magnetic recording head and the optimum properties for magnetic recording and reproduction at a recording density in practice can be controlled and the magnetic flux converges to the ferromagnetic layer. As a result, the magnetic recording medium exhibits significantly increased write efficiency, requires a decreased write current and has markedly improved overwrite properties compared with conventional equivalents.
The soft magnetic layer can be formed by any known suitable method such as electrodeposition.
The nanoholes in the porous layer may further include a nonmagnetic layer (interlayer) between the ferromagnetic layer and the soft magnetic layer. The nonmagnetic layer (interlayer) works to reduce the action of an exchange coupling force between the ferromagnetic layer and the soft magnetic layer to thereby control and adjust the reproduction properties in magnetic recording at desired levels.
The material for the nonmagnetic layer can be any suitable one selected from known materials such as Cu, Al, Cr, Pt, W, Nb, Ru, Ta and Ti. These materials can be used singly or in combination.
The nonmagnetic layer can have any suitable thickness according to the purpose.
The nonmagnetic layer can be formed by any known suitable method such as electrodeposition.
The magnetic recording medium may further have a soft magnetic underlayer between the substrate and porous layer.
The soft magnetic underlayer can be formed from any suitable material heretofore known such as those exemplified as the materials for the soft magnetic layer. These materials can be used singly or in combination. The material for the soft magnetic underlayer can be the same as or different from that for the soft magnetic layer.
The soft magnetic underlayer preferably has its axis of easy magnetization in an in-plane direction of the substrate. Thus, a magnetic flux from the magnetic head for recording effectively closes to form a magnetic circuit to thereby increase the vertical component of the magnetic field of the magnetic head. The use of the soft magnetic underlayer is also effective in recording in single domain at a bit size (diameter of opening of the nanoholes) of 100 nm or less.
The soft magnetic underlayer can be formed by any known suitable method such as electrodeposition or electroless plating.
The magnetic recording medium may further have one or more other layers according to the purpose, such as an electrode layer and protective layer.
The electrode layer works as an electrode during the formation of the magnetic layer (including the ferromagnetic layer and soft magnetic layer) by electrodeposition and is generally arranged on the substrate and below the ferromagnetic layer. To form the magnetic layer by electrodeposition, the electrode layer as well as the soft magnetic underlayer or another layer can be used as the electrode.
The electrode layer can be formed from any suitable material according to the purpose, such as Cr, Co, Pt, Cu, Ir, Rh, and alloys thereof. These can be used singly or in combination. The electrode layer may further contain any of other substances such as W, Nb, Ti, Ta, Si and O in addition to the aforementioned materials.
The electrode layer can have any suitable thickness according to the purpose. The magnetic recording medium may have one or more of such electrode layers.
The electrode layer can be formed according to any known suitable procedure such as sputtering or vapor deposition.
The protective layer works to protect the ferromagnetic layer and is arranged on or above the ferromagnetic layer. The magnetic recording medium may have one or more of such protective layers which have a single-layer structure or multilayer structure.
The protective layer can be formed from any suitable material according to the purpose, such as diamond-like carbon (DLC).
The protective layer can have any suitable thickness according to the purpose.
The protective layer can be formed by any known suitable method, such as sputtering, plasma CVD or coating.
The magnetic recording medium according to the present invention can be used in various magnetic recording systems using a magnetic head, and can favorably be used in magnetic recording using a single pole head.
The magnetic recording medium according to the present invention enables recording of information at high density and high speed with a large storage capacity and is of very high quality. Thus, the magnetic recording medium can be designed and used as a variety of magnetic recording media. For example, the magnetic recording medium can be designed and used as a hard disk drive widely used in external storage device for a computer and house-hold video recorders and can particularly suitably be designed and used as a magnetic disk such as a hard disk.
Examples of the present invention will hereinafter be described. It is however to be noted that these Examples are merely illustrative purpose only and shall not be construed as limiting the present invention.
Ni molds N1 and N2 having the same shape as a glass substrate for 1 inch HDD were prepared. The Ni mold Ni has, on its surface, a concentrically formed land/groove pattern (concavo-convex pattern) with a pitch of 90 nm, and N1 mold N2 has, on its surface, a concentrically formed land/groove pattern (concavo-convex pattern) with a pitch of 150 nm. The height of the land portions in the concavo-convex pattern was set to about 50 nm in both the Ni molds N1 and N2.
The Ni mold Ni (or N2) was bonded and fixed to a base made of SUS and then immersed in a releasing agent (“Novec EGC-1720” manufactured by Sumitomo 3M Ltd.) by a dip method, followed by withdrawal from the releasing agent at a speed of about 3 mm/s to 4 mm/s, whereby the coating of the releasing agent on the concavo-convex pattern in the Ni mold Ni (N2) was completed. Subsequently, the resultant Ni mold Ni (N2) was dried and heated at 100° C. for 30 minutes, followed by cooling to room temperature.
Then, the Ni mold Ni (N2) was set in a DC magnetron sputtering apparatus and subjected sputtering for 120 minutes using a 99.99% pure Al target at an Ar gas pressure of 0.3 Pa at an input power of 50 W to thereby form an aluminum layer having a thickness of 5 μm on the respective concavo-convex patterns of the Ni molds N1 and N2.
An adhesive (Bond-white for repairing enameled products” manufactured by Konishi Co., Ltd.), was applied to the surfaces of the obtained aluminum layers on the side opposite to the Ni molds N1 and N2, i.e., the sputtered surfaces of the Aluminum layers, and then glass substrates for 1 inch HDD were bonded to the respective aluminum layers. After curing of the adhesive, portions of the adhesive protruding out from the glass substrates were removed using a knife.
A separation tool having a push-up mechanism, which is as shown in
The separation tool shown in
The pressure pin 53 of the separation tool was pressed. Then, in the same manner as the push-up mechanism 20 described above (
Wrinkles did not appear on the surface of the aluminum layer after the substrate separation step, as shown in
Anodizing was applied to the aluminum layer 13 having, on its surface, the concavo-convex pattern P2 to form a plurality of nanoholes, thereby obtaining a porous layer shown in
The anodizing was carried out at an anodizing voltage of 40 V using 0.3 ML oxalic acid as anodizing solution at a bath temperature of 16° C. Further, current recovery was made in order to charging a magnetic material (Co) into the nanoholes by plating. The pitch of nanoholes can be represented by the following expression (1).
An observation was made for the nanohole pattern in the fine pore array (porous layer) obtained by the anodizing using a scanning electron microscope (SEM). As a result, a nanohole array as shown in
As shown in
Further, as shown in
It was confirmed from the above results that by using, as the nanohole source, the concavo-convex pattern which has been obtained by precisely transferring the land/grove pattern (concavo-convex pattern) in the Ni mold to the aluminum layer, the nanoholes can be formed as expected.
Ni mold was immersed in 0.1 wt % solution of silane coupling agent (“Optool DSX” manufactured by Daikin Industries Ltd.) in place of the releasing agent (“Novec EGC-1720” manufactured by Sumitomo 3M Ltd.) used in the metallic layer formation step in the transfer experiment (1), followed by drying the coating for about 3 hours. Subsequent substrate bonding step, mold separation step, and porous layer formation step were carried out in the same manner as the transfer experiment (1).
As a result, in the mold separation step, the mold was satisfactorily separated by means of the push-up mechanism from the aluminum layer without occurrence of wrinkles, and the land/groove pattern (concavo-convex pattern) in the Ni mold was precisely transferred onto the aluminum layer, whereby a concavo-convex pattern was formed on the aluminum layer. Further, in the porous layer formation step, it was confirmed that the nanoholes can be formed as expected by using the obtained concavo-convex pattern as the nanohole source.
The metallic layer formation step and substrate bonding step were carried out in the same manner as in the transfer experiment (1), and the mold separation step was carried out in the following manner to remove the mold from the aluminum layer.
A knife edge was inserted between the glass substrate for HDD and Ni mold to separate the glass substrate from the Ni mold. Although this separation step was carried out four or five times, wrinkles occurred on the surface of the aluminum layer as shown in
The pattern in the Ni mold was transferred onto the aluminum layer in the same manner as in the transfer experiment (1) to manufacture a double-sided magnetic recording medium.
As in the case of the transfer experiment (1), a Ni mold Ni for A-side having the same shape as a glass substrate for 1 inch HDD was prepared. The Ni mold Ni has, on its surface, a concentrically formed land/groove pattern (concavo-convex pattern) with a pitch of 90 nm. The height of the land portions in the concavo-convex pattern was set to about 50 nm.
The Ni mold Ni was bonded and fixed to a base made of SUS and then immersed in a releasing agent (“Novec EGC-1720” manufactured by Sumitomo 3M Ltd.) by dipping, followed by withdrawal from the releasing agent at a speed of about 3 mm/s to 4 mm/s, whereby application of the releasing agent over the concavo-convex pattern in the Ni mold Ni was completed. Subsequently, the resultant Ni mold Ni was dried and heated at 100° C. for 30 minutes, followed by cooling to room temperature.
Then, the Ni mold Ni was placed in a DC magnetron sputtering apparatus and sputtering was conducted under the same condition as in the transfer experiment (1) to thereby deposit an aluminum layer having a thickness of 300 nm on the concavo-concave patterns of the Ni mold Ni.
A CoZrNb/Ru/CoZrNb film is formed, as so-called an APS-SUL (Anti-Parallel Structure-Soft Magnetic Underlayer) on the obtained aluminum layer.
Further, a Ta film is so formed, as a metallic layer for mechanical strength to have a 1 μm thickness.
After the substrate bonding step was carried out in the same manner as the transfer experiment (1), the mold separation step was carried out using the push-up mechanism to remove the Ni mold (for A-side) from the aluminum layer, thereby obtaining a bonded article 16 composed of the glass substrate for HDD, aluminum layer, and soft magnetic underlayer (and further a unillustrated metallic layer for increased mechanical strength).
Meanwhile, as in the case of the metallic layer formation step and soft magnetic underlayer formation step, a Ni mold 32 (for B-side) having the same shape as the Ni mold (for A-side) was used to obtain a laminated structure in which an aluminum layer 13 and soft magnetic underlayer 14 (and further a unillustrated metallic layer for increased mechanical strength) are laminated in this order, as shown in
Then, the surface of the substrate 15 of the bonded article 16 shown in
Subsequently, the mold separation step was carried out using the push-up mechanism to remove the Ni mold 32 (for B-side) from the aluminum layer 13 (B-side) (see
Anodizing was applied to the respective aluminum layers 13 (A-side and B-side) having on the surfaces thereof the concavo-convex patterns under the same condition as in the transfer experiment (1) to form a plurality of nanoholes 17A, thus obtaining a porous layer 17 as shown in
Electrolytic deposition was carried out in an electrolyte containing 50 g/l of cobalt sulfate heptahydrate and 20 g/l of boracic acid at 50 Hz and at 10 V for 10 minutes to charge cobalt (Co) serving as a magnetic material 18 into the nanoholes to thereby form a ferromagnetic layer in the nanoholes 17A.
After the magnetic material charging step, the surface polishing was applied to the porous layer by flattening the cobalt (Co) protruded out from the nanoholes by CMP (see
After that, as shown in
Characterization of the obtained magnetic disk sample was conducted as follows.
Subsequently, the magnetic head was allowed to move up while rotating the disk sample for characteristic evaluation to record a magnetic signal of 400 nm frequency, and reproduction of the magnetic signal was performed. The obtained reproduction waveform is shown in
According to the present invention, it is possible to solve the problems inherent to related arts and to provide a low cost manufacturing method of a magnetic recording medium capable of transferring a pattern that can serve as a source for forming anodized alumina-nanoholes with high precision and realizing high productivity, and a large-capacity magnetic recording medium which is suitably used in a hard disk drive widely used as an external storage device for a computer, a household video recording device, and the like and which is capable of achieving high density recording.
The magnetic recording medium according to the present invention can suitably be used in a hard disk drive widely used as an external storage device for a computer, a household video recording device, and the like.
The magnetic recording medium manufacturing method according to the present invention can manufacture a large capacity magnetic recording medium capable of achieving high density recording with high productivity and at low cost and can particularly suitably be applied to the manufacturing of the magnetic recording medium according to the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-000566 | Jan 2007 | JP | national |
