Patent Application
20110070462
The present invention relates to a pattern forming method, a method for fabricating a discrete track magnetic recording medium using this pattern forming method, and a discrete track magnetic recording/reproducing apparatus equipped with a magnetic recording medium fabricated by this fabrication method. Priority is claimed on Japanese Patent Application No. 2008-129700, filed May 16, 2008, the content of which is incorporated herein by reference.
In magnetic disk units, as the track density increases, for example, magnetic record information, between adjacent tracks interferes with each other, and as a result, the magnetic transition area in the boundary region becomes a noise source, thereby easily causing problems such as a deterioration of the signal-to-noise ratio (SNR).
In order to avoid such problems, attempts have been made to form recessed and protruding portions (a protruding portion may be referred to as a land or peak portion and a recessed portion as a groove or valley portion, for example) on the surface of the magnetic recording medium to physically separate recording tracks, thereby enabling an increase in the track density. Such a technique is called a discrete track method or a patterned media method due to the shape of recessed and protruding portions.
Nanoimprint lithography has been attracting attention as a technique for forming a more precise recessed and protruding structure using the aforementioned methods with improved throughput (see Patent Document 1, for example). Particularly, when a precise pattern is formed, it is said that among the various techniques of nanoimprint lithography, UV nanoimprinting using an ultraviolet curable resin in a layer of the side to which the pattern is transferred is effective (see Patent Document 2, for example).
By the way, ultraviolet rays irradiated from an ultraviolet light source often cause unevenness in the illuminance of ultraviolet rays depending on the irradiated portion. If such unevenness in the illuminance of ultraviolet ray occurs on a substrate (or a workpiece) having an ultraviolet curable resin layer while the UV nanoimprint method is used, problems such as uneven curing of ultraviolet curable resin on the substrate may occur, and mold releasing failure may also occur along with the uneven curing. Consequently, further problems might be caused such that the succeeding process of microfabrication which utilizes the precise pattern formed on the substrate may not be carried out evenly.
Especially, when a magnetic recording medium is processed utilizing the UV nanoimprint method, a defect in only a very small portion of the medium might cause the entire medium to be defective. Therefore, problems such as uneven curing occurred in the ultraviolet curable resin are serious.
The present invention is proposed and intended to solve the above conventional problems and to provide a pattern forming method which prevents unevenness in the illuminance of ultraviolet rays irradiated onto a substrate and enables an ultraviolet curable resin on the substrate to be cured evenly.
The present invention also provides a method for fabricating a discrete track magnetic recording medium using this pattern forming method, and a discrete track magnetic recording/reproducing apparatus equipped with a magnetic recording medium fabricated by this fabrication method.
The present invention provides:
(1) a pattern forming method including: a first step of forming a first ultraviolet curable resin layer on a substrate; a second step of leading a pattern-formed surface of a first mold wherein a predetermined pattern is formed to oppose the first ultraviolet curable resin layer, and attaching the substrate to the first mold by applying a pressure; and a third step of irradiating diffused ultraviolet rays on the first ultraviolet curable resin layer, to which the pattern of the first mold is transferred by the pressure-attaching, the irradiated ultraviolet rays being diffused by disposing an ultraviolet light diffusion member between the ultraviolet curable resin layer and an ultraviolet light source;
(2) a pattern forming method as described in (1), wherein the third step is carried out simultaneously with the second step;
(3) a pattern forming method as described in (1), wherein the third step is carried out after the second step;
(4) a pattern forming method as described in any one of (1) to (3), further includes a step of preparing the first mold wherein the predetermined pattern is formed by forming a second ultraviolet curable resin layer on a resin sheet having a thickness in a range of 10 μm to 1 mm, and attaching a second mold having a pattern, wherein protruding portions and recessed portions are inverse to those of the predetermined pattern of the first mold, to the second ultraviolet curable resin layer in a manner in which the pattern having the inverse recessed and protruding portions comes into contact with the surface of the second ultraviolet curable resin layer, by applying a pressure to thereby transfer the pattern having the inverse recessed and protruding portions to the second ultraviolet curable resin layer;
(5) a pattern forming method as described in any one of (1) to (4), wherein the first mold has an ultraviolet ray transmittance of 20% or higher;
(6) a pattern forming method as described in any one of (1) to (5), wherein the first ultraviolet curable resin layer is formed by coating a liquid ultraviolet curable resin on the substrate;
(7) a pattern forming method as described in any one of (4) to (6), wherein the second ultraviolet curable resin layer is formed by coating a liquid ultraviolet curable resin on the resin sheet;
(8) a pattern forming method as described in any one of (1) to (7), wherein a diffusion plate or a fly eye lens is used as the ultraviolet light diffusion member;
(9) a pattern forming method as described in any one of (1) to (8), wherein the substrate is a magnetic recording medium;
(10) a method for fabricating a discrete track magnetic recording medium using a pattern forming method as described in any one of (1) to (9); and
(11) a magnetic recording/reproducing apparatus equipped with a discrete track magnetic recording medium fabricated by a method as described in (10).
The above-stated (2) to (9) are not essential factors, but illustrate preferable examples of the present invention.
According to the present invention, a pattern forming method which prevents unevenness in the illuminance of ultraviolet ray irradiated on a substrate and enables an ultraviolet curable resin on the substrate to be cured evenly can be provided.
According to the present invention, further proposed is a method for fabricating a discrete track magnetic recording medium using this pattern forming method, and a discrete track magnetic recording/reproducing apparatus equipped with a magnetic recording medium fabricated by this fabrication method.
The present invention relates to a pattern forming method to form a predetermined pattern on an ultraviolet curable resin using imprint technique, a method for fabricating a discrete track magnetic recording medium using this pattern forming method, and a discrete track magnetic recording/reproducing apparatus equipped with a magnetic recording medium fabricated by this fabrication method. A pattern forming method, a method for fabricating a discrete track magnetic recording medium, and a discrete track magnetic recording/reproducing apparatus to which the present invention is applied will be described below in detail with reference to the drawings. In the drawings used in the following description, featuring parts might be enlarged, for convenience, in order to make such features comprehensible, and the aspect ratio, etc. of each component might be different from the actual one. Moreover, the present invention is not limited to these embodiments, and addition, omission, substitution of the structure and various other changes and modifications (e.g. number, position, size and the like) may be made without departing from the spirit of the invention.
First of all, an embodiment of a pattern forming method to which the present invention is applied will be described.
UV nanoimprint technique using the pattern forming method of the present invention can be applied, for example, to fabrication of a magnetic recording medium having a pattern film.
Concretely, in order to apply the present invention to the fabrication of a magnetic recording medium having a pattern film, first of all, a magnetic recording medium 1 is prepared as a substrate as shown in
For a magnetic recording layer used in an in-plane magnetic recording medium, a lamination structure including a basal layer of non-magnetic CrMo and a magnetic layer of ferromagnetic CoCrPtTa, for example, can be used. For the magnetic recording layer used in a perpendicular magnetic recording medium, a lamination including a backing layer made of a soft magnetic FeCo alloy (such as FeCoB, FeCoSiB, FeCoZr, FeCoZrB, FeCoZrBCu, and the like), an FeTa alloy (such as FeTaN, FeTaC, and the like), a Co alloy (such as CoTaZr, CoZrNB, CoB, and the like) or the like, an orientation controlling film made of such as Pt, Pd, NiCr, NiFeCr and the like, an interlayer film made of Ru etc. if necessary, and a magnetic layer made of, for example, a 70Co-15Cr-15Pt alloy, a 90(80Co-5Cr-15Pt)/10SiO2 alloy, and the like can be used.
While the thickness of the magnetic recording layer may be selected according to necessity, it is generally in a range of 3 to 20 nm, and preferably in a range of 5 to 15 nm. The magnetic recording layer is required to be formed so as to obtain sufficient head input and output in accordance with the kind of magnetic alloys used and the lamination structure. The magnetic layer is required to have more than a certain film thickness in order to achieve a certain level of output when reproducing is performed. On the other hand, various parameters showing recording and reproducing properties are generally degraded with the elevation of output. Therefore, it is necessary to adjust the film thickness suitably. The magnetic recording layer is generally formed as a membrane by sputtering, and during this process, for example, a recessed and protruding structure is formed on the magnetic recording layer.
On a surface of the magnetic recording layer, a protective film layer is formed. For the protective film layer, a carbonaceous layer of such as carbon (C), hydrogenated carbon (H×C), nitride carbon (CN), amorphous carbon, silicon carbide (SiC), and the like, and other materials generally used for the protective film layer such as SiO2, ZrO2, Ti3N4 and the like can be used. Moreover, the protective film may be formed of two or more layers.
While the film thickness of the protective layer 3 is selected according to necessity, it is preferably less than 10 nm. When the film thickness exceeds 10 nm, the distance between the head and the magnetic layer gets wider, so that sufficient strength of input and output signals might not be obtained.
The protective film layer is generally formed by sputtering, and during this process, a protective film having recessed and protruding portions is formed following the aforementioned recessed and protruding structure. The protective film in the recessed portions tends to be thicker than that in the protruding portions.
Next, as shown in
Examples of the compounds having the (meth)acryloyl group include monomers such as: aliphatic mono (meth)acrylate such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, hexyl (meth)acrylate, octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, decyl (meth)acrylate, isobornyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate and the like; aromatic mono (meth)acrylate such as phenyl (meth)acrylate, benzyl (meth)acrylate, 2-hydroxyphenyl ethyl (meth)acrylate and the like; (meth)acrylamide such as N,N-dimethyl (meth)acrylamide, N,N-diethyl (meth)acrylamide, N-acryloyl morpholine and the like; aliphatic polyfunctional (meth)acrylate such as ethylene glycol di(meth)acrylate, propylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, trimethylolpropane di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol penta (meth)acrylate and the like; aromatic polyfunctional (meth)acrylate such as ethylene oxide-modified bisphenol A (meth)acrylate, propylene oxide-modified bisphenol A (meth)acrylate and the like; and fluorine-containing (meth)acrylate such as 2-trifluoromethyl propenoic acid trifluoroethyl ester, 2-trifluoromethyl propenoic acid t-butyl ester, 2,2,2-trifluoroethyl (meth)acrylate, 2,2,3,3-tetrafluoropropyl (meth)acrylate, 1H,1H,5H-octafluoropenthyl (meth)acrylate, perfluorooctyl ethyl (meth)acrylate and the like. Examples further include generally-called epoxy (meth)acrylates, which are formed by adding (meth)acrylate to epoxy resins such as bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, brominated bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolak type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, alicyclic epoxy resin, N-glycidyl type epoxy resin, bisphenol A novolak (type) epoxy resin, chelate type epoxy resin, glyoxal type epoxy resin, amino group containing epoxy resin, rubber-modified epoxy resin, dicyclopentadiene phenolic type epoxy resin, silicone-modified epoxy resin, epsilon-caprolactone modified epoxy resin, and the like, and various types of urethane (meth)acrylates are also included.
Examples of compounds having a vinyl ether group include: aliphatic monovinyl ethers such as 2-ethylhexyl vinyl ether, octadecyl vinyl ether, 4-hydroxybutyl vinyl ether, diethylene glycol monovinyl ether, triethylene glycol monovinyl ether, 9-hydroxynonyl vinyl ether, methoxyethyl vinyl ether, ethoxyethyl vinyl ether and the like; alicyclic monovinyl ethers such as cyclohexyl vinyl ether, 4-hydroxycyclohexyl vinyl ether, cyclohexanedimethanol monovinyl ether, tricyclodecanyl vinyl ether and the like; aliphatic divinyl ethers such as 1,4-butanediol divinyl ether, nonanediol divinyl ether, triethylene glycol divinyl ether and the like; alicyclic divinyl ethers such as cyclohexanediol divinyl ether, cyclohexanedimethanol divinyl ether, tricyclodecan dimethanol divinyl ether, pentacyclo pentadecan dimethanol divinyl ether and the like; and polyfunctional vinyl ethers such as trimethylolpropane trivinyl ether, pentaerythritol tetravinyl ether and the like.
Examples of the compounds having an N-vinyl amide group include N-vinyl formaldehyde, N-vinylpyrrolidone and the like.
Examples of the compounds having a cyclohexene oxide group include cyclohexene oxide and its derivatives such as 3′,4′-epoxycyclohexane carboxylate 3,4-epoxycyclohexylmethyl, limonene dioxide, vinyl cyclohexene oxide, bis-(3,4-epoxycyclohexylmethyl adipate), epoxidated butane tetracarboxylate tetrakis-(3-cyclohexenylmethyl) modified epsilon-caprolactone, 1,2-epoxy-4-(2-oxylanyl)cyclohexane adduct of 2,2-bis(hydroxymethyl)-1-butanol, 3,4-epoxycyclohexane-1-carboxylic acid allyl ester, 3,4-epoxycyclohexane-1-methyl-1-carboxylic acid allyl ester and the like. Examples of the compounds having a glycidyl group include epoxy resin such as bisphenol A type epoxy resin, hydrogenated bisphenol A type epoxy resin, brominated bisphenol A type epoxy resin, bisphenol F type epoxy resin, novolak type epoxy resin, phenol novolak type epoxy resin, cresol novolak type epoxy resin, alicyclic epoxy resin, N-glycidyl type epoxy resin, bisphenol A novolak type epoxy resin, chelate type epoxy resin, glyoxal type epoxy resin, amino group containing epoxy resin, rubber-modified epoxy resin, dicyclopentadiene phenolic type epoxy resin, silicone-modified epoxy resin, epsilon-caprolactone modified epoxy resin and the like. Examples of compounds having an oxetanyl group include oxethane resin such as ARON OXETANE series (trade name) manufactured by Toagosei Co., Ltd., ETERNACOLL OXETAN series (trade name) manufactured by Ube Industries, Ltd. and the like.
Besides those mentioned above, commercially available UV curable resins for nanoimprinting such as PAK-01 (product of Toyo Gosei Co., Ltd.), NIF-A-1 (product of Asahi Glass Co., Ltd.) and the like may be used. These ultraviolet curable resins may be used alone or in combination of two or more kinds. Further, when these ultraviolet curable resins are applied on substrates, one or more materials such as a surface conditioner, a viscosity control agent, a solvent and the like, for example, besides a photopolymerization initiator and a sensitizer may be added according to necessity.
Furthermore, it is desirable that the viscosity of the ultraviolet curable resin 5 at room temperature after the solvent is dried is not more than 10000 mPa·s from the viewpoint of a pattern transfer property described later. The thickness of the ultraviolet curable resin layer is preferably in a range of 30 to 300 nm, and more preferably in a range of 50 to 200 nm.
The method for forming the ultraviolet curable resin layer 5 is not particularly limited. For example, methods such as spin coating, dip coating, spray coating, ink jet printing and the like may be used and may be selected suitably according to the conditions such as viscosity of the ultraviolet curable resin 5 to be used.
Next, one or more first molds 7 having a pattern-formed surface are prepared. The number and/or shapes of the mold may be selected according to necessity. On the pattern-formed surface, a pattern 7A has been formed which has protruding portions that correspond to non-magnetic portions of the discrete track magnetic recording medium described later and recessed portions that correspond to magnetic portions thereof. As shown in
Materials and shapes of the stage 8 are not particularly limited as long as the stage can maintain the workpiece 6 and the first molds 7 stably. For example, the stage 8 may be a stage having grabbing jig 9 so as to chuck the molds 7 as shown in
For the first mold 7, it is desirable to use materials which transmit 20% or more of the ultraviolet rays irradiated upon the UV nanoimprinting. For example, molds formed by materials such as quartz, glass, cyclo-olefin polymer (e.g., trade name: ZEONOR, manufactured by Zeon Corporation), cyclo-olefin copolymer (e.g., trade name: APL, manufactured by Mitsui Chemicals Inc.; and trade name: TOPAS, manufactured by Polyplastics Co., Ltd.), polyethylene terephthalate, poly(4-methyl-pentene-1), polycarbonate and the like may be used. Moreover, these materials may be used alone or in combination of two or more by mixing or by laminating two or more layers in order to form the mold. The thickness of the first mold 7 is preferably in a range of 10 to 1000 μm, and more preferably in a range of 25 to 500 μm.
The first mold 7 can also be obtained by forming a second ultraviolet curable resin layer on a resin sheet, followed by forming the aforementioned pattern 7A on a surface of this second ultraviolet curable resin layer. For example, by attaching a second mold having a pattern inverse to the pattern 7A to the second ultraviolet curable resin layer by applying pressure in a manner in which the inverse pattern comes into contact with the surface of the second ultraviolet curable resin layer, the transferred pattern of this pattern may be used as the pattern 7A. Here, the inverse pattern signifies that the protruding and recessed parts are formed inverse. Therefore, the inverse pattern corresponds to the configuration of the pattern 7A, that is, the two patterns have the same configuration, and when the inverse pattern and the pattern 7A are laminated, the two patterns fit each other perfectly just as a casting and a mold. While the mold pattern may be selected according to necessity, to give a single example, the width of the protruding and/or recessed portions of the pattern is preferably in a range of 20 to 200 nm, and more preferably in a range of 30 to 150 nm. The difference of height between the protruding portion and the recessed portion is preferably in a range of 40 to 150 nm, and more preferably in a range of 60 to 100 nm.
As a concrete example, the second ultraviolet curable resin is applied on a resin sheet made of a material such as cyclo-olefin polymer, cyclo-olefin copolymer, polyethylene terephthalate, poly(4-methyl-pentene-1), polycarbonate and the like, and then a mother stamper (the second mold) is attached thereto by applying a pressure using UV nanoimprinting, and the pattern transferred thereby on the resin is used preferably as the first mold 7, since external waviness on the surface of the workpiece 6 can be easily followed and a high accuracy of mold pattern can be achieved according to this method. The pattern of the mother stamper has a pattern in which the protruding and recessed portions are inverse to those in the pattern 7A of the first mold 7.
While the thickness of the resin sheet may be selected based on necessity, from the viewpoint of handling property and following easiness with respect to the surface of the workpiece 6, it is preferably in a range of from 10 μm to 1 mm. While the thickness of the second ultraviolet curable resin may also be selected based on necessity, it is preferably in a range of from 1 μm to 100 μm from the viewpoint of accuracy and the like upon transferring the pattern of the mother stamper.
For the second ultraviolet curable resin, the same materials as those listed for the first ultraviolet curable resin 5 may be used. Further, in case that the resin sheet is stored for a long term after being coated by the second ultraviolet curable resin, it is preferable for the second ultraviolet curable resin that the second ultraviolet curable resin contains 50% by mass or more of, and preferably 70% to 100% by mass of solid resin or resin which has viscosity of 100000 mPa·s or more and preferably 500000 mPa·s or more at room temperature. Furthermore, in case great importance is attached particularly to the precision of the pattern of the prepared resin-made replica mold, it is desirable to use liquid resins having a viscosity of 50000 mPa·s or less, and preferably in a range of 3000 to 30000 mPa·s at room temperature. The viscosity of liquid resins may be measured using, for example, a rotational viscometer.
Members for attaching the workpiece 6 and the first mold 7 by pressure are not particularly limited. For example, a manner to hold them by hands, a manner to put a weight 12 on them as shown in
Here, the intensity of pressure for pressing down the first mold 7 to the workpiece 6 differs depending on the conditions such as the material and shape of the first mold 7, the material and shape of a substrate of the workpiece 6, the kind of the first ultraviolet curable resin 5 and the like. The pressure is preferably larger than 0 Pa and 50 Mpa or smaller. More preferably, the pressure is in a range of 0.001 to 3 Mpa. If pressure is not applied thereto at all, the surface of the workpiece 6 and the first mold 7 will not become parallel, so that there might be a portion where the first ultraviolet curable resin 5 and the first mold 7 do not come into contact with each other and/or the surface wherein the pattern 7A is formed might not become parallel with the substrate surface of the workpiece 6 but become oblique instead. On the other hand, when the pressure is too strong, the first mold 7 might be strained, and so the transfer accuracy might fall.
Next, an ultraviolet light source 17 irradiating ultraviolet (UV) rays on the stage 8 is disposed as shown in
A light diffusion member 18 which diffuses ultraviolet rays (UV) is disposed between the ultraviolet light source 17 and the first workpiece 6. The ultraviolet rays (UV) diffused by the light diffusion member 18 are irradiated on the first ultraviolet curable resin layer 5 via the first mold 7 to thereby cure the first ultraviolet curable resin layer 5 which exists at the upper side. Following this, the workpiece 6 and the first mold 7 are turned upside down as they remain attached together due to pressure. In addition, in the same manner, the first ultraviolet curable resin layer 5 which is now in the upper side by being turned is cured by irradiation of the diffused ultraviolet rays. As described above, the pattern 7A of the first mold 7 is transferred to the first ultraviolet curable resin layer 5 (referred to as a third step hereinafter).
The light diffusion member 18 may be selected based on necessity. For example, commercially available diffusion plates, fly eye lenses and the like can be used. The diffusion plates are roughly divided into three types: i) a type in which micro irregularities are formed as a rugged micro structure on a surface of a plate or sheet made of quartz, glass, resin and the like to thereby diffuse the light; ii) a type in which, in a matrix which is a plate or a sheet similar to type (i), particles having a refractive index different from that of the matrix are dispersed to thereby diffuse the light; and iii) a type in which a coating film which can diffuse the light is formed on a surface of a plate or sheet similar to type (i) to thereby diffuse the light. However, any type of light diffusion members can be used. The thickness of the light diffusion member 18 is preferably in a range of from 0.5 to 5 mm, and more preferably in a range of from 1 to 3 mm. The size of the light diffusion member is preferably larger than the size of the workpiece. Another desirable property for the light diffusion member 18 is to have a high ultraviolet ray transmittance in all of a wavelength region of 250 nm to 400 nm. Since resin generally has low light transmittance of light with a wavelength of 350 nm or less, light transmittance of the light diffusion member 18 of light with a wavelength of 380 nm, for example, is preferably in a range of 10 to 95%, and more preferably in a range of 40 to 95%. Further, it is desirable that light transmittance of infrared light having a wavelength of 800 nm or longer, i.e. a heat ray, is low so as not to cause distortion of the workpiece 6 and/or the first mold 7 due to a temperature rise.
These light diffusion members 18 may be used singly or in combination of two or more. The first mold 7 may have a function to diffuse ultraviolet rays (UV). Examples of the first mold 7 capable of diffusing the ultraviolet ray (UV) include those molds having micro irregularities, a coating film capable of scattering light or the like being formed on a surface opposite to the pattern formed surface wherein the pattern 7A has been formed.
For the ultraviolet light source 17, any light source may be used with no particular limitation as long as it can cure the first ultraviolet curable resin layer 5. From the viewpoint of reducing the influence of the heat ray irradiated on the workpiece 6 along with the ultraviolet ray (UV), it is desirable to use an LED (light emitting diode) type light source or continuous/pulsed light emitting type light source. The former does not irradiate a heat ray concurrently with the ultraviolet ray (UV) and the latter irradiates the heat ray only intermittently. Thus, there is a characteristic that the workpiece 6 and the first mold 7 may not be distorted easily due to high temperature during the ultraviolet ray (UV) irradiation. While the illuminance may be selected according to necessity, it is preferably in a range of from about 50 to 3000 mj/cm2, and more preferably in a range of from 100 to 1000 mj/cm2.
The shapes of the ultraviolet light source 17 can be selected according to necessity. Commercially available spot type light sources, lamp units and the like may be used. When an LED type light source is used, such an exclusive light source may be created to be used so that LED devices are disposed in accordance with the shape etc. of the workpiece 6. Furthermore, these ultraviolet light sources 17 may be used singly or in combination of two or more. Different types of light sources can also be combined to be used. However, it is desirable to dispose the light sources so that the illuminance of the ultraviolet rays (UV) the workpiece 6 receives may be as uniform as possible.
When the temperature of the ultraviolet light source 17 rises too much, the life thereof might be shortened remarkably, meaning it is not economical.
The illuminance of the ultraviolet rays (UV) the workpiece 6 receives can be measured as illustrated in
According to the present invention, the distance between the workpiece 6 and the ultraviolet light source 17, or that between the first mold 7 and the ultraviolet light source 17 is not particularly limited. However, it is desirable to leave a space of 1 mm or more so that the heat generated by the LED devices and/or peripheral wirings might not be conducted. If the heat is conducted to the first mold 7 and/or the workpiece 6, the pattern 7A might be distorted, and consequently the pattern might not be transferred with high precision.
While the distance from the ultraviolet light source 17 to the light diffusion member 18 may also be selected based on necessity, it is preferably in a range of from 5 to 300 mm, and more preferably in a range of from 10 to 100 mm. Further, while the distance from the light diffusion member 18 to the first ultraviolet curable resin layer 5 may also be selected based on necessity, in case the light diffusion member 18 is provided separately, it is preferably in a range of from 100 to 500 mm, and more preferably in a range of from 100 to 300 mm.
According to the present invention, there is no particular limitation to the atmosphere within which the ultraviolet ray irradiation is carried out. However, in case where the ultraviolet curable resin 5 coated on the magnetic recording medium 1 is radically curable, it is desirable to replace the atmosphere by an inert gas such as nitrogen. On the other hand, in the case that the ultraviolet curable resin 5 is of cation curable, it is desirable to perform replacement of atmosphere using dry air and the like. In these cases, the cure rate can increase. Further, carrying out the ultraviolet ray irradiation under a vacuum atmosphere (or a decompression atmosphere) has effects of preventing generation of void, and is also effective in increasing the cure rate.
Next, as shown in
As described above, by using the pattern forming method according to the present invention, a pattern film 5a having uniform tolerance to various kinds of processes in any part and having few defects such as deformation of a pattern due to the difference in curing shrinkage ratios and/or mold releasing failure can be fabricated on the magnetic recording medium 1. Consequently, a magnetic recording medium with a pattern film having excellent yield rate and processing precision can be fabricated.
The pattern forming method according to the present invention is not necessarily limited to the foregoing embodiments. Various changes and modifications may be made without departing from the spirit of the invention.
For example, in the above-described embodiments, one workpiece 6 prepared by forming the first ultraviolet curable resin layers 5 on both faces of the magnetic recording medium 1 is disposed on the stage 8 along with two first molds 7 sandwiching the workpiece 6 as shown in
Another embodiment is illustrated in
For the method for irradiating ultraviolet rays (UV), examples are illustrated in
In the above-described embodiments, after the second step wherein the workpiece 6 and the first mold 7 are attached by the application of a pressure, the third step wherein the diffused ultraviolet rays (UV) are irradiated on the workpiece 6 is carried out. However, such a process in the third step may be carried out simultaneously with the second step. For example, as illustrated in
Next, an example of a procedure for fabricating a discrete track magnetic recording medium will be described.
First of all, when a discrete track magnetic recording medium is fabricated, a magnetic recording medium 25 having pattern films 24, as shown in
Next, as shown in
Subsequently, the pattern film 24 and the protective layer 23 are peeled off as shown in
Then, as shown in
The discrete track magnetic recording medium 28 of the present invention can be obtained by following the above-described steps.
An example of a procedure for fabricating the discrete track magnetic recording medium of the present invention by carrying out the UV nanoimprinting using the pattern forming method according to the present invention has been described. However, the present invention is not necessarily limited to such a procedure.
For example, a magnetic recording medium 25 structured with magnetic layer(s) and protective layer(s) formed on a non-magnetic substrate is prepared. Mask layer(s) made of metal and the like is/are formed thereon, and an ultraviolet curable resin is coated further on the mask layer(s). Subsequently, a pattern film 24 made of an ultraviolet curable resin is formed by using the UV nanoimprinting method according to the present invention, and the pattern film 24 thus formed is used as a mask to thereby pattern the mask layer(s). Then, the patterned mask layer(s) may be used to pattern the magnetic layer(s) 22.
Still further, according to the present invention, methods other than partially removing the magnetic layer 22 can also be used in order to separate track areas mutually. For example, the pattern film 24 formed by the UV nanoimprinting method according to the present invention on the magnetic recording medium 25 is used as a mask, and on a part of the magnetic layer 22, atoms such as silicon, boron, fluorine, phosphor, tungsten, carbon, indium, germanium, bismuth, krypton, argon and the like may be injected by an ion beam method or the like as disclosed, for example, in Japanese Unexamined Patent Application, First Publication No. 2007-273067 so as to make an area where the magnetic part becomes amorphous to thereby separate track areas mutually.
Next, a magnetic recording/reproducing apparatus (HDD) employing the present invention will be described.
For example, the magnetic recording/reproducing apparatus employing the present invention as illustrated in
The head gimbal assembly 30 includes, as illustrated in
The magnetic head 31 is disposed in the vicinity part of the discrete magnetic recording medium 28 which is in the trailing side of the head slider 42 opposite to the leading side thereof on which slopes are formed.
The magnetic head 31 is composed of a recording part and a reproducing part. The magnetic head 31 may be selected according to necessity. For example, not only heads having an MR (magnetoresistance) device and the like utilizing a giant magnetoresistive (GMR) effect, but also heads, suitable for high recording density, having a TMR (Tunnel-type Magneto Resistive) device and the like utilizing a tunnel-type magneto resistive (TMR) effect can be used as a reproducing device. By using the TMR device, recordings of still higher density may be possible.
Since the magnetic recording/reproducing apparatus structured as described above includes the discrete magnetic recording medium 28 to which the present invention is applied, the amount of levitation of the magnetic head 31 can be reduced, thereby enhancing stability and heightening recording density.
For example, when the magnetic head 31 is levitated at height of 0.005 μm to 0.020 μm which is lower than conventional levitation amount, the output thereof improves so as to obtain high SNR (signal to noise ratio), so that the magnetic recording device with mass volume and high reliability can be provided.
Moreover, the magnetic recording/reproducing apparatus includes the discrete magnetic recording medium 28 on which such a pattern is provided that is composed of protruding portions formed by a magnetic layer and recessed separative regions. Consequently, a respective track is not easily affected by adjacent tracks, so that without changing the width of operating field such that widening upon recording and narrowing upon reproduction, both of the recording and the reproducing can be operated in almost the same head width. Therefore, compared with the case in which the reproducing head width is made narrower than the recording head width, this magnetic recording/reproducing apparatus can obtain enhanced reproducing output and a high signal to noise ratio (SNR).
Furthermore, in the magnetic recording/reproducing apparatus of the present invention, by forming the reproducing part of the magnetic head 31 with a GMR head or a TMR head, a satisfactory signal intensity can be obtained even in high recording density, so that a magnetic recording/reproducing apparatus having a high recording density can be provided.
Still further, when signal processing circuits adopting maximum likelihood decoding algorithm is combined to the magnetic recording/reproducing apparatus of the present invention, the recording density can be improved still further, and a satisfactory SNR can be obtained even when recording and reproduction are operated at recording densities such as a track density of 100 K track/inch or more, a linear recording density of 1000 Kbit/inch or more, and an a real recording density of 100 Gbit/in2 or more, for example.
The effect of the present invention will be described with reference to the following examples. The present invention is not limited to the following examples, and can be practiced by making various changes and modifications properly without modifying the fundamentals of the invention.
In an example, first of all, as illustrated in
Next, a circular plate 53 made of Ni having a diameter of 65 mm, a thickness of 0.3 mm, and a central pore 53a with a diameter of 12 mm was prepared, and a pattern 54 was formed on the circular plate 53 to thereby prepare a mother stamper 55 as shown in
Then, as shown in
Subsequently, as shown in
The lamination film 52 was then peeled off from the mother stamper 55 to thereby obtain a replica mold 61 having a pattern portion 60 which has an inverse shape of the pattern 54 of the mother stamper 55 as shown in
Next, 0.20 g of cationic photopolymerization initiator (product of San-Apro Ltd., trade name: CPI-100P), 0.10 g of 9,10-dibutoxyanthracene as a sensitizer, and 93.2 g of propylene glycol monomethyl ether acetate as a solvent were added to 6.5 g of oxetanyl group-containing silsesquioxane resin (product of Toagosei Co., Ltd., trade name: OX-SQ-H) and the mixture was dispersed in a dark room by using a mix rotor at 60 rpm for 12 hours to prepare an ultraviolet curable resin solution A.
Next, a magnetic recording medium 62 formed by depositing a magnetic layer for perpendicular recording and a protective layer on one side of a disc-like glass substrate having a diameter of 48 mm, a thickness of 0.6 mm, and a central pore with a diameter of 12 mm was prepared. The ultraviolet curable resin solution A prepared as above was then coated on one side of the magnetic recording medium 62 by spin coating to a thickness of about 60 nm. Following the coating step, the replica mold 61 fabricated previously was disposed in a manner in which the pattern portion 60 faces downward as shown in
Subsequently, as shown in
After irradiation, the replica mold 61 was separated from the magnetic recording medium 62. As a result of visually inspecting the pattern film formed on the magnetic recording medium 62, defects such as transfer failure, mold releasing failure, and the like were not confirmed.
This comparative example was carried out in the same manner as the above-described example except that in the UV nanoimprint step on the magnetic recording medium, the aforementioned diffusion plate 65 was not mounted onto the ultraviolet irradiation device 66 upon irradiation of the ultraviolet rays. As a result, it was confirmed that upon mold releasing, the pattern film was peeled off from the magnetic recording medium 62 and adhered to the replica mold 61 in 5 places.
The present invention can provide a pattern forming method which prevents unevenness in the illuminance of the ultraviolet rays irradiated on the substrate and enables to cure the ultraviolet curable resin on the substrate evenly.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-129700 | May 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/059014 | 5/14/2009 | WO | 00 | 11/12/2010 |
