Patent Application
20090073593
1. Field of the Invention
The present invention relates to a master carrier for magnetic transfer and a magnetic transfer method using this, and a magnetic recording medium created by the method, and particularly relates to a technique of magnetically transferring an information pattern such as servo information to a perpendicular magnetic recording type magnetic recording medium (magnetic disk) with a large capacity and high recording density.
2. Description of the Related Art
In recent years, magnetic recording and reproducing apparatuses tend to have high densification in recording density in order to realize miniaturization and a large capacity, and especially in the field of a hard disk drive (HDD) which is a typical magnetic storage device, abrupt advance in technology is seen.
With an increase in information content, inexpensive high density magnetic recording media with a large capacity capable of recording a large amount of information and preferably providing so-called quick access capable of reading a required point within a short time are desired. In these high density magnetic recording media, information recording regions are constituted of narrow tracks. In order to accurately scan a narrow track width by a magnetic head and reproduce a signal at a high S/N, a so-called tracking servo technology plays an important role. In order to perform tracking servo, a sector servo method is widely adopted.
The sector servo method is a method in which servo information including servo signals for positioning tracks, address information signals for the tracks, reproduction clock signals and the like is recorded in servo fields correctly arranged at constant angles or the like on the data surface of a magnetic recording medium such as a magnetic disk, and a magnetic head scans the servo fields to read the servo information and makes correction while confirming its own position.
Servo information needs to be recorded beforehand as a pre-format on a magnetic recording medium when the magnetic recording medium is fabricated. Presently, pre-formatting is performed using a dedicated servo recording device. The servo recording device which is presently used includes a magnetic head having a head width of about 75% of a track pitch, for example, and while rotating a magnetic disk with the magnetic head close to the magnetic disk, the servo recording device records servo signals while moving the magnetic head from the outer circumference of the magnetic disk to the inner circumference at every half track. Therefore, the servo recording device requires a long time for pre-format recording of one magnetic disk, and has a problem in production efficiency, which becomes a factor that increases cost.
Therefore, as a method for performing pre-formatting accurately and efficiently, there is proposed a method for magnetically transferring the information of the master recording medium on which a pattern corresponding to the servo information is formed to a magnetic recording medium (Japanese Patent Application Laid-Open No. 2003-203325, Japanese Patent Application Laid-Open No. 2000-195048, U.S. Pat. No. 7,218,465B1 and the like).
In the magnetic transfer, by using a master carrier having a magnetic layer pattern corresponding to information (for example, servo information) to be transferred to a magnetic recording medium (slave medium) such as a magnetic disk for transfer, a recording magnetic field is applied with the master carrier and the magnetic recording medium (slave medium) in tight contact with each other, and thereby, the magnetic pattern corresponding to the magnetic layer pattern of the master carrier is magnetically transferred to the magnetic recording medium. This method has the advantages that recording can be statically performed without changing relative positions of the master carrier and the magnetic recording medium, accurate pre-format information can be recorded, and the time required for recording is an extremely short time.
With high densification of magnetic recording, high-density (short bit) recording is also desired in magnetic transfer. However, magnetic transfer is under severe circumstances in which as the bits become shorter, the magnetic fields themselves of the convex portions usable for transfer become smaller, a magnetic difference between the convex portion and concave portion decreases, and with this, a magnetization difference of slave media does not increase, while spacing loss becomes larger in shorter bit. Therefore, new technical innovation is desired.
As is obvious from the graph of
Conventionally, an isotropic (without magnetic anisotropy) soft magnetic material is frequently used for the magnetic layers of master carriers. As the soft magnetic layer which is applied to a master carrier, the one with large saturation magnetization Ms is generally said to be preferable, and conventionally, Fe7Co3 and the like are used as the magnetic layers of master carriers. Further, paragraph [0006] of Japanese Patent Application Laid-Open No. 2003-203325 also has the description that the saturation magnetization Ms of the master magnetic layer is preferably made large.
However, it is not such a simple matter as the larger the saturation magnetization Ms is made, the better. Specifically, when a magnetic layer with large saturation magnetization Ms is provided on the master carrier, a demagnetizing field (4π×Ms in the case of a plane) also becomes large, and therefore, even if a magnetic field is applied, only a part of it contributes to magnetization.
Occurrence of a demagnetizing field depends on the shape of a magnetic substance (relative relationship of the shape length), and an example of it is shown in
When transfer to the slave medium with a coercive force Hc=4000 Oe is taken as an example, magnetization of the master magnetic layer (Fe7Co3 in this case) when a magnetic field Ha=5000 Oe is applied is about 950 emu/cc from the graph of
As the transfer magnetic field Ha is increased, the amount of magnetization at the point which is in contact with the slave medium (master convex portion) increases, but a lot of magnetic field leaks out to the concave portion (portion which should maintain initial magnetization of the slave medium) of the master carrier, and therefore, there arises the problem that the value of the initial magnetization significantly decreases and the S/N of the transfer signals degrades. Accordingly, from the viewpoint of keeping balance, a magnetic field close to the coercive force Hc of the slave medium is applied in the conventional magnetic transfer to set the magnetization difference between the convex portion and the concave portion to be the maximum. However, in this case, a considerable amount of magnetic field also flows into the concave portion due to a demagnetizing field to degrade the initial magnetization of that portion.
Further, in perpendicular magnetic transfer, magnetic transfer is caused by moving the magnetic field of the master concave portion (between bits not contacting the magnetic layer) to the convex portion. When high density recording is performed and an area between bits becomes short, spacing loss becomes large as the bits become shorter while a usable magnetic field becomes less. Therefore, requirement of the magnetic transfer by short bits cannot be satisfied by the conventional magnetic layer.
Meanwhile, Japanese Patent Application Laid-Open No. 2000-195048 has the description that a perpendicular magnetization film having magnetic anisotropy in the perpendicular direction is preferable (paragraph [0037] of Japanese Patent Application Laid-Open No. 2000-195048) as the master magnetic layer in the case of perpendicular recording, but has no disclosure of required physical property values and the like. A number of studies on a perpendicular magnetic anisotropy film have been done following development of magnetic recording media, but these studies relate to perpendicular magnetization films for magnetic recording, and do not relate to the magnetic film used for a master carrier. The physical property required as the magnetic film for a perpendicular magnetic recording medium and the physical property required as a master magnetic layer are significantly different, and if the perpendicular magnetic film for a magnetic recording medium which has been conventionally studied is directly applied to a master magnetic layer, a favorable transfer characteristic cannot be obtained.
Application of the magnetic layer with the M-H curve as in
As described above, it is found out that when the perpendicular magnetization film, which is required in the magnetic recording media, is used as the magnetic layer of the master carrier, favorable characteristics are not obtained.
U.S. Pat. No. 7,218,465B1 proposes the configuration of the master carrier in which the permanent magnetization film with perpendicular magnetic anisotropy is buried in a concave portion, but with the technical content described in U.S. Pat. No. 7,218,465B1, transfer of a short bit cannot be realized. As the reason of it, first of all, U.S. Pat. No. 7,218,465B1 does not describe the viewpoint of the perpendicular magnetic anisotropic film with what property being effective. As the magnetic properties, the conditions of saturation magnetization Bsat≧about 0.5 T, magnetic permeabilityμ≧about 5 are described (column 4, lines 58 to 60 of U.S. Pat. No. 7,218,465B1), but it is already described that with only the condition of Bsat≧about 0.5 T, transfer cannot be performed sufficiently favorably due to a demagnetizing field. Further, with regard to the master carrier, larger μ is more preferable, but it is already known that μ≧100 are sufficient, and a new condition is not especially proposed.
Secondarily, U.S. Pat. No. 7,218,465B1 describes that the material of the magnetic film is selected from Ni, NiFe, CoNiFe, CoSiFe, CoFe and CoFeV, but these materials cannot satisfy the characteristics of the present invention which will be describe later, and favorable transfer characteristics cannot be obtained.
Thirdly, the configuration described in U.S. Pat. No. 7,218,465B1 has the form in which a magnetic layer 304 is buried in a concave portion of a master carrier 300, and a transfer surface of the master carrier 300 is a plane with respect to a slave. It is a difficult technique to bring such a flat master and a flat slave into tight contact with each other over a large area. Especially in a short bit, the influence of spacing loss becomes large, and therefore, the burying method which makes a contact area large is not suitable.
Further, the master and the slave need to be separated after tight contact. However, since the contact area increases (since the contact area increases to be about twice as large as the concavo-convex type), adhesive force increases, and since the magnetic coupling and a force for binding all the positive and negative bits to the master are about doubled, separation becomes difficult, which is unfavorable in suitability for mass production.
Fourthly, when the slave and the master are separated after transfer, they cannot avoid moving in the disk radius direction. Therefore, in the case of a permanent magnetization film, there arises the problem that the slave undergoes modulation by the magnetic field from the master, and the S/N degrades.
Further, the art described in Japanese Patent Application Laid-Open No. 2003-203325 is not suitable for transfer of a short bit from the following reason. Specifically, Japanese Patent Application Laid-Open No. 2003-203325 is the art of preventing spread of the transfer pattern by reversing the direction of a magnetic flux between the magnetic bits by using a two-layer perpendicular ferromagnetic film as the magnetic layer of the master carrier. However, only the materials with low saturation magnetization Ms are known as the materials which can actually realize the art, and in the disclosure example of Japanese Patent Application Laid-Open No. 2003-203325, the Ms of TbFeCo is 40 emu/cc and the Ms of TbFe is 300 emu/cc, which are extremely small. Accordingly, they are insufficient for being applied to the coercive force Hc≧4000 Oe which is required in the high density media.
Further, the master carrier described in Japanese Patent Application Laid-Open No. 2003-203325 requires two layers of different materials as the magnetic layer, and therefore, fabrication process is complicated. In addition, the entire transfer portion is flat in Japanese Patent Application Laid-Open No. 2003-203325 as the embedded type master carrier (FIG. 22) of U.S. Pat. No. 7,218,465B1, and therefore, it is also a difficult art as described above to bring the flat master carrier and the flat slave medium into tight contact with each other over the entire slave to the level which enables recording of short bits. Further, as in U.S. Pat. No. 7,218,465B1, separation of the master carrier and the slave medium is difficult, which is unfavorable in suitability for mass production.
As described above, with the conventionally proposed arts, realization of magnetic transfer of a short bit is difficult.
The present invention is made in view of the above circumstances, and has an object to provide a master carrier capable of generating a high magnetic field which enables transfer of a short bit to a high density medium, and an object to provide a master carrier which can be fabricated by a simple process and has a form which facilitates tight contact with and separation from a slave. Further, the present invention has an object to provide a magnetic transfer method using such a master carrier and a magnetic recording medium fabricated by the method.
In order to attain the above-described object, a master carrier for magnetic transfer according to an aspect of the present invention, for magnetic transfer which is brought into contact with a magnetic recording medium when magnetic information is transferred to the magnetic recording medium, comprises: a transfer portion on which a magnetic layer corresponding to magnetic information for transfer is formed; and a non-transfer portion which forms a concave shape relatively low with respect to the transfer portion having the magnetic layer, wherein the magnetic layer has perpendicular magnetic anisotropy, with residual magnetization Mr of 500 emu/cc or less, and saturation magnetization Ms of 900 emu/cc or more.
As the magnetic material of the magnetic layer, for example, CoPt can be used, and of CoPt, Co4Pt1 (at %) is more preferable.
Further, the master carrier for magnetic transfer may further comprise an under layer, under the magnetic layer, which is made of any one of CoCr, Ru, and Pt, or a combination of any of CoCr, Ru, and Pt
Further, as another aspect of the present invention, the magnetic layer of the transfer portion on the master medium for magnetic transfer may be more convex (more specifically, relatively high) than other portions.
Further, the present invention provides a magnetic transfer method using the above described master carrier for magnetic transfer according to the aspects of the present invention. Specifically, a magnetic transfer method according to the present invention comprises: an initial magnetizing step of, using a perpendicular magnetic recording medium with a coercive force Hc of 4000 Oe or more, initially magnetizing the perpendicular magnetic recording medium in a perpendicular direction; a tight contact step of bringing the master carrier for magnetic transfer according to any one of the aspects of the present invention, into tight contact with the perpendicular magnetic recording medium after the initial magnetizing step; and a transfer step of applying a perpendicular magnetic field whose direction is opposite to that of the initial magnetization with the perpendicular magnetic recording medium in tight contact with the master carrier for magnetic transfer, and transferring magnetic information to the perpendicular magnetic recording medium.
By using the master carrier for magnetic transfer or the magnetic transfer method according to any one of the aspects of the present invention, a perpendicular magnetic recording medium in which information such as a servo signal is recorded can be produced.
According to the master carrier for magnetic transfer according to the aspects of the present invention, by the height difference between the transfer portion and non-transfer portion, tighter contact can be ensured in the transfer portion at the time of transfer, and after transfer, the master carrier and the magnetic recording medium (slave medium) can be easily separated. Further, the master carrier for magnetic transfer according to the aspects of the present invention has large saturation magnetization Ms, and therefore, a transfer magnetic field capable of sufficient recording can be applied to a magnetic recording medium with high density and a high coercive force Hc. In addition, the master carrier has small residual magnetization Mr, and therefore, degradation (occurrence of noise) of a transfer signal due to a residual magnetic field can be suppressed when the master carrier is separated after transfer.
As above, according to the aspects of the present invention, transfer with high density and high performance (favorable S/N) can be realized. Further, the structure of the master carrier for magnetic transfer is simple as compared with the configuration of Japanese Patent Application Laid-Open No. 2003-203325, and can be easily fabricated.
Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the attached drawings.
First, a magnetic transfer technique of perpendicular magnetic recording will be roughly described by using
First, as shown in
The slave disk 10 used in the embodiment is such that a magnetic layer constituted of a perpendicular magnetization film is formed on one surface or both surfaces of a disk-shaped substrate, and a high density hard disk or the like can be cited in concrete.
The disk-shaped substrate 12 comprises a nonmagnetic material such as glass and Al (aluminum). After the soft magnetic layer 13 is formed on the substrate 12, the nonmagnetic layer 14 and the magnetic layer 16 are formed.
The soft magnetic layer 13 is useful for stabilizing the perpendicular magnetization state of the magnetic layer 16, and enhancing sensitivity at the time of recording and reproducing. As the materials used for the soft magnetic layer 13, soft magnetic materials such as CoZrNb, FeTaC, FeZrN, an FeSi alloy, an FeAl alloy, an FeNi alloy such as permalloy, and an FeCo alloy such as permendur are preferable. The soft magnetic layer 13 is provided with magnetic anisotropy in a radius direction (radially) from the center of the disk to the circumference.
The thickness of the soft magnetic layer 13 is preferably 50 nm to 2000 nm, and more preferably, 80 nm to 400 nm.
The nonmagnetic layer 14 is provided for the reason of increasing the magnetic anisotropy in the perpendicular direction of the magnetic layer 16 which is formed later and the like. As the materials used for the nonmagnetic layer 14, Ti (titanium), Cr (chromium), CrTi, CoCr, CrTa, CrMo, NiAl, Ru (ruthenium), Pd (palladium), Ta, Pt and the like are preferable. The nonmagnetic layer 14 is formed by depositing the above described material by a sputtering method. The thickness of the nonmagnetic layer 14 is preferably 10 nm to 150 nm, and more preferably 20 nm to 80 nm.
The magnetic layer 16 is formed from a perpendicular magnetization film (the easy axis of magnetization in the magnetic film is mainly oriented perpendicularly to the substrate), and information is recorded in the magnetic layer 16. As the material used for the magnetic layer 16, Co (cobalt), Co alloys (CoPtCr, CoCr, CoPtCrTa, CoPtCrNbTa, CoCrB, CoNi and the like), Co alloy-SiO2, Co alloy-TiO2, Fe, Fe alloys (FeCo, FePt, FeCoNi and the like) and the like are preferable. The materials have large magnetic flux density, and perpendicular magnetic anisotropy by adjusting the deposition conditions and compositions. The magnetic layer 16 is formed by depositing the above described material by a sputtering method. The thickness of the magnetic layer 16 is preferably 10 nm to 500 nm, and more preferably 20 nm to 200 nm.
In the present embodiment, a disk-shaped glass substrate of an outside diameter of 65 mm is used as the substrate 12 of the slave disk 10, and the glass substrate is placed in the chamber of a sputtering device. After decompression to 1.33×10−5 Pa (1.0×10−7 Torr), Ar (argon) gas is introduced into the chamber. By using a CoZrNb target in the chamber and setting the temperature of the substrate in the chamber at a room temperature, an SUL first layer of a thickness of 80 nm is deposited by sputtering. Next, on the SUL first layer, an Ru layer of 0.8 nm is deposited by sputtering by using an Ru target in the chamber. Further, on the Ru layer, an SUL second layer of a thickness of 80 nm is deposited by sputtering by using the CoZrNb target. The SUL thus deposited by sputtering is heated and then cooled to the room temperature, with a magnetic field of 50 Oe or more applied in the radius direction.
Next, sputtering deposition is performed by using the Ru target and causing discharge under the condition of the substrate temperature at a room temperature. Thereby, the nonmagnetic layer 14 constituted of CrTi is deposited to 60 nm.
Thereafter, Ar gas is introduced similarly to the above description, and by using the CoCrPt target in the same chamber, discharge is caused under the condition of the substrate temperature at the same room temperature, whereby deposition by sputtering is performed. Thereby, the magnetic layer 16 of the granular structure constituted of CoCrPt—SiO2 is deposited to 25 nm.
By the above process, the magnetic disk for transfer (slave disk) 10 in which the soft magnetic layer, the nonmagnetic layer and the magnetic layer are deposited on the glass substrate is produced.
Next, initial magnetization of the slave disk 10 which is formed is performed. As described in
Next, the master disk 20 which is a master carrier will be described.
In the form of
In the present description, the term “bit is short” or “short bit” means that the width of the magnetic layer 204 on the convex portion 206 is short as shown in the example of
In both forms of
In the following description, an example of adopting the form of
Desirable magnetic properties as the magnetic film 204 of the master disk 20 are shown in Table 1. In Table 1, the properties of the perpendicular magnetic recording film used for the recording layer of the slave disk 10 are shown in contrast for comparison.
Hereinafter, appropriateness of the conditions of Table 1 as the magnetic layer of the master carrier will be described.
As shown in
The horizontal axis of
As shown in
The effect leads to decrease in the magnetic field of the concave portion, and the magnetic field distribution in the transition region becomes sharp (change of the magnetic field of the convex portion and the magnetic field of the concave portion becomes steep).
The vertical axis of
The residual magnetization Mr of the master magnetic layer has desirably a small value. If the residual magnetization Mr is larger than a certain value, a magnetic field occurs from the master disk even after application of the transfer magnetic field is released. Therefore, unnecessary transfer occurs when the master disk 20 is separated from the slave disk 10, and this becomes noise of the signal.
After the transfer step shown in
The slave magnetization state of the region (reference numeral 102) except for the portions in contact with the convex portions has to keep the state of initial magnetization, but when the residual magnetization Mr of the master magnetic layer is high, the magnetic field still occurs from the master magnetic layer even after the transfer magnetic field is eliminated, a part (reference numeral 103) of the portions 102 corresponding to the concave portions receives the influence of the residual magnetic field by movement in the in-plane direction at the time of separation of the master, whereby the state of the initial magnetization degrades.
From the viewpoint of avoiding such a problem, the residual magnetization Mr of the master magnetic layer is desirably set at 500 emu/cc or less. The reason of this will be described hereinafter.
According to
The horizontal axis of
The influence such that a residual magnetic field has on the slave disk after transfer will be discussed. In the slave disk of the magnetic layer having the characteristics of the M-H curve shown in
When the master disk 20 is assumed to move by several tens nm in the in-plane direction when the master disk 20 is separated from the slave disk 10 after the transfer magnetic field is made zero after the magnetic transfer step, in the case of the master of the perpendicular anisotropic film of the residual magnetization Mr 1000 emu/cc (SQ=1), the value of the initial magnetization of the slave becomes “−0.5” from “−1” from the M-H curve in
On the other hand, in the case of the master of the perpendicular anisotropic film of the residual magnetization Mr=500 emu/cc (SQ=0.5), the magnetic field which is generated from the convex portions becomes smaller than 2 kOe (
Therefore, in the case of the perpendicular anisotropic film with the residual magnetization Mr=500 emu/cc (SQ=0.5), even if in-plane movement occurs at the time of separation of the master, influence by the generated magnetic field (magnetic field smaller than 2 kOe) hardly exists, and since the value of the initial magnetization of the slave is substantially the same value as that at the time of transfer from the M-H curve in
In the case of the perpendicular anisotropic films with the residual magnetization Mr smaller than 500 emu/cc, the graphs of them are located at the lower side than the graph of that of Mr=500 emu/cc in
In the actual fabrication process, movement of about 100 nm in the disk radius direction is unavoidable when the master disk 20 and the slave disk 10 are separated after the magnetic transfer step, and therefore, the condition of setting the residual magnetization Mr of the master magnetic layer at 500 emu/cc or less is important.
The validity of evaluating the influence of the residual magnetic field in the position 10 nm from the master surface is for the following reason. Specifically, in the film constitution of the slave disk 10 (see
Specifically, even in the tight contact state of the master disk 20 and the slave disk 10 at the time of transfer, the nonmagnetic film such as the protection layer is interposed between the magnetic layer of the master disk 20 and the magnetic layer 16 of the slave disk 10, and the distance of about 10 nm exists between the magnetic layers. The distance may be actually longer than this, but as the distance between the magnetic layers becomes longer, the magnetic field becomes weaker, and therefore, consideration of the spacing position of 10 nm is sufficient.
Concerning an anisotropy constant Ku (erg/cm3), the perpendicular magnetic recording media are considered to need a value of KuV/(kT) of 60 or more to allow record by magnetization to remain. Here, V represents a magnetization reversal volume (cm3), k represents a Boltzman constant (1.38×10−16 erg/deg), and T represents a temperature.
Since the magnetization reversal volume V becomes small with high densification, in the case of the perpendicular magnetic recording media, a material with a large anisotropy constant Ku is indispensable.
On the other hand, with regard to the master magnetic layer, recording of information is determined by the pattern shape of the magnetic layer, and it is desirable that a magnetic pattern occurs only at the time of transfer (at the time of application of a magnetic field for recording) and the magnetic pattern disappears after the transfer (when application of the magnetic field for recording is released).
Accordingly, the anisotropy constant Ku of the master magnetic layer may be small. In this point, the magnetic material for the perpendicular magnetic recording media and the magnetic material for the master carrier differ greatly.
The reverse domain nucleation magnetic field Hn of the master magnetic layer preferably becomes an applied magnetic field or less since the saturation magnetization Ms of the master magnetic layer can be effectively utilized. The applied magnetic field does not usually exceed the coercive force Hc of the magnetic layer of the slave disk 10, and therefore, Hn of the master magnetic layer is set at Hc of the slave magnetic layer or less (the master magnetic layer Hn≦slave magnetic layer Hc).
When the coercive force Hc of the master magnetic layer is too large, the master magnetic layer is not magnetized with an applied magnetic field. Further, magnetic transfer cannot be performed after transfer. Application of a large transfer magnetic field has an adverse effect of causing a magnetic field to the concave portions. Accordingly, the coercive force Hc of the master magnetic layer is preferably set at 2000 Oe or less, and more preferably at 500 Oe or less.
As described above, according to the master disk 20 using the perpendicular magnetization film for the master which satisfies the magnetic properties shown in Table 1, there are provided the advantage of enabling transfer with a favorable S/N in the four senses, because (1) the transfer magnetic field of the convex portions (transfer portions) which are in contact the slave disk 10 increases, (2) the magnetic field of the concave portions (non-transfer portions) decreases since a demagnetizing field does not exist, as a result (3) the magnetic field distribution in the transition region becomes sharp, and further (4) transfer by residual magnetization of the master disk 20 does not occur after transfer.
As the material of the master magnetic layer which satisfies the magnetic properties organized in Table 1, for example, CoPt is preferable, and an example of more preferable Co4Pt1 (at %) is described in Table 1.
Naturally, when the present invention is carried out, the material is not limited to the above material, and the other materials may be used if only they satisfy the aforementioned required physical property values.
Further, an under layer may exist under the magnetic layer in the master disk 20. As the material of the under layer, for example, Pt, Ru and CoCr are preferable, and CoCr with Cr of 25 at % or more, Pt and Ru are more preferable. Any one of these materials or two or more of these materials may be combined. The thickness of the under layer is preferably 0.5 to 30 nm, and more preferably is 1 to 10 nm.
As described in
When the conventional isotropic magnetic film is used as the magnetic layer in the concavo-convex master carrier, a large aspect ratio of the bit (ratio of the size in the direction of down track and the size of the depth) needs to be taken. This is for the purpose of concentrating the applied magnetic field at the time of transfer on the convex portions as effectively as possible due to the demagnetizing magnetic field.
However, when a large aspect ratio is taken, the convex portion sometimes breaks at the time of fabrication of the concavo-convex master carrier, for example, when the master is peeled from the original plate, and at the time of duplication, and a defective occurs. When the aspect ratio exceeds one, the defective ratio abruptly increases.
On the other hand, when the magnetic film having perpendicular magnetic anisotropy according to the present invention is provided, a demagnetizing magnetic field does not have to be worried about. Therefore, the aspect ratio may be small, and therefore, production yield is dramatically enhanced.
Further, the master disk 20 according to the present invention has a smaller contact area than the embedded type master (
In order to further increase the effect, the portions other than transfer signals are preferably concave. In the case of transfer of a servo signal, the data region is concave. There is the case in which the concave region is so large that when the master and slave are superimposed, the concave portions of the master may deform and overlap the slave portion, and in order to prevent this, a slightly convex portion is preferably formed in the large concave portion.
Next, an example of the fabricating method of the master disk 20 will be described with reference to
Next, the original plate 30 is set on a stage of an electron beam aligner not illustrated including a high precision rotary stage or X-Y stage. While the original plate 30 is rotating, an electron beam which is modulated corresponding to a servo signal is irradiated, and lithography exposure (electron beam lithography) of a predetermined pattern 33 is performed on a substantially entire surface of the resist layer 32, for example, lithography exposure of a pattern corresponding to a servo signal linearly extending in a radius direction from a rotational center to each track is performed for the portion corresponding to each frame on the circumference (
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
Subsequently, the original master 36 on which the metal plate 40 is stacked as described above is taken out of the electrolytic solution of the electroforming apparatus, and is soaked in pure water in a release tank (not illustrated).
Next, in the release tank, the metal plate 40 is separated from the original master 36 (separating step), and a master substrate 42 having the concavo-convex pattern reversed from the original master 36 as shown in
Next, as shown in
Thereafter, the inside diameter and the outside diameter of the master substrate 42 is stamped to predetermined sizes. By the above process, the master disk 20 having the concavo-convex pattern provided with the magnetic layer 48 (corresponding to the magnetic layer 204 in
The master disk 20 is brought into tight contact with the slave disk 10, but the magnetic layer 48 is easily damaged when it is brought into tight contact, and therefore, the protection film and the lubricant layer are provided to prevent the master 20 from being unusable. Further, the lubricant layer has the effect of preventing occurrence of a scar or the like due to friction which occurs when contacting the slave disk 10 to enhance durability.
More specifically, the constitution in which as the protection film, a carbon film of a thickness of 2 to 30 nm is formed, and a lubricant layer is further formed on the carbon film is preferable. Further, in order to reinforce adhesiveness of the magnetic layer 48 and the protection film, an adhesion reinforcing layer of Si or the like is formed on the magnetic layer 48, and the protection film may be formed thereafter.
Next, the step (tight contact step) of superimposing the master disk 20 produced by the above described process and the slave disk 10 after initial magnetizing step on each other as in
As shown in
Cleaning processing (burnishing or the like) for removing microscopic projections or attached dust on the surface is applied to the slave disk 10 by a glide head, a grinder and the like in accordance with necessity, before being brought into tight contact with the master disk 20.
The tight contact step includes the case of bringing the master disk 20 into tight contact with only one surface of the slave disk 10 as shown in
Next, referring to
For the slave disk 10 and the master disk 20 which are brought into tight contact with each other by the above described tight contact step, the recording magnetic field Hd is generated in the opposite direction to the direction of the initializing magnetic field Hi by a magnetic applying device not illustrated. Magnetic flux occurring by generating the recording magnetic field Hd enters the slave disk 10 and the master disk 20, and thereby, magnetic transfer is performed.
In the present embodiment, the magnitude of the recording magnetic field HD has substantially the same value as that of the Hc of the magnetic material which constitutes the magnetic layer 16 of the slave disk 10.
As for magnetic transfer, the recording magnetic field Hd is applied by the magnetic field applying device while the slave disk 10 and the master disk 20 which are brought into tight contact with each other are rotated by a rotating device not illustrated, and the information constituted of the projected pattern recorded in the master disk 20 is magnetically transferred to the magnetic layer 16 of the slave disk 10. Other than this constitution, the method in which a mechanism for rotating the magnetic field applying device is provided, and the magnetic field applying device is rotated relatively with respect to the slave disk 10 and the master disk 20 may be adopted.
The state of the sections of the slave disk 10 and the master disk 20 in the magnetic transfer step is shown in
When magnetic transfer is performed after initial magnetization is performed by the magnetic transfer apparatus, a current in the direction opposite to the direction of the current passed to the coil 63 when initial magnetization is performed is passed to the coil 63 of the magnetic applying device 60. Thereby, a recording magnetic field can be generated in the direction opposite to the magnetizing direction at the time of the initial magnetization. As for magnetic transfer, the recording magnetic field Hd is applied by the magnetic applying device 60 while the slave disk 10 and the master disk 20 which are in tight contact with each other are rotated, and the information constituted of the projected pattern recorded in the master disk 20 is magnetically transferred to the magnetic layer 16 of the slave disk 10. Therefore, a rotating device not illustrated is provided. Other than this constitution, the method in which a mechanism for rotating the magnetic field applying device 60 is provided, and the magnetic field applying device is rotated relatively with respect to the slave disk 10 and the master disk 20 may be adopted.
In the present embodiment, as for the recording magnetic field Hd, magnetic transfer is performed by applying the magnetic field of strength of 60 to 125%, preferably 70 to 115% of the coercive force Hc of the magnetic layer 16 of the slave disk 10 used in the present embodiment.
Thereby, the information of the magnetic pattern such as a servo signal is recorded in the magnetic layer 16 of the slave disk 10 as recording magnetization Pd which is magnetization in the direction opposite to the initial magnetization Pi (see
When the present invention is carried out, the projected pattern formed on the master disk 20 may be a negative pattern opposite to the positive pattern described in
The perpendicular magnetic recording medium fabricated by the method according to the aforementioned embodiment of the present invention is used by being incorporated into a magnetic recording and reproducing device such as a hard disk device, for example. Thereby, a high recording density magnetic recording and reproducing device with high servo accuracy and favorable recording and reproducing characteristics can be obtained.
Experimental conditions: by using the master carrier having the perpendicular magnetic anisotropy according to the present invention, transfer was carried out with 70% of the medium coercive force (Hc), and the reproduced waveform of the medium was measured. For comparison, transfer was performed under the same conditions by using the conventional magnetic layer, and the reproduced waveform of the medium was measured. Table 2 shows the measurement results.
The viewpoints of the measurement evaluation of the reproduced waveforms were “waveform amplitude”, “waveform width variation”, and “incomplete pulse occurrence rate”, and each of the values was normalized by the measurement result of the master carrier having the conventional magnetic layer.
The waveform amplitude is the amount (both amplitudes of the reproduction signal) represented by “A” in
The incomplete pulse occurrence rate is the occurrence rate of the pulse of which amplitude is 50% or less as compared with the other pulses as the pulse enclosed by the two-dot chain line in
The constitution for evaluating the servo signal transferred to the slave disk will be described hereinafter.
The slave disk is mounted to the shaft of a spindle motor, and is rotated at a predetermined speed (rotational frequency). A magnetic head is provided to be close to the surface of the slave disk at a predetermined flying height. The magnetic head is movable to a predetermined position by a positioner. The magnetic head is for performing recording and reproduction.
Further, a synchroscope (oscilloscope) is connected to the magnetic head, so that the lead signal waveform from the magnetic head is displayed on the display of the synchroscope. A spindle motor is further connected to the synchroscope, so that an index signal outputted when the rotor of the spindle motor is at a predetermined rotational angle is inputted as a trigger signal.
As shown in Table 2, the reproduction signal by transfer using the master carrier having the perpendicular magnetic anisotropy according to the present invention provides more favorable results than conventional one in all the items that are “waveform amplitude”, “waveform width variation” and “incomplete pulse occurrence rate”.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2007-237537 | Sep 2007 | JP | national |
