U.S. patent application number 11/441087 was filed with the patent office on 2007-08-16 for magnetic recording medium and manufacturing method therefor.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Hiroyoshi Kodama, Atsushi Tanaka, Takuya Uzumaki, Wataru Yamagishi.
Application Number | 20070190365 11/441087 |
Document ID | / |
Family ID | 38368934 |
Filed Date | 2007-08-16 |
United States Patent
Application |
20070190365 |
Kind Code |
A1 |
Kodama; Hiroyoshi ; et
al. |
August 16, 2007 |
Magnetic recording medium and manufacturing method therefor
Abstract
The present invention provides a novel discrete track medium
having a high magnetic recording density and manufacturing method
therefor. This magnetic recording medium is a disk-shaped magnetic
recording medium comprising a soft magnetic layer, a magnetic layer
thereover, and an intermediate layer directly under the magnetic
recording layer, wherein the magnetic recording layer comprises a
plurality of magnetic recording tracks arranged in the radial
direction of the magnetic recording medium, and each magnetic
recording track is separated from the other in the radial direction
of the disk by concave sections and convex sections formed
alternately on the upper surface of the intermediate layer in the
radial direction of the disk.
Inventors: |
Kodama; Hiroyoshi;
(Kawasaki, JP) ; Yamagishi; Wataru; (Kawasaki,
JP) ; Uzumaki; Takuya; (Kawasaki, JP) ;
Tanaka; Atsushi; (Kawasaki, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
FUJITSU LIMITED
Kawasaki
JP
|
Family ID: |
38368934 |
Appl. No.: |
11/441087 |
Filed: |
May 26, 2006 |
Current U.S.
Class: |
428/832 ;
360/135; 427/131; 427/180; 428/836; G9B/5.293; G9B/5.306 |
Current CPC
Class: |
G11B 5/855 20130101;
G11B 5/746 20130101; G11B 5/653 20130101; B82Y 10/00 20130101; G11B
5/82 20130101 |
Class at
Publication: |
428/832 ;
428/836; 360/135; 427/131; 427/180 |
International
Class: |
G11B 5/82 20060101
G11B005/82; G11B 5/65 20060101 G11B005/65; B05D 5/12 20060101
B05D005/12; B05D 1/12 20060101 B05D001/12 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 16, 2006 |
JP |
2006-039197 |
Claims
1. A magnetic recording medium in a shape of a disk, comprising: a
soft magnetic layer; a magnetic recording layer over the soft
magnetic layer; and an intermediate layer directly under said
magnetic recording layer, wherein said magnetic recording layer
comprises a plurality of magnetic recording tracks arranged in the
radial direction of the magnetic recording medium, and each
magnetic recording track is separated from the other in the radial
direction of said disk by concave sections and convex sections
formed alternately on the upper surface of said intermediate layer
in the radial direction of said disk.
2. The magnetic recording medium according to claim 1, further
comprising a portion where said magnetic recording tracks are
separated also in the circumferential direction of said disk by the
concave sections and convex sections formed on the upper surface of
said intermediate layer in the circumferential direction of said
disk.
3. The magnetic recording medium according to claim 1, wherein said
convex sections are made of carbon.
4. The magnetic recording medium according to claim 1, wherein the
average particle size of magnetic particles used for said magnetic
recording layer is in a 2-15 nm range.
5. The magnetic recording medium according to claim 4, wherein the
surfaces of said magnetic particles are surface-treated so that the
minute particles attract each other in a self-assembling way.
6. The magnetic recording medium according to claim 4, wherein said
magnetic particles are FePt nano-particles.
7. The magnetic recording medium according to claim 1, wherein said
intermediate layer is formed of one or more layers of non-magnetic
material.
8. A method for manufacturing a magnetic recording medium in a
shape of a disk comprising a soft magnetic layer, a magnetic
recording layer over the soft magnetic layer, and an intermediate
layer directly under said magnetic recording layer, the method
comprising: forming concave sections and convex sections
alternately on the upper surface of said intermediate layer in the
radial direction of said disk; and filling magnetic particles into
said concave sections in a self-assembling way.
9. The method for manufacturing a magnetic recording medium
according to claim 8, further comprising forming concave sections
and convex sections on the upper surface of said intermediate layer
in the circumferential direction of said disk.
10. The method for manufacturing a magnetic recording medium
according to claim 8, further comprising treating the upper
surfaces of the convex sections to be hydrophilic or hydrophobic so
as to repel the magnetic particles.
11. The method for manufacturing a magnetic recording medium
according to claim 10, wherein the upper surfaces of said convex
sections are treated to be hydrophilic, and when said magnetic
particles are filled into said concave sections, said magnetic
particles are surrounded by a dispersion stabilizing agent, and
hydrophobic groups of the dispersion stabilizing agent are facing
the outside.
12. The method for manufacturing a magnetic recording medium
according to claim 8, further comprising: forming a layer made of
carbon on at least the uppermost part of the intermediate layer;
forming a resist pattern on said carbon layer; forming concave
sections on the upper surface of said intermediate layer by etching
said carbon layer; and then, forming convex sections on the upper
surface of said intermediate layer by partially removing said
resist pattern.
13. The method for manufacturing a magnetic recording medium
according to claim 8, wherein the average particle size of said
magnetic particles is in a 2-15 nm range.
14. The method for manufacturing a magnetic recording medium
according to claim 8, wherein the surfaces of the magnetic
particles are surface-treated so that the minute particles attract
each other in a self-assembling way.
15. The method for manufacturing a magnetic recording medium
according to claim 14, wherein said magnetic particles are FePt
nano-particles.
16. The method for manufacturing a magnetic recording medium
according to any of claim 8, wherein said intermediate layer is
formed of one or more layers of non-magnetic material.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from the prior Japanese Patent Application No. 2006-39197,
filed on Feb. 16, 2006, the entire contents of which are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a magnetic recording medium
used for an information recording/reproducing device, such as a
hard disk device.
[0004] 2. Description of the Related Art
[0005] In recent years, moves towards the downsizing and increasing
in capacity of magnetic recording/reproducing devices are rapidly
progressing. In order to increase the magnetic recording density of
the magnetic recording medium used for a magnetic
recording/reproducing device, it is essential to decrease the
noises of the magnetic recording medium, and for this purpose, it
is necessary to decrease and make uniform the particle size of a
hard magnetic substance used for the magnetic recording layer. In
addition, in the case of a disk-shaped magnetic recording medium,
the magnetic recording density is determined by the magnetic
recording track density in the radial direction and the density in
the circumferential direction which is called the "line recording
density". Accordingly, in order to improve the magnetic recording
density of the magnetic recording medium, it is also important to
increase the magnetic recording track density in the radial
direction. As a method for increasing the magnetic recording track
density in the radial direction, a magnetic recording medium called
"discrete track medium" has been proposed and researched/developed.
This is a magnetic recording medium having a structure to make
magnetic recording tracks narrower by separating adjacent magnetic
recording tracks {see Japanese Unexamined Patent Application
Publication No. H4-310621 (Claims)}.
[0006] As a means for separating the magnetic recording tracks of a
magnetic recording layer as described above, a structure for
separating the magnetic recording layer structurally by a
non-magnetic material, and a structure for separating the magnetic
recording tracks magnetically by separating the soft magnetic
material of the backing layer (or soft magnetic layer), are
proposed. In the latter case, the soft magnetic layer is
structurally separated, so the magnetic recording layer has a
structure which forms a continuous layer without separation.
[0007] A feature in common in both means is that
protrusions/recesses for the purpose of separation are created on
the non-magnetic material or on the surface of the substrate under
the backing layer. Therefore a final step of flattening the
magnetic recording layer surface is always required so that the
magnetic head smoothly flies and moves over the layer.
[0008] In a type wherein the magnetic recording layer is separated
by a non-magnetic material, for example, protrusions/recesses are
created by a resist pattern or the like after an intermediate layer
is formed, for example, then steps of stripping the resist, forming
a non-magnetic material film, forming a magnetic recording layer
film by a sputtering method or the like, polishing for surface
smoothing, etc. are required.
[0009] In the structure wherein the backing layer is separated, on
the other hand, protrusions/recesses are created on the substrate
by a resist pattern, for example, then steps of forming a backing
layer film, stripping the resist, forming a non-magnetic material
film, surface smoothing, polishing and forming a magnetic recording
layer film by a sputtering method or the like are required.
[0010] In other words, in both cases a polishing step or other
steps are required. Details on the fabrication methods may be
different from the example shown here, but such a situation is the
same for the two methods.
[0011] The flying height of a magnetic head, however, is about 10
nm, and it is very difficult to accomplish the surface smoothness
of the magnetic recording layer (surface of the sputtered film)
required for this flying height. Even if it is accomplished, a very
large number of processing steps and manufacturing facilities are
required, resulting in a serious problem in terms of cost.
[0012] It is an object of the present invention to solve the
above-described problems, and provide a new discrete track medium
which has a high magnetic recording density, and a manufacturing
method therefor. Other objects and advantages of the present
invention shall be clarified by the following description.
SUMMARY OF THE INVENTION
[0013] According to an aspect of the present invention, a
disk-shaped magnetic recording medium, having a soft magnetic
layer, a magnetic recording layer over the soft magnetic layer, and
an intermediate layer directly under the magnetic recording layer,
wherein the magnetic recording layer has a plurality of magnetic
recording tracks arranged in the radial direction of the magnetic
recording medium, and each magnetic recording track is separated
from the other in the radial direction of the disk by concave
sections and convex sections formed alternately on the upper
surface of the intermediate layer in the radial direction of the
disk, is provided.
[0014] By this aspect of the present invention, a new discrete
track medium having a high magnetic recording density is
implemented.
[0015] Preferable are that the magnetic recording medium further
has parts where the magnetic recording tracks are separated also in
the circumferential direction of the disk by the concave sections
and convex sections formed on the upper surface of the intermediate
layer in the circumferential direction of the disk; that the convex
sections are made of carbon; that the average particle size of
magnetic particles used for the magnetic recording layer is in a
2-15 nm range; that the surfaces of the magnetic particles are
surface-treated so that the minute particles attract each other in
a self-assembling way; that the magnetic particles are FePt
nano-particles; and that the intermediate layer is composed of one
or more layers of a non-magnetic material.
[0016] According to another aspect of the present invention, a
method for manufacturing a magnetic recording medium in a shape of
a disk, which comprises a soft magnetic layer, a magnetic recording
layer over the soft magnetic layer, and an intermediate layer
directly under the magnetic recording layer, comprising forming
concave sections and convex sections alternately on the upper
surface of the intermediate layer in the radial direction of the
disk, and filling magnetic particles into the concave sections in a
self-assembling way, is provided.
[0017] By this aspect of the present invention, a new discrete
track medium having a high magnetic recording density can be
produced. It is also possible to omit or decrease the burden of the
polishing step.
[0018] Preferable are that the manufacturing method further
comprises forming concave sections and convex sections on the upper
surface of the intermediate layer in the circumferential direction
of the disk; that the method comprises treating the upper surfaces
of the convex sections to be hydrophilic or hydrophobic so as to
repel magnetic particles; that the method comprises treating the
upper surfaces of the convex sections to be hydrophilic, so that
when the magnetic particles are filled into the concave sections,
the magnetic particles are surrounded by a dispersion stabilizing
agent, and the hydrophobic groups of the dispersion stabilizing
agent are facing the outside; and that the method comprises forming
a layer made of carbon on at least the uppermost part of the
intermediate layer, forming a resist pattern on the carbon layer,
forming concave sections on the upper surface of the intermediate
layer by etching the carbon layer, and then forming convex sections
on the upper surface of the intermediate layer by partially
removing the resist pattern; that the average particle size of the
magnetic particles is in a 2-15 nm range; that the surfaces of the
magnetic particles are surface-treated so that the minute particles
attract each other in a self-assembling way; that the magnetic
particles are FePt nano-particles; and that the intermediate layer
is formed of one or more layers of a non-magnetic material.
[0019] According to the present invention, a new discrete track
medium having a high magnetic recording density and manufacturing
method therefor are implemented. According to the present
invention, the magnetic recording density in the radial direction
of the disk-shaped magnetic recording medium can be improved. The
magnetic recording density in the circumferential direction (or
rotation direction or bit direction of the disk) can also be
improved. It is also possible to omit or decrease the burden of the
polishing step.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic perspective view depicting a part of a
discrete track medium where the soft magnetic layer is structurally
separated by non-magnetic portions;
[0021] FIG. 2 is a schematic perspective view depicting a part of a
discrete track medium where the magnetic recording layer is
structurally separated by non-magnetic portions;
[0022] FIG. 3 is a schematic perspective view depicting a part of a
discrete track medium according to the present invention;
[0023] FIG. 4 is a (schematic) plan view depicting a disk-shaped
magnetic recording medium;
[0024] FIG. 5 is a cross-sectional view of the part in FIG. 3
viewed from the Y direction;
[0025] FIG. 6 is a schematic diagram depicting a dispersion
stabilizing agent surrounding a magnetic particle;
[0026] FIG. 7 shows schematic cross-sectional views of a magnetic
recording medium illustrating an example of a manufacturing
procedure of a magnetic recording medium according to the present
invention;
[0027] FIG. 8 shows schematic cross-sectional views of a magnetic
recording medium depicting an example of a manufacturing procedure
of a magnetic recording medium according to the present
invention;
[0028] FIG. 9 shows schematic cross-sectional views of a magnetic
recording medium depicting an example of a manufacturing procedure
of a magnetic recording medium according to the present invention;
and
[0029] FIG. 10 shows schematic cross-sectional views of a magnetic
recording medium depicting an example of a manufacturing procedure
of a magnetic recording medium according to the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Embodiments of the present invention will now be described
with reference to drawings, examples, etc. These drawings,
examples, etc. as well as the explanations are for describing the
present invention, and shall not restrict the scope of the present
invention. Needless to say, other embodiments are within the scope
of the present invention as along as they conform to the essential
character of the present invention. The same elements in the
drawings may be denoted with the same reference symbols.
[0031] The magnetic recording medium according to the present
invention is a so-called "discrete track medium". This is a
disk-shaped magnetic recording medium having a soft magnetic layer,
a magnetic recording layer thereover, and an intermediate layer
directly under the magnetic recording layer, wherein the magnetic
recording layer has a plurality of magnetic recording tracks
arranged in the radial direction of the magnetic recording medium,
and each magnetic recording track is separated from the other in
the radial direction of the disk by concave sections and convex
sections alternately formed on the upper surface of the
intermediate layer in the radial direction of the disk. In other
words, the magnetic recording layer is structurally separated by
the convex sections, which is part of the intermediate layer. In
this way, the magnetic recording density in the radial direction of
the disk-shaped magnetic recording medium can be improved.
[0032] FIGS. 1-5 show this status compared with prior art. The
arrow X in FIGS. 1-3 corresponds to the arrow B direction (radial
direction) in FIG. 4, and arrow Y in FIGS. 1-3 corresponds to the
arrow A direction (circumferential direction) in FIG. 4.
[0033] FIG. 1 is a perspective view depicting a part of a discrete
track medium, where the soft magnetic layer 2 on the substrate 1 is
structurally separated by non-magnetic portions 5. Because of these
non-magnetic portions 5, the boundary portions 7 of the magnetic
recording tracks 6, on the magnetic recording medium 1 in FIG. 4
(plan view of the disk-shaped magnetic recording medium), are
formed on the magnetic recording layer 4 on the intermediate layer
3 in a circular form in the circumferential direction (arrow A
direction) of the disk. As a result, a plurality of magnetic
recording tracks 6 are formed in the radial direction.
[0034] FIG. 2 is a perspective view depicting a part of the
discrete track medium, where the magnetic recording layer 4 on the
intermediate layer 3 is structurally separated by the non-magnetic
portions 8. In this case, because of the non- magnetic portions 8,
the boundary portions 7 of the magnetic recording tracks 6 on the
magnetic recording medium 1 in FIG. 4 are formed on the magnetic
recording layer 4 in the circumferential direction of the disk. As
a result, a plurality of magnetic recording tracks 6 are formed in
the radial direction.
[0035] FIG. 3, on the other hand, is a perspective view depicting a
part of a discrete track medium, where the magnetic recording layer
4 is structurally separated by the convex portions 9, which are
part of the intermediate layer 3 according to the present
invention. Because of the convex portions 9, in the magnetic
recording layer 4, the boundary portions 7 of the magnetic
recording tracks 6 on the magnetic recording medium 1 in FIG. 4 are
formed in a circular form in the circumferential direction of the
disk. As a result, a plurality of magnetic recording tracks 6 are
formed in the radial direction. In FIG. 4, only one magnetic
recording track 6 and two boundary portions 7 are shown.
[0036] FIG. 5 is a cross-sectional view of the part in FIG. 3 in
the arrow Y direction. As FIG. 5 shows, the upper surface of the
intermediate layer 3 according to the present invention is composed
of the alternately formed convex sections 9 and concave sections
10, and each magnetic recording track 6 is separate from the other
by the convex sections 9 in the radial direction of this disk. In
FIGS. 3 and 5, magnetic particles are shown in a one-particle
layer, but the present invention is not limited to this, and the
magnetic recording layer 4 may also be composed of a plurality of
layers of magnetic particles.
[0037] FIG. 3 also shows a convex section 11 which is perpendicular
to a convex section 9. Since the convex sections of the present
invention can easily be created in a desired direction, the
boundary portions (not illustrated in FIG. 4) separating the
magnetic recording tracks can be formed in the circumferential
direction of the disk (arrow A direction ), as in the case of the
convex section 11. If there are too many boundary portions like
this, portions are increased where magnetic particles are not
present, causing decrease of the magnetic recording density in the
circumferential direction of the disk drops. However, when the
magnetic material is arrayed with some regularity in the magnetic
recording layer, and the array is disturbed, an appropriate number
of boundary portions can be created to prevent the propagation of
this disturbance, whereby the magnetic recording density in the
circumferential direction of the disk can be improved as a whole.
This could be advantageous.
[0038] The magnetic recording medium according to the present
invention may include layers other than the above, if necessary.
For example, an adhesion layer made of Ti may be formed between the
soft magnetic layer and the substrate. Also, on the magnetic
recording layer, a protective film and a lubricant layer are
normally formed. In the present invention, there is no particular
limitation to the materials for the substrate, soft magnetic layer
and other optional layers, and they can be appropriately selected
from known materials.
[0039] The intermediate layer according to the present invention is
a layer made of a non-magnetic material, and is directly under the
magnetic recording layer. This is normally formed to suppress the
magnetic interaction caused by direct contact of the soft magnetic
layer and the magnetic recording layer, but may have another
purpose, or may be formed only to create the protrusions/recesses
of the present invention. The material for the intermediate layer
can be appropriately selected from any non-magnetic materials
conforming to this purpose, but it is preferable to be compatible
with the material to be used for the magnetic recording layer. For
example, if the material to be used for the magnetic recording
layer is hydrophobic, then a material which is not hydrophilic, or
a material which is hydrophobic is preferable.
[0040] The intermediate layer according to the present invention is
directly under the magnetic recording layer. However not all of the
intermediate layer is directly under the magnetic recording layer,
but as the relationship between the convex sections 9 and the
magnetic recording tracks 6 in FIG. 5 shows, the convex sections of
the intermediate layer form the same plane as the magnetic
recording layer.
[0041] The intermediate layer according to the present invention
may be composed of one layer. They may also be composed of two or
more layers of non-magnetic material. In such a case, the
protrusions/recesses may be formed only on the uppermost layer. The
uppermost layer may be composed only of convex sections.
[0042] Examples of specific materials for the intermediate layer
are ruthenium (Ru), carbon, platinum (Pt), rhodium (Rh), etc.
Carbon is particularly preferable for at least the section for
forming protrusions/recesses, since it is highly compatible, in
many cases, with materials to be used for the magnetic recording
layer, and protrusions/recesses can be processed easily.
[0043] The height difference between the concave sections and the
convex sections (that is, the depth of the concave sections) and
their width can be determined according to purposes. To use the
later-described nano-magnetic particles for the magnetic material
of the magnetic recording layer, the height difference of the
concave sections and the convex sections in the range equivalent to
the thickness of 1-20 particle layers is often preferable.
[0044] The magnetic particles to be used for the magnetic recording
layer according to the present invention are not specifically
limited, and can be appropriately selected from known hard magnetic
minute particles. The average particle size (diameter) thereof is
preferable in a 2-15 nm range, since the particles must be filled
in the concave sections. The average particle size can be measured
by an x-ray diffraction method, by means of transmission electron
microscope or the like.
[0045] From the viewpoints of being filled regularly in the concave
sections and therefore being able to be expected to have a high
magnetic recording density, it is preferable that the surfaces of
the magnetic particles are surface-treated so that the minute
particles attract each other in a self-assembling way. Here,
"minute particles attract each other in a self-assembling way"
means that when minute particles or materials containing minute
particles (e.g. minute particles surrounded by a dispersion agent)
are deposited on the intermediate layer by some method, the minute
particles attract each other and will line up with some regularity,
just like a self-assembling film. It is unnecessary to confirm that
the minute particles attract each other, and it can be considered
as the requirement of "minute particles attract each other in a
self-assembling way" according to the present invention being
satisfied, if the minute particles are arranged with some
regularity when the minute particles or materials containing the
minute particles are deposited on the intermediate layer by some
method. For such magnetic minute particles, FePt nano-particles are
preferable.
[0046] The magnetic recording medium having the above structure can
be manufactured by a method for manufacturing a disk-shaped
magnetic recording medium having a soft magnetic layer, magnetic
recording layer thereover, and intermediate layer directly under
the magnetic recording layer, wherein concave sections and convex
sections are alternately formed on the upper surface of the
intermediate layer in the radial direction of this disk, and
magnetic particles are filled into the concave sections in a
self-assembling way. By this manufacturing method, the magnetic
recording density of the disk-shaped magnetic recording medium in
the radial direction can be improved. It is also possible to omit
the polishing step or decrease the burden thereof. By forming
concave sections and convex sections on the upper surface of the
intermediate layer in the circumferential direction of the disk,
the magnetic recording density in the circumferential direction can
be improved.
[0047] Requirements for the soft magnetic layer, magnetic recording
layer, intermediate layer and other layers as well as materials for
forming these layers used in the present invention, and preferred
embodiments are the same as those requirements for the above
described magnetic recording medium and preferable embodiments.
[0048] Methods of fabricating the soft magnetic layer, magnetic
recording layer and intermediate layer are not specifically
restricted either, and can be appropriately selected from known
methods. Examples are a sputtering method, electro-plating method,
etc. for the soft magnetic layer; a sputtering method, vacuum
deposition method and method for coating a slurry containing minute
particles followed by forming a layer using the properties of the
minute particles which attract each other in a self-assembling way,
for the magnetic recording layer; and a sputtering method using
carbon, ruthenium and platinum, a deposition method, etc. for the
intermediate layer.
[0049] The method for fabricating the protrusions/recesses
according to the present invention is not specifically restricted,
and can be appropriately selected from known methods. Dry etching,
wet etching and a press method using a mold are examples.
[0050] In the present method, it is preferable to treat the upper
surfaces of the convex sections to be hydrophilic or hydrophobic so
as to repel the magnetic particles to be used. By this, the upper
surfaces of the convex sections and the magnetic particles are
repelled from each other, so it is easy to fill the magnetic
particles selectively into the concave sections merely by placing
the magnetic particles on the intermediate layer. The method to
treat the surface to be hydrophilic or hydrophobic is not
specifically restricted. An example is a method in which a
hydrophilic or hydrophobic material film is formed by application
or the like of the material on the upper surfaces of the convex
sections.
[0051] More specifically, it is preferable that the upper surfaces
of the convex sections are treated to be hydrophilic, and when the
magnetic particles are filled into the concave sections, the
magnetic particles are surrounded by a dispersion stabilizing
agent, and the hydrophobic groups of the dispersion stabilizing
agent are facing the outside. The status that hydrophobic groups of
a dispersion stabilizing agent are facing the outside means a state
where hydrophobic groups 63 are present on the outside of
dispersion stabilizing agents 62 around magnetic particles 61, as
shown in FIG. 6. Normally hydrophilic groups 64 are present on the
inside of the dispersion stabilizing agent 62. In this status, the
hydrophobic groups 63 repel the hydrophilic upper surfaces of the
convex sections, so the magnetic particles can be easily filled
into the concave sections selectively.
[0052] A specific manufacturing method according to the present
invention is a method for forming a carbon layer at least on the
uppermost part of the intermediate layer, forming a resist pattern
on the carbon layer, forming concave sections on the upper surface
of the intermediate layer by etching the carbon layer, then forming
convex sections on the upper surface of the intermediate layer by
partially removing the resist pattern.
[0053] In the case of a carbon layer, protrusions/recesses can be
easily formed by etching, such as plasma etching. If the resist
pattern is partially removed, it is possible to make the magnetic
particles placed on the intermediate layer repel the upper surfaces
of the convex sections, utilizing hydrophilic or hydrophobic
properties of the remaining portions of the resist pattern.
[0054] Partially removing the resist pattern means removing the
resist pattern so that the film thickness of the resist pattern
becomes thinner, but it is unnecessary to confirm how the resist
pattern is removed. It is sufficient to confirm whether magnetic
particles can be selectively filled into the concave sections
easily, merely by placing the magnetic particles on the
intermediate layer. A partial removal can be implemented by
selecting an appropriate processing time using a conventional
resist pattern removal technology.
[0055] FIGS. 7-10 show an example of the manufacturing procedures
of a magnetic recording medium according to the present invention.
First, according to step 1, a soft magnetic layer 2, Ru layer 71
and carbon layer 72 are sequentially formed on a substrate 1. The
carbon layer 72 corresponds to the intermediate layer 3 according
to the present invention. It may be considered that the Ru layer 71
in combination with the carbon layer 72 corresponds to the
intermediate layer 3 according to the present invention. Then,
according to step 2, a resist layer 73 is formed on the carbon
layer 72. If a self-assembling type mono-molecular resist layer is
formed (e.g. Takayuki Honma, "Functional Nanostructure Thin Film
Formation by Wet Process", Japanese Applied Magnetics Society
Magazine, 2005, Vol. 29, No. 12, pp. 1035-1040), a very thin layer
can be formed.
[0056] Then, according to step 3, magnetic recording track forms
are patterned in the resist layer 73, then according to step 4, the
carbon layer 72 is etched by reactive ion etching (RIE), for
example, to form concave sections 10. Then, according to step 5,
the resist layer 73 is processed so that the resist layer 73
slightly remains. This can be implemented by adjusting the
processing time of alkali processing, for example.
[0057] Then, according to step 6, the magnetic particles (e.g. FePt
nano-particles) 74 are placed on the carbon layer 72, then the
magnetic particles are deposited only in the concave sections 10,
since the slightly remaining resist layer 73 on the surfaces of the
convex sections 9 and 11 repels the magnetic particles. Then,
according to step 7, the remaining resist layer 73 is removed. And
then according to step 8, annealing is performed in the magnetic
field, and the magnetic recording medium, where the magnetic
recording tracks 6 are separated by the convex sections 9 and 11,
as shown in FIG. 3 and FIG. 5, can be acquired.
EXAMPLES
[0058] Now an example of the present invention will be described in
detail.
Example 1 (Structure with a Two-Tier Intermediate Layer)
[0059] First, the synthesis of nano-particles to be used as the
magnetic recording layer material will be described. Nano-particles
can be synthesized by a super hydride method, a polyol method
disclosed in Sun et al, "Journal of Applied Physics", 1999, Vol.
85, pp. 4325, and also disclosed in "Science", 2000, Vol. 287, pp.
1989-1992, or Japanese Unexamined Patent Application Publication
No. 2000-54012 (Claims), etc. In these methods, various alloys can
be synthesized by selecting raw materials.
[0060] Then, a specific method for synthesizing FePt nano-particles
will be described. Under an argon atmosphere, 20 mL of dioctyl
ether was added to a flask containing 197 mg (0.5 mmol) of platinum
bisacetylacetonate and 390 mg of 1,2-hexadecanediol, and 0.32 mL
(1.0 mmol) of oleic acid and 0.34 mL (1.0 mmol) of oleyl amine were
also added, then 0.13 mL (1.0 mmol) of Fe (CO).sub.5 was added, and
the mixture was reacted at 230.degree. C. while mixing.
[0061] After thirty minutes of reaction, the solution was cooled
down to room temperature, 40 mL of ethanol was added, and
centrifugation was performed, and the sediment was dispersed in
hexane to form a liquid in which FePt nano-particles were
dispersed. The average particle size of the FePt nano-particles
acquired under these conditions was 4.3 nm. This average particle
size was measured by a transmission electron microscope. The
composition ratio of FePt was 50 atomic % of Fe and 50 atomic % of
Pt. By changing the mixing ratio of raw materials, Fe rich or Pt
rich nano-particles can be created. The nano-particles created by
this method are in the status where the hydrophobic groups of the
dispersion stabilizing agent (oleic acid, oleyl amine) are facing
the outside.
[0062] Now steps for manufacturing a magnetic recording medium of
the present invention will be described. In the present example, an
Si substrate with a thermally oxidized film having an outer
diameter of 65 mm and an inner diameter 20 mm was used.
[0063] First, 3 nm of a Ti film was deposited on the Si substrate
by a sputtering method. This layer has a role to improve the
adhesion between the substrate and the layer to be formed above it.
Therefore materials other than Ti can be used only if they furnish
adhesiveness.
[0064] Then, 100 nm of an FeSi film, which is a soft magnetic
material, was deposited by a sputtering method. Then, 3 nm of an Ru
film was deposited. Then, 12 nm of a carbon film was deposited by a
sputtering method. This Ru film together with a carbon film form an
intermediate layer according to the present invention. In other
words, this carbon film corresponds to a "carbon layer formed at
least on the uppermost part of the intermediate layer".
[0065] Here, protrusions/recesses were formed on the carbon film by
a lithography process. First, a hydrophilic resist was formed on
the carbon film by a spin coat method. After exposure, unnecessary
part of the resist was removed with an organic solvent. By the
processes thus far, a pattern was formed which comprised the
hydrophilic resist surface and carbon film surface where the resist
was not present and carbon was exposed. Then, the carbon film
portion where carbon was exposed was removed by plasma etching. By
this, the "concave sections on the upper surface of the
intermediate layer" were formed.
[0066] Then, the resist was removed. At this time, the resist was
removed such that a 1 nm or less thickness of the resist remained.
By this, the "convex sections on the upper surface of the
intermediate layer" according to the present invention were formed.
The resist that slightly remained on the upper surfaces of the
convex sections had hydrophilic properties. Since there was no
resist remained in areas other than the upper surfaces of the
convex sections, only the upper surfaces of the convex sections can
have hydrophilic properties.
[0067] In this way, doughnut-shaped concave sections and convex
sections, alternately arranged in the radial direction of the disk,
were fabricated. The width of a convex section was 10 nm, the width
of a concave section was 30 nm, and the height difference between
the convex sections and the concave sections was 16 nm.
[0068] Then, nano-particles of FePt were deposited in the concave
sections using a spin coater. At this time, the conditions of the
spin coat method were optimized so that the height of the convex
sections was made to match the height of the portions where the
nano-particles were filled. The upper surfaces of the convex
sections were treated to be hydrophilic, so the adhesion of
nano-particles was weak there, and it was possible to fill the
nano-particles only into the concave sections by optimizing the
conditions of the spin coat method. Then, using an asher, the
slightly remaining resist was completely removed.
[0069] Then, heat treatment was performed at 500.degree. C. for 30
minutes in vacuum while an external magnetic field was vertically
applied to the substrate. By this, an axis of easy magnetization of
the nano-particles was aligned in the vertical direction which was
the external magnetic field applying direction, to furnish vertical
alignment properties.
[0070] Then, in order to implement a protective film function to
the magnetic recording medium, a 4 nm film of carbon was deposited
by a sputtering method, and a film of lubricant was formed by a dip
method.
[0071] By the processes described above, a magnetic recording
medium could be manufactured where magnetic recording tracks
separated from each other were formed on the intermediate layer.
The track pitch of the discrete track medium of the present
invention was 40 nm, resulting in 635 kTPI (Truck Per Inch), so a
track density of 10 times or more as high as that of the current
medium was implemented.
* * * * *