Stock material or miscellaneous articles – Circular sheet or circular blank – Recording medium or carrier
Reexamination Certificate
1998-05-12
2001-04-10
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Circular sheet or circular blank
Recording medium or carrier
C428S065100, C428S065100, C428S141000, C428S690000, C428S690000, C428S690000, C428S690000, C428S690000, C428S900000, C427S128000, C427S129000, C427S130000, C204S192200, C205S119000
Reexamination Certificate
active
06214434
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of magnetic recording media and more particularly, to high density recording media with isolated single-domains.
BACKGROUND OF THE INVENTION
The costs of electronic data storage have been dramatically reduced as the storage densities on recording media have increased. This trend is particularly evident in hard disk drive technology. A conventional magnetic recording disk
10
for use in hard disk drives is depicted in
FIG. 1. A
cross section A of
FIG. 1
is enlarged and depicted schematically in
FIG. 2A. A
typical recording disk
10
includes an aluminum (Al) substrate
12
covered by a nickel-phosphorous (NiP) plating layer
14
. A chromium (Cr) underlayer
16
is provided on the nickel phosphorous plating. A magnetic material such as nickel, cobalt (Co), or a magnetic alloy is electroplated or sputtered onto the chromium underlayer
16
to form a continuous magnetic layer
18
. A carbon overcoat
20
is deposited on top of the magnetic layer
18
and serves to protect the magnetic layer
18
.
An enlarged top view of section B of the recording disk
10
of
FIG. 1
is depicted in FIG.
2
B. This view is not a physical view, but rather one provided by a magnetic force microscope following writing of data onto the disk
10
. As recorded by a write head, the bits are substantially rectangular in shape and arranged in concentric tracks. In the illustrated example, a track width is approximately 2,000 nm. A small separation exists between the bits within a track as well as between bits of radially adjacent tracks.
The approximate shape and dimensions of a bit of a conventional longitudinally recorded magnetic bit are provided in
FIG. 5
a.
The length of the bit is approximately 2,000 nm, the width of the bit is approximately 150 nm, and the depth of the bit is approximately 15 nm. A magnetic disk
10
that has been formed with a continuous magnetic layer
18
as depicted in
FIG. 2A
with the bit size described above has a recording density of approximately 1.7 Gbit/in
2
.
Increases in the areal density of magnetic storage media have been driven by the downward rescaling of hard drive assemblies. This resealing includes reducing the size of the grains making up the magnetic layer. In longitudinal recording, each bit is composed of numerous grains in order to maintain an adequate signal-to-noise ratio. However, reducing the grain size in order to reach higher storage densities is limited by the superparamagnetic limit. This limit occurs at the grain size at which thermal energy alone can trigger random magnetic switching of the grains.
A technology has been proposed to greatly increase the recording density of a magnetic disk by using discrete, single-domain magnetic elements embedded in a non-magnetic material. As proposed in
Ultra High
-
Density Recording Storing Data in Nanostructures,
Stephen Chou,
Data Storage,
September/October 1995 (pages 35-40), thin-film magnetic media are replaced by media that include discrete magnetic elements embedded in a non-magnetic disk. A corresponding cross-section A is depicted in
FIG. 3A
for a magnetic disk
10
having the proposed quantum magnetic structure. A silicon substrate
30
is covered by a plating base layer
32
. A silicon dioxide layer
34
is provided on the plating base layer. The silicon dioxide forms a non-magnetic isolation layer in which magnetic columns are provided. The non-magnetic layer
34
has a depth of approximately 100 nm. Magnetic columns
38
, approximately 50 nm in diameter, are provided in a vertical orientation in the non-magnetic layer
34
. The magnetic columns
38
may be made of nickel or cobalt, for example. The non-magnetic layer
34
and the magnetic columns
38
are protected by an overcoat layer
36
.
A schematic top sectional view of the proposed quantum magnetic disk is depicted in
FIG. 3B
, without the overcoat layer
36
, to illustrate the arrangement of magnetic columns
38
. In contrast to the magnetic force view of
FIG. 2B
, the view in
FIG. 3B
is a physical view. The centers of the magnetic columns
38
are separated by a distance of approximately 100 nm and are arranged in a grid-like manner. Each of the magnetic columns
38
represents a single bit for magnetic recording. The size of the bits (approximately 50 nm diameter) and the center-to-center separation of the columns (approximately 100 nm) produces a recording density of approximately 65 Gbit/in
2
.
The costs associated with achieving such a large storage density are prohibitive as the proposed manufacture of quantum magnetic disks utilizes expensive semiconductor processing techniques. An exemplary fabrication process was described in Chuo as including electron beam lithography to define the size and location of each bit in the disk. After development and chrome etching, a reactive ion etching step is performed to create a silicon dioxide template with column openings. Nickel or another electromagnetic material is then electroplated into the column openings to form the magnetic columns. The disk is then polished to planarize its surface.
In addition to the greatly increased costs of manufacture of the disks, the proposed quantum magnetic disk requires complicated non-Winchester recording technology not currently available. Hence, although providing a very high recording density, the proposed magnetic disk remains an impractical alternative to conventional magnetic recording media.
SUMMARY OF THE INVENTION
There is a need for magnetic recording media that have a much higher recording density than conventional, longitudinally recorded magnetic media, but can still be used with conventional Winchester-type recording technology. There is also a need for a method of producing magnetic recording media that have a much higher recording density than conventional media but at a greatly reduced cost in comparison to manufacturing processes employing semiconductor processing techniques.
These and other needs are met by certain embodiments of the present invention which provide a magnetic recording medium comprising a carrier layer and means for magnetically recording data located in the carrier layer. In certain embodiments, the carrier layer is a non-magnetic layer with a top surface having a plurality of recesses and magnetic material located within the recesses. The recesses may have an average depth between approximately 20 and 80 nm and a radius between approximately 10 and 100 nm. The recesses may be arranged in tracks separated from each other by a center-to-center distance of approximately 50 nm to 200 nm.
The magnetic recording media of the present invention exhibits a high recording density (e.g. 60-120 Gbit/in
2
) based on the dimensions of the recesses described above. Since the bits are isolated, the magnetic performance is high with low noise and no cross-talk between bits. Although the recording density is not as high as in quantum magnetic disks, it is an order of magnitude greater than conventional magnetic recording media. The media of the present invention can also be used with Winchester type recording technology.
The earlier stated needs are also met by certain embodiments of the present invention which provide a method of manufacturing a magnetic recording medium comprising the steps of machining recesses into a carrier layer and depositing a magnetic material in the recesses. In certain embodiments, the step of machining includes focusing laser energy on the top surface of the carrier layer to create the recesses. A continuous wave, pulsed or modulated laser beam is focused at the surface to produce very small holes (e.g. 20 nm diameter, 50 nm depth, 100 nm separation) by melting or ablating the carrier layer.
Once the small recesses are created in the non-magnetic carrier layer, the magnetic material may be deposited through electroplating or sputtering processes. Machining of recesses into a carrier layer and depositing magnetic material into the recesses is a less complicated and less expensive process of providing isolated single-magnetic d
Shih Chung Y.
Xuan Jialuo J.
Kiliman Leszek
McDermott & Will & Emery
Seagate Technology LLC
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