Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-12-18
2003-11-04
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S336000, C428S611000, C428S667000, C428S900000, C427S128000, C427S131000, C204S192200
Reexamination Certificate
active
06641936
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an improved magnetic recording medium, such as a thin film magnetic recording disk, and to a method of manufacturing the medium. The invention has particular applicability to longitudinal magnetic recording media exhibiting high areal recording density, low noise, high SMNR, and high coercivity.
BACKGROUND OF THE INVENTION
The continuously increasing requirements for thin film magnetic recording media with very high areal recording densities impose increasingly greater requirements on the magnetic properties of the various thin film layers constituting the media, such as increased remanent magnetic coercivity (H
r
), and coercivity squareness (S
r
*), low medium noise, e.g., expressed as signal-to-medium noise ratio (SMNR), and improved narrow track recording performance. As the areal recording density requirement increases, it becomes increasingly difficult to fabricate magnetic recording media, e.g., thin film longitudinal media, which satisfy each of these demanding requirements.
The linear recording density can be increased by increasing the H
r
of the media; however, this objective can only be achieved by decreasing the media noise, as by formation and maintenance of magnetic recording layers with very finely dimensioned, non-magnetically coupled grains. Media noise is a dominant factor restricting obtainment of further increases in areal recording density of high density magnetic hard disk drives. The problem, or cause, of media noise is generally attributed, in large part, to inhomogeneous magnetic grain size and inter-granular exchange coupling. Accordingly, it is considered that, in order to increase linear recording density of thin film magnetic media, the media noise must be minimized by suitable control of the microstructure of the magnetic recording layer(s).
A portion of a conventional thin film, longitudinal magnetic recording medium
1
, such as is commonly employed in hard disk form in computer-related applications, is depicted in
FIG. 1
in simplified, schematic cross-sectional view, and comprises a substantially rigid, non-magnetic substrate
10
, typically of aluminum (Al) or an aluminum-based alloy, such as an aluminum-magnesium (Al—Mg) alloy, or of glass, glass-ceramic, etc., having sequentially deposited or otherwise formed on a surface
10
A thereof a plurality of thin film layers. When substrate
10
comprises Al or an Al-based alloy a plating layer
11
, such as of amorphous nickel-phosphorus (Ni—P), is typically initially provided on substrate surface
10
A (such NiP plating layer
11
generally is omitted when substrate
10
comprises glass). The plurality of thin film layers formed over plating layer
11
or substrate surface
10
A include a system
12
of layers for control of the microstructure of medium
1
, comprising a first, or seed layer
12
A of an amorphous or fine-grained material, e.g., a chromium-titanium (Cr—Ti) alloy and a second, polycrystalline underlayer
12
B, typically of Cr, a Cr-based alloy, or a B
2
-structured Ni—Al alloy (as first described by Li-Lien Lee et al. in IEEE
Transactions on Magnetics
, 30 (6), 3951-3953 (1994)); a magnetic recording layer
13
, e.g., of a cobalt (Co)-based alloy with one or more of platinum (Pt), Cr, boron (B), etc.; a protective overcoat layer
14
, typically containing carbon (C), e.g., diamond-like carbon (“DLC”); and a lubricant topcoat layer
15
, e.g., of a perfluoropolyether. Each of layers
11
-
14
may be deposited by suitable physical vapor deposition (“PVD”) techniques, such as sputtering, and layer
15
is typically deposited by dipping or spraying.
In operation of medium
1
, the magnetic layer
13
is locally magnetized by a write transducer, or write “head”, to record and thereby store data/information therein. The write transducer or head creates a highly concentrated magnetic field which alternates direction based on the bits of information to be stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the material of the recording medium layer
13
, the grains of the polycrystalline material at that location are magnetized. The grains retain their magnetization after the magnetic field applied thereto by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The magnetization of the recording medium layer
13
can subsequently produce an electrical response in a read transducer, or read “head”, allowing the stored information to be read.
As indicated above, it is recognized that the magnetic properties which are critical to the performance of the magnetic recording. layer
13
, i.e., H
r
, M
r
(magnetic remanence), S*, and SMNR, depend primarily on the microstructure of the magnetic recording layer
13
which, in turn, is strongly influenced by the microstructure of the underlying system
12
of seed and underlayers
12
A and
12
B, respectively. It is also recognized that underlayers having a very fine grain structure are highly desirable, particularly for growing fine grains of hexagonal close-packed (hcp) Co-based magnetic alloys deposited thereon.
Adverting to
FIG. 2
, a recent approach for improving the microstructure, texture, and crystallographic orientation of magnetic alloys in the fabrication of thin film, high recording density, longitudinal magnetic recording media
1
′, involves modification of layer system
12
for microstructure control to include a third, intermediate (or “onset”) layer
12
C between underlayer
12
B and magnetic recording layer
13
. A number of Co-based alloy materials, such as CoCr, magnetic CoPtCr, CoPtCrTa, CoCrB, CoCrTa, and CoCrTaO
x
(where O
x
indicates surface-oxidized CoCrTa), etc., have been studied for use as intermediate layers
12
C according to such approach, as disclosed in, for example, U.S. Pat. Nos. 5,736,262; 5,922,442; 6,001,447; 6,010,795; 6,143,388; 6,150,016; 6,221,481 B1; and 6,242,086 B1, the entire disclosures of which are incorporated herein by reference.
Currently, the most widely utilized magnetic alloy for the active recording layer of thin film, high areal recording density, longitudinal media is high Pt, high B content CoCrPtB, i.e., with more than about 5 at. % each of Pt and B. However, the use of such high Pt, high B content CoCrPtB magnetic alloys presents several difficulties and drawbacks with respect to the design of high areal density, high SMNR media having a film structure similar to that of
FIG. 2
including a layer system
12
for microstructure control, comprised of one or more of seed layer
12
A, underlayer
12
B, and intermediate layer
12
C.
Specifically, as disclosed in commonly assigned U.S. Pat. No. 6,132,863 and U.S. patent application Ser. No. 09/497,524, filed Feb. 4, 2000, the entire disclosures of which are incorporated herein by reference, magnetic media can be advantageously fabricated with simultaneous crystallographic orientation and grain size refinement, by interposition of a “double underlayer” structure (equivalent to a structure represented as
12
B
1
/
12
B
2
, wherein
12
B
1
and
12
B
2
respectively indicate first-deposited and second-deposited underlayers) between the substrate and the magnetic recording layer, e.g., a Cr/CrV or Cr/CrW double underlayer structure, with the Cr first underlayer (=
12
B
1
) being deposited directly on the substrate. Such media with a Cr first underlayer deposited directly on the substrate or via an intervening seed layer (=
12
A) exhibit high SMNR. However, the lattice mismatch between the Cr first underlayers and the high Pt, high B CoCrPtB magnetic recording layer is very large. In addition, since the typically utilized NiAl-based, B-
2
structured underlayer
12
B has lattice constants similar to that of the Cr underlayers
12
B or
12
B
1
, the difference in lattice constants between the NiAl-based underlayer
12
B and the CoCrPtB recording layer(s)
13
is similarly large. More particularly, for good lattice matching, the (110) planes of Cr and
Chen Qixu
Harkness, IV Samuel D.
Ranjan Rajiv Yadav
Rou Shanghsien
McDermott & Will & Emery
Rickman Holly
Seagate Technology LLC
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