Coating processes – Magnetic base or coating – Magnetic coating
Reexamination Certificate
1999-09-29
2003-11-11
Rickman, Holly (Department: 1773)
Coating processes
Magnetic base or coating
Magnetic coating
C427S131000, C427S132000
Reexamination Certificate
active
06645551
ABSTRACT:
BACKGROUND OF THE INVENTION
Magnetic thin film recording disks are commonly manufactured by a series of sputtering processes in an environment of low pressure inert gases. Disk
2
, see
FIG. 1
, is commonly comprised of a substrate
4
made of nickel phosphorus (NiP) or ceramic glass, an optional magnetic seedlayer
6
, a non-magnetic underlayer
8
, made of either pure chromium (Cr) or a chrome alloy (CrX), covered by a magnetic layer
10
made of a cobalt (Co)-based alloy. A protective layer
12
made of sputtered carbon is typically used on top of the magnetic layer and an organic lubricant
14
may be used on top of the protective layer. It has been found that it is important to match the underlayer and magnetic layer lattice parameters for thin films in longitudinal recording. In the case of body centered cubic (bcc) Cr or CrX underlayer, the lattice dimension is defined by the parameter aCr. For hexagonal close-packed (hcp) Co alloy, the lattice dimension is defined by two orthogonal vectors: aCo and cCo. See
FIGS. 1A-1D
. For a well-matched Co/Cr film stack, 2 a
Cr
=c
Co
.
Lattice matching between the Cr or CrX underlayer and the Co alloy magnetic layer is commonly done to achieve optimal magnetic and parametric properties. See D. E. Laughlin et al.,
Scripta Metallurgica et Materialia
33, 1525 (1995).
Common Co alloys include chromium (Cr), platinum (Pt), boron (B), niobium (Nb), tungsten (W) and tantalum (Ta). While the cobalt platinum alloy has a hexagonal close-packed (hcp) crystalline structure, the chromium-based underlayer has a body centered cubic (bcc) lattice structure. With the addition of platinum, the CoPt-based alloys have a larger lattice structure than the chromium-based underlayer so that elements such as Vanadium (V), Molybdenum (Mo), titanium (Ti) and tungsten (W) have been used to create chromium-based alloys to accommodate the larger lattice of the CoPt-based magnetic layers and maintain lattice union across the interface between the two. These alloys expand the unit cell structure so as to improve the lattice matching between the underlayer and the magnetic film because of the larger sized atoms of the alloying elements.
One of the problems with the conventional method for trying to match the lattice perimeter of the chromium-based underlayer with the CoPt-based magnetic layers is that it requires incremental experimentation with chromium alloying as to both what is used and the percentages. Therefore, each time the composition of the cobalt-based magnetic layer changes, which occurs relatively often as improved magnetic layers are developed, the composition of the chromium-based underlayer must be changed to complement the changed composition of the magnetic layer. However, this composition adjustment is tedious, time-consuming and, thus, expensive.
SUMMARY OF THE INVENTION
The present invention is directed to an underlayer of a magnetic recording medium in which the underlayer includes first and second non-magnetic, chromium-based layers, at least one of the first and second chromium-based layers being a chromium alloy. The lattice parameter of the composite underlayer is between the lattice parameters of the first and second chromium-based layers. Recognizing this permits one to predictably adjust the lattice parameter of the composite underlayer to be close to the lattice parameter of the magnetic layer so to optimize magnetic and parametric properties.
Another aspect of the invention relates to a method for obtaining a desired lattice parameter of a non-magnetic underlayer in the manufacture of a magnetic recording medium of the type comprising a substrate, a non-magnetic underlayer on the substrate, and a magnetic layer on the underlayer. The method includes determining a desired lattice parameter, typically the lattice parameter of the magnetic layer, for the underlayer. A number of non-magnetic, chromium-based layers, typically two, are selected for the underlayer, at least one of the chromium-based layers is a chromium alloy. The thickness of each chromium-based layer is chosen according to the desired lattice parameter, the sum of the thicknesses of each of the chromium-based layers being equal to the underlayer thickness. One way of choosing the thicknesses of the chromium-based layers is to use a plot of the ratio of the two thicknesses of the two chromium-based layers versus corresponding (002) interplanar spacing as the lattice parameter. The choosing step is preferably carried out so that the difference between the lattice parameter of the underlayer and the desired lattice parameter, typically the lattice parameter of the magnetic layer, is minimized. The final lattice parameter of this composite underlayer lies between the lattice parameters of the two respective Cr or CrX layers.
In some embodiments a protective layer is deposited on the magnetic layer, a lubricant is deposited on the protective layer and a non-magnetic seedlayer layer is provided between the substrate and the underlayer. The thickness of the underlayer is preferably less than about 350 Å, and more preferably between about 180-200 Å. The chromium-based layers are preferably between about 10-500 Å thick. If desired, more than two chromium-based layers may be used in making up the underlayer.
Other features and advantages of the invention will appear from the following description in which the preferred embodiment has been set forth in detail in conjunction with the accompanying drawings.
REFERENCES:
patent: 4652499 (1987-03-01), Howard
patent: 5693426 (1997-12-01), Lee et al.
patent: 5900324 (1999-05-01), Moroishi et al.
patent: 6001447 (1999-12-01), Tanahashi et al.
patent: 6551703 (2003-04-01), Falcone et al.
David N. Lambeth et al., “Magnetic Media Performance: Control Methods for Crystalline Texture and Orientation”, submitted for publication inMRS ProceedingsMRS Sym L: paper #L8.1, Apr. 15, 1998 (Jun. 1, 1998), 12 pages.
Maxtor Corporation
Rickman Holly
Sigmond David M.
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