Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
1998-10-02
2001-10-16
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S336000, C428S690000, C428S900000
Reexamination Certificate
active
06303217
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a magnetic recording medium having a first underlayer and a second underlayer. The medium is of the type formed on a rigid disc for use in magnetic recording devices, such as a computer disc drive.
BACKGROUND OF THE INVENTION
Thin-film magnetic discs or media are widely used as data storage media for digital computers. The discs are typically formed by successively sputtering onto a rigid disc substrate and underlayer, a magnetic recording layer and a carbon overcoat which protects the magnetic layer from wear and reduces the frictional forces between the disc and the read\write head.
It is desirable that such media have excellent magnetic recording properties, for example, a high coercivity, high amplitude and low noise and numerous approaches have been described for improving the magnetic recording performance. One approach has focused on tailoring the underlayer to provide a surface that controls the grain size of the magnetic layer and/or permits epitaxial growth of the magnetic layer.
Approaches to tailoring the underlayer to control the ultimate magnetic recording properties of the disc have included controlling the thickness of the underlayer, the deposition conditions of the underlayer, the composition of the underlayer and/or the number of underlayers present. For example, increasing the thickness of the underlayer has been shown to improve coercivity, up to underlayer thicknesses of several thousand angstroms, e.g. 2,000-5,000 Å (Fisher, et al.,
IEE Trans. Magn
., 22:352 (1986), Johnson, K. E., et al.,
J. Appl, Phys
., 67(9):4686 (1990)). The effect of depositing a chromium underlayer under a substrate bias has been examined (Lal, B. B. et al.,
IEEE Trans. Magn
., 30(6):3954 (1994) and shown to improve coercivity.
Magnetic media having underlayers varying in composition have been described, for example, underlayers composed of chromium-based alloys such as CrMo, CrW, CrV (Ahlert, U.S. Pat. No. 5,051,288). Others have described magnetic media having more than one underlayer as an approach to controlling or improving magnetic recording properties (Shiroishi, et al. U.S. Pat. No. 4,833,020; Suzuki, et al. U.S. Pat. No. 5,316,844). There is still a need, however, for media which have improved recording performance.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide a magnetic recording disc having improved magnetic recording properties.
It is another object of the invention to provide a magnetic recording medium having an underlayer structure which provides an improved signal amplitude.
In one aspect, the invention includes a magnetic recording medium, comprising a nonmagnetic, metallic, rigid disc substrate; a first underlayer formed on the substrate, the first underlayer being composed of chromium or a chromium-based alloy and having a thickness between 25-200 Å; a second underlayer formed on the first underlayer and being composed of a chromium-based alloy and having a thickness between 25-200 Å; a magnetic recording layer formed on the second underlayer; and a protective overcoat.
In one embodiment the first underlayer is composed of a binary alloy of chromium and between 5-30 atomic percent of an element selected from the group consisting of Mo, Ta, Mn, V, W, Ru, Ti, Hf, Zr, Pt, Si, Ni, Al, Cu, B and Nb.
In another embodiment the second underlayer is composed of a binary alloy of chromium and between 5-30 atomic percent of an element selected from the group consisting of Mo, Ta, Mn, V, W, Ru, Ti, Hf, Zr, Pt, Si, Ni, Al, Cu. B and Nb.
In yet another embodiment, the first underlayer is composed of chromium and the second underlayer is composed of a chromium-based alloy. In a preferred embodiment the second underlayer is CrMo, CrTa, CrMn, CrV, CrW or CrRu.
In another embodiment, the second underlayer is composed of a ternary alloy of chromium and between 5-30 atomic percent of two elements selected from the group consisting of Mo, Ta, Mn, V, W, Ru, Ti, Hf, Zr, Pt, Si, Ni, Al, Cu, B and Nb.
In still another embodiment, the first and second underlayers are of the same thickness.
The magnetic recording layer, in one embodiment, is composed of cobalt, chromium, platinum and tantalum.
In another aspect, the invention includes an improvement in a magnetic recording medium formed on a rigid disc substrate and having a chromium underlayer, a magnetic recording layer and a protective overcoat. The improvement includes a second underlayer disposed between the chromium underlayer and the magnetic recording layer, the second underlayer composed of a chromium alloy containing between 5-30 atomic percent of at least one element selected from the group consisting of Mo, Ta, Mn, V, W, Ru, Ti, Hf, Zr, Pt, Si, Ni, Al, Cu, B and Nb.
In one embodiment of this aspect, the second underlayer is composed of a binary alloy of chromium and one element from the recited group. In a preferred embodiment, the second underlayer is CrMo, CrTa, CrMn, CrV, CrW or CrRu.
In another embodiment, the second underlayer is composed of a ternary alloy of chromium and two elements from the recited group.
The second underlayer has a thickness between 25-200 Å.
These and other objects and features of the invention will be more fully appreciated when the following detailed description of the invention is read in conjunction with the accompanying drawings.
REFERENCES:
patent: 4833020 (1989-05-01), Shiroishi
patent: 5122423 (1992-06-01), Hase et al.
patent: 5316844 (1994-05-01), Suzuki et al.
patent: 5456978 (1995-10-01), Lal et al.
patent: 5569533 (1996-10-01), Lal et al.
Lal Brij Bihari
Malhotra Sudhir S.
Russak Michael A.
HMT Technology Corporation
Kiliman Leszek
Mohr Judy M.
Perkins Coie LLP
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