Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1997-01-08
2001-04-17
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S690000, C428S690000, C428S900000, C427S128000, C427S129000, C427S130000, C204S192200
Reexamination Certificate
active
06218033
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to magnetic recording media, and more particularly to high density magnetic recording disks having textured surfaces.
Thin film magnetic recording disks generally comprise a disk substrate having a magnetic layer and a number of underlayers and overlayers deposited thereon. The nature and composition of each layer is selected to provide the desired magnetic recording characteristics, as generally recognized in the industry. An exemplary present day thin film disk is illustrated in FIG.
1
and comprises a non-magnetic disk substrate
10
, typically composed of aluminum or an aluminum alloy. An amorphous nickel-phosphorus (NiP) layer
12
is formed over each surface of the disk substrate
10
, typically by plating. The NiP layer is hard, and imparts rigidity to the aluminum substrate. A second underlayer in the form of a chromium ground layer
14
is formed over the NiP layer
12
, typically by sputtering, and a magnetic layer
16
is formed over the ground layer
14
. The magnetic layer
16
comprises a thin film of a ferromagnetic material, such as a magnetic oxide or magnetic alloy. Usually, a protective layer
18
, such as carbon film, is formed over the magnetic layer
16
, and a lubricating layer
20
is formed over the protective layer.
The presence of the NiP layer
12
and the chromium ground layer
14
have been found to improve the recording characteristics of the magnetic layer
16
. In particular, a chromium ground layer formed over a NiP layer has been found to provide enhanced coercivity and reduced noise characteristics. Additionally, the NiP layer is often mechanically textured to create a roughened surface prior to formation of the chromium ground layer. This surface texturing has a substantial effect on the mechanical properties of the disk and its interaction with the recording transducer (read/write head), which typically “flies” over the disk surface on a cushion of air that is moved by the rotating disk. In particular, texturizing is highly beneficial to the magnetic recording system's ability to reliably withstand repeated starting and stopping of the disk, with its associated repeated contact between the read/write head and the disk's surface. The texturing may be circumferential, crosswise, or separated into start/stop and data zones, with the preferred geometry depending on the particular composition of the cobalt-containing magnetic layer, and on the specific disk drive design.
Such magnetic recording constructions have been very successful and allow for relatively high recording densities. As with all successes, however, it is desired to provide magnetic recording disks having even higher recording densities. To increase recording densities beyond those of known practical magnetic recording media, it would be beneficial to minimize any anisotropy of the magnetic recording layer within the structure of the magnetic recording media.
Work in connection with the present invention has shown that anisotropy (here referring to differing circumferential and radial magnetic recording characteristics) may deteriorate certain electrical and magnetic parameters of high density magnetic recording media, such as the pulse width, the overwrite, the non-linear transition shift, and the signal-to-noise ratio. Specifically, scratches in the disk structure prior to deposition of the magnetic layer are a recognized source of magnetic recording defects. These defects are worsened by magnetic layer anisotropy, as the film stress along the scratch will tend to align the preferred magnetic orientation of a subsequent anisotropic magnetic layer with the direction of the scratch. Where the scratch has a radial orientation and the recording media has a circumferential orientation, the scratch produces a localized radial orientation of the magnetics, which will cause disk magnetic defects and missing pulses. Clearly, such defects should be minimized. Therefore, it is desirable to provide isotropic media (media having substantially equivalent circumferential and radial recording characteristics) to optimize magnetic recording densities.
Unfortunately, the texture imposed on the NiP-coated substrate to provide acceptable mechanical characteristics and reliability can also induce substantial anisotropy in the final magnetic recording media. This is the same effect as the scratch-induced localized anisotropy, only it occurs along a texture line, generally with a circumferential orientation. This texture-induced anisotropy, which can result in coercivities in the circumferential direction being twice the radial coercivity or more, typically requires a tradeoff between mechanical and magnetic recording characteristics. In other words, the texture-induced anisotropy of present magnetic recording media structures requires some compromise of either reliability or recording density.
For these reasons, it would be desirable to provide an improved magnetic recording disk which allowed optimization of the texture for mechanical properties, and which avoided the texture-induced anisotropy of known magnetic recording media. It would be particularly desirable if such isotropic textured media maintained the enhanced magnetic properties which are provided by known media structures. It would further be desirable if such improved magnetic recording media were readily fabricated using existing thin film deposition and texturing equipment, and provided the enhanced magnetic properties of recent cobalt-containing magnetic layers.
2. Description of the Background Art
The magnetic properties and read/write characteristics of CoCrPt and CoCrTa magnetic layers disposed over ground layers of Cr or CrTi were described by Y. Shiroishi et al. in the
Journal of Applied Physics
, Vol. 73, No. 10, p. 5569 (May 1993). The CrTi underlayer was found to enhance the inplane coercive forces of these specific cobalt-containing magnetic layers. The magnetic recording characteristics of glass disks having pre-coat layers of Cr, Ta, W, or Zr were described by Hiroyuki Kataoka et al. in IEEE
Transactions on Magnetics,
Vol. 31, No. 6, p. 2734 (November 1995). In particular, the magnetic and recording characteristics of a CoCrPt magnetic layer disposed over a CrTi ground layer, in turn disposed over the pre-coated glass disks, were compared, with the Ta pre-coated glass disk being preferred due to its relatively large output signal and relatively low noise.
U.S. Pat. No. 5,166,006 describes a method for selectively chemically etching a substrate to form an isotropic texture of a desired density and roughness. Selective texturing of specific zones of the substrate are also described. U.S. Pat. No. 5,302,434 describes a contact recording media having an NiO film between an NiP-coated substrate and Cr or CrV layer to increase the coercivity of a subsequent cobalt alloy magnetic layer. U.S. Pat. Nos. 5,388,020, 4,698,251, 4,996,622, 5,478,622, and 4,939,614 describe textured recording media and methods for their production. U.S. Pat. No. 5,113,302 is generally relevant.
SUMMARY OF THE INVENTION
The present invention provides magnetic recording media comprising a rigid substrate and an underlayer disposed over the substrate, in which the underlayer comprises CrTiCu or CrTiV. A magnetic layer is disposed over this underlayer, and is also disposed over a texturized surface. Generally, the substrate comprises aluminum, and an NiP layer is disposed over the substrate and below the underlayer; the texture is typically imposed on this NiP layer. Advantageously, the CrTiCu or CrTiV underlayer has been found to compensate for texture-induced anisotropy of the recording media, limiting a ratio of circumferential coercivity to radial coercivity within the range between about 0.8 and 1.25, and in some cases, between about 0.95 and 1.10.
Preferably, the underlayer comprises Ti in the range between about 2 and 20%. When it is present, Cu will provide between about 2 and 6 atomic percent of the underlayer. Alternatively, the underlayer
Cao Wei
Tregoning Mike
Ward James
Yang Xingbo
Akashic Memories Corporation
Bains, Esq. Nena
Kiliman Leszek
Townsend & Townsend & Crew LLP
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