Stock material or miscellaneous articles – Structurally defined web or sheet – Including variation in thickness
Reexamination Certificate
2001-05-10
2004-06-08
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including variation in thickness
C428S448000, C428S426000, C428S690000, C428S690000
Reexamination Certificate
active
06746754
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods for forming mechanically textured substrates for magnetic recording media utilized in high areal density recording applications, and to magnetic recording media produced thereby. The invention has particular utility in the manufacture of magnetic data/information storage and retrieval media, e.g., hard disks, utilizing very hard-surfaced, high modulus substrates, such as of glass, ceramic, and glass-ceramic materials.
BACKGROUND OF THE INVENTION
Magnetic recording media are widely used in various applications, particularly in the computer industry. A portion of a conventional recording medium
1
utilized in disk form in computer-related applications is schematically depicted in FIG.
1
and comprises a non-magnetic substrate
10
, typically of metal, e.g., an aluminum-magnesium (Al—Mg) alloy, having sequentially deposited thereon a plating layer
11
, such as of amorphous nickel-phosphorus (NiP), a polycrystalline underlayer
12
, typically of chromium (Cr) or a Cr-based alloy, a magnetic layer
13
, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer
14
, typically containing carbon (C), e.g., diamond-like carbon (“DLC”), and a lubricant topcoat layer
15
, typically of a perfluoropolyether compound applied by dipping, spraying, etc.
In operation of medium
1
, the magnetic layer
13
can be locally magnetized by a write transducer or write head, to record and store data/information. The write, transducer creates a highly concentrated magnetic field which alternates direction based on the bits of information being stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the recording medium layer
13
, then the grains of the polycrystalline medium at that location are magnetized. The grains retain their magnetization after the magnetic field produced by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The pattern of magnetization of the recording medium can subsequently produce an electrical response in a read transducer, allowing the stored medium to be read.
Thin film magnetic recording media are conventionally employed in disk form for use with disk drives for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (“CSS”) method commences when the head begins to slide against the surface of the disk as the disk begins to rotate. Upon reaching a predetermined high rotational speed, the head floats in air at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the head can be freely moved in both the circumferential and radial directions, allowing data to be recorded on and retrieved from the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the static position, and during deceleration just prior to completely stopping. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic sequence consisting of stopping, sliding against the surface of the disk, floating in air, sliding against the surface of the disk, and stopping.
It is considered desirable driving reading and recording operations, and for obtainment of high areal recording densities, to maintain the transducer head as close to the associated recording surface as is possible, i.e., to minimize the “flying height” of the head. Thus, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head, thereby permitting the head and the disk surface to be positioned in close proximity, with an attendant increase in predictability and consistent behavior of the air bearing supporting the head during motion.
Meanwhile, the continuing trend toward manufacture of very high areal density magnetic recording media at reduced cost provides impetus for the development of lower cost materials, e.g., polymers, glasses, ceramics, and glass-ceramics composites as replacements for the conventional Al alloy-based substrates for magnetic disk media. However, poor mechanical and tribological performance, track mis-registration (“TMR”), and poor flyability have been particularly problematic in the case of polymer-based substrates fabricated as to essentially copy or mimic conventional hard disk design features and criteria. On the other hand, glass, ceramic, or glass-ceramic materials are attractive candidates for use as substrates for very high areal density disk recording media because of the requirements for high performance of the anisotropic thin film media and high modulus of the substrate. However, the extreme difficulties encountered with grinding and lapping of glass, ceramic, and glass-ceramic composite materials have limited their use to only higher cost applications, such as mobile disk drives for “notebook”-type computers.
As employed herein, the term “glass” is taken to include, in the broadest sense, non-crystalline silicates, aluminosilicates, borosilicates, boroaluminosilicates, as well as polycrystalline silicates, aluminosilicates, and oxide materials; the term “ceramic” is taken to include materials consisting of crystalline particles bonded together either with a glass (i.e., vitreous) matrix or via fusion of the particles at their grain boundaries, as by sintering, as well as refractory nitrides, carbides, and borides when prepared in the form of bodies, as by sintering with or without a glass matrix or a silicon- or boron-containing matrix material, e.g., silicon nitride (Si
3
N
4
), silicon carbide (SiC), and boron carbide (B
4
C); and the term “glass-ceramics” is taken to include those materials which are melted and fabricated as true glasses, and then converted to a partly crystalline state, such materials being mechanically stronger, tougher, and harder than the parent glass, as well as non-porous and finer-grained than conventional polycrystalline materials.
Presently, media anisotropy for obtaining high performance magnetic recording media is typically achieved by circumferentially polishing (“mechanically texturing”) Al alloy substrates with NiP plating layers thereon by using a diamond or other relatively hard abrasive in slurry form dispensed on an absorbent and compliant polishing pad or tape. The circumferential texture pattern, produced by holding the surface of a rotating disk substrate against the polishing pad or tape with the abrasive slurry therebetween, simultaneously fulfills two desirable purposes: (1) tribologically—by minimizing stiction and friction at the head-disk interface; and (2) enhancing magnetic anisotropy—by providing a preferred orientation of the subsequently deposited polycrystalline Cr underlayer
12
and Co-based magnetic layer
13
along the circumferential textture lines of the pattern, resulting in an in-plane circumferential vs. radial anisotropy which improves the read/write parameters (e.g., coercivity H
c
, residual magnetic susceptibility B
r
, coercive squareness S*, magnetic anisotropy K
&mgr;
) of the Co-based magnetic alloy layer.
The aforementioned circumferential texturing is thus effective for improving wear resistance and read/write characteristics of thin-film magnetic recording media; however, the benefits of texturing vary greatly upon the microscopic contours of the texture surface. Specifically, in order to form a medium having uniform
Deeman Neil
Kuo David
Leigh Joseph
Wang Hong Ying
McDermott & Will & Emery
Resan Stevan A.
Seagate Technology LLC
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