Stock material or miscellaneous articles – Structurally defined web or sheet – Including components having same physical characteristic in...
Reexamination Certificate
1998-04-21
2001-06-12
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including components having same physical characteristic in...
C428S336000, C428S408000, C428S690000, C428S690000, C428S690000, C428S698000, C428S900000
Reexamination Certificate
active
06245417
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a magnetic recording medium, particularly a rotatable magnetic recording medium, such as a thin film magnetic disk cooperating with a magnetic transducer head. The invention has particular applicability to high areal recording density magnetic recording media designed for drive programs having reduced flying heights, or pseudocontact/proximity recording.
BACKGROUND ART
Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. In operation, a typical contact start/stop (CSS) method commences when a data transducing 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 where it is maintained during reading and recording operations. Upon terminating operation of the disk drive, the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Each time the head and disk assembly is driven, the sliding surface of the head repeats the cyclic operation consisting of stopping, sliding against the surface of the disk, floating in the air, sliding against the surface of the disk and stopping.
For optimum consistency and predictability, it is necessary to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. Accordingly, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducer head. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to excessive stiction and friction during the start up and stopping phases, thereby causing wear to the head and recording surfaces, eventually leading to what is referred to as a “head crash.” Thus, there are competing goals of reduced head/disk friction and minimum transducer flying height.
Conventional practices for addressing these apparent competing objectives involve providing a magnetic disk with a roughened recording surface to reduce the head/disk friction by techniques generally referred to as “texturing.” Conventional texturing techniques involve mechanical polishing or laser texturing the surface of a disk substrate to provide a texture thereon prior to subsequent deposition of layers, such as an underlayer, a magnetic layer, a protective overcoat, and a lubricant topcoat, wherein the textured surface on the substrate is intended to be substantially replicated in the subsequently deposited layers. The surface of an underlayer can also be textured, and the texture substantially replicated in subsequently deposited layers.
A typical longitudinal recording medium is depicted in FIG.
1
and comprises a substrate
10
, typically an aluminum (Al)-alloy, such as an aluminum-magnesium (Al—Mg)-alloy, plated with a layer of amorphous nickel-phosphorus (NiP). Alternative substrates include glass, glass-ceramic materials and graphite. Substrate
10
typically contains sequentially deposited on each side thereof a chromium (Cr) or Cr-alloy underlayer
11
,
11
′, a cobalt (Co)-base alloy magnetic layer
12
,
12
′, a protective overcoat
13
,
13
′, typically containing carbon, and a lubricant topcoat
14
,
14
′. Cr underlayer
11
,
11
′ can be applied as a composite comprising a plurality of sub-underlayers
11
A,
11
A′. Cr underlayer
11
,
11
′, Co-base alloy magnetic layer
12
,
12
′ and protective overcoat
13
,
13
′, typically containing carbon, are usually deposited by sputtering techniques performed in an apparatus containing sequential deposition chambers. A conventional Al-alloy substrate is provided with a NiP plating, primarily to increase the hardness of the Al substrate, serving as a suitable surface to provide a texture, which is substantially reproduced on the disk surface.
In accordance with conventional practices, a lubricant topcoat is uniformly applied over the protective overcoat to prevent wear between the disk and head interface during drive operation. Excessive wear of the protective overcoat increases friction between the head and disk, thereby causing catastrophic drive failure. Excess lubricant at the head-disk interface causes high stiction between the head and disk. If stiction is excessive, the drive cannot start and catastrophic failure occurs. Accordingly, the lubricant thickness must be optimized for stiction and friction.
A conventional material employed for the lubricant topcoat comprises a perfluoro polyether (PFPE) which consists essentially of carbon, fluorine and oxygen atoms. The lubricant is usually dissolved in an organic solvent applied and bonded to the carbon overcoat of the magnetic recording medium by techniques such as thermal treatment, ultraviolet (UV) irradiation and soaking. A significant factor in the performance of a lubricant topcoat is the bonded lube ratio which is the ratio of the amount of lubricant bonded directly to the carbon overcoat of the magnetic recording medium to the amount of lubricant bonded to itself or to a mobile lubricant. Desirably, the bonded lube ratio should be high to realize a meaningful improvement in stiction and wear performance of the resulting magnetic recording medium.
The escalating requirements for high areal recording density impose increasingly greater requirements on thin film magnetic media in terms of coercivity, stiction, squareness, low medium noise and narrow track recording performance. In addition, increasingly high areal recording density and large-capacity magnetic disks require increasingly smaller flying heights, i.e., the distance by which the head floats above the surface of the disk in the CSS drive (head-disk interface). For conventional media design, a decrease in the head to media spacing increases stiction and drive crash, thereby imposing an indispensable role on the carbon-protective overcoat.
There are various types of carbon, some of which have been employed for a protective overcoat in manufacturing a magnetic recording medium. Such types of carbon include hydrogenated carbon, graphitic carbon or graphite and carbon nitride. These types of carbon are well known in the art and, hence, not set forth herein in great detail. See, for example, L. J. Huang et al., “Structure of Nitrogenated Carbon Overcoats on Thin Film Hard Disks,” IEEE Transaction on Magnetics, Vol. 33, 1997; L. J. Huang et al., “Characterization of the head-disk interface for proximity recording,” IEEE Transaction on Magnetics, 1997, Vol. 33, pp. 3112-3114; and Tsai et al., “Character Review Characterization of diamondlike carbon films and their application as overcoats on thin-film media for magnetic recording,” J. Vac. Sci. Technol., A5(6), Nov/Dec, 1987, pp. 3287-3311.
Generally, hydrogenated carbon has a hydrogen concentration of about 5 at.% to about 40 at.%, typically about 20 at.% to about 30 at. %, and does not bond well to a subsequently applied lubricant topcoat by virtue of the passivation of carbon dangling bonds by hydrogen. Accordingly, it is difficult to effectively bond a lubricant topcoat to a hydrogenated carbon protective overcoat at a suitable thickness. Hydrogenated carbon has a lower conductivity due to the elimination of the carbon band-gap states by hydrogen. Hydrogenated carbon also provides effective corrosion protection to an underlying magnetic layer.
Amorphous carbon nitride, sometimes referred to as nitrogenated carbon, generally has a nitrogen to hydrogen concentration ratio of about 5:20 to about 30:0. Amorphous carbon nitride generally has more carbon band-gap states than hydrogenated carbon and, hence, a higher conductivity. In addition, amorphous carbon nitride contains more dangling bonds than hydrogenated carbon, which dangling bonds promote interactions between lubricant and carbon and, hence, enable the application of a thicker bonded lubrica
McDermott & Will & Emery
Resan Stevan A.
Seagate Technology LLC
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