Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-07-12
2003-07-08
Rickman, Holly (Department: 1773)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S690000, C428S216000, C428S336000, C428S900000, C427S130000, C427S131000, C427S528000, C427S531000, C204S192100, C204S192200
Reexamination Certificate
active
06589676
ABSTRACT:
TECHNICAL FIELD
The present invention relates to magnetic recording media, particularly rotatable recording media, such as thin film magnetic disks cooperating with a magnetic transducer head, particularly a magnetoresistive (MR) or a giant magnetoresistive (GMR) head. The present invention has particular applicability to high areal density magnetic recording media designed for drive programs having reduced flying height, or pseudo-contact/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 smooth, 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.
Conventional longitudinal recording media typically comprise a substrate, such as aluminum (Al) or an Al alloy, e.g., aluminum-magnesium (Al—Mg) alloy, plated with a layer of amorphous nickel-phosphorus (NiP). Alternative substrates include glass, ceramic, glass-ceramic, and polymeric materials and graphite. The substrate typically contains sequentially deposited on each side thereof at least one seedlayer and/or at least one underlayer, such as chromium (Cr) or a Cr-alloy, e.g., chromium vanadium (CrV), a cobalt (Co)-base alloy magnetic layer, a protective overcoat typically containing carbon, and a lubricant. The underlayer, magnetic layer and protective overcoat, are typically sputter deposited 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.
Conventional practices further include forming a servo pattern on the magnetic layer thereby producing topographical nonuniformities, such servo patterns can be formed by photolithographic or laser techniques.
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 typically dissolved in an organic solvent, applied and bonded to the carbon overcoat of the magnetic recording medium by techniques such as dipping, buffing, thermal treatment, ultraviolet (UV) irradiation and soaking.
The escalating requirements for high areal recording density impose increasingly greater requirements on thin film magnetic recording media in terms of coercivity, stiction, squareness, medium noise and narrow track recording performance. In addition, increasingly high areal recording density and large-capacity magnetic disks require smaller flying heights, i.e., the distance by which the head floats above the surface of the disk in the disk 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 nitrogenated carbon or carbon nitride and hydrogen-nitrogenated carbon. These types of carbon are well known in the art and, hence, not set forth herein in great detail.
The drive for high areal recording density and, consequently, reduced flying heights, challenges the capabilities of conventional manufacturing practices. For example, a suitable protective overcoat must be capable of preventing corrosion of the underlying magnetic layer, which is an electrochemical phenomenon dependent upon factors such as environmental conditions, e.g., humidity and temperature. In addition, a suitable protective overcoat must prevent migration of ions, such as cobalt (Co) and nickel (Ni), from underlying layers into the lubricant topcoat and to the surface of the magnetic recording medium forming defects such as asperities. A protective overcoat must also exhibit the requisite surface for wear resistance, lower stiction, and some polarity to enable bonding thereto of a lubricant topcoat in an adequate thickness.
The continuing drive for increased recording areal density in the magnetic recording media industry mandates reduction of the thickness of the protective overcoats, e.g., the carbon protective overcoat and lubricant film, since such layers constitute part of the head-medium separation. In order to satisfy the continuing drive for higher recording areal densities, the head-medium separation requirement at, for example, 100 Gb/in
2
recording areal density, the protective overcoat thickness must be as low as 20 Å, and the lubricant film thickness must be as low as 10 Å. However, at such extreme low thicknesses, significant issues arise in that the continuity and integrity of the protective and lubricant films are difficult to maintain. Consequently, imperfections in the protective overcoats increase leading to degradation of recording performance due to environmental attacks, such as corrosion. Thus, the corrosion problem prevents reduction of protective overcoats to a thickness less than the physical limit below which the films are no longer continuous, thereby significantly limiting reduction of the head-medium separati
Gui Jing
Harkness, IV Samuel Dacke
Rauch Gary Clark
Ristau Roger Alan
Thangaraj Raj
McDermott & Will & Emery
Rickman Holly
Seagate Technology LLC
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