Coating processes – Direct application of electrical – magnetic – wave – or... – Polymerization of coating utilizing direct application of...
Reexamination Certificate
2000-05-25
2002-10-22
Beck, Shrive P. (Department: 1762)
Coating processes
Direct application of electrical, magnetic, wave, or...
Polymerization of coating utilizing direct application of...
C427S554000, C427S596000
Reexamination Certificate
active
06468596
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method of manufacturing a magnetic recording medium having a lubricant topcoat exhibiting improved tribological performance and reduced stiction failures. The present invention has particular applicability in manufacturing magnetic recording media suitable for high density recording and long term magnetic performance stability.
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 include laser texturing the surface of a non-magnetic substrate to provide a textured landing zone in which a magnetic head can land when the drive is not in use, and can take off when the drive is reading and writing data. Typically, the surface of the non-magnetic substrate is polished to a specular finish prior to laser texturing to form the landing zone leaving a substantially smooth data zone. Subsequently, an underlayer, a magnetic layer, a protective overcoat and a lubricant topcoat are sequentially deposited, wherein the textured surface on the substrate is intended to be substantially replicated in the subsequently deposited layers. Typical substrate materials include an aluminum alloy with a layer of amorphous nickel phosphorous thereon, glasses, ceramics and glass-ceramic materials, as well as graphite. Underlayers typically comprise chromium or a chromium alloy, while the magnetic layer typically comprises a cobalt based alloy. Protective overcoats typically contain carbon. Such layers are typically deposited by sputtering techniques preformed in an apparatus containing sequential deposition chambers.
In accordance with conventional practices, a lubricant topcoat is uniformly bonded to the protective overcoat. The lubricant topcoat applied to the protective overcoat performs several functions. The lubricant topcoat improves tribological performance for reduced friction, stiction and crash rate at the heat-disk-interface. In addition, a lubricant topcoat prevents 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. In addition, the lubricant topcoat prevents the protective overcoat from corrosion and other damage, thereby providing long-term magnetic performance stability.
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.
Conventional employed lubricants include perfluoro polyethers (PFPEs) which are long chain polymers composed of repeat units of a small perfluoronated aliphatic oxides, such as perfluoroethylene oxide or perfluoropropylene oxide. PFPEs typically provide excellent lubricity, a wide liquid-phase temperature range, low vapor pressure, small temperature dependence of viscosity, high thermal stability and low chemical reactivity. PFPEs also exhibit low surface tension, resistant to oxidation at elevated temperatures, low toxicity and moderately high solubility for oxygen. Various PFPE polymers are commercially available, such as Fromblinz, Fromblinz Y including Z-dol and am2001 from Montedison and Demnum from Daikin.
A typical lubricant coating comprises a bonded lube layer and a mobile lube layer thereon. The bonded lube layer contains lubricant molecules which are chemically or physically bonded to the overcoat, i.e., carbon, on the disk. The bonded lubricant molecules can not be removed by washing with a solvent as can the mobile lube layer. Bonding assists in reducing lubricant which can be lost due to spin off, evaporation or chemical displacement. It has been theorized that a bonded lube layer contributes to lower stiction forces. The mobile lube layer contains molecules that are not bonded and can be easily removed with an appropriate solvent.
Conventional practices in texturing the substrate, e.g., a non-magnetic substrate or underlayer provided thereon, comprise decoupling the magnetic requirements (data zone on which information is recorded and read) from the mechanical requirements (landing zone), by forming a dedicated landing zone where the slider is parked and lands after the drive has been shut down. Adverting to
FIG. 1
, a conventional magnetic recording disk
10
for a Winchester hard-drive design comprises an inner annular landing zone
11
and an outer annular data zone
12
. As a result of such zone design, the thickness of the lubricant topcoat is typically optimized for improved tribological performance and reduced friction, stiction and crash rate at the head-disk interface. Accordingly, the thickness required for the landing zone, which undergoes a large number of head-disk contacts, is required to be greater than the thickness of the lubricant topcoat overlying the data zone, where only a thin continuous lubricant layer is required to prevent corrosion and damage to the underlying protective overcoat thereby ensuring long-term magnetic performance stability.
However, conventional methods for forming a lubricant topcoat in the magnetic media industry, such as “dip-lube”, “vapor-lube” and “spray-lube”, are only capable of forming a lubricant topcoat at a substantially uniform thickness across the entire disk surface without differentiating the lubricant thickness between the different radial zones, i.e., landing zone and data zone. The conventional practice of depositing a lubricant topcoat at a uniform thickness overlying both the data zone and landing zone is problematic. For example, upon applying a thick lubricant topcoat for improved tribological performance, fly-stiction occurs as a result of lubricant transferred to the head when it flies over the data zone, and lubricant is transferred from the head to the head-disk interface when it rests at the landing zone, thereby causing stiction failure.
Eltoukhy et al. in U.S. Pat. No. 5,674,582 disclose a method of manufacturing a thin film disk media with differential lubricant thicknesses by initially applying a lubricant area and then buffing the lubricant over the data area as to provide a substantially reduced lubricant layer overlying the data zone
Gubbi Vidya K.
Liu Youming
Shih Chung-Yuang
Xuan Jialuo Jack
Yang Xiaohua Shel
Beck Shrive P.
Fuller Eric B.
McDermott & Will & Emery
Seagate Technology LLC
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