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 air, sliding against the surface ot 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 opposing surfaces 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 substrate surfaces are 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, ceramic, 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 11A, 11A'. 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 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 magnetic recording medium to the amount of lubricant bonded to itself or the 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.
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.
The drive for high areal recording density and, consequently, reduced flying heights, challenges the limitations of conventional practices in manufacturing a magnetic recording medium containing a carbon protective overcoat. For example, a suitable protective overcoat must be capable of preventing corrosion of the underlying magnetic layer, which is an electrochemical phenomenon dependent upon such factors as environmental conditions, e.g., humidity and temperature. In addition, a suitable protective overcoat must prevent migration of ions from underlying layers into the lubricant topcoat and to the external surface of the magnetic recording medium. Thus, the protective overcoat must seal the magnetic layer. Furthermore, in media comprising a glass or glass-ceramic substrate, the protective overcoat must also seal the underlying substrate from the outside environment. Such sealing is necessary, particularly in warm and humid conditions, characteristic of the running disk drive, which are conducive to corrosion of the magnetic recording layer. When a glass or glass-ceramic substrate is employed, sodium, lithium and/or potassium ions accelerate corrosion by diffusing to the top surface of the disk.
In order to prevent corrosion, conventional practices comprise sputter depositing a carbon-containing overcoat on magnetic recording media, or a silicon nitride or aluminum nitride overcoat on magneto-optical media. The protective overcoat is typically sputter deposited on the surface of the disk comprising the substrate and magnetic layer.
Conventional practices also comprise sputter depositing a plurality of protective overcoats and/or incorporating a corrosion resistant additive in the glass or glass-ceramic substrate, such as zinc, to provide adequate corrosion resistance. Such conventional techniques have not proved entirely satisfactory for insuring adequate corrosion resistance. Moreover, as the head disk interface decreases to less than one microinch, it is necessary to reduce the thickness of the protective overcoat below about 200 .ANG.. It is, therefore, extremely difficult, if not impossible, to deposit a plurality of protective overcoats and satisfy the esculating requirements of increased areal recording density.
Ahonen, U.S. Pat. No. 5,482,604, discloses a sputter deposition technique for manufacturing a mirror, wherein the substrate is rotated to improve coating uniformity. Givens et al. U.S. Pat. No. 5,658,438, discloses a collimating sputter deposition technique for filling high aspect ratio openings in manufacturing semiconductor devices.
There exists a need for method of sputter depositing protective overcoat to provide superior corrosion resistance of magnetic thin film media, particularly with respect to the underlying magnetic layer, and to prevent migration of ions from underlying layers or the substrate itself. There also exists a need for a method of sputter depositing a protective overcoat on a magnetic thin film media having a thickness satisfying the imposing demands for high areal recording density and reduced head-disk interface.