Media with a metal oxide sealing layer

Details Media with a metal oxide sealing layer Media with a metal oxide sealing layer

2000-05-15

2002-07-09

Resan, Stevan A. (Department: 1773)

Stock material or miscellaneous articles

All metal or with adjacent metals

Having magnetic properties, or preformed fiber orientation...

C428S640000, C428S666000, C428S332000, C428S690000, C428S701000, C428S900000, C204S192200

Reexamination Certificate

active

06416881

ABSTRACT:

TECHNICAL FIELD
This invention relates to a magnetic medium, such as a thin film magnetic recording medium, and the method of manufacturing the medium. The invention has particular applicability to high density magnetic recording media having a total film thickness above a substrate of about 1000 Å or less while still exhibiting low noise, improved flying stability, glide performance and head-media interface reliability.
BACKGROUND ART
Magnetic disks and disk drives are conventionally employed for storing data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducing heads positioned in close proximity to the recording surfaces of the disks and moved generally radially with respect thereto. Magnetic disks are usually housed in a magnetic disk unit in a stationary state with a magnetic head having a specific load elastically in contact with and pressed against the surface of the disk.
Data are written onto and read from a rapidly rotating recording disk by means of a magnetic head transducer assembly that flies closely over the surface of the disk. It is considered desirable during reading and recording operations to maintain each transducer head as close to its associated recording surface as possible, i.e., to minimize the flying height of the head. This objective becomes particularly significant as the areal recording density increases. The areal density (Mbits/in
2
) is the recording density per unit area and is equal to the track density (TPI) in terms of tracks per inch times the linear density (BPI) in terms of bits per inch.
The increasing demands for higher areal recording density impose increasingly greater demands on flying the head lower because the output voltage of a disk drive (or the readback signal of a reader head in disk drive) is proportional to 1/exp(HMS), where HMS is the space between the head and the media. Therefore, 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 to be positioned in closer proximity with an attendant increase in predictability and consistent behavior of the air bearing supporting the head.
A substrate material conventionally employed in producing magnetic recording rigid disks comprises an aluminum-magnesium (Al—Mg) alloy. Such Al—Mg alloys are typically electrolessly plated with a pre-coat layer of NiP at a thickness of about 15 microns to increase the hardness of the substrates, thereby providing a suitable surface for polishing to provide the requisite surface roughness or texture.
Other substrate materials have been employed, such as aluminum, glass, e.g., an amorphous glass, glass-ceramic material which comprise a mixture of amorphous and crystalline materials, and ceramic materials. Glass-ceramic materials do not normally exhibit a crystalline surface. Glasses and glass-ceramics generally exhibit high resistance to shocks. The use of glass-based materials, such as glass-ceramic materials, is disclosed by Hoover et al., U.S. Pat. No. 5,273,834, which is incorporated herein by reference.
A conventional longitudinal recording disk medium is depicted in FIG.
1
. It typically comprises a substrate
10
, comprising an aluminum platter with a 10-15 microns thick NiP pre-coat layer, and sequentially deposited on each side of the substrate are an underlayer
11
,
11
′, such as chromium (Cr) or Cr-alloy, a magnetic layer
12
,
12
′, typically comprising a cobalt (Co)-base alloy, and a protective overcoat
13
,
13
′, typically containing carbon. Conventional practices also comprise bonding a lubricant topcoat (not shown) to the protective overcoat. Underlayer
11
,
11
′, magnetic layer
12
,
12
′, and protective overcoat
13
,
13
′, are typically deposited by sputtering techniques. The Co-base alloy magnetic layer deposited by conventional techniques normally comprises polycrystallites epitaxially grown on the polycrystal Cr or Cr-alloy underlayer. A conventional perpendicular recording disk medium is similar to the longitudinal recording medium depicted in
FIG. 1
, but does not comprise Cr-containing underlayers.
Conventional methods for manufacturing longitudinal magnetic recording medium comprise applying a seed layer between the substrate and underlayer. A seed layer seeds the nucleation of a particular crystallographic texture of the underlayer.
Longitudinal magnetic recording media with substrates having an Al, Al—Mg, glass or glass-ceramic support are commercially available from different manufacturers with a pre-coat layer of materials that influence the crystallographic orientation of subsequently deposited seed layer and/or underlayer and magnetic layers. Pre-coat on the support of the substrate also facilitates laser texturing and mechanical texturing process. Such conventional pre-coat layer materials include nickel-phosphorous (Ni—P) which is typically sputter deposited on the surface of the bare substrate.
Conventional longitudinal magnetic recording media comprising a substrate having NiP sputtered thereon also comprise, sequentially deposited thereon, a Cr or Cr-alloy seed layer and/or underlayer at an appropriate thickness, e.g., about 750 Å, a magnetic layer such as Co—Cr-platinum (Pt)-tantalum (Ta) at an appropriate thickness, e.g., 250 Å, and a protective carbon overcoat at an appropriate thickness, e.g., about 75 Å. Conventional Cr-alloy seed layer and/or underlayer comprise vanadium (V), titanium (Ti), tungsten (W) or molybdenum (Mo). Other conventional magnetic layers are CoCrTa, CoCrPtB, CoCrPt, CoCrPtTaNb and CoNiCr. The seed layer, underlayer, and magnetic layer are conventionally sequentially sputter deposited on the glass or glass-ceramic substrate in an inert gas environment, such as an environment of pure argon. A conventional carbon overcoat is typically deposited in argon with nitrogen, hydrogen or ethylene plasma. Conventional lubricant topcoats are typically about 20 Å thick. In short, in conventional recording media the thickness of all of the layers deposited on the substrate having a NiP pre-coat layer is typically more than 1000 Å. When the thickness of all the layers above the NiP pre-coat layer is about 1000 Å or more, migration of Ni to the top surface of the recording was not recognized to be a problem.
SUMMARY OF THE INVENTION
However it has been observed that Ni ion migration onto the top surface of the recording media becomes more severe as the total film thickness of the media decreases. Ni atoms can diffuse to the top of overcoat and form micro-crystal clusters, which make recording head more vulnerable and cause disk drive failure. Applicants found that Ni from the NiP layer leaches from the substrate to the top surface of the medium while also promoting leaching of Co from the magnetic layer to the top surface of the medium when the thickness of all layers on top of the NiP pre-coat layer is 1000 Å or less, particularly about 500 Å or less. Applicants also found that corrosion products on the top surface are picked up by a low-flying recording head of a high density medium causing smearing on the recording head and disc surface, resulting in increased stiction and eventual drive failure. Therefore, applicants recognized that there is a need to find sealing layers, which enhance magnetic recording performances, reduce Ni migration, and have good adhesion to the substrates. This invention provides a method to prevent Ni migration onto the top surface of the media during the manufacturing process and the life of the recording media.
The present invention is a magnetic recording medium comprising a substrate containing Ni that does not significantly migrate to the surface of the recording medium. In one embodiment, the substrate comprises a support and a Ni-containing pre-coat layer on the support.
Another advantage of the present invention is a method of manufacturing a magnetic recording medium comprising a substrate containing Ni tha

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