Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2001-02-21
2002-10-29
Resan, Stevan A. (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S336000, C428S611000, C428S673000, C428S674000, C428S668000, C428S690000, C204S192150, C204S192200, C427S131000, C427S132000
Reexamination Certificate
active
06472049
ABSTRACT:
TECHNICAL FIELD
The present invention relates to the recording, storage and reading of magnetic data, particularly rotatable magnetic recording media, such as thin film magnetic disks having textured surfaces or contact with cooperating magnetic transducing heads. The invention has particular applicability to high density magnetic recording media exhibiting low noise, reduced flying heights and high coercivity.
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. It is extremely difficult to produce a magnetic recording medium for ultra-high density recording having suitable magnetic properties, such as high coercivity, e.g., greater than 2500 Oersteads, and a high overwrite, e.g., about 40 dB, while at the same time exhibiting suitable mechanical properties for read-write performance, such as a small glide height avalanche, e.g., about 0.75 to about 0.85 &mgr;m.
In operation, the magnetic disk is normally driven by the contact start stop (CSS) method, wherein the 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 due to dynamic pressure effects caused by the air flow generated between the sliding surface of the head and the disk. During reading and recording operations, the transducing head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates. The magnetic head unit is arranged such that the head can be freely moved in both the circumferential and radial directions of the disk in this floating state allowing data to be recorded on and retrieved from the surface of the disk at a desired position.
Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head begins to slide against the surface of the disk again and eventually stops in contact with and pressing against the disk. Thus, the transducing head contacts the recording surface whenever the disk is stationary, accelerated from a stop and during deceleration just prior to completely stopping. 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.
It is considered desirable during reading and recording operations to maintain each transducing 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. Thus, a smooth recording surface is preferred, as well as a smooth opposing surface of the associated transducing 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. However, another factor operates against that objective. If the head surface and 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.
In order to satisfy these competing objectives, the recording surfaces of magnetic disks are conventionally provided with a roughened surface to reduce the head/disk friction by techniques referred to as “texturing.” Conventional texturing techniques involve polishing the surface of a disk substrate to provide a texture thereon prior to subsequent deposition of coatings, such as an underlayer, magnetic layer, carbon overcoat and lubricant topcoat, wherein the textured surface on the substrate is reproduced on the surface of the magnetic disk.
A typical magnetic recording medium is depicted in FIG.
1
and comprises a substrate
10
, typically an aluminum (Al)-base alloy, such as an aluminum-magnesium (Al—Mg) alloy, chemically plated with a layer of amorphous nickel-phosphorous (NiP). Substrate
10
typically contains sequentially deposited thereon a chromium (Cr) underlayer
11
, a cobalt (Co)-base alloy magnetic layer
12
, a protective carbon overcoat
13
and a lubricant topcoat
14
. Cr underlayer
11
, Co-base alloy magnetic layer
12
and protective carbon overcoat
13
are typically deposited by sputtering techniques. Conventional Al-alloy substrates are provided with a NiP chemical plating, typically at a thickness greater than about 10,000 Å, primarily to increase the hardness of the Al substrate, serving as a suitable surface for polishing to provide the requisite surface roughness or texture, which is substantially reproduced on the disk surface.
In addition, increasingly high density and large-capacity magnetic disks require increasingly small flying heights, i.e., the distance by which the head floats above the surface of the disk in the CSS drive. The requirement to further reduce the flying height of the head imposed by increasingly higher recording density and capacity render it particularly difficult to satisfy the requirements for controlled texturing to avoid head crash.
Conventional techniques for providing a disk substrate with a textured surface comprise a mechanical operation, such as polishing. See, for example, Nakamura et al., U.S. Pat. No. 5,202,810. Conventional mechanical texturing techniques are attendant with numerous disadvantages. For example, it is extremely difficult to provide a clean textured surface due to debris formed by mechanical abrasions. Moreover, the surface inevitably becomes scratched during mechanical operations, which contributes to poor glide characteristics and higher defects. In addition, various desirable substrates are difficult to process by mechanical texturing. This undesirably limiting facet of mechanical texturing, virtually excludes the use of many inexpensive substrates as well as conductive graphite substrates which facilitate achieving high coercivities.
Alternative texturing techniques to mechanical processing have been attempted. One such alternative to mechanical texturing involves the use of lasers. See, for example, Ranjan et al., U.S. Pat. No. 5,062,021. Another alternative to mechanical texturing is disclosed by Lal et al., U.S. Pat. No. 5,166,006, and involves chemical etching. Such alternative techniques have proven less than successful, in that it is extremely difficult to provide repeatable and controllable textured patterns on non-metallic substrates, such as glass, glass-ceramic materials and electrically conductive graphites. In addition, laser textured substrates also require cleaning.
In copending U.S. patent application Ser. No. 08/608,072 filed on Feb. 28, 1995 now U.S. Pat. No. 5,718,811, issued Feb. 17, 1998, a magnetic recording medium is disclosed which has a textured surface formed by sputtering a metallic layer, such as titanium or a titanium alloy, on a non-magnetic substrate, inclusive of a glass, glass-ceramics materials and NiP chemically plated Ni—Mg alloy substrates. It has, however, been found difficult to produce a magnetic recording medium having a suitably high coercivity greater than 2500 Oersteads, such as gr
Chen Ga-Lane
Chen Qixu
Leu Charles
Song Xing
Resan Stevan A.
Seagate Technology LLC
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