Abrasive tape for texturing magnetic recording media

Details Abrasive tape for texturing magnetic recording media Abrasive tape for texturing magnetic recording media

1998-03-26

2001-02-27

Eley, Timothy V. (Department: 3723)

Abrading

Machine

Reciprocating tool

C451S168000, C451S303000, C451S304000

Reexamination Certificate

active

06193590

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to generally to magnetic recording media, and more particularly to recording media having a landing zone with an independently optimized surface texture.
Magnetic recording disks generally comprise a disk substrate having a magnetic layer and a number of underlayers and overlayers deposited thereon. The nature and composition of each layer is selected to provide desired magnetic recording characteristics. An exemplary present day disk is illustrated in FIG.
1
and comprises a non-magnetic disk substrate
10
typically composed of an aluminum alloy. Alternative substrates comprise non-metallic materials such as glass, ceramics, glass ceramic composites, carbon, carbon ceramic composites, and the like. Generally, an amorphous nickel phosphorus (Ni—P) layer
12
is formed over each surface of disk substrate
10
, typically by plating. The Ni—P layer is hard, and imparts rigidity to aluminum alloy substrates. A chromium ground layer
14
is formed over the Ni—P layer
12
, typically by sputtering, and the magnetic layer
16
is formed over the ground layer
14
. The magnetic layer
16
comprises a thin film of a ferromagnetic material, typically including an alloy of cobalt. Usually, a protective layer
18
, such as a carbon film, is formed over the magnetic layer
16
, and a lubricating layer
20
is formed over the protective layer.
The presence of the Ni—P layer
12
and the chromium ground layer
14
has been found to improve the recording characteristics of the magnetic layer
16
. In particular, the chromium ground layer formed over an Ni—P layer has been found to provide enhanced coercivity and reduced noise characteristics. Such improvements are further enhanced when the Ni—P layer is treated by mechanical texturing to create a roughened surface prior to formation of the chromium ground layer. The texturing may be circumferential or crosswise, with the preferred geometry depending on the particular composition of the cobalt-containing magnetic layer.
Such magnetic recording disk structures have been very successful and allow for high recording densities. As with all successes, however, it is presently desired to provide magnetic recording disks having even higher recording densities. Recording densities can be improved by reducing the spacing between the recording transducer (read/write head) and the magnetic disk surface while the disk is rotating. In modern magnetic recording systems, the read/write head often glides over the recording surface on an “air bearing,” a layer of air which moves with the rotating disk. Thus, the spacing between the read/write head and recording surface, referred to as the “glide height,” depends in part on the surface topology of the disk.
Surface topology affects both the magnetic recording characteristics and durability of magnetic recording media. Surface topology is often measured by surface roughness (Ra), the arithmetic average of the absolute height and depth of peaks and valleys in a profiler scan. Recording densities generally benefit from low glide heights which are associated with smooth recording surfaces having a low surface roughness. As might be expected, magnetic recording media noise, as measured in terms of bit shift, increases as roughness increases. Furthermore, certification errors per data track, the number of individual bits which exhibit less than a threshold percentage of the nominal signal strength, also increase with increasing roughness. Thus, magnetic recording characteristics generally benefit from recording surfaces having a relatively low average surface roughness.
Unfortunately, the reliability of magnetic recording systems generally improves with increased recording surface roughness. Smooth surfaces do not build up the moving layer of air over the disk's surface required to “fly” the read/write head as quickly as rough surfaces. Frictional contact between the rotating disk and read/write head, called “stiction,” is particularly problematic during start up and stopping of the magnetic recording system, and has a profound impact on the durability of magnetic recording media.
For these reasons, it would be desirable to provide improved magnetic recording media having optimized surface topologies and methods for their fabrication. It would be particularly desirable if such recording media provided improved magnetic recording characteristics of low surface roughness without compromising the mechanical durability of magnetic recording systems. The methods should provide for texturing the substrate or layer structure of magnetic recording media without greatly increasing production costs and capital equipment requirements.
2. Description of the Background Art
U.S. Pat. No. 4,786,564 describes the texturing of a nickel phosphorus layer over an aluminum substrate to enable a read/write head to fly over the surface of the disk. U.S. Pat. No. 5,314,745 describes a magnetic recording media having a glass substrate with an optionally textured Ni—P layer.
SUMMARY OF THE INVENTION
Magnetic recording media according to the principles of the present invention comprise a read/write head interaction surface including a contact start stop zone having a relatively high surface roughness to improve durability, and data zone having a relatively low surface roughness as compared to the contact start stop zone to improve magnetic recording characteristics. As used herein, a “read/write head interaction surface” means the surface over which the head glides, lands, rests or slides during standard operation of a magnetic recording media system of the type utilizing an air bearing. The data storage of the present magnetic recording media is physically separated from the read/write head landing site, allowing the surface topology of the specialized zones to be individually optimized for either mechanical durability or data storage. Specifically, the relatively high surface roughness of the contact start stop zone exhibits excellent head glide height, stiction, and durability performance, while the relatively low surface roughness of the data zone promotes a low glide height to improve data density, minimize media noise as measured in bit shift errors, and reduce the incidence of certification errors, particularly at higher threshold percentages.
Optimization of the read/write head interface surface of magnetic recording media for both mechanical durability and high-density recording characteristics has been problematic, requiring compromises between competing criteria. In connection with the present invention, it has been discovered that friction between the read/write head and separately optimized contact start stop zone increases greatly when the contact start stop zone has a roughness (Ra) of less than 40 Å. Conversely, surface topologies having a roughness of over 55 Å suffer head crash at a higher rate than lower roughness surfaces. Mechanical durability is optimized where the contact start stop zone has an average surface roughness in the range between 45 Å and 55 Å. It has further been discovered that recording density can be increased by limiting the average surface roughness of the data zone to 35 Å or less. Glide height, certification errors, and media noise are optimized with a data zone surface topology having an average surface roughness in the range between 15 Å and 35 Å.
In another aspect, the present invention provides improved magnetic recording media of the type having a textured surface. Such textured surfaces are generally imposed on an underlayer or the substrate of the magnetic recording media, typically by abrading an Ni—P underlayer with an abrasive tape, a diamond slurry, or the like. The improvement comprises a contact start stop zone on the textured surface having a first surface texture, and a data zone on the textured surface having a second surface texture, in which the second texture has a lower average surface roughness than the first texture. A transition zone extends betwee

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