Dynamic magnetic information storage or retrieval – Record medium – Disk
Reexamination Certificate
2000-01-14
2001-05-08
Heinz, A. J. (Department: 2652)
Dynamic magnetic information storage or retrieval
Record medium
Disk
Reexamination Certificate
active
06229670
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to texturing of magnetic data storage media, and more particularly to the texturing of dedicated transducing head contact zones of such media to minimize system resonance.
Laser texturing of magnetic disks, particularly over areas designed for contact with data transducing heads, is known to reduce friction and improve wear characteristics as compared to mechanically textured disks. Traditional laser texturing involves focusing a laser beam onto a disk substrate surface at multiple locations, forming at each location a depression surrounded by a raised rim as disclosed in U.S. Pat. No. 5,062,021 (Ranjan) and U.S. Pat. No. 5,108,781 (Ranjan). An alternative, as disclosed in International Publications No. WO 97/07931 and No. WO 97/43079, is to use a laser beam to form domes or nodules, rather than rims. In some cases, each of the domes is surrounded by a raised rim. The features can be axisymetric, i.e. with circular profiles, or can have non-axisymetric or elliptical profiles. In the latter case, the long axes of the texturing features preferably extend circumferentially relative to the disk.
Collectively, the texturing features are formed in a desired pattern or distribution throughout the head contact zone. A particularly preferred pattern is a spiral, formed by rotating the disk at a desired angular speed while at the same time moving a laser radially with respect to the disk. The laser is pulsed to form the individual texturing features. For example, the disk can be rotated at a speed, variable depending on the radial position of the laser, to provide a linear (arcuate) velocity of about one meter per second. Then, operating the laser at 50,000 pulses per second would provide a 20 micron circumferential pitch, i.e. distance between adjacent texturing features. The radial speed of the laser module controls the radial pitch or spacing between adjacent turns of the spiral, which also can be about 20 microns.
Although this approach has been highly successful in terms of reducing dynamic friction and improving the wear characteristics of dedicated transducing head contact zones, the regular, repeating pattern of the laser texture features produces strong input excitations based on the fundamental frequency of the circumferential pitch, including higher order harmonics. When the excitation frequencies coincide with natural frequencies of the slider or its gimbal and support system, resonance occurs which results in a high amplitude acoustic emission signal, which can increase the difficulty of determining the glide avalanche breaking point (a disk/transducing head spacing value), and yield a false indication that the disk has failed a glide test.
Apart from their contribution to resonance, the regularly spaced apart texturing features are thought to contribute to transducing head disturbances in two further respects. First, an intermittent contact of the peaks of texturing features with the data transducing head during disk accelerations and decelerations can disturb the head. Second, the texturing features contribute to turbulence in the air bearing that supports the transducing head slider during portions of accelerations and decelerations.
Therefore, it is an object of the present invention to provide a texturing feature adapted to impart a desired surface roughness to the dedicated transducing head contact zone of a recording medium while minimizing undesirable resonant frequency effects.
Another object is to provide a magnetic data storage medium in which a head contact zone has a topography that is directionally controlled, in that surface height gradients occur primarily in the direction perpendicular to the direction of transducing head travel relative to the disk.
A further object is to provide a process for laser texturing a data storage medium to form texturizing features that are elongate and highly uniform in the direction of storage media travel.
Yet another object is to provide magnetic data storage media that exhibit the highly favorable dynamic friction and wear characteristics of laser textured media, and further exhibit low resonance interactions with transducing heads during head take-offs and landings.
SUMMARY OF THE INVENTION
To achieve these and other objects, there is provided a magnetic data storage disk. The disk includes a substrate body formed of a non-magnetizable material and having a substantially planar surface including an annular contact region. The contact region is adapted for surface engagement with a magnetic data transducing head during accelerations and decelerations of the substrate in a circumferential direction with respect to the transducing head. A plurality of elongate ridge sections extend substantially circumferentially along the contact region. Each of the ridge sections has a circumferential length, a width in the radial direction, and an axial height above a nominal surface plane of the contact region. Each ridge section is substantially uniform in height over substantially its entire length. Each ridge section is convex in the direction away from the nominal surface plane. Adjacent ridge sections are spaced radially apart from one another by a radial pitch at least ten times the radial ridge section widths. The ridge sections have substantially the same height, and thus cooperate to determine a substantially uniform surface roughness throughout the contact zone.
There are several suitable arrangements of the ridge sections. In one highly preferred arrangement, the ridge sections are part of and cooperate to form a single, continuous spiral-line textured pattern. In this case, each complete turn or revolution of the spiral is conveniently considered as one of the ridge sections. The spiral pattern is favored, since it involves a single, continuous path that facilitates a complete laser texturing of the contact region in a matter of seconds. Disk rotation and radial travel are coordinated to maintain a substantially uniform radial pitch.
Alternatively, the ridge section can be formed as a series of concentric rings. In this case, the radial position of the laser module is kept constant during each revolution, and between revolutions is stepped by an amount that determines the radial pitch.
The profile of the ridge sections is preferably uniform, and is primarily a function of the impingement energy of the laser beam at the disk surface. Impingement energy, in turn, depends on a combination of factors including laser power, the degree of attenuation if any, and degree of focus of the laser beam, and the mode in which the laser is operated. For example, in the TEM
00
mode, the power distribution is Gaussian, concentrating more energy toward the center of the beam.
Preferably the ridge sections have a height in the range of 5-30 nm, more preferably in the range of 5-20 nm. The widths of the ridges are substantially greater than the height, typically at least one micron and more preferably at least two microns.
The substrate body typically is formed of aluminum, with a nickel phosphorous layer plated over the aluminum. Subsequent films or layers applied over the Ni—P layer include a non-magnetizable underlayer, a magnetizable thin film recording layer, and a protective carbon layer. Preferably the ridge sections are formed in the nickel phosphorous layer. Then, the underlayer, recording layer and cover layer, being of uniform thickness, replicate the substrate topography including the texturing throughout the contact zone. Alternatively, the ridge sections can be formed in either the underlayer or the thin film recording layer.
Further according to the invention, there is provided a process for surface texturing a magnetic data storage medium, including the following steps:
a. directing a coherent energy beam toward a magnetic data storage medium, to cause the coherent energy beam to impinge upon a selected surface of the storage medium at an impingement area thereon, wherein the selected surface has a nominal surface defines a nominal surface plane; and
b. translating the da
Kuo David S.
Sundaram Ramesh
Yao Wei H.
Heinz A. J.
Larkin Hoffman Daly & Lindgren Ltd.
Niebuhr, Esq. Frederick W.
Seagate Technology LLC
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