Coating processes – Magnetic base or coating – Magnetic coating
Reexamination Certificate
2001-09-17
2003-09-30
Pianalto, Bernard (Department: 1762)
Coating processes
Magnetic base or coating
Magnetic coating
C427S128000, C427S131000, C427S270000, C427S275000, C427S287000, C427S327000
Reexamination Certificate
active
06627254
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to methods and apparatus for forming patterned landing zones, as well as servo patterns, in substrates for magnetic recording media utilized in high areal and high track density applications, and to magnetic recording media produced thereby. The invention has particular utility in the manufacture of magnetic data/information storage and retrieval media, e.g., hard disks, utilizing conventional metal-based substrate materials, e.g., of Al or an Al alloy, as well as very hard surfaced, high modulus substrates, e.g., of glass, ceramic, and glass-ceramic materials.
BACKGROUND OF THE INVENTION
Magnetic recording media are widely used in various applications, particularly in the computer industry. A portion of a conventional recording medium
1
utilized in disk form in computer-related applications is schematically depicted in FIG.
1
and comprises a non-magnetic substrate
10
, typically of metal, e.g., an aluminum-magnesium (Al—Mg) alloy, having sequentially deposited thereon a plating layer
11
, such as of amorphous nickel-phosphorus (NiP), a polycrystalline underlayer
12
, typically of chromium (Cr) or a Cr-based alloy, a magnetic layer
13
, e.g., of a cobalt (Co)-based alloy, a protective overcoat layer
14
, typically containing carbon (C), e.g., diamond-like carbon (“DLC”), and a lubricant topcoat layer
15
, typically of a perfluoropolyether compound applied by dipping, spraying, etc.
In operation of medium
1
, the magnetic layer
13
can be locally magnetized by a write transducer or write head, to record and store data/information. The write transducer creates a highly concentrated magnetic field which alternates direction based on the bits of information being stored. When the local magnetic field produced by the write transducer is greater than the coercivity of the recording medium layer
13
, then the grains of the polycrystalline medium at that location are magnetized. The grains retain their magnetization after the magnetic field produced by the write transducer is removed. The direction of the magnetization matches the direction of the applied magnetic field. The pattern of magnetization of the recording medium can subsequently produce an electrical response in a read transducer, allowing the stored medium to be read.
Thin film magnetic recording media are conventionally employed in disk form for use with disk drives for storing large amounts of data in magnetizable form. Typically, one or more disks are rotated on a central axis in combination with data transducer heads. In operation, a typical contact start/stop (“CSS”) method commences when 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 transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the head can be freely moved in both the circumferential and radial directions, allowing data to be recorded on and retrieved from the disk at a desired position. Upon terminating operation of the disk drive, the rotational speed of the disk decreases and the head again begins to slide against the surface of the disk and eventually stops in contact with and pressing against the disk. Thus, the transducer head contacts the recording surface whenever the disk is stationary, accelerated from the static position, 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 sequence consisting of stopping, sliding against the surface of the disk, floating in air, sliding against the surface of the disk, and stopping.
The air bearing design for the head slider/transducer utilized for CSS-type operation as described above provides an interface between the slider and the disk which prevents damage to the disk over the life of the disk/slider/transducer head system, and provides damping in the event the disk drive system undergoes mechanical shock due to vibrations of external origin. The air bearing also provides the desired spacing between the transducer and the disk surface. A bias force is applied to the slider by a flexure armature in a direction toward the disk surface. This bias force is counter-acted by lifting forces from the air bearing until an equilibrium state is achieved. The slider will contact the disk surface if the rotating speed of the disk is insufficient to cause the slider to “fly”, as during start-up and shut-down phases of the CSS cycle. If the slider contacts a data region of the disk, the data may be lost and the disk permanently damaged.
Referring now to
FIG. 2
, shown therein in perspective view, is a conventionally configured magnetic hard disk
30
having a CSS (i.e., “landing”) zone
36
and a data (i.e., recording) zone
40
. More specifically,
FIG. 2
illustrates an annularly-shaped magnetic hard disk
30
including an inner diameter
32
and an outer diameter
34
. Adjacent to the inner diameter is an annularly-shaped, inner CSS or “landing” zone
36
(however, the landing zone
36
may, in other instances, be located adjacent the outer diameter
34
). When disk
30
is operated in conjunction with a magnetic transducer head (not shown in the drawing), the CSS or “landing” zone
36
is the region where the head makes contact with the disk surface during the above-described start-stop cycles or other intermittent occurrences. In
FIG. 2
, the radially outer edge of the CSS or “landing” zone
36
is indicated by line
38
, which is the boundary between CSS zone
36
and data zone
40
where information in magnetic form is stored within the magnetic recording medium layer of disk
30
.
It is generally considered desirable for reliably and predictably performing reading and recording operations, and essential for obtaining high areal density magnetic recording, that the transducer head be maintained as close to the disk surface as possible in order to minimize its flying height. Thus, a smooth disk surface is preferred, as well as a smooth opposing surface of the transducer head, thereby permitting the head and the disk to be positioned in very close proximity, with an attendant increase in predictability and consistent behavior of the air bearing supporting the transducer head during motion. However, if the head surface and the recording surface are too flat, the precision match of these surfaces gives rise to friction and “stiction” at the disk surface which causes the transducer head to adhere to the surface, particularly after periods of non-use, thereby making it more difficult for the transducer head to initiate movement therefrom. Excessive stiction and friction during the start-up and stopping phases of the above-described cyclic sequence causes wear of the transducer and disk surfaces, eventually leading to what is referred to as “head crash”. Another drawback associated with smooth disk surfaces is lack of durability resulting from the very small amount of lubricant which is retained thereon. Thus, there are competing goals of minimizing transducer head flying height (as by the use of smooth surfaces) and reducing transducer head/disk friction (as by avoiding use of smooth surfaces).
Conventional practices for addressing these apparent competing objectives include providing at least the CSS or “landing” zone of the magnetic disk recording medium with a roughened surface to reduce transducer head/disk friction and stiction by a number of different techniques generally known as “texturing”. Referring again to
FIG. 1
, current texturing techniques (see, e.g., U.S. Pat. Nos. 5,062,021 and 5,108,781) include, inter alia, circumferential polishing and localized laser heating of the surface of the disk substrate
10
(e.g., of A
Angelo James Edward
Ellis Timothy Francis
Fayeulle Serge Jacques
Kuo David
Rao Mukund Channagiri
Pianalto Bernard
Seagate Technology LLC
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