Eliminating gel particle-related defects for obtaining...

Details Eliminating gel particle-related defects for obtaining... Eliminating gel particle-related defects for obtaining...

2001-07-24

2003-06-03

Beck, Shrive P. (Department: 1762)

Coating processes

Centrifugal force utilized

C427S355000, C427S389700, C427S393600, C427S397700, C427S419200, C427S419700

Reexamination Certificate

active

06572922

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to methods for forming servo patterns in substrates for magnetic recording media utilized in high areal, 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 very hard surfaced, high modulus substrates such as 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.
It is considered desirable during reading and recording operations, and for obtainment of high areal recording densities, to maintain the transducer head(s) as close to the associated recording surface(s) as is possible, i.e., to minimize the “flying height” of the head(s). Thus 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 surface to be positioned in close proximity, with an attendant increase in predictability and consistent behavior of the air bearing supporting the head during motion.
Disk drives typically comprise a magnetic head assembly mounted on the end of a support or actuator arm which positions the head radially over the disk surface. If the actuator arm is held stationary, the magnetic head assembly will pass over a circular path on the disk surface known as a track, and information can be read from or written to that track. Each concentric track has a unique radius, and reading and writing information from or to a specific track requires the magnetic head to be located above the track. By moving the actuator arm, the magnetic head assembly is moved radially over the disk surface between tracks.
The disk drive must be able to differentiate between tracks on the disk and to center the magnetic head over any particular track. Most disk drives use embedded “servo patterns” of magnetically recorded information on the disk. The servo patterns are read by the magnetic head assembly to inform the disk drive of the track location. Tracks typically include both data sectors and servo patterns. Each data sector contains a header followed by a data section. The header may include synchronization information to synchronize various timers in the disk drive to the speed of disk rotation, while the data section is used for recording data. Typical servo patterns are described in, for example, U.S. Pat. No. 6,086,961, the disclosure of which is incorporated herein by reference.
Servo patterns are usually written on the disk during manufacture of the disk drive, after the drive is assembled and operational. The servo pattern information, and particularly the track spacing and centering information, needs to be located very precisely on the disk surface. However, at the time the servo patterns are written, there are no reference locations on the disk surface which can be perceived by the disk drive. Accordingly, a highly specialized device known as a “servo-writer” is used during writing of the servo-patterns. Largely because of the locational precision needed, servo-writers are expensive, and servo-writing is a time-consuming process.
One approach (i.e., “PERM” disks, manufactured by Sony Corp.) to avoid traditional servo-writing has been to injection mold or stamp servo patterns on a polymer-based substrate disk. A constant thickness layer of magnetic recording material is then applied over the entire disk surface, including the depressions and protrusions of the servo patterns. After all of the constituent layers of the medium have been applied to the disk, a magnetic bias is recorded on the servo patterns. For example, a first magnetic field may magnetically initialize the entire disk at a one setting. Then a second magnetic field, located at the surface of the disk and e.g., provided by the magnetic head of the disk drive, is used to magnetize the protruding portions of the servo patterns relative to the depressions. Because the protrusions are closer than the depressions to the magnetic initialization, the magnetization carried by the protrusions may be different than the magnetization carried by the depressions. When read, the resulting disk servo patterns show magnetic transitions between the depressions and the protrusions.
Meanwhile, the continuing trend toward manufacture of very high areal density magnetic recording media at reduced cost provides impetus for the development of lower cost materials, e.g., polymers, glass, ceramics, and glass-ceramics composites as replacements for the conventional Al alloy-based substrates for magnetic disk media. However, poor mechanical and tribological performance, track mis-registration (“TMR”), and poor flyability have been particula

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