U.S. patent application number 13/033551 was filed with the patent office on 2011-06-16 for data zone lube removal.
This patent application is currently assigned to Seagate Technology LLC. Invention is credited to Jeffrey Shane Reiter.
Application Number | 20110143171 13/033551 |
Document ID | / |
Family ID | 41568931 |
Filed Date | 2011-06-16 |
United States Patent
Application |
20110143171 |
Kind Code |
A1 |
Reiter; Jeffrey Shane |
June 16, 2011 |
DATA ZONE LUBE REMOVAL
Abstract
In an embodiment, a magnetic disk comprising a substrate having
a non-data zone region and a data zone region and a lubrication
layer on the substrate, wherein a portion of the lubrication layer
on the non-data zone region has a greater thickness of higher
viscosity than a portion of the lubrication layer on the data zone
region.
Inventors: |
Reiter; Jeffrey Shane; (Palo
Alto, CA) |
Assignee: |
Seagate Technology LLC
Scotts Valley
CA
|
Family ID: |
41568931 |
Appl. No.: |
13/033551 |
Filed: |
February 23, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12179825 |
Jul 25, 2008 |
7914845 |
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13033551 |
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Current U.S.
Class: |
428/848.1 |
Current CPC
Class: |
G11B 5/8408
20130101 |
Class at
Publication: |
428/848.1 |
International
Class: |
G11B 5/73 20060101
G11B005/73 |
Claims
1. A magnetic disk comprising: a substrate surface having a
non-data zone region and a data zone region; and a lubrication
layer on the substrate, wherein at least a portion of the
lubrication layer on the non-data zone region has a greater
thickness and higher viscosity than at least a portion of the
lubrication layer on the data zone region.
2. The magnetic disk of claim 1, wherein said at least a portion of
the lubrication layer on the data zone region overlies the entirety
of the data zone region.
3. The magnetic disk of claim 1, wherein the viscosity of the
portion of the lubrication layer on the non-data zone region is
increased by polymerization.
4. The magnetic disk of claim 1, wherein viscosity of the
lubrication layer on the non-data zone region is increased by
exposure to radiation.
5. The magnetic disk of claim 1, wherein the lubrication layer is
on both sides of the substrate, and wherein both sides of the
substrate comprise the non-data zone region and the data zone
region.
6. The magnetic disk of claim 1, wherein a thickness of the
lubrication layer on the data zone region is made thinner with a
lubrication removal head.
7. The magnetic disk of claim 1, wherein a thickness of the
lubrication layer on the data zone region is made thinner with an
application of solvent.
8. The magnetic disk of claim 1, wherein the thickness of at least
a portion of the lubrication layer on the data zone region is made
thinner with a tape pickup.
9. The magnetic disk of claim 8, wherein the tape pickup is cleaned
while being used.
10. The magnetic disk of claim 1, wherein at least a portion of the
magnetic disk is burnished.
11. The magnetic disk of claim 10, wherein the portion of the
magnetic disk burnished comprises the data zone region.
12. The magnetic disk of claim 1, wherein the thickness of the
lubrication layer in the data zone region is less than 10
angstroms.
13. The magnetic disk of claim 1, wherein the magnetic disk has
substantially a same texturing over the entire surface of the
substrate.
14. The magnetic disk of claim 1, wherein a coefficient of friction
of the lubrication layer on the data zone region is less than half
of a coefficient of friction of the non-data zone region.
15. A magnetic disk comprising: a substrate surface having a
non-data zone region and a data zone region; a first layer of
lubrication of substantially equal thickness over the entire
substrate surface, wherein the first layer of lubrication is bonded
at least to the non-data zone region; and a second layer of
lubrication over at least a portion of the non-data zone region
that is less than the entire substrate surface, wherein the first
and second layers of lubrication over said at least a portion of
the non-data zone has a higher viscosity and greater thickness than
the first layer of lubrication in the data zone region.
16. The magnetic disk of claim 15, wherein at least a portion of
the first layer of lubrication is removed from the data zone region
after the first layer of lubrication is bonded to the said at least
a portion of the non-data zone region.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This is a Divisional application which claims the benefit of
pending U.S. patent application Ser. No. 12/179,825, entitled "Head
Media Spacing Reduction through Data Zone Lube Removal," filed on
Jul. 25, 2008, which is expressly incorporated by reference herein
in its entirety.
BACKGROUND
[0002] The present invention relates to a manufacturing method of
improving the signal-to-medium noise ratio of a magnetic media disk
through closer head-to-media spacing, and the resulting disk, by
evenly lubricating a magnetic media disk, increasing the viscosity
of a selected region of the disk, and removing at least a portion
of the lower viscosity region of the lubrication layer, thereby
decreasing the thickness of the lubrication layer in the portion of
the lower viscosity region, producing a magnetic media disk capable
of closer head-to-media spacing in the portion of the lower
viscosity region of the lubrication layer.
SUMMARY
[0003] The present invention is a method and apparatus for
manufacturing of sputtered magnetic media disks, in which the
lubricant layer overlying the data zones is thinner than the
lubricant layer overlying at least a portion of the non-data zones
of the disk. This permits reduced head-to-media spacing, thereby
allowing better recording and read-back performance while
mitigating the degradation in durability from an increased
probability of head-to-media contact or pickup of lubrication by
the head.
[0004] Additional advantages of this invention will become readily
apparent to those skilled in this art from the following detailed
description, wherein only the preferred embodiments of this
invention is shown and described, simply by way of illustration of
the best mode contemplated for carrying out this invention. As will
be realized, this invention a property of other and different
embodiments, and its details are capable of modifications in
various obvious respects, all without departing from this
invention. Accordingly, the drawings and description are to be
regarded as illustrative in nature and not as restrictive.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a view of a magnetic disk drive.
[0006] FIG. 2 is a schematic representation of the film structure
in accordance with a magnetic recording medium of the prior
art.
[0007] FIG. 3 is perspective view of a magnetic head and a magnetic
disk.
[0008] FIGS. 4A-4B are block diagrams of the method used to create
a thinner lube layer over the data zone, compared to the lube layer
outside the data zone.
DETAILED DESCRIPTION
[0009] This disclosure relates to perpendicular recording media,
such as thin film magnetic recording disks using perpendicular
recording, having improved reading and recording performance.
Embodiments described herein also relate to a method of
manufacturing the media. Embodiments of the disclosure have
particular applicability to high areal density magnetic recording
media exhibiting low noise.
[0010] Magnetic discs with magnetizable media are used for data
storage in most all computer systems. FIG. 1 shows a disk recording
medium and a cross section of a disc showing the difference between
longitudinal and perpendicular recording. Even though FIG. 1 shows
one side of the non-magnetic disk, magnetic recording layers are
sputter deposited on both sides of the non-magnetic aluminum
substrate. Also, even though FIG. 1 shows an aluminum substrate,
other embodiments include a substrate made of glass, glass-ceramic,
NiP/aluminum, metal alloys, plastic/polymer material, ceramic,
glass-polymer, composite materials or other non-magnetic
materials.
[0011] Current magnetic hard disc drives operate with the
read-write heads only a few nanometers above the disc surface and
at rather high speeds, typically a few meters per second. Because
the read-write heads can contact the disc surface during operation,
a layer of lubricant is coated on the disc surface to reduce wear
and friction. The lubricant film on hard discs provides protection
to the underlying magnetic alloy by preventing wear of the carbon
overcoat. In addition, it works in combination with the overcoat to
provide protection against corrosion of the underlying magnetic
alloy. The reliability of hard disks depends on the durability of
the thin film media. As the spacing between head disk is being
reduced aggressively to improve area storage density, media are
facing many severe technical obstacles, such as weak durability,
heavy lubricant pickup by the read-write head, unmanageable
stiction/friction, etc. Lubrication plays unquestionably an
important role in overcoming these technical difficulties. Previous
efforts have attempted selective lube thinning using solvents, but
lube migration then becomes more prominent.
[0012] The mathematical and physical basis of reading from and
writing to perpendicular magnetic recording media is known in the
scientific literature, for instance H. J. Richter, The Transition
from Longitudinal to Perpendicular Recording, JOURNAL OF PHYSICS D:
APPLIED PHYSICS, 19 Apr. 2007 (doi:10.1088/0022-3727/40/9/R01), the
entire contents of which are hereby incorporated by reference. The
increasing demands for higher areal recording density impose
increasingly greater demands on thin film magnetic recording media
in terms of remanent coercivity (Hr), magnetic remanance (Mr),
coercivity squareness (S*), medium noise, i.e., signal-to-medium
noise ratio (SMNR), and narrow track recording performance. It is
extremely difficult to produce a magnetic recording medium
satisfying such demanding requirements. One way of improving the
SMNR performance is by reducing the head-to-media spacing (HMS).
Therefore, there exists a need to reduce the HMS, while mitigating
the probability that the head would come in contact with the
lubrication, and further while providing greater head protection
when HMS need not be reduced.
[0013] In operation, a typical contact start/stop (CSS) method
involves a floating transducer head gliding at a predetermined
distance from the surface of the disk due to dynamic pressure
effects caused by air flow generated between the sliding surfaces
of the transducer head and the disk. During reading and recording
(writing) 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 transducer head
can be freely moved in both the circumferential and radially
directions allowing data to be recorded on and retrieved from the
surface of the disk at a desired position in a data zone.
[0014] To record information on the disc, the transducer creates a
highly concentrated magnetic field in close proximity to the
magnetic recording medium. During writing, the strength of the
concentrated magnetic field directly under the write transducer is
greater than the coercivity of the recording medium (known as
"saturating" the medium), and grains of the recording medium at
that location are magnetized with a direction which matches the
direction of the applied magnetic field. The grains of the
recording medium retain their magnetization after the saturating
magnetic field is removed. As the disc rotates, the direction of
the writing magnetic field is alternated based on bits of the
information being stored, thereby recording a magnetic pattern on
the track directly under the write transducer.
[0015] A cross sectional view of a conventional longitudinal
recording disk medium is depicted in FIG. 2. A longitudinal
recording medium typically comprises a non-magnetic substrate 20
having sequentially deposited on each side thereof an underlayer
21, 21', such as chromium (Cr) or Cr-alloy, a magnetic layer 22,
22', typically comprising a cobalt (Co)-base alloy, and a
protective overcoat 23, 23', typically containing carbon.
Conventional practices also comprise bonding a lubricant topcoat
(not shown) to the protective overcoat. Underlayer 21, 21',
magnetic layer 22, 22', and protective overcoat 23, 23', are
typically deposited by sputtering techniques. The Co-base alloy
magnetic layer deposited by conventional techniques normally
comprises polycrystallites epitaxially grown on the polycrystal Cr
or Cr-alloy underlayer. Conventional lubricant topcoats are
typically about 20 A thick. Almost all the manufacturing of a disk
media takes place in clean rooms where the amount of dust in the
atmosphere is kept very low, and is strictly controlled and
monitored.
[0016] For optimum consistency and predictability, it is necessary
to maintain each transducer head as close to its associated
recording surface as possible, i.e., to minimize the flying height
of the head. Accordingly, a smooth recording surface is preferred,
as well as a smooth opposing surface of the associated transducer
head. Furthermore, the continuing requirements for increased
recording density and faster data transfer rates necessitates
minimizing the spacing between the transducing head and the
magnetic media layer, i.e., a reduced head-to-media spacing (HMS).
However, if the head surface and the 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." As the HMS is
reduced, there is a greater probability that the head will make
contact with the lubrication. As the HMS in hard disk drives is
reduced below 5 nm, there is a need to ensure that the lubricant
layer over the data portions of the disk is less than 5 nm in
thickness. Lubricant menisci form at the contact points when the
head touches the disk. These lubricant menisci can have large
capillary forces, resulting in a large friction force when a head
contacts a disk. Such contact will result in poor durability due to
frequent contact, and from accumulation of lubrication on the head.
Thus, there are competing goals of reduced head/disk friction and
minimum transducer flying height.
[0017] According to conventional practices, a lubricant topcoat is
uniformly applied over the protective overcoat layer to prevent
wear between the disk and the facing surface of the read/write
transducer head during CSS operation. However, an excess amount of
lubricant at the head-disk interface causes high stiction between
the head and the disk, which stiction, if excessive, prevents
starting of disk rotation, hence causing catastrophic failure of
the disk drive. Accordingly, the lubricant thickness must be
optimized for stiction and friction.
[0018] Reducing HMS and minimizing friction/stiction of the
head-disk interface have served as an impetus for the development
of specialized lubricants for serving as the lubricant topcoat
layer overlying the protective overcoat layer. Such lubricants are
required to fulfill a variety of functions requiring diverse
characteristics and attributes. For example, the lubricant material
forming the topcoat layer must be chemically inert, have a low
vapor pressure, low surface tension, high thermal stability,
mechanical stability under shear stress, and good boundary
lubrication properties. In addition to the foregoing, it is
critical that the lubricant adhere tightly (as, for example,
reflected in the "bonded lube thickness" or "bonded lube ratio") to
the underlying surface, i.e., the protective overcoat layer
(typically carbon-based), over the lifetime of the disk drive
comprising the recording disk and associated flying head data
transducer. Free lube is that portion of the lube which is not
bonded to the protective overcoat layer of the magnetic disk.
[0019] Fluoropolyether (FPE) lubricants are of particular interest
in lubricating magnetic recording media. These lubricants are
uniquely suited to form lubricant topcoats on magnetic media
because of such properties as chemical inertness, low vapor
pressure, low surface tension, high thermal stability, stability
under high shear stress and good boundary lubrication properties.
Among the many lubricants available, liquid perfluoropolyethers
(PFPE) are the most typically used in forming topcoat lubricants on
magnetic recording media.
[0020] Liquid lubrication of the disk surface encounters several
problems, however, which limit its effectiveness as used in
rotating storage media. For example, it is well known that free
lube will migrate and spin off a thin film disk with a carbon
overcoat. Typically, PFPE lubricants do not have a retention means
so that when the disk rotates, the lubricant tends to spins off the
disk. The depletion of the lubricant from the disk surface
increases the friction between the disk and the read/write
head.
[0021] Further, the depletion of the lubricant results in
non-uniformity across the surface of the disk resulting in
additional operational difficulties. For example, where the
thickness is too thin, the head can cause wear on the disk surface
and where the lubricant thickness is too great, the head will
become stuck in the lubricant (from static friction) and the head
or disk could be damaged when the head suddenly becomes unstuck due
to the rotating disk.
[0022] Head contact with the data portion of the media is to be
avoided during normal operation. However, when the disk is not in
normal operation, for instance when it is being turned off, the
head is designed to move to an area of the disk known as the
landing zone. At the landing zone, the media incorporates design
features that permit the head to contact the media, and these
design features may optionally include usage of a thicker
lubrication layer as compared to the data zone.
[0023] Reducing the lube layer thickness over the data zone of a
magnetic recording disk as compared to the landing zone of the
magnetic recording disk, permits a smaller HMS spacing in the data
zone. Removing free lube from the data zone while the disk is being
manufactured will significantly reduce the probability of lube
pickup by the head, and lube puddling in the drive as well as lube
ripples during operation.
[0024] At least some areas outside the data zone, for instance the
landing zone of the magnetic media, will not undergo lube thinning
and therefore after processing will have a relatively thicker layer
of lube compared the lube layer overlying the data zone. It is not
critical to minimize the head-to-media spacing in non-data zone
areas to the same extent that it is in the data zone, because the
disk does not have the same stringent performance requirements on
reading and writing data in the non-data zone areas as compared to
the data zone areas. For instance, a greater HMS is allowable in
the landing zone or servo track zone (if one is present) at either
the inner or outer periphery of the magnetic media disk, thereby
permitting a thicker layer of lube compared to the lube thickness
in the data zone. The greater HMS and potentially greater lube
thickness in non-data areas will allow for decreased risk of
damaging contact between the head and the disk in those areas.
Contact between the head and the thicker lube layer over the
landing zone is permitted when the magnetic disk is not rotating,
and when the disk accelerates or decelerates to or from the
operational rotation speed.
[0025] In an aspect of the disclosure, an embodiment of a method is
described for achieving a thinner layer of lube in the data zone of
the magnetic disk, as compared to the lube thickness in the
non-data portions of the disk, while mitigating the problem of lube
migration. One method of decreasing the ability of the lube to
migrate is to increase the viscosity of the free lube over non-data
portions of the disk. This method does not require texturing of the
disk surface or any other structure to assist in retaining
lubrication. Once the lube over selected portions of the disk is
made more viscous, free lube may be removed from areas of the disk
having less viscous lube, thereby resulting in a thinner lube
thickness. In a preferred embodiment, the more viscous lube will
overlie the non-data portions of the disk, and the less viscous
lube will overlie the data portion. The region comprising the data
portions of the disk having the less viscous lube may have a
coefficient of friction that is approximately less than half of the
coefficient of friction of the region comprising the non-data
portions of the disk having more viscous lube.
[0026] In an embodiment of the method to increase the lubrication
viscosity, a PFPE capable of cross-linking is applied to the
magnetic recording medium having a distribution of non-data zones
therein and polymerized to form a cross-linked PFPE topcoat
lubricant. The PFPE may comprise homopolymers, random polymers or
block polymers, i.e. the repeating units of the PFPE can be the
same or different. In addition, different repeat units may be
randomly distributed along the backbone of the polymer or
distributed as a block of one type of repeat unit and subsequent
blocks of different repeat units along the backbone of the polymer.
The lubricants may be completely fluorinated or partially
fluorinated and may be linear or branched.
[0027] The lubricant topcoat is then made more viscous by
cross-linking at least that portion of the lubricant overlying the
non-data portions of the disk. Any convenient source of radiation
can be used, e.g. a UV laser, to effect polymerization or
cross-linking of the applied PFPE on the magnetic disk. The
magnetic disk having polymerizable or cross-linkable PFPE thereon
may be exposed to UV radiation from a low pressure mercury lamp UV
lamp which emits radiation over the range of about 254 nm to about
185 nm. The coated disc may be exposed to UV radiation having an
intensity of about several to about 100 or more milliwatts/cm.sup.2
for an exposure duration of approximately 10 seconds to about 4
minutes or more to form a cross-linked PFPE lubricant topcoat.
[0028] The cross-linked topcoat advantageously forms a relatively
immobile coating that serves to prevent migration of any
lubrication so cross-linked. Lubrication over at least the data
portion of the recording disk may then be thinned without causing
migration of the cross-linked lube from the non-data portions of
the disk into the data portion of the disk.
[0029] Lube thinning over the data zone may be achieved using a
pickup head designed for lube pickup, or may be achieved using a
tape-based extractor that provides an adjustable amount of
pressure, friction, and duration between the disk having the lube
to be thinned and the extractor. This may be achieved with or
without the use of a solvent to help remove the free lube from the
surface of the data portion of the disk. When used, a predetermined
amount of solvent is introduced to the data zone area, such that it
dissolves a portion of the lube layer overlying the data layer. The
solvent is then removed. A similar technique is known in the prior
art, for instance as described in U.S. Pat. No. 6,168,831.
Optionally, a tape-cleaning device may be used during the cleaning
process to remove from the tape any material the tape has removed
from the disk.
[0030] After lube thinning, the disk may be further processed, for
instance by buffing the areas in which lubrication had been
removed.
[0031] The above description is presented to enable a person
skilled in the art to make and use the invention, and is provided
in the context of a particular application and its requirements.
Various modifications to the preferred embodiments will be readily
apparent to those skilled in the art, and the generic principles
defined herein may be applied to other embodiments and applications
without departing from the spirit and scope of the invention. For
example, applying lubrication may be applied to the magnetic media
disk, thereby forming a first lubrication layer, where the first
lubrication layer being of substantially equal thickness over the
entire surface. A portion of the first lubrication layer, such as
the region including the non-data zone, may be bonded to the
magnetic media disk, making the first lubrication layer more
viscous. The bonding method may be, for example, the use of
radiation, as described above. A second layer of lubrication may be
applied over the non-data zone portion of the disk, i.e., over less
than the entire disk. The viscosity of the second lubrication layer
over the non-data zone portion of the disk may be increased,
thereby producing a higher viscosity region of greater thickness
than the region without the second lubrication layer. This results
in the magnetic media disk being capable of improved disk-head
contact protection in the higher viscosity region of greater
thickness. A portion of the first lubrication layer over the data
zone portion of the disk may be thinned by removal. Thus, this
invention is not intended to be limited to the embodiments shown,
but is to be accorded the widest scope consistent with the
principles and features disclosed herein.
[0032] This application may disclose several numerical range
limitations. Persons skilled in the art would recognize that the
numerical ranges disclosed inherently support any range within the
disclosed numerical ranges even though a precise range limitation
is not stated verbatim in the specification because this invention
can be practiced throughout the disclosed numerical ranges. A
holding to the contrary would "let form triumph over substance" and
allow the written description requirement to eviscerate claims that
might be narrowed during prosecution simply because the applicants
broadly disclose in this application but then might narrow their
claims during prosecution. Where the term "plurality" is used, that
term shall be construed to include the quantity of one, unless
otherwise stated. The entire disclosure of the patents and
publications referred in this application are hereby incorporated
herein by reference. Finally, the implementations described above
and other implementations are within the scope of the following
claims.
* * * * *