U.S. patent application number 11/030299 was filed with the patent office on 2005-07-28 for highly oriented longitudinal magnetic media on direct textured glass substrates.
This patent application is currently assigned to SEAGATE TECHNOLOGY LLC. Invention is credited to Ata, Romulo, Chour, Kueir-Weei, Rou, Shanghsien (Alex), Wang, John.
Application Number | 20050164038 11/030299 |
Document ID | / |
Family ID | 34116805 |
Filed Date | 2005-07-28 |
United States Patent
Application |
20050164038 |
Kind Code |
A1 |
Rou, Shanghsien (Alex) ; et
al. |
July 28, 2005 |
Highly oriented longitudinal magnetic media on direct textured
glass substrates
Abstract
Oriented longitudinal magnetic recording media on direct texture
glass or glass-ceramic substrates with a film structure of one or
more Ni-containing layer, a Cr-containing underlayer, a
Co-containing magnetic layer and carbon overcoat exhibits are
capable of achieving Mrt OR of >1.5, preferably >1.85. Such
highly oriented glass media shows a significant SNR (>2 dB) and
parametric improvement over the counterpart isotropic media with
the same film structure on non-textured glass or glass-ceramic
substrates.
Inventors: |
Rou, Shanghsien (Alex);
(Fremont, CA) ; Wang, John; (Fremont, CA) ;
Ata, Romulo; (San Jose, CA) ; Chour, Kueir-Weei;
(San Jose, CA) |
Correspondence
Address: |
MORRISON & FOERSTER LLP
1650 TYSONS BOULEVARD
SUITE 300
MCLEAN
VA
22102
US
|
Assignee: |
SEAGATE TECHNOLOGY LLC
Scotts Valley
CA
|
Family ID: |
34116805 |
Appl. No.: |
11/030299 |
Filed: |
January 7, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11030299 |
Jan 7, 2005 |
|
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10662427 |
Sep 16, 2003 |
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6855439 |
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Current U.S.
Class: |
428/835.5 ;
427/128; G9B/5.288 |
Current CPC
Class: |
G11B 5/737 20190501;
G11B 5/7379 20190501; Y10S 428/90 20130101; G11B 5/73921 20190501;
G11B 5/7369 20190501; Y10T 428/265 20150115 |
Class at
Publication: |
428/694.0TR ;
427/128 |
International
Class: |
B05D 005/12; G11B
005/64 |
Claims
1-20. (canceled)
21. A method for manufacturing a magnetic recording medium
comprising introducing a direct texture glass or glass-ceramic
substrate into a sputtering chamber and forming a film structure on
the direct texture glass or glass-ceramic substrate without removal
of the glass or glass-ceramic substrate from the sputtering
chamber.
22. The method of claim 21, wherein the medium is an oriented
longitudinal magnetic recording medium having Mrt OR of 1.5 or
more.
23. The method of claim 21, wherein the medium has SNR of greater
than 2 dB over an isotropic medium with a defined film structure
directly on a non-textured glass or glass-ceramic substrate, the
defined film structure being identical to the film structure
directly on the direct texture glass or glass-ceramic
substrate.
24. The method of claim 21, wherein the film structure comprises an
oxidized NiP layer.
25. The method of claim 24, wherein the oxidized NiP layer has a
texture resulting substantially from a texture of the texture glass
or glass-ceramic substrate and the texture of the oxidized NiP is
not a mechanical texture.
26. The method of claim 24, wherein the oxidized NiP layer if
formed under a partial pressure of oxygen of between about 2 mT to
20 mT in the sputtering chamber.
27. The method of claim 24, wherein the oxidized NiP layer is
deposited at about ambient temperature.
28. The method of claim 24, wherein the film structure further
comprises a Cr-containing underlayer on the oxidized NiP layer.
29. The method of claim 28, wherein the Cr-containing underlayer is
deposited at a temperature of about 120.degree. C. to 250.degree.
C.
Description
FIELD OF INVENTION
[0001] The present invention relates to the recording, storage and
reading of magnetic data, particularly magnetic recording media on
textured glass substrates.
BACKGROUND
[0002] Magnetic disks and disk drives are conventionally employed
for storing data in magnetizable form. Preferably, one or more
disks are rotated on a central axis in combination with data
transducing heads positioned in close proximity to the recording
surfaces of the disks and moved generally radially with respect
thereto. Magnetic disks are usually housed in a magnetic disk unit
in a stationary state with a magnetic head having a specific load
elastically in contact with and pressed against the surface of the
disk. Data are written onto and read from a rapidly rotating
recording disk by means of a magnetic head transducer assembly that
flies closely over the surface of the disk. Preferably, each face
of each disk will have its own independent head.
[0003] Disc drives at their most basic level work on the same
mechanical principles as media such as compact discs or even
records, however, magnetic disc drives can write and read
information much more quickly than compact discs (or records for
that matter!). The specific data is placed on a rotating platter
and information is then read or written via a head that moves
across the platter as it spins. Records do this in an analog
fashion where the disc's grooves pick up various vibrations that
then translate to audio signals, and compact discs use a laser to
pick up and write information optically.
[0004] In a magnetic disc drive, however, digital information
(expressed as combinations of "0's" and "1's") is written on tiny
magnetic bits (which themselves are made up of many even smaller
grains). When a bit is written, a magnetic field produced by the
disc drive's head orients the bit's magnetization in a particular
direction, corresponding to either a 0 or 1. The magnetism in the
head in essence "flips" the magnetization in the bit between two
stable orientations. In currently produced hard disc drives,
longitudinal recording is used. In longitudinal recording, the
magnetization in the bits is flipped between lying parallel and
anti-parallel to the direction in which the head is moving relative
to the disc.
[0005] Increasing areal densities within disc drives is no small
task. For the past few years, technologists have been increasing
areal densities in longitudinal recording at a rate in excess of
100% per year. But it is becoming more challenging to increase
areal densities, and this rate is expected to eventually slow until
new magnetic recording methods are developed.
[0006] To continue pushing areal densities in longitudinal
recording and increase overall storage capacity, the data bits must
be made smaller and put closer together. However, there are limits
to how small the bits may be made. If the bit becomes too small,
the magnetic energy holding the bit in place may become so small
that thermal energy may cause it to demagnetize over time. This
phenomenon is known as superparamagnetism. To avoid
superparamagnetic effects, disc media manufacturers have been
increasing the coercivity (the "field" required to write a bit) of
the disc. However, the fields that can be applied are limited by
the magnetic materials from which the head is made, and these
limits are being approached.
[0007] Newer longitudinal recording methods could allow beyond 140
gigabits per square inch in density. A great challenge however is
maintaining a strong signal-to-noise ratio for the bits recorded on
the media. When the bit size is reduced, the signal-to-noise ratio
is decreased, making the bits more difficult to detect, as well as
more difficult to maintain stable recorded information.
[0008] Perpendicular recording could enable one to record bits at a
higher density than longitudinal recording, because it can produce
higher magnetic fields in the recording medium. In perpendicular
recording, the magnetization of the disc, instead of lying in the
disc's plane as it does in longitudinal recording, stands on end
perpendicular to the plane of the disc. The bits are then
represented as regions of upward or downward directed magnetization
(corresponding to the 1's and 0's of the digital data).
[0009] A disk recording medium is shown in FIG. 1. 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 of FIG. 1. FIG. 1 shows a cross section of a
disc showing the difference between longitudinal and perpendicular
recording.
[0010] Perpendicular recording still has other unsolved problems.
On the other hand, longitudinal recording still has room left
before reaching the superparamagnetic limit. Thus in recent years,
considerable effort has been expended to achieve higher areal
recording density using longitudinal recording. Ever increasing
hard disk drive areal recording density requires continuously
aggressive media signal to noise ratio (SNR) enhancement. One way
for creating in a high density magnetic recording with a high
signal to noise ratio (SNR) is by enhancing the media Mrt oriented
ratio (OR). Media on textured aluminum substrates can achieve Mrt
OR higher than 1.8. However, it has been a great challenge to
obtain even Mrt OR of about 1.3 on textured glass substrates. This
invention provides a solution to satisfy this long-standing need of
increasing the Mrt OR of recording media on textured glass
substrate beyond about 1.3.
SUMMARY OF THE INVENTION
[0011] This invention relates preferably relates to a highly
oriented longitudinal magnetic media on direct texture glass
substrates. One embodiment is a magnetic recording medium
comprising a direct texture glass or glass-ceramic substrate and a
film structure directly on the direct texture glass or
glass-ceramic substrate, wherein the medium is an oriented
longitudinal magnetic recording medium having Mrt OR of 1.5 or
more. The medium could have SNR of greater than 2 dB over an
isotropic medium with a defined film structure directly on a
non-textured glass or glass-ceramic substrate, the defined film
structure being identical to the film structure directly on the
direct texture glass or glass-ceramic substrate. The film structure
could comprise an oxidized NiP layer. The oxidized NiP layer is
preferably directly on the direct texture glass or glass-ceramic
substrate. The structure could further comprise a NiNb layer
between the oxidized NiP layer and the direct texture glass or
glass-ceramic substrate. Preferably, the NiNb layer is directly on
the direct texture glass or glass-ceramic substrate. Also, the
oxidized NiP layer could have a texture resulting substantially
from a texture of the texture glass or glass-ceramic substrate and
the texture of the oxidized NiP is not a mechanical texture.
Preferably, a thickness of the oxidized NiP layer is in the range
of about 60-150 .ANG.. Also, the film structure could further
comprise a Cr-containing underlayer on the oxidized NiP layer.
Preferably, the Mrt OR of the media is 1.5 or more.
[0012] Another embodiment is a method for manufacturing a magnetic
recording medium comprising introducing a direct texture glass or
glass-ceramic substrate into a sputtering chamber and forming a
film structure on the direct texture glass or glass-ceramic
substrate without removal of the glass or glass-ceramic substrate
from the sputtering chamber.
[0013] Yet another embodiment is a magnetic recording medium
comprising a direct texture glass or glass-ceramic substrate and
means for recording data, wherein the medium is an oriented
longitudinal magnetic recording medium having Mrt OR of 1.5 or
more.
[0014] 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 is capable 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
[0015] FIG. 1 schematically shows a magnetic disk recording medium
comparing longitudinal or perpendicular recording.
[0016] FIG. 2 shows the layer structure of one embodiment of a
highly oriented direct texture glass media.
[0017] FIG. 3 shows an embodiment of a sputtering system for
implementing embodiments of this invention.
[0018] FIG. 4 shows the film structure utilized to generate the
data of FIGS. 5-13.
[0019] FIG. 5 shows Mrt OR changes with different level of NiP
oxidation.
[0020] FIG. 6 shows Mrt OR changes with different NiPOx
thickness.
[0021] FIG. 7 shows Mrt OR changes with changing NiPOx deposition
rate.
[0022] FIG. 8 shows Mrt OR changes with changing NiPOx deposition
pressure.
[0023] FIG. 9 shows Mrt OR changes with changing underlayer
materials.
[0024] FIG. 10 shows Mrt OR changes with changing underlayer
thickness.
[0025] FIG. 11 shows Mrt OR changes with changing adhesion layer
thickness.
[0026] FIG. 12 shows Mrt OR changes with changing post NiPOx
substrate temperature.
[0027] FIG. 13 shows Mrt OR changes with changing pre-NiNb/NiPOx
substrate temperature.
DETAILED DESCRIPTION
[0028] Almost all the manufacturing of the disks takes place in
clean rooms, where the amount of dust in the atmosphere is kept
very low, and is strictly controlled and monitored. The disk
substrates come to the disk fabrication site packed in shipping
cassettes. For certain types of media, the disk substrate has a
polished nickel-coated surface. The substrates are preferably
transferred to process cassettes to be moved from one process to
another. Preferably, the cassettes are moved from one room to
another on automatic guided vehicles to prevent contamination due
to human contact.
[0029] The first step in preparing a disk for recording data is
mechanical texturing by applying hard particle slurry to the
polished surface of the substrate and to utilize proper tape
materials on circumferential motion disk to create
circumferentially texture grooves. This substrate treatment helps
in depositing of a preferred underlayer crystallographic
orientation and subsequently helps preferentially growth of
magnetic recording material on the substrate. During the texturing
process, small amounts of substrate materials get removed from
surface of the disk and remain there. To remove this, the substrate
is usually washed. Also, techniques for polishing the surface of
the non-magnetic substrate of a recording medium use slurry
polishing, which requires wash treatment. Thus, disk substrates are
washed after texturing and polishing. However, wash defects could
be one of the top yield detractors.
[0030] A final cleaning of the substrate is then done using a
series of ultrasonic, megasonic and quick dump rinse .(QDR) steps.
At the end of the final clean, the substrate has an ultra-clean
surface and is ready for the deposition of layers of magnetic media
on the substrate. Preferably, the deposition is done by
sputtering.
[0031] Sputtering is perhaps the most important step in the whole
process of creating recording media. There are two types of
sputtering: pass-by sputtering and static sputtering. In pass-by
sputtering, disks are passed inside a vacuum chamber, where they
are bombarded with the magnetic and non-magnetic materials that are
deposited as one or more layers on the substrate. Static sputtering
uses smaller machines, and each disk is picked up and sputtered
individually.
[0032] The sputtering layers are deposited in what are called
bombs, which are loaded onto the sputtering machine. The bombs are
vacuum chambers with targets on either side. The substrate is
lifted into the bomb and is bombarded with the sputtered
material.
[0033] Sputtering leads to some particulates formation on the post
sputter disks. These particulates need to be removed to ensure that
they do not lead to the scratching between the head and substrate.
Thus, a lube is preferably applied to the substrate surface as one
of the top layers on the substrate.
[0034] Once a lube is applied, the substrates move to the
buffing/burnishing stage, where the substrate is polished while it
preferentially spins around a spindle. After buffing/burnishing,
the substrate is wiped and a clean lube is evenly applied on the
surface.
[0035] Subsequently, the disk is prepared and tested for quality
thorough a three-stage process. First, a burnishing head passes
over the surface, removing any bumps (asperities as the technical
term goes). The glide head then goes over the disk, checking for
remaining bumps, if any. Finally the certifying head checks the
surface for manufacturing defects and also measures the magnetic
recording ability of the substrate.
[0036] When referring to magnetic recording media, there are two
basic types: oriented and isotropic. The differences between the
two include the processes and materials used to produce the media.
In order for the disc to be capable of storing data, it needs to
have a magnetic layer applied to it. Isotropic media has the
magnetic layer and under-layers, which are used to control the
crystallographic orientation of the magnetic layer, applied to a
non preferentially polished substrate.
[0037] Oriented media, however, requires two additional steps
before applying the under-layers and magnetic layer. The first
extra step is the application of a nickel-phosphorus (NiP) layer to
the disc substrate by plating or sputtering. The second extra step
is texturing of the NiP layer.
[0038] The application of the nickel phosphorus layer for oriented
media serves two purposes. First, it allows the use of an aluminum
substrate, which would otherwise be too soft to be polished to the
smooth surface required. Secondly, by applying the nickel
phosphorus plating, it becomes possible to texture the disc. The
texturing process applies a scratch pattern to the disc surface.
The texture process improves magnetic orientation and enhances film
performance by initiating grain growth. The scratch pattern causes
magnetic properties in down-track and cross-track directions to be
different, which greatly increases media signal-to-noise ratio,
thereby greatly improving media performance and density.
[0039] Isotropic media can be produced on either aluminum or glass
media, but is most often produced on glass for mobile and consumer
applications where shock tolerance is a necessity. The glass
substrate is very stiff and shock tolerant. Although isotropic
media does not require extra processing and is somewhat simpler to
produce, it still lacks the extra signal-to-noise ratio that
oriented media yields. In fact, because the under-layers and
magnetic film are added to a polished surface, the recording
surface is slightly smoother than the textured surface of oriented
media.
[0040] Also, because both the surface of the glass and the
recording head are so smooth, it becomes increasingly difficult to
avoid stiction. Stiction is the result of having two completely
smooth surfaces resting against each other with a lubricant in
between; they want to stick together. For example, if two pieces of
glass were set one on top of the other with some water or lubricant
in between, it would be very difficult to pull them apart. The same
is true when a recording head lands on a glass substrate during a
power-down cycle. When the head attempted to take off, it would not
be able to due to stiction. This is what makes it necessary to use
ramp load technology.
[0041] Ramp load technology employs a lifting mechanism that
removes each head from the disc surface prior to power-down and
returns the heads to the disc surface only after a sufficient
rotation rate has been reached on the next start-up. Since the
technology does not employ a traditional landing zone, the head
never touches the disc surface and avoids stiction. Without a
landing zone, start/stop testing becomes obsolete too. However,
ramp load is somewhat inefficient because it uses a sizeable amount
of real estate on the disc-at the outer disc radius where lost area
really decreases drive capacity.
[0042] In short, the isotropic media itself affords a path to
continue media manufacturing cost reduction and provide higher
shock tolerance, but sacrifices valuable signal-to-noise yields and
requires the use of ramp load technology. Thus it is desired to
obtain an oriented magnetic media on textured glass to minimize
stiction and increase media signal-to-noise ratio.
[0043] Although glass substrates can be oriented, the preferred
choice is aluminum substrate discs when producing oriented media.
When using aluminum, a bias voltage can more easily be applied to
the substrate during deposition, which produces better magnetic
film structure. Glass substrates are also very difficult to orient.
To texture the surface of a glass substrate, seedlayer materials
such as a nickel phosphorus layer must be applied, just as with
aluminum substrates. However, this layer cannot be applied directly
by plating-the lower cost method of applying nickel phosphorus
because non-conductive nature of the glass substrate materials; the
layer must be applied by sputtering, or in a two-step process
involving both sputtering and plating. The second application of
nickel phosphorus is more expensive and increases the chances of
latent defects.
[0044] Despite the high cost of manufacturing a textured glass
substrate by applying a NiP layer on glass and then texturing the
NiP layer. The media performance of such textured glass substrates
was not capable of achieving high SNR than NiP plated aluminum
substrate because the substrate bias is still relative difficult to
apply onto such substrate. This poor SNR performance substantially
limited the applications of glass media in high areal density and
high data rate applications.
[0045] This invention overcomes the problems of the high cost of
applying a NiP layer on a glass substrate and then texturing the
NiP layer by sputtering a NiP layer directly on a textured glass
substrate. It was unexpectedly found that the sputtered NiP on the
textured glass substrate itself develops a texture resulting at
least partially from the texture of the textured glass substrate.
One embodiment of the process of this invention allows deposition
of subsequent layers on the NiP layer, which could optionally be an
oxidized NiP layer, without removing the textured glass substrate
from the sputtering chamber after sputtering the NiP layer for to
produce mechanical texture on the glass substrate as would be
required for an aluminum substrate. "Mechanical texture" means
texture caused by removal of material from the surface of a
material.
[0046] In different embodiments, texture of the textured glass
substrate can be induced by the methods of U.S. Pat. Nos. 6,246,543
and 6,294,058, or by the methods disclosed in the U.S. patents
disclosed in U.S. Pat. Nos. 6,246,543 and 6,294,058. Note that U.S.
Pat. Nos. 6,246,543 and 6,294,058 and the U.S. patents disclosed in
U.S. Pat. Nos. 6,246,543 and 6,294,058 are incorporated herein by
reference. Most of the above methods rely on the use of lithography
and etching.
[0047] In another embodiment, texture of the textured glass
substrate can be induced by an electron-beam (e-beam) to produce
patterns on the surface of the glass substrate without the use of
lithography and etching. One procedure for producing the e-beam
induced patterns is the following.
[0048] Prepare amorphous silicon samples through plasma enhanced
chemical vapor deposition at 170 degrees Centigrade of amorphous
hydrogenated Si on glass substrates until a thickness of 1000
Angstroms is reached. Treat a sample with an e-beam writer
operating at 50 keV to create a pattern of 400 by 400 spots with a
spot diameter of approximately 0.5 microns. The current could be
approximately 1000 nA, with a spot size of about 0.5 microns, and a
dosage of about 1,000,000 microCurie/cm2. With the help of an
optical microscope to look at reflectance patterns, "texture" could
be observed at the spots exposed. By using a pattern-creating
program along with an e-beam writer, texture on the glass substrate
can be created without the use of lithography and etching. On the
textured glass substrate made by e-beam patterning, any metal can
be deposited by sputtering to create an oriented media.
[0049] The recording media on direct textured substrate could be
fabricated with DC magnetron sputtering except carbon films could
be made with ion beam sputtering. FIG. 2 shows the layer structure
of recording media on textured glass substrates according to one
embodiment of this invention. In accordance with embodiments of
this invention, a first Ni-containing layer is deposited on a
direct texture substrate, such as a glass or glass-ceramic
substrate, as an adhesion layer and a second Ni-containing layer is
deposited on the adhesion layer as a seedlayer. The Ni-containing
layer could be a, a NiNb layer, a Cr/NiNb layer, a NiP layer or any
other Ni-containing layer. The surface of the Ni-containing layer
is optionally oxidized. Subsequently, a Cr-containing underlayer is
deposited on the seed layer. Then, a Co-containing magnetic layer
is deposited on the Cr-containing underlayer. Another embodiment of
this invention could include depositing a thin intermediate
magnetic layer on the underlayer and depositing the magnetic layer
on the intermediate layer.
[0050] In a preferred embodiment, the magnetic layer is Co-Cr-Pt-B.
In another embodiment, the Co-Cr-Pt-B comprises at least 8-26
atomic percent Cr, 5 to 21 atomic percent Pt, 2 to 18 atomic
percent B, and Co in the balance.
[0051] In a preferred embodiment, the thickness of the seed layer
is about 100 .ANG. to about 2000 .ANG., the thickness of the
underlayer is about 10 .ANG. to about 1000 .ANG., and the thickness
of the magnetic layer is about 100 .ANG. to about 300 .ANG.. In
another preferred embodiment, the thickness of the adhesion layer
is about 3 .ANG. to about 1000 .ANG., the thickness of the seed
layer is about 40 .ANG. to about 2000 .ANG., the thickness of the
underlayer is about 10 .ANG. to about 1000 .ANG., and the thickness
of the magnetic layer is about 100 .ANG. to about 300 .ANG..
[0052] In a preferred embodiment, the thickness of the adhesion
layer is 70 .ANG. to about 250 .ANG., preferably between 75 .ANG.
and 150 .ANG., and most preferably about 100 .ANG.. In a preferred
embodiment, the thickness of the seed layer is 200 .ANG. to about
1600 .ANG., preferably between 300 .ANG. and 1200 .ANG., and most
preferably about 600 .ANG.. In a preferred embodiment, the
thickness of the underlayer is 12 .ANG. to about 500 .ANG.,
preferably between 15 .ANG. and 250 .ANG., and most preferably
about 25 .ANG.. In a preferred embodiment, the thickness of the
magnetic layer is 150 .ANG. to about 250 .ANG., preferably between
175 .ANG. and 225 .ANG., and most preferably about 200 .ANG.. In a
preferred embodiment, the thickness of the protective layer is 20
.ANG. to about 300 .ANG., preferably between 30 .ANG. and 100
.ANG., and most preferably about 50 .ANG.. The protective layer is
made of hydrogenated carbon (CH.sub.x).
[0053] The magnetic recording medium has a remanent coercivity of
about 2000 to about 10,000 Oersted, and an Mrt (product of
remanance, Mr, and magnetic layer thickness, t) of about 0.2 to
about 2.0 memu/cm.sup.2. In a preferred embodiment, the coercivity
is about 2500 to about 9000 Oersted, more preferably in the range
of about 3000 to about 6000 Oersted, and most preferably in the
range of about 3350 to about 5000 Oersted. In a preferred
embodiment, the Mrt is about 0.25 to about 1 memu/cm.sup.2, more
preferably in the range of about 0.3 to about 0.7 memu/cm.sup.2,
and most preferably in the range of about 0.3 to about 0.6
memu/cm.sup.2.
[0054] Embodiments of this invention include sputter depositing a
Ni-containing layer on a glass or glass-ceramic substrate and
oxidizing the surface of the sputter deposited Ni-containing layer
at a suitable temperature, e.g., about 100.degree. C. to about
300.degree. C., in an oxidizing atmosphere to form an oxidized
Ni-containing layer. Suitable oxidizing atmospheres contain about 1
to about 100 volume percent of oxygen (O.sub.2), the remainder an
inert gas, such as argon (Ar), e.g., about 20 to about 50 volume
percent oxygen, such as about 50 to 80 percent by volume oxygen.
The degree of oxidation can be such that the amount of oxygen in
the top 5A to full layer thickness of the oxidized Ni-containing
layer, after in situ sputter removal of the 40 .ANG. surface layer,
is about 15 atomic percent to about 0-50 atomic percent, such as
about 0 atomic percent to about 10 atomic percent.
[0055] In embodiments of this invention, the oxidized surface of
the Ni-containing layer contains substantially elemental Ni,
because preferably Ni is predominately present substantially in its
elemental form throughout the Ni-containing layer. On the other
hand, the second element of the oxidized Ni-containing layer, if
present, is partially (about 75 atomic percent) an oxide and
partially in substantially elemental form to a depth of about 0 to
200 .ANG. from the surface.
[0056] Embodiments of this invention include deposition of an
underlayer, such as Cr or a Cr-alloy underlayer, e.g., CrMo, on the
Ni-containing seed layer. An embodiment of this invention also
includes depositing a magnetic layer on the Ni-containing seed
layer. Another embodiment of this invention includes depositing a
thin intermediate magnetic layer on the underlayer and depositing
the magnetic layer on the intermediate layer. The intermediate
layer comprises a CoCrTa layer, which can comprise about 10 to
about 40 atomic percent Cr and about 0 to about 6 atomic percent
Ta. Embodiments of this invention include the use of any of the
various magnetic alloys containing B, Cr and Co, such as CoCrB,
CoCrPtB, CoCrNiB, CoCrNiPtB, CoCrNiTaB, CoCrNiNbB, CoCrPtTaB,
CoCrPtNbB and CoCrPtTaNbB, and other combinations of B, Cr, Co, Pt,
Ni, Ta and Nb, in the magnetic layer.
[0057] An apparatus for manufacturing magnetic recording media in
accordance with the embodiments of the present invention is
schematically illustrated in FIG. 3. The disk substrates travel
sequentially from heater I to a first Ni-containing layer
deposition station. Then, the disk substrates travel to a second
Ni-containing layer deposition station where the reactive sputter
takes place to oxidize the deposited films, and then to the heater
station II where surface oxidation of sputtered Ni-containing
seedlayer can be oxidized. As a result, the oxidized Ni-containing
seed layer is formed on the disk substrates. Subsequent to the
deposition of the seed layer, the disk substrates are passed
through the Cr-containing underlayer deposition station wherein the
Cr-containing underlayer is deposited. Optionally the disk
substrates are passed through an intermediate layer deposition
station. The disks are then passed to the magnetic layer deposition
station and then to the protective carbon overcoat deposition
station.
EXAMPLES
[0058] In one embodiment, reactive sputtering of NiPOx on textured
glass substrates created a chemically suitable surface to promote
underlayer Cr growth with [200] perpendicular to the glass
substrates. This typically creates a bi-crystal oriented magnetic
structure. With the assist of circumferential substrate texture
grooves of the direct texture glass substrate, a magnetic film
itself was oriented with the c-axis along circumferential
direction. This then created a magnetic film with a high Mrt
orientation ratio.
[0059] For example, the media layer structure of FIG. 2 was capable
of achieving Mrt OR of 0.8 to 3 depending on various combinations
of seedlayer/underlayer/magnetic layer/processes. This desired
highly oriented glass media design and yield a significant SNR
(>2 dB) and parametric improvement over the counterpart best
isotropic media. The parametric and SNR performance are tabulated
in Table 1. To better illustrate the difference in performance, a
2-3 dB increase in SNR would result in doubling the disc density;
therefore, this invention has been able to improve disc density of
glass media by at least about 40 percent using direct textured
glass to create oriented media.
1TABLE 1 Parametric performance comparison between isotropic and
oriented media on glass substrates. HF TAA LF TAA Description Hc
MrT S* (mV) (mV) Res PW50 OW SNR BER Oriented 4765 0.331 0.818
1.827 2.465 74.09 3.95 37.84 16.48 4.57 Isotropic 4699 0.362 0.838
0.991 1.471 67.37 3.87 40.11 14.68 3.56
[0060] The sputter process parameters that were studied so as to
produce high Mrt OR media include substrate heating, adhesion and
seedlayer materials, adhesion and seedlayer thicknesses, the amount
of NiP oxidation, NiPOx layer thickness, NiP oxidation process
pressure, and underlayer materials, underlayer thickness, and
underlayer processes. The results of these studies are summarized
below.
[0061] The film structure utilized to generate the following data
is shown in FIG. 4. The layer structure containing 1) mechanically
texture substrate, 2) adhesion layer Ni50Nb50, 3) oxidized Ni81P19,
4) Cr100 , 5)CrMo10Ta3, 6)Co82Cr14Ta4, 7) Co57Cr24Pt13B6,
8)Co58Cr15Pt16B12, 9) CHxNy. The data indicate the optimized
process combination are required to achieve the best Mrt
orientation.
[0062] FIG. 5 shows Mrt OR changes with different level of NiP
oxidation. Media Mrt OR changes with NiP oxidation processes. The
preferred pressure for oxygen in reactive sputtering is between 2
mT-12 mT. Both lower and higher oxidation minimizes the Mrt OR.
This result shows oxidation level control surface mobility of the
underlayr species. The underlayer species mobility affects the
nucleation density and the species ability to move to the desired
nucleation site on the substrate surface and subsequently determine
the level Mrt OR. Too low mobility species can yield higher
nucleation density, however the species will not be able to
oriented properly to provide magnetic film to have c-axis
preferentially oriented circumferentially. Too high mobility can
result in low nucleation density and results in less magnetically
induced Mrt OR.
[0063] FIG. 6 shows Mrt OR changes with different NiPOx thickness.
Media Mrt OR changes with NiPOx thickness. The preferred thickness
of NiPOx is between 30-150 .ANG.. Higher and lower NiPOx thickness
reduces Mrt OR. The results indicate the NiPOx minimum thickness is
required to establish desired surface chemistry for proper
underlayer orientation and subsequently for preferred
circumferential c-axis alignment. However, the preferred underlayer
and magnetic nucleation sites for high Mrt OR are eliminated with
the increase of the NiPOx thickness.
[0064] FIG. 7 shows Mrt OR changes with changing NiPOx deposition
rate. Low NiPOx deposition rate enhances Mrt OR. The deposition
rate should be less than 80 A/sec to achieve better Mrt OR. The
deposition rate can be translated to the level of seedlayer
oxidation. High deposition rate of NiPOx seedlayer results in low
level of seedlayer oxidation, hence yields the low Mrt OR. However,
the prolong of the deposition can have an adverse effect of low
throughput.
[0065] FIG. 8 shows Mrt OR changes with changing NiPOx deposition
pressure. The preferred total NiPOx deposition pressure is between
8 mT to 20 mT.
[0066] FIG. 9 shows Mrt OR changes with changing underlayer
materials. Different underlayer materials can induce different
level of Mrt OR. Different underlayer materials can result in
different mobilities and nucleation density on the similarly
oxidized seedlayer surface. As described earlier, the optimized
mobility can yield highest Mrt OR. The underlayer materials which
can achieve high Mrt OR include Cr, CrWx (x=2%-30%), CrMoxTay
(x=2%-30%; y=1%-20%), CrVx (x=2-30%), CrTix (x=2-30%), CrTixBy
(x=2-30%; y=2-10%).
[0067] FIG. 10 shows Mrt OR changes with changing underlayer
thickness. Underlayer material thickness changes Mrt OR. The
preferred underlayer thickness to achieve high Mrt OR is between 20
A-150 .ANG..
[0068] FIG. 11 shows Mrt OR changes with changing adhesion layer
thickness. The preferred nucleation sites are eliminated with the
increase of the adhesion layer thickness. Mrt OR improves with
decreasing adhesion layer thickness. The preferred adhesion layer
thickness range is between 3-60 .ANG..
[0069] FIG. 12 shows Mrt OR changes with changing post NiPOx
substrate temperature. Lower post-NiPOx substrate temperature
enhances Mrt OR. Elevated substrate temperature is required for
underlayer CrXY deposition to be oriented properly. Note that X and
Y are any elements. Optimum post-NiPOx deposition temperature is
between 120.degree. C. to 250.degree. C.
[0070] FIG. 13 shows Mrt OR changes with changing pre-NiNb/NiPOx
substrate temperature. Low pre-NiPOx substrate temperature improves
Mrt OR. Ambient temperature deposition of the NiPOx is desired.
High temperature deposition of adhesion layer and seedlayer tend to
destroy high energy preferred nucleation site. Hence, the Mrt OR
decreases.
[0071] In addition, it was found that low mobility seedlayer
materials can enhance Mrt OR. The materials selected for adhesion
layer includes but not limited to NiNb, Cr, CrTax, CrWx, NiAl,
RuAl, CoWx, CoMox, TaWx. Note "x" refers to atomic percent. The
described embodiments of adhesion, seedlayer and underlayer can be
employed for both a simple magnetic structure (e.g., conventional)
and a complicated magnetic layer structure (e.g., anti-Ferro
magnetic coupling) media design.
[0072] This application discloses several numerical ranges in the
text and figures. The numerical ranges disclosed inherently support
any range or value 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.
[0073] 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. 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. Finally, the entire
disclosure of the patents and publications referred in this
application are hereby incorporated herein by reference.
* * * * *