U.S. patent application number 09/947287 was filed with the patent office on 2003-03-06 for laser textured magnetic disk.
Invention is credited to Kavosh, Iraj, Shuster, James, Tam, Andrew Ching.
Application Number | 20030044647 09/947287 |
Document ID | / |
Family ID | 25485895 |
Filed Date | 2003-03-06 |
United States Patent
Application |
20030044647 |
Kind Code |
A1 |
Kavosh, Iraj ; et
al. |
March 6, 2003 |
Laser textured magnetic disk
Abstract
A magnetic disk is provided which comprises a nonmetallic glass
or glass ceramic substrate having one or more under layers, a
magnetic layer applied over the under layers, and a hard carbon
layer applied over the magnetic layer. A plurality of bumps are
formed on the magnetic disk by applying a beam from a near infrared
wavelength laser to the surface of the carbon layer.
Inventors: |
Kavosh, Iraj; (San Jose,
CA) ; Shuster, James; (Gilroy, CA) ; Tam,
Andrew Ching; (Saratoga, CA) |
Correspondence
Address: |
Esther E. Klein
IBM Corporation
IP Law Department
5600 Cottle Road (L2PA/014-2)
San Jose
CA
95193
US
|
Family ID: |
25485895 |
Appl. No.: |
09/947287 |
Filed: |
September 5, 2001 |
Current U.S.
Class: |
428/848 ;
G9B/5.288; G9B/5.293; G9B/5.3 |
Current CPC
Class: |
B23K 26/0648 20130101;
G11B 5/73921 20190501; G11B 5/82 20130101; G11B 5/8408 20130101;
B23K 26/244 20151001; G11B 5/7379 20190501; G11B 5/851 20130101;
B23K 26/0665 20130101; G11B 5/656 20130101; G11B 5/7369 20190501;
G11B 5/7368 20190501; B23K 26/06 20130101 |
Class at
Publication: |
428/693 ;
428/694.0TP; 428/694.0TR; 428/694.0SG; 428/694.0BR |
International
Class: |
B32B 027/14 |
Claims
We claim:
1. A magnetic disk comprising: a glass or glass-ceramic substrate;
at least one under layer of a metal alloy applied over the
substrate; a magnetic layer applied over said seed layer; a carbon
layer applied over said magnetic layer; and at least one bump
formed by applying a beam from a near IR laser to the surface of
the carbon layer.
2. The magnetic disk of claim 1 wherein a plurality of bumps form
an annular area for a contact start/stop zone.
3. The magnetic disk of claim 1 wherein the at least one bump is
used as part of a glide height calibration process.
4. The magnetic disk of claim 1 wherein the magnetic disk has a
first side and a second side and wherein a plurality of bumps form
an annular ring on a side of the disk to mark the side as not being
used.
5. The magnetic disk of claim 1 wherein the at least one bump is
part of a disk identifier.
6. The magnetic disk of claim 1 wherein the at least one bump is an
elongated bump formed by passing the laser beam through a
cylindrical lens system and wherein the bump shape and aspect ratio
of the elongated bump are adjusted by adjusting the cylindrical
lens system.
7. The magnetic disk of claim 1 further comprising a lubrication
layer applied over the carbon layer.
8. The magnetic disk of claim 1 wherein a plurality of under layers
are applied to the substrate comprising: a layer of NiAl; a layer
of CrV; and a layer of CoCr, and wherein the magnetic layer
comprises CoCrPtBo.
9. The magnetic disk of claim 1 wherein the at least one bump has a
height between 10 and 25 nanometers.
10. The magnetic disk of claim 1 wherein the laser beam is produced
by an Nd:Vanadate laser.
11. A method of manufacturing a magnetic disk comprising the steps
of: a) sputtering at least one under layer of a metal alloy over a
glass or glass ceramic substrate disk; b) sputtering as a magnetic
layer over said under layer; c) sputtering a hard carbon coating
over said magnetic layer; and d) applying a beam from a near IR
wavelength laser to the surface of the carbon layer to form at
least one bump.
12. The method of claim 11 wherein a plurality of bumps form an
annular area for a contact start/stop zone.
13. The method of claim 11 wherein the at least one bump is used as
part of a glide height calibration process.
14. The method of claim 11 wherein a plurality of bumps form an
annular ring to mark a side of the disk for not being used.
15. The method of claim 11 wherein the at least one bump is part of
a disk identifier.
16. The method of claim 11 wherein the at least one bump is an
elongated bump formed by passing the laser beam through a
cylindrical lens system and wherein the bump shape and aspect ratio
of the elongated bump are adjusted by adjusting the cylindrical
lens system.
17. The method of claim 11 wherein the near IR wavelength laser is
an Nd:Vanadate laser.
18. A magnetic disk comprising: a glass or glass-ceramic substrate;
at least one under layer of a metal alloy applied over the
substrate; a magnetic layer applied over said seed layer; a carbon
layer applied over said magnetic layer; and at least one elongated
bump formed by applying a laser beam, from a near IR laser, passed
through a cylindrical lens system, to the surface of the carbon
layer, wherein the aspect ratio and shape of the bump are adjusted
by adjusting the cylindrical lens system.
19. The magnetic disk of claim 18 wherein the at least one bump is
used as part of a glide height calibration process.
20. The magnetic disk of claim 18 wherein a plurality of bumps form
an annular area for a contact start/stop zone.
Description
FIELD OF THE INVENTION
[0001] The present invention pertains to the texturing of magnetic
disks. More particularly this invention pertains to using a near
infrared wavelength laser to create bumps on a nonmetallic
substrate based magnetic disk.
BACKGROUND OF THE INVENTION
[0002] A direct access storage device uses magnetic disks to store
electronic data. The disks are rotated on a central axis in
combination with magnetic heads for reading and writing magnetic
signals.
[0003] A "contact start/stop" (CSS) system uses a magnetic head
which is in contact with the magnetic disk surface only when the
disk is stationary. When the disk starts to rotate the magnetic
head slides off the surface eventually flying fully lifted from the
disk surface.
[0004] A smooth recording surface is preferred to permit the
magnetic head to ride as close as possible to the disk surface. In
order to avoid stiction, which occurs during the start process in a
CSS system, a textured region of the rotating disk surface is used
for the contact area with the magnetic head. The surface texture in
a contact start/stop region reduces the contact stiction and
friction. The magnetic head is moved to the contact region at the
appropriate times by the drive controller.
[0005] It is known in the art to use a laser to create bumps on the
surface of the disk to produce a textured region as a contact area
in a CSS disk drive system. Laser zone texturing (LZT) processes
are widely used in the hard disk drive industry to allow precise
control of the roughness of the hard disk contact area. In laser
zone texturing, an annular area typically 2-3 mm wide of the disk
surface is roughened by a laser. The laser produces micro-sized
bumps to provide a take off and landing zone for the flying head
during the contact start/stop operation. Usually, the laser
texturing process is applied to a nonmagnetic substrate prior to
conventionally employed processes for producing the magnetic
recording disks.
[0006] Traditionally, a magnetic disk is manufactured by initially
starting with an aluminum magnesium (AlMg) substrate which is then
plated with nickel phosphorus (NiP). The texturing is then
performed on the plated NiP layer. On top of the NiP plated AlMg
substrate, a magnetic layer is sputter deposited.
[0007] In particular, because of their performance characteristics,
it is desirable to use a tightly focused laser beam, with TEM00
spatial mode and Gaussian intensity distribution profile, from
diode pumped neodymium-doped yttrium-lithium-fluoride (Nd:YLF) or a
neodymium-doped yttrium-vanadate (Nd:YVO4) solid state laser to
create the bumps on a disk surface. The Nd:YVO4 laser is also
referred to as an Nd:Vanadate laser or a Vanadate laser. These
lasers are in the near infrared (near-IR) family of lasers. The
near-IR wavelength lasers provide sufficient absorption and
coupling of laser energy into the smooth amorphous NiP material
that had been deposited onto the AlMg substrate.
[0008] An example of a laser texturing tool is provided in commonly
owned U.S. Pat. No. 6,013,336, Baumgart et al, "Procedure Employing
a Diode Pumped Laser for Controllably Texturing a Disk Surface".
Other laser texturing tools are well known to those skilled in the
art.
[0009] In the last few years the use of alternative nonmetallic
substrates such as glass or glass-ceramic substrates has become
widely accepted in the industry due to the superior mechanical
advantages of glass and glass-ceramic material. A glass based
substrate provides a smoother surface for the magnetic layer. The
smoother the recording surface, the closer the proximity of the
head to the disk. This allows more consistent and predictable
behavior of the air bearing support for the head which enables a
higher recording density.
[0010] However, since glass materials are optically transparent in
the near IR wavelength range, the vanadate laser based texturing
tools cannot be used for the laser zone texturing process on the
raw glass substrate.
[0011] As an alternative laser texturing process, a CO.sub.2 laser
based system is known in the industry to be used for zone texturing
raw glass substrates. This is because the glass substrate material
is sufficiently absorbent at wavelengths produced by CO.sub.2
lasers. The textured glass substrate can then be processed to the
finished magnetic disk by depositing at least one underlayer, then
a magnetic layer and then a protective overcoat (commonly a carbon
or carbon-based layer). Examples of a laser texturing tool for
glass substrates is found in commonly owned U.S. Pat. No.
6,107,599, Baumgart et al, "Method and Tool for Laser Texturing of
Glass Substrates".
[0012] However, the bump formation mechanism as well as the bump
shape for the above processes are different. Bump formation on a
NiP-plated AlMg disks is governed by rapid melting and
resolidification process of the heated spot on the substrate
surface, and the final bump shape depends on thermocapillary and
chemicapillary effects created by the laser pulse. While the bump
formation on a glass disks (using CO.sub.2 laser) is due to laser
absorption in the glass and the consequent thermal expansion of the
heated area.
[0013] While the CO.sub.2 laser can be used to texture raw glass
substrates, there are limitations in the ability of CO.sub.2 laser
texturing tools to optimally texture disks. Therefore, it is
desirable to provide a method for texturing the glass based
substrate disks using the Nd:Vanadate laser because Nd:Vanadate
lasers provides greater flexibility in the process of producing a
textured zone.
[0014] Furthermore, the Nd:Vanadate laser texturing systems are
currently widely used in the manufacturing texturing process of
NiP-plated AlMg substrates. It is more economical to be able to use
the more readily available laser systems for the glass substrate
disks.
[0015] An approach to providing zone texturing of a glass substrate
has been demonstrated in U.S. Pat. No. 5,980,997. In this approach,
a smooth metallic layer is first deposited on a glass substrate,
and the metallic layer is then textured by a laser beam. The
metallic layer is preferably impact resistant, hard and has a
high-melting temperature greater than 1000 degrees centigrade.
Since such a deposited metallic layer (i.e., texture layer) absorbs
laser energy at near-IR wavelengths, a Vanadate laser based
texturing tool can be used to produce a textured zone on the glass
substrate deposited with a texture layer. The textured glass
substrate then undergoes the conventional processes for the
manufacturing of a magnetic disk. A disadvantage of this approach
is that an extra step is added to the manufacturing process of
depositing a texture layer before the laser texturing process is
completed. Such a step obviously adds to the manufacturing costs of
a magnetic disk production. Therefore, there is a need for a laser
texturing process for glass-substrate magnetic disks which does not
add to any of the production costs and allows for greater
flexibility in the use of the Vanadate-laser-based texturing
tool.
[0016] It is also desirable to provide a process for marking a
disk, including alphanumeric writing, on a sputtered or finished
disk. Disk marking can be used to distinguish a good and a
defective side of a single sided finished disk by producing a
textured ring or other arbitrary pattern on the defective side of
the finished glass disk. Such a marked finished glass disk can be
used in a load/unload drive and not necessarily in a contact
start/stop drive. Implementation of such marking process in
manufacturing can extend applicability of the existing texturing
systems to disk marking processes.
[0017] The marking of a disk can also be useful for identifying a
disk. When a disk is in use, installed in a computer system, it is
helpful to be able to determine when and where the disk was
manufactured. Marking a disk with this information enhances quality
assurance processes.
[0018] It is also desirable to use textured glass substrate disks
to determine the glide height of a magnetic head over a magnetic
disk. It is currently known in the industry to use textured disks
to test whether a magnetic head flying over a disk touches the disk
surface which causes problems.
[0019] During reading and recording operations, the head is
positioned as close to the disk surface as possible. There are
topological asperities, typically, only a few microns (or smaller)
in diameter and height range from about a few micro-inches to
sub-micro inches, formed on the surface of a disk which make it
necessary to limit the proximity of the head to the disk surface.
Conventional disk drives are manufactured with precise
specifications including maximum glide height for a magnetic head
above the data zone. In recognition of the inevitable topographical
asperities, conventional practice comprises testing each magnetic
disk to determine if the maximum glide height requirement is met.
Such testing typically comprises the use of a device known as a
glide tester.
[0020] Conventional glide testers typically use a reference disk
containing a single (or multiple) protusions formed by
photolythographic techniques, or single (or multiple)
laser-textured bump(s) on AlMg substrates, or raw glass substrates,
having a defined height. The referenced disk is rotated and a
magnetic head is lowered until the magnetic head contacts the bump
at which point an electrical signal is generated indicating the
glide height. Of particular significance is the need for the bumps
on the reference disk to accurately simulate asperities inevitably
present on the surface of a magnetic disk. There exists a need for
an efficient and cost-effective method to produce such a reference
disk.
[0021] There is also a need to better control the shape and
orientation of laser produced bumps to provide a more controllable
contact start/stop zone wherein stiction is reduced without
compromising durability. It is also desirable to control and adjust
the bump shape for a glide tester reference disk to optimize
electrical signal generation during the process of glide height
calibration, and to overcome signal generation issues associated
with CO2 laser produced bumps on raw glass substrates. More
particularly, it is desirable to efficiently produce bumps with
elongated shapes to achieve these goals.
[0022] One or more of the foregoing problems are solved and one or
more of the foregoing needs are met by the present invention.
SUMMARY OF THE INVENTION
[0023] A magnetic disk is provided which comprises a glass or
glass/ceramic substrate, one or more under layers, a magnetic layer
applied over the substrate, and a carbon layer applied over the
magnetic layer. A plurality of bumps are formed on the magnetic
disk by applying a laser beam to the surface of the carbon
layer.
[0024] In a further embodiment of the present invention a method is
provided for preparing a magnetic disk comprising first applying
one or more under layer(s) and a magnetic layer to a glass or glass
ceramic substrate. A carbon overcoat layer is then applied over the
magnetic layer. A plurality of bumps are incorporated onto the
surface of the disk by applying a laser to the surface of the
carbon layer. In a further embodiment a lubricant is applied over
the carbon overcoat layer.
[0025] In a further embodiment of the present invention the bump
formation process can be conducted after applying the lubricant
layer on the magnetically sputtered disk.
[0026] In a further embodiment, a plurality of bumps formed in a
concentric circle using the laser provides a contact start/stop
zone for the magnetic disk.
[0027] In a further embodiment, a single or a plurality of bumps
provide a means for calibrating glide height of a transducer head
flying over the magnetic disk.
[0028] In a further embodiment, a plurality of bumps provide a
means for marking the magnetic disk.
[0029] In a further embodiment, a cylindrical lens system is used
to form elliptical or elongated bumps on the surface of the
finished glass substrate magnetic disk.
BRIEF DESCRIPTION OF THE DRAWINGS
[0030] FIG. 1 illustrates a cross-section of a glass substrate
based magnetic disk containing a bump.
[0031] FIG. 2 illustrates a magnetic disk containing landing and
data zones and showing a block diagram of a laser creating the
bumps for the landing zone.
[0032] FIG. 3 is a graph showing the bump height variation versus
the laser power on a finished glass disk.
[0033] FIGS. 4a-d are illustrations of the bumps created by various
powers of the Nd:Vanadate laser on the finished glass disk.
[0034] FIG. 5 is an illustration of a one sided glass disk marked
with a ring.
[0035] FIG. 6 illustrates a glide height test disk.
[0036] FIG. 7 illustrates a cylindrical lens system that converts a
circular beam into elliptical shape.
[0037] FIG. 8 illustrates elongated bumps on the surface of the
finished glass disk.
[0038] FIG. 9 illustrates a three dimensional view of the central
portion of an elongated bump of FIG. 8.
[0039] FIG. 10 illustrates the profile of the elongated bump along
the short axis A of FIG. 9.
[0040] FIG. 11 illustrates the profile of the elongated bump along
the central portion of the long axis B of FIG. 9.
[0041] FIG. 12 illustrates a graph of bump height variation versus
laser power for elongated bumps.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
[0042] The present invention applies a near IR wavelength laser
zone texturing tool for use on a nonmetallic substrate, such as a
glass or ceramic-glass, finished magnetic disk. While the preferred
embodiment is described herein with reference to a glass substrate,
it is understood by those skilled in the art, that the invention
described herein may also be implemented using ceramic glass
substrates and other nonmetallic substances known to be used in the
manufacturing of magnetic disks for data storage. Therefore,
throughout this description of the invention, the reference to
"glass" is used to generally refer to glass and ceramic glass
substrates, as well as other nonmetallic substrates.
[0043] The magnetic disk is conventionally produced by sputter
depositing one or more underlayer(s), a magnetic layer and a
protective carbon overcoat layer. After all the layers have been
added a near IR wavelength laser beam such as a vanadate laser
system is used to provide texturing. The process may also be
applied to a magnetically sputtered glass substrate based disk
after it has been lubed in accordance with the normal lube process
for magnetic disks.
[0044] Referencing FIG. 1, a cross section of a magnetic glass
substrate disk 10 is shown. According to standard industry
practices, a series of under layers of metal alloys are sputter
applied, according to conventional techniques, prior to the
application of the actual magnetic layer which holds the electronic
data. These under layers are used to improve the magnetic
performance quality of the recording substrate. The first under
layer 14 is preferably nickel aluminum (NiAl) which is the first
substance sputtered onto the glass substrate 12. This layer is
sometimes referred to as a seed layer. The next under layer that is
applied is the chromium vanadium (CrV) 18 which is followed by a
layer of cobalt chromium (CoCr) 20. After these under layers have
been applied, a magnetic layer of cobalt chromium platinum boron
(CoCrPlBo) 22 is applied. After the magnetic layer is sputtered
onto the disk, a carbon overcoat (coc) layer 24 is applied. The
carbon overcoat material comprises a carbon which has been
nitrogenated or hydrogenated in order to produce a protective,
diamond-like substance. After the sputter processes are completed,
the magnetic disk goes through a lubrication process to complete
the production process of the magnetic disk by adding a layer of
lubricant 26. In the preferred embodiment, a common lubricant that
is used in the industry is the commercially available Z-dol 4000
lubricant. Other lubricants may also be used. A lubricated disk is
referred to as a "finished disk".
[0045] In the preferred embodiment, the seed layer is a nickel
aluminum alloy. However, other conventionally employed metal alloy
underlayer substances known to be used in the production of
magnetic disks may also be used in accordance with the present
invention. Likewise, in the preferred embodiment the under layers
and magnetic layer of the present invention comprises cobalt based
alloys with the carbon overcoat protection. Other under layers,
magnetic layers and hard protective overcoat layers may also be
used.
[0046] The thicknesses of the under layer, magnetic layer, and
carbon overcoat layer are consistent with conventional practices in
the manufacturing of a magnetic disk media. In the preferred
embodiment, the nickel aluminum is approximately 300 angstroms, the
CrV is approximately 300 angstroms, the CoCr is approximately 40
angstroms and the CoCrPlBo is approximately 200 angstroms. The
carbon overcoat layer is applied at a thickness of approximately 50
angstroms.
[0047] Referencing FIG. 2, in accordance with the present
invention, the surface of the finished glass or glass/ceramic
substrate based magnetic disk 30 is provided with a textured
takeoff and landing (contact start/stop) zone by utilizing a pulse
focused laser beam 34 provided by a near IR wavelength laser such
as an Nd:Vanadate laser 36. The beam 34 is directed onto the
locations of the disk surface 30 by passing the beam 34 through a
focusing lens 37.
[0048] The resulting laser texture comprises a plurality of
accurately positioned protrusions or bumps 39 with controlled
height and geometry to optimize tribologic and magnetic
requirements compatible with the requirements of a high density
storage landing zone 38. The bumps 39 in the landing zone 38 are
spaced according to the tribology performance requirements or can
be spaced randomly. The disk 30 has an outer diameter 40 and an
inner diameter 42. The width of the landing zone 38 is typically
about 2-3 mm. The landing zone 38 is preferably spaced 31/2-5 or 6
mm from the disk inner diameter. The remaining surface area of the
disk is referred to as the data zone 41.
[0049] The preferred near IR wavelength laser used is an
Nd:Vanadate (Nd:YVO4) laser system. In an Nd:Vanadate laser, a
neodymium-doped yttrium-lithium-vanadate crystal 43 is used as the
lasing medium to produce the laser stream. Other near IR wavelength
lasers, such as Nd:YLF laser, may also be used. An example of a
commercially available vanadate laser is the T-Series Laser System
available from Spectra-Physics.
[0050] One of the critical optical parameters in a laser texturing
process for achieving tight control on the bump height is the depth
of focus of the laser spot on the disk surface. A laser texturing
tool system with a longer depth of focus is less sensitive to
disk-to-disk thickness variations and more forgiving of minor
imperfections in the optical and mechanical alignment in the
system. A longer depth of focus has the advantage of providing a
tighter control on the average bump height during manufacturing
production. In order to achieve the same bump diameter, the depth
of focus for an Nd:Vanadate laser texturing system is a few times
longer than the depth of focus for the CO.sub.2 laser based system.
This provides greater consistency in the textured zones between
disks and provides a more economical way of producing the
bumps.
[0051] The Nd:Vanadate laser pulse width used in texturing process,
is typically a few times shorter than the CO.sub.2 laser pulse
width. Therefore the Nd:Vanadate laser has less thermal diffusion
in the glass substrate and therefore has the ability to form
smaller bumps. The Nd:Vanadate laser pulse energy is mostly
absorbed by the sputtered film which is consistently opaque to the
vanadate laser beam. This process also takes advantage of the
better disk to disk compositional and structural consistency of the
sputtered magnetic layers (film) on the glass/glass ceramic
substrate.
[0052] The shape of the bumps formed on a sputtered or finished
disk, for a fixed laser spot size and pulse duration, is mainly
dependent on the pulse energy that is applied. The bumps created on
a sputtered disk can be dome-shaped (similar to those formed by a
CO.sub.2 based laser on a raw glass substrate), or quasi-dome
shape, or sombrero-shaped, or even have a V-shape crater in the
center of the bump if the laser pulse energy is increased. The
laser pulse energy can also cause cracking or breakage in the
sputtered layer resulting in other mostly irregular bump
shapes.
[0053] The bump height range of interest for a contact start/stop
zone, the 10-30 nanometer range (or lower), does not require high
laser pulse energy that can damage, or burn through, the sputtered
layers.
[0054] FIG. 3 illustrates a graph of the bump height variation 45
relative to various laser powers 46 (the power curve 47). The bump
height range of practical interest on a sample production disk is
between 10 and 25 nanometers. The graph depicts the power curve for
tested disks having the disclosed sputtered layer structure. The
laser power used to produce the desired bump height is dependent on
the laser beam spot diameter, pulse duration and pulse energy. As
shown, the slope of the curve is not the same at different segments
of the curve. This relates to the fact that the increase in laser
power not only increases the bump height, it also induces changes
in the bump slope and shape.
[0055] FIGS. 4a-4e illustrates the variations in the bumps produced
by the various laser powers. FIG. 4a illustrates a dome-shaped bump
produced by 49.9 micro watts of power. FIG. 4b shows a semi dome
shaped bump produced by 57.5 micro watts of power. The bump
diameter is slightly larger than the dome-shaped bump. FIG. 4c
shows a sombrero-shaped bump produced by 67 micro watts of power
and FIG. 4d illustrates a crater-shaped bump produced by 72.6 micro
watts of power.
[0056] The foregoing process may also be implemented for disk
marking. The disk marking process can be used to produce, but is
not limited to, alphanumeric writing on the sputtered or finished
disk. An example of the disk marking process is the markings used
for distinguishing a good and a defective side of a single-sided
finished disk.
[0057] Referencing FIG. 5, in order to identify the defective side
50 of a one sided finished glass or glass ceramic substrate based
magnetic disk 51, a textured ring 52 or other arbitrary pattern is
produced on the defective side of the finished glass disk. Such a
marked, finished glass disk can be used in a load/unload drive and
not necessarily in a contact start/stop drive. The ring-marking of
a finished glass substrate disk by the application of available
Nd:Vanadate laser, or other near-IR-wavelength lasers, texturing
systems can be produced by the foregoing process.
[0058] Currently, one common practice is to mark a one sided disk
with a pen. With the trend towards increasing volume of one-sided
disks there is a need for a more consistent, lower cost,
non-contaminant, and machine-readable marking system as is
provided. The Nd:Vanadate-laser based texturing systems can be used
to make patterns of rings, ridges and bumps near the inner
diameter.
[0059] Additionally, bar-codes and even alphanumeric characters
could be written on the finished glass substrate magnetic disk
surface, with the use of galvonometer systems, for identifying the
production site for the disk.
[0060] Referring to FIG. 6, in a further embodiment of the present
invention, a reference disk 60 is produced to calibrate flight
height of a transducer head 62 over a magnetic disk. The reference
disk 60 contains a protrusion or a pattern of protrusions 64 which
substantially simulate asperities typically formed on the surface
of magnetic disk. Preferably, a plurality of radially spaced
circumferential rows of protrusions are produced. The protrusions
can be spaced apart either randomly or substantially uniformly in
the radial direction and circumferential directions.
[0061] In a preferred embodiment of the invention, the laser light
beam from a Nd:Vanadate laser is focused on a finished glass or
glass/ceramic substrate based magnetic disk to obtain the array of
protrusions. Preferably, the height of the protrusions is between
12 and 29 nanometers for use in calibrating the flight height. The
process for calibrating transducer heads using such a reference is
well known in the art.
[0062] Glide height calibration bumps made by a Nd:Vanadate laser
texturing tool on a finished disk is superior to corresponding
bumps made by a CO.sub.2 laser on a glass substrate. The
Nd:Vanadate laser provides a more consistent bump height and shape
because the Vanadate laser provides total surface absorption rather
than bulk absorption as provided by a CO.sub.2 based laser.
Furthermore, the Vanadate tool can be used for smaller bump
diameter ranges with less focus sensitivity than a CO.sub.2 laser
based tool. Also, vanadate laser based tools are a preferable
approach for producing glide height test disks since the existing
vanadate laser based tools can be utilized.
[0063] In a further embodiment of the invention, an improved design
for a laser texture tool is shown in FIG. 2 and FIG. 7. The
illustrated cylindrical lens system 70 converts a circular beam 72
into an elliptically shaped laser beam 74 prior to subjecting the
beam to a focusing lens 37 which directs the beam onto the desired
location of the disk surface 30.
[0064] It is advantageous to be able to adjust the shape and
orientation of the laser produced bumps in order to gain a
tribological improvement in a CSS drive. It is also advantageous to
adjust and optimize the contact area between the head and a bump
(protrusion) in a glide height calibration test system. The greater
the contact area, the greater the impulse impact (signal
generation) between the head and bump during the testing
procedure.
[0065] The cylindrical lens assembly 70 (a Keplerian cylindrical
telescope) provides a system for adjusting the size and aspect
ratio of the elliptical beam 74. The size and aspect ratio of the
elliptical beam can be adjusted by altering the distance between
the two cylindrical lenses 76 and 80. In the preferred embodiment a
Keplerian cylindrical telescope is shown. However, it is understood
by those skilled in the art that a Galilean cylindrical telescope
would also provide the same capabilities for re-sizing and
adjusting the laser beam. The cylindrical lens system as shown is
simple to assemble and provides for easy adjustment of the size and
aspect ratio of the elliptical beam.
[0066] The bump axes with respect to the disk radial direction can
be easily adjusted. Preferably, a cylindrical rotator (not shown)
is installed with scale markings (in degrees) to rotate the
telescope and thus the axes of the elliptical laser beam. Using
round shaped cylindrical lenses and simultaneously rotating both
lens axes provides the same advantage as the cylindrical rotator.
Thus the aspect ratio and bump axes direction can be adjusted for
optimized contact start stop operation. Preferably this optical
assembly can be employed in an existing laser texturing tool before
the final focusing lens in order to adjust the shape of the laser
beam entering the focusing lens, and therefore, the shape of the
focused spot size on the disk.
[0067] The circular laser beam 72 enters the first cylindrical lens
76 which elongates the beam. At the focal point 78 for the first
cylindrical lens, the beam is elongated. That is, focussed in one
direction. The beam then passes a second cylindrical lens 80. The
beam exits the second cylindrical lens as an elliptically shaped
laser beam 74. The exit beam 74 is focused in a tight elliptical
spot with an adjustable aspect ratio.
[0068] In general, the aspect ratio and the size of the exit beam
is determined by the focusing power of the two lenses and by the
spacing of the lenses. The direction of the elliptical axis can be
adjusted by rotation of the lenses. In the preferred embodiment,
the first and second cylindrical lenses have the dimensions
required to accommodate a beam diameter of 1 to 6 millimeters.
[0069] FIG. 8 illustrates the resulting elongated bumps on the
surface of the finished glass disk. The area shown is 163
micrometers by 123 micrometers.
[0070] FIG. 9 illustrates a three dimensional view of the central
portion of an elongated bump of FIG. 8. The illustrated bump height
is approximately 14 nanometers. The length of the mainly flat
central portion of the bump is approximately 22 micrometers.
[0071] FIG. 10 illustrates the profile of the elongated bump along
the short axis A of FIG. 9. FIG. 11 illustrates the profile of the
elongated bump along the central portion of the long axis B of FIG.
9. FIGS. 10 and 11 provide a cross sectional illustration of the
bump shape as seen in axis A of FIG. 9. The bump profile along the
short axis A could be dome shaped, semi-dome shaped, or sombrero
shaped. The various shapes have advantageous applications for CSS
disks and glide height calibration testing.
[0072] FIG. 12 illustrates a graph of bump height variation versus
laser power for elongated bumps. The bump heights range from 8
nanometers to 18 nanometers using a range of laser power between
550 and 670 arbitrary units.
[0073] While elliptical shaped bumps may also be produced by using
other optical components, this system and method is an efficient
and versatile way of producing the elliptical bumps.
[0074] The invention has been described with particularity as to
preferred embodiments. Those skilled in the art will know that
variations are possible that do not depart from the spirit and
scope of the invention. Accordingly the invention is limited only
by the following claims.
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