U.S. patent application number 09/920013 was filed with the patent office on 2002-02-21 for disk medium.
Invention is credited to Bar-Gadda, Ronny.
Application Number | 20020022198 09/920013 |
Document ID | / |
Family ID | 22573028 |
Filed Date | 2002-02-21 |
United States Patent
Application |
20020022198 |
Kind Code |
A1 |
Bar-Gadda, Ronny |
February 21, 2002 |
Disk medium
Abstract
A disk medium includes a substrate and a designed topography of
individually magnetizable features formed on the surface of the
substrate. At least a portion of the topography is formed from an
etched layer of magnetizable material deposited on the surface of
the substrate. An information handling system records information
on the disk medium magnetically and reads the recorded information
optically or magnetically.
Inventors: |
Bar-Gadda, Ronny; (Palo
Alto, CA) |
Correspondence
Address: |
Robert E. krebs
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
22573028 |
Appl. No.: |
09/920013 |
Filed: |
August 2, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09920013 |
Aug 2, 2001 |
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09017698 |
Feb 3, 1998 |
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6309802 |
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09017698 |
Feb 3, 1998 |
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08159552 |
Dec 1, 1993 |
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5768075 |
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09017698 |
Feb 3, 1998 |
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07808867 |
Dec 17, 1991 |
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Current U.S.
Class: |
430/320 ;
428/848.2; 430/945; G9B/11.01; G9B/11.047; G9B/11.048; G9B/5;
G9B/5.231; G9B/5.288; G9B/5.293; G9B/5.299; G9B/5.306 |
Current CPC
Class: |
G11B 5/6005 20130101;
G11B 11/10584 20130101; G11B 5/82 20130101; G11B 5/00 20130101;
G11B 5/855 20130101; G11B 11/10582 20130101; G11B 5/8404 20130101;
G11B 5/73921 20190501; B82Y 10/00 20130101; G11B 5/743 20130101;
G11B 11/10502 20130101 |
Class at
Publication: |
430/320 ;
430/945; 428/65.3; 428/65.7 |
International
Class: |
B32B 003/02 |
Claims
What is claimed is:
1. A method for handling information, comprising the steps of:
etching a designed topography in a disk; forming individually
magnetizable features on the disk, the features corresponding to
the designed topography; and storing information on the disk by
selectively changing a magnetic state of individual ones of the
features.
2. The method as set forth in claim 1, comprising the further step
of reading the stored information by detecting the magnetic state
of the features.
3. The method as set forth in claim 2, wherein the magnetic state
of the features is detected by determining effects of the features
upon a beam of light.
4. The method as set forth in claim 3, wherein the magnetic state
of the features is detected by determining whether the features
alter a polarization angle of the beam of light.
5. The method as set forth in claim 3, wherein the beam of light is
a reflected beam.
6. The method as set forth in claim 3, wherein the beam of light is
transmitted through the features on the disk.
7. The method as set forth in claim 2, wherein the magnetic state
of the features is detected by a magnetic head.
8. The method as set forth in claim 1, wherein, prior to etching, a
pattern is transferred onto the disk by a contact method and is
developed thereon.
9. The method as set forth in claim 1, wherein, prior to etching, a
pattern is transferred onto the disk by a projection method and is
developed thereon.
10. The method as set forth in claim 1, wherein the disk includes
an exterior disk surface having a designed R.sub.a, the method
comprising the further steps of forming an air bearing at the
exterior disk surface by rotating the disk so that aerodynamic
effects characteristic of the R.sub.a are developed at the exterior
disk surface, and suspending at least one of means for selectively
magnetizing the features and means for detecting a magnetic state
of the features at a distance from the exterior disk surface with
the air bearing.
11. The method as set forth in claim 1, wherein the disk includes
an exterior disk surface, and magnetizing means for selectively
magnetizing the features selectively change the magnetic state of
individual ones of the features, and detecting means for detecting
a magnetic state of the features detect a magnetic state of the
features, the method comprising the further steps of stopping and
starting rotation of the disk relative to a contacting means that
contacts the exterior disk surface as rotation of the disk is
started and stopped, the contacting means including at least one of
the magnetizing means and the detecting means, and wherein the
designed topography is etched to control a C.sub.f between the
exterior disk surface and the contacting means.
12. The method as set forth in claim 1, wherein the features are
formed by filling recesses etched in the disk with magnetizable
material.
13. The method as set forth in claim 1, wherein the features are
formed by etching the desigened topography in magnetizable material
on the disk.
14. A disk medium, comprising: an etched, designed topography in a
disk; and individually magnetizable features formed on the disk and
corresponding to the designed topography.
15. The disk medium as set forth in claim 14, wherein the features
are separated from one another by non-magnetic material.
16. The disk medium as set forth in claim 14, wherein the features
reflect light.
17. The disk medium as set forth in claim 14, wherein the features
transmit light.
18. The disk medium as set forth in claim 14, wherein the disk
includes a substrate, the substrate including at least one material
selected from the group consisting of ceramic, polycarbonate,
silicon, glass, and carbon materials.
19. The disk medium as set forth in claim 14, wherein the features
include magnetizable material, the magnetizable material including
a layer of chromium and a layer of material selected from the group
consisting of NiCoCr, PtCoCr, Fe, and Co deposited over the layer
of chromium.
20. The disk medium as set forth in claim 14, wherein the features
include magnetizable material, the magnetizable material including
a layer of material selected from the group consisting of NiCoCr,
PtCoCr, Fe, and Co.
21. The disk medium as set forth in claim 14, further comprising
means for facilitating data retrieval.
22. The disk medium as set forth in claim 21, wherein the data
retrieval facilitating means include additional designed features
formed on the disk.
23. The disk medium as set forth in claim 22, wherein the
additional designed features include track identification
features.
24. The disk medium as set forth in claim 14, further comprising an
exterior disk surface having a designed R.sub.a.
25. The disk medium as set forth in claim 24, wherein the designed
R.sub.a is characteristic of the designed topography.
26. The disk medium as set forth in claim 14, wherein the designed
topography includes recesses etched in the disk and the features
include magnetizable material filled in the recesses.
27. The disk medium as set forth in claim 14, wherein the features
include magnetizable material etched to form the designed
topography.
28. A memory system. comprising: a disk medium including an etched,
designed topography in a disk and individually magnetizable
features formed on the disk and corresponding to the designed
topography; means for magnetizing individual ones of the features;
and means for detecting the magnetic state of the features.
29. The memory system as set forth in claim 28, wherein the
magnetizing means includes a magnetic head assembly.
30. The memory system as set forth in claim 28, wherein the
detecting means includes a magnetic head assembly.
31. The memory system as set forth in claim 28, wherein the
detecting means includes an optical head assembly.
32. The memory system as set forth in claim 31, wherein the optical
head assembly includes means for determining effects of the
features on a beam of light.
33. The memory system as set forth in claim 32, wherein the effects
determining means determine effects of the features on polarity of
the beam of light.
34. The memory system as set forth in claim 28, further comprising
means for rotating the disk medium.
35. The memory system as set forth in claim 34, wherein the disk
medium has an exterior disk surface having a designed R.sub.a.
36. The memory system as set forth in claim 35, wherein the
designed R.sub.a is characteristic of the designed topography.
37. The memory system as set forth in claim 35, wherein rotation of
the disk medium by the rotating means causes an air bearing to form
at the exterior disk surface that is characteristic of the designed
R.sub.a.
38. The memory system as set forth in claim 37, wherein the air
bearing suspends at least one of the magnetizing means and the
detecting means at a distance above the exterior disk surface that
is characteristic of the designed R.sub.a.
39. The memory system as set forth in claim 34, wherein, during
starting and stopping of rotation of the disk medium, an exterior
disk surface of the disk medium is contacted by contacting means
including at least one of the magnetizing means and the detecting
means, and wherein the disk exterior surface and the contacting
means have a designed C.sub.f.
40. The memory system as set forth in claim 39, wherein the
designed C.sub.f is characteristic of the designed topography.
41. A method for making a disk medium, comprising the steps of:
etching a designed topography in a disk; and forming individually
magnetizable features on the disk, the features corresponding to
the designed topography.
42. The method as set forth in claim 41, wherein the features are
formed by filling recesses etched in the disk with magnetizable
material.
43. The method as set forth in claim 41, wherein the features are
formed by etching the designed topography in magnetizable material
on the disk.
44. The method as set forth in claim 41, comprising the further
step of forming a designed R.sub.a on an exterior surface of the
disk by controlling the etching of the designed topography.
Description
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 07/808,867, filed Dec. 17, 1991.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates Generally to disk media.
[0004] 2. State of the Art
[0005] Magnetic disk drive assemblies as used for mass data storage
in computers and electronic systems today comprise either rigid
("hard") disk drives or flexible ("floppy") drives. Both types of
drives incorporate low cost data storage capacity with rapid
recovery of stored data. This rapid availability of stored data is
a function of the rotational speed of the disk relative to the
read/write transducer as well as the proximity of the transducer to
the magnetic medium. In practice, a read/write transducer is
mounted in a head assembly that accurately follows the surface of a
disk at flying, heights of less than 1 micron. In particular, the
head suspension assemblies are designed to prevent contact between
the read/write head and the magnetic recording medium during,
operation: such contact, called head crash, can destroy a
read/write head and the magnetic medium in a short time due to the
friction that results from the high rotational speed of the disk
relative to the head. Although current technology provides
lubrication and protective layers on the disk, these measures are
generally intended to compensate only for transient friction events
during stop/start cycles.
[0006] In general, control of the texture characteristics of the
disk surface is required to reduce the substantial attractive
forces that are generated between the read/write head and the
stationary disk surface. Smoother disk surface textures result in
higher attractive forces that prevent proper head liftoff and
flying characteristics when disk rotation is commenced. Current
disk manufacturing techniques must also assure that the disk
surface roughness does not exceed certain upper-bound values; if
excessive surface roughness results from the texturing process,
undesirable increases in flying height also limit the density with
which data can be stored on the disk. A central issue in current
disk texturing processes is the reliability and consistency with
which the desired surface roughness is obtained. The disk surface
texture is typically characterized in terms of an arithmetic
average roughness value (R.sub.a). Current disk texturing processes
generally produce R.sub.a values in the range of 10-200 nm; the
most modern disk drives achieve head flying heights of 0.2-0.3
microns with R.sub.a values of approximately 10-50 nm. These
texturing processes utilize special abrasives for producing
circumferential patterns of scratches on the surface of metallic
(predominantly aluminum) disk substrates which inevitably create
surface feature extremes in the form of peaks and valleys. U.S.
Pat. Nos. 4,996,622, 4,939,614 and 4,931,338 describe variations of
this general process. Several of these patents propose different
textures for separate areas of the disk optimized for stop/start
operations and for read/write operations. These patents document
the difficulty of obtaining low flying heights (i.e., less than 0.3
microns) while simultaneously achieving acceptably low head/disk
attractive forces with current disk texturing processes.
[0007] Other texturing processes combine abrasive texturing
processes with chemical processes. For example, U.S. Pat. No.
4,985,306 describes a recording disk produced by subjecting a base
plate containing S.sub.iO.sub.2--Li.sub.2O--Al.sub.2O.sub.3 series
crystallized glass to crystallizing treatment, polishing the
surface of the base plate to attain a surface roughness of 15 .ANG.
to 50 .ANG. to evenly distribute, regularly and two-dimensionally,
very fine and uniform crystal grains in the amorphous layer. The
base plate is then etched with an etchant having different degrees
of dissolution with respect to the crystal grains and the amorphous
layer to form uniform and regular convexities and concavities on
the surface of the base plate. A magnetic film and a protective
layer are applied over the base plate. Because the system described
in this patent relies on an abrasive texturing process for
distributing crystal grains, there is an inevitable randomness to
the ultimate distribution of concavities and convexities.
[0008] The trend toward smaller diameter disks has also presented
difficulties for prior-art manufacturing techniques. It has become
progressively more difficult to achieve the required consistency in
R.sub.a values and in disk flatness with decreasing disk diameter
using conventional methods. Disk flatness variations cause axial
runout of the read/write head during disk rotation. In current disk
drives it is desirable to maintain this axial runout value at less
than 1-2 microns. Conventional abrasive texturing techniques
applied to current metallic disk substrates are becoming less
viable as disk diameters are progressing downwards.
[0009] The trend toward smaller diameter, higher density disks has
made optical information storage technology a more attractive
alternative for the future. Optical disks are typically made by
first coating a thin layer of photosensitive material such as a
thin metal film on one side of a glass disk. A laser beam is
chopped by an electro-optic modulator to which a frequency
modulated digital signal corresponding to the input information,
such as an analog signal, is applied. The laser beam is focused
onto the disk as it is rotated and the information is recorded as a
series of pits in the thin metal film.
[0010] Reading of optical disks can be accomplished in several
ways. For example, in a Video High Density Disk System (VHD),
reading is accomplished by an electrode on a stylus that slides
along the surface of the disk. Signals recorded on the disk are
picked up as capacitance variations between the disk surface and
the electrode on the stylus. In other systems, however, such as
Video Long Play Systems, a low-power laser beam is focused on a
small read spot on the surface of the disk. Optical energy is
reflected by (or transmitted through) the disk and directed to a
photodetector. The energy received at the photodetector changes
according to the presence or absence of pits recorded on the disk.
The received energy is processed by further electronic circuitry,
such as by being processed into digitized form, and then into
output signals.
[0011] While optical disks offer the advantage of recording large
amounts of information in a small space, optical information
storage technology suffers from certain disadvantages. For example,
since information is normally stored on an optical disk by the heat
of a laser beam causing the thin metal film over the substrate to
develop pits, optical disks suffer the disadvantage of not being
inherently erasable. Further, the technique of forming pits in the
thin metal film by means of a laser involves heating the film to a
higher temperature to affect the grain structure of the film. Bit
errors resulting from factors such as changes in ambient
temperature are common and have been a primary factor in limiting
commercial application of optical technology beyond fields in which
bit error rate is not highly critical. Accordingly, it is desirable
to provide an information storage system coupling the advantages of
optical systems, such as high density recording, with an erasable
medium that is not subject to error due to changes in ambient
temperatures.
SUMMARY OF THE INVENTION
[0012] The present invention, generally speaking, provides a disk
medium possessing the capacity to magnetically store large amounts
of information. The magnetically stored information is readable, in
accordance with one embodiment of the invention, by a magnetic head
assembly, or, in accordance with another embodiment of the
invention, by an optical head assembly.
[0013] The present invention provides a disk medium that is formed,
by the processes generally associated with the shaping of layers in
semiconductor chip products, to have great capacity to store
information. A pattern of designed, individually magnetizable
features is formed on a substrate, the features corresponding to
individual bits of information. The features are physically
separated from one another by non-magnetic material, thereby
minimizing certain problems associated with magnetic information
storage systems. Particularly, the effects of crosstalk between
adjacent magnetic "bits" are minimized, such as the need to
maintain head flying heights as low as possible in order to
magnetically read and write on a disk on which large quantities of
information can be stored is reduced and the need to use high
coercivity magnetic materials for forming the magnetizable features
in order to store large amounts of information on the disk is
reduced.
[0014] Reading of information stored on the disk medium may be
accomplished with an optical head assembly by focussing a laser
beam on the disk, reflecting the beam off of or transmitting the
beam through the disk and the individual features on the disk, and
detecting the reflected or transmitted beam with means such as a
photodetector which detects whether the individual features are
magnetized or not as a function of magneto-optical effects
occurring as a result of the laser beam passing through the
magnetic or non-magnetic field of the individual features. Because
information recording or writing on the disk medium can be
performed with a magnetic head assembly and reading can be
performed by an optical head assembly, the disk medium of the
present invention does not suffer from disadvantages of
conventional optical memory storage systems including high bit
error rates due to factors such as changes in surrounding
temperatures.
[0015] The present invention further provides a disk medium that,
in one embodiment, contacts a magnetic head with a low coefficient
of friction, provides smooth and stable travel performance in
conjunction with a magnetic head for prolonged periods of time, has
improved wear resistance in use and stability in storage
environments, and is capable of consistent reproduction. In
practice, a magnetic disk medium according to the present invention
optimizes operational conditions in a system for reading
information stored on the magnetic disk medium. Surface roughness
characteristics of the magnetic disk medium are controlled by the
processes generally associated with the shaping of layers in
semiconductor chip products. These processes permit formation of
disks having an average surface roughness that creates particular
aerodynamic effects when the disk is rotated at particular speeds,
the aerodynamic effects being useful for suspending a magnetic head
at a desired flying height above the surface of the disk during
read/write operations. The same processes permit control of surface
characteristics relating to friction effects between the disk
surface and a magnetic head during start-up and stopping of
rotation of the disk. Information storage density characteristics
of the magnetic disk medium may be raised to substantially whatever
density is capable of being written on or read by a magnetic head
of a magnetic disk assembly, the limits on the readable density
being primarily those associated with conventional apparatus
operational conditions, many of which, such as magnetic head flying
height, are controllable through optimization of surface roughness
characteristics of the magnetic disk medium of the present
invention. Further, the magnetic disk medium is readable by fixed
head assemblies.
[0016] The magnetic disk medium according to an embodiment of the
present invention is textured without relying on known abrasive
techniques. The texturing is controlled, and is therefore less
susceptible to random variations of known texturing methods. There
is, consequently, a consistently reproduced disk manufactured with
the above method. Because the flying height of a magnetic head can
be set at a known, lower height than in systems using disks
manufactured by known methods, and because transient friction
events can be minimized, the disk produced by a method according to
the present invention is capable of storing information with a
greater density than in known disks.
[0017] In accordance with one aspect of the present invention, a
method for handling information is described. In the method, a
designed topography is etched in a disk. Individually magnetizable
features are formed on the disk, the features corresponding to the
designed topography. Information is stored on the disk by
selectively changing a magnetic state of individual ones of the
features.
[0018] In accordance with another aspect of the invention, a disk
medium an etched. designed topography in a disk, and individually
magnetizable features formed on the disk and corresponding to the
designed topography.
[0019] In accordance with another aspect of the invention, a memory
system includes a disk medium including an etched, designed
topography in a disk and individually magnetizable features formed
on the disk and corresponding to the designed topography. Means are
provided for magnetizing individual ones of the features and means
are provided for detecting the magnetic state of the features.
[0020] In accordance with yet another aspect of the present
invention, a method for making a disk medium includes the steps of
etching a designed topography in a disk and forming individually
magnetizable features on the disk, the features corresponding to
the designed topography.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] The present invention can be further understood with
reference to the following description in conjunction with the
appended drawings, wherein like elements are provided with the same
reference numerals. In the drawings:
[0022] FIG. 1A is a cross-sectional schematic view of a portion of
an unetched disk according to an embodiment of the present
invention, and FIGS. 1B and 1C are cross-sectional schematic views
of the portion of a disk according to FIG. 1A after etching;
[0023] FIG. 2A is a cross-sectional schematic view of a portion of
a disk etched to form a topography including recesses in a
substrate according to an embodiment of the present invention, and
FIGS. 2B-2D are cross-sectional schematic views of a disk including
the portion of the disk according to FIG. 2A after filling the
recesses with magnetizable material:
[0024] FIG. 3 is a perspective schematic view of a portion of a
surface of a disk according to an embodiment of the present
invention:
[0025] FIGS. 4A and 4B are top, plan schematic views of portions of
disks according to embodiments of the present invention;
[0026] FIG. 5 is a schematic view of an information recording
system and magnetic reading assembly including a suspended head for
recording and reading information on a disk according to an
embodiment of the present invention; and
[0027] FIGS. 6A and 6B are schematic views of optical reading
assemblies for reading a disk according to embodiments of the
present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] A disk medium 21 according to an embodiment of the present
invention is shown in FIG. 1A. The disk medium 21 is made up of a
substrate 23 which is non-magnetic and well-known and is in the
form of, for example, a chemically etchable glass layer over a
ceramic disk, or a polycarbonate disk, or other appropriate
materials, such as glass, silicon, carbon, etc. The substrate 23 in
FIG. 1A is coated with a thin layer of magnetizable material 25.
The magnetizable material 25 is also well-known, and is in the form
of, for example, a layer of NiCoCr, PtCoCr, Fe, or Co deposited on
the surface 27 of the substrate 23 or over layer of chromium
deposited on the surface of the substrate, chromium being
understood to particularly facilitate increasing information
storage density.
[0029] A pattern or mask for forming an etched, designed topography
29 to be etched in the magnetizable material 25 or the magnetizable
material 25 and the substrate 23 is designed and generated. The
pattern is transferred onto the magnetizable material 25 by known
methods, such as by contact or projection methods. The pattern is
developed onto the surface 33 of the magnetizable material 25. The
developed pattern is then etched into the magnetizable material 25,
as seen in FIG. 1B, or into the magnetizable material and the
substrate 23, as seen in FIG. 1C, to form the topography 29.
[0030] As the designed topography 29 is etched into the
magnetizable material 25 (and, if desired, the substrate 23)
individual magnetizable features 31 separated from one another by
the non-magnetic substrate are formed. Accordingly, the features 31
correspond to the designed topography 29. The features 31 may be in
any desired, preferably easily reproducible, form. such as the
offset and aligned squares shown in FIGS. 3 and 4A. respectively,
or the hexagons shown in FIG. 4B, or in the form of circles (not
shown), etc.
[0031] The features 31 of the disk medium 21 are preferably
arranged in a series of substantially circular tracks 34
(identified by dashed, annular lines on the disk 21 shown in FIG.
5) and the topography 29 preferably further includes additional,
designed track identification features 35 at desired points.
Annular track identification features 35 are shown in cross-section
in FIGS. 1B-1C as enlarged magnetizable features, however, track
identification features can be provided in any appropriate
form.
[0032] After formation of the topography 29, a layer of a material
such as a protective coating 37 is preferably applied over the
exposed surface 27 of the substrate 23 and the exposed surfaces 33
of the features 31 formed from the magnetizable material 25. The
protective coating 37 is known, and is preferably a hard protective
material such as a SiN, SiC, SiO.sub.2, or C material and/or a soft
protective material such as a chlororluorocarbon (CFC)
material.
[0033] FIG. 2A shows another embodiment of a substrate 23' similar
to the substrate 23 of the disk medium 21 and FIGS. 2B-2D show
another embodiment of a disk medium 21' including the substrate
23'. A pattern or mask for forming an etched, designed topography
29' to be etched on the surface 27' of the substrate 23' is
designed and generated. The pattern is transferred onto the
substrate 23' by known methods. The pattern is developed onto the
surface 27' of the substrate 23'. The pattern is then etched into
the substrate 23', as seen in FIG. 2A, to form a topography 29'
including recesses in the surface 27' of the substrate.
[0034] Magnetizable material 25' is deposited on the surface 27' of
the substrate 23' to fill (FIG. 2B), partially fill (FIG. 2C), or
over-fill (FIG. 2D) the recesses with magnetizable material and
form individually magnetizable features 31' corresponding to the
designed topography 29'. For example, the features 31' may be
formed by depositing magnetizable material over the entire surface
27' of the substrate 23' and separating the features from other
ones of the features by chemically etching away any magnetizable
material that is deposited on the non-recessed portions of the
surface 27' of the substrate. If necessary, the deposited
magnetizable material 25' for forming the recessed features 31 ' is
masked prior to etching. The features 31' are also preferably in
easily reproducible forms. such as circles, squares, hexagons,
etc.
[0035] The features 31' of the disk medium 21' are also preferably
arranged in a series of tracks and the topography 29' preferably
further includes track identification features 35' at desired
points. After formation of the topography 29', a protective coating
37' is preferably applied over the exposed surface 27' of the
substrate 23' and the exposed surfaces 33' of the features 31'.
[0036] Information recording systems 39 and 39' for use in
conjunction with either one of the disk media 21 or 21' are shown
in FIGS. 5 and 5B, respectively. The information recording systems
39 and 39' are described in conjunction with the disk medium 21 by
way of example. In the system 39 shown in FIG. 5, the disk medium
21 is rotated, as in conventional disk apparatuses, by a known
driver 41. Information is recorded on the disk medium 21 by a
magnetic head 43 which selectively magnetizes individual ones of
the features 31. Each feature 31 thereby corresponds, in effect, to
an individual bit of information.
[0037] As noted above, the features 31 formed from the magnetizable
material 25 are preferably physically separated from one another as
a result of the etching process. The nonmagnetic material of the
substrate 23 surrounds the features 31 and, because the features
are discrete, unlike in conventional magnetic disks, problems
associated with interfering, adjacent magnetic fields are
minimized. Particularly, the discrete features 31 permit reduction
of the crosstalk that occurs in conventional magnetic disks that
makes low magnetic head flying heights and high coercivity thin
films necessary and limits magnetic disk storage capacity.
[0038] As a consequence of the physical separation of the
individual features 31 by the non-magnetic material of the
substrate 23, high coercivity magnetizable material 25 is less
necessary in the disk medium 21 of the present invention than in
conventional disks. Further, because of less interference, the need
to minimize magnetic head flying heights during read/write
operations is less necessary. Nonetheless, features of the present
invention such as the physical separation of the individual
features and the ability to control surface roughness
characteristics on the disk media of the present invention through
control of the etching process facilitate increasing information
storage density on the disk medium. The reduced interference
facilitates the use of higher coercivity magnetizable materials and
the high degree of regularity of surface features that can be
achieved on the disk media of the present invention facilitates
lowering head flying heights. As in conventional disks, the use of
such higher coercivity materials and/or lower head flying heights
facilitates increasing information storage density.
[0039] The information stored on the disk media 21 or 21' in the
manner described above is preferably readable by an optical read
system 45 such as is shown in FIG. 6A. In the optical read system
45, which is preferably provided in a single apparatus with the
information recording system 39 or 39', the disk medium 21 is
rotated by the driver 41. The optical read system 45 further
includes a known laser beam generating assembly 47 for focusing a
laser beam L on a read spot on the surface 49 of the disk medium
21. The laser beam L is reflected off of the surface 49 of the disk
medium 21 and directed to a photodetector 51. Alternatively, as
shown in FIG. 6B, the laser beam L may be transmitted through the
disk medium 21 and directed to the photodetector 51.
[0040] Using the embodiment depicted in FIG. 6A for discussion
purposes, when the laser beam L passes through the magnetic field M
of the features on the disk medium 21 that have been magnetized,
magneto-optic effects alter the polarization angle of the laser
beam. For example, the Faraday effect, whereby the plane of
polarization of light is rotated when light traverses a substance
in a magnetic field, can be used to detect the presence or absence
of magnetization of each of the features by the photodetector 51 as
a result of the altered or unaltered polarization angle of the
laser beam L. For example, if a polaroid 53 is provided in the path
of the laser beam L prior to its incidence on the disk medium 21
and the laser beam is plane polarized in one plane, and a second
polaroid 55 is provided in the path of the laser beam between the
disk medium and the photodetector 51 so that the laser beam
transmits through the second polaroid only in its unaltered (or,
alternatively, only in its altered) state, the photodetector will
detect the absence (or presence) of magnetization of a feature.
[0041] When a feature is magnetized, the plane of polarization of
the laser beam L is rotated, the plane polarized laser beam is not
transmitted through the second polaroid 55, and the laser beam is
not detected by the photodetector. Electronic circuitry 57 is
provided to process the information read in the form of detected
and undetected laser beams. As noted above, the preferred example
of an optical read system just discussed uses the Faraday
magneto-optic effect to read information stored on the disk medium
21. One of ordinary skill in the art will appreciate that other
magneto-optic effects, such as the Kerr and Pockels effects, can be
used in an analogous manner to detect whether a feature is
magnetized or not.
[0042] With reference to FIG. 5, the magnetic head 43 of the
information recording system 39 may also be used to read recorded
information on the disk medium 21 in a conventional manner. As
noted above, because the features 31 of the topography 29 are
preferably surrounded by the non-magnetic material of the substrate
23, problems associated with crosstalk in magnetic information
read/write systems are minimized.
[0043] In a system including means, such as the driver 41, for
rotating the disk medium 21 at a predetermined rotational speed and
utilizing a magnetic head 43, such as the magnetic information
reading system and magnetic information recording system 39 shown
in FIG. 5, when rotation of the disk is stopped, the magnetic head
43 generally rests on the surface 49 of the disk medium 21.
Ordinarily, the magnetic head 43 is suspended relative to the disk
medium by movable suspension means 59 such as a known suspension
arm.
[0044] In magnetic read/write apparatuses having movable heads,
such as the magnetic head 43 suspended by the suspension, arm 59 of
the apparatus 39 shown in FIG. 5, it is desirable to maintain a
particular magnetic head 43 flying height. The etching of the
magnetic material and/or the substrate to form the etched, designed
topography of the disk media 21 and 21' is preferably controlled so
that the exterior surfaces of the disk media are provided with a
designed R.sub.a characteristic of the designed topography. As, for
example, the disk medium 21 is rotated by the driver 41,
aerodynamic effects at the surface 49 of the disk medium create an
air bearing characteristic of the designed R.sub.a. The air bearing
is preferably capable of suspending the magnetic head 43 at a
characteristic flying height above the surface 49 of the disk
medium. Thus, the head flying height is characteristic of the
designed topography 29 and control of the etching process. A
designed topography of features in a disk medium for optimizing
operational characteristics such as head flying heights in a
magnetic information storage system is disclosed in U.S. patent
application Ser. No. 07/808,867, the disclosure of which is hereby
incorporated by reference.
[0045] Further, where movable head devices, such as the magnetic
head device shown in FIG. 5, contact the disk media 21 and 21'
during starting and stopping of rotation of the disk media it is
desirable to reduce transient friction events which tend to damage
the disk media and the head devices. A coefficient of friction
C.sub.f characteristic of the surface of the disk media, for
example the surface 49 of the disk medium 21, in contact with the
contacting head is preferably designed to minimize such transient
friction events. The etching of the magnetic material and/or the
substrate to form the etched, designed topography of the disk
medium 21 is preferably controlled so that the exterior surface 49
of the disk medium in contact with a particular head surface has a
designed C.sub.f characteristic of the designed topography. Like
the disk medium 21, the disk medium 21' shown in FIGS. 2B-2D can be
formed to achieve desired R.sub.a and C.sub.f values for optimizing
head flying heights and controlling and minimizing adverse friction
effects. The disk medium 21' particularly facilitates minimizing
adverse transient friction events between the disk surface and
contacting members such as a movable head because the surface of
the disk medium can be made almost perfectly smooth. Known etching
processes are capable of producing highly regular surfaces, and
permit lowering head flying heights to levels limited substantially
only by designed topographical features.
[0046] The designed R.sub.a and C.sub.f values are preferably
obtained by controlling factors such as the size and frequency of
recesses and protrusions etched to form the topography of the disk
media. Such factors are preferably controlled by controlling the
topography etching process. Accordingly, the features 31 on the
disk medium 21 corresponding to the topography 29, shown in the
embodiments of FIGS. 1B and 1C, are formed, by etching the
magnetizable material 25 and if desired, the substrate 23, to be of
a desired area, height, and frequency corresponding to designed
R.sub.a and C.sub.f values. Similarly, the features 31' on the disk
medium 21' corresponding to the topography 29', shown in the
embodiments of FIGS. 2B-2D, are formed, by etching the substrate
23' and filling the etched recesses with magnetizable material 25',
to be of a desired height or depth, and a desired area and
frequency corresponding to designed R.sub.a and C.sub.f values. In
both instances, optimal roughness and frictional characteristics of
the disk media are preferably obtained by at least lengthening or
shortening the etching process. In both instances, optimal
roughness and frictional characteristics may further be obtained as
a function of the amount of magnetizable material deposited on the
surface of the substrate, either before etching, as in the
embodiments of FIGS. 1B-1C, or after etching, as in the embodiments
of FIGS. 2B-2D.
[0047] It is contemplated that, if the features 31 are sized at 1
micron and the interfeature spacing is 1 micron, a disk medium
according the present invention will provide the capacity to record
600 Megabytes of information.
[0048] The foregoing has described the principles, preferred
embodiments and modes of operation of the present invention.
However, the invention should not be construed as limited to the
particular embodiments discussed. Instead, the above-described
embodiments should be regarded as illustrative rather than
restrictive, and it should be appreciated that variations may be
made in those embodiments by workers skilled in the art without
departing from the scope of present invention as defined by the
following claims.
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