U.S. patent application number 16/882843 was filed with the patent office on 2020-11-12 for embedded disconnected circuits in magnetic storage media of data storage devices.
This patent application is currently assigned to Western Digital Technologies, Inc.. The applicant listed for this patent is Western Digital Technologies, Inc.. Invention is credited to Sridhar CHATRADHI, Jordan A. KATINE, Bernd LAMBERTS, Pankaj MEHRA.
Application Number | 20200357435 16/882843 |
Document ID | / |
Family ID | 1000005178532 |
Filed Date | 2020-11-12 |
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United States Patent
Application |
20200357435 |
Kind Code |
A1 |
MEHRA; Pankaj ; et
al. |
November 12, 2020 |
EMBEDDED DISCONNECTED CIRCUITS IN MAGNETIC STORAGE MEDIA OF DATA
STORAGE DEVICES
Abstract
Disclosed herein are magnetic storage media with embedded
disconnected circuits, and magnetic storage systems comprising such
media. A magnetic storage media comprises a recording layer
comprising a storage location, and an embedded disconnected circuit
(EDC) configured to assist in at least one of writing to or reading
from the storage location in response to a wireless activation
signal. A magnetic storage system comprises a signal generator
configured to generate a wireless activation signal, a magnetic
storage media with a plurality of storage locations, and a write
transducer and/or a read receiver. The magnetic storage media has
at least one EDC configured to assist in writing to and/or reading
from at least one of the plurality of storage locations in response
to the wireless activation signal.
Inventors: |
MEHRA; Pankaj; (San Jose,
CA) ; LAMBERTS; Bernd; (San Jose, US) ;
CHATRADHI; Sridhar; (San Jose, CA) ; KATINE; Jordan
A.; (Mountain View, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Western Digital Technologies, Inc. |
San Jose |
CA |
US |
|
|
Assignee: |
Western Digital Technologies,
Inc.
San Jose
CA
|
Family ID: |
1000005178532 |
Appl. No.: |
16/882843 |
Filed: |
May 26, 2020 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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16018360 |
Jun 26, 2018 |
10672425 |
|
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16882843 |
|
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62525272 |
Jun 27, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11B 5/4976 20130101;
G11B 5/82 20130101; G11B 5/746 20130101; G11B 5/4886 20130101; G11B
5/66 20130101; G11B 5/667 20130101 |
International
Class: |
G11B 5/66 20060101
G11B005/66; G11B 5/74 20060101 G11B005/74; G11B 5/82 20060101
G11B005/82; G11B 5/49 20060101 G11B005/49; G11B 5/48 20060101
G11B005/48 |
Claims
1-46. (canceled)
47. A method of using an embedded disconnected circuit (EDC)
embedded entirely within an EDC layer of a magnetic storage media
to read a storage location in a recording layer of the magnetic
storage media, the EDC layer being situated above or below the
recording layer, the EDC being disconnected from the storage
location, the method comprising: a signal generator transmitting a
wireless activation signal; the EDC receiving the wireless
activation signal; the EDC determining a contents of the storage
location in response to receiving the wireless activation signal;
and the EDC transmitting a read response signal indicating the
contents of the storage location.
48. The method of claim 47, wherein transmitting the wireless
activation signal comprises directing the wireless activation
signal toward the EDC.
49. The method of claim 47, wherein the wireless activation signal
comprises a read command.
50. The method of claim 47, further comprising the signal generator
configuring an aspect of the wireless activation signal based on an
identity of the EDC.
51. The method of claim 50, wherein the aspect of the wireless
activation signal is a frequency, a modulation, an amplitude, a
duty cycle, or a bandwidth.
52. The method of claim 47, further comprising: the EDC
constructing the read response signal.
53. The method of claim 52, wherein a format of the read response
signal is dependent on one or more of: an identity of the EDC, an
identity of the storage location, a location of the EDC, or a
location of the storage location.
54. The method of claim 47, further comprising: a read receiver
receiving the read response signal.
55. The method of claim 54, wherein the read response signal is
included in an aggregate received signal, and wherein the read
receiver receiving the read response signal comprises the read
receiver receiving the aggregate received signal, and further
comprising: the read receiver extracting an indication of the
contents of the storage location from the aggregate received
signal.
56. The method of claim 54, further comprising: the read receiver
extracting an indication of a location or identity of the storage
location from the read response signal.
57. The method of claim 54, further comprising: the read receiver
extracting an indication of a location or identity of the EDC from
the read response signal.
58. The method of claim 57, wherein extracting the indication of
the location or identity of the EDC comprises inspecting a
header.
59. The method of claim 57, wherein extracting the indication of
the location or identity of the EDC comprises detecting a format of
the read response signal.
60. The method of claim 57, wherein extracting the indication of
the location or identity of the EDC comprises using
triangulation.
61. The method of claim 54, further comprising the read receiver
adjusting a configuration of the read receiver based on a location
or identity of the EDC.
62. The method of claim 61, wherein adjusting the configuration of
the read receiver comprises tuning a receive circuitry to a
specified frequency.
63. The method of claim 61, wherein adjusting the configuration of
the read receiver comprises configuring an aspect of the read
receiver based on an expected pattern or modulation
characteristic.
64. The method of claim 47, wherein a characteristic of the read
response signal provides an indication of one or more of: a
location of the storage location, an identity of the storage
location, a location of the EDC, or an identity of the EDC.
65. The method of claim 64, wherein the characteristic is a
frequency.
66. The method of claim 64, wherein the characteristic is an
amplitude, a modulation, a duty cycle, or a bandwidth.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of co-pending U.S.
application Ser. No. 16/018,360, filed Jun. 26, 2018 and entitled
"EMBEDDED DISCONNECTED CIRCUITS IN MAGNETIC STORAGE MEDIA OF DATA
STORAGE DEVICES" (Attorney Docket No. SDA-3214*A-US), which
published on Dec. 28, 2018 as U.S. Patent Publication No.
20180373452. U.S. application Ser. No. 16/018,360 claims priority
to and incorporates by reference the contents of U.S. Provisional
Application No. 62/525,272, filed Jun. 27, 2017 and entitled
"EMBEDDED DISCONNECTED PASSIVE CIRCUITS IN DATA STORAGE
DEVICES."
[0002] This application hereby incorporates by reference for all
purposes the entirety of the above-referenced U.S. application Ser.
No. 16/018,360 and U.S. Provisional Application No. 62/525,272.
Additionally, as did U.S. application Ser. No. 16/018,360, this
application hereby incorporates by reference for all purposes the
entirety of the contents of co-pending U.S. application Ser. No.
16/018,915, filed Jun. 26, 2018 and entitled "METHODS OF USING
EMBEDDED DISCONNECTED CIRCUITS IN MAGNETIC STORAGE MEDIA OF DATA
STORAGE DEVICES" (Attorney Docket No. SDA-3214*B-US), which
published on Dec. 27, 2018 as U.S. Patent Publication No.
20180373453.
BACKGROUND
[0003] Data storage devices (such as, for example, disk drives)
enable the storage of large amounts of information in a small
physical space. As areal densities have increased, the sizes of
write tracks and, therefore, write transducers have decreased
accordingly. As a consequence, the amount of flux generated by the
write transducer decreases, which means the head carrying the write
transducer must fly closer to the surface of the disk in order to
record data on the disk. As the head flies closer to the surface of
the disk, which is not entirely smooth and/or may pick up particles
that stick to its surface, the head can sometimes contact the disk,
which may damage the head, the disk, or both, or it may result in
read or write errors.
[0004] Solid-state storage devices (SSDs) (i.e., devices that store
data electrically rather than magnetically) provide arrays of
storage cells that are addressable and do not require moving parts,
such as a head to fly over the media to write and read data. SSDs
require addressing lines, however, which reduce the amount of space
on the device available for the storage of data.
[0005] There is, therefore, an ongoing need for improvements to
data storage devices.
SUMMARY
[0006] This summary represents non-limiting embodiments of the
disclosure.
[0007] Disclosed herein are systems and methods using embedded
disconnected circuits (EDC) within a data storage media and using
the EDC to write to and read from the data storage media (e.g., a
hard disk or other storage media). One or more components of an EDC
are energized by an electromagnetic field (of which there are many
varieties, including, by way of example and not limitation, optical
and radio waves) received by an antenna of the EDC. The energized
EDC may be used to read and/or write data to storage locations of
the media as described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] Objects, features, and advantages of the disclosure will be
readily apparent from the following description of certain
embodiments taken in conjunction with the accompanying drawings in
which:
[0009] FIG. 1 illustrates a hard disk drive that may embody one or
more embodiments disclosed herein.
[0010] FIG. 2A illustrates a cross-sectional view of an exemplary
layered media stack.
[0011] FIGS. 2B and 2C illustrate two possible arrangements of a
recording layer of a magnetic recording media in accordance with
some embodiments.
[0012] FIG. 2D illustrates a cross-sectional view of an exemplary
media stack that includes an EDC layer in accordance with some
embodiments.
[0013] FIG. 2E illustrates an exemplary EDC layer in accordance
with some embodiments.
[0014] FIG. 2F illustrates a cross-sectional view of another
exemplary layered media stack that includes an EDC layer in
accordance with some embodiments.
[0015] FIG. 2G illustrates a cross-sectional view of another
exemplary layered media stack that includes an EDC layer in
accordance with some embodiments.
[0016] FIGS. 3A-3C are simplified illustrations of exemplary
magnetic storage systems in accordance with some embodiments.
[0017] FIGS. 4A-4D illustrate certain elements of exemplary
magnetic recording systems in accordance with some embodiments.
[0018] FIGS. 5A-5B are simplified illustrations of exemplary
magnetic storage systems in accordance with some embodiments.
[0019] FIGS. 6A-6D illustrate certain elements of exemplary
magnetic recording systems in accordance with some embodiments.
[0020] FIGS. 7A-7G illustrate various exemplary embedded
disconnected circuits in accordance with some embodiments.
[0021] FIGS. 8A and 8B illustrate a magnetic storage system in
accordance with some embodiments.
[0022] FIG. 9 is a diagram illustrating an EDC in accordance with
some embodiments.
[0023] FIG. 10 is a flowchart illustrating the process to read one
or more EDC-assisted storage locations using EDC in accordance with
some embodiments.
[0024] FIG. 11 illustrates a process performed by an EDC to read
one or more EDC-assisted storage locations in accordance with some
embodiments.
[0025] FIG. 12 illustrates the use of EDC in the context of reading
from and writing to a hard disk drive in accordance with some
embodiments.
[0026] FIG. 13 illustrates an exemplary archival storage system in
accordance with some embodiments.
DETAILED DESCRIPTION
[0027] FIG. 1 illustrates several components of a hard disk drive
500. The magnetic hard disk drive 500 includes a spindle 515 that
supports and rotates a magnetic disk 520. The spindle 515 is
rotated by a spindle motor (not shown) that is controlled by a
motor controller (not shown) that may be implemented in electronics
of the hard disk drive 500. A slider 525, which is supported by a
suspension and actuator arm 530, includes a combined read and write
magnetic head 540. An actuator 535 rotatably positions the
suspension and actuator arm 530 over the magnetic disk 520. The
components of the hard disk drive 500 may be mounted on a housing
545. It is to be understood that although FIG. 1 illustrates a
single disk 520, a single slider 525, a single head 540, and a
single suspension and actuator arm 530, hard disk drive 500 may
include a plurality (i.e., more than one) of disks 520, sliders
525, heads 540, and suspension and actuator arms 530.
[0028] The slider 525 has a gas-bearing surface that faces the
surface of the disk 520 and counteracts a preload bias that pushes
the slider toward the disk 520. For convenience, in this document
the gas-bearing surface is referred to as the air-bearing surface
(ABS) and the gas is generally referred to as "air," although it is
to be understood that the gas used in a hard disk drive 500 may be
a gas other than air (e.g., the gas may be helium). For simplicity,
throughout this disclosure, the surface of the slider 525 that
faces or that will eventually face the disk 520 is referred to as
the ABS.
[0029] As the disk 520 rotates, the disk 520 drags air under the
slider 525 and along the ABS in a direction approximately parallel
to the tangential velocity of the disk 520. As the air passes under
the ABS, air compression along the air flow path causes the air
pressure between the disk 520 and the ABS to increase, which
creates a hydrodynamic lifting force that counteracts the tendency
of the suspension and actuator arm 530 to push the slider 525
toward the disk 520. The slider 525 thus flies above the disk 520
but in close proximity to the surface of the disk 520.
[0030] In operation, the actuator 535 moves the suspension and
actuator arm 530 to position the slider 525 so that the magnetic
head 540 is in a transducing relationship with the surface of the
magnetic disk 520. The head 540 may be used to write information to
one or more tracks on the surface of the disk 520 and to read
previously-recorded information from the tracks on the surface of
the disk 520. Processing circuitry 510 provides to the head 540
signals representing information to be written to the disk 520 and
receives from the head 540 signals representing information read
from the disk 520. The processing circuitry 510 also provides
signals to the spindle motor to rotate the magnetic disk 520, and
to the actuator 535 to move the slider 525 to various tracks.
[0031] For writing, the head 540 may use a single pole writer
(i.e., a write transducer) that has a main pole surrounded by
magnetic shield materials. The main pole is typically separated
from the magnetic shield materials by a non-magnetic spacer. The
main pole may have a tapered shape with a tip that faces the
magnetic recording media and is part of the ABS. The single pole
writer may include a conductive coil encircling the writer pole in
a helical or pancake-like configuration.
[0032] To write to the disk 520, the slider 525 passes over a
region of the disk 520, and an electric current is applied through
the coil of the head 540, which causes a large magnetic field to be
generated from the main pole tip. The polarity of the generated
field causes a region of the magnetic disk 520 to assume a
polarity, thus enabling information to be stored on the disk
520.
[0033] To read information from the disk 520, the head 540 may
include only one read sensor, or it may include multiple read
sensors. The read sensor(s) in the head 540 may include, for
example, one or more giant magnetoresistance (GMR) sensors,
tunneling magnetoresistance (TMR) sensors, or another type of
magnetoresistive sensor. When the slider 525 passes over a region
of the disk 520, the head 540 detects changes in resistance due to
magnetic field variations recorded on the disk 520, which represent
the recorded bits.
[0034] Traditionally, the size of the bits has been reduced in
order to increase the amount of data that can be stored on the disk
520. Correspondingly, the size of the write transducer has
decreased roughly in proportion to the size of the bits. But to
obtain high recording density, a write field of sufficient
magnitude must be focused on a small area of the disk, which is
increasingly difficult as the size of the write transducer
decreases. Consequently, techniques such as microwave-assisted
magnetic recording (MAMR) and heat-assisted magnetic recording
(HAMR) have been developed to improve writing technology. In MAMR,
elements added to the head 540 generate an additional field that
supplements the magnetic field ordinarily produced by the write
transducer, thereby providing a stronger effective write field. In
HAMR, elements added to the head 540 heat a localized area on the
surface of the recording media (e.g., the disk 520) to reduce its
coercivity, thereby enabling the magnetic field generated by the
write transducer, which otherwise would be of insufficient
strength, to set the magnetization of the localized area. Although
these more advanced techniques can provide improved storage
density, there is a limit to how small the storage locations can
be, and the head 540 needs to fly close to the surface of the disk
520 to provide sufficiently strong magnetic fields.
[0035] The inventors had the insight that adding an assistive
mechanism to the storage media instead of, or in addition to, the
head 540 would offer several advantages relative to prior-art
recording techniques. First, if used in a media with a single
recording layer, an assistive mechanism could allow the head 540 to
fly further from the surface of the media because an assist would
be provided from within the media, in closer proximity to the
storage location being written to or read from. Second, if used in
a media with two or more recording layers, an assistive mechanism
could enable the media to record more data, thereby increasing its
overall storage capacity. Third, an assistive mechanism within the
media could be used to enable remote reading of the data on a
storage media, thereby eliminating the need for a head 540 to fly
over the media to read data. Such a system may be particularly
attractive for archived data.
[0036] These and other advantages are enabled in the systems and
methods disclosed herein. Some embodiments of data storage systems
include embedded disconnected circuits (EDC) within a data storage
media to improve the performance of the data storage system (e.g.,
one or more of its data storage capacity, its durability, its data
access speed, etc.) or to relax the requirements on elements of the
data storage system (e.g., the distance between the write
transducer and the media during write and/or read operations, the
slider's fly height, the density of storage locations one or more
recording layers of the media, etc.). As discussed herein, the EDC
may be used in a number of ways to assist recording data to the
media and/or reading data from the media.
[0037] In some embodiments, the EDC assist a write transducer to
write data to a recording layer of a media. The write transducer
may be a conventional write transducer (e.g., it may or may not
include components in addition to the write pole, coil, and return
pole, such as those used in HAMR, MAMR, etc.). The recording layer
assisted by the EDC may be the only recording layer on the media,
or it may be an additional (e.g., second, third, etc.) recording
layer added to the media. In some embodiments, the media includes
at two recording layers, and the EDC enable the use of at least one
of the two recording layers.
[0038] In some embodiments, the EDC assist in reading data from a
recording layer. In some embodiments, the EDC include a read sensor
that is positioned near (e.g., over, under, adjacent to, etc.) one
or more storage locations to read the contents of the one or more
storage locations and to send a wireless signal providing the
contents of the storage location(s) to a signal processing
component of the data storage device. For example, the read sensor
may comprise a resistive element, the resistance of which changes
in response to the magnetization of the storage location(s). In
some embodiments, the EDC are capable of reading one or more nearby
storage locations and transmitting a wireless signal providing
information (e.g., about the contents, identity, and/or location of
the storage location(s); about the identity and/or location of the
EDC; etc.) to a receiver embedded in a slider that flies over the
media. In some embodiments, reading is coordinated by reader
circuitry that is located remotely from the media (i.e., the reader
circuitry is not included in a slider that flies over the media),
and the EDC are capable of receiving wireless read commands and
transmitting wireless read responses.
Media with EDC
[0039] FIG. 2A illustrates a cross-sectional view of an exemplary
layered media stack 200A that may be included in a conventional
hard disk 520 using perpendicular magnetic recording (PMR) with a
single depth of bits stored in a single recording layer 260 located
near the surface of the media. The media includes a bottom
substrate 205 (e.g., an aluminum platter), an adhesion layer 210
(e.g., NiP plating, an AlTi layer, etc.), a soft underlayer (SUL)
215 (e.g., a soft alloy containing cobalt, nickel, iron, tantalum,
and/or zirconium), a ruthenium (Ru) interlayer 220, a recording
layer 260, a carbon overcoat layer 235 (e.g., a carbon bilayer, the
bottom layer being CHx and the top layer being CNx), and a
lubricant layer 240.
[0040] The recording layer 260 may include, for example, thin films
with a plurality of magnetic grains, each grain having a magnetic
easy axis substantially perpendicular to the media surface, thereby
allowing the grains to be vertically magnetized. The magnetic
grains may comprise a magnetic material such as, for example, CoPt,
CoPtCr, CoPtCrB, etc. To maintain a highly segregated magnetic
layer, one or more segregants may be added to the magnetic
material.
[0041] The recording layer 260 may be configured in any suitable
arrangement. FIGS. 2B and 2C illustrate two possible arrangements
of the recording layer 260. FIG. 2B shows a recording layer 260
with two sublayers: an oxide sublayer 228, which includes an oxide,
and a capping sublayer 230, which does not include an oxide. The
oxide sublayer 228 may comprise, for example, a CoPtCr alloy with
one or more segregants including various oxides such as SiOx, TaOx,
TiOx, and/or CrOx, and/or various elements such as B and Ti.
[0042] FIG. 2C shows a recording layer 260 with an exchange
coupling sublayer 232 inserted between the oxide sublayer 228 and
the capping sublayer 230. The exchange coupling sublayer 232 may be
formed of materials such as, for example, Co alloys including Ru,
Cr, Pt and/or B. The exchange coupling sublayer 232 provides for a
reduction of interfacial exchange coupling strength between the
oxide sublayer 228 and the capping sublayer 230. In addition to or
instead of the exchange coupling sublayer 232, various other layers
can be introduced between the oxide sublayer 228 and the capping
sublayer 230 to improve the performance of the recording layer
260.
[0043] The media stack 200A illustrated in FIG. 2A and the
recording layers 260 illustrated in FIGS. 2B and 2C are merely
examples of the layers that may be included in a media stack.
Variants may include media with different numbers of layers and
different materials than shown in FIGS. 2A-2C. For example, U.S.
Pat. No. 7,998,607 to Ikeda, which is hereby incorporated by
reference in its entirety for all purposes, discloses a
partially-oxidized capping layer that may be used in accordance
with some embodiments. U.S. Pat. No. 8,202,636 to Choe et al.,
which is also hereby incorporated by reference in its entirety for
all purposes, discloses media for perpendicular magnetic recording
that control anisotropy levels in different sublayers of the
magnetic recording layer(s) 260 of the media.
[0044] FIGS. 2D-2F illustrate how the exemplary media stack 200A of
FIG. 2A may be modified to include the EDC disclosed herein. Again,
the materials and layers illustrated are merely examples, and a
media stack may include additional or fewer layers having different
characteristics. It is to be understood that the principles
disclosed herein are applicable to other media having different
numbers or orders of layers, or using different materials.
[0045] FIG. 2D illustrates a cross-sectional view of an exemplary
media stack 200B in accordance with some embodiments. The media
stack 200B includes many of the layers discussed above in the
context of FIG. 2A. Instead of the conventional recording layer
260, the media stack 200B includes an EDC-assisted recording layer
225, which is assisted by an EDC layer 250 added to the media stack
200B. The EDC-assisted recording layer 225 may be indistinguishable
from a conventional recording layer 260 but is referred to as the
EDC-assisted recording layer 225 because the EDC layer 250 assists
in the reading from and/or writing to the EDC-assisted recording
layer 225. In general, the discussion above of the conventional
recording layer 260 (e.g., regarding materials, layers, properties,
etc.) applies with equal force to the EDC-assisted recording layer
225. One key difference between a conventional recording layer 260
and an EDC-assisted recording layer 225, as those terms are used
herein, is that reading from and/or writing to the EDC-assisted
recording layer 225 is potentially assisted by EDC, whereas reading
from and/or writing to the conventional recording layer 260 is
accomplished without the assistance of EDC.
[0046] In the media stack 200B, the EDC layer 250 is embedded
between the SUL 215 and the Ru interlayer 220. FIG. 2E illustrates
an exemplary EDC layer 250 in accordance with some embodiments. As
shown in FIG. 2E, the EDC layer 250 may comprise a set of at least
one EDC 150, which may be sandwiched by structural support layers
255A, 255B. The structural components of the EDC 150 are discussed
below. In general, the structural support layers 255A, 255B provide
topological support for the EDC 150 and for other layers that may
be used in magnetic recording (e.g., the exemplary layers 210, 215,
220, etc.). If present, the structural support layers 255A, 255B
above and below the EDC layer 250 may be different, depending on
the requirements for fabricating the layers adjacent to the
structural support layers 255A, 255B. Armed with the disclosures
herein, skilled artisans will understand how to select the
characteristics (e.g., material, thickness, etc.) of and fabricate
the structural support layers 255A, 255B.
[0047] FIG. 2F illustrates a cross-sectional view of another
exemplary layered media stack 200C in accordance with some
embodiments. In the media stack 200C, an EDC layer 250 is embedded
in the media between two adhesion layers 210A, 210B, which reside
between the SUL 215 and the substrate 205, and the EDC-assisted
recording layer 225 resides between the carbon overcoat layer 235
and the Ru interlayer 220. As in FIG. 2D, the EDC layer 250 may
comprise the EDC 150 sandwiched by structural support layers 255A,
255B. In other words, the EDC 150, which may be sandwiched by
structural support layers 255A, 255B, are sandwiched between the
two adhesion layers 210A, 210B in the embodiment of FIG. 2F.
[0048] FIG. 2G illustrates a cross-sectional view of another
exemplary layered media stack 200D in accordance with some
embodiments. In the media stack 200D, an EDC layer 250 is embedded
in the media between the adhesion layer 210 and the Ru interlayer
220, and the EDC-assisted recording layer 225 is disposed between
the Ru interlayer 220 and the carbon overcoat layer 235. As in
FIGS. 2D and 2F, the EDC layer 250 may comprise the EDC 150
sandwiched between structural support layers 255A, 255B as shown in
FIG. 2E. In the example of FIG. 2G, the EDC layer 250 replaces the
SUL 215 and, as a result, may also be imbued with some or all of
the characteristics of the SUL 215.
[0049] In some embodiments, the EDC 150 are added to assist writing
to and/or reading from a media that includes only one EDC-assisted
recording layer 225 instead of a conventional recording layer. In
some embodiments, the EDC 150 are added to convert the media from a
two-dimensional storage media having only a single recording layer
(whether conventional or EDC-assisted) to a three-dimensional
storage media by providing the ability to store data in
EDC-assisted recording layers 225 that are under the single
recording layer (i.e., whether a conventional recording layer 260
or an EDC-assisted recording layer 225).
[0050] FIGS. 3A-3C and 5A-5B are simplified illustrations of
magnetic storage systems in accordance with some embodiments. For
ease of description, FIGS. 3A-3C and 5A-5B show only the head 540,
the recording layer(s) 260, 225, the EDC layer(s) 250, and, if
present, an optional isolation layer 170 of the media stack. As
explained above, the media stack generally includes additional
layers that are not illustrated in FIGS. 3A-3C and 5A-5B.
[0051] FIG. 3A illustrates an exemplary magnetic storage system
100A with a media stack that includes an EDC-assisted recording
layer 225 and an EDC layer 250 in accordance with some embodiments.
As explained below, the EDC 150 in the EDC layer 250 may assist the
head 540 to write data to and/or read data from the recording layer
225. In the example illustrated in FIG. 3A, the EDC-assisted
recording layer 225 replaces a conventional recording layer 260 and
may result in a media stack that looks similar or identical to the
media stack 200B, 200C, or 200D of FIGS. 2D, 2F, and 2G,
respectively.
[0052] FIG. 3B illustrates the use of EDC 150 in an example
magnetic recording system 100B to enable the use of an EDC-assisted
recording layer 225 in addition to a conventional recording layer
260 in accordance with some embodiments. In the example shown in
FIG. 3B, an EDC layer 250 resides between the conventional
recording layer 260 and the EDC-assisted recording layer 225. The
conventional recording layer 260 is used in the conventional way,
i.e., it is written to and read from by the head 540 without
assistance from the EDC 150 in the EDC layer 250. An optional
isolation layer 170, which may provide structural, electromagnetic,
and/or thermal isolation, may be disposed between the conventional
recording layer 260 and the EDC layer 250 to mitigate interactions
between the EDC 150 and the conventional recording layer 260, or to
prevent the EDC 150 from interacting with or affecting the
conventional recording layer 260. Armed with the disclosures
herein, skilled artisans will understand how to select suitable
materials for and characteristics of the isolation layer 170.
[0053] FIGS. 4A and 4B illustrate certain elements of the magnetic
recording system 100B in more detail. FIG. 4A shows a write
transducer 110 and a portion of the media 120. As shown in FIG. 4A,
a magnetic storage media 120 comprises a conventional recording
layer 260 near the surface of the media 120 that faces the write
transducer 110, and an EDC-assisted recording layer 225 located
deeper in the media 120, further away from the write transducer
110. An EDC layer 250 is disposed above and adjacent to the
EDC-assisted recording layer 225. It is to be understood that the
EDC layer 250 need not be adjacent to the EDC-assisted recording
layer 225, but close proximity may be desirable to maximize the
impact of the EDC 150 on the EDC-assisted recording layer 225. In
the example illustrated in FIG. 4A, the isolation layer 170 is
shown between the EDC layer 250 and the conventional recording
layer 260. As discussed above, the isolation layer 170 may mitigate
or prevent interaction between the EDC 150 and the conventional
recording layer 260.
[0054] FIG. 4B is a closer view of a portion of the magnetic
storage media 120 of FIG. 4A. As shown, the conventional recording
layer 260 includes a plurality of storage locations 135A, 135B,
135C, etc. The EDC-assisted recording layer 225 includes a
plurality of EDC-assisted storage locations 145A, 145B, 145C, etc.,
and the EDC layer 250 includes a plurality of EDC 150A, 150B, 150C,
etc. (To avoid obscuring the drawing, FIG. 4B does not illustrate
any structural support layers 255 that might be present in the EDC
layer 250.) A storage location 135, 145 can be any defined portion
of the media that stores data. For example, the storage locations
135 and/or 145 may be within a track or sector. As another example,
the storage locations 135 and/or 145 may be in the form of
bit-patterned media. Bit patterned media are described in U.S. Pat.
No. 7,324,294 to Moser and U.S. Pat. No. 6,947,235 to Albrecht et
al., both of which are hereby incorporated by reference in their
entireties.
[0055] The EDC-assisted storage locations 145 in the EDC-assisted
recording layer 225 may be written to and/or read from by
selectively activating one or more associated EDC 150 in the EDC
layer 250 to write to and/or read from selected ones of the
EDC-assisted storage locations 145. As illustrated in FIGS. 4A and
4B, the number and dimensions of the storage locations 135 need not
be the same as the number and dimensions of the EDC-assisted
storage locations 145. For example, it may be desirable to use
different or optimized sizes and/or shapes (e.g., geometrics,
dimensions, configurations, etc.) for the storage locations 145 in
the EDC-assisted recording layer 225 than in the conventional
recording layer 260 to maximize the effectiveness of the EDC 150.
Furthermore, although FIG. 4B illustrates the EDC-assisted storage
locations 145 and the EDC 150 in a one-to-one ratio, a single EDC
150 may be used during read and/or write operations involving
multiple EDC-assisted storage locations 145. For example, the EDC
150 may enable bank reading or bank writing whereby multiple
EDC-assisted storage locations 145 are read from or written to
simultaneously. Similarly, multiple EDC 150 may be used during read
and/or write operations involving a single EDC-assisted storage
location 145. For example, a first EDC 150 may assist in the
writing process, and a second EDC 150 may assist in the reading
process.
[0056] FIG. 3C illustrates another exemplary magnetic recording
system 100C that enables the use of an EDC-assisted recording layer
225 in addition to a conventional recording layer 260 in accordance
with some embodiments. In the example system 100C, the EDC layer
250 resides below the EDC-assisted recording layer 225. This
positioning of the EDC layer 250 may reduce or eliminate any need
for an optional isolation layer 170 between the first and second
recording layers 225A, 225B. Although not illustrated in FIG. 3C,
the example system 100C may also include an isolation layer 170,
which may be disposed, for example, between the first and second
recording layers 225A, 225B.
[0057] FIGS. 4C and 4D illustrate certain elements of the magnetic
recording system 100C shown in FIG. 3C in more detail. As shown in
FIG. 4C, a magnetic storage media 120 comprises a conventional
recording layer 260 near the surface of the media 120, and an
EDC-assisted recording layer 225 located deeper in the media 120.
An EDC layer 250 is disposed below and adjacent to the EDC-assisted
recording layer 225. It is to be understood that the EDC layer 250
need not be adjacent to the EDC-assisted recording layer 225, but
close proximity may be desirable to maximize the ability of the EDC
150 to assist the EDC-assisted recording layer 225. Unlike in FIG.
3C, in the example illustrated in FIG. 4C, an optional isolation
layer 170 is provided between the EDC-assisted recording layer 225
and the conventional recording layer 260.
[0058] FIG. 4D is a closer view of a portion of the magnetic
storage media 120 of FIG. 4C. As shown, the conventional recording
layer 260 includes a plurality of storage locations 135A, 135B,
135C, etc. The EDC-assisted recording layer 225 includes a
plurality of EDC-assisted storage locations 145A, 145B, 145C, etc.,
and the EDC layer 250 includes a plurality of EDC 150A, 150B, 150C,
etc. (and may also include structural support layers 255 as
discussed above). As illustrated in FIGS. 4C and 4D, and as
discussed above in the context of FIGS. 4A and 4B, the number and
dimensions of the EDC-assisted storage locations 145 need not be
the same as the number and dimensions of the conventional storage
locations 135. Furthermore, a single EDC 150 may be used during
read and/or write operations involving multiple EDC-assisted
storage locations 145. Similarly, multiple EDC 150 may be used
during read and/or write operations involving a single EDC-assisted
storage location 145. For example, a first EDC 150 may assist in
the writing process, and a second EDC 150 may assist in the reading
process.
[0059] FIG. 5A illustrates another exemplary magnetic recording
system 100D that enables the use of multiple EDC-assisted recording
layers 225 in accordance with some embodiments. The example system
100D includes two EDC layers 250. The first EDC layer 250A assists
the head 540 to write to the first EDC-assisted recording layer
225A, and the second EDC layer 250B assists the head 540 to write
to the second EDC-assisted recording layer 225B. Thus, the
recording process for each of the first and second EDC-assisted
recording layers 225A, 225B takes advantage of EDC 150. Similarly,
the reading process may also take advantage of the EDC 150 in the
EDC layers 250A, 250B. An optional isolation layer 170 (e.g., as
described above in the context of FIG. 3B) may be disposed between
the first EDC layer 250A and the second EDC-assisted recording
layer 225B to mitigate or prevent interactions between the EDC 150
in the first EDC layer 250A and the storage locations 145 in the
second EDC-assisted recording layer 225B.
[0060] FIGS. 6A and 6B illustrate certain elements of the magnetic
recording system 100D in more detail. As shown in FIG. 6A, a
magnetic storage media 120 comprises a first EDC-assisted recording
layer 225A near the surface of the media 120, and a second
EDC-assisted recording layer 225B located deeper in the media 120.
A first EDC layer 250A is disposed below and adjacent to the first
EDC-assisted recording layer 225A, and a second EDC layer 250B is
disposed below and adjacent to the second EDC-assisted recording
layer 225B. It is to be understood that the first and second EDC
layers 250A, 250B need not be adjacent to their respective
EDC-assisted recording layers 225, but close proximity may be
desirable to maximize the impact of the EDC 150 on the EDC-assisted
recording layers 225. In the example illustrated in FIG. 6A, an
isolation layer 170 is provided between the second EDC-assisted
recording layer 225B and the first EDC layer 250A.
[0061] FIG. 6B is a closer view of a portion of the magnetic
storage media 120 of FIG. 6A. As shown, the first EDC-assisted
recording layer 225A includes a plurality of EDC-assisted storage
locations 145P, 145Q, 145R, etc., and the second EDC-assisted
recording layer 225B includes a plurality of EDC-assisted storage
locations 145A, 145B, 145C, etc. The first EDC layer 250A includes
a plurality of EDC 150F, 150G, 150H, etc., and the second EDC layer
250B includes a plurality of EDC 150A, 150B, 150C, etc. One or both
of the first and second EDC layers 250A, 250B may also include
structural support layers 255 as discussed above. As illustrated in
FIGS. 6A and 6B, the number and dimensions of the EDC-assisted
storage locations 145 in the first EDC-assisted recording layer
225A need not be the same as the number and dimensions of the
EDC-assisted storage locations 145 in the second EDC-assisted
recording layer 225B. Furthermore, a single EDC 150 in the first
EDC layer 250A maybe used during read and/or write operations
involving multiple EDC-assisted storage locations 145 in the first
EDC-assisted recording layer 225A, and a single EDC 150 in the
second EDC layer 250B may be used during read and/or write
operations involving multiple EDC-assisted storage locations 145 in
the second EDC-assisted recording layer 225B. Similarly, multiple
EDC 150 in either EDC layer 250A, 250B may be used during read
and/or write operations involving a single EDC-assisted storage
location 145. For example, a first EDC 150 may assist in the
writing process, and a second EDC 150 may assist in the reading
process.
[0062] FIG. 5B illustrates another exemplary magnetic recording
system 100E that enables the use of multiple EDC-assisted recording
layers 225 in accordance with some embodiments. Like the exemplary
system 100D of FIG. 5A, the example system 100E includes two EDC
layers 250. The first EDC layer 250A assists the head 540 to write
to the first EDC-assisted recording layer 225A, and the second EDC
layer 250B assists the head 540 to write to the second EDC-assisted
recording layer 225B. Thus the recording process for each of the
first and second EDC-assisted recording layers 225A, 225B takes
advantage of EDC 150. In the system 100E, the first and second
EDC-assisted recording layers 225A, 225B are separated by the first
and second EDC layers 250A, 250B. An optional isolation layer 170
(e.g., as described above in the context of FIG. 3B) may be
disposed between the first and second EDC layers 250A and 250B to
mitigate or prevent interactions between the EDC 150 in the first
EDC layer 250A and the second EDC-assisted recording layer 225B,
and to mitigate or prevent interactions between the EDC 150 in the
second EDC layer 250B and the first EDC-assisted recording layer
225A.
[0063] FIGS. 6C and 6D illustrate certain elements of the magnetic
recording system 100E in more detail. As shown in FIG. 6C, a
magnetic storage media 120 comprises a first EDC-assisted recording
layer 225A near the surface of the media 120, and a second
EDC-assisted recording layer 225B located deeper in the media 120.
A first EDC layer 250A is disposed below and adjacent to the first
EDC-assisted recording layer 225A, and a second EDC layer 250B is
disposed above and adjacent to the second EDC-assisted recording
layer 225B. It is to be understood that the first and second EDC
layers 250A, 250B need not be adjacent to their respective
EDC-assisted recording layers 225, but close proximity may be
desirable to maximize the impact of the EDC 150 in an EDC layer 250
on the target EDC-assisted recording layer 225. In the example
illustrated in FIG. 6C, an isolation layer 170 is provided between
the first and second EDC layers 250A and 250B.
[0064] FIG. 6D is a closer view of a portion of the magnetic
storage media 120 of FIG. 6C. As shown, the first EDC-assisted
recording layer 225A includes a plurality of EDC-assisted storage
locations 145P, 145Q, 145R, etc., and the second EDC-assisted
recording layer 225B includes a plurality of EDC-assisted storage
locations 145A, 145B, 145C, etc. The first EDC layer 250A includes
a plurality of EDC 150F, 150G, 150H, etc., and the second EDC layer
250B includes a plurality of EDC 150A, 150B, 150C, etc. One or both
of the first and second EDC layers 250A, 250B may also include
structural support layers 255 as discussed above. As illustrated in
FIGS. 6C and 6D, and as discussed above in the context of FIGS. 4A
and 4B, the number and dimensions of the EDC-assisted storage
locations 145P, 145Q, 145R, etc. in the first EDC-assisted
recording layer 225A need not be the same as the number and
dimensions of the EDC-assisted storage locations 145A, 145B, 145C,
etc. in the second EDC-assisted recording layer 225B. Furthermore,
a single EDC 150 in the first EDC layer 250A maybe used during read
and/or write operations involving multiple storage locations 145 in
the first EDC-assisted recording layer 225A, and a single EDC 150
in the second EDC layer 250B may be used during read and/or write
operations involving multiple EDC-assisted storage locations 145 in
the second EDC-assisted recording layer 225B.
[0065] It is to be understood that in general, a recording media
can include any number of recording layers 260, 225, conventional
and/or EDC-assisted, and EDC layers 250. The presence of
EDC-assisted recording layers 225 in addition to conventional
recording layers 260 may provide an opportunity to relax some of
the requirements on the conventional recording layer(s) 260 and/or
the head 540. For example, if a media includes both a conventional
recording layer 260 and an EDC-assisted recording layer 225, the
total number of storage locations, some of which are EDC-assisted
and others of which are not, may exceed the total number available
in a conventional media. Therefore, it is possible to relax some of
the requirements on the conventional recording layer 260 and/or
other characteristics of the data storage device 100 (e.g., slider
fly height, density of storage locations, etc.) without sacrificing
the overall data storage capacity of the data storage device 100.
Moreover, the total number of storage locations 135, 145 in a media
that includes one or more EDC layers 250 may substantially exceed
the number that would be available in a media with only a
conventional recording layer 260, even if the storage density
within a conventional recording layer 260 is reduced.
[0066] Moreover, the number of EDC layers 250 included in a
recording media need not be the same as the number of additional
recording layers. A single EDC layer 150 may be capable of
assisting reading and/or writing of multiple EDC-assisted recording
layers 225. For example, an EDC layer 250 may be sandwiched between
two EDC-assisted recording layers 225 and capable of assisting to
read from and/or write to both EDC-assisted recording layers 225.
The EDC 150 in such an EDC layer 250 may be capable of selectively
reading from/writing to each of the EDC-assisted recording layers
225.
[0067] Furthermore, as explained above, EDC 150 may be added to a
media that includes only a single recording layer to assist in
writing to and/or reading from that recording layer, thereby
converting a conventional recording layer 260 to an EDC-assisted
recording layer 225.
The EDC
[0068] The exemplary media illustrated in FIGS. 2D, 2F, 2G, and
3A-6D can store data in the EDC-assisted recording layers 225 by
setting the magnetizations of the EDC-assisted storage locations
145. As described below, the EDC 150 embedded in the EDC layer(s)
250 of the media provide assistance during the writing process, the
reading process, or both.
[0069] FIG. 7A illustrates an EDC 150 in accordance with some
embodiments. The EDC 150 includes an antenna 152 and circuitry 155.
The EDC 150 may be a frequency-selective circuit. For example, the
antenna 152 may comprise a frequency-selective antenna in which the
oscillating electric and magnetic fields of an incoming radio wave
create oscillating currents in the antenna 152 only if the incoming
radio wave is of a particular frequency or within a particular
frequency range. Alternatively or in addition, the antenna 152 may
include a frequency-selective surface (FSS) (e.g., an optical
filter, a metal-mesh optical filter, or any surface having a
pattern designed to reflect, transmit, or absorb electromagnetic
fields based on the frequency of the field). The antenna 152 may be
omnidirectional (i.e., capable of receiving energy approximately
equally from all directions) or directional (i.e., more sensitive
to energy received from a particular direction). If directional,
the antenna 152 may be configured (e.g., in design, in placement,
in orientation, etc.) to maximize its coupling to electromagnetic
energy in a particular direction. The antenna 152 may be of any
suitable type (e.g., a monopole antenna, a dipole antenna, etc.).
Furthermore, the antenna 152 may be an array of antennas (e.g., a
phased array, a log-periodic dipole array, etc.).
[0070] Different EDC 150 may have antennas 152 with differing
characteristics. For example, in some embodiments, frequency
diversity enables the selective activation of the EDC 150. In such
embodiments, the antenna 152 of a first EDC 150 may be configured
to create oscillating currents only when a signal having a first
frequency is received, and the antenna 152 of a second EDC 150 may
be configured to create oscillating currents only when a signal
having a second frequency is received so that the first EDC 150 may
be activated independently of the second EDC 150, and vice
versa.
[0071] The circuitry 155 of the EDC 150 may include circuitry for
reading from the media and/or circuitry for writing to the media.
In general, the circuitry 155 of the EDC 150 may comprise any
circuit element (e.g., active, passive, analog, digital, etc.).
Examples of circuit elements that may be included in the circuitry
155 include resistors, capacitors, inductors, transistors,
operational amplifiers, diodes, gates, transformers, switches, etc.
In operation, the EDC 150 is energized by a time-varying
electromagnetic radio-frequency (RF) signal transmitted by a
circuit of the data storage device (e.g., a circuit that is
separate from the EDC 150 and its circuitry 155). The RF signal
generates an AC voltage across the antenna 152, which supplies
power to the circuitry 155. The AC voltage may optionally be
rectified. As described below, the energized EDC 150 can then (a)
assist the head 540 to write to a recording layer 225 and/or (b)
read or assist in reading data previously-stored in a recording
layer 225.
[0072] The EDC 150 may be distributed or embedded within the EDC
layer 250 in any suitable pattern and at any suitable density. As
just one example, one EDC 150 may be included in the media for
every 200 bits in a Tb/in.sup.2 surface, assuming the area of the
antenna 152 is 1 .mu.m.sup.2.
[0073] FIG. 7B illustrates an exemplary EDC 150 in which the
circuitry 155 comprises a resistive element 156 in accordance with
some embodiments. In operation, the power supplied by the antenna
152 to the resistive element 156 causes the resistive element 156
to generate heat. As a result, because the EDC layer 250 is
adjacent to or near the recording layer 225, the portion of the
recording layer 225 near the resistive element 156 is heated, which
lowers its coercivity and allows the write transducer 110 of the
head 540 to record data to the heated storage location(s) in that
localized region of the media.
[0074] FIG. 7C illustrates an exemplary EDC 150 in which the
circuitry 155 comprises a resonator 157 in accordance with some
embodiments. In operation, the power supplied by the antenna 152 to
the resonator 157 causes the resonator 157 to emit electromagnetic
waves that add constructively to the write field generated by the
write transducer 110, thereby providing a sufficient field to
switch nearby storage locations in the recording layer 225.
[0075] FIG. 7D illustrates an exemplary EDC 150 in which the
circuitry 155 comprises a heat generator 158. Similarly to the
resistive element 156 described above, the heat generator 158
causes the portion of the recording layer 225 near it to heat,
which lowers its coercivity and allows the write transducer 110 to
more easily record data to the heated storage location(s) near the
heat generator 158.
[0076] FIG. 7E illustrates an exemplary EDC 150 in which the
circuitry 155 comprises an active circuit 160. In operation, the
power supplied by the antenna 152 to the active circuit 160 causes
the active circuit 160 to provide an assist to the write transducer
110. For example, the active circuit 160 may generate a microwave
field that augments the write field. As another example, the active
circuit 160 may generate electromagnetic energy that heats the
recording layer near the active circuit 160 to lower its coercivity
and allow the magnetization of one or more storage locations to be
adjusted more easily.
[0077] FIG. 7F illustrates an exemplary EDC 150 in which the
circuitry 155 comprises a spin-torque oscillator (STO) 162, or a
similar spin-torque nanodevice. In operation, the power supplied by
the antenna 152 to the STO 162 causes the magnetization of the STO
162 to oscillate and generate a microwave field that augments the
field of the write transducer 110, thereby enabling writing to the
storage location(s) assisted by that EDC 150.
[0078] FIG. 7G illustrates an exemplary EDC 150 in which the
circuitry 155 comprises a read sensor 164. The read sensor 164 may
be configured to vary in response to a magnetization of one or more
storage location(s) assisted by the EDC 150. In some embodiments,
the read sensor 164 is a conventional magnetoresistive (MR) sensor
(i.e., a "spin-valve" sensor based on the giant magnetoresistance
(GMR) effect). A GMR spin-valve sensor has a stack of layers that
includes two ferromagnetic layers separated by a nonmagnetic
electrically conductive spacer layer, which is typically copper
(Cu). One ferromagnetic layer adjacent the spacer layer has its
magnetization direction fixed, such as by being pinned by exchange
coupling with an adjacent antiferromagnetic layer, and is referred
to as the reference layer. The other ferromagnetic layer adjacent
the spacer layer has its magnetization direction free to rotate in
the presence of an external magnetic field and is referred to as
the sensing or free layer. With a sense current applied to the
sensor, the rotation of the free-layer magnetization relative to
the reference-layer magnetization due to the presence of an
external magnetic field is detectable as a change in electrical
resistance.
[0079] In some embodiments, the read sensor 164 is a magnetic
tunnel junction sensor, also called a tunneling MR or TMR sensor,
in which the nonmagnetic spacer layer is a very thin nonmagnetic
insulating tunnel barrier layer such as TiO.sub.2, MgO or
Al.sub.2O.sub.3. The barrier layer is sufficiently thin that
quantum-mechanical tunneling of charge carriers occurs between the
two ferromagnetic layers. This quantum-mechanical tunneling process
is electron spin dependent, which means that an electrical
resistance measured when applying a sense current across the
junction depends on the spin-dependent electronic properties of the
ferromagnetic and barrier layers, and is a function of the relative
orientation of the magnetizations of the two ferromagnetic
layers.
[0080] As will be appreciated by skilled artisans, there are myriad
possible elements and combinations of elements that may be included
in the circuitry 155, and the examples provided herein are not
intended to be limiting. Moreover, an EDC 150 may include more than
one of the elements described in the context of FIGS. 7A-7G. For
example, an EDC 150 may comprise an element (e.g., 156, 157, 158,
160, 162, etc.) to assist in writing to the EDC-assisted recording
layer 225 and a separate element (e.g., 164, etc.) to assist in
reading from the EDC-assisted recording layer 225.
Using EDC to Write to a Deeper Recording Layer Using a Conventional
Head
[0081] For ease of terminology, many of the exemplary embodiments
discussed below are typically discussed as if the media includes
only one EDC-assisted recording layer 225, but it is to be
appreciated that, as explained previously, the techniques disclosed
herein can be used advantageously to provide additional
EDC-assisted recording layers 225. For example, if the surface of
the platter is in the x-y plane, the disclosures herein may be used
to provide for multiple EDC-assisted recording layers 225 in the
z-direction.
[0082] In some embodiments, because the EDC-assisted recording
layer 225 lies underneath the conventional recording layer 260, the
objective is to write data to the EDC-assisted recording layer 225
while preserving information recorded in other layers (e.g., in the
conventional recording layer 260 and in any additional EDC-assisted
recording layers 225 previously written to). In other words, the
goal is to write to the conventional recording layer 260 and the
EDC-assisted recording layer(s) 225 independently.
[0083] In some embodiments, the exchange break layers of the media
are tuned so that, absent the assistance of the EDC 150, the
EDC-assisted recording layer 225 is more difficult to write than
the conventional recording layer 260. In such embodiments, when the
EDC 150 are not energized, the magnetic field generated by the
write transducer 110 is insufficient to overcome the coercivity of
the EDC-assisted storage locations 145 in the EDC-assisted
recording layer 225, and none of the cells in the EDC-assisted
recording layer 225 are written to. When an EDC 150 is energized,
it generates a field that augments the writer's magnetic field (or
otherwise provides an assist, such as, e.g., by heating the
EDC-assisted recording layer 225) and allows one or more storage
locations 145 in the EDC-assisted recording layer 225 to be written
to.
[0084] In embodiments in which the media includes one conventional
recording layer 260 and an EDC-assisted recording layer 225, the
coercivities of the layers can be different to provide more control
over recording in the EDC-assisted recording layer 225. For
example, referring again to FIG. 3C, the EDC-assisted recording
layer 225 can have a higher coercivity than the conventional
recording layer 260 so that when the EDC 150 in the EDC layer 250
are inactive, the magnetic field generated by the write transducer
110 is strong enough to switch the magnetization in the
conventional recording layer 260, but it is insufficient to switch
the magnetization of the EDC-assisted recording layer 225. In
contrast, when the EDC 150 in the EDC layer 250 are energized, the
magnetic field generated by the write transducer 110, with the
assistance provided by the EDC 150 (e.g., in the form of heat or a
field that adds constructively to or otherwise augments the field
generated by the write transducer 110, as described above) is
sufficient to switch the magnetization of the EDC-assisted
recording layer 225.
[0085] In some embodiments, the conventional recording layer 260
can be written to without affecting the EDC-assisted recording
layer 225, but writing to the EDC-assisted recording layer 225
affects the conventional recording layer 260. For example, the
coercivity of the conventional recording layer 260 may be lower
than the coercivity of the EDC-assisted recording layer 225. In
some such embodiments, the write process comprises two steps: a
first step in which at least one EDC 150 in the EDC layer 250 is
activated, and both the conventional recording layer 260 and the
EDC-assisted recording layer 225 are written to, and a second step
in which all EDC 150 are inactive and only the conventional
recording layer 260 is written to.
[0086] In some embodiments in which a two-step recording procedure
is used, the EDC 150 are used in conjunction with a recording
process in the first step to enable the EDC-assisted recording
layer 225 to be written. Because the coercivity of the conventional
recording layer 260 is lower than that of the EDC-assisted
recording layer 225, the EDC-assisted recording process may also
cause one or more storage locations 135 in the conventional
recording layer 260 to be written to. For example, the field
emitted by the write transducer 110 may change the magnetization of
an EDC-assisted storage location 145 in the EDC-assisted recording
layer 225, which is desired, and it may also change the
magnetization of one or more conventional storage locations 135 in
the conventional recording layer 260, which is not desired. In
general, the storage locations 135 in the conventional recording
layer 260 that are most likely to be overwritten when the
EDC-assisted storage locations 145 are written to are those closest
to the EDC-assisted storage locations 145, because those storage
locations 135 are most likely to be affected by the write
transducer 110's magnetic field. In the second step, the EDC 150
are not activated, and the magnetic field strength may be reduced
to a level that is insufficient to overcome the coercivity of the
EDC-assisted recording layer 225. The storage locations 135 in the
conventional recording layer 260 may then be written to without
affecting the data previously stored in the EDC-assisted recording
layer 225 in the first step.
[0087] A similar approach allows the preservation of data
previously stored in the conventional recording layer 260 when the
EDC-assisted recording layer 225 is written. In some embodiments,
prior to beginning the process to write to the EDC-assisted
recording layer 225, the contents of the storage location(s) 135 of
the conventional recording layer 260 that may be affected by the
process of writing to the EDC-assisted recording layer 225 (e.g.,
the storage locations 135 that are closest to the EDC-assisted
storage locations 145 to be written to) are noted. Then the EDC(s)
150 are activated, and selected EDC-assisted storage locations 145
in the EDC-assisted recording layer 225 are written to. As
explained above, this process may modify the contents of certain
storage locations(s) 135 of the conventional recording layer 260
(e.g., those that are closest to the EDC-assisted storage locations
145 being written to). The EDC(s) 150 are then deactivated, and the
affected storage location(s) 135 of the conventional recording
layer 260 are re-written to restore the contents of the storage
location(s) 135.
[0088] It is also possible to write to the EDC-assisted recording
layer 225 without affecting the contents of storage locations 135
in the conventional recording layer 260. For example, resonators
may be used to enable independent selection of the EDC-assisted
recording layer 225 for writing without affecting the conventional
recording layer 260.
[0089] In order for the EDC 150 to assist in writing to an
EDC-assisted recording layer 225, the EDC 150 must be activated.
FIG. 8A is a conceptual illustration of a magnetic storage system
100 in accordance with some embodiments. As shown in FIG. 8A, the
media has been partitioned into sectors. Sectors 1 and 2 are shown.
Each sector includes a plurality of EDC 150 and EDC-assisted
storage locations 145. FIG. 8A illustrates one EDC 150 per
EDC-assisted storage location 145, but, as explained above, the EDC
150 and EDC-assisted storage locations 145 need not be in a
one-to-one relationship. For ease of explanation, each sector shown
in FIG. 8A is illustrated having only four EDC 150 and four
EDC-assisted storage locations 145. Sector 1 includes EDC 150A,
150B, 150C, and 150D and corresponding EDC-assisted storage
locations 145A, 145B, 145C, and 145D. Sector 2 includes EDC 150E,
150F, 150G, and 150H and corresponding EDC-assisted storage
locations 145E, 145F, 145G, and 145H. The EDC 150A and 150E are
configured to be activated by an activation signal 180 having a
frequency of f1. The EDC 150B and 150F are configured to be
activated by an activation signal 180 having a frequency of f2. The
EDC 150C and 150G are configured to be activated by an activation
signal 180 having a frequency of f3, and the EDC 150D and 150H are
configured to be activated by an activation signal 180 having a
frequency of f4.
[0090] As shown in FIG. 8A, the magnetic storage system 100
comprises a signal generator 190 wirelessly coupled to (i.e.,
configured to transmit wireless signals to and/or receive wireless
signals from) the EDC 150. The signal generator 190 includes
circuitry to generate wireless signals and a transmitter capable of
transmitting wireless signals. It is to be understood that the
transmitter of the signal generator 190 may be positioned in or on
the slider 525, or it may be in another location within the data
storage device 100 (e.g., in a fixed position not in the immediate
vicinity of the storage location 135, 145 of the media to be
written to/read from).
[0091] In embodiments in which the transmitter of the signal
generator 190 is positioned in or on the slider 525, the signal
generator 190 may be in close proximity to the EDC 150 to be
activated and may be able to direct an activation signal toward
only the EDC 150 to be activated. In such cases, there may be
little risk of unintended activation of other EDC 150.
[0092] In embodiments in which the signal generator 190 transmits
activation signals from further away (e.g., when the signal
generator 190 is in a location away from the head 540 and/or
media), there may be a risk that the activation signal activates
EDC 150 in addition to the intended one(s). To mitigate the
unintended activation of EDC 150 other than the one(s) intended,
the signal generator 190 may comprise a directional antenna
enabling the signal generator 190 to launch the activation signal
180 in a particular direction (e.g., toward a target EDC 150). In
the example shown in FIG. 8A, the signal generator 190 is targeting
the EDC 150A in Sector 1 and launches the activation signal 180,
having the frequency f1, in the direction of EDC 150A. As
illustrated, the activation signal 180 may also travel in other
directions, such as toward Sector 2 (which may be, e.g., an
adjacent sector, a sector in an EDC layer 250 other than the one
targeted, etc.). Thus, the EDC 150E, which is also configured to
respond to activation signals 180 having the frequency f1, may also
be activated by the activation signal 180.
[0093] In operation, to activate a specific EDC 150, the signal
generator 190 generates an activation signal 180 and transmits it
to that EDC 150 (and, as described above, potentially to other EDC
150), potentially using a directional antenna. The signal generator
190 may be capable of generating activation signals 180 having
different characteristics (e.g., frequencies, etc.), as explained
further below. To provide selectivity in EDC 150 activation,
different EDC antennas 152 may be configured to respond to
different RF frequencies so that an activation signal 180 of a
selected frequency activates a particular EDC 150 (or set of more
than one EDC 150). Moreover, the EDC antennas 152 may be
directional antennas so that, for example, a selected EDC 150 is
activated by a first activation signal 180 having a frequency of f1
received from a first direction but not a second signal having a
frequency of f1 received from a second direction (e.g., 90 degrees
away). Thus, one or more characteristics of the RF activation
signals 180 (e.g., frequency, timing, phase, direction, etc.) that
activate the various EDC 150 may be used to address or target
particular EDC 150 and the memory cells within range of those EDC
150.
[0094] In some embodiments, such as shown in FIG. 8A, the EDC 150
are in sectors, and only one EDC 150 in each sector responds to an
activation signal 180 having a particular set of characteristics.
In such embodiments, the activation signal 180 may activate more
than one EDC 150 (for example, the activation signal 180 shown in
FIG. 8A may activate both EDC 150A in Sector 1 and EDC 150E in
Sector 2), but each activated EDC 150 is in a different sector. For
write operations using a write transducer 110 as described above,
the write transducer 110 is over only the portion of the media to
be written, which corresponds to the EDC-assisted storage
location(s) 145 associated with the activated EDC 150, and
therefore the activation of one or more EDC 150 outside of that
sector does not cause writing to unintended EDC-assisted storage
locations 145 away from the write transducer 110. As a concrete
example, referring to FIG. 8A, the write transducer 110 would be
over the EDC-assisted storage location 145A, so even if the
activation signal 180 were to activate EDC 150E, only the
EDC-assisted storage location 145A would be written to. The
EDC-assisted storage location 145E would not be affected because
the write transducer 110 would not generate a field strong enough
to switch the magnetization of the EDC-assisted storage location
145E.
[0095] In the example shown in FIG. 8A, the activation signal 180
has a characteristic, namely its frequency, selected to activate a
particular EDC 150 (or set of EDC 150) in the media. It is to be
appreciated that other aspects of the activation signal 180 may be
used instead of or in addition to the frequency to activate
selected EDC 150. Examples of other characteristics include
amplitude, modulation, duty cycle, bandwidth, or any other
controllable characteristic of a transmitted signal.
[0096] There are many benefits of using EDC 150 to write to a
storage media. For example, higher-capacity storage is feasible
because of the ability to store data in three dimensions of the
media instead of only two. Furthermore, the use of EDC 150 eases
requirements on the write head and media because the EDC 150
provide an assist to the write transducer 110. As a consequence,
the write head can be larger, and the same magnitude magnetic field
can be used to write to storage locations 145 in the EDC-assisted
recording layer 225 because the EDC 150 supply an assisting field
or other assistive function (e.g., heat to reduce coercivity).
Moreover, the media does not need to be as smooth as it needs to be
without the use of EDC 150 because the head 540 can fly higher
above the media and still provide the same or better performance as
in a conventional storage device. Also, the storage device 100 does
not need to provide power to the EDC 150 corresponding to storage
locations 145 that are not being written to. Another advantage is
that the EDC 150 can enable bulk or bank writes. The writer may
turn on an array of EDC 150 in the media and target an RF signal
toward that location (or those locations), thereby writing to an
area of the media.
Reading from a Data Storage Media Using EDC
[0097] In some embodiments, EDC 150 embedded in a media are used to
read data stored in an EDC-assisted recording layer 225. For
example, as explained above, the circuitry 155 of an EDC 150 may
include read circuitry (e.g., a read sensor 164) that is activated
by an activation signal 180 received by the EDC 150 antenna 152.
The read circuitry enables an EDC 150 to interrogate a nearby
EDC-assisted storage location 145 (or a nearby set of EDC-assisted
storage locations 145). The EDC 150 may also include transmitting
circuitry that enables the EDC 150 to wirelessly transmit a signal
reporting the result of the interrogation to a receiver in the
storage system. The receiver may be located on or in a slider 525
that flies over the media, or it may be located away from the
media.
[0098] FIGS. 8A and 8B illustrate reading from an EDC-assisted
storage location 145 in accordance with some embodiments. In
operation, the signal generator 190 generates and transmits an
activation signal 180. As explained above, if the transmitter of
the signal generator 190 is located on or in a slider 525 that
flies over the media, the activation signal 180 may be in close
proximity to the EDC 150 intended to be activated. In such
embodiments, the activation signal 180 may activate only the
intended EDC 150. In some embodiments, the transmitter of the
signal generator 190 is not in close proximity to the EDC 150 to be
activated, and there is a risk of activating unintended EDC 150.
FIG. 8A illustrates a situation in which both EDC 150A in Sector 1
and EDC 150E in Sector 2 are activated by the activation signal
180, which has a frequency f1.
[0099] As shown in FIG. 8B, in response to the activation signal
180, both EDC 150A, in Sector 1, and EDC 150E, in Sector 2,
determine the contents of their respective EDC-assisted storage
locations 145A, 145E and transmit wireless signals representing the
contents to the read receiver 195. The wireless signals may also
provide other information, such as, for example, information
indicating the identity (e.g., address or other identifying
information) or location (e.g., exact or approximate, sector, etc.)
of the EDC-assisted storage location 145A, 145E or of the EDC 150A,
150E. EDC 150A transmits the read response signal 185A,
representing the contents of EDC-assisted storage location 145A
(and possibly other information), and EDC 150E transmits the read
response signal 185B, representing the contents of EDC-assisted
storage location 145E. (As explained previously, the read response
signals 185 may report the contents of more than one EDC-assisted
storage location 145, and/or they may include other information,
such as, for example, information indicating or allowing the read
receiver 195 to determine the location and/or identity of the
EDC(s) 150 and/or the EDC-assisted storage locations 145.)
[0100] The read receiver 195 may be located in or on a slider 525
that flies over the media, or it may be positioned in a location
away from the media. In embodiments in which the read receiver 195
is located in or on the slider 525, the read receiver 195 may
detect only the desired read response signal 185A, or it may detect
both the desired read response signal 185A and the unwanted read
response signal 185B. Similarly, in embodiments in which the read
receiver 195 is in a location remote from the media, the read
receiver 195 may receive both read response signals 185A and 185B.
The read receiver 195 can apply signal processing techniques to
extract the desired read information (e.g., the contents of the
EDC-assisted storage location 145A) from the aggregate received
signal when more than one EDC 150 transmits a read response signal
185.
[0101] To assist the read receiver 195 to distinguish between read
response signals 185 from different EDC 150 and to extract the
desired information, the EDC 150 may transmit read response signals
185 that have different characteristics. For example, referring to
FIG. 8B, the read response signal 185A may have a different
characteristic (e.g., frequency, modulation, etc.) than the read
response signal 185B. The read receiver 195 may include or have
access to a listing or database of EDC 150 read response signal 185
characteristics (e.g., a look-up table) and may be capable of
configuring itself to receive the target EDC 150's read response
signal 185 (e.g., by tuning its receive circuitry to a particular
frequency, by looking for a particular pattern/modulation, etc.).
As just one example, the read receiver 195 may know that EDC 150A
responds to activation signals 180 having a frequency f1 and
transmits read response signals 185 at a first frequency or with a
first modulation characteristic, whereas EDC 150E responds to
activation signals 180 having a frequency f1 and transmits read
response signals 185 at a second frequency or with a second
modulation characteristic. By tuning its receiver to look for read
response signals 185 at the first frequency or with the first
modulation characteristic, the read receiver 195 can distinguish
the read response signal 185A from the read response signal
185B.
[0102] FIG. 9 is a block diagram illustrating an EDC 150. To obtain
the contents of one or more EDC-assisted storage locations 145 in
an EDC-assisted recording layer 225 of the media, the signal
generator 190 (or, collectively, multiple ones) of the storage
device directs an RF activation signal 180 having suitable
characteristics to activate a desired EDC 150 within the
EDC-assisted recording layer 225 toward the EDC 150. The activation
signal 180 causes the EDC antenna 152 to generate power for the
EDC's read circuitry 164. The read circuitry 164 interrogates one
or more EDC-assisted storage locations 145 near the EDC 150 and
constructs a response signal 185 for wireless transmission to the
read receiver 195.
[0103] As explained above, the interrogation mechanisms may be
implemented in a number of ways, including using magneto-resistive
sensors used by conventional disk drives adapted for this
application. The response signal 185 provides information to convey
the contents of the interrogated one or more EDC-assisted storage
locations 145. The response signal 185 may also include bits
identifying the location(s) of the interrogated EDC-assisted
storage location(s) 145. For example, the response signal 185 may
have a format that includes a header identifying the address or
location of the interrogated EDC-assisted storage location(s) 145
and/or activated EDC 150 followed by a body that reports the
contents of the interrogated EDC-assisted storage location(s) 145.
As another example, the response signal 185 may have a format that
itself varies depending on the address or location of the
interrogated EDC-assisted storage location(s) 145 and/or activated
EDC 150. In addition, or alternatively, the reader may use
triangulation techniques to identify the EDC 150 responding to a
read request or to identify the locations of the EDC-assisted
storage location(s) 145 being read. If the EDC 150 transmits a read
response signal 185 that includes the contents of interrogated
EDC-assisted storage location(s) 145 that the signal generator 190
did not request, the reader may extract or reconstruct (e.g.,
decode) only the desired information from the response signal
185.
[0104] Because the EDC 150 transmit the contents of the
EDC-assisted storage locations 145 wirelessly, it is desirable to
ensure that the EDC 150 respond only to energy from within the data
storage device 100. For example, the chassis of the data storage
device 100 may be shielded to prevent stray activation signals 180
from entering the data storage device and read response signals 185
from exiting the data storage device 100.
[0105] FIG. 10 is a flowchart illustrating an exemplary process
1000 to read an EDC-assisted storage location 145 (or more than one
EDC-assisted storage location 145) using EDC 150. At 1010, the
process begins. At 1020, whether the EDC 150 is energized is
determined. If the EDC 150 is energized, the process proceeds to
1030, where it is determined whether the EDC 150 is selected. If
so, the process proceeds to 1040, where the contents of at least
one EDC-assisted storage location 145 are sensed, computed, and
transmitted.
[0106] FIG. 11 illustrates a process 1100 performed by an EDC 150
to read an EDC-assisted storage location 145 (or multiple
EDC-assisted storage locations 145). At 1110, the process begins.
At 1120, the EDC 150 receives, wirelessly, a read command (e.g.,
via an activation signal 180). The read command instructs the EDC
150 to read one or more EDC-assisted storage locations 145 and to
report the contents. At 1130, the EDC 150 senses one or more
EDC-assisted storage locations 145 in response to the read command.
At 1140, the EDC 150 determines the read response signal 185, which
reports the contents of the sensed one or more EDC-assisted storage
locations 145. In some embodiments, the read response signal 185
may also include information identifying the EDC 150 or the sensed
EDC-assisted storage location 145. For example, this information
may include the location(s) or address(es) of the sensed
EDC-assisted storage location(s) 145 and/or the EDC 150. At 1150,
the EDC 150 wirelessly transmits the read response signal 185 to
the reader. At 1160, the process ends.
[0107] FIG. 12 illustrates the use of EDC 150 in the context of
reading from and writing to a hard disk drive 500. FIG. 12 shows
the communication paths between the read/write circuitry and the
EDC 150; the storage locations are not illustrated at the
microscopic level in FIG. 12.
[0108] There are many benefits of using EDC 150 to read from a
storage media. For example, the use of EDC 150 can eliminate the
need for a read head on the slider 525. Furthermore, because, in
some embodiments, the EDC 150 transmit wireless signals to report
the contents of EDC-assisted storage locations 145, the storage
device 100 does not need to spin the media to read the stored data.
In addition, the storage device 100 does not need to provide power
to EDC-assisted storage locations 145 that are not being read.
Moreover, the use of EDC 150 provides a way to read not only the
conventional recording layer 260, but also the EDC-assisted
recording layer(s) 225 of the media.
Additional Applications
[0109] In addition to hard disk drive applications, in which EDC
150 may be added to a hard disk 520 to increase the data storage
capacity of the disk 520, the techniques disclosed herein may be
used advantageously in archival storage systems. Archival storage
systems store data that is not used often but might need to be
accessed in the future, or data that must be kept for regulatory
compliance purposes. In some embodiments, an archival storage
system uses media with EDC 150 as discussed above.
[0110] FIG. 13 illustrates an archival storage system in accordance
with some embodiments. In contrast to a hard disk drive, in which
the reader and writer are both within the storage device, the
archival storage system's writer and reader are physically
separated. As shown in FIG. 13, the writer may be incorporated in a
first device that accepts a cartridge into which a media (e.g., a
disk with EDC 150) is inserted. After the data has been written to
the media, the media may be moved to a different physical location
for storage and, if necessary, reading at a later time. For
example, as shown in FIG. 13, the media may be moved to a storage
tower in which the media are closely stacked. The storage tower may
house hundreds of media. The storage tower includes one or more
readers that, as described above, generate RF activation signals
180 having suitable characteristics to activate desired EDC 150
within the EDC-assisted recording layers 225 of the media and
receive from the EDC 150 the results of the interrogations of the
EDC-assisted storage locations 145 (as described above). Each shelf
of the storage tower may include a separate reader (or multiple
ones), or a single reader (or multiple ones collectively) may be
capable of reading from media on more than one shelf. The storage
tower may also include a power supply circuit that provides power
(e.g., selectively if the storage tower includes multiple readers)
to individual readers in the storage tower.
[0111] The use of EDC 150 in archival storage systems eliminates
the need to spin a disk to read archived data. Therefore, less
space is required for the media because there is no need for a
conventional read head, slider, or armature. Consequently, large
numbers of disks may be stored in close proximity while still
allowing their contents to be read using the EDC 150 and the
techniques disclosed herein.
[0112] It is to be understood that although the archival data
storage system shown and described herein suggests the use of disks
with EDC 150, there is no requirement that the system use media of
any particular size or shape. The techniques disclosed herein apply
to all media in which EDC 150 have been scattered, distributed,
embedded, or incorporated. For example, the media may have shapes
other than round, and they may be thicker or thinner than
conventional hard disks.
[0113] In the foregoing description and in the accompanying
drawings, specific terminology has been set forth to provide a
thorough understanding of the disclosed embodiments. In some
instances, the terminology or drawings may imply specific details
that are not required to practice the invention.
[0114] Although this document explains aspects of certain
embodiments in the context of data storage devices, using hard disk
drives as examples of data storage devices, the disclosures herein
are not limited to use in data storage device applications.
Specifically, the various embodiments are applicable to other
electronic devices storage needs. Furthermore, although certain
embodiments are explained in the context of hard disk drives, and
some of the drawings show a hard disk drive as an example data
storage device, the various embodiments may be applicable to other
data storage devices such as solid state drives, solid state hybrid
disk drives, optical disk drives, tape drives, and the like.
[0115] To avoid obscuring the present disclosure unnecessarily,
well-known components (e.g., of a disk drive) are shown in block
diagram form and/or are not discussed in detail or, in some cases,
at all.
[0116] Unless otherwise specifically defined herein, all terms are
to be given their broadest possible interpretation, including
meanings implied from the specification and drawings and meanings
understood by those skilled in the art and/or as defined in
dictionaries, treatises, etc. As set forth explicitly herein, some
terms may not comport with their ordinary or customary
meanings.
[0117] As used in the specification, the singular forms "a," "an"
and "the" do not exclude plural referents unless otherwise
specified. The word "or" is to be interpreted as inclusive unless
otherwise specified. Thus, the phrase "A or B" is to be interpreted
as meaning all of the following: "both A and B," "A but not B," and
"B but not A." Any use of "and/or" herein does not mean that the
word "or" alone connotes exclusivity.
[0118] As used herein, phrases of the form "at least one of A, B,
and C," "at least one of A, B, or C," "one or more of A, B, or C,"
and "one or more of A, B, and C" are interchangeable, and each
encompasses all of the following meanings: "A only," "B only," "C
only," "A and B but not C," "A and C but not B," "B and C but not
A," and "all of A, B, and C."
[0119] To the extent that the terms "include(s)," "having," "has,"
"with," and variants thereof are used in the description, such
terms are intended to be inclusive in a manner similar to the term
"comprising," i.e., meaning "including but not limited to." The
terms "exemplary" and "embodiment" are used to express examples,
not preferences or requirements.
[0120] The terms "over," "under," "between," and "on" are used
herein refer to a relative position of one feature (e.g., a layer
of a media) with respect to other features. For example, one
feature disposed "over" or "under" another feature may be directly
in contact with the other feature or may have intervening material.
Moreover, one feature disposed "between" two features may be
directly in contact with the two features or may have one or more
intervening features or materials. In contrast, a first feature
"on" a second feature is in contact with that second feature.
[0121] The drawings are not necessarily to scale, and the
dimensions, shapes, and sizes of the features may differ
substantially from how they are depicted in the drawings.
[0122] Although specific embodiments have been disclosed, it will
be evident that various modifications and changes may be made
thereto without departing from the broader spirit and scope of the
disclosure. For example, features or aspects of any of the
embodiments may be applied, at least where practicable, in
combination with any other of the embodiments or in place of
counterpart features or aspects thereof. Accordingly, the
specification and drawings are to be regarded in an illustrative
rather than a restrictive sense.
* * * * *