U.S. patent application number 15/445870 was filed with the patent office on 2018-08-30 for magnetic head having arrays of tunnel valve read transducers.
The applicant listed for this patent is International Business Machines Corporation. Invention is credited to Robert G. Biskeborn, Hugo E. Rothuizen.
Application Number | 20180247664 15/445870 |
Document ID | / |
Family ID | 63209008 |
Filed Date | 2018-08-30 |
United States Patent
Application |
20180247664 |
Kind Code |
A1 |
Biskeborn; Robert G. ; et
al. |
August 30, 2018 |
MAGNETIC HEAD HAVING ARRAYS OF TUNNEL VALVE READ TRANSDUCERS
Abstract
An apparatus, according to one embodiment, includes: a module,
and a plurality of tunnel valve read transducers arranged in an
array extending along the module. Each of the tunnel valve read
transducers includes: a sensor structure, an upper magnetic shield,
a lower magnetic shield, an upper conducting spacer layer between
the sensor structure and the upper magnetic shield, a lower
conducting spacer layer between the sensor structure and the lower
magnetic shield, and electrically insulating layers on opposite
sides of the sensor structure. The sensor structure includes a cap
layer, a free layer, a tunnel barrier layer, a reference layer and
an antiferromagnetic layer. Moreover, a height of the free layer
measured in a direction perpendicular to a media bearing surface of
the module is less than a width of the free layer measured in a
cross-track direction perpendicular to an intended direction of
media travel.
Inventors: |
Biskeborn; Robert G.;
(Hollister, CA) ; Rothuizen; Hugo E.; (Oberrieden,
CH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
International Business Machines Corporation |
Armonk |
NY |
US |
|
|
Family ID: |
63209008 |
Appl. No.: |
15/445870 |
Filed: |
February 28, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11B 5/3951 20130101;
G11B 5/3948 20130101; G11B 5/3906 20130101; G11B 5/3958 20130101;
G11B 5/3932 20130101; G11B 5/00821 20130101; G11B 5/3909 20130101;
G11B 5/3912 20130101 |
International
Class: |
G11B 5/39 20060101
G11B005/39; G11B 15/46 20060101 G11B015/46; G11B 5/008 20060101
G11B005/008; G11B 5/23 20060101 G11B005/23 |
Claims
1. An apparatus, comprising: a module; and a plurality of tunnel
valve read transducers arranged in an array extending along the
module, wherein each of the tunnel valve read transducers includes:
a sensor structure having a cap layer, a free layer, a tunnel
barrier layer, a reference layer and an antiferromagnetic layer; an
upper magnetic shield; a lower magnetic shield; an upper conducting
spacer layer between the sensor structure and the upper magnetic
shield; a lower conducting spacer layer between the sensor
structure and the lower magnetic shield; and electrically
insulating layers on opposite sides of the sensor structure,
wherein a height of the free layer measured in a direction
perpendicular to a media bearing surface of the module is less than
a width of the free layer measured in a cross-track direction
perpendicular to an intended direction of media travel.
2. The apparatus as recited in claim 1, wherein the height of the
sensor structure is less than 0.8 times the width of the sensor
structure.
3. The apparatus as recited in claim 1, wherein the electrically
insulating layers separate the upper conducting spacer layer from
the lower conducting spacer layer and from the opposite sides of
the sensor structure.
4. The apparatus as recited in claim 1, wherein the width of the
free layer is less than 2 .mu.m.
5. The apparatus as recited in claim 1, wherein a separation
between the upper and lower magnetic shields proximate to the
sensor and along the intended direction of media travel is less
than 120 nm.
6. The apparatus as recited in claim 1, wherein each of the tunnel
valve read transducers includes: a hard bias magnet, wherein the
hard bias magnet is positioned proximate to a side of the sensor
structure along a cross-track direction, wherein the electrically
insulating layers separate the hard bias magnet from the sensor
structure and the lower conducting spacer layer.
7. The apparatus as recited in claim 6, wherein a thickness of the
electrically insulating layers is less than 8 nm.
8. The apparatus as recited in claim 6, wherein the electrically
insulating layers include a dielectric material.
9. The apparatus as recited in claim 6, wherein a thickness of the
free layer is at least 4 nm.
10. The apparatus as recited in claim 6, wherein a thickness of the
hard bias magnet at a thickest portion thereof is at least 8 times
greater than a thickness of the free layer.
11. The apparatus as recited in claim 6, wherein a thickness of the
hard bias magnet at a thickest portion thereof is at least 12 times
greater than a thickness of the free layer times a ratio of a
magnetic moment of the free layer divided by a magnetic moment of
the hard bias magnet.
12. The apparatus as recited in claim 6, wherein a thickness of the
hard bias magnet at an edge closest to the free layer is greater
than the thickness of the free layer.
13. The apparatus as recited in claim 12, wherein a first portion
of each of the hard bias magnet is positioned below a lower surface
of the free layer and a second portion of the hard bias magnet is
positioned above an upper surface of the free layer, wherein the
upper and lower surfaces are opposite each other along a deposition
direction.
14. The apparatus as recited in claim 12, wherein an edge of the
hard bias magnet closest to the free layer is oriented between
70.degree. and 90.degree. relative to a plane of deposition of the
free layer.
15. The apparatus as recited in claim 6, wherein a seed layer is
present between the hard bias magnet and the electrically
insulating layers, wherein the hard bias magnet is at least
partially crystalline.
16. The apparatus as recited in claim 6, wherein a width of the
hard bias magnet measured in the cross-track direction is at least
0.3 .mu.m.
17. The apparatus as recited in claim 6, wherein the hard bias
magnet is characterized by having a magnetic field produced by the
hard bias magnet that is greater than or equal to 90% of a maximum
achievable magnetic field for a material of the hard bias
magnet.
18. The apparatus as recited in claim 6, wherein the hard bias
magnet is a split hard bias structure having two seed layers, each
of the seed layers having an at least partially crystalline
structure formed thereabove.
19. The apparatus as recited in claim 1, wherein the plurality of
tunnel valve read transducers share a common media-facing surface
of the module.
20. The apparatus as recited in claim 1, comprising: a drive
mechanism for passing a magnetic medium over the tunnel valve read
transducers; and a controller electrically coupled to the tunnel
valve read transducers.
Description
BACKGROUND
[0001] The present invention relates to data storage systems, and
more particularly, this invention relates to magnetic tape heads
having tunnel valve read transducers with tunnel magnetoresistive
(TMR) sensor configurations which achieve reduced magnetic
noise.
[0002] In magnetic storage systems, magnetic transducers read data
from and write data onto magnetic recording media. Data is written
on the magnetic recording media by moving a magnetic recording
transducer to a position over the media where the data is to be
stored. The magnetic recording transducer then generates a magnetic
field, which encodes the data into the magnetic media. Data is read
from the media by similarly positioning the magnetic read
transducer and then sensing the magnetic field of the magnetic
media. Read and write operations may be independently synchronized
with the movement of the media to ensure that the data can be read
from and written to the desired location on the media.
[0003] An important and continuing goal in the data storage
industry is that of increasing the density of data stored on a
medium. For tape storage systems, that goal has led to increasing
the track and linear bit density on recording tape, and decreasing
the thickness of the magnetic tape medium. However, the development
of small footprint, higher performance tape drive systems has
created various problems in the design of a tape head assembly for
use in such systems.
[0004] In a tape drive system, the drive moves the magnetic tape
over the surface of the tape head at high speed. Usually the tape
head is designed to minimize the spacing between the head and the
tape. The spacing between the magnetic head and the magnetic tape
is crucial and so goals in these systems are to have the recording
gaps of the transducers, which are the source of the magnetic
recording flux in near contact with the tape to effect writing
sharp transitions, and to have the read elements in near contact
with the tape to provide effective coupling of the magnetic field
from the tape to the read elements.
[0005] Minimization of the spacing between the head and the tape,
however, induces frequent contact between the tape and the media
facing side of the head, causing tape operations to be deemed a
type of contact recording. This contact, in view of the high tape
speeds and tape abrasivity, quickly affects the integrity of the
materials used to form the media facing surface of the head, e.g.,
causing wear thereto, smearing which is known to cause shorts,
bending ductility, etc. Furthermore, shorting may occur when an
asperity of the tape media drags any of the conductive metallic
films near the sensor across the tunnel junction.
[0006] Implementing TMR sensor configurations to read from and/or
write to magnetic tape has also reduced the shield-to-shield
spacing which allows for more detailed reading and/or writing to
magnetic tape by allowing the linear density of transitions on tape
to increase. However, this increase has not come without drawbacks.
For instance, at smaller dimensions, conventional free layers have
proven to be magnetically unstable, thereby introducing magnetic
switching noise.
SUMMARY
[0007] An apparatus, according to one embodiment, includes: a
module, and a plurality of tunnel valve read transducers arranged
in an array extending along the module. Each of the tunnel valve
read transducers includes: a sensor structure, an upper magnetic
shield, a lower magnetic shield, an upper conducting spacer layer
between the sensor structure and the upper magnetic shield, a lower
conducting spacer layer between the sensor structure and the lower
magnetic shield, and electrically insulating layers on opposite
sides of the sensor structure. The sensor structure includes a cap
layer, a free layer, a tunnel barrier layer, a reference layer and
an antiferromagnetic layer. Moreover, a height of the free layer
measured in a direction perpendicular to a media bearing surface of
the module is less than a width of the free layer measured in a
cross-track direction perpendicular to an intended direction of
media travel.
[0008] Any of these embodiments may be implemented in a magnetic
data storage system such as a tape drive system, which may include
a magnetic head, a drive mechanism for passing a magnetic medium
(e.g., recording tape) over the magnetic head, and a controller
electrically coupled to the magnetic head.
[0009] Other aspects and embodiments of the present invention will
become apparent from the following detailed description, which,
when taken in conjunction with the drawings, illustrate by way of
example the principles of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] FIG. 1A is a schematic diagram of a simplified tape drive
system according to one embodiment.
[0011] FIG. 1B is a schematic diagram of a tape cartridge according
to one embodiment.
[0012] FIG. 2A is a side view of a flat-lapped, bi-directional,
two-module magnetic tape head according to one embodiment.
[0013] FIG. 2B is a tape facing surface view taken from Line 2B of
FIG. 2A.
[0014] FIG. 2C is a detailed view taken from Circle 2C of FIG.
2B.
[0015] FIG. 2D is a detailed view of a partial tape facing surface
of a pair of modules.
[0016] FIG. 3 is a partial tape facing surface view of a magnetic
head having a write-read-write configuration.
[0017] FIG. 4 is a partial tape facing surface view of a magnetic
head having a read-write-read configuration.
[0018] FIG. 5 is a side view of a magnetic tape head with three
modules according to one embodiment where the modules all generally
lie along about parallel planes.
[0019] FIG. 6 is a side view of a magnetic tape head with three
modules in a tangent (angled) configuration.
[0020] FIG. 7 is a side view of a magnetic tape head with three
modules in an overwrap configuration.
[0021] FIGS. 8A-8C are schematics depicting the principles of tape
tenting.
[0022] FIG. 9 is a representational diagram of files and indexes
stored on a magnetic tape according to one embodiment.
[0023] FIG. 10A is a partial tape facing surface view of a magnetic
tape head according to one embodiment.
[0024] FIG. 10B is a partial detailed tape facing surface view of a
tunnel valve read transducer from FIG. 10A.
[0025] FIG. 10C is a detailed view of the free layer from FIG. 10B
shown along a plane perpendicular to the plane of deposition of the
free layer, according to one embodiment.
[0026] FIG. 10D is a detailed view of the sensor structure from
FIG. 10B shown along a plane perpendicular to the plane of
deposition of the sensor structure, according to one
embodiment.
[0027] FIG. 10E is a partial detailed tape facing surface view of a
tunnel valve read transducer according to one embodiment.
[0028] FIG. 10F is a detailed view of the free layer and hard bias
magnets from FIG. 10E shown along a plane perpendicular to the
plane of deposition of the free layer and the hard bias magnets,
according to one embodiment.
[0029] FIG. 10G is a partial detailed tape facing surface view of a
tunnel valve read transducer according to one embodiment.
[0030] FIG. 11A is a partial detailed view of a hard bias structure
and a free layer according to the prior art.
[0031] FIG. 11B is a partial detailed view of a hard bias magnet
and a free layer according to one embodiment.
[0032] FIG. 11C is a partial detailed view of a hard bias magnet
and a free layer according to one embodiment.
[0033] FIG. 12 is a graph plotting the calculated magnetization of
the free layer for each of the structures in FIGS. 11A-11C vs. the
distance from the sensor edge.
DETAILED DESCRIPTION
[0034] The following description is made for the purpose of
illustrating the general principles of the present invention and is
not meant to limit the inventive concepts claimed herein. Further,
particular features described herein can be used in combination
with other described features in each of the various possible
combinations and permutations.
[0035] Unless otherwise specifically defined herein, all terms are
to be given their broadest possible interpretation including
meanings implied from the specification as well as meanings
understood by those skilled in the art and/or as defined in
dictionaries, treatises, etc.
[0036] It must also be noted that, as used in the specification and
the appended claims, the singular forms "a," "an" and "the" include
plural referents unless otherwise specified.
[0037] The following description discloses several preferred
embodiments of magnetic storage systems, as well as operation
and/or component parts thereof, which include improved free layer
performance. Shape anisotropy resulting from free layer dimensions
and/or the introduction of hard bias magnets as described herein
may be able to provide a desirable level of stabilization to the
free layer, and thereby achieve unexpected improvements over
conventional implementations, e.g., as will be described in further
detail below.
[0038] In one general embodiment, an apparatus includes: a module,
and a plurality of tunnel valve read transducers arranged in an
array extending along the module. Each of the tunnel valve read
transducers includes: a sensor structure, an upper magnetic shield,
a lower magnetic shield, an upper conducting spacer layer between
the sensor structure and the upper magnetic shield, a lower
conducting spacer layer between the sensor structure and the lower
magnetic shield, and electrically insulating layers on opposite
sides of the sensor structure. The sensor structure includes a cap
layer, a free layer, a tunnel barrier layer, a reference layer and
an antiferromagnetic layer. Moreover, a height of the free layer
measured in a direction perpendicular to a media bearing surface of
the module is less than a width of the free layer measured in a
cross-track direction perpendicular to an intended direction of
media travel.
[0039] FIG. 1A illustrates a simplified tape drive 100 of a
tape-based data storage system, which may be employed in the
context of the present invention. While one specific implementation
of a tape drive is shown in FIG. 1A, it should be noted that the
embodiments described herein may be implemented in the context of
any type of tape drive system.
[0040] As shown, a tape supply cartridge 120 and a take-up reel 121
are provided to support a tape 122. One or more of the reels may
form part of a removable cartridge and are not necessarily part of
the drive 100. The tape drive, such as that illustrated in FIG. 1A,
may further include drive motor(s) to drive the tape supply
cartridge 120 and the take-up reel 121 to move the tape 122 over a
tape head 126 of any type. Such head may include an array of
readers, writers, or both.
[0041] Guides 125 guide the tape 122 across the tape head 126. Such
tape head 126 is in turn coupled to a controller 128 via a cable
130. The controller 128, may be or include a processor and/or any
logic for controlling any subsystem of the drive 100. For example,
the controller 128 typically controls head functions such as servo
following, data writing, data reading, etc. The controller 128 may
include at least one servo channel and at least one data channel,
each of which include data flow processing logic configured to
process and/or store information to be written to and/or read from
the tape 122. The controller 128 may operate under logic known in
the art, as well as any logic disclosed herein, and thus may be
considered as a processor for any of the descriptions of tape
drives included herein, in various embodiments. The controller 128
may be coupled to a memory 136 of any known type, which may store
instructions executable by the controller 128. Moreover, the
controller 128 may be configured and/or programmable to perform or
control some or all of the methodology presented herein. Thus, the
controller 128 may be considered to be configured to perform
various operations by way of logic programmed into one or more
chips, modules, and/or blocks; software, firmware, and/or other
instructions being available to one or more processors; etc., and
combinations thereof.
[0042] The cable 130 may include read/write circuits to transmit
data to the head 126 to be recorded on the tape 122 and to receive
data read by the head 126 from the tape 122. An actuator 132
controls position of the head 126 relative to the tape 122.
[0043] An interface 134 may also be provided for communication
between the tape drive 100 and a host (internal or external) to
send and receive the data and for controlling the operation of the
tape drive 100 and communicating the status of the tape drive 100
to the host, all as will be understood by those of skill in the
art.
[0044] FIG. 1B illustrates an exemplary tape cartridge 150
according to one embodiment. Such tape cartridge 150 may be used
with a system such as that shown in FIG. 1A. As shown, the tape
cartridge 150 includes a housing 152, a tape 122 in the housing
152, and a nonvolatile memory 156 coupled to the housing 152. In
some approaches, the nonvolatile memory 156 may be embedded inside
the housing 152, as shown in FIG. 1B. In more approaches, the
nonvolatile memory 156 may be attached to the inside or outside of
the housing 152 without modification of the housing 152. For
example, the nonvolatile memory may be embedded in a self-adhesive
label 154. In one preferred embodiment, the nonvolatile memory 156
may be a Flash memory device, read-only memory (ROM) device, etc.,
embedded into or coupled to the inside or outside of the tape
cartridge 150. The nonvolatile memory is accessible by the tape
drive and the tape operating software (the driver software), and/or
another device.
[0045] By way of example, FIG. 2A illustrates a side view of a
flat-lapped, bi-directional, two-module magnetic tape head 200
which may be implemented in the context of the present invention.
As shown, the head includes a pair of bases 202, each equipped with
a module 204, and fixed at a small angle .alpha. with respect to
each other. The bases may be "U-beams" that are adhesively coupled
together. Each module 204 includes a substrate 204A and a closure
204B with a thin film portion, commonly referred to as a "gap" in
which the readers and/or writers 206 are formed. In use, a tape 208
is moved over the modules 204 along a media (tape) bearing surface
209 in the manner shown for reading and writing data on the tape
208 using the readers and writers. The wrap angle .theta. of the
tape 208 at edges going onto and exiting the flat media support
surfaces 209 are usually between about 0.1 degree and about 3
degrees.
[0046] The substrates 204A are typically constructed of a wear
resistant material, such as a ceramic. The closures 204B may be
made of the same or similar ceramic as the substrates 204A.
[0047] The readers and writers may be arranged in a piggyback or
merged configuration. An illustrative piggybacked configuration
includes a (magnetically inductive) writer transducer on top of (or
below) a (magnetically shielded) reader transducer (e.g., a
magnetoresistive reader, etc.), wherein the poles of the writer and
the shields of the reader are generally separated. An illustrative
merged configuration includes one reader shield in the same
physical layer as one writer pole (hence, "merged"). The readers
and writers may also be arranged in an interleaved configuration.
Alternatively, each array of channels may be readers or writers
only. Any of these arrays may contain one or more servo track
readers for reading servo data on the medium.
[0048] FIG. 2B illustrates the tape bearing surface 209 of one of
the modules 204 taken from Line 2B of FIG. 2A. A representative
tape 208 is shown in dashed lines. The module 204 is preferably
long enough to be able to support the tape as the head steps
between data bands.
[0049] In this example, the tape 208 includes 4 to 32 data bands,
e.g., with 16 data bands and 17 servo tracks 210, as shown in FIG.
2B on a one-half inch wide tape 208. The data bands are defined
between servo tracks 210. Each data band may include a number of
data tracks, for example 1024 data tracks (not shown). During
read/write operations, the readers and/or writers 206 are
positioned to specific track positions within one of the data
bands. Outer readers, sometimes called servo readers, read the
servo tracks 210. The servo signals are in turn used to keep the
readers and/or writers 206 aligned with a particular set of tracks
during the read/write operations.
[0050] FIG. 2C depicts a plurality of readers and/or writers 206
formed in a gap 218 on the module 204 in Circle 2C of FIG. 2B. As
shown, the array of readers and writers 206 includes, for example,
16 writers 214, 16 readers 216 and two servo readers 212, though
the number of elements may vary. Illustrative embodiments include
8, 16, 32, 40, and 64 active readers and/or writers 206 per array,
and alternatively interleaved designs having odd numbers of reader
or writers such as 17, 25, 33, etc. An illustrative embodiment
includes 32 readers per array and/or 32 writers per array, where
the actual number of transducer elements could be greater, e.g.,
33, 34, etc. This allows the tape to travel more slowly, thereby
reducing speed-induced tracking and mechanical difficulties and/or
execute fewer "wraps" to fill or read the tape. While the readers
and writers may be arranged in a piggyback configuration as shown
in FIG. 2C, the readers 216 and writers 214 may also be arranged in
an interleaved configuration. Alternatively, each array of readers
and/or writers 206 may be readers or writers only, and the arrays
may contain one or more servo readers 212. As noted by considering
FIGS. 2A and 2B-2C together, each module 204 may include a
complementary set of readers and/or writers 206 for such things as
bi-directional reading and writing, read-while-write capability,
backward compatibility, etc.
[0051] FIG. 2D shows a partial tape bearing surface view of
complementary modules of a magnetic tape head 200 according to one
embodiment. In this embodiment, each module has a plurality of
read/write (R/W) pairs in a piggyback configuration formed on a
common substrate 204A and an optional electrically insulative layer
236. The writers, exemplified by the write transducer 214 and the
readers, exemplified by the read transducer 216, are aligned
parallel to an intended direction of travel of a tape medium
thereacross to form an R/W pair, exemplified by the R/W pair 222.
Note that the intended direction of tape travel is sometimes
referred to herein as the direction of tape travel, and such terms
may be used interchangeably. Such direction of tape travel may be
inferred from the design of the system, e.g., by examining the
guides; observing the actual direction of tape travel relative to
the reference point; etc. Moreover, in a system operable for
bi-direction reading and/or writing, the direction of tape travel
in both directions is typically parallel and thus both directions
may be considered equivalent to each other.
[0052] Several R/W pairs 222 may be present, such as 8, 16, 32
pairs, etc. The R/W pairs 222 as shown are linearly aligned in a
direction generally perpendicular to a direction of tape travel
thereacross. However, the pairs may also be aligned diagonally,
etc. Servo readers 212 are positioned on the outside of the array
of R/W pairs, the function of which is well known.
[0053] Generally, the magnetic tape medium moves in either a
forward or reverse direction as indicated by arrow 220. The
magnetic tape medium and head assembly 200 operate in a transducing
relationship in the manner well-known in the art. The piggybacked
magnetoresistive (MR) head assembly 200 includes two thin-film
modules 224 and 226 of generally identical construction.
[0054] Modules 224 and 226 are joined together with a space present
between closures 204B thereof (partially shown) to form a single
physical unit to provide read-while-write capability by activating
the writer of the leading module and reader of the trailing module
aligned with the writer of the leading module parallel to the
direction of tape travel relative thereto. When a module 224, 226
of a piggyback head 200 is constructed, layers are formed in the
gap 218 created above an electrically conductive substrate 204A
(partially shown), e.g., of AlTiC, in generally the following order
for the R/W pairs 222: an insulating layer 236, a first shield 232
typically of an iron alloy such as NiFe (--), cobalt zirconium
tantalum (CZT) or Al--Fe--Si (Sendust), a sensor 234 for sensing a
data track on a magnetic medium, a second shield 238 typically of a
nickel-iron alloy (e.g., .about.80/20 at % NiFe, also known as
permalloy), first and second writer pole tips 228, 230, and a coil
(not shown). The sensor may be of any known type, including those
based on MR, GMR, AMR, TMR, etc.
[0055] The first and second writer poles 228, 230 may be fabricated
from high magnetic moment materials such as .about.45/55 NiFe. Note
that these materials are provided by way of example only, and other
materials may be used. Additional layers such as insulation between
the shields and/or pole tips and an insulation layer surrounding
the sensor may be present. Illustrative materials for the
insulation include alumina and other oxides, insulative polymers,
etc.
[0056] The configuration of the tape head 126 according to one
embodiment includes multiple modules, preferably three or more. In
a write-read-write (W-R-W) head, outer modules for writing flank
one or more inner modules for reading. Referring to FIG. 3,
depicting a W-R-W configuration, the outer modules 252, 256 each
include one or more arrays of writers 260. The inner module 254 of
FIG. 3 includes one or more arrays of readers 258 in a similar
configuration. Variations of a multi-module head include a R-W-R
head (FIG. 4), a R-R-W head, a W-W-R head, etc. In yet other
variations, one or more of the modules may have read/write pairs of
transducers. Moreover, more than three modules may be present. In
further approaches, two outer modules may flank two or more inner
modules, e.g., in a W-R-R-W, a R-W-W-R arrangement, etc. For
simplicity, a W-R-W head is used primarily herein to exemplify
embodiments of the present invention. One skilled in the art
apprised with the teachings herein will appreciate how permutations
of the present invention would apply to configurations other than a
W-R-W configuration.
[0057] FIG. 5 illustrates a magnetic head 126 according to one
embodiment of the present invention that includes first, second and
third modules 302, 304, 306 each having a tape bearing surface 308,
310, 312 respectively, which may be flat, contoured, etc. Note that
while the term "tape bearing surface" appears to imply that the
surface facing the tape 315 is in physical contact with the tape
bearing surface, this is not necessarily the case. Rather, only a
portion of the tape may be in contact with the tape bearing
surface, constantly or intermittently, with other portions of the
tape riding (or "flying") above the tape bearing surface on a layer
of air, sometimes referred to as an "air bearing". The first module
302 will be referred to as the "leading" module as it is the first
module encountered by the tape in a three module design for tape
moving in the indicated direction. The third module 306 will be
referred to as the "trailing" module. The trailing module follows
the middle module and is the last module seen by the tape in a
three module design. The leading and trailing modules 302, 306 are
referred to collectively as outer modules. Also note that the outer
modules 302, 306 will alternate as leading modules, depending on
the direction of travel of the tape 315.
[0058] In one embodiment, the tape bearing surfaces 308, 310, 312
of the first, second and third modules 302, 304, 306 lie on about
parallel planes (which is meant to include parallel and nearly
parallel planes, e.g., between parallel and tangential as in FIG.
6), and the tape bearing surface 310 of the second module 304 is
above the tape bearing surfaces 308, 312 of the first and third
modules 302, 306. As described below, this has the effect of
creating the desired wrap angle .alpha..sub.2 of the tape relative
to the tape bearing surface 310 of the second module 304.
[0059] Where the tape bearing surfaces 308, 310, 312 lie along
parallel or nearly parallel yet offset planes, intuitively, the
tape should peel off of the tape bearing surface 308 of the leading
module 302. However, the vacuum created by the skiving edge 318 of
the leading module 302 has been found by experimentation to be
sufficient to keep the tape adhered to the tape bearing surface 308
of the leading module 302. The trailing edge 320 of the leading
module 302 (the end from which the tape leaves the leading module
302) is the approximate reference point which defines the wrap
angle .alpha..sub.2 over the tape bearing surface 310 of the second
module 304. The tape stays in close proximity to the tape bearing
surface until close to the trailing edge 320 of the leading module
302. Accordingly, read and/or write elements 322 may be located
near the trailing edges of the outer modules 302, 306. These
embodiments are particularly adapted for write-read-write
applications.
[0060] A benefit of this and other embodiments described herein is
that, because the outer modules 302, 306 are fixed at a determined
offset from the second module 304, the inner wrap angle
.alpha..sub.2 is fixed when the modules 302, 304, 306 are coupled
together or are otherwise fixed into a head. The inner wrap angle
.alpha..sub.2 is approximately tan.sup.-1(.delta./W) where .delta.
is the height difference between the planes of the tape bearing
surfaces 308, 310 and W is the width between the opposing ends of
the tape bearing surfaces 308, 310. An illustrative inner wrap
angle .alpha..sub.2 is in a range of about 0.3.degree. to about
1.1.degree., though can be any angle required by the design.
[0061] Beneficially, the inner wrap angle .alpha..sub.2 on the side
of the module 304 receiving the tape (leading edge) will be larger
than the inner wrap angle .alpha..sub.3 on the trailing edge, as
the tape 315 rides above the trailing module 306. This difference
is generally beneficial as a smaller .alpha..sub.3 tends to oppose
what has heretofore been a steeper exiting effective wrap
angle.
[0062] Note that the tape bearing surfaces 308, 312 of the outer
modules 302, 306 are positioned to achieve a negative wrap angle at
the trailing edge 320 of the leading module 302. This is generally
beneficial in helping to reduce friction due to contact with the
trailing edge 320, provided that proper consideration is given to
the location of the crowbar region that forms in the tape where it
peels off the head. This negative wrap angle also reduces flutter
and scrubbing damage to the elements on the leading module 302.
Further, at the trailing module 306, the tape 315 flies over the
tape bearing surface 312 so there is virtually no wear on the
elements when tape is moving in this direction. Particularly, the
tape 315 entrains air and so will not significantly ride on the
tape bearing surface 312 of the third module 306 (some contact may
occur). This is permissible, because the leading module 302 is
writing while the trailing module 306 is idle.
[0063] Writing and reading functions are performed by different
modules at any given time. In one embodiment, the second module 304
includes a plurality of data and optional servo readers 331 and no
writers. The first and third modules 302, 306 include a plurality
of writers 322 and no data readers, with the exception that the
outer modules 302, 306 may include optional servo readers. The
servo readers may be used to position the head during reading
and/or writing operations. The servo reader(s) on each module are
typically located towards the end of the array of readers or
writers.
[0064] By having only readers or side by side writers and servo
readers in the gap between the substrate and closure, the gap
length can be substantially reduced. Typical heads have piggybacked
readers and writers, where the writer is formed above each reader.
A typical gap is 20-35 microns. However, irregularities on the tape
may tend to droop into the gap and create gap erosion. Thus, the
smaller the gap is the better. The smaller gap enabled herein
exhibits fewer wear related problems.
[0065] In some embodiments, the second module 304 has a closure,
while the first and third modules 302, 306 do not have a closure.
Where there is no closure, preferably a hard coating is added to
the module. One preferred coating is diamond-like carbon (DLC).
[0066] In the embodiment shown in FIG. 5, the first, second, and
third modules 302, 304, 306 each have a closure 332, 334, 336,
which extends the tape bearing surface of the associated module,
thereby effectively positioning the read/write elements away from
the edge of the tape bearing surface. The closure 332 on the second
module 304 can be a ceramic closure of a type typically found on
tape heads. The closures 334, 336 of the first and third modules
302, 306, however, may be shorter than the closure 332 of the
second module 304 as measured parallel to a direction of tape
travel over the respective module. This enables positioning the
modules closer together. One way to produce shorter closures 334,
336 is to lap the standard ceramic closures of the second module
304 an additional amount. Another way is to plate or deposit thin
film closures above the elements during thin film processing. For
example, a thin film closure of a hard material such as Sendust or
nickel-iron alloy (e.g., 45/55) can be formed on the module.
[0067] With reduced-thickness ceramic or thin film closures 334,
336 or no closures on the outer modules 302, 306, the write-to-read
gap spacing can be reduced to less than about 1 mm, e.g., about
0.75 mm, or 50% less than commonly-used linear tape open (LTO) tape
head spacing. The open space between the modules 302, 304, 306 can
still be set to approximately 0.5 to 0.6 mm, which in some
embodiments is ideal for stabilizing tape motion over the second
module 304.
[0068] Depending on tape tension and stiffness, it may be desirable
to angle the tape bearing surfaces of the outer modules relative to
the tape bearing surface of the second module. FIG. 6 illustrates
an embodiment where the modules 302, 304, 306 are in a tangent or
nearly tangent (angled) configuration. Particularly, the tape
bearing surfaces of the outer modules 302, 306 are about parallel
to the tape at the desired wrap angle .alpha..sub.2 of the second
module 304. In other words, the planes of the tape bearing surfaces
308, 312 of the outer modules 302, 306 are oriented at about the
desired wrap angle .alpha..sub.2 of the tape 315 relative to the
second module 304. The tape will also pop off of the trailing
module 306 in this embodiment, thereby reducing wear on the
elements in the trailing module 306. These embodiments are
particularly useful for write-read-write applications. Additional
aspects of these embodiments are similar to those given above.
[0069] Typically, the tape wrap angles may be set about midway
between the embodiments shown in FIGS. 5 and 6.
[0070] FIG. 7 illustrates an embodiment where the modules 302, 304,
306 are in an overwrap configuration. Particularly, the tape
bearing surfaces 308, 312 of the outer modules 302, 306 are angled
slightly more than the tape 315 when set at the desired wrap angle
.alpha..sub.2 relative to the second module 304. In this
embodiment, the tape does not pop off of the trailing module,
allowing it to be used for writing or reading. Accordingly, the
leading and middle modules can both perform reading and/or writing
functions while the trailing module can read any just-written data.
Thus, these embodiments are preferred for write-read-write,
read-write-read, and write-write-read applications. In the latter
embodiments, closures should be wider than the tape canopies for
ensuring read capability. The wider closures may require a wider
gap-to-gap separation. Therefore, a preferred embodiment has a
write-read-write configuration, which may use shortened closures
that thus allow closer gap-to-gap separation.
[0071] Additional aspects of the embodiments shown in FIGS. 6 and 7
are similar to those given above.
[0072] A 32 channel version of a multi-module head 126 may use
cables 350 having leads on the same or smaller pitch as current 16
channel piggyback LTO modules, or alternatively the connections on
the module may be organ-keyboarded for a 50% reduction in cable
span. Over-under, writing pair unshielded cables may be used for
the writers, which may have integrated servo readers.
[0073] The outer wrap angles .alpha..sub.1 may be set in the drive,
such as by guides of any type known in the art, such as adjustable
rollers, slides, etc. or alternatively by outriggers, which are
integral to the head. For example, rollers having an offset axis
may be used to set the wrap angles. The offset axis creates an
orbital arc of rotation, allowing precise alignment of the wrap
angle .alpha..sub.1.
[0074] To assemble any of the embodiments described above,
conventional u-beam assembly can be used. Accordingly, the mass of
the resultant head may be maintained or even reduced relative to
heads of previous generations. In other approaches, the modules may
be constructed as a unitary body. Those skilled in the art, armed
with the present teachings, will appreciate that other known
methods of manufacturing such heads may be adapted for use in
constructing such heads. Moreover, unless otherwise specified,
processes and materials of types known in the art may be adapted
for use in various embodiments in conformance with the teachings
herein, as would become apparent to one skilled in the art upon
reading the present disclosure.
[0075] As a tape is run over a module, it is preferred that the
tape passes sufficiently close to magnetic transducers on the
module such that reading and/or writing is efficiently performed,
e.g., with a low error rate. According to some approaches, tape
tenting may be used to ensure the tape passes sufficiently close to
the portion of the module having the magnetic transducers. To
better understand this process, FIGS. 8A-8C illustrate the
principles of tape tenting. FIG. 8A shows a module 800 having an
upper tape bearing surface 802 extending between opposite edges
804, 806. A stationary tape 808 is shown wrapping around the edges
804, 806. As shown, the bending stiffness of the tape 808 lifts the
tape off of the tape bearing surface 802. Tape tension tends to
flatten the tape profile, as shown in FIG. 8A. Where tape tension
is minimal, the curvature of the tape is more parabolic than
shown.
[0076] FIG. 8B depicts the tape 808 in motion. The leading edge,
i.e., the first edge the tape encounters when moving, may serve to
skive air from the tape, thereby creating a subambient air pressure
between the tape 808 and the tape bearing surface 802. In FIG. 8B,
the leading edge is the left edge and the right edge is the
trailing edge when the tape is moving left to right. As a result,
atmospheric pressure above the tape urges the tape toward the tape
bearing surface 802, thereby creating tape tenting proximate each
of the edges. The tape bending stiffness resists the effect of the
atmospheric pressure, thereby causing the tape tenting proximate
both the leading and trailing edges. Modeling predicts that the two
tents are very similar in shape.
[0077] FIG. 8C depicts how the subambient pressure urges the tape
808 toward the tape bearing surface 802 even when a trailing guide
810 is positioned above the plane of the tape bearing surface.
[0078] It follows that tape tenting may be used to direct the path
of a tape as it passes over a module. As previously mentioned, tape
tenting may be used to ensure the tape passes sufficiently close to
the portion of the module having the magnetic transducers,
preferably such that reading and/or writing is efficiently
performed, e.g., with a low error rate.
[0079] Magnetic tapes may be stored in tape cartridges that are, in
turn, stored at storage slots or the like inside a data storage
library. The tape cartridges may be stored in the library such that
they are accessible for physical retrieval. In addition to magnetic
tapes and tape cartridges, data storage libraries may include data
storage drives that store data to, and/or retrieve data from, the
magnetic tapes. Moreover, tape libraries and the components
included therein may implement a file system which enables access
to tape and data stored on the tape.
[0080] File systems may be used to control how data is stored in,
and retrieved from, memory. Thus, a file system may include the
processes and data structures that an operating system uses to keep
track of files in memory, e.g., the way the files are organized in
memory. Linear Tape File System (LTFS) is an exemplary format of a
file system that may be implemented in a given library in order to
enables access to compliant tapes. It should be appreciated that
various embodiments herein can be implemented with a wide range of
file system formats, including for example IBM Spectrum Archive
Library Edition (LTFS LE). However, to provide a context, and
solely to assist the reader, some of the embodiments below may be
described with reference to LTFS which is a type of file system
format. This has been done by way of example only, and should not
be deemed limiting on the invention defined in the claims.
[0081] A tape cartridge may be "loaded" by inserting the cartridge
into the tape drive, and the tape cartridge may be "unloaded" by
removing the tape cartridge from the tape drive. Once loaded in a
tape drive, the tape in the cartridge may be "threaded" through the
drive by physically pulling the tape (the magnetic recording
portion) from the tape cartridge, and passing it above a magnetic
head of a tape drive. Furthermore, the tape may be attached on a
take-up reel (e.g., see 121 of FIG. 1A above) to move the tape over
the magnetic head.
[0082] Once threaded in the tape drive, the tape in the cartridge
may be "mounted" by reading metadata on a tape and bringing the
tape into a state where the LTFS is able to use the tape as a
constituent component of a file system. Moreover, in order to
"unmount" a tape, metadata is preferably first written on the tape
(e.g., as an index), after which the tape may be removed from the
state where the LTFS is allowed to use the tape as a constituent
component of a file system. Finally, to "unthread" the tape, the
tape is unattached from the take-up reel and is physically placed
back into the inside of a tape cartridge again. The cartridge may
remain loaded in the tape drive even after the tape has been
unthreaded, e.g., waiting for another read and/or write request.
However, in other instances, the tape cartridge may be unloaded
from the tape drive upon the tape being unthreaded, e.g., as
described above.
[0083] Magnetic tape is a sequential access medium. Thus, new data
is written to the tape by appending the data at the end of
previously written data. It follows that when data is recorded in a
tape having only one partition, metadata (e.g., allocation
information) is continuously appended to an end of the previously
written data as it frequently updates and is accordingly rewritten
to tape. As a result, the rearmost information is read when a tape
is first mounted in order to access the most recent copy of the
metadata corresponding to the tape. However, this introduces a
considerable amount of delay in the process of mounting a given
tape.
[0084] To overcome this delay caused by single partition tape
mediums, the LTFS format includes a tape that is divided into two
partitions, which include an index partition and a data partition.
The index partition may be configured to record metadata (meta
information), e.g., such as file allocation information (Index),
while the data partition may be configured to record the body of
the data, e.g., the data itself.
[0085] Looking to FIG. 9, a magnetic tape 900 having an index
partition 902 and a data partition 904 is illustrated according to
one embodiment. As shown, data files and indexes are stored on the
tape. The LTFS format allows for index information to be recorded
in the index partition 902 at the beginning of tape 906, as would
be appreciated by one skilled in the art upon reading the present
description.
[0086] As index information is updated, it preferably overwrites
the previous version of the index information, thereby allowing the
currently updated index information to be accessible at the
beginning of tape in the index partition. According to the specific
example illustrated in FIG. 9, a most recent version of metadata
Index 3 is recorded in the index partition 902 at the beginning of
the tape 906. Conversely, all three version of metadata Index 1,
Index 2, Index 3 as well as data File A, File B, File C, File D are
recorded in the data partition 904 of the tape. Although Index 1
and Index 2 are old (e.g., outdated) indexes, because information
is written to tape by appending it to the end of the previously
written data as described above, these old indexes Index 1, Index 2
remain stored on the tape 900 in the data partition 904 without
being overwritten.
[0087] The metadata may be updated in the index partition 902
and/or the data partition 904 differently depending on the desired
embodiment. According to some embodiments, the metadata of the
index partition 902 may be updated in response to the tape being
unmounted, e.g., such that the index may be read from the index
partition when that tape is mounted again. The metadata may also be
written in the data partition 902 so the tape may be mounted using
the metadata recorded in the data partition 902, e.g., as a backup
option.
[0088] According to one example, which is no way intended to limit
the invention, LTFS LE may be used to provide the functionality of
writing an index in the data partition when a user explicitly
instructs the system to do so, or at a time designated by a
predetermined period which may be set by the user, e.g., such that
data loss in the event of sudden power stoppage can be
mitigated.
[0089] As alluded to above, there is a need to address the issue of
magnetic noise as experienced in conventional magnetic tape heads
due to thermally and/or magnetically induced switching of unstable
domains in free layers thereof. To overcome such issues, some of
the embodiments included herein provide magnetic tape heads which
include modules having tunnel valve transducers with free layers
having favorable dimensions in order to achieve shape anisotropy.
Moreover, other embodiments included herein provide magnetic tape
heads which include modules having tunnel valve transducers with
hard bias magnets. It follows that various embodiments included
herein achieve a resulting structure which is both structurally and
functionally different than those seen in conventional tape and/or
hard disk drive (HDD) heads.
[0090] In order to operate as a magnetic sensor with a linear and
symmetric response, the magnetization throughout the free layer
slab should ideally constitute a single domain and be aligned to
the specific direction for which the rest of the sensor layers are
configured at zero applied sense field. Although it is preferred
that the aforementioned "specific direction" is the cross-track
direction 1052, it may vary depending on the specific embodiment.
Moreover, this state of alignment is also preferably energetically
stable, such that it is restored after an external sensing field
(e.g. from magnetized tape) is applied and then removed again.
[0091] As described herein, free layer slab dimensions may be able
to cause the free layer to form a largely homogeneous single
magnetic domain aligned along the cross-track direction as a result
of shape anisotropy. This may directly result in improved sensor
performance and overall increased efficiency of a magnetic head,
thereby achieving a significant improvement compared to
conventional implementations.
[0092] However, in some instances, such as sensors having non-ideal
shape anisotropy may also give rise to distortions of the magnetic
alignment near the lateral edges of the domain. In these edge
regions, the free layer magnetization may be locally torqued by
demagnetizations fields towards a direction perpendicular to the
air-bearing surface. Energetically, this causes bifurcation in the
magnetic state at the lateral edges, and switching between these
states may occur under the impulse of an external field transient
(e.g. fringing fields from written tape traveling thereover) and/or
thermal agitation. Such switching events undesirably translate into
noise in the readback signal.
[0093] Biasing the entire free layer to this state of alignment may
serve as a first purpose for using hard bias magnets in such
instances, particularly as free layer slab dimensions typical for
sensors in HDDs may not able to form a magnetization which is
sufficiently homogeneous, and with a singly-aligned domain absent
the implementation of hard bias magnets.
[0094] A further purpose of implementing hard bias magnets is to
subject these distorted edge regions of the free layer to a
magnetic field which favors torqueing their magnetic orientation
back to being about parallel to the cross-track direction. The
magnetic field from the hard bias magnets is preferably strong
enough to dominate over the local demagnetization fields. The
resulting magnetization of the free layer may thereby be influenced
such that it constitutes a more homogeneous single domain. The edge
regions may also be stabilized in the sense that they are held to
this orientation and bifurcated-energy states are suppressed.
[0095] Applying a relatively weak magnetic bias to the edge regions
of a free layer may create more split states resulting in an
upshift of the spectral response of noise in the sensor, especially
absent desirable shape anisotropy. However, increasing magnetic
hard bias strength to overcome this may attenuate signal
sensitivity. Thus, choosing the strength of the hard bias magnets
involves a compromise between noise and signal strength. For
instance, implementing relatively stronger hard bias magnets may
decrease the sensitivity of the free layer particularly in the edge
regions (which are a significant source of noise), but may also
shift the spectral characteristics of the noise processes such that
system signal to noise ratio (SNR) is less affected. Conversely,
while relatively weaker hard bias magnets allow for retaining
better overall signal sensitivity, it comes at a cost in noise
performance due to a less homogeneous free layer domain which may
include states between which switching can occur.
[0096] For reference, sensors implemented in HDDs have small width
dimensions (about 50 nm) compared to the length scale of flux
leakage toward the shields, resulting in little variation of the
field strength from the hard bias across the width of the HDD
sensor. There is therefore little latitude to engineer a
high-susceptibility sensing region at the center of the free layer
separate from low-susceptibility regions at the edges. Overall
sensitivity being at a premium for HDDs, the compromise may
generally gravitate towards implementing a moderate-to-small
strength hard bias.
[0097] On the contrary, magnetic sensors for magnetic tape
typically have widths that are much larger than the length scale of
flux leakage towards the shields. According to an example, the
width of a magnetic tape sensor may be about 1.5 .mu.m, while the
length scale of flux leakage towards the shields may be about 200
nm for a shield to shield spacing of about 100 nm. As a result, the
outer edge regions of a free layer in the sensor stack may be
strongly anchored in order to reduce noise. Moreover, this may be
achieved while also exploiting the relatively steep decay of the
hard bias field strength over distance from the free layer edges,
thereby leaving the susceptibility largely unmodified near the
central region of the free layer along its longitudinal axis. As a
result, the effective magnetic width and the signal output of the
sensor may be decreased moderately, e.g., by an amount in
proportion with the width of the edge regions, whereas its noise
performance may be significantly improved.
[0098] It follows that hard bias magnets may be used to stabilize a
free layer and reduce magnetic switching noise in some of the
embodiments described herein. However, due to the reduced field
overlap between hard bias magnet pairs, and given that the peak
bias strength corresponding to achieving optimal biasing conditions
for a tape sensor is likely larger than that for an HDD, desirable
biasing strengths are not achievable for tape simply by performing
incremental changes to conventional HDD hard bias geometry. In
sharp contrast to traditional structures and conventional wisdom,
various embodiments described herein include new geometric
characteristics for free layers and hard bias layers, each of which
are able to achieve substantial improvements over conventional
implementations, e.g., as will be described in further detail
below.
[0099] FIGS. 10A-10B depict an apparatus 1000 in accordance with
one embodiment. As an option, the present apparatus 1000 may be
implemented in conjunction with features from any other embodiment
listed herein, such as those described with reference to the other
FIGS. However, such apparatus 1000 and others presented herein may
be used in various applications and/or in permutations which may or
may not be specifically described in the illustrative embodiments
listed herein. Further, the apparatus 1000 presented herein may be
used in any desired environment. Thus FIGS. 10A-10B (and the other
FIGS.) may be deemed to include any possible permutation.
[0100] It should also be noted that additional layers may be
present, and unless otherwise specified, the various layers in this
and other embodiments may be formed using conventional processes.
Additionally, the different figures are not drawn to scale, but
rather features may have been exaggerated to help exemplify the
descriptions herein.
[0101] As shown in FIG. 10A, apparatus 1000 includes a magnetic
tape head 1002 which further includes a module 1004. It should be
noted that magnetic tape heads are unique in that magnetic tape
transducer widths are currently about 30 to about 50 times greater
than transducer widths for HDD heads. Moreover, in preferred
embodiments, the module 1004 of tape head 1002 includes an array of
read transducers. Accordingly, the module 1004 includes a plurality
of tunnel valve read transducers 1006 for reading data from data
tracks on a magnetic tape. As shown, the plurality of tunnel valve
read transducers 1006 are arranged in an array which extends along
a longitudinal axis 1008 of the module 1004. Furthermore, in some
approaches the module 1004 may further include tunnel valve
transducers which are positioned and configured to read data
written to servo patterns (e.g., see servo readers 212 of FIG.
2B-2C).
[0102] The plurality of tunnel valve read transducers 1006 also
share a common media-facing surface 1005 of the module 1004.
According to the present embodiment, no write transducers are
present on the common media-facing surface 1005, or even the module
1004 itself. However, it should be noted that in other embodiments,
an array of write transducers may also be included on module 1004,
on an adjacent module, etc., e.g., as shown in any one or more of
FIGS. 2A-7. Moreover, in some embodiments, the apparatus 1000 may
include a drive mechanism for passing a magnetic medium over the
magnetic tape head, e.g., see 100 of FIG. 1A, and a controller
electrically coupled to the sensor, e.g., see 128 of FIG. 1A.
[0103] Looking now to FIG. 10B, a partial detailed view of the tape
facing surface of one of the tunnel valve read transducers 1006 in
FIG. 10A is shown according to one embodiment. It should be noted
that although a partial detailed view of only one of the tunnel
valve read transducers 1006 is shown, any one or more of the tunnel
valve read transducers 1006 included on module 1004 of FIG. 10A may
have the same or a similar construction.
[0104] As shown, the tunnel valve read transducer 1006 includes a
sensor structure 1012 as well as upper and lower magnetic shields
1014, 1016 respectively, which flank (sandwich) the sensor
structure 1012. The separation between the upper and lower magnetic
shields 1014, 1016 proximate to the sensor and measured along the
intended direction of tape (e.g., media) travel 1050 is preferably
less than about 120 nm, but could be lower or higher depending on
the embodiment. Moreover, upper and lower electrically conductive,
non-magnetic spacer layers 1018, 1020 are positioned between the
sensor structure 1012 and the magnetic shields 1014, 1016,
respectively. In a preferred embodiment, the electrically
conductive, non-magnetic spacer layers 1018, 1020 include iridium,
ruthenium, titanium-nitride, etc.
[0105] Between the non-magnetic conductive spacer layers 1018,
1020, the sensor structure 1012 includes an antiferromagnetic layer
1022 and has a sensor cap layer 1024. The sensor structure 1012
also preferably has an active TMR region. Thus, the sensor
structure 1012 is shown as also including a free layer 1026, a
tunnel barrier layer 1028 and a reference layer 1030. According to
various embodiments, the free layer 1026, the tunnel barrier layer
1028 and/or the reference layer 1030 may include construction
parameters, e.g., materials, dimensions, properties, etc.,
according to any of the embodiments described herein, and/or
conventional construction parameters, depending on the desired
embodiment. In exemplary embodiments, the free layer 1026 may
include layers of permalloy and/or cobalt-iron. Illustrative
materials for the tunnel barrier layer 1028 include amorphous
and/or crystalline forms of, but are not limited to, TiOx, MgO and
Al.sub.2O.sub.3.
[0106] The tunnel valve read transducer 1006 illustrated in FIG.
10B further includes electrically insulating layers 1034 on
opposite sides of the sensor structure 1012. The electrically
insulating layers 1034 separate the upper conducting spacer layer
1018 from the lower conducting spacer layer 1020 and the sensor
structure 1012 to avoid electrical shorting therebetween. According
to some approaches, the thickness t.sub.1 of the electrically
insulating layers 1034 may be less than about 8 nm, but may be
higher or lower depending on the desired embodiment. Moreover, it
is preferred that the electrically insulating layers 1034 include a
dielectric material.
[0107] Looking to FIG. 10C, a view of the free layer 1026 of FIG.
10B is shown along a plane perpendicular to the plane of deposition
of the free layer 1026. Arrows indicating the cross-track direction
1052 and the intended direction of tape travel 1050 have been added
for reference. As shown, the height H.sub.f of the free layer 1026
is less than the width W.sub.f of the free layer 1026. As shown,
the height H.sub.f of the free layer 1026 is measured in a
direction perpendicular to a media bearing surface of the module
shown in FIGS. 10A-10B. According to an illustrative approach,
which is in no way intended to limit the invention, the width
W.sub.f of the free layer 1026 may be less than about 2 .mu.m, but
could be higher or lower depending on the desired approach. As
mentioned above, free layer slab dimensions may be able to cause
the free layer to form a largely homogeneous single magnetic domain
aligned along the cross-track direction as a result of shape
anisotropy alone. This may directly result in improved sensor
performance and overall increased efficiency of a magnetic head.
This is a significant improvement compared to conventional
implementations which are unable to implement free layers having a
width and height as shown in FIG. 10C.
[0108] The general shape of the free layer shown in FIG. 10C may
also translate to the height and width of the overall sensor
structure 1012 shown in FIG. 10B. Looking to FIG. 10D, a view of
the sensor structure 1012 is shown along a plane perpendicular to
the plane of deposition thereof (the same plane of view as shown in
FIG. 10C). Although the sensor cap layer 1024 is in full view,
portions of the other layers are also visible along the cross-track
direction 1052 in FIG. 10D due to the sensor structure's flared
profile shown in FIG. 10B. As described above for the free layer,
it is preferred that the height H.sub.ss of the sensor structure
1012 is less than the width W.sub.ss of the sensor structure 1012.
According to some approaches, the height H.sub.ss of the sensor
structure 1012 may be less than about 0.8 times the width W.sub.ss
of the sensor structure 1012. More preferably, in some approaches
the height H.sub.ss of the sensor structure 1012 may be less than
about 0.5 times the width W.sub.ss of the sensor structure 1012,
but could be higher or lower depending on the desired embodiment.
This general shape of the sensor structure 1012 may desirably
provide improved sensor performance and overall increased
efficiency of a magnetic head as a result of shape anisotropy,
e.g., as described above in relation to the height H.sub.f and
width W.sub.f of the free layer 1026 in FIG. 10C.
[0109] Although tunnel valve read transducers having slab
dimensions which form a largely homogeneous single magnetic domain
aligned along the cross-track direction of the free layer as a
result of shape anisotropy alone are desirable, performance may
further be improved by implementing hard bias magnets in some
embodiments. As mentioned above, hard bias magnets may be used to
further stabilize a free layer and reduce magnetic switching noise.
Looking to FIG. 10E, a tunnel valve read transducer 1070 is shown
in accordance with one embodiment. As an option, the present tunnel
valve read transducer 1070 may be implemented in conjunction with
features from any other embodiment listed herein, such as those
described with reference to the other FIGS. Specifically, FIG. 10E
illustrate variations of the embodiment of FIG. 10B depicting
several exemplary configurations within a tunnel valve read
transducer 1070. Accordingly, various components of FIG. 10E have
common numbering with those of FIG. 10B.
[0110] However, such tunnel valve read transducer 1070 and others
presented herein may be used in various applications and/or in
permutations which may or may not be specifically described in the
illustrative embodiments listed herein. Further, the tunnel valve
read transducer 1070 presented herein may be used in any desired
environment. Thus FIG. 10E (and the other FIGS.) may be deemed to
include any possible permutation.
[0111] As shown, the tunnel valve read transducer 1070 includes
upper and lower shields 1014, 1016, a sensor structure 1012, as
well as upper and lower conducting spacer layers 1018, 1020
positioned between the sensor structure 1012 and the magnetic
shields 1014, 1016, respectively.
[0112] Furthermore, the sensor structure 1012 is sandwiched
laterally along the cross-track direction 1052, by a pair of hard
bias magnets 1032. In other words, the hard bias magnets 1032 are
positioned proximate to a side of the sensor structure 1012 along a
cross-track direction 1052 on opposite sides thereof. The hard bias
magnets 1032 may include cobalt-platinum, cobalt-platinum-chrome,
etc., or any other hard bias materials which would become apparent
to one skilled in the art after reading the present
description.
[0113] Moreover, electrically insulating layers 1034 are included
on opposite sides of the sensor structure 1012. More specifically,
an electrically insulating layer 1034 separates each of the hard
bias magnets 1032 from the sensor structure 1012 and the lower
conducting spacer layer 1020, to avoid electrical shorting
therebetween. A seed layer 1044 is also present between each of the
hard bias magnets 1032 and the respective electrically insulating
layers 1034 which may be used to form hard bias magnets 1032 having
an at least partially crystalline composition, e.g., as will be
described in further detail below.
[0114] Although the insulating layer 1034 is positioned between
each of the hard bias magnets 1032 and the sensor structure 1012,
each of the hard bias magnets 1032 are preferably magnetically
coupled to (e.g., are in magnetic communication with) the free
layer 1026 sandwiched therebetween. As would be appreciated by one
skilled in the art, magnetic coupling may be achieved between two
layers when the layers have proper characteristics, which may
include: being positioned sufficiently close to each other, having
the proper material composition, having proper dimensions, etc.,
e.g., as will soon become apparent.
[0115] As alluded to above, the construction of the hard bias
magnets implemented in a given magnetic tape head were found by the
inventors to have a significant impact on the performance of the
overall magnetic tape head. The inventors were surprised to
discover that by increasing a thickness of the hard bias magnets
above what was previously considered to be adequate resulted in a
very low incidence of noisy tracks. Previously, it was believed
that increasing the thickness of the hard bias layers beyond a
certain thickness would actually degrade read performance by
causing a detrimental amount of hard bias flux to permeate the free
layer, thereby reducing readback signal strengths. In sharp
contrast, the improvements included herein were achieved, at least
in part, by the increased magnetization from the thicker hard bias
magnets effectively stabilizing the magnetic domains of the free
layer near the lateral edges thereof. Moreover, magnetic tape heads
implementing these thicker hard bias magnets were also discovered
to be tolerant to variation in other aspects of the sensor, e.g.,
such as free layer magnetostriction and/or pinned layer design.
Thus, by implementing hard bias magnet structures which go directly
against conventional wisdom, the inventors were able to realize
significant improvements in the performance of free layers in
tunnel valve read transducers.
[0116] Specifically, referring still to FIG. 10E, the inventors
were surprised to discover that implementing hard bias magnets 1032
having a deposition thickness t.sub.2 that is 10 or more times
greater than a deposition thickness t.sub.3 of the free layer 1026
results in substantial improvements to the magnetization stability
of the free layer 1026 (e.g., see graph 1200 of FIG. 12 below).
Without wishing to be bound by any theory, the inventors believe
that this surprising result is achieved because the thicker hard
bias magnets 1032 are able to overcome the loss of field at the
ends of the hard bias magnets 1032 due to magnetic flux leakage
into the magnetic shields 1014, 1016 over the relatively large
dimensions (e.g., large widths) of the tape transducer layers. It
follows that, a deposition thickness t.sub.2 of each of the hard
bias magnets 1032 at about a thickest portion thereof is preferably
at least 8 times greater, more preferably at least 10 times greater
than a deposition thickness t.sub.3 of the free layer 1026. In some
embodiments, the thickness of the hard bias magnets may be
expressed as a multiple of the thickness of the free layer times
the ratio of the magnetic moment of the free layer divided by the
magnetic moment of the hard bias magnets. Accordingly, the
inventors found that while conventionally this ratio is about 8, a
ratio of about 16 may be implemented for stabilizing the free
layer. According to one approach, a thickness of the hard bias
magnets at a thickest portion thereof may be at least 12 times
greater than a thickness of the free layer times a ratio of the
magnetic moment of the free layer divided by the magnetic moment of
the respective hard bias magnet. According to another approach, the
deposition thickness t.sub.2 of each of the hard bias magnets 1032
at about a thickest portion thereof may be about 65 nm, while the
deposition thickness t.sub.3 of the free layer 1026 is about 6.5
nm. In preferred approaches, the deposition thickness t.sub.3 of
the free layer 1026 is at least 4 nm. However, it should be noted
that the thickness t.sub.2 of each of the hard bias magnets 1032 at
about a thickest portion thereof may vary, e.g., depending on the
material composition of the layer.
[0117] Moreover, the deposition thickness of each of the hard bias
magnets 1032 may diminish toward the free layer 1026, thereby
resulting in a tapered profile of the hard bias magnets 1032 toward
the free layer 1026. According to an exemplary approach, the taper
length of the hard bias magnets 1032 may be less than the maximum
thickness t.sub.2 of each of the hard bias magnets 1032. However, a
deposition thickness t.sub.4 of each of the hard bias magnets 1032
at an edge closest to the free layer 1026 is preferably at least
greater than the deposition thickness t.sub.3 of the free layer
1026. As a result, a significant amount of hard bias material is
present at the interface between each of the hard bias magnets 1032
and the free layer 1026, thereby increasing the total amount of
flux density that may be produced from the edge of the hard bias
magnets 1032.
[0118] It is also preferred that the a first portion of each of the
hard bias magnets 1032 is positioned below a lower surface of the
free layer 1026, and a second portion of each of the hard bias
magnets 1032 is positioned above an upper surface of the free layer
1026. Referring to the present description, the terms
"lower"/"below" and "upper"/"above" are intended to be relative to
each other along a deposition direction of the layers, the
deposition direction being parallel to the intended direction of
tape travel 1050 in the present embodiment. In other words, it is
desirable that the edge of each of the hard bias magnets 1032
facing the free layer 1026 overlaps the free layer 1026 along the
intended direction of tape travel 1050, and may even be centered
relative to the free layer 1026, e.g., as shown in FIG. 10E.
[0119] The edge of each of the hard bias magnets 1032 closest to
the free layer 1026 preferably has about a vertical profile. In
other words, it is desirable that the edge of each of the hard bias
magnets 1032 closest to the free layer 1026 is oriented at an angle
.sigma. relative to a plane of deposition of the free layer, where
the angle .sigma. may be in a range from about 65.degree. to about
105.degree., more preferably in a range from about 70.degree. to
about 95.degree., ideally in a range from about 70.degree. to about
90.degree.. By implementing hard bias magnets 1032 having an edge
closest to the free layer 1026 that is sufficiently vertical
relative to a horizontally-oriented plane of deposition of the free
layer, magnetization of the free layer 1026 is significantly
improved as a result (e.g., see graph 1200 of FIG. 12 below).
However, the angle .sigma. of one or more of the hard bias magnets
1032 may be higher or lower depending on the desired embodiment.
Furthermore, a free layer 1026 having edges facing the hard bias
magnets which are about perpendicular (e.g., between about
80.degree. and about 100.degree.) relative to a plane of deposition
thereof may also improve magnetization of the free layer 1026, as
will soon become apparent.
[0120] It should be noted that in other embodiments, the shape and
thickness of the hard bias magnets 1032 may be selected to result
in maximum coupling of magnetic flux into the free layer 1026.
Accordingly, depending upon the thickness t.sub.3 of the free layer
1026, the magnetic flux from the hard bias magnets 1032 may serve
to reduce the output of the free layer 1026 in response to recorded
data on a tape. While not ideal in terms of signal output, such
designs may be more magnetically stable.
[0121] Referring momentarily to FIGS. 11A-11C, three different hard
bias magnet configurations are illustrated relative to a free
layer. Moreover, graph 1200 of FIG. 12 includes plots showing
magnetization of the free layer vs. the distance from the sensor
edge (along the width of the free layer) for each of the three
configurations in FIGS. 11A-11C. It should be noted that the plots
included in graph 1200 were obtained using finite element analysis,
and well-known materials properties for the free layer and hard
bias magnets, while keeping the variables therebetween equal, other
than the geometric differences of the hard bias and free layers as
described below.
[0122] Looking first to FIG. 11A, the hard bias structure 1102
included therein is consistent with conventional hard bias
structures. As shown, the hard bias structure 1102 is only slightly
thicker than the free layer 1104, and the hard bias structure 1102
oriented almost entirely above the free layer 1104. As illustrated
by the corresponding plot in graph 1200 of FIG. 12, the resulting
magnetization of the free layer is adversely low. Moreover, the
magnetization of the free layer makes an adverse dip before rising
to a maximum value at the distance of about 50 nm.
[0123] Conversely, FIG. 11B includes a hard bias magnet 1112 which
has a maximum thickness that is much greater than the thickness of
the free layer 1114, e.g., according to any of the approaches
included herein. The corresponding plot in graph 1200 of FIG. 12
illustrates that the increased thickness of the hard bias magnet
1112 desirably causes a significant increase to the magnetization
of the free layer 1114, thereby improving the magnetic stability of
the free layer 1114, particularly at its lateral edge. Although the
resulting increase to the magnetization of the free layer 1114 is
desirable, the plot in graph 1200 corresponding to the structure of
FIG. 11B still includes an undesirable dip before rising to a
maximum value at the distance of about 75 nm.
[0124] However, as described above, the inventors discovered that
by orienting the hard bias magnet such that it is about centered
with the free layer along the deposition direction and/or by making
an edge of the hard bias magnet facing the free layer about
perpendicular to the plane of deposition, even greater improvements
may be achieved. Accordingly, the embodiment illustrated in FIG.
11C illustrates a hard bias magnet 1122 which is about centered
with the free layer 1124 along the deposition direction 1126. The
hard bias magnet 1122 also has an edge facing the free layer which
is about perpendicular to the plane of deposition (or about
parallel to the deposition direction 1126). Moreover, by forming
the free layer 1124 such that an edge thereof facing the hard bias
magnet 1122 is also about perpendicular to the plane of deposition,
performance may even further be improved. As a result, the
corresponding plot in graph 1200 of FIG. 12 indicates significant
improvements to the magnetization of the free layer relative to
what was conventionally achievable (see plot for FIG. 11A), while
also eliminating the previously experienced dip in the
magnetization of the free layer. It follows that various
embodiments described herein were surprisingly discovered by the
inventors to provide a sufficient magnetic field to stabilize the
free layer and reduce magnetic noise.
[0125] Referring again to FIG. 10E, the hard bias magnets 1032 may
be formed to have different dimensions (e.g., a different
structure) according to various approaches. However, according to
preferred approaches, the hard bias magnets 1032 included herein
are formed such that the magnetic field produced by each of the
hard bias magnets 1032 is close to a maximum achievable value. In
other words, each of the hard bias magnets 1032 is preferably
characterized as producing a magnetic field that is greater than or
equal to 90% of a maximum achievable magnetic field for the
material of the respective hard bias magnet 1032. Producing a
magnetic field close to the maximum achievable magnetic field for
the material of the respective hard bias magnet 1032 may be
accomplished by implementing favored (e.g., ideal) processing steps
during the manufacture thereof, e.g., such as ensuring proper seed
layer templated growth, performing a proper annealing process on
the resulting structure, etc.
[0126] Referring momentarily to FIG. 10F, a view of the hard bias
magnets 1032 and free layer 1026 of FIG. 10E are shown along a
plane perpendicular to the plane of deposition of the hard bias
magnets 1032 and the free layer 1026. Arrows indicating the
cross-track direction 1052 and the intended direction of tape
travel 1050 have been added for reference. As shown, the width
W.sub.HB of the hard bias magnets 1032 are measured in the
cross-track direction 1052. Moreover, according to preferred
embodiments, the width of the hard bias magnets 1032 is at least
about 0.3 .mu.m, but could be higher or lower depending on the
desired embodiment.
[0127] Referring again to FIG. 10E, according to some approaches,
each of the hard bias magnets 1032 may be at least partially
crystalline. In other words, the hard bias magnets 1032 may be
formed in such a way that the material composition thereof is
crystalline in nature.
[0128] As previously mentioned, the hard bias magnets 1032 in FIG.
10E may have an at least partially crystalline material
composition. A hard bias magnet 1032 having a crystalline material
composition may be formed by first depositing a seed layer 1044,
and then forming the hard bias magnet layer 1032 from the seed
layer 1044. By using the seed layer 1044 as a base, the hard bias
magnet layer 1032 may desirably form such that the material
composition thereof is crystalline in nature.
[0129] Accordingly, the hard bias magnet 1032 may be formed in full
above the seed layer in some approaches. However, crystalline
structure growth may become less uniform as the hard bias magnet
becomes thicker, and the distance from the seed layer increases.
Thus, in some approaches, additional seed layers may be implemented
to avoid structural degradations caused by a loss of templating. In
one such approach, a hard bias magnet may be a split hard bias
structure which includes two seed layers, each of the seed layers
having an at least partially crystalline structure formed
thereabove.
[0130] Referring momentarily now to FIG. 10G, a tunnel valve read
transducer 1080 having a split hard bias magnets 1060 having a
crystalline material composition may be formed by first depositing
a seed layer 1062, and then forming a first hard bias layer 1064
from the seed layer 1062, e.g., as described above. Once a portion,
e.g., about one half, of the total hard bias magnet 1060 has been
formed, formation of the first hard bias layer 1064 may be stopped,
and a second seed layer 1066 is deposited on an upper surface of
the first hard bias layer 1064 as shown. Thereafter, a second hard
bias layer 1068 may be formed from the second seed layer 1066. The
first and second hard bias layers 1064, 1068 may be formed using a
same or similar materials, e.g., depending on the desired
embodiment. It should be additionally noted that FIG. 10G
illustrates variations of the embodiment of FIG. 10E depicting an
exemplary configuration within a magnetic tape head 1002.
Accordingly, various components of FIG. 10G also have common
numbering with those of FIG. 10E.
[0131] As mentioned above, shape anisotropy achieved by free layer
dimensions and/or dimensions of the sensor structure as a whole
were able to improve overall performance of various tunnel valve
read transducers described herein. Furthermore, hard bias magnets
according to various embodiments described herein were surprisingly
discovered by the inventors to provide a magnetic field that more
effectively stabilizes the free layer. Without wishing to be bound
by any theory, the inventors believe that this surprising result is
achieved because the thicker hard bias magnets are able to overcome
the loss of field at the ends of the hard bias magnets due to
magnetic flux leakage into the magnetic shields over the larger
dimensions (e.g., width and/or length) of the tape transducer.
Accordingly, some of the embodiments included herein are
successfully able to significantly reduce magnetic noise in
magnetic tape heads conventionally caused by thermally and/or
magnetically induced switching of unstable domains in a tunnel
valve free layer.
[0132] It will be clear that the various features of the foregoing
systems and/or methodologies may be combined in any way, creating a
plurality of combinations from the descriptions presented
above.
[0133] The inventive concepts disclosed herein have been presented
by way of example to illustrate the myriad features thereof in a
plurality of illustrative scenarios, embodiments, and/or
implementations. It should be appreciated that the concepts
generally disclosed are to be considered as modular, and may be
implemented in any combination, permutation, or synthesis thereof.
In addition, any modification, alteration, or equivalent of the
presently disclosed features, functions, and concepts that would be
appreciated by a person having ordinary skill in the art upon
reading the instant descriptions should also be considered within
the scope of this disclosure.
[0134] While various embodiments have been described above, it
should be understood that they have been presented by way of
example only, and not limitation. Thus, the breadth and scope of an
embodiment of the present invention should not be limited by any of
the above-described exemplary embodiments, but should be defined
only in accordance with the following claims and their
equivalents.
* * * * *