U.S. patent application number 13/276527 was filed with the patent office on 2012-02-16 for current-perpendicular-to-plane (cpp) read sensor with multiple reference layers.
Invention is credited to Tsann Lin.
Application Number | 20120040089 13/276527 |
Document ID | / |
Family ID | 40797993 |
Filed Date | 2012-02-16 |
United States Patent
Application |
20120040089 |
Kind Code |
A1 |
Lin; Tsann |
February 16, 2012 |
CURRENT-PERPENDICULAR-TO-PLANE (CPP) READ SENSOR WITH MULTIPLE
REFERENCE LAYERS
Abstract
A current-to-perpendicular-to-plane (CPP) read sensor with
multiple reference layers and associated fabrication methods are
disclosed. According to one embodiment of the invention, the
multiple reference layers of a CPP tunneling magnetoresistance
(TMR) read sensor includes a first reference layer formed by a
ferromagnetic polycrystalline Co--Fe film, a second reference layer
formed by a ferromagnetic substitute-type amorphous Co--Fe--X film
where X is Hf, Zr or Y, and a third reference layer formed by a
ferromagnetic interstitial-type amorphous Co--Fe--B film. The first
reference layer facilitates the CPP TMR read sensor to exhibit high
exchange and antiparallel-coupling fields. The second reference
layer provides a thermally stable flat surface, thus facilitating
the CPP TMR read sensor to exhibit a low ferromagnetic-coupling
field. The multiple reference layers may induce spin-dependent
scattering, thus facilitating the CPP TMR sensor to exhibit a high
TMR coefficient.
Inventors: |
Lin; Tsann; (Saratoga,
CA) |
Family ID: |
40797993 |
Appl. No.: |
13/276527 |
Filed: |
October 19, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11964673 |
Dec 26, 2007 |
|
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|
13276527 |
|
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Current U.S.
Class: |
427/131 |
Current CPC
Class: |
G11B 5/3906 20130101;
B82Y 10/00 20130101; G11B 5/3909 20130101; B82Y 25/00 20130101;
G11B 2005/3996 20130101 |
Class at
Publication: |
427/131 |
International
Class: |
B05D 5/00 20060101
B05D005/00; B05D 1/36 20060101 B05D001/36 |
Claims
1. A method of fabricating a flux-closure structure for a
current-perpendicular-to-plane (CPP) read sensor, the method
comprising: depositing a keeper layer; depositing an antiparallel
coupling layer on the keeper layer; depositing a first reference
layer of a ferromagnetic polycrystalline film on the antiparallel
coupling layer; depositing a second reference layer of a
ferromagnetic substitute-type amorphous film on the first reference
layer; and depositing a third reference layer of a ferromagnetic
interstitial-type amorphous film on the second reference layer.
2. The method of claim 1 wherein the first reference layer is
formed by a Co--Fe film including Co with a content ranging from 50
to 90 at % and Fe with a content ranging from 10 to 50 at %, and
having a thickness ranging from 0.2 to 1 nanometers.
3. The method of claim 1 wherein the second reference layer is
formed by a Co--Fe--X film including Co with a content ranging from
60 to 80 at %, Fe with a content ranging from 0 to 40 at %, and X
with a content ranging from 6 to 30 at %, where X is Hf, Zr or Y,
and having a thickness ranging from 0.6 to 2 nanometers.
4. The method of claim 1 wherein the third reference layer is
formed by a Co--Fe--B film including Co with a content ranging from
60 to 80 at %, Fe with a content ranging from 0 to 40 at %, and B
with a content ranging from 6 to 30 at %, and having a thickness
ranging from 1 to 2 nanometers.
Description
RELATED APPLICATIONS
[0001] The patent application is a divisional of U.S. patent
application having the Ser. No. 11/964,673, and filed on Dec. 26,
2007, which is incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The invention is related to the field of magnetic storage
systems, and in particular, to a disk drive including a
current-perpendicular-to-plane (CPP) read sensor with multiple
reference layers.
[0004] 2. Statement of the Problem
[0005] In many magnetic storage systems, a hard disk drive is the
most extensively used to store data. The hard disk drive typically
includes a hard disk along with an assembly of write and read
heads. The assembly of write and read heads is supported by a
slider that is mounted on a suspension arm. When the hard disk
rotates, an actuator swings the suspension arm to place the slider
over selected circular data tracks on the surface of the rotating
hard disk. An air flow generated by the rotation of the hard disk
causes the slider with an air bearing surface (ABS) to fly on a
cushion of air at a particular height over the rotating hard disk.
The height depends on the shape of the ABS. As the slider flies on
the air bearing, the actuator moves the suspension arm to position
the write and read heads over selected data tracks on the surface
of the hard disk. The write and read heads thus write data to and
read data from, respectively, a recording medium on the rotating
hard disk. Processing circuitry connected to the write and read
heads then operates according to a computer program to implement
writing and reading functions.
[0006] In a reading process, the read head passes over transitions
of a data track in the magnetic medium, and magnetic fields
emitting from the transitions modulate the resistance of a read
sensor in the read head. Changes in the resistance of the read
sensor are detected by a sense current passing through the read
sensor, and are then converted into voltage changes that generate
read signals. The resulting read signals are used to decode data
encoded in the transitions of the data track.
[0007] In a typical read head, a current-perpendicular-to-plane
(CPP) giant magnetoresistance (GMR) or tunneling magnetoresistance
(TMR) read sensor is electrically separated by side oxide layers
from longitudinal bias layers in two side regions for preventing a
sense current from shunting into the two side regions, but is
electrically connected with lower and upper shields for the sense
current to flow in a direction perpendicular to the sensor plane. A
typical CPP GMR read sensor comprises an electrically conducting
spacer layer sandwiched between lower and upper sensor stacks. The
spacer layer is typically formed by a nonmagnetic Cu or
oxygen-doped Cu (Cu--O) film having a thickness ranging from 1.6 to
4 nanometers. When the sense current flows across the Cu or Cu--O
spacer layer, changes in the resistance of the CPP GMR read sensor
is detected through a GMR effect. A typical CPP TMR read sensor
comprises an electrically insulating barrier layer sandwiched
between the lower and upper sensor stacks. The barrier layer is
typically formed by a nonmagnetic oxygen-doped Mg (Mg--O) or Mg
oxide (MgO.sub.X) film having a thickness ranging from 0.4 to 1
nanometers. When the sense current "quantum-jumps" across the Mg--O
or MgO.sub.X barrier layer, changes in the resistance of the CPP
GMR read sensor is detected through a TMR effect.
[0008] The lower sensor stack comprises nonmagnetic seed layers, an
antiferromagnetic pinning layer, a ferromagnetic keeper layer, a
nonmagnetic antiparallel-coupling layer, and a ferromagnetic
reference layer. The upper sensor stack comprises ferromagnetic
sense (free) layers and a nonmagnetic cap layer. In the lower
sensor stack, the keeper layer, the antiparallel-coupling layer,
and the reference layer form a flux-closure structure where four
fields are induced. First, a unidirectional anisotropy field
(H.sub.UA) is induced by exchange coupling between the
antiferromagnetic pinning layer and the keeper layer. Second, an
antiparallel-coupling field (H.sub.APC) is induced by antiparallel
coupling between the keeper layer and the reference layer across
the antiparallel-coupling layer. Third, a demagnetizing field
(H.sub.D) is induced by the net magnetization of the keeper layer
and the reference layer. Fourth, a ferromagnetic-coupling field
(H.sub.F) is induced by ferromagnetic coupling between the
reference layer and the sense layer across the spacer or barrier
layer. To ensure proper sensor operation, H.sub.UA and H.sub.APC
should be high enough to rigidly pin magnetizations of the keeper
layer and the reference layer in opposite transverse directions
perpendicular to the ABS, while H.sub.D and H.sub.F should be small
and balance with each other to orient the magnetization of the
sense layers in a longitudinal direction parallel to the ABS.
[0009] In the flux-closure structure of the CPP TMR read sensor,
the Co--Fe keeper layer is selected to ensure high exchange and
antiparallel coupling. Its composition is optimized and its
magnetic moment is small, so that high H.sub.UA and H.sub.APC can
be attained. The Co--Fe--B reference layer is selected to ensure a
strong TMR effect and mild ferromagnetic coupling. Its B content is
high enough for B atoms, which are much smaller than Co and Fe
atoms, to occupy interstitial sites of a crystalline structure and
thus interfere with the ability of the Co and Fe atoms to
crystallize. As a result, an interstitial-type amorphous film with
a flat surface is formed, which facilitates the Mg--O or MgO.sub.X
barrier layer to grow with a preferred <001> crystalline
texture on the flat surface, thus increasing a TMR coefficient
(.DELTA.R.sub.T/R.sub.J) and decreasing H.sub.F. Its Co and Fe
contents are optimized and its magnetic moment is small, so that a
high H.sub.APC can be attained.
[0010] The use of the Co--Fe--B reference layer in the prior art
generally meets the requirements of high H.sub.APC, low H.sub.F,
and high .DELTA.R.sub.T/R.sub.J. However, it is still desirable to
further improve the reference layer for the CPP TMR sensor to
operate more robustly.
SUMMARY
[0011] Embodiments of the invention include a CPP read sensor with
multiple reference layers. According to one embodiment, the
multiple reference layers of a CPP TMR read sensor include a first
reference layer formed by a ferromagnetic polycrystalline Co--Fe
film, a second reference layer formed by a ferromagnetic
substitute-type amorphous Co--Fe--X film where X is Zr, Hf or Y,
and a third reference layer formed by a ferromagnetic
interstitial-type amorphous Co--Fe--B film. The first reference
layer facilitates the TMR sensor to exhibit high exchange and
antiparallel-coupling fields. The second reference layer provides a
thermally stable flat surface, thus facilitating the CPP TMR sensor
to exhibit a low ferromagnetic-coupling field. The multiple
reference layers induce spin-dependent scattering, thus
facilitating the CPP TMR sensor to exhibit a high TMR
coefficient.
[0012] The invention may include other exemplary embodiments as
described below.
DESCRIPTION OF THE DRAWINGS
[0013] The same reference number represents the same element or
same type of element on all drawings.
[0014] FIG. 1 illustrates a hard disk drive used as a magnetic
storage system.
[0015] FIG. 2 is a side view of a hard disk drive.
[0016] FIG. 3 is an ABS view of a slider.
[0017] FIG. 4 illustrates an ABS view of a typical read head
fabricated on a slider.
[0018] FIG. 5 illustrates an ABS view of a TMR read sensor in an
exemplary embodiment of the invention.
[0019] FIG. 6 illustrates multiple reference layers in an exemplary
embodiment of the invention.
[0020] FIG. 7 is a flow chart illustrating a method of fabricating
a TMR read sensor in an exemplary embodiment of the invention.
[0021] FIG. 8 illustrates an ABS view of the detailed structure of
a TMR read sensor in an exemplary embodiment of the invention.
[0022] FIG. 9 illustrates magnetic responses of
Ta(3)/Ru(3)/77.5Co-22.5Fe(2.1)/Ru(0.8)/X/Ta(3) films (thickness in
nanometer), where X is 77.5Co-22.5Fe (2.1), 64.6Co-19.7Fe-15.7Zr
(2.4), or 51.9Co-34.6Fe-13.5B (2.4) in an exemplary embodiment of
the invention.
[0023] FIG. 10 illustrates the ferromagnetic coupling field
(H.sub.F) versus the resistance-area product (R.sub.JA.sub.J) for
TMR read sensors in an exemplary embodiment of the invention.
[0024] FIG. 11 illustrates the TMR coefficient
(.DELTA.R.sub.T/R.sub.J) versus the resistance-area product
(R.sub.JA.sub.J) for the TMR read sensors in an exemplary
embodiment of the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0025] FIGS. 1-11 and the following description depict specific
exemplary embodiments of the invention to teach those skilled in
the art how to make and use the invention. For the purpose of
teaching inventive principles, some conventional aspects of the
invention have been simplified or omitted. Those skilled in the art
will appreciate variations from these embodiments that fall within
the scope of the invention. Those skilled in the art will
appreciate that the features described below can be combined in
various ways to form multiple variations of the invention. As a
result, the invention is not limited to the specific embodiments
described below, but only by the claims and their equivalents.
[0026] FIG. 1 illustrates a hard disk drive 100 used as a magnetic
storage system. The hard disk drive 100 includes a spindle 102, a
hard disk 104, a control system 106, an actuator 108, a suspension
arm 110, and a slider 114 having an assembly of write and read
heads. The spindle 102 supports and rotates the hard disk 104 in a
direction indicated by the arrow. A spindle motor (not shown)
rotates the spindle 102 according to control signals from the
control system 106. The slider 114 is supported by the suspension
arm 110, and the actuator 108 is configured to rotate the
suspension arm 110 in order to position the assembly of write and
read heads over a desired data track in a magnetic medium on the
hard disk 104. The hard disk drive 100 may include other components
not shown in FIG. 1, such as a plurality of hard disks, actuators,
suspension arms, and sliders.
[0027] When the hard disk 104 rotates, an air flow generated by the
rotation of the hard disk 104 causes the slider 114 with an air
bearing surface (ABS) to fly on a cushion of air at a particular
height over the rotating hard disk 104. The height depends on the
shape of the ABS. As the slider 114 flies on the air, the actuator
108 moves the suspension arm 110 to position a write head (not
shown) and a read head (not shown) over selected data tracks on the
surface of the hard disk 104. The write and read heads write data
to and read data from, respectively, a recording medium on the
rotating hard disk 104. Processing circuitry connected to the write
and read heads then operates according to a computer program to
implement writing and reading functions.
[0028] FIG. 2 is a side view of hard disk drive 100. The slider 114
is supported above the surface of the hard disk 104. The slider 114
includes a front end 202 and an opposing trailing end 204. The
slider 114 also includes an air bearing surface 206 that faces
toward the surface of the hard disk 104. A write head (not shown)
and a read head (not shown) are formed proximate to the trailing
end 204, which is further illustrated in FIG. 3.
[0029] FIG. 3 is an ABS view of slider 114. The ABS 206 of slider
114 is the surface of the page in FIG. 3. The slider 114 has a
cross rail 303, two side rails 304, 305, and a center rail 306 on
the ABS 206. The rails, which define how the slider 114 flies over
the surface of the hard disk 104, illustrate just one embodiment,
and the configuration of the ABS 206 of the slider 114 may take on
any desired form. The slider 114 includes a write head 210 and a
read head 112 fabricated proximate to the trailing end 204.
[0030] FIG. 4 illustrates an ABS view of a typical read head 212
fabricated on the slider 116. The read head 212 includes a first
(lower) shield 401 and a second (upper) shield 402 that sandwich a
TMR read sensor 404 and two side regions at edges of the TMR read
sensor 404. In the two side regions, side oxide layers 405-406
separate longitudinal bias layers 407-408, respectively, from the
first shield 401 and the TMR read sensor 404.
[0031] FIG. 5 illustrates an ABS view of a TMR read sensor 404 in
an exemplary embodiment of the invention. The layers 511-517 shown
for the TMR read sensor 404 illustrate just one embodiment, and the
TMR read sensor 404 may include additional layers or different
layers in other embodiments. The TMR read sensor 404 includes an
electrically insulating barrier layer 515 sandwiched between a
lower sensor stack and an upper sensor stack. The lower sensor
stack includes one or more nonmagnetic seed layers 510, an
antiferromagnetic pinning layer 511, a ferromagnetic keeper layer
512, an antiparallel-coupling layer 513, and multiple reference
layers 514. The upper sensor stack includes one or more
ferromagnetic sense layers 516, and a nonmagnetic cap layer
517.
[0032] FIG. 6 illustrates multiple reference layers 514 in an
exemplary embodiment of the invention. The multiple reference
layers 514 include a first reference layer 601 formed by a
ferromagnetic polycrystalline Co--Fe film. The first reference
layer 601 may be formed by a Co--Fe film including Co with a
content ranging from 50 to 90 at % and Fe with a content ranging
from 10 to 50 at %, and having a thickness ranging from 0.2 to 1
nanometers. The multiple reference layers 514 further include the
second reference layer 602 formed by a ferromagnetic
substitute-type amorphous Co--Fe--X (where X is Zr, Hf or Y) film.
The second reference layer 602 may be formed by a Co--Fe--X film
including Co with a content ranging from 60 to 80 at %, Fe with a
content ranging from 0 to 40 at %, and X with a content ranging
from 6 to 30 at %, where X is Hf, Zr, or Y, and having a thickness
ranging from 0.6 to 2 nanometers. The substitute-type amorphous
film is formed by adding Zr, Hf or Y atoms, which are much larger
than Co and Fe atoms, to occupy substitute sites of a crystalline
structure and thus to interfere with the ability of the Co and Fe
atoms to crystallize. The multiple reference layers 514 further
include a third reference layer 603 formed by a ferromagnetic
interstitial-type amorphous Co--Fe--B film. The third reference
layer 603 may be formed by a Co--Fe--B film including Co with a
content ranging from 60 to 80 at %, Fe with a content ranging from
0 to 40 at %, and B with a content ranging from 6 to 30 at %, and
having a thickness ranging from 1 to 2 nanometers. The
interstitial-type amorphous film is formed by adding B atoms, which
are much smaller than Co and Fe atoms, to occupy interstitial sites
of a crystalline structure and thus to interfere with the ability
of the Co and Fe atoms to crystallize.
[0033] Although FIG. 5 illustrates a TMR read sensor, those skilled
in the art will appreciate that that the concept of multiple
reference layers as described in FIG. 6 may also apply to other CPP
read sensors, such as a CPP GMR read sensor. In a CPP GMR read
sensor, a nonmagnetic spacer layer replaces the barrier layer 515
in the CPP GMR lower and upper sensor stacks.
[0034] FIG. 7 is a flow chart illustrating a method 700 of
fabricating the TMR read sensor 404 in an exemplary embodiment of
the invention. The steps of the flow chart in FIG. 7 are not all
inclusive and may include other steps not shown. Step 702 comprises
forming a first or lower ferromagnetic shield 401 on a wafer. The
wafer is then smoothened with chemical mechanical polishing (CMP)
in order for the lower shield 401 to provide a smooth surface for
the TMR read sensor to grow. Step 703 comprises depositing one or
more nonmagnetic seed layers 510 on the lower shield 401. Step 704
comprises depositing an antiferromagnetic pinning layer 511 on the
seed layers 510. The term "on" as used herein may refer to being
deposited directly on top of a previously deposited film. Step 706
comprises depositing a ferromagnetic keeper layer 512 on the
antiferromagnetic pinning layer 511. Step 708 comprises depositing
a nonmagnetic antiparallel coupling layer 513 on the keeper layer
512. Step 710 comprises depositing the first reference layer 601 on
the antiparallel coupling layer 513. Step 712 comprises depositing
the second reference layer 602 on the first reference layer 601.
Step 714 comprises depositing the third reference layer 603 on the
second reference layer 602. Steps 710-714 may be performed in situ
in the same module of a sputtering system for improving processing
efficiency and TMR properties. Step 716 comprises forming the
barrier layer 515 on the third reference layer 603. Step 718
comprises depositing one or more sense layers 516 on the barrier
layer 515. Step 720 comprises depositing a cap layer 517 on the
sense layers 516. After patterning the TMR read sensor 404 and
depositing side oxide and longitudinal bias layers into side
regions of the TMR read sensor 404, step 722 is performed to form
the second shield 402 on the cap layer 517.
[0035] FIG. 8 illustrates an ABS view of the detailed structure of
a TMR read head 800 in an exemplary embodiment of the invention.
The TMR read head 800 is a detailed embodiment that is in no way
intended to limit the scope of the invention, as exemplary layers
of the TMR read head 800 are shown. Thus, those skilled in the art
understand that the TMR read head 800 may include other layers in
other exemplary embodiments. In FIG. 8, the TMR read head 800
includes a TMR read sensor 810 sandwiched between a first or lower
shield 831 formed by a 1 .mu.m thick Ni--Fe film and a second or
upper shield 832 formed by another 1 .mu.m thick Ni--Fe film.
[0036] The TMR read sensor 810 includes an electrically insulating
barrier layer 819 sandwiched between a lower sensor stack and an
upper sensor stack. The barrier layer 819 may be formed by a
nonmagnetic oxygen-doped Mg (Mg--O) film in-situ formed in only one
module of a sputtering system, as described below. After heavily
cleaning a Mg target for 60 seconds with a target power of 600 W, a
0.2 nanometer thick Mg film is DC sputtered in an argon gas of
3.times.10.sup.-4 torr with a target power of 40 W. A first oxygen
treatment in an oxygen gas of 5.times.10.sup.-7 torr is then
applied to the Mg film, resulting in oxygen doping into the Mg
film. A 0.4 nanometer thick Mg--O film is then DC sputtered in a
mixture of argon and oxygen gases of 3 and 0.4.times.10.sup.-4
torr, respectively, with a target power of 100 W. A second oxygen
treatment in an oxygen gas of 5.times.10.sup.-7 ton is then applied
to the Mg--O film. A 0.2 nanometer thick Mg--O film is then DC
sputtered in a mixture of argon and oxygen gases of 3 and
0.1.times.10.sup.-4 ton, respectively, with a target power of 100
W. A third oxygen treatment in an oxygen gas of 5.times.10.sup.-5
ton is then applied to the Mg--O film.
[0037] The lower sensor stack comprises a first seed layer 811
formed by a 3 nanometer thick nonmagnetic Ta film, a second seed
layer 812 formed by a 3 nanometer thick nonmagnetic Ru film, a
pinning layer 813 formed by a 6 nanometer thick antiferromagnetic
21.7Ir-78.3Mn film (composition in atomic percent), a keeper layer
814 formed by a 2.1 nanometer thick ferromagnetic 77.5Co-22.5 Fe
film, and an antiparallel coupling layer 815 formed by a 0.8
nanometer thick nonmagnetic Ru film. The lower sensor stack further
comprises a first reference layer 816 formed by a 0.4 nanometer
thick ferromagnetic 77.5Co-22.5 Fe film, a second reference layer
817 formed by a 0.6 nanometer thick ferromagnetic 64.6Co-19.7
Fe-15.7Zr film, and a third reference layer 818 formed by a 1
nanometer thick ferromagnetic 51.9Co-34.6Fe-13.5B film.
[0038] The upper sensor stack comprises a first sense layer 820
formed by a 0.4 nanometer thick ferromagnetic 87.1Co-12.9Fe film, a
second sense layer 821 formed by a 2.6 nanometer thick
ferromagnetic 71.5Co-7.4Fe-21.1B film, and a cap layer 822 formed
by a 6 nanometer thick nonmagnetic Ru film.
[0039] The first reference layer 816 facilitates the flux-closure
structure to exhibit a high antiparallel-coupling field
(H.sub.APC), which is defined as a critical field aligning 95% of
the saturation magnetization of the flux-closure structure in its
direction. FIG. 9 illustrates magnetic responses of
Ta(3)/Ru(3)/77.5Co-22.5Fe(2.1)/Ru(0.8)/X/Ta(3) films (thickness in
nanometer), where X is 77.5Co-22.5Fe(2.1), 64.6Co-19.7Fe-15.7Zr
(2.4) or 51.9Co-34.6Fe-13.5B (2.4). H.sub.APC values reach 6,299,
4,136 and 6,450 Oe for the Co--Fe(2.1), Co--Fe--Zr(2.4) and
Co--Fe--B(2.4), respectively. The Co--Fe first reference layer 816
acts as a buffer layer to achieve a high H.sub.APC. While the
Co--Fe--B can also act as a buffer layer to achieve a litter higher
H.sub.APC, it is still suggested to use the Co--Fe first reference
layer 816 but with a higher Fe content to achieve an even higher
H.sub.APC.
[0040] The second reference layer 817 provides a thermally stable
flat surface, thus facilitating the TMR read sensor 800 to exhibit
a low ferromagnetic-coupling field (H.sub.F). FIG. 10 illustrates
the ferromagnetic coupling field (H.sub.F) versus the
resistance-area product (R.sub.JA.sub.J) for the TMR read sensors
in an exemplary embodiment of the invention. After annealing for 5
hours at 240 and 280.degree. C., the TMR read sensors with
Co--Fe--B and Co--Fe/Co--Fe--Zr/Co--Fe--B reference layers exhibit
comparable H.sub.F, indicating that the Co--Fe--Zr second reference
layer 817 plays the same role as the Co--Fe--B third reference
layer 818 in facilitating the Mg--O film to grow as a flat barrier
layer. In addition, it is found from cross-sectional transmission
electron microscopy that, after annealing for 5 hours at
280.degree. C., the substitute-type amorphous Co--Fe--Zr second
reference layer 817 still remains as amorphous, while the
interstitial-type amorphous Co--Fe--B third reference layer 818
becomes polycrystalline. It is thus expected that the
substitute-type amorphous Co--Fe--Zr reference layer 817 might play
a better role than the Co--Fe--B third reference layer 818 in
facilitating the Mg--O film to grow as a flat barrier layer in the
TMR read sensor annealed at even higher temperatures.
[0041] The multiple reference layers might induce spin-dependent
scattering, thus facilitating the TMR read sensor 800 to exhibit a
high TMR coefficient (.DELTA.R.sub.T/R.sub.J). FIG. 11 shows
.DELTA.R.sub.T/R.sub.J versus the resistance-area product
(R.sub.JA.sub.J) for the TMR read sensors in an exemplary
embodiment of the invention. After annealing for 5 hour at
240.degree. C., the TMR read sensor with the
Co--Fe/Co--Fe--Zr/Co--Fe--B reference layers exhibits
.DELTA.R.sub.T/R.sub.J higher than that with the Co--Fe--B
reference layer. In addition, after annealing for 5 hour at
280.degree. C., while .DELTA.R.sub.T/R.sub.J for the TMR read
sensor with the Co--Fe--B reference layer slightly increases,
.DELTA.R.sub.T/R.sub.J for the TMR read sensor with the
Co--Fe/Co--Fe--Zr/Co--Fe--B reference layers substantially
increases. It should be noted that the thickness of the Co--Fe--B
reference layer in the prior art must be large enough to exhibit a
high .DELTA.R.sub.T/R.sub.J, while that of the Co--Fe--B third
reference layer in the exemplary embodiment of the invention is
reduced by 50%, but an even higher .DELTA.R.sub.T/R.sub.J is
attained. The Co--Fe first reference layer and the Co--Fe--Zr
second reference layer, as well as two newly created interfaces in
the multiple reference layers, thus also play crucial roles in
increasing .DELTA.R.sub.T/R.sub.J.
[0042] Although specific embodiments were described herein, the
scope of the invention is not limited to those specific
embodiments. The scope of the invention is defined by the following
claims and any equivalents thereof.
* * * * *