U.S. patent application number 11/866609 was filed with the patent office on 2008-10-23 for tunneling magnetoresistive element including multilayer free magnetic layer having inserted nonmagnetic metal sublayer.
Invention is credited to Akio Hanada, Naoya Hasegawa, Yosuke Ide, Masahiko Ishizone, Hidekazu Kobayashi, Ryo Nakabayashi, Kazumasa Nishimura, Yoshihiro Nishiyama, Masamichi Saito.
Application Number | 20080261082 11/866609 |
Document ID | / |
Family ID | 46329431 |
Filed Date | 2008-10-23 |
United States Patent
Application |
20080261082 |
Kind Code |
A1 |
Nishimura; Kazumasa ; et
al. |
October 23, 2008 |
TUNNELING MAGNETORESISTIVE ELEMENT INCLUDING MULTILAYER FREE
MAGNETIC LAYER HAVING INSERTED NONMAGNETIC METAL SUBLAYER
Abstract
A tunnel magnetoresistive element includes a laminate including
a pinned magnetic layer, an insulating barrier layer, and a free
magnetic layer. The insulating barrier layer is composed of
Ti--Mg--O or Ti--O. The free magnetic layer includes an enhancement
sublayer, a first soft magnetic sublayer, a nonmagnetic metal
sublayer, and a second soft magnetic sublayer. For example, the
enhancement sublayer is composed of Co--Fe, the first soft magnetic
sublayer and the second soft magnetic sublayer are composed of
Ni--Fe, and the nonmagnetic metal sublayer is composed of Ta. The
total thickness of the average thickness of the enhancement
sublayer and the average thickness of the first soft magnetic
sublayer is in the range of 25 to 80 angstroms. Accordingly, the
tunneling magnetoresistive element can consistently have a higher
rate of resistance change than before.
Inventors: |
Nishimura; Kazumasa;
(Niigata-ken, JP) ; Nakabayashi; Ryo;
(Niigata-ken, JP) ; Ide; Yosuke; (Niigata-ken,
JP) ; Ishizone; Masahiko; (Niigata-ken, JP) ;
Saito; Masamichi; (Niigata-ken, JP) ; Hasegawa;
Naoya; (Niigata-ken, JP) ; Nishiyama; Yoshihiro;
(Niigata-ken, JP) ; Hanada; Akio; (Niigata-ken,
JP) ; Kobayashi; Hidekazu; (Niigata-ken, JP) |
Correspondence
Address: |
BRINKS HOFER GILSON & LIONE
P.O. BOX 10395
CHICAGO
IL
60610
US
|
Family ID: |
46329431 |
Appl. No.: |
11/866609 |
Filed: |
October 3, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11671783 |
Feb 6, 2007 |
|
|
|
11866609 |
|
|
|
|
Current U.S.
Class: |
428/846.8 ;
360/324.2; G9B/5.117 |
Current CPC
Class: |
B82Y 25/00 20130101;
B82Y 10/00 20130101; G11B 5/3906 20130101; G11B 5/3909 20130101;
H01L 43/08 20130101 |
Class at
Publication: |
428/846.8 ;
360/324.2 |
International
Class: |
G11B 5/706 20060101
G11B005/706 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 28, 2006 |
JP |
2006-355019 |
Apr 5, 2007 |
JP |
2007-099278 |
Claims
1. A tunneling magnetoresistive element comprising: a laminate
direction, an insulting barrier layer, and a free magnetic layer
having a variable magnetization direction according to an external
magnetic field, laminated in that order from the bottom, or a
laminate that includes the free magnetic layer, the insulating
barrier layer, and the pinned magnetic layer, laminated in that
order from the bottom, wherein the insulating barrier layer is
composed of Ti--Mg--O or Ti--O, the free magnetic layer includes a
plurality of soft magnetic sublayers, a nonmagnetic metal sublayer
separating the soft magnetic sublayers, and an enhancement sublayer
disposed between a first soft magnetic sublayer and the insulating
barrier layer and having a spin polarizability higher than those of
the soft magnetic sublayers, the first soft magnetic sublayer being
the soft magnetic sublayer closest to the insulating barrier layer,
the soft magnetic sublayers are magnetically coupled to each other
and thereby have the same magnetization direction, and the total of
the average thickness of the first soft magnetic sublayer and the
average thickness of the enhancement sublayer is at least 25
angstroms.
2. The tunneling magnetoresistive element according to claim 1,
wherein the total thickness is 80 angstroms or less.
3. The tunneling magnetoresistive element according to claim 1,
wherein the average thickness of the first soft magnetic sublayer
is in the range of 15 to 70 angstroms.
4. The tunneling magnetoresistive element according to claim 1,
wherein the average thickness of the enhancement sublayer is in the
range of 10 to 30 angstroms.
5. The tunneling magnetoresistive element according to claim 1,
wherein the laminate further includes a protective layer, as a top
layer, that includes a first protective sublayer as a bottom
sublayer and that is composed of at least one selected from the
group consisting of Ru, Al, Ni--Fe--Cr, Ir--Mn, and Cr.
6. A tunneling magnetoresistive element comprising: a laminate that
includes a pinned magnetic layer having a fixed magnetization
direction, an insulating barrier layer, and a free magnetic layer
having a variable magnetization direction according to an external
magnetic field, laminated in that order from the bottom, or a
laminate that includes the free magnetic layer, the insulating
barrier layer, and the pinned magnetic layer, laminated in that
order from the bottom, wherein the free magnetic layer includes a
plurality of soft magnetic sublayers, a nonmagnetic metal sublayer
separating the soft magnetic sublayers, and an enhancement sublayer
disposed between a first soft magnetic sublayer and the insulating
barrier layer and having a spin polarizability higher than those of
the soft magnetic sublayers, the first soft magnetic sublayer being
the soft magnetic sublayer closest to the insulating barrier layer,
the soft magnetic sublayers are magnetically coupled to each other
and thereby have the same magnetization direction, and the laminate
further includes a protective layer, as a top layer, that includes
a first protective sublayer as a bottom sublayer and that is
composed of at least one selected from the group consisting of Ru,
Al, Ni--Fe--Cr, Ir--Mn, and Cr.
7. The tunneling magnetoresistive element according to claim 6,
wherein the protective layer further includes a second protective
sublayer disposed on the first protective sublayer and composed of
Ta.
8. The tunneling magnetoresistive element according to claim 1,
wherein the nonmagnetic metal sublayer is composed of at least one
selected from the group consisting of Ti, V, Zr, Nb, Mo, Hf, Ta,
and W.
9. The tunneling magnetoresistive element according to claim 8,
wherein the nonmagnetic metal sublayer is composed of Ta.
10. The tunneling magnetoresistive element according to claim 1,
wherein the average thickness of the nonmagnetic metal sublayer is
in the range of one to four angstroms.
11. The tunneling magnetoresistive element according to claim 1,
wherein the soft magnetic sublayers are formed of a Ni--Fe alloy,
and the enhancement sublayer is formed of a Co--Fe alloy.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 11/671,783 filed on Jun. 2, 2007, which is
entirely incorporated by reference herein.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a tunneling
magnetoresistive element that may be installed in hard disk drives
or magnetic detectors, and more particularly, it relates to a
tunneling magnetoresistive element that can achieve a high rate of
resistance change (AR/R).
[0004] 2. Description of the Related Art
[0005] Tunneling magnetoresistive (TMR) elements generate a
resistance change by utilizing a tunneling effect. When the
magnetization direction of a pinned magnetic layer is antiparallel
to the magnetization direction of a free magnetic layer, less
tunneling current flows through an insulating barrier layer (tunnel
barrier layer) disposed between the pinned magnetic layer and the
free magnetic layer, and thereby the resistance reaches its peak.
On the other hand, when the magnetization direction of the pinned
magnetic layer is parallel to the magnetization direction of the
free magnetic layer, the tunneling current reaches the maximum, and
the resistance reaches the minimum.
[0006] According to this principle, an external magnetic field
changes the magnetization of the free magnetic layer and thereby
changes the electrical resistance. The tunneling magnetoresistive
elements detect the change in electrical resistance as a voltage
change and thereby detect a leakage magnetic field from a recording
medium.
[0007] Japanese Unexamined Patent Application Publication No.
2006-261637 discloses a tunneling magnetoresistive element that
includes a free magnetic layer having a layered ferri
structure.
[0008] In this patent document, the free magnetic layer includes
ferromagnetic layers and a first orientation control buffer
disposed between the ferromagnetic layers to generate large
exchange coupling. A free magnetic layer including
Ni.sub.81Fe.sub.19 (2 nm)/Ta (0.4 nm)/Ni.sub.81Fe.sub.19 (2 nm)/Ru
(2.1 nm)/Ni.sub.81Fe.sub.19 (4 nm) laminated in that order from the
bottom is disclosed in paragraph [0139].
[0009] However, this patent document does not disclose a structure
that can achieve a high rate of resistance change (.DELTA.R/R).
SUMMARY OF THE INVENTION
[0010] Accordingly, the present invention aims to solve the
problems described above. The present invention provides a
tunneling magnetoresistive element that can achieve a high rate of
resistance change (.DELTA.R/R).
[0011] According to one aspect of the present invention, a
tunneling magnetoresistive element includes a laminate that
includes a pinned magnetic layer having a fixed magnetization
direction, an insulating barrier layer, and a free magnetic layer
having a variable magnetization direction according to an external
magnetic field, laminated in that order from the bottom, or a
laminate that includes the free magnetic layer, the insulating
barrier layer, and the pinned magnetic layer, laminated in that
order from the bottom. The insulating barrier layer is composed of
Ti--Mg--O (titanium oxide/magnesium oxide) or Ti--O (titanium
oxide). The free magnetic layer includes a plurality of soft
magnetic sublayers, a nonmagnetic metal sublayer separating the
soft magnetic sublayers, and an enhancement sublayer disposed
between a first soft magnetic sublayer and the insulating barrier
layer and having a spin polarizability higher than those of the
soft magnetic sublayers. The first soft magnetic sublayer is
closest to the insulating barrier layer of the soft magnetic
sublayers. The soft magnetic sublayers are magnetically coupled to
each other and thereby have the same magnetization direction. The
total of the average thickness of the first soft magnetic sublayer
and the average thickness of the enhancement sublayer is at least
25 angstroms. The tunneling magnetoresistive element including the
Ti--Mg--O or Ti--O insulating barrier layer exhibits a rate of
resistance change (.DELTA.R/R) higher than before. This is achieved
by separating the soft magnetic sublayers in the free magnetic
layer with a nonmagnetic metal sublayer and optimizing the distance
between the nonmagnetic metal sublayer and the insulating barrier
layer (the total of the average thickness of the first soft
magnetic sublayer and the average thickness of the enhancement
sublayer).
[0012] Unlike Japanese Unexamined Patent Application Publication
No. 2006-261637, the free magnetic layer according to the present
invention does not have a layered ferri structure. If the free
magnetic layer has a layered ferri structure, a unidirectional bias
magnetic field, which flows into the free magnetic layer from hard
bias layers disposed on both sides of the free magnetic layer in
the track width direction, disturbs the antiparallel magnetization
state of two pinned magnetic sublayers separated by a nonmagnetic
intermediate sublayer in the pinned magnetic layer, thus often
causing Barkhausen noise. Furthermore, if the free magnetic layer
has a layered ferri structure, the free magnetic layer often has a
large coercive force. The coercive force is preferably as small as
possible.
[0013] The nonmagnetic metal sublayer disposed between the soft
magnetic sublayers has a small thickness to magnetically couple the
soft magnetic sublayers and magnetize all the soft magnetic
sublayers in one direction. Thus, the nonmagnetic metal sublayer
does not interrupt the magnetic coupling between the soft magnetic
sublayers. Furthermore, the absence of a layered ferri structure
results in reduced or no Barkhausen noise and a lower coercive
force. Hence, a tunneling magnetoresistive element according to the
present invention has stable read characteristics.
[0014] Preferably, the total of the average thickness of the first
soft magnetic sublayer and the average thickness of the enhancement
sublayer is 80 angstroms or less. Thus, a tunneling
magnetoresistive element according to the present invention can
consistently have a high rate of resistance change
(.DELTA.R/R).
[0015] Preferably, the average thickness of the first soft magnetic
sublayer is in the range of 15 to 70 angstroms. Preferably, the
average thickness of the enhancement sublayer is in the range of 10
to 30 angstroms. Thus, a tunneling magnetoresistive element
according to the present invention can consistently have a high
rate of resistance change (.DELTA.R/R).
[0016] Preferably, the laminate further includes a protective layer
as a top layer. The protective layer includes a first protective
sublayer as a bottom sublayer and is composed of at least one
selected from the group consisting of Ru, Al, Ni--Fe--Cr, Ir--Mn,
and Cr.
[0017] According to another aspect of the present invention, a
tunneling magnetoresistive element includes a laminate that
includes a pinned magnetic layer having a fixed magnetization
direction, an insulating barrier layer, and a free magnetic layer
having a variable magnetization direction according to an external
magnetic field, laminated in that order from the bottom, or a
laminate that includes the free magnetic layer, the insulating
barrier layer, and the pinned magnetic layer, laminated in that
order from the bottom. The free magnetic layer includes a plurality
of soft magnetic sublayers, a nonmagnetic metal sublayer separating
the soft magnetic sublayers, and an enhancement sublayer disposed
between a first soft magnetic sublayer and the insulating barrier
layer and having a spin polarizability higher than those of the
soft magnetic sublayers. The first soft magnetic sublayer is
closest to the insulating barrier layer of the soft magnetic
sublayers. The soft magnetic sublayers are magnetically coupled to
each other and thereby have the same magnetization direction. The
laminate further includes a protective layer, as a top layer, that
includes a first protective sublayer as a bottom sublayer and that
is composed of at least one selected from the group consisting of
Ru, Al, Ni--Fe--Cr, Ir--Mn, and Cr.
[0018] The tunneling magnetoresistive element that includes the
first protective sublayer composed of at least one selected from
the group consisting of Ru, Al, Ni--Fe--Cr, Ir--Mn, and Cr exhibits
a rate of resistance change (AR/R) higher than before. This is
achieved by separating the soft magnetic sublayers in the free
magnetic layer with a nonmagnetic metal sublayer.
[0019] A tunneling magnetoresistive element that further includes a
second protective sublayer disposed on the first protective
sublayer and composed of Ta can effectively achieve a high rate of
resistance change (AR/R).
[0020] Preferably, the nonmagnetic metal sublayer is composed of at
least one selected from the group consisting of Ti, V, Zr, Nb, Mo,
Hf, Ta, and W. More preferably, the nonmagnetic metal sublayer is
composed of Ta. These can effectively increase the rate of
resistance change (AR/R).
[0021] Preferably, the average thickness of the nonmagnetic metal
sublayer is in the range of one to four angstroms. Because the
nonmagnetic metal sublayer has such a small thickness, the soft
magnetic sublayers can be magnetically coupled in an appropriate
manner. This results in an increase in rate of resistance change
(.DELTA.R/R), reduced or no Barkhausen noise, and reduced
variations in asymmetry of reproduced waveform, thus improving the
stability of the read characteristics.
[0022] Preferably, the soft magnetic sublayers are formed of a
Ni--Fe alloy, and the enhancement sublayer is formed of a Co--Fe
alloy, in terms of a rate of resistance change (AR/R).
[0023] Consequently, a tunneling magnetoresistive element according
to the present invention can have a rate of resistance change
(.DELTA.R/R) higher than before.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] FIG. 1 is a cross-sectional view of a tunneling
magnetoresistive element, taken parallel to a plane of a recording
medium;
[0025] FIG. 2 is a fragmentary enlarged cross-sectional view of a
tunneling magnetoresistive element according to an embodiment of
the present invention, taken in the same direction as in FIG.
1;
[0026] FIG. 3 is a fragmentary enlarged cross-sectional view of a
tunneling magnetoresistive element according to another embodiment
of the present invention, taken in the same direction as in FIG.
1;
[0027] FIG. 4 is a fragmentary enlarged cross-sectional view of a
tunneling magnetoresistive element according to still another
embodiment of the present invention, taken in the same direction as
in FIG. 1;
[0028] FIG. 5 is a fragmentary enlarged cross-sectional view of a
tunneling magnetoresistive element according to still another
embodiment of the present invention, taken in the same direction as
in FIG. 1;
[0029] FIG. 6 is a cross-sectional view illustrating a step of
manufacturing a tunneling magnetoresistive element according to an
embodiment of the present invention, taken in the same direction as
in FIG. 1;
[0030] FIG. 7 is a cross-sectional view illustrating a step
subsequent to the step illustrated in FIG. 6;
[0031] FIG. 8 is a cross-sectional view illustrating a step
subsequent to the step illustrated in FIG. 7;
[0032] FIG. 9 is a cross-sectional view illustrating a step
subsequent to the step illustrated in FIG. 8;
[0033] FIG. 10 is a graph showing the rate of resistance change
(.DELTA.R/R) as a function of the average thickness (X) of a first
soft magnetic sublayer in a tunneling magnetoresistive element with
or without an enhancement sublayer, in which the tunneling
magnetoresistive element includes a Ti--Mg--O insulating barrier
layer and a free magnetic layer that includes the first soft
magnetic sublayer, a second soft magnetic sublayer, and a Ta
nonmagnetic metal sublayer disposed between the first and second
soft magnetic sublayers;
[0034] FIG. 11 is a graph showing the rate of resistance change
(.DELTA.R/R) as a function of the average thickness (Y) of an
enhancement sublayer in a tunneling magnetoresistive element that
includes a Ti--Mg--O insulating barrier layer and a free magnetic
layer including a first soft magnetic sublayer, a second soft
magnetic sublayer, and a Ta nonmagnetic metal sublayer disposed
between the first and second soft magnetic sublayers;
[0035] FIG. 12 is a graph showing the rate of resistance change
(.DELTA.R/R) as a function of resistance-area (RA) product in a
tunneling magnetoresistive element that includes a Ti--Mg--O
insulating barrier layer and a free magnetic layer that includes a
first soft magnetic sublayer, a second soft magnetic sublayer, and
a Ta nonmagnetic metal sublayer disposed between the first and
second soft magnetic sublayers and having a thickness of 0, 1, 2,
3, or 4 angstroms;
[0036] FIG. 13 is a graph showing the rate of resistance change
(.DELTA.R/R) as a function of the average thickness (X) of a first
soft magnetic sublayer in a tunneling magnetoresistive element with
or without an enhancement sublayer, in which the tunneling
magnetoresistive element includes a Ti--O insulating barrier layer
and a free magnetic layer that includes the first soft magnetic
sublayer, a second soft magnetic sublayer, and a Ta nonmagnetic
metal sublayer disposed between the first and second soft magnetic
sublayers;
[0037] FIG. 14 is a graph showing the rate of resistance change
(.DELTA.R/R) as a function of the average thickness (Y) of an
enhancement sublayer in a tunneling magnetoresistive element that
includes a Ti--O insulating barrier layer and a free magnetic layer
including a first soft magnetic sublayer, a second soft magnetic
sublayer, and a Ta nonmagnetic metal sublayer disposed between the
first and second soft magnetic sublayers;
[0038] FIG. 15 is a graph showing the rate of resistance change
(.DELTA.R/R) as a function of resistance-area (RA) product in a
tunneling magnetoresistive element that includes a Ti--O insulating
barrier layer and a free magnetic layer that includes a first soft
magnetic sublayer, a second soft magnetic sublayer, and a Ta
nonmagnetic metal sublayer disposed between the first and second
soft magnetic sublayers and having a thickness of 0, 1, 2, 3, 4, or
5 angstroms;
[0039] FIG. 16 is a graph showing the rate of resistance change
(AR/R) as a function of resistance-area (RA) product in a tunneling
magnetoresistive element that includes a first protective sublayer
composed of Al, Ni--Fe--Cr, Ir--Mn, or Cr and a free magnetic layer
that includes a first soft magnetic sublayer, a second soft
magnetic sublayer, and a Ta nonmagnetic metal sublayer disposed
between the first and second soft magnetic sublayers (working
example); and
[0040] FIG. 17 is a graph showing the rate of resistance change
(.DELTA.R/R) as a function of resistance-area (RA) product in a
tunneling magnetoresistive element that includes a first protective
sublayer composed of Al, Ni--Fe--Cr, Ir--Mn, or Cr and a free
magnetic layer that includes a first soft magnetic sublayer, a
second soft magnetic sublayer, and no Ta nonmagnetic metal sublayer
disposed between the first and second soft magnetic sublayers
(comparative example).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0041] FIG. 1 is a cross-sectional view of a tunneling
magnetoresistive element according to an embodiment of the present
invention, taken parallel to a plane of a recording medium. FIGS. 2
and 3 are fragmentary enlarged cross-sectional views of a tunneling
magnetoresistive element according to an embodiment of the present
invention. Common components in FIGS. 1 to 3 are principally
described with reference to FIG. 1. Thus, while a free magnetic
layer illustrated in FIG. 1 appears to have a monolayer structure,
the free magnetic layer actually has a structure illustrated in
FIGS. 2 and 3.
[0042] A tunneling magnetoresistive element is, for example,
mounted on a trailing edge of a flying slider in a hard disk drive
to detect a leakage magnetic field (recorded magnetic field) from a
magnetic recording medium. In the drawings, the X direction is the
track width direction, the Y direction is the direction of a
leakage field from a magnetic recording medium (height direction),
and the Z direction is the traveling direction of the magnetic
recording medium or the lamination direction in the tunneling
magnetoresistive element.
[0043] The bottom layer in FIG. 1 is a first shielding layer 21,
for example, formed of a Ni--Fe alloy. A laminate 10 is disposed on
the first shielding layer 21. The tunneling magnetoresistive
element includes the laminate 10, and first insulating layers 22,
hard bias layers 23, and second insulating layers 24, disposed on
both sides of the laminate 10 in the track width direction (X
direction).
[0044] The bottom layer of the laminate 10 is an underlying layer 1
composed of at least one nonmagnetic element selected from the
group consisting of Ta, Hf, Nb, Zr, Ti, Mo, and W. A seed layer 2
is disposed on the underlying layer 1. The seed layer 2 is composed
of Ni--Fe--Cr or Cr. The underlying layer 1 may be eliminated.
[0045] An antiferromagnetic layer 3 disposed on the seed layer 2 is
preferably formed of an antiferromagnetic material containing an
element X and Mn, wherein X is at least one element selected from
the group consisting of Pt, Pd, Ir, Rh, Ru, and Os.
[0046] Alternatively, the antiferromagnetic layer 3 may be formed
of an antiferromagnetic material containing an element X, an
element X', and Mn, wherein the element X' is at least one element
selected from the group consisting of Ne, Ar, Kr, Xe, Be, B, C, N,
Mg, Al, Si, P, Ti, V, Cr, Fe, Co, Ni, Cu, Zn, Ga, Ge, Zr, Nb, Mo,
Ag, Cd, Sn, Hf, Ta, W, Re, Au, Pb, and rare-earth elements.
[0047] The antiferromagnetic layer 3 may be composed of Ir--Mn. A
pinned magnetic layer 4 is disposed on the antiferromagnetic layer
3. The pinned magnetic layer 4 has a layered ferri structure
including a first pinned magnetic sublayer 4a, a nonmagnetic
intermediate sublayer 4b, and a second pinned magnetic sublayer 4c,
laminated in that order from the bottom. The magnetization
directions of the first pinned magnetic sublayer 4a and the second
pinned magnetic sublayer 4c are antiparallel to each other owing to
an exchange coupling magnetic field (Hex) at an interface between
the antiferromagnetic layer 3 and the pinned magnetic layer 4 and
owing to an antiferromagnetic exchange coupling magnetic field
(RKKY interaction) via the nonmagnetic intermediate sublayer 4b.
The pinned magnetic layer 4 can have a stable magnetization because
of the layered ferri structure. The layered ferri structure can
also increase an apparent exchange coupling magnetic field
generated at the interface between the pinned magnetic layer 4 and
the antiferromagnetic layer 3. The first pinned magnetic sublayer
4a and the second pinned magnetic sublayer 4c may have a thickness
in the range of 10 to 40 angstroms. The nonmagnetic intermediate
sublayer 4b may have a thickness in the range of 8 to 10
angstroms.
[0048] The first pinned magnetic sublayer 4a and the second pinned
magnetic sublayer 4c are formed of a ferromagnetic material such as
Co--Fe, Ni--Fe, or Co--Fe--Ni. The nonmagnetic intermediate
sublayer 4b is formed of a nonmagnetic conductive material such as
Ru, Rh, Ir, Cr, Re, or Cu.
[0049] An insulating barrier layer 5 and a free magnetic layer 6
are disposed in that order on the pinned magnetic layer 4. The free
magnetic layer 6 has a structure as described below.
[0050] The width of the free magnetic layer 6 in the track width
direction (X direction) defines the track width Tw. A protective
layer 7, for example, composed of Ta is disposed on the free
magnetic layer 6.
[0051] End faces 11 of the laminate 10 in the track width direction
(X direction) are such inclined faces that the width of the
laminate 10 in the track width direction decreases gradually from
the bottom to the top.
[0052] As illustrated in FIG. 1, the first insulating layers 22 are
disposed on the first shielding layer 21 along the end faces 11 of
the laminate 10. The hard bias layers 23 are disposed on the first
insulating layers 22. The second insulating layers 24 are disposed
on the hard bias layers 23.
[0053] Bias underlying layers (not shown) may be disposed between
the first insulating layers 22 and the hard bias layers 23. The
bias underlying layers may be composed of Cr, W, and/or Ti.
[0054] The first insulating layers 22 and the second insulating
layers 24 are formed of an insulating material such as
Al.sub.2O.sub.3 or SiO.sub.2. The first insulating layers 22 and
the second insulating layers 24 insulate the hard bias layers 23 to
prevent an electric current flowing through the laminate 10 in a
direction perpendicular to the interfaces between the layers of the
laminate 10 from being shunted to both sides of the laminate 10 in
the track width direction. The hard bias layers 23 may be formed of
a Co--Pt alloy or a Co--Cr--Pt alloy.
[0055] A second shielding layer 26, for example, formed of a Ni--Fe
alloy is disposed on the laminate 10 and the second insulating
layers 24.
[0056] In the tunneling magnetoresistive element illustrated in
FIG. 1, the first shielding layer 21 and the second shielding layer
26 function as electrode layers of the laminate 10. An electric
current therefore flows in a direction perpendicular to the layers
of the laminate 10 (in a direction parallel to the Z
direction).
[0057] The free magnetic layer 6 is magnetized in a direction
parallel to the track width direction (X direction) under the
influence of a bias magnetic field of the hard bias layers 23. The
first pinned magnetic sublayer 4a and the second pinned magnetic
sublayer 4c in the pinned magnetic layer 4 are magnetized in a
direction parallel to the height direction (Y direction). Because
the pinned magnetic layer 4 has the layered ferri structure, the
magnetization direction of the first pinned magnetic sublayer 4a is
antiparallel to the magnetization direction of the second pinned
magnetic sublayer 4c. While the magnetization of the pinned
magnetic layer 4 is fixed (does not change with an external
magnetic field), the magnetization of the free magnetic layer 6
changes with the external magnetic field.
[0058] When the magnetization direction of the second pinned
magnetic sublayer 4c is antiparallel to the magnetization direction
of the free magnetic layer 6, a change in the magnetization of the
free magnetic layer 6 caused by an external magnetic field reduces
a tunneling current flowing through the insulating barrier layer 5
disposed between the second pinned magnetic sublayer 4c and the
free magnetic layer 6, thus maximizing the resistance. On the other
hand, when the magnetization direction of the second pinned
magnetic sublayer 4c is parallel to the magnetization direction of
the free magnetic layer 6, a change in the magnetization of the
free magnetic layer 6 caused by an external magnetic field
maximizes the tunneling current, thus minimizing the
resistance.
[0059] According to this principle, an external magnetic field
changes the magnetization of the free magnetic layer 6 and thereby
changes the electrical resistance. The tunneling magnetoresistive
element detects the change in electrical resistance as a voltage
change and thereby detects a leakage field from a magnetic
recording medium.
[0060] The features of the tunneling magnetoresistive element
according to the present embodiment will be described below. FIG. 2
is an enlarged cross-sectional view of the free magnetic layer 6 in
the tunneling magnetoresistive element illustrated in FIG. 1.
[0061] As illustrated in FIG. 2, the free magnetic layer 6 includes
an enhancement sublayer 12, a first soft magnetic sublayer 13, a
nonmagnetic metal sublayer 14, and a second soft magnetic sublayer
15, laminated in that order from the bottom.
[0062] The enhancement sublayer 12 is formed of a magnetic material
having a spin polarizability higher than those of the first soft
magnetic sublayer 13 and the second soft magnetic sublayer 15.
Preferably, the enhancement sublayer 12 is formed of a Co--Fe
alloy. In the absence of the enhancement sublayer 12, the rate of
resistance change (.DELTA.R/R) is known to decrease significantly.
The enhancement sublayer 12 is therefore indispensable. An increase
in the Fe content in the Co--Fe alloy constituting the enhancement
sublayer 12 can lead to a higher rate of resistance change (AR/R).
Preferably, the Fe content in the Co--Fe alloy is in the range of
50 to 100 atomic percent.
[0063] The first soft magnetic sublayer 13 and the second soft
magnetic sublayer 15 have a lower coercive force and a smaller
anisotropic magnetic field than the enhancement sublayer 12, and
therefore excellent soft magnetic characteristics. While the first
soft magnetic sublayer 13 and the second soft magnetic layer 15 may
be formed of different soft magnetic materials, these soft magnetic
sublayers are preferably formed of a Ni--Fe alloy. Preferably, the
Fe content in the Ni--Fe alloy is in the range of 5 to 20 atomic
percent.
[0064] The nonmagnetic metal sublayer 14 is composed of at least
one nonmagnetic metal selected from the group consisting of Ti, V,
Zr, Nb, Mo, Hf, Ta, and W. When the nonmagnetic metal sublayer 14
is composed of at least two nonmagnetic metals, the nonmagnetic
metal sublayer 14 may be formed of an alloy or a laminate of
nonmagnetic metal layers.
[0065] In the present embodiment, the nonmagnetic metal sublayer 14
is preferably composed of Ta. The nonmagnetic metal sublayer 14 has
a small thickness to magnetically couple the first soft magnetic
sublayer 13 and the second soft magnetic sublayer 15, and to
magnetize the first soft magnetic sublayer 13 and the second soft
magnetic sublayer 15 in one direction. For example, the first soft
magnetic sublayer 13 and the second soft magnetic sublayer 15 are
magnetized in the X direction. Furthermore, the enhancement
sublayer 12 is also magnetized in the X direction.
[0066] Preferably, the average thickness of the nonmagnetic metal
sublayer 14 is in the range of one to four angstroms. The average
thickness of the nonmagnetic metal sublayer 14 less than one
angstrom results in a low rate of resistance change (.DELTA.R/R).
On the other hand, the average thickness of the nonmagnetic metal
sublayer 14 more than four angstroms may result in an interruption
of the magnetically coupling between the first soft magnetic
sublayer 13 and the second soft magnetic sublayer 15. This
interruption may cause Barkhausen noise and variations in asymmetry
of reproduced waveform, resulting in unstable read characteristics.
In the present embodiment, therefore, the average thickness of the
nonmagnetic metal sublayer 14 is preferably in the range of one to
four angstroms.
[0067] As described above, the average thickness of the nonmagnetic
metal sublayer 14 is very small. Thus, the nonmagnetic metal
sublayer 14 may discontinuously be formed on the first soft
magnetic sublayer 13, unlike the continuous film having a constant
thickness as illustrated in FIG. 2. A discontinuous nonmagnetic
metal sublayer 14 can enhance the magnetic coupling (ferromagnetic
coupling) between the first soft magnetic sublayer 13 and the
second soft magnetic sublayer 15. "The average thickness of
nonmagnetic metal sublayer 14" is the thickness of a nonmagnetic
metal sublayer 14 uniformly formed over the first soft magnetic
sublayer 13. Thus, the "average thickness" of a discontinuous
nonmagnetic metal sublayer 14 is determined with consideration
given to portions (pinholes) at which the nonmagnetic metal
sublayer 14 is not formed on the first soft magnetic sublayer
13.
[0068] In FIG. 2, the insulating barrier layer 5 is composed of
Ti--Mg--O. Preferably, the Mg content is in the range of 4 to 20
atomic percent per 100 atomic percent of Ti and Mg. This can
effectively increase the rate of resistance change
(.DELTA.R/R).
[0069] In the present embodiment, the total thickness T3 of the
average thickness T1 of the enhancement sublayer 12 and the average
thickness T2 of the first soft magnetic sublayer 13 is at least 25
angstroms. Thus, the distance between the nonmagnetic metal
sublayer 14 and the insulating barrier layer 5 is at least 25
angstroms.
[0070] This increases the rate of resistance change (AR/R) as
compared with existing structures including no nonmagnetic metal
sublayer 14 in the free magnetic layer 6. It is possible to set the
resistance-area (RA) product to be substantially the same as those
of the existing structures, and reduce variations in
resistance-area (RA) product.
[0071] The reason for the increase in rate of resistance change
(AR/R) is probably as follows: oxygen atoms diffusing from the
insulating barrier layer 5 into the first and second soft magnetic
sublayers 13 and 15 or into the enhancement sublayer 12 are
preferentially chemically bonded to the nonmagnetic metal sublayer
14. This reduces the oxygen contents and thereby optimizes the band
structures in the first and second soft magnetic sublayers 13 and
15 or the enhancement sublayer 12, thus improving the spin
polarizability.
[0072] In the present embodiment, the second soft magnetic sublayer
15 may effectively have a face-centered cubic (fcc) structure in
which equivalent crystal faces represented by a {111} plane are
preferably oriented parallel to the second soft magnetic sublayer
15 (X-Y plane).
[0073] Preferably, the total thickness T3 is 80 angstroms or less.
The total thickness T3 more than 80 angstroms results in no
increase in rate of resistance change (AR/R). Hence, a high rate of
resistance change (AR/R) can consistently be achieved at the total
thickness T3 in the range of 25 to 80 angstroms.
[0074] Preferably, the average thickness T2 of the first soft
magnetic sublayer 13 is in the range of 15 to 70 angstroms. In this
range, a tunneling magnetoresistive element according to the
present embodiment can consistently have a higher rate of
resistance change (AR/R) than before. More preferably, the average
thickness T2 is 60 angstroms or less.
[0075] Preferably, the total thickness T3 is more than 30
angstroms. In this case, the average thickness T2 of the first soft
magnetic sublayer 13 is more preferably more than 20 angstroms.
[0076] The average thickness T2 of the first soft magnetic sublayer
13 preferably accounts for 50% to 90%, more preferably 60% to
87.5%, and still more preferably 67% to 87.5% of the total
thickness T3.
[0077] In these ranges, a tunneling magnetoresistive element
according to the present embodiment can consistently have a high
rate of resistance change (AR/R).
[0078] Preferably, the average thickness T1 of the enhancement
sublayer 12 is in the range of 10 to 30 angstroms. In this range, a
tunneling magnetoresistive element according to the present
embodiment can consistently have a high rate of resistance change
(.DELTA.R/R).
[0079] Preferably, the average thickness T4 of the second soft
magnetic sublayer 15 is in the range of 20 to 50 angstroms.
[0080] Preferably, the total thickness of the first and second soft
magnetic sublayers 13 and 15 is in the range of 35 to 80
angstroms.
[0081] While the insulating barrier layer 5 is composed of
Ti--Mg--O in the present embodiment, the insulating barrier layer 5
composed of Ti--O can also achieve the same resistance-area (RA)
product as before, and a higher rate of resistance change (AR/R)
than before.
[0082] Also in the insulating barrier layer 5 composed of Ti--O,
the rate of resistance change (AR/R) can be higher than before at a
total thickness T3 of at least 25 angstroms. Furthermore, in the
insulating barrier layer 5 composed of Ti--O, the upper limit and
the preferred range of the total thickness T3 and the preferred
range of the average thickness T2 of the first soft magnetic
sublayer 13 are the same as in the insulating barrier layer 5
composed of Ti--Mg--O.
[0083] FIG. 3 is an enlarged cross-sectional view of the free
magnetic layer 6 and a protective layer 7 in the tunneling
magnetoresistive element illustrated in FIG. 1
[0084] The free magnetic layer 6 has the same structure as that
described with reference to FIG. 2.
[0085] The protective layer 7 composed of a first protective
sublayer 7a and a second protective sublayer 7b is disposed on the
free magnetic layer 6.
[0086] The first protective sublayer 7a is composed of at least one
selected from the group consisting of Ru, Al, Ni--Fe--Cr, Ir--Mn,
and Cr. When the first protective sublayer 7a is composed of at
least two metals, the first protective sublayer 7a may be formed of
an alloy or a laminate of metal layers. The first protective
sublayer 7a composed of Ni--Fe--Cr may have a composition of
Ni.sub.49at%Fe.sub.12at%Cr.sub.39at%. The first protective sublayer
7a composed of Ir--Mn may have a composition of
Ir.sub.26at%Mn.sub.74at%. The second protective sublayer 7b may be
composed of a metal, such as Ta, Ti, Al, Cu, Fe, Ni, Mn, Co, or V,
or an oxide or a nitride thereof, which has been used in existing
protective layers. Preferably, the second protective sublayer 7b is
composed of Ta in terms of low electrical resistance and mechanical
protection.
[0087] In FIG. 3, the insulating barrier layer 5 may be composed of
a material other than Ti--Mg--O and Ti--O. For example, the
insulating barrier layer 5 may be composed of Al--O (aluminum
oxide) or Mg--O (magnesium oxide).
[0088] In FIG. 3, while the average thickness T1 of the enhancement
sublayer 12, the average thickness T2 of the first soft magnetic
sublayer 13, and the total thickness T3 of T1 and T2 are preferably
in the ranges described with reference to FIG. 2, these thicknesses
are not limited to these ranges. As in FIG. 2, the nonmagnetic
metal sublayer 14 in FIG. 3 also has a small thickness (more
specifically in the range of one to four angstroms) to magnetically
couple the first soft magnetic sublayer 13 and the second soft
magnetic sublayer 15, and to magnetize the first soft magnetic
sublayer 13 and the second soft magnetic sublayer 15 in one
direction.
[0089] The first protective sublayer 7a is composed of Ru, Al,
Ni--Fe--Cr, Ir--Mn, or Cr. The nonmagnetic metal sublayer 14
separates the first soft magnetic sublayer 13 from the second soft
magnetic sublayer 15. Thus, the tunneling magnetoresistive element
according to the present embodiment can have a high rate of
resistance change (.DELTA.R/R). Furthermore, it is possible to set
the resistance-area (RA) product to be substantially the same as
those of existing structures including no nonmagnetic metal
sublayer 14, and reduce variations in resistance-area (RA) product.
In the examples described below, first protective sublayers 7a each
composed of Ru, Al, Ni--Fe--Cr, Ir--Mn, or Cr equally achieved a
high rate of resistance change (AR/R).
[0090] Because a high rate of resistance change (AR/R) can be
achieved with any of the candidate materials for the first
protective sublayer 7a, any of various materials may be used for
the first protective sublayer 7a.
[0091] The reason for the increase in rate of resistance change
(.DELTA.R/R) is probably as follows: oxygen atoms diffusing from
the insulating barrier layer 5 into the first and second soft
magnetic sublayers 13 and 15 or into the enhancement sublayer 12
are preferentially chemically bonded to the nonmagnetic metal
sublayer 14. This reduces the oxygen contents and thereby optimizes
the band structures in the first and second soft magnetic sublayers
13 and 15 or the enhancement sublayer 12, thus improving the spin
polarizability. In addition, the nonmagnetic metal sublayer 14
reduces the diffusion of an element constituting the protective
layer 7 into the first soft magnetic sublayer 13 or the enhancement
sublayer 12.
[0092] In FIG. 2, the protective layer 7 may have a monolayer
structure of the second protective sublayer 7b. For example, the
protective layer 7 may have a Ta monolayer structure. However, also
in FIG. 2, the protective layer 7 having a monolayer structure of
the first protective sublayer 7a or a layered structure of the
first protective sublayer 7a and the second protective sublayer 7b,
as illustrated in FIG. 3, is preferred in terms of the rate of
resistance change (.DELTA.R/R).
[0093] In FIGS. 1 to 3, while the antiferromagnetic layer 3, the
pinned magnetic layer 4, the insulating barrier layer 5, the free
magnetic layer 6, and the protective layer 7 are laminated in that
order from the bottom, the free magnetic layer 6, the insulating
barrier layer 5, the pinned magnetic layer 4, the antiferromagnetic
layer 3, and the protective layer 7 may be laminated in that order
from the bottom.
[0094] In the latter case, as illustrated in FIG. 4, the free
magnetic layer 6 includes the second soft magnetic sublayer 15, the
nonmagnetic metal sublayer 14, the first soft magnetic sublayer 13,
and the enhancement sublayer 12, laminated in that order from the
bottom, and the insulating barrier layer 5 is disposed on the free
magnetic layer 6. The sublayers of the free magnetic layer 6 have
the same thicknesses and are formed of the same materials as those
described with reference to FIG. 2.
[0095] A tunneling magnetoresistive element may be a dual-type
tunneling magnetoresistive element composed of a first
antiferromagnetic layer, a first pinned magnetic layer, a first
insulating barrier layer, a free magnetic layer, a second
insulating barrier layer, a second pinned magnetic layer, and a
second antiferromagnetic layer, laminated in that order from the
bottom.
[0096] In the dual-type tunneling magnetoresistive element, as
illustrated in FIG. 5, the free magnetic layer 6 is composed of the
enhancement sublayer 12, the first soft magnetic sublayer 13, the
nonmagnetic metal sublayer 14, a first soft magnetic sublayer 25,
and an enhancement sublayer 27, laminated in that order from the
bottom. A first insulating barrier layer 17 is disposed under the
enhancement sublayer 12 of the free magnetic layer 6. A second
insulating barrier layer 18 is disposed on the enhancement sublayer
27 of the free magnetic layer 6. The sublayers of the free magnetic
layer 6 have the same thicknesses and are formed of the same
materials as those described with reference to FIG. 2. In FIG. 5,
the total thickness T6 of the average thickness of the enhancement
sublayer 27 and the average thickness of the first soft magnetic
sublayer 25 is preferably in the range of 25 to 80 angstroms, as in
the total thickness T3 of the average thickness T1 of the
enhancement sublayer 12 and the average thickness T2 of the first
soft magnetic sublayer 13.
[0097] In FIGS. 2 to 5, while the free magnetic layer 6 includes a
single nonmagnetic metal sublayer 14, the free magnetic layer 6 may
include two or more nonmagnetic metal sublayers 14. In the latter
case, the free magnetic layer 6 may include a first soft magnetic
sublayer, a first nonmagnetic metal sublayer, a second soft
magnetic sublayer, a second nonmagnetic metal sublayer, and a third
soft magnetic sublayer. The number of nonmagnetic metal sublayers
14 is about eight or less.
[0098] A method for manufacturing a tunneling magnetoresistive
element according to an embodiment of the present invention will be
described below. FIGS. 6 to 9 are cross-sectional views each
illustrating a step of manufacturing a tunneling magnetoresistive
element according to an embodiment of the present invention, taken
in the same direction as in FIG. 1. In FIGS. 7 to 9, while a free
magnetic layer 6 appears to have a monolayer structure, the free
magnetic layer 6 actually has a structure illustrated in FIGS. 2
and 3.
[0099] In a step illustrated in FIG. 6, an underlying layer 1, a
seed layer 2, an antiferromagnetic layer 3, a first pinned magnetic
sublayer 4a, a nonmagnetic intermediate sublayer 4b, and a second
pinned magnetic sublayer 4c are successively formed on a first
shielding layer 21.
[0100] In the manufacture of a tunneling magnetoresistive element
illustrated in FIG. 1, an insulating barrier layer 5 composed of
Ti--Mg--O or Ti--O is formed on the second pinned magnetic sublayer
4c. The insulating barrier layer 5 composed of Ti--Mg--O may be
formed by depositing a Ti layer on the second pinned magnetic
sublayer 4c by sputtering, depositing a Mg layer on the Ti layer by
sputtering, and then oxidizing the Ti layer and the Mg layer. The
insulating barrier layer 5 composed of Ti--O may be formed by
depositing a Ti layer on the second pinned magnetic sublayer 4c by
sputtering and then oxidizing the Ti layer.
[0101] As illustrated in FIG. 7, a free magnetic layer 6 and a
protective layer 7 are formed on the insulating barrier layer
5.
[0102] An enhancement sublayer 12, a first soft magnetic sublayer
13, a nonmagnetic metal sublayer 14, and a second soft magnetic
sublayer 15 may be deposited to form the free magnetic layer 6, as
illustrated in FIG. 2. Preferably, the enhancement sublayer 12 is
formed of a Co--Fe alloy, the first soft magnetic sublayer 13 and
the second soft magnetic sublayer 15 are formed of a Ni--Fe alloy,
and the nonmagnetic metal sublayer 14 is composed of Ta.
[0103] The thicknesses of the enhancement sublayer 12 and the first
soft magnetic sublayer 13 are adjusted so that the total thickness
T3 of these sublayers is at least 25 angstroms, as described for
FIG. 2. The nonmagnetic metal sublayer 14 is formed so as to have a
small thickness, more specifically, in the range of one to four
angstroms to magnetically couple the first soft magnetic sublayer
13 and the second soft magnetic sublayer 15 and to magnetize the
first soft magnetic sublayer 13 and the second soft magnetic
sublayer 15 in one direction.
[0104] Thus, a laminate 10 including the underlying layer 1 to the
protective layer 7 is formed.
[0105] A lift-off resist layer 30 is then formed on the laminate
10. Both ends of the laminate 10 in the track width direction (X
direction) that are not covered with the lift-off resist layer 30
are removed, for example, by etching (see FIG. 8).
[0106] First insulating layers 22, hard bias layers 23, and second
insulating layers 24 are then formed on the first shielding layer
21 on both sides of the laminate 10 in the track width direction (X
direction) (see FIG. 9).
[0107] After the lift-off resist layer 30 is removed, a second
shielding layer 26 is formed on the laminate 10 and the second
insulating layers 24.
[0108] In this method for manufacturing a tunneling
magnetoresistive element, the laminate 10 is annealed. Annealing is
typically performed to generate an exchange coupling magnetic field
(Hex) between the antiferromagnetic layer 3 and the first pinned
magnetic sublayer 4a.
[0109] The protective layer 7 may have a layered structure of a
first protective sublayer 7a and a second protective sublayer 7b,
as illustrated in FIG. 3. The insulating barrier layer 5 may be
composed of a material other than Ti--Mg--O and Ti--O. In FIG. 3,
while the average thickness T1 of the enhancement sublayer 12, the
average thickness T2 of the first soft magnetic sublayer 13, and
the total thickness T3 of T1 and T2 are preferably in the ranges
described with reference to FIG. 2, these thicknesses are not
limited to these ranges.
[0110] The layered structure of the free magnetic layer 6, the
insulating barrier layer 5, and pinned magnetic layer 4, laminated
in that order from the bottom, and the dual-type structure as
illustrated in FIG. 5 may also be manufactured according to the
method described with reference to FIGS. 6 to 9.
[0111] A tunneling magnetoresistive element according to the
present invention can be used as a magnetoresistive random access
memory (MRAM) and a magnetic sensor, as well as a magnetic head
installed in hard disk drives.
Example 1
[0112] A tunneling magnetoresistive element including a laminate 10
was fabricated. The laminate 10 included a free magnetic layer 6
including a first soft magnetic sublayer 13, a second soft magnetic
sublayer 15, and a nonmagnetic metal sublayer 14 disposed there
between, as illustrated in FIG. 2.
[0113] The laminate 10 included an underlying layer 1; Ta (30)/seed
layer 2; Ni.sub.49at%Fe.sub.12at%Cr.sub.39at%(50)/antiferromagnetic
layer 3; Ir.sub.26at%Mn.sub.74at% (70)/pinned magnetic layer 4
[first pinned magnetic sublayer 4a;
Fe.sub.30at%Co.sub.70at%(16)/nonmagnetic intermediate sublayer 4b;
Ru (8.5)/second pinned magnetic sublayer 4c;
Co.sub.90at%Fe.sub.10at% (18)]/insulating barrier layer 5/free
magnetic layer 6 [enhancement sublayer 12; Fe.sub.90at%Co.sub.10at%
(10)/first soft magnetic sublayer 13;
Ni.sub.88at%Fe.sub.12at%(X)/nonmagnetic metal sublayer 14; Ta
(3)/second soft magnetic sublayer 15;
Ni.sub.88at%Fe.sub.12at%(20)]/first protective sublayer 7a; Ru
(10)/second protective sublayer 7b; Ta (180), laminated in that
order from the bottom.
[0114] The insulating barrier layer 5 was composed of Ti--Mg--O
that was prepared by depositing Ti (4.6)/Mg (0.6) and oxidizing the
Ti/Mg layer.
[0115] The values in parentheses are average thicknesses expressed
in angstrom.
[0116] The laminate 10 was annealed at 270.degree. C. for 3 hours
40 minutes.
[0117] A tunneling magnetoresistive element that included a
laminate 10 having no enhancement sublayer 12 was also
fabricated.
[0118] The rate of resistance change (.DELTA.R/R) was determined as
a function of the average thickness of the first soft magnetic
sublayer 13. FIG. 10 is a graph showing the rate of resistance
change (.DELTA.R/R) as a function of the average thickness (X) of
the first soft magnetic sublayer 13.
[0119] As shown in FIG. 10, in the absence of the enhancement
sublayer 12, the rate of resistance change (.DELTA.R/R) did not
increase significantly with increasing average thickness of the
first soft magnetic sublayer 13.
[0120] By contrast, in the presence of the enhancement sublayer 12,
the rate of resistance change (.DELTA.R/R) increased sharply with
increasing average thickness of the first soft magnetic sublayer 13
and leveled off at an average thickness of about 15 angstroms. The
rate of resistance change (.DELTA.R/R) remained high at an average
thickness of the first soft magnetic sublayer 13 of 15 angstroms or
more.
[0121] It was therefore found that, in the tunneling
magnetoresistive element including the Ti--Mg--O insulating barrier
layer 5, a high rate of resistance change (.DELTA.R/R) can be
achieved when the total thickness T3 of the average thickness T1 of
the enhancement sublayer 12 (10 angstroms) and the average
thickness T2 of the first soft magnetic sublayer 13 is 25 angstroms
or more. Because the total thickness T3 corresponds to the distance
between the insulating barrier layer 5 and the nonmagnetic metal
sublayer 14, a high rate of resistance change (.DELTA.R/R) can be
achieved when the nonmagnetic metal sublayer 14 is placed away from
the insulating barrier layer 5 by 25 angstroms or more.
[0122] Furthermore, in the presence of the enhancement sublayer 12,
the rate of resistance change (.DELTA.R/R) remained high at an
average thickness T2 of the first soft magnetic sublayer 13 as
large as 70 angstroms. Thus, the rate of resistance change
(.DELTA.R/R) remained high when the total thickness T3 of the
average thickness T1 of the enhancement sublayer 12 and the average
thickness T2 of the first soft magnetic sublayer 13 was 80
angstroms or less.
[0123] The results show that the average thickness T2 of the first
soft magnetic sublayer 13 is preferably in the range of 15 to 70
angstroms in the tunneling magnetoresistive element including the
Ti--Mg--O insulating barrier layer.
Example 2
[0124] A tunneling magnetoresistive element including a laminate 10
was fabricated. The laminate 10 included a free magnetic layer 6
including a first soft magnetic sublayer 13, a second soft magnetic
sublayer 15, and a nonmagnetic metal sublayer 14 disposed
therebetween, as illustrated in FIG. 2.
[0125] The laminate 10 included an underlying layer 1; Ta (30)/seed
layer 2; Ni.sub.49at%Fe.sub.12at%Cr.sub.39at%(50)/antiferromagnetic
layer 3; Ir.sub.26at%Mn.sub.74at% (70)/pinned magnetic layer 4
[first pinned magnetic sublayer 4a;
Fe.sub.30at%Co.sub.70at%(16)/nonmagnetic intermediate sublayer 4b;
Ru (8.5)/second pinned magnetic sublayer 4c;
Co.sub.90at%Fe.sub.10at%(18)]/insulating barrier layer 5/free
magnetic layer 6 [enhancement sublayer 12;
Fe.sub.90at%Co.sub.10at%(Y)/first soft magnetic sublayer 13;
Ni.sub.88at%Fe.sub.12at%(20)/nonmagnetic metal sublayer 14; Ta
(3)/second soft magnetic sublayer 15;
Ni.sub.88at%Fe.sub.12at%(40)]/first protective sublayer 7a; Ru
(10)/second protective sublayer 7b; Ta (180), laminated in that
order from the bottom
[0126] The insulating barrier layer 5 was composed of Ti--Mg--O
that was prepared by depositing Ti (4.6)/Mg (0.6) and oxidizing the
Ti/Mg layer.
[0127] The values in parentheses are average thicknesses expressed
in angstrom.
[0128] The laminate 10 was annealed at 270.degree. C. for 3 hours
40 minutes.
[0129] The rate of resistance change (.DELTA.R/R) was determined as
a function of the average thickness of the enhancement sublayer 12.
FIG. 11 is a graph showing the rate of resistance change
(.DELTA.R/R) as a function of the average thickness (Y) of the
enhancement sublayer 12.
[0130] The rate of resistance change (.DELTA.R/R) increased sharply
with increasing average thickness of the enhancement sublayer 12
and leveled off at an average thickness of 10 angstroms.
[0131] The result shows that the average thickness T1 of the
enhancement sublayer 12 is preferably in the range of 10 to 30
angstroms in the tunneling magnetoresistive element including the
Ti--Mg--O insulating barrier layer 5.
Example 3
[0132] A tunneling magnetoresistive element including a laminate 10
was fabricated. The laminate 10 included a free magnetic layer 6
including a first soft magnetic sublayer 13, a second soft magnetic
sublayer 15, and a nonmagnetic metal sublayer 14 disposed
therebetween, as illustrated in FIG. 2.
[0133] The laminate 10 included an underlying layer 1; Ta (30)/seed
layer 2; Ni.sub.49at%Fe.sub.12at%Cr.sub.39at%(50)/antiferromagnetic
layer 3; Ir.sub.26at%Mn.sub.74at% (70)/pinned magnetic layer 4
[first pinned magnetic sublayer 4a;
Fe.sub.30at%Co.sub.70at%(16)/nonmagnetic intermediate sublayer 4b;
Ru (8.5)/second pinned magnetic sublayer 4c;
Co.sub.90at%Fe.sub.10at%(18)]/insulating barrier layer 5/free
magnetic layer 6 [enhancement sublayer 12;
Fe.sub.90at%Co.sub.10at%(10)/first soft magnetic sublayer 13;
Ni.sub.88at%Fe.sub.12at%(20)/nonmagnetic metal sublayer 14; Ta
(Z)/second soft magnetic sublayer 15;
Ni.sub.88at%Fe.sub.12at%(40)]/first protective sublayer 7a; Ru
(10)/second protective sublayer 7b; Ta (180), laminated in that
order from the bottom
[0134] The insulating barrier layer 5 was composed of Ti--Mg--O
that was prepared by depositing Ti (4.6)/Mg (0.6) and oxidizing the
Ti/Mg layer.
[0135] The values in parentheses are average thicknesses expressed
in angstrom.
[0136] The laminate 10 was annealed at 270.degree. C. for 3 hours
40 minutes.
[0137] As shown in FIG. 12, the rate of resistance change
(.DELTA.R/R) was determined as a function of the resistance-area
(RA) product for tunneling magnetoresistive elements that include
nonmagnetic metal sublayers 14 having different average thicknesses
(Z) of 0 (conventional example), 1, 2, 3, and 4 angstroms. The
tunneling magnetoresistive elements that include the nonmagnetic
metal sublayers 14 having the same average thickness and different
resistance-area (RA) products were prepared by changing the
oxidation time of the Ti/Mg layer in the insulating barrier layer 5
in the tunneling magnetoresistive elements that include the
nonmagnetic metal sublayers 14 having the same average
thickness.
[0138] FIG. 12 shows that the examples including the nonmagnetic
metal sublayers 14 had rates of resistance change (.DELTA.R/R)
higher than that of the conventional example including no
nonmagnetic metal sublayer 14, while the examples had substantially
the same resistance-area (RA) products as the conventional
example.
[0139] These results show that the average thickness of the
nonmagnetic metal sublayer 14 was preferably in the range of one to
four angstroms in the tunneling magnetoresistive element including
the Ti--Mg--O insulating barrier layer 5.
Example 4
[0140] A tunneling magnetoresistive element including a laminate 10
was fabricated. The laminate 10 included a free magnetic layer 6
including a first soft magnetic sublayer 13, a second soft magnetic
sublayer 15, and a nonmagnetic metal sublayer 14 disposed
therebetween, as illustrated in FIG. 2.
[0141] The laminate 10 included an underlying layer 1; Ta (30)/seed
layer 2; Ni.sub.49at%Fe.sub.12at%Cr.sub.39at%(50)/antiferromagnetic
layer 3; Ir.sub.26at%Mn.sub.74at% (70)/pinned magnetic layer 4
[first pinned magnetic sublayer 4a;
Fe.sub.30at%Co.sub.70at%(16)/nonmagnetic intermediate sublayer 4b;
Ru (8.5)/second pinned magnetic sublayer 4c;
Co.sub.90at%Fe.sub.10at%(18)]/insulating barrier layer 5/free
magnetic layer 6 [enhancement sublayer 12;
Fe.sub.90at%Co.sub.10at%(10)/first soft magnetic sublayer 13;
Ni.sub.88at%Fe.sub.12at%(X)/nonmagnetic metal sublayer 14; Ta
(3)/second soft magnetic sublayer 15;
Ni.sub.88at%Fe.sub.12at%(20)]/first protective sublayer 7a; Ru
(10)/second protective sublayer 7b; Ta (180), laminated in that
order from the bottom.
[0142] The insulating barrier layer 5 was composed of Ti--O that is
prepared by depositing Ti (5.2) on the second pinned magnetic
sublayer 4c by sputtering and oxidizing the Ti layer.
[0143] The values in parentheses are average thicknesses expressed
in angstrom.
[0144] The laminate was annealed at 270.degree. C. for 3 hours 40
minutes.
[0145] A tunneling magnetoresistive element that included a
laminate 10 having no enhancement sublayer 12 was also
fabricated.
[0146] The rate of resistance change (.DELTA.R/R) was determined as
a function of the average thickness of the first soft magnetic
sublayer 13. FIG. 13 is a graph showing the rate of resistance
change (.DELTA.R/R) as a function of the average thickness (X) of
the first soft magnetic sublayer 13.
[0147] As shown in FIG. 13, in the absence of the enhancement
sublayer 12, the rate of resistance change (.DELTA.R/R) did not
increase significantly with increasing average thickness of the
first soft magnetic sublayer 13.
[0148] By contrast, in the presence of the enhancement sublayer 12,
the rate of resistance change (.DELTA.R/R) increased sharply with
increasing average thickness of the first soft magnetic sublayer 13
and leveled off at an average thickness of about 15 angstroms. The
rate of resistance change (.DELTA.R/R) remained high at an average
thickness of the first soft magnetic sublayer 13 of 15 angstroms or
more.
[0149] It was therefore found that, in the tunneling
magnetoresistive element including the Ti--O insulating barrier
layer 5, a high rate of resistance change (.DELTA.R/R) can be
achieved when the total thickness T3 of the average thickness T1 of
the enhancement sublayer 12 (10 angstroms) and the average
thickness T2 of the first soft magnetic sublayer 13 is 25 angstroms
or more. Because the total thickness T3 corresponds to the distance
between the insulating barrier layer 5 and the nonmagnetic metal
sublayer 14, a high rate of resistance change (.DELTA.R/R) can be
achieved when the nonmagnetic metal sublayer 14 is placed away from
the insulating barrier layer 5 by 25 angstroms or more.
[0150] Furthermore, in the presence of the enhancement sublayer 12,
the rate of resistance change (.DELTA.R/R) remained high at an
average thickness T2 of the first soft magnetic sublayer 13 as
large as 70 angstroms. Thus, the rate of resistance change
(.DELTA.R/R) remained high when the total thickness T3 of the
average thickness T1 of the enhancement sublayer 12 and the average
thickness T2 of the first soft magnetic sublayer 13 was 80
angstroms or less.
[0151] The results show that the average thickness T2 of the first
soft magnetic sublayer 13 is preferably in the range of 15 to 70
angstroms in the tunneling magnetoresistive element including the
Ti--O insulating barrier layer 5.
Example 5
[0152] A tunneling magnetoresistive element including a laminate 10
was fabricated. The laminate 10 included a free magnetic layer 6
including a first soft magnetic sublayer 13, a second soft magnetic
sublayer 15, and a nonmagnetic metal sublayer 14 disposed
therebetween, as illustrated in FIG. 2.
[0153] The laminate 10 included an underlying layer 1; Ta (30)/seed
layer 2; Ni.sub.49at%Fe.sub.12at%Cr.sub.39at%(50)/antiferromagnetic
layer 3; Ir.sub.26at%Mn.sub.74at% (70)/pinned magnetic layer 4
[first pinned magnetic sublayer 4a;
Fe.sub.30at%Co.sub.70at%(16)/nonmagnetic intermediate sublayer 4b;
Ru (8.5)/second pinned magnetic sublayer 4c;
Co.sub.90at%Fe.sub.10at%(18)]/insulating barrier layer 5/free
magnetic layer 6 [enhancement sublayer 12;
Fe.sub.90at%Co.sub.10at%(Y)/first soft magnetic sublayer 13;
Ni.sub.88at%Fe.sub.12at%(20)/nonmagnetic metal sublayer 14; Ta
(3)/second soft magnetic sublayer 15;
Ni.sub.88at%Fe.sub.12at%(40)]/first protective sublayer 7a; Ru
(10)/second protective sublayer 7b; Ta (180), laminated in that
order from the bottom.
[0154] The insulating barrier layer 5 was composed of Ti--O that is
prepared by depositing Ti (5.2) on the second pinned magnetic
sublayer 4c by sputtering and oxidizing the Ti layer.
[0155] The values in parentheses are average thicknesses expressed
in angstrom.
[0156] The laminate 10 was annealed at 270.degree. C. for 3 hours
40 minutes.
[0157] The rate of resistance change (.DELTA.R/R) was determined as
a function of the average thickness of the enhancement sublayer 12.
FIG. 14 is a graph showing the rate of resistance change
(.DELTA.R/R) as a function of the average thickness (Y) of the
enhancement sublayer 12.
[0158] The rate of resistance change (.DELTA.R/R) increased sharply
with increasing average thickness of the enhancement sublayer 12
and leveled off at an average thickness of 10 angstroms.
[0159] The result shows that the average thickness T1 of the
enhancement sublayer 12 is preferably in the range of 10 to 30
angstroms in the tunneling magnetoresistive sensor including the
Ti--O insulating barrier layer 5.
Example 6
[0160] A tunneling magnetoresistive element including a laminate 10
was fabricated. The laminate 10 included a free magnetic layer 6
including a first soft magnetic sublayer 13, a second soft magnetic
sublayer 15, and a nonmagnetic metal sublayer 14 disposed
therebetween, as illustrated in FIG. 2.
[0161] The laminate 10 included an underlying layer 1; Ta (30)/seed
layer 2; Ni.sub.49at%Fe.sub.12at%Cr.sub.39at%(50)/antiferromagnetic
layer 3; Ir.sub.26at%Mn.sub.74at% (70)/pinned magnetic layer 4
[first pinned magnetic sublayer 4a;
Fe.sub.30at%Co.sub.70at%(16)/nonmagnetic intermediate sublayer 4b;
Ru (8.5)/second pinned magnetic sublayer 4c;
Co.sub.90at%Fe.sub.10at%(18)]/insulating barrier layer 5/free
magnetic layer 6 [enhancement sublayer 12;
Fe.sub.90at%Co.sub.10at%(10)/first soft magnetic sublayer 13;
Ni.sub.88at%Fe.sub.12at%(20)/nonmagnetic metal sublayer 14; Ta
(Z)/second soft magnetic sublayer 15;
Ni.sub.88at%Fe.sub.12at%(40)]/first protective sublayer 7a; Ru
(10)/second protective sublayer 7b; Ta (180), laminated in that
order from the bottom.
[0162] The insulating barrier layer 5 was composed of Ti--O that is
prepared by depositing Ti (4.6) on the second pinned magnetic
sublayer 4c by sputtering and oxidizing the Ti layer.
[0163] The values in parentheses are average thicknesses expressed
in angstrom.
[0164] The laminate 10 was annealed at 270.degree. C. for 3 hours
40 minutes.
[0165] As shown in FIG. 15, the rate of resistance change
(.DELTA.R/R) was determined as a function of the resistance-area
(RA) product for tunneling magnetoresistive elements that include
nonmagnetic metal sublayers 14 having different average thicknesses
(Z) of 0 (conventional example), 1, 2, 3, 4, and 5 angstroms. The
oxidation time of the Ti layer in the insulating barrier layer 5
was fixed at a predetermined time for the tunneling
magnetoresistive elements that include nonmagnetic metal sublayers
14 having different average thicknesses.
[0166] FIG. 15 shows that the examples including the nonmagnetic
metal sublayers 14 had rates of resistance change (.DELTA.R/R)
higher than that of the conventional example including no
nonmagnetic metal sublayer 14. While the resistance-area (RA)
products of the examples were smaller than that of the conventional
example, the differences in the resistance-area (RA) product were
not significantly large. The differences may therefore be
compensated, for example, by changing the oxidation time of the Ti
layer.
[0167] When the average thickness of the nonmagnetic metal sublayer
14 (Z) was five angstroms, the rate of resistance change
(.DELTA.R/R) was advantageously high, but variations in asymmetry
of reproduced waveform increased and therefore the read
characteristics became unstable, because the magnetic coupling
between the first soft magnetic sublayer 13 and the second soft
magnetic sublayer 15 was interrupted.
[0168] These results show that the average thickness of the
nonmagnetic metal sublayer 14 was preferably in the range of one to
four angstroms in the tunneling magnetoresistive element including
the Ti--O insulating barrier layer 5.
Example 7
[0169] A tunneling magnetoresistive element including a laminate 10
was fabricated. The laminate 10 included a first protective
sublayer 7a and a second protective sublayer 7b on a free magnetic
layer 6, as illustrated in FIG. 3.
[0170] The laminate 10 included an underlying layer 1; Ta (30)/seed
layer 2; Ni.sub.49at%Fe.sub.12at%Cr.sub.39at%(50)/antiferromagnetic
layer 3; Ir.sub.26at%Mn.sub.74at% (70)/pinned magnetic layer 4
[first pinned magnetic sublayer 4a;
Fe.sub.30at%Co.sub.70at%(16)/nonmagnetic intermediate sublayer 4b;
Ru (8.5)/second pinned magnetic sublayer 4c;
Co.sub.90at%Fe.sub.10at%(18)]/insulating barrier layer 5/free
magnetic layer 6 [enhancement sublayer 12;
Fe.sub.90at%Co.sub.10at%(10)/first soft magnetic sublayer 13;
Ni.sub.88at%Fe.sub.12at%(20)/nonmagnetic metal sublayer 14; Ta
(3)/second soft magnetic sublayer 15;
Ni.sub.88at%Fe.sub.12at%(40)]/first protective sublayer 7a; Ru
(10)/second protective sublayer 7b; Ta (180), laminated in that
order from the bottom
[0171] The insulating barrier layer 5 was composed of Ti--Mg--O
that was prepared by depositing Ti (4.6)/Mg (0.6) and oxidizing the
Ti/Mg layer.
[0172] The values in parentheses are average thicknesses expressed
in angstrom.
[0173] The laminate 10 was annealed at 270.degree. C. for 3 hours
40 minutes.
[0174] As shown in FIG. 16, the rate of resistance change
(.DELTA.R/R) was determined as a function of resistance-area (RA)
product for tunneling magnetoresistive elements that include a
first protective sublayer 7a composed of Al,
Ni.sub.49at%Fe.sub.12at%Cr.sub.39at%, Ir.sub.26at%Mn.sub.74at%, or
Cr.
Comparative Example 1
[0175] As shown in FIG. 17, the rate of resistance change
(.DELTA.R/R) was determined as a function of resistance-area (RA)
product for tunneling magnetoresistive elements that include a
first protective sublayer 7a composed of Al,
Ni.sub.49at%Fe.sub.12at%Cr.sub.39at%, Ir.sub.26at%Mn.sub.74at%, or
Cr and the same laminate as that described in Example 3 except that
the nonmagnetic metal sublayer 14 was eliminated
[0176] As is evident from comparison between FIG. 16 and FIG. 17,
while the examples and the comparative examples have almost the
same resistance-area (RA) product, the examples had rates of
resistance change (.DELTA.R/R) higher than those of the comparative
examples. The tunneling magnetoresistive elements having different
first protective sublayers 7a had substantially the same rate of
resistance change (.DELTA.R/R), as shown in FIG. 16.
[0177] Thus, in the tunneling magnetoresistive elements including
the nonmagnetic metal sublayer 14 in the free magnetic layer 6, any
of various candidate materials may be used for the first protective
sublayer 7a.
* * * * *