U.S. patent application number 14/024114 was filed with the patent office on 2014-09-25 for magnetoresistive element and manufacturing method thereof.
The applicant listed for this patent is Youngmin EEH, Tadashi KAI, Toshihiko NAGASE, Kazuya SAWADA, Koji UEDA, Daisuke WATANABE, Hiroaki YODA. Invention is credited to Youngmin EEH, Tadashi KAI, Toshihiko NAGASE, Kazuya SAWADA, Koji UEDA, Daisuke WATANABE, Hiroaki YODA.
Application Number | 20140284534 14/024114 |
Document ID | / |
Family ID | 51568440 |
Filed Date | 2014-09-25 |
United States Patent
Application |
20140284534 |
Kind Code |
A1 |
NAGASE; Toshihiko ; et
al. |
September 25, 2014 |
MAGNETORESISTIVE ELEMENT AND MANUFACTURING METHOD THEREOF
Abstract
According to one embodiment, a magnetoresistive element is
disclosed. The magnetoresistive element includes a first magnetic
layer having a variable magnetization direction. A first
nonmagnetic layer is provided on the first magnetic layer. A second
magnetic layer having a fixed magnetization direction is provided
on the first nonmagnetic layer. The first magnetic layer, the first
nonmagnetic layer and the second magnetic layer are preferredly
oriented in a cubical crystal (111) plane.
Inventors: |
NAGASE; Toshihiko; (Tokyo,
JP) ; KAI; Tadashi; (Tokyo, JP) ; EEH;
Youngmin; (Kawagoe-shi, JP) ; UEDA; Koji;
(Fukuoka-shi, JP) ; WATANABE; Daisuke; (Kai-shi,
JP) ; SAWADA; Kazuya; (Morioka-shi, JP) ;
YODA; Hiroaki; (Kawasaki-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
NAGASE; Toshihiko
KAI; Tadashi
EEH; Youngmin
UEDA; Koji
WATANABE; Daisuke
SAWADA; Kazuya
YODA; Hiroaki |
Tokyo
Tokyo
Kawagoe-shi
Fukuoka-shi
Kai-shi
Morioka-shi
Kawasaki-shi |
|
JP
JP
JP
JP
JP
JP
JP |
|
|
Family ID: |
51568440 |
Appl. No.: |
14/024114 |
Filed: |
September 11, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61804420 |
Mar 22, 2013 |
|
|
|
Current U.S.
Class: |
257/1 ;
438/3 |
Current CPC
Class: |
H01L 43/12 20130101;
H01L 43/02 20130101; H01L 43/10 20130101; H01L 43/08 20130101 |
Class at
Publication: |
257/1 ;
438/3 |
International
Class: |
H01L 43/02 20060101
H01L043/02; H01L 43/12 20060101 H01L043/12 |
Claims
1. A magnetoresistive element comprising: a first magnetic layer
having a variable magnetization direction; a first nonmagnetic
layer provided on the first magnetic layer; and a second magnetic
layer provided on the first nonmagnetic layer and having a fixed
magnetization direction, wherein the first magnetic layer, the
first nonmagnetic layer, and the second magnetic layer are
preferredly oriented in a cubical crystal (111) plane or a
hexagonal crystal (0002) plane.
2. The magnetoresistive element according to claim 1, wherein a
material of the first and second magnetic layers is a monometal of
Co, a monometal of Ni, an alloy of Co and Fe, an alloy of Co and
Ni, an alloy of Fe and Ni, or an alloy of Co, Fe and Ni, when the
layers are preferredly oriented in the cubical crystal (111).
3. The magnetoresistive element according to claim 1, wherein a
material of the first nonmagnetic layer is a SrTiO.sub.3,
SrFeO.sub.3, SrFeO.sub.3, LaAlO.sub.3, NdCoO.sub.3, or BN which is
of a ZnS structure, when the layers are preferredly oriented in the
cubical crystal (111).
4. The magnetoresistive element according to claim 1, wherein a
material of the first and second magnetic layers is Co, an alloy of
Co and Fe, an alloy of Co and Ni, or an alloy of Co, Fe and Ni,
when the layers are preferredly oriented in the hexagonal crystal
(0002).
5. The magnetoresistive element according to claim 1, wherein a
material of the first nonmagnetic layer is an alloy of B and N, or
an alloy of Al and O, when the layers are preferredly oriented in
the hexagonal crystal (0002).
6. A magnetoresistive element comprising: a first magnetic layer
having a variable magnetization direction; a first nonmagnetic
layer provided on the first magnetic layer; and a second magnetic
layer provided on the first nonmagnetic layer and having a fixed
magnetization direction, wherein each of the first and second
magnetic layers includes a highly polarized magnetic material.
7. The magnetoresistive element according to claim 6, wherein the
highly polarized magnetic material includes a half-metal.
8. The magnetoresistive element according to claim 6, wherein the
half-metal is represented by X.sub.2YZ or XYZ, wherein X, Y and Z
represent different elements.
9. The magnetoresistive element according to claim 8, wherein the X
is Co.
10. The magnetoresistive element according to claim 8, wherein the
first nonmagnetic layer includes an alloy of Zn and S, an alloy of
Ce and O, an alloy of Mg and O, or an alloy of Al and O.
11. The magnetoresistive element according to claim 1, further
comprising: an underlying layer, and wherein the first magnetic
layer is formed on the underlying layer.
12. The magnetoresistive element according to claim 1, further
comprising: a second nonmagnetic layer provided on the second
magnetic layer; and a shift cancelling layer provided on the second
nonmagnetic layer.
13. The magnetoresistive element according to claim 12, wherein the
second magnetic layer is Ru.
14. A method for manufacturing a magnetoresistive element,
comprising: forming a first magnetic layer by depositing a magnetic
material having a variable magnetization direction; forming a
nonmagnetic layer on the first magnetic layer by depositing a
nonmagnetic material; and forming a second magnetic layer on the
nonmagnetic layer by depositing a magnetic material having a fixed
magnetization direction, wherein the first magnetic layer, the
nonmagnetic layer, and the second magnetic layer are preferredly
oriented in a cubical crystal (111) plane or a hexagonal crystal
(0002) plane.
15. The method according to claim 14, wherein the first magnetic
layer, the nonmagnetic layer, and the second magnetic layer are
formed by a sputtering method.
16. The method according to claim 14, wherein forming the first
magnetic layer, the nonmagnetic layer, and the second magnetic
layer are performed in a state in which the first magnetic layer,
the nonmagnetic layer, and the second magnetic layer are
preferredly oriented in the cubical crystal (111) plane or a
hexagonal crystal (0002) plane.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/804,420, filed Mar. 22, 2013, the entire
contents of which are incorporated herein by reference.
FIELD
[0002] Embodiments described herein relate generally to a
magnetoresistive element and a manufacturing method thereof.
BACKGROUND
[0003] In recent years, a semiconductor memory with a resistance
change element such as a PRAM (phase-change random access memory)
or an MRAM (magnetic random access memory), has been attracting
attention and being developed, in which the resistance change
element is utilized as a memory element. The MRAM is a device which
performs a memory operation by storing "1" or "0" information in a
memory cell by using a magnetoresistive effect, and has such
features as nonvolatility, high-speed operation, high integration
and high reliability.
[0004] A large number of MRAMs, which use elements exhibiting a
tunneling magnetoresistive (TMR) effect, among other
magnetoresistive effects, have been reported. One of
magnetoresistive effect elements is a magnetic tunnel junction
(MTJ) element including a three-layer multilayer structure of a
recording layer having a variable magnetization direction, an
insulation film as a tunnel barrier, and a reference layer which
maintains a predetermined magnetization direction.
[0005] The resistance of the MTJ element varies depending on the
magnetization directions of the recording layer and reference
layer. When these magnetization directions are parallel, the
resistance takes a minimum value, and when the magnetization
directions are antiparallel, the resistance takes a maximum value,
and information is stored by associating the parallel state and
antiparallel state with binary information "0" and binary
information "1", respectively.
[0006] Write of information to the MTJ element involves a
magnetic-field write scheme in which only the magnetization
direction in the recording layer is inverted by a current magnetic
field resulting from a current flowing through a write wire and a
write (spin injection write) scheme using spin angular momentum
movement in which the magnetization direction in the recording
layer is inverted by passing a spin polarization current through
the MTJ element itself.
[0007] In the former scheme, when the element size is reduced, the
coercivity of a magnetic body constituting the recording layer
increases and the write current tends to increase, and thus it is
difficult to achieve both the miniaturization and reduction in
electric current.
[0008] On the other hand, in the latter scheme (spin injection
write scheme), as the volume of the magnetic layer constituting the
recording layer becomes smaller, the number of spin-polarized
electrons to be injected, may be smaller, and thus it is expected
that both the miniaturization and reduction in electric current can
be easily achieved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is a cross-sectional view schematically illustrating
a magnetoresistive element according to an embodiment;
[0010] FIG. 2 is a cross-sectional view for describing an example
of a structure of underlying layer of a magnetoresistive element
according to an embodiment;
[0011] FIG. 3 is a cross-sectional view for describing an example
of an SAF structure of magnetoresistive element according to an
embodiment;
[0012] FIG. 4 is a cross-sectional view schematically illustrating
a main part of magnetoresistive element including a high anisotropy
magnetic field layer according to an embodiment;
[0013] FIG. 5 is a cross-sectional view for describing a
manufacturing method of a magnetoresistive element according to an
embodiment;
[0014] FIG. 6 is a cross-sectional view for describing the
manufacturing method of the magnetoresistive element according to
the embodiment following FIG. 5;
[0015] FIG. 7 is a cross-sectional view for describing a
manufacturing method of the magnetoresistive element according to
the embodiment following FIG. 6;
[0016] FIG. 8 is a cross-sectional view for describing a
manufacturing method of the magnetoresistive element according to
the embodiment following FIG. 7; and
[0017] FIG. 9 is a cross-sectional view for describing a
manufacturing method of the magnetoresistive element according to
the embodiment following FIG. 8.
DETAILED DESCRIPTION
[0018] Various embodiments will be described hereinafter with
reference to the accompanying drawings. In the drawings to be
described below, the parts corresponding to those in a preceding
drawing are denoted by like reference numerals, and an overlapping
description is omitted.
[0019] According to an embodiment, a magnetoresistive element is
disclosed. The magnetoresistive element includes a first magnetic
layer having a variable magnetization direction. A first
nonmagnetic layer is provided on the first magnetic layer. A second
magnetic layer having a fixed magnetization direction is provided
on the first nonmagnetic layer. The first magnetic layer, the first
nonmagnetic layer, and the second magnetic layer are preferredly
oriented in a cubical crystal (111) plane or a hexagonal crystal
(0002) plane.
[0020] According to another embodiment, a method for manufacturing
a magnetoresistive element is disclosed. The method includes
forming a first magnetic layer by depositing a magnetic material
having a variable magnetization direction, forming a nonmagnetic
layer on the first magnetic layer by depositing a nonmagnetic
material, and forming a second magnetic layer on the nonmagnetic
layer by depositing a magnetic material having a fixed
magnetization direction. The first magnetic layer, the nonmagnetic
layer, and the second magnetic layer are preferredly oriented in a
hexagonal crystal (111) plane or a hexagonal crystal (0002)
plane.
First Embodiment
[0021] FIG. 1 is a cross-sectional view schematically illustrating
a magnetoresistive element according to a first embodiment, and
more specifically a cross-sectional structure of an MTJ
element.
[0022] In the Figure, numeral 101 denotes a bottom electrode (BE)
101 provided on a silicon substrate (semiconductor substrate) which
is not illustrated, a buffer layer (BL) 102 is provided on this
bottom electrode 101. An underlying layer (UL) 103 is provided on
the buffer layer 102.
[0023] A first magnetic layer 104, which is used as a recording
layer and is preferredly oriented in, e.g. a (111) plane of
face-centered cubic structure, is provided on the underlying layer
103.
[0024] A first nonmagnetic layer 105, which is used as a tunnel
barrier layer and is preferredly oriented in, e.g. a (111) plane of
face-centered cubic structure, is provided on the first magnetic
layer 104. The first nonmagnetic layer 105 is formed to be
lattice-matched to the first magnetic layer 104.
[0025] A second magnetic layer 106, which is used as a reference
layer and is preferredly oriented in, e.g. a (111) plane of
face-centered cubic structure, is provided on the first nonmagnetic
layer 105. The second magnetic layer 106 is formed to be
lattice-matched to the first nonmagnetic layer 105.
[0026] A shift cancelling layer (SCL) 107, which is preferredly
oriented in, e.g. a (111) plane, is provided on the second magnetic
layer 106. The shift cancelling layer 107 is formed to be
lattice-matched to the second magnetic layer 106. A top electrode
(TE) 108 is provided on the shift cancelling layer 107.
[0027] In the case of the present embodiment, the first magnetic
layer 104, first nonmagnetic layer 105 and second magnetic layer
106 (MTJ) are formed to be lattice-matched. When a magnetic layer,
a nonmagnetic layer and a magnetic layer, which have close lattice
constants, are stacked, a high MR can be expected because of
continuity of band structures of the respective layers and a
specific spin filtering effect at interfaces.
[0028] Here, a desirable lattice matching in an invention is
described. Each layer of a (111) plane of a face-centered cubic
(fcc) structure, which is a basic crystal structure, is a
close-packed layer. In the face-centered cubic structure, lattice
points exist at the corners of a cubic and at the centers of the
respective planes. If the lattice constant is "a", the lattice
points form a regular triangle of a/ {square root over (2)}. In a
hexagonal close-packed (hop) structure, if the lattice constant of
an a-axis is "a'", each layer of a (0001) plane is a close-packed
layer, and lattice points form a regular triangle with one side of
"a'". For example, the (111) plane of the face-centered cubic
structure with the lattice constant "a" and the (0001) plane of the
hexagonal close-packed structure with the lattice constant "a'" of
the a-axis are lattice-matched when a/ {square root over (2)}=na'.
Here, n is an integer. In the case of considering the lattice match
of identical crystal structures, it should suffice if the lattice
constant is an integer multiple. Moreover, in the case of a
structure including lattice points of a face-centered cubic
structure, such as an NaCl structure, a diamond structure, a ZnS
structure, a CaF.sub.2 structure or a perovskite structure, that
is, in the case of a structure in which lattice points exist at the
corners of a cubic and at the centers of the respective planes,
lattice points forming a regular triangle exist at least in the
(111) plane, and lattices are matched. In the case of the lattice
of the (0001) plane of the hexagonal close-packed structure, such
as a wurtzite structure, a CdI structure, a NiAs structure or a
corundum structure, that is, if lattice points forming a regular
triangle exist at least in the (0001) plane, lattices are
matched.
[0029] The materials of the first magnetic layer 104, first
nonmagnetic layer 105 and second magnetic layer 106 are, for
example, as follows.
[0030] The material of the first magnetic layer 104 is a material
having a face-centered cubic (fcc) structure and including at least
one of Co, Fe and Ni (however, an elemental substance of Fe is
excluded). In the description below, this material is expressed as
fcc-Co--Fe--Ni. The (111) plane of the first magnetic layer 104 is
an atomically close-packed plane.
[0031] Examples of the material of the first nonmagnetic layer 105
are SrTiO.sub.3, SrFeO.sub.3, LaAlO.sub.3 and NdCoO.sub.3, which
are of a perovskite structure, or BN which is of a ZnS
structure.
[0032] The material of the second magnetic layer 106 is
fcc-Co--Fe--Ni. The (111) plane of the second magnetic layer 104 is
an atomically close-packed plane. The first magnetic layer 104 and
second magnetic layer 106 may be formed of the same material or may
be formed of different materials.
[0033] The lattice constant of the above-described fcc-Co--Fe--Ni
is 3.5 to 3.65 angstroms. In addition, one side of the regular
triangle of the above-described close-packed layer is 2.45 to 2.6
angstroms. SrTiO.sub.3, SrFeO.sub.3, LaAlO.sub.3 and NdCoO.sub.3
are cubic crystal systems with a perovskite structure, and their
lattice constants are 3.90, 3.87, 3.79 and 3.78 angstroms,
respectively. BN is of the ZnS structure, and the lattice constant
thereof is 3.62 angstroms.
[0034] As regards a lattice mismatch between the first magnetic
layer 104 and first nonmagnetic layer 105 and a lattice mismatch
between the second magnetic layer 106 and first nonmagnetic layer
105, the materials and process conditions are properly selected and
the mismatch is controlled to be reduced to, e.g. 10% or less. In
the present embodiment, the (111) plane of the face-centered cubic
structure of the first magnetic layer 104, first nonmagnetic layer
105 and second magnetic layer 106 is preferredly oriented.
Alternatively, as in a third embodiment which will be described
later, the (0002) plane of the hexagonal close-packed structure of
each of these layers may be preferredly oriented, or any one of the
layers may have a face-centered cubic structure or a hexagonal
close-packed structure.
[0035] In the present embodiment, the first magnetic layer 104,
first nonmagnetic layer layer 105 and second magnetic layer 106 are
preferredly oriented in the (111) plane of face-centered cubic
structure. Thus, the shift cancelling layer 107, which is
preferredly oriented in the (111) plane of face-centered cubic
structure, is easily formed on the second magnetic layer 106, and
as a result the thickness of the shift cancelling layer 107 can be
reduced. For example, the thickness of the shift cancelling layer
107 can be set at 10 nm or less. Thereby, an MTJ element with a
very small film thickness of the entire MTJ structure can be
realized, and the amount of etching at a time of device-processing
the MTJ film can be reduced.
[0036] FIG. 2 is a cross-sectional view for describing an example
of the structure of the buffer layer 102 and underlying layer 103
of the magnetoresistive element according to the embodiment.
[0037] The buffer layer 102 is formed of a Ta layer, and Ru of the
underlying layer 103, which is formed on the buffer layer 102,
grows with a preferred orientation of a (0002) plane of hexagonal
close-packed structure. For example, in the case where the magnetic
material 104 is a Co layer, the Co layer also grows with a
preferred orientation of a (0002) plane of hexagonal close-packed
structure, by the influence of the orientation plane of Ru. The Ta
layer 102 has a structure of amorphous or microcrystal, and has a
function of eliminating the influence of the crystal orientation of
a layer (e.g. bottom electrode 101) which is located under the Ta
layer 102. Thus, a Ru layer 1032 and Co layer 104, which are
preferredly oriented in the (0002) plane of hexagonal close-packed
structure, can easily be formed.
[0038] FIG. 3 is a cross-sectional view for describing an example
of an SAF (Synthetic Anti-Ferromagnet) structure of the
magnetoresistive element according to the embodiment. Here, the SAF
structure refers to a structure comprising two magnetic layers and
a nonmagnetic layer therebetween in which the magnetic layers have
magnetization directions antiparallel each other. A second
nonmagnetic layer (e.g. Ru layer) 201 is provided between the
second magnetic layer 106 and shift cancelling layer 107. A
multilayer structure formed of the second magnetic layer 106,
second nonmagnetic layer 201 and shift cancelling layer 107,
constitutes the SAF structure. By using that kind of SAF structure,
the magnetization fixing force of the second magnetic layer 106 and
shift cancelling layer 107 is increased, and as a result the
tolerance to external magnetization and the thermal stability are
improved.
[0039] As illustrated in FIG. 4, the magnetoresistive element
according to the present embodiment may include a high anisotropy
magnetic field layer 109 which includes a material having a large
magnetic anisotropy, namely a material (high Hk material) having a
large anisotropic magnetic field, and is preferredly oriented in an
atomically close-packed plane such as an fcc (111) plane or an hcp
(0002) plane. The first magnetic layer 104 or the like are formed
on the high anisotropy magnetic field layer 109. By the provision
of the high anisotropy magnetic field layer 109, an MTJ element
(vertical magnetization-type MTJ element), which includes a
vertical magnetization magnetic film with an axis of easy
magnetization in a direction perpendicular to the film surface, can
easily be realized.
[0040] FIG. 5 to FIG. 9 are cross-sectional views for describing a
manufacturing method of the magnetoresistive element according to
the present embodiment.
[0041] As shown in FIG. 5, a bottom electrode 101, a buffer layer
102 and an underlying layer 103 are formed on a silicon substrate
that is not shown.
[0042] Next, as shown in FIG. 6, a first magnetic layer 104, which
is preferredly oriented in a (111) plane of face-centered cubic
structure, is formed on the underlying layer 103. The first
magnetic layer 104 is formed by, e.g. a sputtering method. By using
the sputtering method, a magnetic material with an atomically
close-packed plane and a variable magnetization direction can be
deposited. That is, the first magnetic layer 104, which is formed
by the method of the embodiment, is not an amorphous magnetic
layer, but a magnetic layer which is preferredly oriented in the
(111) plane of face-centered cubic structure. Thus, the first
magnetic layer 104 is not obtained by crystallizing an amorphous
magnetic layer by heat treatment.
[0043] Next, as illustrated in FIG. 7, a first nonmagnetic layer
105, which is preferredly oriented in a (111) plane of
face-centered cubic structure, is formed on the first magnetic
layer 104. The first nonmagnetic layer 105 is formed by, e.g. a
sputtering method. By using the sputtering method, a nonmagnetic
material with an atomically close-packed plane can be deposited.
That is, the first nonmagnetic layer 105, which is formed by the
method of the embodiment, is not an amorphous nonmagnetic layer,
but a nonmagnetic layer which is preferredly oriented in the (111)
plane of face-centered cubic structure. Namely, the first
nonmagnetic layer 105 is formed in the state in which the first
nonmagnetic layer 105 takes over the crystal orientation from the
first magnetic layer 104 and is preferredly oriented in the (111)
plane of face-centered cubic structure. Thus, the first nonmagnetic
layer 105 is not obtained by crystallizing an amorphous nonmagnetic
layer by heat treatment.
[0044] Next, as shown in FIG. 8, a second magnetic layer 106, which
is preferredly oriented in a (111) plane of face-centered cubic
structure, is formed on the first nonmagnetic layer 105. The second
magnetic layer 106 is formed by, e.g. a sputtering method. Like the
case of the first magnetic layer 104, the second magnetic layer
106, which is formed by the method of the embodiment, is not an
amorphous magnetic layer, but a magnetic layer which is preferredly
oriented in the (111) plane of face-centered cubic structure. That
is, the second magnetic layer 106 is formed in the state in which
the second magnetic layer 106 takes over the crystal orientation
from the first nonmagnetic layer 105 and is preferredly oriented in
the (111) plane of face-centered cubic structure. Thus, the second
magnetic layer 106 is not obtained by crystallizing an amorphous
magnetic layer by heat treatment.
[0045] Next, as illustrated in FIG. 9, a shift cancelling layer
107, which is preferredly oriented in a (111) plane of
face-centered cubic structure, is formed on the second magnetic
layer 106. The shift cancelling layer 107 is formed in the state in
which the shift cancelling layer 107 takes over the crystal
orientation from the second magnetic layer 106 and is preferredly
oriented in the (111) plane of face-centered cubic structure. Like
the layers 104, 105 and 106, the shift cancelling layer 107 is
formed by, e.g. a sputtering method.
[0046] Since the second magnetic layer 106, which is the underlying
layer of the shift cancelling layer 107, is preferredly oriented in
the (111) plane of face-centered cubic structure, the shift
cancelling layer 107 is easily preferredly oriented in the (111)
plane of face-centered cubic structure. Thus, there is no need to
form the shift cancelling layer 107 with a large thickness in order
to obtain the shift cancelling layer 107 having a (111) plane of
face-centered cubic structure with a small lattice mismatch.
[0047] Thereafter, an etching mask 301 is formed on the shift
cancelling layer 107, the by using the etching mask 301 as a mask,
the layers 108, 107, 106, 105, 103, 102 and 101 are successively
etched to obtain the magnetoresistive element shown in FIG. 1.
Second Embodiment
[0048] In the first embodiment, a magnetic material, which is
preferredly oriented in a (111) plane of face-centered cubic
structure, is used as the material of the first and second magnetic
layers 104 and 106, and a nonmagnetic material, which is
preferredly oriented in a (111) plane of face-centered cubic
structure, is used as the material of the first nonmagnetic layer
105.
[0049] In the present embodiment, a magnetic material, which is
preferredly oriented in a (0002) plane of hexagonal close-packed
structure, is used as the material of the first and second magnetic
layers 104 and 106, and a nonmagnetic material, which is
preferredly oriented in a (0002) plane of hexagonal close-packed
structure, is used as the material of the first nonmagnetic layer
105.
[0050] In the following, the first magnetic layer 104, first
nonmagnetic layer 105 and second magnetic layer 106 are preferredly
oriented in the (0002) plane of hexagonal close-packed structure in
the description below, alternatively a mixture of the (111) plane
of face-centered cubic structure and (0002) plane of hexagonal
close-packed structure may be exist in those films as the preferred
orientation plane. For example, the first magnetic layer 104 may
have the (111) plane of face-centered cubic structure, the first
nonmagnetic layer may have the (0002) plane of hexagonal
close-packed structure, and the second magnetic layer may have the
(111) plane of face-centered cubic structure.
[0051] The material of the first and second magnetic layers 104 and
106 is a material having a hexagonal close-packed (hcp) and
including at least one of Co, Fe and Ni (however, an elemental
substance of Fe is excluded). In the description below, this
material is expressed as hcp-Co--Fe--Ni.
[0052] The (0002) plane of hexagonal close-packed structure of the
first magnetic layer 104 is an atomically close-packed plane. The
lattice constant of the a-axis of the hcp-Co--Fe--Ni is 2.5 to 2.6
angstroms. Moreover, one side of the regular triangle of the
above-described close-packed layer is 2.5 to 2.6 angstroms.
[0053] The material of the first nonmagnetic layer 105 is an alloy
of B and N, or an alloy of Al and O, for example, BN, BeO, or
Al.sub.2O.sub.3. BN and BeO are of a wurtzite structure, and the
lattice constants of the a-axis thereof are 2.5 angstroms and 2.7
angstroms, respectively. Al.sub.2O.sub.3 is of a corundum
structure, and the lattice constant of the a-axis thereof is 2.5
.ANG..
[0054] As regards a lattice mismatch between the first magnetic
layer 104 and first nonmagnetic layer 105 and a lattice mismatch
between the second magnetic layer 106 and first nonmagnetic layer
105, the materials and process conditions are properly selected and
the mismatch is controlled to be reduced to, e.g. 10% or less.
Third Embodiment
[0055] In the present embodiment, highly polarized magnetic
materials are used as the materials of the first and second
magnetic layers 104 and 106, thereby realizing a high TMR
ratio.
[0056] In addition, from the standpoint of a high TMR ratio, it is
not always necessary that the first magnetic layer 104, first
nonmagnetic layer 105 and second magnetic layer 106 are
latticed-matched. However, from the standpoint of crystal growth,
it is desirable that these layers be lattice-matched. A half-metal,
which is preferredly oriented in a (111) plane, is used as the
highly polarized magnetic material.
[0057] In the present embodiment, a Heusler alloy is used as the
half-metal. The Heusler alloy is represented by X.sub.2YZ. The
crystal structures are a L2.sub.1 structure and a B2 structure
which are regularized, and these are cubic crystal systems. X, Y
and Z represent different elements. Examples of the Heusler alloy
are Co.sub.2MsSi, Co.sub.2FeSi, Co.sub.2FeAl, Co.sub.2(FeCr)Al,
Co.sub.2MnGa, Co.sub.2MnGe, and Fe.sub.2CrSi.
[0058] The material of the first nonmagnetic layer 105 is an
insulation material or a semiconductor material, which is
preferredly oriented in a (111) plane or a (0002) plane. Examples
of the structure including a face-centered cubic structure are SrO
(5.16 angstroms) of a NaCl structure, BaO (5.52 angstroms),
CaF.sub.2 (5.46 angstroms) of a CaF.sub.2 structure, SrF.sub.2
(5.80 angstroms), CeO.sub.2 (5.41 angstroms). Examples of a
structure derived from a hexagonal close-packed structure are ZnO
(3.25 angstroms @ a-axis) of the wurtzite structure, and ZnS (3.82
angstroms @ a-axis).
[0059] The lattice constant of Co.sub.2YZ, which is an
X.sub.2YZ-type Heusler alloy, is about 5.6 to 5.8 angstroms in the
case of, for example, the above-described material systems. In the
case of the material of the cubic crystal system, materials having
similar lattice constants of 5.6 to 5.8 angstroms are preferable.
In the case of the material of the hexagonal crystal system,
materials having lattice constants of the a-axis of 3.9 to 4.1
angstroms are preferable. As will be described later, when it is
assumed that the lattice mismatch is higher than 10%, materials
having lattice constants of about .+-.10% from the range of the
above-described lattice constants may be used.
[0060] As regards a lattice mismatch between the first magnetic
layer 104 and first nonmagnetic layer 105 and a lattice mismatch
between the second magnetic layer 106 and first nonmagnetic layer
105, the materials and process conditions are properly selected and
the mismatch is controlled to be reduced to, e.g. 10% or less. The
Heusler alloy, which is used as the first and second magnetic
layers 104 and 106, is formed by using, for example, a sputtering
method or an evaporation deposition method. As the manufacturing
method of the magnetoresistive element of the present embodiment,
the method of the first embodiment is applicable.
[0061] In addition, the magnetoresistive element of the present
embodiment can adopt the structures illustrated in FIG. 2 to FIG.
4. However, the crystal plane is changed from (111) to (0002).
[0062] Each of the above-described MTJ structures can be introduced
as MTJ elements of memory cells. Memory cells, memory cell arrays
and memory devices are disclosed in U.S. patent application Ser.
No. 13/420,106, Asao, the entire contents of which are incorporated
by reference herein.
[0063] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
embodiments described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the embodiments described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
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