U.S. patent application number 16/126823 was filed with the patent office on 2019-09-19 for magnetic memory device.
This patent application is currently assigned to TOSHIBA MEMORY CORPORATION. The applicant listed for this patent is TOSHIBA MEMORY CORPORATION. Invention is credited to Masatoshi YOSHIKAWA.
Application Number | 20190287590 16/126823 |
Document ID | / |
Family ID | 67906001 |
Filed Date | 2019-09-19 |
United States Patent
Application |
20190287590 |
Kind Code |
A1 |
YOSHIKAWA; Masatoshi |
September 19, 2019 |
MAGNETIC MEMORY DEVICE
Abstract
According to one embodiment, a magnetic memory device includes a
first magnetic layer having a variable magnetization direction, a
second magnetic layer having a fixed magnetization direction, and a
nonmagnetic layer between the first magnetic layer and the second
magnetic layer, wherein the first magnetic layer includes a first
sub-magnetic layer, a second sub-magnetic layer, and a first
intermediate layer between the first sub-magnetic layer and the
second sub-magnetic layer, and the first sub-magnetic layer is
provided between the nonmagnetic layer and the second sub-magnetic
layer and has a magnetization direction antiparallel to a
magnetization direction of the second sub-magnetic layer and has a
magnetization amount smaller than that of the second sub-magnetic
layer.
Inventors: |
YOSHIKAWA; Masatoshi;
(Seoul, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
TOSHIBA MEMORY CORPORATION |
Tokyo |
|
JP |
|
|
Assignee: |
TOSHIBA MEMORY CORPORATION
Tokyo
JP
|
Family ID: |
67906001 |
Appl. No.: |
16/126823 |
Filed: |
September 10, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G11C 11/161 20130101;
H01L 43/08 20130101; H01L 43/02 20130101; H01L 43/10 20130101 |
International
Class: |
G11C 11/16 20060101
G11C011/16; H01L 43/02 20060101 H01L043/02; H01L 43/08 20060101
H01L043/08; H01L 43/10 20060101 H01L043/10 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 16, 2018 |
JP |
2018-049873 |
Claims
1. A magnetic memory device comprising: a first magnetic layer
having a variable magnetization direction; a second magnetic layer
having a fixed magnetization direction; and a nonmagnetic layer
provided between the first magnetic layer and the second magnetic
layer, wherein the first magnetic layer includes a first
sub-magnetic layer, a second sub-magnetic layer, and a first
intermediate layer provided between the first sub-magnetic layer
and the second sub-magnetic layer, and the first sub-magnetic layer
is provided between the nonmagnetic layer and the second
sub-magnetic layer and has a magnetization direction antiparallel
to a magnetization direction of the second sub-magnetic layer and
has a magnetization amount smaller than that of the second
sub-magnetic layer.
2. The device according to claim 1, wherein the first magnetic
layer further includes a third sub-magnetic layer having a
magnetization direction antiparallel to that of the second
sub-magnetic layer, and a second intermediate layer provided
between the second sub-magnetic layer and the third sub-magnetic
layer, and the second sub-magnetic layer is provided between the
first sub-magnetic layer and the third sub-magnetic layer.
3. The device according to claim 2, wherein the third sub-magnetic
layer has a magnetization amount smaller than that of the second
sub-magnetic layer.
4. The device according to claim 2, wherein a sum of the
magnetization amount of the first sub-magnetic layer and a
magnetization amount of the third sub-magnetic layer is equal to a
magnetization amount of the second sub-magnetic layer.
5. The device according to claim 1, further comprising: a third
magnetic layer having a fixed magnetization direction antiparallel
to the magnetization direction of the second magnetic layer and
canceling a magnetic field applied from the second magnetic layer
to the first magnetic layer.
6. The device according to claim 1, wherein the first sub-magnetic
layer and the second sub-magnetic layer contain at least cobalt
(Co).
7. The device according to claim 1, wherein the first intermediate
layer contains at least one element selected from ruthenium (Ru),
rhodium (Rh), osmium (Os), and iridium (Ir).
8. A magnetic memory device comprising: a first magnetic layer
having a variable magnetization direction; a second magnetic layer
having a fixed magnetization direction; and a nonmagnetic layer
provided between the first magnetic layer and the second magnetic
layer, wherein the first magnetic layer includes a first
sub-magnetic layer, a second sub-magnetic layer, and a first
intermediate layer provided between the first sub-magnetic layer
and the second sub-magnetic layer, and the first sub-magnetic layer
is provided between the nonmagnetic layer and the second
sub-magnetic layer and has a magnetization direction antiparallel
to a magnetization direction of the second sub-magnetic layer and
has a thickness smaller than that of the second sub-magnetic
layer.
9. The device according to claim 8, wherein the first magnetic
layer further includes a third sub-magnetic layer having a
magnetization direction antiparallel to that of the second
sub-magnetic layer, and a second intermediate layer provided
between the second sub-magnetic layer and the third sub-magnetic
layer, and the second sub-magnetic layer is provided between the
first sub-magnetic layer and the third sub-magnetic layer.
10. The device according to claim 9, wherein the third sub-magnetic
layer has a thickness smaller than that of the second sub-magnetic
layer.
11. The device according to claim 8, further comprising: a third
magnetic layer having a fixed magnetization direction antiparallel
to a magnetization direction of the second magnetic layer and
canceling a magnetic field applied from the second magnetic layer
to the first magnetic layer.
12. The device according to claim 8, wherein the first sub-magnetic
layer and the second sub-magnetic layer contain at least cobalt
(Co).
13. The device according to claim 8, wherein the first intermediate
layer contains at least one element selected from ruthenium (Ru),
rhodium (Rh), osmium (Os), and iridium (Ir).
14. A magnetic memory device comprising: a first magnetic layer
having a variable magnetization direction; a second magnetic layer
having a fixed magnetization direction; and a nonmagnetic layer
provided between the first magnetic layer and the second magnetic
layer, wherein the first magnetic layer includes a first
sub-magnetic layer, a second sub-magnetic layer, and a first
intermediate layer provided between the first sub-magnetic layer
and the second sub-magnetic layer, and the first sub-magnetic layer
is provided between the nonmagnetic layer and the second
sub-magnetic layer and has a magnetization direction antiparallel
to a magnetization direction of the second sub-magnetic layer and
has a saturation magnetization smaller than that of the second
sub-magnetic layer.
15. The device according to claim 14, wherein the first magnetic
layer further includes a third sub-magnetic layer having a
magnetization direction antiparallel to that of the second
sub-magnetic layer and a second intermediate layer provided between
the second sub-magnetic layer and the third sub-magnetic layer, and
the second sub-magnetic layer is provided between the first
sub-magnetic layer and the third sub-magnetic layer.
16. The device according to claim 15, wherein the third
sub-magnetic layer has a saturation magnetization smaller than that
of the second sub-magnetic layer.
17. The device according to claim 14, further comprising: a third
magnetic layer having a fixed magnetization direction antiparallel
to a magnetization direction of the second magnetic layer and
canceling a magnetic field applied from the second magnetic layer
to the first magnetic layer.
18. The device according to claim 14, wherein the first
sub-magnetic layer and the second sub-magnetic layer contain at
least cobalt (Co).
19. The device according to claim 14, wherein the first
intermediate layer contains at least one element selected from
ruthenium (Ru), rhodium (Rh), osmium (Os), and iridium (Ir).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2018-049873, filed
Mar. 16, 2010, the entire contents of which are incorporated herein
by reference.
FIELD
[0002] Embodiments described herein relate generally to a magnetic
memory device.
BACKGROUND
[0003] A magnetic memory device (semiconductor integrated circuit
device) in which a magnetoresistive element and a transistor are
integrated on a semiconductor substrate has been proposed. The
magnetoresistive element includes a storage layer having a variable
magnetization direction, a reference layer having a fixed
magnetization direction, and a tunnel barrier layer provided
between the storage layer and the reference layer.
[0004] As a magnetoresistive element, an STT (spin transfer torque)
type magnetoresistive element using a spin transfer torque effect
(spin transfer torque magnetization reversal) has been proposed. In
the STT type magnetoresistive element, the magnetization direction
of the storage layer is reversed by passing a current perpendicular
to the film surface of each layer constituting the magnetoresistive
element. In this case, it is necessary to prevent the magnetization
direction of the reference layer from being reversed even if the
magnetization direction of the storage layer is reversed.
[0005] When, as described above, magnetization of the storage layer
is reversed using spin transfer torque magnetization reversal, the
magnetization direction of the reference layer needs to be fixed.
That is, compared with the storage layer, the reference layer needs
to be sufficiently stable. However, in the spin transfer torque
magnetization reversal in which a current is passed through the
magnetoresistive element to perform magnetization reversal of the
storage layer, spin torque is applied to the storage layer. After
the magnetization direction of the storage layer is reversed, spin
torque also acts on the reference layer as its reaction. As a
result, the magnetization direction of the reference layer may be
reversed. In particular, when the magnetoresistive element is
refined, the probability that the magnetization direction of the
reference layer is reversed tends to increase. Therefore, as the
magnetoresistive element is refined, a normal operation of the
magnetoresistive element becomes increasingly difficult.
[0006] Therefore, there is a demand for a magnetic memory device
capable of preventing the reversal of the magnetization direction
of the reference layer even when the element is refined.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1 is a sectional view schematically showing the
configuration of a magnetic memory device according to a first
embodiment;
[0008] FIG. 2 is a diagram showing an RH loop;
[0009] FIG. 3 is a diagram showing the relationship between the
size of a magnetoresistive element and Hoff;
[0010] FIG. 4 is a diagram showing the relationship between Mst and
Hoff of the storage layer;
[0011] FIG. 5 is a diagram showing the relationship between the
size of the magnetoresistive element and an accumulated stray
magnetic field from the storage layer of neighboring cells;
[0012] FIG. 6 is a diagram showing the relationship between
saturation magnetization Ms of the storage layer and the
accumulated stray magnetic field from the storage layer of
neighboring cells;
[0013] FIG. 7 is a sectional view schematically showing the
configuration of a magnetic memory device according to a second
embodiment; and
[0014] FIG. 8 is a sectional view schematically showing the
configuration of a magnetic memory device using the
magnetoresistive element.
DETAILED DESCRIPTION
[0015] In general, according to one embodiment, a magnetic memory
device includes: a first magnetic layer having a variable
magnetization direction; a second magnetic layer having a fixed
magnetization direction; and a nonmagnetic layer provided between
the first magnetic layer and the second magnetic layer, wherein the
first magnetic layer includes a first sub-magnetic layer, a second
sub-magnetic layer, and a first intermediate layer provided between
the first sub-magnetic layer and the second sub-magnetic layer, and
the first sub-magnetic layer is provided between the nonmagnetic
layer and the second sub-magnetic layer and has a magnetization
direction antiparallel to a magnetization direction of the second
sub-magnetic layer and has a magnetization amount smaller than that
of the second sub-magnetic layer.
[0016] Hereinafter, embodiments will be described with reference to
the drawings.
First Embodiment
[0017] FIG. 1 is a sectional view schematically showing the
configuration of a magnetic memory device according to a first
embodiment and mainly shows the configuration of a magnetoresistive
element. The magnetoresistive element is also called a magnetic
tunnel junction (MTJ) element.
[0018] The magnetoresistive element shown in FIG. 1 includes a
storage layer (first magnetic layer) 10, a reference layer (second
magnetic layer) 20, a tunnel barrier layer (nonmagnetic layer) 30
provided between the storage layer 10 and the reference layer 20, a
shift canceling layer 40, and an intermediate layer 50 provided
between the reference layer 20 and the shift canceling layer (third
magnetic layer) 40. The storage layer 10 is provided on an
underlayer 60 and a cap layer 70 is provided on the shift canceling
layer 40.
[0019] The storage layer (first magnetic layer) 10 has a variable
magnetization direction and includes a first sub-magnetic layer 11,
a second sub-magnetic layer 12, and an intermediate layer (first
intermediate layer) 13 provided between the first sub-magnetic
layer 11 and the second sub-magnetic layer 12. The variable
magnetization direction means that the magnetization direction
varies for a predetermined write current. The first sub-magnetic
layer 11 is provided between the tunnel barrier layer 30 and the
second sub-magnetic layer 12 and has a magnetization direction
antiparallel to the magnetization direction of the second
sub-magnetic layer 12. Also, the first sub-magnetic layer 11 has a
magnetization amount Mst smaller than that of the second
sub-magnetic layer 12. The first sub-magnetic layer 11 may have a
thickness t smaller than that of the second sub-magnetic layer 12
or the first sub-magnetic layer 11 may have saturation
magnetization Ms smaller than that of the second sub-magnetic layer
12. Incidentally, the magnetization amount Mst corresponds to the
product (Ms.times.t) of the saturation magnetization Ms and the
thickness t.
[0020] Each of the first sub-magnetic layer 11 and the second
sub-magnetic layer 12 contains at least cobalt (Co). In addition to
cobalt (Co), the first sub-magnetic layer 11 and the second
sub-magnetic layer 12 may further contain iron (Fe) or boron (B).
In the present embodiment, the first sub-magnetic layer 11 and the
second sub-magnetic layer 12 are formed of CoFeB.
[0021] In the present embodiment, it is preferable that the first
sub-magnetic layer 11 contains Fe at least 50 at % near the tunnel
barrier layer 30 in view of an improvement of the TMR ratio.
Further, in a case of a magnetic layer which contains B, it is
preferable that the Co/Fe composition ratio is smaller than 1.0. It
is more preferable that the Fe ratio is at least 80 at %.
Furthermore, it is preferable that the first sub-magnetic layer 11
contains Co at least 50 at % near the interface between the first
sub-magnetic layer 11 and the intermediate layer 13. It is
preferable that the second sub-magnetic layer 12 contains Co at
least 50 at % near the interface between the second sub-magnetic
layer 12 and the intermediate layer 13. In a case of a magnetic
layer which contains B, it is preferable that the Co/Fe composition
ratio is at least 1.0. In a case where a composition near the
interface of the intermediate layer 13 is Co rich, an antiparallel
coupling between the first sub-magnetic layer 11 and the second
sub-magnetic layer 12 via the intermediate layer 13, that is an
antiferromagnetic coupling, can be more stabilized. Specifically,
an exchange coupling constant Jex, which is a physical constant of
a magnetic coupling, can be improved. The composition ratio of Fe
and Co of each magnetic layer can be decided by a composition
analysis using XPS, SIMS, EDX or EELS. Further, the saturation
magnetization Ms of each of the first sub-magnetic layer 11 and the
second sub-magnetic layer 12 is normally controlled within a range
from 600 to 2100 emu/cc. The saturation magnetization can be
appropriately controlled by a composition of Co, Fe, and B, and the
maximum saturation magnetization Ms can be obtained at a
composition ration of about Fe:Co=70:30. In a case where Ms of each
of the sub-magnetic layer is low, a stability of antiparallel state
is improved. Accordingly, Ms of each of the sub-magnetic layers 11
and 12 is preferably 1000 emu/cc, and more preferably 800 emu/cc.
In the CoFeB layer of the present embodiment, B is contained 30 at
% or less. In order to reduce the saturation magnetization Ms of
the magnetic layer, an adding of B is effective. On the other hand,
in order to stabilize an antiparallel coupling between the first
sub-magnetic layer 11 and the second sub-magnetic layer 12 via the
intermediate layer 13, that is, an antiferromagnetic coupling, it
is preferable to decrease a ratio of B. In other word, in order to
improve an exchange coupling constant Jex, it is preferable to
decrease a ratio of B. Accordingly, it is preferable that the ratio
of B is 10 at % or less near the interface between the intermediate
layer 13 and the first sub-magnetic layers 11 and near the
interface between the intermediate layer 13 and the second
sub-magnetic layers 12.
[0022] The intermediate layer (first intermediate layer) 13
contains at least one element selected from ruthenium (Ru), rhodium
(Rh), osmium (Os), and iridium (Ir). More specifically, the
intermediate layer 13 may be formed of a single layer film of a
ruthenium (Ru) film, a rhodium (Rh) film, an osmium (Os) film, or
an iridium (Ir) film or a laminated film arbitrarily combining the
ruthenium (Ru) film, the rhodium (Rh) film, the osmium (Os) film,
and the iridium (Ir) film. Also, the intermediate layer 13 may be
formed of an alloy film containing at least one of ruthenium (Ru),
rhodium (Rh), osmium (Os), and iridium (Ir). The thickness of the
intermediate layer 13 is preferably 1 nm or less. The first
sub-magnetic layer 11 and the second sub-magnetic layer 12 are
antiferromagnetically coupled via the intermediate layer 13.
Further, a Pt layer, Pd layer, Au layer, or Cu layer may be stacked
on the intermediate layer 13. In a case where the intermediate
layer 13 has a face-centered cubic (FCC) structure, the
intermediate layer 13 has a crystal orientation in which a (111)
face is preferentially oriented. In a case where the intermediate
layer 13 has a hexagonal close-packed (HOP) structure, the
intermediate layer 13 has a crystal orientation in which a (001)
face is preferentially oriented.
[0023] The reference layer (second magnetic layer) 20 has a fixed
magnetization direction. The fixed magnetization direction means
that the magnetization direction does not vary for a predetermined
write current. The reference layer 20 is formed of a first
sub-magnetic layer containing at least iron (Fe), cobalt (Co), and
boron (B) and a second sub-magnetic layer containing cobalt (Co)
and at least one element from platinum (Pt), nickel (Ni), iron
(Fe), and palladium (Pd). In the present embodiment, the reference
layer 20 is formed of a stacked film of CoFeB and Co/Pt (or Co/Ni
or Co/Pd).
[0024] The tunnel barrier layer (nonmagnetic layer) 30 is
interposed between the storage layer 10 and the reference layer 20
and contains magnesium (Mg) and oxygen (O). In the present
embodiment, the tunnel barrier layer 30 is formed of MgO. The MgO
layer of the tunnel barrier layer 30 has a crystal orientation in
which a (001) face is preferentially oriented.
[0025] The shift canceling layer (third magnetic layer) 40 has a
fixed magnetization direction antiparallel to the magnetization
direction of the reference layer 20. It is possible to cancel the
magnetic field applied from the reference layer 20 to the storage
layer 10 by the magnetic field from the shift canceling layer 40.
The shift canceling layer 40 contains cobalt (Co) and at least one
element from platinum (Pt), nickel (Ni), iron (Fe), and palladium
(Pd). In the present embodiment, the shift canceling layer 40 is
formed of Co/Pt, Co/Ni, or Co/Pd.
[0026] The intermediate layer 50 is interposed between the
reference layer 20 and the shift canceling layer 40 and is formed
of ruthenium (Ru).
[0027] Both the underlayer 60 and the cap layer 70 are formed of a
conductive material. A bottom electrode (not shown) is connected to
the underlayer 60 and a top electrode (not shown) is connected to
the cap layer 70.
[0028] In the present embodiment, as described above, the first
sub-magnetic layer 11 has a magnetization amount Mst smaller than
that of the second sub-magnetic layer 12. With the above
configuration, in the present embodiment, the total stray magnetic
field from the storage layer 10 to the reference layer 20 can be
reduced so that the magnetization direction of the reference layer
20 can be effectively prevented from being reversed. That is, a
stable reference layer 20 can be obtained. At this point, the
reference layer 20 obtains a sufficiently large Hoff. Hereinafter,
a description thereof is provided.
[0029] FIG. 2 is a diagram showing a general R-H
(resistance-magnetic field) loop. The horizontal axis represents
the magnetic field H and the vertical axis represents the
resistance R. Both the storage layer and the reference layer draw a
hysteresis loop. The width amount of the hysteresis loop of the
storage layer and the reference layer is called coercive force Hc.
In order to reverse the magnetization of only the storage layer in
a stable manner, a magnetic field exceeding the Hc of the storage
layer or corresponding spin torque is applied. Also, the hysteresis
loop of the reference layer is shifted by the magnetic field Hoff.
Basically, the Hoff depends on an antiferromagnetic coupling
magnetic field between the shift canceling layer and the reference
layer, which is weakened by the stray magnetic field from the
storage layer and the shift canceling layer. When the magnetic
field H is small, the magnetization direction of the reference
layer is not reversed, but when the magnetic field H becomes larger
than (Hoff+Hc of the reference layer), the magnetization direction
of the reference layer is reversed. Therefore, in order to operate
the magnetoresistive element normally, a sufficiently large Hoff is
needed and it is necessary to prevent the magnetization of the
reference layer from being reversed by the spin torque applied to
the reference layer. However, as the magnetoresistive element is
refined, the stray magnetic field from the storage layer and the
shift canceling layer increases and Hoff becomes small.
[0030] In general, Hoff is expressed as:
Hoff=Hex-Hs1-Hs2
Hs1>0
Hs2>0.
[0031] where, Hex is an exchange coupling field and
Hex=2Jex/Mst>0.
[0032] Hs1 is a stray magnetic field from the shift canceling
layer, which increases as the saturation magnetization Ms of the
shift canceling layer and the thickness t of the shift canceling
layer increase. Hs2 is a stray magnetic field from the storage
layer and increase as the saturation magnetization Ms of the
storage layer and the thickness t of the storage layer
increase.
[0033] The exchange coupling magnetic field Hex depends on a
material characteristic Jex. Also, the stray magnetic field Hs1
from the shift canceling layer is automatically determined by the
Mst of the shift canceling layer and the size of the
magnetoresistive element. Therefore, in order to improve Hoff, the
stray magnetic field Hs2 from the storage layer needs to be
reduced.
[0034] In order to obtain a sufficiently stable reference layer
characteristic and perform the spin transfer torque magnetization
reversal of the storage layer in a sufficiently stable manner, a
sufficiently large Hoff is needed. In order to maximize Hoff, it is
necessary to reduce the stray magnetic field from the storage layer
and the shift canceling layer. In particular, since the film
thickness of the storage layer is thinner than that of the shift
canceling layer and the center of gravity of the magnetization
amount thereof is closer to the reference layer than that of the
shift canceling layer, reducing the stray magnetic field of the
storage layer is effective in stabilizing the reference layer.
[0035] FIGS. 3 and 4 are diagrams showing the above-mentioned
problems and show simulation results when the storage layer is
formed as a single layer.
[0036] FIG. 3 is a diagram showing the relationship between the
size of the magnetoresistive element and Hoff. With a decreasing
size of the magnetoresistive element, the value of Hoff also
decreases. When the value of the saturation magnetization Ms is
1700 emu/cc, as the size of the magnetoresistive element decreases,
the value of Hoff is far below a target line T.
[0037] FIG. 4 is a diagram showing the relationship between Mst and
Hoff of the storage layer. As Mst of the storage layer increases,
the value of Hoff falls significantly below the target line T.
[0038] In the present embodiment, the value of Hoff is prevented
from becoming small due to the configuration shown in FIG. 1. That
is, in the present embodiment, the storage layer 10 is formed of
the first sub-magnetic layer 11, the second sub-magnetic layer 12,
and the intermediate layer 13 between The first sub-magnetic layer
11 and the second sub-magnetic layer 12 and the magnetization
direction of the first sub-magnetic layer 11 and the magnetization
direction of the second sub-magnetic layer 12 are antiparallel to
each other. Therefore, it is possible to reduce the total stray
magnetic field of the storage layer 10 (ideally, to zero).
[0039] However, since the second sub-magnetic layer 12 is farther
from the reference layer 20 than the first sub-magnetic layer 11,
if Mst of the first sub-magnetic layer 11 and Mst of the second
sub-magnetic layer 12 are equal, the total stray magnetic field
from the storage layer 10 with respect to the reference layer 20
cannot be reduced to zero. In the present embodiment, since the
first sub-magnetic layer 11 has a magnetization amount Mst smaller
than that of the second sub-magnetic layer 12, the total stray
magnetic field from the storage layer 10 with respect to the
reference layer 20 can be reduced to zero. It is preferable that
the film thickness t be the same and the saturation magnetization
Ms of the first sub-magnetic layer 11 be larger than the saturation
magnetization Ms of the second sub-magnetic layer 12 even if both
sub-magnetic layers have the same Mst. This is because the centers
of gravity of the magnetization amounts of the first sub-magnetic
layer 11 and the second sub-magnetic layer 12 become closer to each
other, which makes it easier to control the stray magnetic field
originating therefrom. By using, for example, the Slater-Pauling
rule, the saturation magnetization of the first sub-magnetic layer
11 and the second sub-magnetic layer 12 can be manipulated by using
an alloy using Co and Fe as the main components. Therefore,
according to the present embodiment, even if the magnetoresistive
element is refined, it is possible to effectively suppress the
reversal of the magnetization direction of the reference layer.
[0040] In addition, according to the present embodiment, it is also
possible to reduce the influence of the stray magnetic field from
neighboring cells (surrounding cells). Hereinafter, a description
thereof is provided.
[0041] FIGS. 5 and 6 show simulation results of the influence of
the stray magnetic field from neighboring cells when the storage
layer is formed as a single layer.
[0042] FIG. 5 is a diagram showing the relationship between the
size of the magnetoresistive element and an accumulated stray
magnetic field from the storage layer of neighboring cells. If the
size of the magnetoresistive element reaches the 10 nm generation,
the influence of the accumulated stray magnetic field from
neighboring cells becomes large, which greatly exceeds the limit
value L.
[0043] FIG. 6 is a diagram showing the relationship between the
saturation magnetization Ms of the storage layer and the
accumulated stray magnetic field from the storage layer of
neighboring cells. When the saturation magnetization Ms of the
storage layer increases, the influence of the accumulated stray
magnetic field from neighboring cells becomes large, which greatly
exceeds the limit value L.
[0044] In the present embodiment, as described above, the stray
magnetic field from the storage layer can be reduced and therefore,
the influence of the accumulated stray magnetic field from
neighboring cells can be reduced and an excellent magnetic memory
device can be obtained.
Second Embodiment
[0045] Next, a second embodiment will be described. Incidentally,
basic matters are similar to those in the first embodiment and
thus, the description of matters provided in the first embodiment
is omitted.
[0046] FIG. 7 is a sectional view schematically showing the
configuration of a magnetic memory device according to the present
embodiment and mainly shows the configuration of a magnetoresistive
element.
[0047] In the present embodiment, as shown in FIG. 7, in addition
to a first sub-magnetic layer 11, a second sub-magnetic layer 12
and a first intermediate layer 13, a storage layer (first magnetic
layer) 10 includes a third sub-magnetic layer 14 and a second
intermediate layer 15. More specifically, the second intermediate
layer 15 is provided between the second sub-magnetic layer 12 and
the third sub-magnetic layer 14 and the second sub-magnetic layer
12 is provided between the first sub-magnetic layer 11 and the
third sub-magnetic layer 14. The third sub-magnetic layer 14 has
the magnetization direction antiparallel to the magnetization
direction of the second sub-magnetic layer 12. The first
sub-magnetic layer 11, the second sub-magnetic layer 12, the first
intermediate layer 13, the third sub-magnetic layer 14 and the
second intermediate layer 15 constitute an entire storage layer
100, and the entire storage layer 100 undergoes magnetization
reversal as a whole.
[0048] Each of the first sub-magnetic layer 11, the second
sub-magnetic layer 12, and the third sub-magnetic layer 14 contains
at least cobalt (Co). In addition to cobalt (Co), the first
sub-magnetic layer 11, the second sub-magnetic layer 12, and the
third sub-magnetic layer 14 may further contain iron (Fe) or boron
(B). In the present embodiment, the first sub-magnetic layer 11,
the second sub-magnetic layer 12, and the third sub-magnetic layer
14 are formed of CoFeB.
[0049] Like the first intermediate layer 13, the second
intermediate layer 15 contains at least one element selected from
ruthenium (Ru), rhodium (Rh), osmium (Os), and iridium (Ir). A
specific configuration of the second intermediate layer 15 is the
same as that of the first intermediate layer 13 described in the
first embodiment. The second sub-magnetic layer 12 and the third
sub-magnetic layer 14 are antiferromagnetically coupled via the
second intermediate layer 15.
[0050] Also in the present embodiment, like in the first
embodiment, the first sub-magnetic layer 11 has a magnetization
amount Mst smaller than that of the second sub-magnetic layer 12.
In addition, in the present embodiment, the third sub-magnetic
layer 14 has a magnetization amount Mst smaller than that of the
second sub-magnetic layer 12. With the above configuration, also in
the present embodiment, like in the first embodiment, the total
stray magnetic field from the storage layer 10 with respect to the
reference layer 20 can be reduced to zero and also, the stray
magnetic field of the entire storage layer 100 (the first
sub-magnetic layer 11, the second sub-magnetic layer 12, the first
intermediate layer 13, the third sub-magnetic layer 14 and the
second intermediate layer 15) with respect to neighboring bits can
be reduced to zero. Therefore, even if the magnetoresistive element
is refined, it is possible to effectively suppress the reversal of
the magnetization direction of the reference layer 20. Also in the
present embodiment, like in the first embodiment, the stray
magnetic field from the storage layer 10 can be reduced and
therefore, the influence of the accumulated stray magnetic field
from neighboring cells can be reduced and an excellent magnetic
memory device can be obtained.
[0051] Also in the present embodiment, the sum of the magnetization
amount Mst of the first sub-magnetic layer 11 and the magnetization
amount Mst of the third sub-magnetic layer 14 is preferably equal
to the magnetization amount Mst of the second sub-magnetic layer
12. When the first sub-magnetic layer 11, the second sub-magnetic
layer 12 and the third sub-magnetic layer 14 have the same
saturation magnetization Ms, the sum of the thickness t of the
first sub-magnetic layer 11 and the thickness t of the third
sub-magnetic layer 14 is preferably equal to the thickness t of the
second sub-magnetic layer 12. With the above configuration, it is
possible to reduce the total stray magnetic field generated from
the storage layer 10 to zero. Therefore, in the present embodiment,
it is possible to suppress the influence of the stray magnetic
field from the storage layer 10 more effectively.
[0052] In the first and second embodiments described above, the
so-called bottom-free type magnetoresistive element in which the
storage layer 10 is positioned below the reference layer 20 has
been described, but the configuration of the storage layer 10 in
the first and second embodiments described above can also be
applied to a so-called top-free type magnetoresistive element in
which the storage layer 10 is positioned above the reference layer
20.
[0053] FIG. 8 is a sectional view schematically showing the
configuration of a magnetic memory device using the
magnetoresistive element described above.
[0054] In a semiconductor substrate SUB, a buried gate type MOS
transistor TR is formed. The gate electrode of the MOS transistor
TR is used as a word line WL. A bottom electrode BEC is connected
to one of a source/drain area S/D of the MOS transistor TR and a
source line contact SC is connected to the other of the
source/drain area S/D.
[0055] A magnetoresistive element MTJ is formed on the bottom
electrode BEC and a top electrode TEC is formed on the
magnetoresistive element MTJ. A bit line BL is connected to the top
electrode TEC. A source line SL is connected to the source line
contact SC.
[0056] By applying the magnetoresistive element described above to
the magnetic memory device as shown in FIG. 8, an excellent
magnetic memory device can be obtained.
[0057] 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.
* * * * *