U.S. patent application number 17/405490 was filed with the patent office on 2021-12-09 for tunnel magnetoresistance (tmr) element having cobalt iron and tantalum layers.
This patent application is currently assigned to Allegro MicroSystems, LLC. The applicant listed for this patent is Allegro MicroSystems, LLC. Invention is credited to Paolo Campiglio, Amal Hamdache, Julien Voillot.
Application Number | 20210383953 17/405490 |
Document ID | / |
Family ID | 1000005782751 |
Filed Date | 2021-12-09 |
United States Patent
Application |
20210383953 |
Kind Code |
A1 |
Campiglio; Paolo ; et
al. |
December 9, 2021 |
TUNNEL MAGNETORESISTANCE (TMR) ELEMENT HAVING COBALT IRON AND
TANTALUM LAYERS
Abstract
In one aspect, a tunnel magnetoresistance (TMR) element includes
a magnesium oxide (MgO) layer, a cobalt iron boron (CoFeB) layer in
direct contact with the MgO layer and a cobalt iron (CoFe) layer.
The TMR element also includes a tantalum layer in direct contact
with the CoFeB layer and the CoFe layer.
Inventors: |
Campiglio; Paolo; (Arcueil,
FR) ; Hamdache; Amal; (Limours, FR) ; Voillot;
Julien; (Chilly Mazarin, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Allegro MicroSystems, LLC |
Manchester |
NH |
US |
|
|
Assignee: |
Allegro MicroSystems, LLC
Manchester
NH
|
Family ID: |
1000005782751 |
Appl. No.: |
17/405490 |
Filed: |
August 18, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
16574419 |
Sep 18, 2019 |
11127518 |
|
|
17405490 |
|
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62894114 |
Aug 30, 2019 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01F 10/3254
20130101 |
International
Class: |
H01F 10/32 20060101
H01F010/32 |
Claims
1. A tunnel magnetoresistance (TMR) element, comprising: a free
layer comprising: a nickel iron layer; a first cobalt iron layer in
direct contact with the NiFe layer; a first tantalum layer in
direct contact with the first CoFe layer; and a first cobalt iron
boron in direct contact with the first Ta layer; a magnesium oxide
layer in direct contact with the first CoFeB layer; a reference
layer in direct contact with the MgO layer, the reference layer
comprising: a second CoFeB layer in direct contact with the MgO
layer; a second CoFe layer; a second Ta layer in direct contact
with the second CoFeB layer and the second CoFe layer; a ruthenium
layer in direct contact with the second CoFe layer; a third CoFe
layer in direct contact with the Ru layer; and a platinum manganese
layer in direct contact with the third CoFe layer.
2. The TMR element of claim 1, further comprising a seed layer in
direct contact with the PtMn layer.
3. The TMR element of claim 1, further comprising an electrode
disposed below the seed layer.
4. The TMR element of claim 3, wherein the seed layer is in direct
contact with the electrode.
5. The TMR element of claim 2, further comprising a cap layer in
direct contact with the free layer.
6. The TMR element of claim 5, wherein the NiFe layer is in direct
contact with the cap layer
7. The TMR element of claim 1, further comprising a cap layer in
direct contact with the free layer.
8. The TMR element of claim 7, wherein the NiFe layer is in direct
contact with the cap layer.
9. The TMR element of claim 1, wherein the second CoFe layer and/or
the first CoFeB layer is 1.0 nanometer thick.
10. The TMR element of claim 1, wherein the second CoFeB layer
and/or the third CoFe layer is 0.9 nanometers thick.
11. The TMR element of claim 1, wherein the first and/or second Ta
layer is 0.1 nanometers thick.
12. The TMR element of claim 1, wherein a thickness of the first
and/or second Ta layer is between 0.05 nanometers and 0.3
nanometers.
13. The TMR element of claim 1, wherein the second CoFeB layer is
0.9 nanometers thick, wherein the third CoFe layer is 0.9
nanometers thick, wherein the first CoFeB layer is 1.0 nanometer
thick, and wherein the second CoFe layer is 1.0 nanometer
thick.
14. The TMR element of claim 13, wherein the first and/or second
tantalum layer is 0.1 nanometers thick.
15. The TMR element of claim 13, wherein a thickness of the first
and/or second tantalum layer is between 0.05 nanometers and 0.3
nanometers.
16. The TMR element of claim 15, further comprising a seed layer in
direct contact with the PtMn layer.
17. The TMR element of claim 16, further comprising an electrode
disposed below the seed layer.
18. The TMR element of claim 17, wherein the seed layer is in
direct contact with the electrode.
19. The TMR element of claim 18, further comprising a cap layer in
direct contact with the free layer.
20. The TMR element of claim 19, wherein the NiFe layer is in
direct contact with the cap layer
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of U.S. patent
application Ser. No. 16/574,419, filed Sep. 18, 2019, entitled
"TUNNEL MAGNETORESISTANCE (TMR) ELEMENT HAVING COBALT IRON AND
TANTALUM LAYERS," which claims the benefit of U.S. Provisional
Application No. 62/894,114, filed Aug. 30, 2019, entitled "TUNNEL
MAGNETORESISTANCE (TMR) ELEMENT HAVING COBALT IRON AND TANTALUM
LAYERS." Both applications cited in this paragraph are incorporated
herein by reference in their entirety.
BACKGROUND
[0002] Magnesium oxide (MgO) magnetic tunnel junctions (MTJs) are
widely used spintronics materials due to their high
magneto-resistance ratio (MR %). The reason for this high ratio is
due to the so-called coherent tunneling mechanism through the MgO
barrier which filters in only highly-spin polarized electronic
states. When compared with similar giant magnetoresistance (GMR)
structures, MTJs generally show lower reference stability (lower
spin flop field) and higher free layer anisotropy (higher
coercivity).
SUMMARY
[0003] In one aspect, a tunnel magnetoresistance (TMR) element
includes a magnesium oxide (MgO) layer, a first cobalt iron boron
(CoFeB) layer in direct contact with the MgO layer and a first
cobalt iron (CoFe) layer. The TMR element also includes a first
tantalum layer in direct contact with the first CoFeB layer and the
first CoFe layer.
[0004] The aspect above may include one or more of the following
features. The first CoFeB layer, the first CoFe layer and the first
tantalum layer may be part of a reference layer. The first CoFeB
layer may be about 0.9 nanometers thick. The first CoFe layer may
be about 0.9 nanometers thick. The first tantalum layer may be
about 0.1 nanometers thick. A thickness of the first tantalum layer
may be between 0.05 nanometers and 0.3 nanometers. The first CoFeB
layer, the first CoFe layer and the first tantalum layer may be
part of a free layer. The free layer may include a nickel iron
(NiFe) layer and the NiFe layer may be in direct contact with the
first CoFe layer. The first CoFeB layer may be about 1.0 nanometer
thick. The first CoFe layer may be about 1.0 nanometer thick. The
TMR element may further include a second CoFeB layer in direct
contact with the MgO layer, a second CoFe layer and a second
tantalum layer in direct contact with the second CoFeB layer and
the second CoFe layer. The second CoFeB layer, the second CoFe
layer and the second tantalum layer may be part of a free layer.
The first CoFeB layer may be about 0.9 nanometers thick, the first
CoFe layer may be about 0.9 nanometers thick, the second CoFeB
layer may be about 1.0 nanometer thick and the second CoFe layer
may be about 1.0 nanometer thick. The second tantalum layer may be
about 0.1 nanometers thick. A thickness of the second tantalum
layer may be between 0.05 nanometers and 0.3 nanometers. The TMR
element may further include a bias layer in direct contact with the
free layer. The bias layer may include a third CoFe layer. The TMR
may be single pinned. The TMR may be double pinned.
DESCRIPTION OF THE DRAWINGS
[0005] The foregoing features may be more fully understood from the
following description of the drawings. The drawings aid in
explaining and understanding the disclosed technology. Since it is
often impractical or impossible to illustrate and describe every
possible embodiment, the provided figures depict one or more
illustrative embodiments. Accordingly, the figures are not intended
to limit the scope of the broad concepts, systems and techniques
described herein. Like numbers in the figures denote like
elements.
[0006] FIG. 1 is a block diagram of a prior art example of a
tunneling magnetoresistance (TMR) element;
[0007] FIG. 2 is a block diagram of an example of a TMR element
with a reference layer having a cobalt iron (CoFe) layer and a
tantalum layer;
[0008] FIG. 3 is a block diagram of another example of a TMR
element with a free layer having the cobalt iron (CoFe) layer and
the tantalum layer;
[0009] FIG. 4 is a block diagram of a further example of a TMR
element with the reference layer and the free layer each having the
cobalt iron (CoFe) layer and the tantalum layer;
[0010] FIG. 5 is a block diagram of a prior art example of a TMR
element that is double pinned; and
[0011] FIG. 6 is a block diagram of a still further example of a
TMR element that is double pinned with the reference layer and the
free layer each having the cobalt iron (CoFe) layer and the
tantalum layer.
DETAIL DESCRIPTION
[0012] Described herein are techniques to improve the fabrication
of a tunnel junction in a tunneling magnetoresistance (TMR) element
by having a reference and/or a free layer include a cobalt iron
(CoFe) layer and a tantalum layer. In one example, the techniques
described herein teach an alternative approach to incorporating
cobalt iron boron (CoFeB)/magnesium oxide (MgO)/CoFeB layers into a
tunnel junction to reduce the impact of a cubic structure with a
hexagonal structure.
[0013] Referring to FIG. 1, an illustrative TMR element 100 can
have a stack 102 of layers 106, 110, 114, 118, 122, 126, 128, 132
indicative of one pillar of a multi-pillar TMR element. Generally,
the layer 106 is a seed layer (e.g., a copper nickel (CuN) layer)
with the layer 110 located on the seed layer 106. The layer 110
includes platinum manganese (PtMn) or iridium manganese (IrMn), for
example. The layer 114 is located on the layer 110 and the layer
118 is located on the layer 114. In one example, the layer 114
includes cobalt iron (CoFe) and the layer 118 is a spacer layer and
includes ruthenium (Ru). On the layer 118, a magnesium oxide (MgO)
layer 126 is sandwiched between two cobalt iron boron (CoFeB)
layers 122, 128. A cap layer 132 (e.g., tantalum (Ta)) is located
on the CoFeB layer 128. The layer 114 is a single layer pinned
layer that is magnetically coupled to the layer 110. The physical
mechanism that is coupling layers 110 and 114 together is sometimes
called an exchange bias.
[0014] A free layer 130 includes the CoFeB layer 128. In some
examples, the free layer 130 may include an additional layer of
nickel iron (NiFe) (not shown) and a thin layer of tantalum (not
shown) between the CoFeB layer 128 and the NiFe layer.
[0015] It will be understood that a driving current running through
the TMR element 100 runs through the layers of the stack, running
between seed and cap layers 106 and 132, i.e., perpendicular to a
surface of a bottom electrode 104. The TMR element 100 can have a
maximum response axis that is parallel to the surface of the bottom
electrode 104 and that is in a direction 129, and also parallel to
the magnetization direction of the reference layer 150, comprised
of layers 110, 114, 118, and 122, most notably in the layer CoFeB
122.
[0016] The TMR element 100 has a maximum response axis (maximum
response to external fields) aligned with the arrow 129, i.e.,
perpendicular to bias directions experienced by the free layer 130,
and parallel to magnetic fields of the reference layer 150, notably
pinned layer 122. Also, in general, it is rotations of the magnetic
direction of the free layer 130 caused by external magnetic fields
that result in changes of resistance of the TMR element 100, which
may be due to a change in angle or a change in amplitude if an
external bias is present because the sum vector of the external
field and the bias is causing a change in the angle between the
reference and free layers.
[0017] The coherent tunneling mechanism through a magnesium oxide
(MgO) barrier (the layer 126) is due to symmetry factors and, as
such, it is essential that the MgO barrier and the neighboring
CoFeB layers 122, 128 crystallize in a cubic, epitaxial fashion. On
the other hand, the non-active part of the MTJs is based on the
hexagonal symmetry typical of the (111) plane of face-centered
cubic structures. Thus, inserting cubic CoFeB/MgO/CoFeB layers 122,
126, 128 in a hexagonal multilayer must be performed carefully in
order not to degrade the response typical of a full-hexagonal
system (e.g., a giant magnetoresistance (GMR)).
[0018] In the reference layer 150, the main problem of the cubic
structure comes from the fact that CoFeB layer 122 is coupled with
another CoFe layer 114 through the Ru spacer layer 118. The
different crystal symmetry makes this coupling less effective than
in an all-hexagonal structure.
[0019] Referring to FIG. 2, to circumvent the difference in crystal
symmetry in TMR element 100 (FIG. 1), a TMR element 200 replaces
the CoFeB layer 122 (FIG. 2) with a tri-layer that includes a CoFe
layer 222, a Ta layer 226 and a CoFeB layer 230. The layers 122,
230 are separated with a thin Ta spacer, which is thin enough to
decouple the crystal structures without breaking the ferromagnetic
coupling between CoFe and CoFeB. A reference layer 250 includes
layers 110, 114, 118, 222, 226, 230.
[0020] In one example, the CoFe layer 222 and the CoFeB layer 230
are each about 0.9 nanometers thick. In one example, the Ta layer
226 is about 0.1 nanometers thick. In another example, the Ta layer
226 ranges from 0.05 nanometers to 0.3 nanometers.
[0021] Referring to FIGS. 1 and 3, in the free layer 130, the cubic
structure of the CoFeB layer 128 causes a higher coercivity in a
response. To reduce the coercivity, a TMR element 300 replaces the
CoFeB layer 128 with a quad-layer that includes a CoFeB layer 328,
a Ta layer 336, a CoFe layer 342 and a nickel iron (NiFe) 346 to
form a free layer 330. In particular, the thickness of CoFeB 328 is
reduced from the CoFeB layer 128 as much as possible to maintain a
good epitaxial structure in the active area. For example, the CoFeB
layer 128 is about 2.5 nanometers thick while the CoFeB 328 is
about 1.0 nanometers thick. The CoFe 342 coupled with a
magnetically softer material of the NiFe layer 346 helps the
rotation of the CoFeB 328 by reducing coercivity. In one example,
the CoFe layer 342 is about 1.0 nanometers thick. In one example,
the Ta layer 336 is about 0.1 nanometers thick. In another example,
the Ta layer 336 ranges from 0.05 nanometers to 0.3 nanometers.
[0022] Referring to FIG. 4, both CoFeB layers 122, 128 (FIG. 1) may
also be replaced. For example, a TMR element 400 includes the
reference layer 250 of FIG. 2 and the free layer 330 of FIG. 3.
[0023] Referring to FIG. 5, a TMR element 500 is the same as TMR
element 100 (FIG. 1) except, for example, the TMR includes a bias
layer 590. The CoFeB 528 forms a free layer 530. The bias layer 590
includes a Ru layer 532 located on the CoFeB layer 528, a CoFe
layer located on the Ru layer 532 and a PtMn layer 536 located on
the CoFe layer 534.
[0024] The TMR element 500 is double pinned, i.e., it has two
pinning layers 536, 110. A pinned layer structure 534, 532, 528 is
magnetically coupled to the pinning layer 536. The single layer
pinned layer 114 is magnetically coupled to the pinning layer 110.
With zero external magnetic field, the free layer 530 takes on a
magnetic alignment parallel to the bias layer 590, with direction
(ferromagnetic or antiferromagnetic coupling) determined by
thickness and material of the spacer layer 532. Thus, double pinned
means that the free layer 530 is stabilized by intra-stack bias
from the bias layer 590. The free layer 530 may go parallel or
antiparallel to the reference layer 150 depending on the direction
of the external field 129.
[0025] Referring to FIG. 6, the techniques described in FIGS. 2 to
4 may also be applied to the TMR element 500 (FIG. 5). For example,
in a TMR element 600, the free layer 530 (FIG. 5) is replaced with
the free layer 330 and the reference layer 150 (FIG. 5) is replaced
with the reference layer 250.
[0026] Elements of different embodiments described herein may be
combined to form other embodiments not specifically set forth
above. Various elements, which are described in the context of a
single embodiment, may also be provided separately or in any
suitable subcombination. Other embodiments not specifically
described herein are also within the scope of the following
claims.
* * * * *