U.S. patent application number 11/876916 was filed with the patent office on 2008-03-06 for magnetoresistance effect device.
This patent application is currently assigned to ANELVA CORPORATION. Invention is credited to David D. Djayaprawira, Hiroki Maehara, Motonobu Nagai, Koji Tsunekawa, Naoki Watanabe, Shinji Yamagata, Shinji Yuasa.
Application Number | 20080055793 11/876916 |
Document ID | / |
Family ID | 35326492 |
Filed Date | 2008-03-06 |
United States Patent
Application |
20080055793 |
Kind Code |
A1 |
Djayaprawira; David D. ; et
al. |
March 6, 2008 |
MAGNETORESISTANCE EFFECT DEVICE
Abstract
A magnetoresistance effect device including a multilayer
structure having a pair of ferromagnetic layers and a barrier layer
positioned between them, wherein at least one ferromagnetic layer
has at least the part contacting the barrier layer made amorphous
and the barrier layer is an MgO layer having a highly oriented
texture structure.
Inventors: |
Djayaprawira; David D.;
(Tama-shi, JP) ; Tsunekawa; Koji; (Hachiooji-shi,
JP) ; Nagai; Motonobu; (Akishima-shi, JP) ;
Maehara; Hiroki; (Mitaka-shi, JP) ; Yamagata;
Shinji; (Fuchu-shi, JP) ; Watanabe; Naoki;
(Nishi-Tokyo-shi, JP) ; Yuasa; Shinji;
(Tsukuba-shi, JP) |
Correspondence
Address: |
BUCHANAN, INGERSOLL & ROONEY PC
POST OFFICE BOX 1404
ALEXANDRIA
VA
22313-1404
US
|
Assignee: |
ANELVA CORPORATION
Fuchu-shi
JP
NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND
TECHNOLOGY
Tsukuba-shi
JP
|
Family ID: |
35326492 |
Appl. No.: |
11/876916 |
Filed: |
October 23, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11219866 |
Sep 7, 2005 |
|
|
|
11876916 |
Oct 23, 2007 |
|
|
|
Current U.S.
Class: |
360/324.2 ;
257/E43.004; 257/E43.006 |
Current CPC
Class: |
H01F 10/3204 20130101;
H01L 43/12 20130101; H01L 43/08 20130101; B82Y 40/00 20130101; G11C
11/16 20130101; B82Y 25/00 20130101; H01F 41/307 20130101; G11C
11/161 20130101; C23C 14/081 20130101; H01F 10/3254 20130101; C23C
14/34 20130101; H01F 41/18 20130101 |
Class at
Publication: |
360/324.2 |
International
Class: |
G11B 5/33 20060101
G11B005/33 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 7, 2004 |
JP |
2004-259280 |
Claims
1. A magnetoresistance effect device including a multilayer
structure comprised of a pair of ferromagnetic layers and a barrier
layer positioned between them, wherein at least a part of at least
one of said ferromagnetic layers contacting said barrier layer is
amorphous, and said barrier layer is an MgO layer having a single
crystal structure.
2. A magnetoresistance effect device including a multilayer
structure comprised of a pair of ferromagnetic layers and a barrier
layer positioned between them, wherein at least a part of at least
one of said ferromagnetic layers contacting said barrier layer is
amorphous, and said barrier layer is an MgO layer having a highly
oriented fiber-texture structure.
3. The magnetoresistance effect device as set forth in claim 1,
wherein said MgO layer is a single crystal layer formed by a
sputtering method.
4. The magnetoresistance effect device as set forth in claim 2,
wherein said MgO layer is a highly oriented fiber-texture layer
formed by a sputtering method.
5. The magnetoresistance effect device as set forth in claim 3,
wherein said MgO layer is a single crystal layer formed using an
MgO target and a sputtering method.
6. The magnetoresistance effect device as set forth in claim 4,
wherein said MgO layer is a a highly oriented fiber-texture layer
formed using an MgO target and a sputtering method.
7. The magnetoresistance effect device as set forth in claim 1,
wherein said ferromagnetic layers are CoFeB layers.
8. The magnetoresistance effect device as set forth in claim 2,
wherein said ferromagnetic layers are CoFeB layers.
9. A magnetoresistance effect device comprising: a barrier layer
having fiber-texture with a crystal, and a first and second
ferromagnetic layers positioned at both sides of said barrier
layer.
10. The magnetoresistance effect device as set forth in claim 9,
wherein said barrier layer includes Mg an O.
11. The magnetoresistance effect device as set forth in claim 10,
wherein both or either of said first and second ferromagnetic
layers includes CoFeB.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/219,866 filed on Sep. 7, 2005, which claims priority to
Japanese Application No. 2004-259280 filed on Sep. 7, 2004, the
entire contents of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a magnetoresistance effect
device and a method of production of the same, more particularly
relates to a magnetoresistance effect device fabricated utilizing a
simple sputtering film-formation method and having an extremely
high magnetoresistance ratio and a method of production of the
same.
[0004] 2. Description of the Related Art
[0005] In recent years, as nonvolatile memories, magnetic memory
devices called "magnetoresistive random access memories (MRAMs)"
have come into attention and have started entering the commercial
stage. MRAMs are simple in structure, so ultra-high density
integration to the gigabit level is easy. In MRAMs, the relative
orientation of the magnetic moment is utilized to create the
storage action. As the result, the number of possible
re-writability is extremely high and the operating speed can be
reduced to the nanosecond level.
[0006] FIG. 4 shows the structure of the MRAM. In the MRAM 101, 102
is a memory device, 103 a word line, and 104 a bit line. The large
number of memory devices 102 are arranged at intersecting positions
of the plurality of word lines 103 and plurality of bit lines 104
and are arranged in a lattice-like positional relationship. Each of
the large number of memory devices 102 stores 1 bit of
information.
[0007] Each memory device 102 of the MRAM 101, as shown in FIG. 5,
is comprised of a magnetoresistance effect device for storing 1 bit
of information, that is, a tunneling magnetoresistance (TMR) device
110, and a transistor 106 having a switching function at the
intersecting position of the word line 103 and bit line 104. The
main element in the memory device 102 is the TMR device 110. The
basic structure of the TMR device, as shown in FIG. 6, is a
three-layer structure comprised of a bottom ferromagnetic metal
electrode (bottom ferromagnetic layer) 107/tunnel barrier layer
108/top ferromagnetic metal electrode (top ferromagnetic layer)
109. The TMR device 110 is therefore comprised of a pair of
ferromagnetic layers 107 and 109 and a tunnel barrier layer 108
positioned between them.
[0008] In the TMR device 110, as shown in FIG. 6, the required
voltage is applied across the ferromagnetic layers 107 and 109 at
the two sides of the tunnel barrier layer 108 to cause the flow of
a predetermined current. In that state, an external magnetic field
is applied. When the directions of magnetization of the
ferromagnetic layers 107 and 109 are parallel and the same (called
the "parallel state"), the electrical resistance of the TMR device
becomes the minimum ((A) state: resistance value R.sub.P), while
when the directions of magnetization of the ferromagnetic layers
are parallel but opposite (called the "anti-parallel state"), the
electrical resistance of the TMR device becomes the maximum ((B)
state: resistance value R.sub.A). Therefore, the TMR device 110 can
take a parallel state and an anti-parallel state induced by an
external magnetic field and store information as a change in
resistance value.
[0009] To realize a practical gigabit class MRAM using the above
TMR device, the difference between the resistance value R.sub.P of
the "parallel state" and resistance value R.sub.A of the
"anti-parallel state" has to be large. As the indicator, the
magnetoresistance ratio (MR ratio) is used. The MR ratio is defined
as "(R.sub.A-R.sub.P)/R.sub.P".
[0010] To raise the MR ratio, in the past, the electrode materials
of the ferromagnetic metal electrodes (ferromagnetic layers) have
been optimized, the method of production of the tunnel barrier
layers have been modified, etc. For example, Japanese Patent
Publication (A) No. 2003-304010 and Japanese Patent Publication (A)
No. 2004-63592 propose several optimum examples of use of
Fe.sub.xCo.sub.yB.sub.z etc. for the material of the ferromagnetic
metal electrode.
[0011] The MR ratio of the TMR device disclosed in Japanese Patent
Publication (A) No. 2003-304010 and Japanese Patent Publication (A)
No. 2004-63592 is lower than about 70%. Further improvement of the
MR ratio is necessary.
[0012] Further, recently, regarding a single crystal TMR thin film
using an MgO barrier layer, there has been a report of using
molecular beam epitaxy (MBE) and an ultra-high vacuum evaporation
system to fabricate an Fe/MgO/Fe single crystal TMR thin film and
obtain an MR ratio of 88% (Yuasa, Shinji et al., "High Tunnel
Magnetoresistance at Room Temperature in Fully Epitaxial
Fe/MgO/Tunnel Junctions due to Coherent Spin-Polarized Tunneling",
Nanoelectronic Institute, Japanese Journal of Applied Physics,
issued Apr. 2, 2004, Vol. 43, No. 4B, p. L588-L590). This TMR thin
film has a completely epitaxial single crystal structure.
[0013] Fabrication of the single crystal TMR thin film used for the
single crystal MgO barrier layer described in the above publication
requires use of an expensive MgO single crystal substrate. Further,
epitaxial growth of an Fe film by an expensive MBE device,
formation of an MgO film by ultrahigh vacuum electron beam
evaporation and other sophisticated film deposition technology are
required. There is the problem that the longer the film deposition
time, the less suitable the process for mass production.
OBJECTS AND SUMMARY
[0014] An object of the present invention is to provide a
magnetoresistance effect device having a high MR ratio, improving
the mass producibility, and improving the practicality and a method
of production of the same.
[0015] One embodiment of the magnetoresistance effect device and
method of production of the same according to the present invention
are configured as follows to achieve the above object.
[0016] This magnetoresistance effect device includes a multilayer
structure comprised of a pair of ferromagnetic layers and a barrier
layer positioned between them, wherein at least the part of at
least one of the ferromagnetic layers contacting the barrier layer
is amorphous, and the barrier layer is an MgO layer having a single
crystal or highly oriented fiber-texture structure. Here, the
fiber-texture structure corresponds to assembly of poly-crystalline
grains, in which the crystal structure is continuous across the
layer thickness. However, in the longitudinal (in-plane) direction
the grain boundaries can be observed. Highly oriented means that
the crystallographic orientation in the film thickness direction is
very uniform, while there is no specific crystallographic
orientation in the plane direction. Preferably, the (001) crystal
plane of MgO barrier layer lies parallel to the ferromagnetic layer
surface. Here, the MgO layer can be either single crystal or highly
oriented fiber-texture structure.
[0017] According to above magnetoresistance effect device, since
the barrier layer has a single crystal or highly oriented
fiber-texture structure, the flow of current between the
ferromagnetic layers can be made straight and the MR ratio can be
made an extremely high value.
[0018] In the magnetoresistance effect device, preferably the MgO
layer is a single crystal layer formed by the sputtering method.
However, an MgO layer with highly oriented fiber-texture structure
also yield excellent properties. According to this configuration,
the intermediate barrier layer can be produced simply. This is
suitable for mass production.
[0019] In the magnetoresistance effect device, preferably the MgO
layer is a single crystal layer formed using an MgO target and the
sputtering method. The MgO layer can also be a highly oriented
fiber-texture structure.
[0020] In the magnetoresistance effect device, preferably the
ferromagnetic layers are CoFeB layers.
[0021] The method of production of a magnetoresistance effect
device is a method of production of a magnetoresistance effect
device including a multilayer structure comprised of a pair of
ferromagnetic layers and a barrier layer positioned between them,
comprising forming at least one ferromagnetic layer so that at
least at least the part contacting the barrier layer is amorphous
and forming the barrier layer having a single crystal or highly
oriented fiber-texture structure by using the sputtering method.
Further, in the method of production of a magnetoresistance effect
device, preferably the MgO layer is formed by RF magnetron
sputtering using an MgO target.
[0022] According to the present invention, since the tunnel barrier
layer forming the intermediate layer of the TMR device or other
magnetoresistance effect device is an MgO layer having a single
crystal or highly oriented fiber-texture structure, the MR ratio
can be made extremely high. When using this as a memory device of
an MRAM, a gigabit class ultra-high integrated MRAM can be
realized. Further, by forming the a single crystal or highly
oriented fiber-texture MgO layer by the sputtering method, it is
possible to fabricate a magnetoresistance effect device suitable
for mass production and having high practical applicability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] These and other objects and features of the present
invention will become clearer from the following description of the
preferred embodiments given with reference to the attached
drawings, wherein:
[0024] FIG. 1 is a view of the structure of a magnetoresistance
effect device (TMR device) according to an embodiment of the
present invention,
[0025] FIG. 2 is a plan view of a system for fabricating a
magnetoresistance effect device (TMR device) according to an
embodiment of the present invention,
[0026] FIG. 3 is a graph of the pressure dependency of magnetic
characteristics of a magnetoresistance effect device (TMR device)
according to an embodiment of the present invention,
[0027] FIG. 4 is a partial perspective view of the principal
structure of an MRAM,
[0028] FIG. 5 is a view of the structure of a memory device of an
MRAM, and
[0029] FIG. 6 is a view for explaining the characteristics of a TMR
device.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Below, a preferred embodiment of the present invention will
be explained with reference to the attached drawings.
[0031] FIG. 1 shows an example of the multilayer structure of a
magnetoresistance effect device according to the present invention,
in particular shows the multilayer structure of a TMR device.
According to this TMR device 10, a substrate 11 is formed with a
multilayer film comprised of for example nine layers forming the
TMR device 10. In this nine-layer multilayer film, magnetic films
etc. are stacked from the bottommost first layer to the topmost
ninth layer with "Ta", "PtMn", "70CoFe", "Ru", "CoFeB", "MgO",
"CoFeB", "Ta", and "Ru" in that order. The first layer (Ta:
tantalum) is an undercoat layer, while the second layer (PtMn) is
an anti-ferromagnetic layer. The layers from the third layer to the
fifth layer (70 CoFe, Ru, CoFeB) form fixed magnetization layers.
The substantive fixed magnetization layer is the fifth layer
ferromagnetic layer comprised of "CoFeB". The sixth layer (MgO:
magnesium oxide) is an insulating layer forming a tunnel barrier
layer. The seventh layer (CoFeB) is a ferromagnetic layer forming a
free magnetization layer. The sixth layer (MgO) forms an
intermediate layer between the pair of ferromagnetic layers (CoFeB)
arranged at the top and bottom. The eighth layer (Ta: tantalum) and
the ninth layer (Ru: ruthenium) form hard mask layers. The fixed
magnetization layer (fifth layer "CoFeB"), the tunnel barrier layer
(sixth layer "MgO"), and free magnetization layer (seventh layer
"CoFeB") form the TMR device part 12 in the strict sense as a basic
structure. The fixed magnetization layer fifth layer "CoFeB" and
the free magnetization layer seventh layer "CoFeB" are known as
amorphous ferromagnetic bodies in the as-deposited state. The
tunnel barrier layer constituted by the MgO layer is formed so as
to have a a single crystal or highly oriented fiber-texture
structure across the thickness direction.
[0032] Note that, in FIG. 1, the figures in parentheses at the
layers indicate the thicknesses of the layers in units of "nm
(nanometers)". The thicknesses are examples. The invention is not
limited to them.
[0033] Next, referring to FIG. 2, a system and method for producing
a TMR device 10 having the above multilayer structure will be
explained. FIG. 2 is a schematic plan view of a system for
producing a TMR device 10. This system can produce a multilayer
film including a plurality of magnetic fields and is a sputtering
film-forming system for mass production.
[0034] The magnetic multilayer film fabrication system 20 shown in
FIG. 2 is a cluster type system provided with a plurality of
film-forming chambers using the sputtering method. In this system
20, a transport chamber 22 provided with not shown robot loaders at
the center position. The transport chamber 22 of the magnetic
multilayer film fabrication system 20 is provided with two
load/unload chambers 25 and 26 which load/unload substrates
(silicon substrates) 11. These load/unload chambers 25 and 26 are
used alternately to enable fabrication of a multilayer film with a
good productivity.
[0035] In this magnetic multilayer film fabrication system 20, the
transport chamber 22 is surrounded with, for example, three
film-forming chambers 27A, 27B, and 27C and one etching chamber 28.
In the etching chamber 28, the required surface of a TMR device 10
is etched. At the interface with each chamber, a gate valve 30
separating the two chambers and able to open/close the passage
between them is provided. Note that each chamber is also provided
with a not shown evacuation mechanism, gas introduction mechanism,
power supply mechanism, etc.
[0036] The film-forming chambers 27A, 27B, and 27C of the magnetic
multilayer film fabrication system 20 use the sputtering method to
deposit the above-mentioned magnetic films on the substrate 11
successively from the bottom. For example, the ceilings of the
film-forming chambers 27A, 27B, and 27C are provided with four or
five targets (31, 32, 33, 34, 35), (41, 42, 43, 44, 45), and (51,
52, 53, 54) arranged on suitable circumferences. Substrate holders
positioned coaxially with the circumferences carry substrates on
them.
[0037] In the above explanation, for example, the target 31 is made
of "Ta", while the target 33 is made of "CoFeB". Further, the
target 41 is made of "PtMn", the target 42 is made of "CoFe", and
the target 43 is made of "Ru". Further, the target 51 is made of
"MgO".
[0038] The above plurality of targets are provided suitably
inclined so as to suitably face the substrate so as to efficiently
deposit magnetic films of suitable formulations, but they may also
be provided in states parallel to the substrate surface. Further,
they are arranged to enable the plurality of targets and the
substrate to relatively rotate. In the system 20 having this
configuration, the film-forming chambers 27A, 27B, and 27C are
utilized to successively form films of the magnetic multilayer film
shown in FIG. 1 on the substrate 11 by the sputtering method.
[0039] The film-forming conditions of the TMR device part 12
forming the portion of the main elements of the present invention
will be explained. The fixed magnetization layer (fifth layer
"CoFeB") is formed using a CoFeB 60/20/20 at % target at an Ar
pressure of 0.03 Pa, a magnetron DC sputtering, and a sputtering
rate of 0.64 .ANG./sec. Next, the tunnel barrier layer (sixth layer
"MgO") is formed using a MgO 50/50 at % target, a sputter gas of
Ar, and a pressure changed in the range of 0.01 to 0.4 Pa.
Magnetron RF sputtering is used to form the film at a sputtering
rate of 0.14 .ANG./sec. Next, the free magnetization layer (seventh
layer "CoFeB") is formed under the same film-forming conditions as
the fixed magnetization layer (fifth layer "CoFeB").
[0040] In this embodiment, the film-forming speed of the MgO film
was 0.14 .ANG./sec, but the film may also be formed at a speed in
the range of 0.01 to 1.0 .ANG./sec.
[0041] The TMR device 10 finished being formed with films by
sputtering in the film-forming chambers 27A, 27B, and 27C is
annealed in a heat treatment oven. At this time, the annealing
temperature is for example about 300.degree. C. The annealing is
performed in a magnetic field of for example 8 kOe (632 kA/m) for
example for 4 hours. Due to this, the PtMn of the second layer of
the TMR device 10 is given the required magnetization
alignment.
[0042] FIG. 3 shows the results of measurement of the magnetic
characteristics of MgO. A high MR ratio is obtained over the entire
measured range. In particular, in the region of a pressure of 0.05
Pa to 0.2 Pa, a high MR ratio was obtained. In the region of a
pressure of 0.05 Pa or more, the pressure on the substrate
increases and the ion impact falls believed resulting in a
reduction in film defects. With a pressure of 0.05 Pa or more, the
MR ratio increases and the tunnel resistance value (R.sub.A)
increases. This is believed to be due to formation of a good single
crystal or highly oriented fiber-texture film and as a result the
leakage current of the film is decreased. On the other hand, in the
region of 0.05 Pa or less, the tunnel resistance value (R.sub.A)
falls and the MR ratio also falls. This is believed to be because
the ion impact increases--resulting in an increase in defects of
the MgO film. A cross-section of a sample was observed by a
transmission electron microscope (TEM). As a result, it was
observed that, over the entire range of the measured pressure, the
MgO film had a single crystal or highly oriented fiber-texture
structure over the entire layer from the bottom interface to the
top interface and that the (001) plane of the MgO single crystal or
highly oriented fiber-texture was oriented parallel to the
interfaces. Further, it was observed that the CoFeB layer was
formed in an amorphous state prior to annealing.
[0043] This sample was formed by sandwiching the two sides of the
MgO layer with ferromagnetic layers of amorphous CoFeB. But even if
only one of the ferromagnetic layers was amorphous CoFeB, similar
results are observed. Preferably, during deposition of MgO layer
the bottom ferromagnetic layer was amorphous. Although the CoFeB
ferromagnetic layers were initially amorphous prior to annealing,
the CoFeB ferromagnetic layers became crystallized or partly
crystallized when subjected to annealing at temperature higher than
300.degree. C. for a few hours. In this case, the MgO layer,
sandwiched with crystallized CoFeB ferromagnetic layers, showed a
single crystal or highly-oriented fiber texture with the (001)
crystal plane of MgO barrier layer lies parallel to the
ferromagnetic layer surface. Compared with the samples annealed at
300.degree. C., the samples annealed at higher temperature did not
show degradation of magnetic and magnetoresistance properties (MR
ratio, R.sub.A etc.).
[0044] On the other hand, when forming CoFe having a
polycrystalline structure as the ferromagnetic layer at the two
sides of the MgO layer, a large number of dislocations are seen in
the MgO layer, a good single crystal or highly oriented
fiber-texture film cannot be obtained, and the magnetoresistance
characteristics are low.
[0045] At this time, as explained above, an MgO target 51 was used
as the target. Preferably, the RF (high frequency) magnetron
sputtering method was used. Note that the reactive sputtering
method may also be used to sputter the Mg target by a mixed gas of
Ar and O.sub.2 and form an MgO film.
[0046] Note that above, the MgO layer is a single crystal or highly
oriented fiber-texture throughout the layer and has a single
crystal or highly oriented fiber-texture structure with an (001)
plane oriented parallel to the interfaces. Further, the pair of
ferromagnetic layers forming the TMR device part 12 may also be,
instead of the CoFeB having an amorphous state, CoFeTaZr, CoTaZr,
CoFeNbZr, CoFeZr, FeTaC, FeTaN, FeC, or other ferromagnetic layers
having an amorphous state.
[0047] The configurations, shapes, sizes (thicknesses), and layouts
explained in the above embodiments are only shown schematically to
an extent enabling the present invention to be understood and
worked. Further, the numerical values and compositions (materials)
are only shown for illustration. Therefore, the present invention
is not limited to the explained embodiments and can be changed in
various ways within the scope of the technical idea shown in the
claims.
[0048] The present invention contains subject matter related to
Japanese Patent Application No. 2004-259280 filed on filed in the
Japan Patent Office on Sep. 7, 2004, the entire contents of which
being incorporated herein by reference.
* * * * *