U.S. patent application number 11/757141 was filed with the patent office on 2007-09-27 for magnetic random access memory, magnetic random access memory manufacturing method, and magnetic random access memory write method.
Invention is credited to Keiji Hosotani.
Application Number | 20070224707 11/757141 |
Document ID | / |
Family ID | 37070201 |
Filed Date | 2007-09-27 |
United States Patent
Application |
20070224707 |
Kind Code |
A1 |
Hosotani; Keiji |
September 27, 2007 |
MAGNETIC RANDOM ACCESS MEMORY, MAGNETIC RANDOM ACCESS MEMORY
MANUFACTURING METHOD, AND MAGNETIC RANDOM ACCESS MEMORY WRITE
METHOD
Abstract
A magnetic random access memory includes first and second write
wirings, the second write wiring having first and second crossing
angles formed by crossing the first write wiring, a first
magnetoresistive element having a first axis of easy magnetization
directed to a side of the first crossing angle and having a first
recording layer including first and second ferromagnetic layers and
a first nonmagnetic layer, and a second magnetoresistive element
being electrically connected to the first magnetoresistive element,
having a second axis of easy magnetization directed to a side of
the second crossing angle, and having a second recording layer
including third and fourth ferromagnetic layers and a second
nonmagnetic layer, wherein in a write operation, magnetizations in
the first and second recording layers execute a toggle operation by
using the first and second write wirings.
Inventors: |
Hosotani; Keiji; (Tokyo,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Family ID: |
37070201 |
Appl. No.: |
11/757141 |
Filed: |
June 1, 2007 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11200105 |
Aug 10, 2005 |
7239545 |
|
|
11757141 |
Jun 1, 2007 |
|
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Current U.S.
Class: |
438/3 |
Current CPC
Class: |
G11C 11/15 20130101 |
Class at
Publication: |
438/003 |
International
Class: |
H01L 21/335 20060101
H01L021/335 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 31, 2005 |
JP |
2005-100972 |
Claims
1. A magnetic random access memory manufacturing method comprising:
forming a first write wiring; forming a first electrode above the
first write wiring; forming a first material layer on the first
electrode; processing the first material layer to form a first
magnetoresistive element having a first axis of easy magnetization
directed in a first direction; forming a interlayer around the
first magnetoresistive element; forming a second electrode on the
first magnetoresistive element; forming a second material layer on
the second electrode; processing the second material layer to form
a second magnetoresistive element having a second axis of easy
magnetization directed in a second direction different from the
first direction; and forming a second write wiring above the second
magnetoresistive element.
2. The method according to claim 1, wherein the second
magnetoresistive element and the second write wiring are connected
directly or through a contact.
3. A magnetic random access memory manufacturing method comprising:
forming a first write wiring; forming a first electrode above the
first write wiring; forming a first material layer, a contact
layer, and a second material layer sequentially on the first
electrode; processing the first material layer, the contact layer,
and the second material layer at once to form a first
magnetoresistive element, a contact, and a second magnetoresistive
element; and forming a second write wiring above the second
magnetoresistive element.
4. The method according to claim 3, wherein the second
magnetoresistive element and the second write wiring are connected
directly or through a contact.
5. A magnetic random access memory manufacturing method comprising:
forming a first write wiring and a first magnetoresistive element
above a first substrate; forming a contact connected to the first
magnetoresistive element; forming a second write wiring and a
second magnetoresistive element above a second substrate different
from the first substrate; and bonding the first substrate and
second substrate to electrically connect the first magnetoresistive
element and second magnetoresistive element through the contact.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a Division of and claims the benefit of
priority under 35 USC .sctn.120 from U.S. Ser. No. 11/200,105,
filed Aug. 10, 2005, and claims the benefit of priority under 35
U.S.C. .sctn.119 from Japanese patent Application No. 2005-100972,
filed Mar. 31, 2005, 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 magnetic random access
memory (MRAM) using a magnetoresistive effect, magnetic random
access memory manufacturing method, and magnetic random access
memory write method.
[0004] 2. Description of the Related Art
[0005] Magnetic random access memories (MRAMs) using a tunneling
magnetoresistive (TMR) effect have been proposed recently as
information storage elements (e.g., Roy Scheuerlein et al., "A 10
ns Read and Write Non-Volatile Memory Array Using a Magnetic Tunnel
Junction and FET Switch in each Cell", ISSCC 2000 Technical Digest,
p. 128).
[0006] A memory cell of a magnetic random access memory comprises
an upper write wiring, lower write wiring, and magnetic tunnel
junction (MTJ) element provided between the upper and lower write
wirings. The MTJ element has a fixed layer, recording layer, and
tunnel barrier layer sandwiched between the fixed layer and the
recording layer.
[0007] In a so-called toggle cell, the direction of axis of easy
magnetization of the MTJ element tilts 45.degree. with respect to
the running direction of the upper or lower write wiring. The
recording layer of the MTJ element has a three-layer structure of
ferromagnetic layer/nonmagnetic layer/ferromagnetic layer. The two
ferromagnetic layers are anti-ferromagnetically coupled through the
nonmagnetic layer.
[0008] In a write operation of such a toggle cell, first, current
is sequentially supplied to the upper and lower write wirings.
Then, supply of the currents is stopped in the same order as that
of its start. With this process, magnetization reversal occurs
regardless of the initial magnetization state. Hence, before the
write, data of the MTJ element is read out to determine the current
cell state. After that, the write operation is started as
needed.
[0009] The resistance state of the MTJ element changes between "1"
and "0" depending on whether the magnetization direction of the
fixed layer and that of the ferromagnetic layer of the recording
layer located on the fixed layer side is parallel or anti-parallel.
The read operation can be executed by extracting the resistance
state.
[0010] The toggle cell is hardly affected by a variation in
magnetization reversal threshold value of each MTJ element in
principle and can advantageously be used for increasing the scale
of magnetic random access memories. However, it is not yet the
standard technique of magnetic random access memories because of
problems such as the large write current and low write speed.
BRIEF SUMMARY OF THE INVENTION
[0011] According to a first aspect of the present invention, there
is provided a magnetic random access memory comprising a first
write wiring which runs in a first direction, a second write wiring
which runs in a second direction different from the first direction
and has a first crossing angle and second crossing angle formed by
crossing the first write wiring, the first crossing angle and
second crossing angle being located on both sides of the first
write wiring serving as a boundary, a first magnetoresistive
element which is arranged at an intersection of the first write
wiring and the second write wiring between the first write wiring
and the second write wiring, has a first axis of easy magnetization
directed to a side of the first crossing angle, and has a first
fixed layer, a first recording layer, and a first tunnel barrier
layer sandwiched between the first fixed layer and the first
recording layer, the first recording layer including a first
ferromagnetic layer located on a side of the first fixed layer, a
second ferromagnetic layer, and a first nonmagnetic layer
sandwiched between the first ferromagnetic layer and the second
ferromagnetic layer, and a second magnetoresistive element which is
arranged at the intersection of the first write wiring and the
second write wiring between the first write wiring and the second
write wiring and electrically connected to the first
magnetoresistive element, has a second axis of easy magnetization
directed to a side of the second crossing angle, and has a second
fixed layer, a second recording layer, and a second tunnel barrier
layer sandwiched between the second fixed layer and the second
recording layer, the second recording layer including a third
ferromagnetic layer located on a side of the second fixed layer, a
fourth ferromagnetic layer, and a second nonmagnetic layer
sandwiched between the third ferromagnetic layer and the fourth
ferromagnetic layer, wherein in a write operation, magnetizations
in the first recording layer and second recording layer execute a
toggle operation by using the first write wiring and second write
wiring.
[0012] According to a second aspect of the present invention, there
is provided a magnetic random access memory comprising a first
write wiring which runs in a first direction, a second write wiring
which runs in a second direction different from the first direction
and has a first crossing angle and second crossing angle formed by
crossing the first write wiring, the first crossing angle and
second crossing angle being located on both sides of the first
write wiring serving as a boundary, a first magnetoresistive
element which is arranged at an intersection of the first write
wiring and the second write wiring between the first write wiring
and the second write wiring, has a first axis of easy magnetization
directed to a side of the first crossing angle, and has a first
fixed layer, a first recording layer, and a first tunnel barrier
layer sandwiched between the first fixed layer and the first
recording layer, the first recording layer including a first
ferromagnetic layer located on a side of the first fixed layer, a
second ferromagnetic layer, and a first nonmagnetic layer
sandwiched between the first ferromagnetic layer and the second
ferromagnetic layer, and a second magnetoresistive element which is
arranged at the intersection of the first write wiring and the
second write wiring between the first write wiring and the second
write wiring and electrically connected to the first
magnetoresistive element, has a second axis of easy magnetization
directed to a side of the second crossing angle, and has a second
fixed layer, a second recording layer, and a second tunnel barrier
layer sandwiched between the second fixed layer and the second
recording layer.
[0013] According to a third aspect of the present invention, there
is provided a write method of a magnetic random access memory which
includes a first write wiring which runs in a first direction, a
second write wiring which runs in a second direction different from
the first direction and has a first crossing angle and second
crossing angle formed by crossing the first write wiring, the first
crossing angle and second crossing angle being located on both
sides of the first write wiring serving as a boundary, a first
magnetoresistive element which is arranged at an intersection of
the first write wiring and the second write wiring between the
first write wiring and the second write wiring, has a first axis of
easy magnetization directed to a side of the first crossing angle,
and has a first fixed layer, a first recording layer, and a first
tunnel barrier layer sandwiched between the first fixed layer and
the first recording layer, the first recording layer including a
first ferromagnetic layer located on a side of the first fixed
layer, a second ferromagnetic layer, and a first nonmagnetic layer
sandwiched between the first ferromagnetic layer and the second
ferromagnetic layer, and a second magnetoresistive element which is
arranged at the intersection of the first write wiring and the
second write wiring between the first write wiring and the second
write wiring and electrically connected to the first
magnetoresistive element, has a second axis of easy magnetization
directed to a side of the second crossing angle, and has a second
fixed layer, a second recording layer, and a second tunnel barrier
layer sandwiched between the second fixed layer and the second
recording layer, the second recording layer including a third
ferromagnetic layer located on a side of the second fixed layer, a
fourth ferromagnetic layer, and a second nonmagnetic layer
sandwiched between the third ferromagnetic layer and the fourth
ferromagnetic layer, the write method writing binary information in
the first magnetoresistive element and second magnetoresistive
element by supplying a first write current to the first write
wiring and a second write current to the second write wiring,
comprising starting supplying one current of one of the first write
current and second write current earlier than the other current of
the other of the first write current and second write current
supplying the other current in addition to the one current,
reducing a current value of the one current to not more than a
write threshold value earlier than the other current, and reducing
a current value of the other current to not more than the write
threshold value, wherein an order of starting or ending supply of
the first write current and second write current and directions in
which the first write current and second write current are supplied
are changed to selectively cause one of the first magnetoresistive
element and second magnetoresistive element to execute a toggle
operation.
[0014] According to a fourth aspect of the present invention, there
is provided a write method of a magnetic random access memory which
includes a first write wiring which runs in a first direction, a
second write wiring which runs in a second direction different from
the first direction and has a first crossing angle and second
crossing angle formed by crossing the first write wiring, the first
crossing angle and second crossing angle being located on both
sides of the first write wiring serving as a boundary, a first
magnetoresistive element which is arranged at an intersection of
the first write wiring and the second write wiring between the
first write wiring and the second write wiring, has a first axis of
easy magnetization directed to a side of the first crossing angle,
and has a first fixed layer, a first recording layer, and a first
tunnel barrier layer sandwiched between the first fixed layer and
the first recording layer, the first recording layer including a
first ferromagnetic layer located on a side of the first fixed
layer, a second ferromagnetic layer, and a first nonmagnetic layer
sandwiched between the first ferromagnetic layer and the second
ferromagnetic layer, and a second magnetoresistive element which is
arranged at the intersection of the first write wiring and the
second write wiring between the first write wiring and the second
write wiring and electrically connected to the first
magnetoresistive element, has a second axis of easy magnetization
directed to a side of the second crossing angle, and has a second
fixed layer, a second recording layer, and a second tunnel barrier
layer sandwiched between the second fixed layer and the second
recording layer, the write method writing binary information in the
first magnetoresistive element and second magnetoresistive element
by supplying a first write current to the first write wiring and a
second write current to the second write wiring, comprising
starting supplying one current of one of the first write current
and second write current earlier than the other current of the
other of the first write current and second write current,
supplying the other current in addition to the one current,
reducing a current value of the one current to not more than a
write threshold value earlier than the other current, and reducing
a current value of the other current to not more than the write
threshold value, wherein an order of starting or ending supply of
the first write current and second write current and directions in
which the first write current and second write current are supplied
are changed to selectively independently execute a first operation
and second operation, the first operation is causing or not causing
the first magnetoresistive element to execute a toggle operation,
and the second operation is reversing magnetization in the second
recording layer of the second magnetoresistive element.
[0015] According to a fifth aspect of the present invention, there
is provided a magnetic random access memory manufacturing method
comprising forming a first write wiring, forming a first electrode
above the first write wiring, forming a first material layer on the
first electrode, processing the first material layer to form a
first magnetoresistive element having a first axis of easy
magnetization directed in a first direction, forming a interlayer
around the first magnetoresistive element, forming a second
electrode on the first magnetoresistive element, forming a second
material layer on the second electrode, processing the second
material layer to form a second magnetoresistive element having a
second axis of easy magnetization directed in a second direction
different from the first direction, and forming a second write
wiring above the second magnetoresistive element.
[0016] According to a sixth aspect of the present invention, there
is provided a magnetic random access memory manufacturing method
comprising forming a first write wiring, forming a first electrode
above the first write wiring, forming a first material layer, a
contact layer, and a second material layer sequentially on the
first electrode, processing the first material layer, the contact
layer, and the second material layer at once to form a first
magnetoresistive element, a contact, and a second magnetoresistive
element, and forming a second write wiring above the second
magnetoresistive element.
[0017] According to a seventh aspect of the present invention,
there is provided a magnetic random access memory manufacturing
method comprising forming a first write wiring and a first
magnetoresistive element above a first substrate, forming a contact
connected to the first magnetoresistive element, forming a second
write wiring and a second magnetoresistive element above a second
substrate different from the first substrate, and bonding the first
substrate and second substrate to electrically connect the first
magnetoresistive element and second magnetoresistive element
through the contact.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0018] FIG. 1A is a plan view showing a magnetic random access
memory according to the first embodiment of the present
invention;
[0019] FIG. 1B is a sectional view of the magnetic random access
memory taken along a line IB-IB in FIG. 1A;
[0020] FIG. 2 is an explanatory view of the cycles of Write Method
Example 1 of the first MTJ element according to the first
embodiment of the present invention;
[0021] FIG. 3 is an explanatory view of the cycles of Write Method
Example 2 of the first MTJ element according to the first
embodiment of the present invention;
[0022] FIG. 4 is an explanatory view of the cycles of Write Method
Example 3 of the first MTJ element according to the first
embodiment of the present invention;
[0023] FIG. 5 is an explanatory view of the cycles of Write Method
Example 4 of the first MTJ element according to the first
embodiment of the present invention;
[0024] FIG. 6 is an explanatory view of the cycles of Write Method
Example 1 of the second MTJ element according to the first
embodiment of the present invention;
[0025] FIG. 7 is an explanatory view of the cycles of Write Method
Example 2 of the second MTJ element according to the first
embodiment of the present invention;
[0026] FIG. 8 is an explanatory view of the cycles of Write Method
Example 3 of the second MTJ element according to the first
embodiment of the present invention;
[0027] FIG. 9 is an explanatory view of the cycles of Write Method
Example 4 of the second MTJ element according to the first
embodiment of the present invention;
[0028] FIG. 10 is a schematic circuit diagram showing the MTJ
element of one cell according to the first embodiment of the
present invention;
[0029] FIG. 12 is a view for explaining the difference in series
resistance between logic states in the read according to the first
embodiment of the present invention;
[0030] FIGS. 12A, 12B, 12C and 12D are views for explaining the
magnetization arrangements of logic states according to the first
embodiment of the present invention;
[0031] FIG. 13A is a plan view showing a magnetic random access
memory according to the second embodiment of the present
invention;
[0032] FIG. 13B is a sectional view of the magnetic random access
memory taken along a line XIIIB-XIIIB in FIG. 13A;
[0033] FIG. 14A is a plan view showing a magnetic random access
memory according to the third embodiment of the present
invention;
[0034] FIG. 14B is a sectional view of the magnetic random access
memory taken along a line XIVB-XIVB in FIG. 14A;
[0035] FIG. 15A is a plan view showing a magnetic random access
memory according to the fourth embodiment of the present
invention;
[0036] FIG. 15B is a sectional view of the magnetic random access
memory taken along a line XVB-XVB in FIG. 15A;
[0037] FIG. 16A is a plan view showing a magnetic random access
memory according to the fifth embodiment of the present
invention;
[0038] FIG. 16B is a sectional view of the magnetic random access
memory taken along a line XVIB-XVIB in FIG. 16A;
[0039] FIG. 17A is a plan view showing a magnetic random access
memory according to the sixth embodiment of the present
invention;
[0040] FIG. 17B is a sectional view of the magnetic random access
memory taken along a line XVIIB-XVIIB in FIG. 17A;
[0041] FIG. 18A is a plan view showing a magnetic random access
memory according to the seventh embodiment of the present
invention;
[0042] FIG. 18B is a sectional view of the magnetic random access
memory taken along a line XVIIIB-XVIIIB in FIG. 18A;
[0043] FIG. 19 is a plan view showing a magnetic random access
memory according to the eighth embodiment of the present
invention;
[0044] FIG. 20 is a view for explaining quaternary states by a
write method according to the eighth embodiment of the present
invention; and
[0045] FIG. 21 is a plan view showing a magnetic random access
memory according to the other embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0046] The embodiments of the present invention will be described
below with reference to the accompanying drawing. The same
reference numerals denote the same parts throughout the
drawing.
[1] First Embodiment
[1-1] Structure
[0047] FIG. 1A is a plan view of a magnetic random access memory
according to the first embodiment of the present invention. FIG. 1B
is a sectional view of the magnetic random access memory taken
along a line IB-IB in FIG. 1A. The structure of the magnetic random
access memory according to the first embodiment of the present
invention will be described below.
[0048] As shown in FIGS. 1A and 1B, a first write wiring W1 runs in
the X direction, and a second write wiring W2 runs in the Y
direction (e.g., the direction almost perpendicular to the X
direction). Series-connected first and second magnetic tunnel
junction (MTJ) elements 100 and 200 are arranged at the
intersection of the first and second write wirings W1 and W2
between them. An upper electrode 20 is arranged between the first
MTJ element 100 and the first write wiring W1. One terminal of the
upper electrode 20 is electrically connected to one terminal of the
first MTJ element 100. The other terminal of the upper electrode 20
is electrically connected to one input of a sense amplifier 41
through a contact 21. A reference cell 42 is connected to the other
input of the sense amplifier 41. A lower electrode 30 is arranged
between the second MTJ element 200 and the second write wiring W2.
One terminal of the lower electrode 30 is electrically connected to
one terminal of the second MTJ element 200. The other terminal of
the lower electrode 30 is connected to a read switching element
(e.g., a transistor) 43 through a contact 31. An intermediate
electrode (metal layer) 10 is arranged between the first and second
MTJ elements 100 and 200. The intermediate electrode 10 is
connected to the first and second MTJ elements 100 and 200. The
first and second MTJ elements 100 and 200 are electrically isolated
from the first and second write wirings W1 and W2.
[0049] When the first and second write wirings W1 and W2 cross,
first and second crossing angles .theta.1 and .theta.2 (e.g.,
.theta.1, .theta.2=90.degree.) are formed. The first and second
crossing angles .theta.1 and .theta.2 are located on both sides of
the first write wiring W1 or second write wiring W2 serving as a
boundary. An axis e1 of easy magnetization of the first MTJ element
100 is directed to the side of the first crossing angle .theta.1
(e.g., the direction in which the first crossing angle .theta.1 is
equally divided into two parts). An axis e2 of easy magnetization
of the second MTJ element 200 is directed to the side of the second
crossing angle .theta.2 (e.g., the direction in which the second
crossing angle .theta.2 is equally divided into two parts).
[0050] Hence, the direction of the axis e1 of easy magnetization of
the first MTJ element 100 tilts almost 45.degree. with respect to
the X or Y direction. The direction of the axis e2 of easy
magnetization of the second MTJ element 200 tilts almost 45.degree.
with respect to the X or Y direction. The directions of the axes e1
and e2 of easy magnetization of the first and second MTJ elements
100 and 200 are different by almost 90.degree..
[0051] The tilt angle of the axes e1 and e2 of easy magnetization
with respect to the X or Y direction is not limited to about
45.degree.. As shown in FIG. 21, the angle can be about 30.degree.
to 60.degree.. In this case, the current value of the write current
flowing in the first write wiring W1 and the current value of the
write current flowing in the second write wiring W2 are different
to each other to set in the optimum value. A writing window of the
first and second MTJ elements 100 and 200 can be extended.
[0052] The first MTJ element 100 has a first fixed layer (pinned
layer) 111 whose magnetization is fixed in the uniaxial direction,
a first recording layer (free layer) 113 whose magnetization
reverses, a first tunnel barrier layer 112 sandwiched between the
first fixed layer 111 and the first recording layer 113, and an
anti-ferromagnetic layer (not shown) to fix magnetization of the
first fixed layer 111. The first recording layer 113 has an
anti-ferromagnetic coupling structure including a nonmagnetic layer
113b and ferromagnetic layers (soft magnetic layers) 113a and 113c
which sandwich the nonmagnetic layer 113b. The ferromagnetic layers
113a and 113c are magnetically coupled while having reverse
magnetization directions. The first recording layer may have a
ferromagnetic coupling structure in which the ferromagnetic layers
113a and 113c are magnetically coupled while having the same
magnetization direction.
[0053] The second MTJ element 200 has a second fixed layer 211
whose magnetization is fixed in the uniaxial direction, a second
recording layer 213 whose magnetization reverses, a second tunnel
barrier layer 212 sandwiched between the second fixed layer 211 and
the second recording layer 213, and an anti-ferromagnetic layer
(not shown) to fix magnetization of the second fixed layer 211. The
second recording layer 213 has an anti-ferromagnetic coupling
structure including a nonmagnetic layer 213b and ferromagnetic
layers (soft magnetic layers) 213a and 213c which sandwich the
nonmagnetic layer 213b. The ferromagnetic layers 213a and 213c are
magnetically coupled while having reverse magnetization directions.
The second recording layer may have a ferromagnetic coupling
structure in which the ferromagnetic layers 213a and 213c are
magnetically coupled while having the same magnetization
direction.
[0054] The first and second MTJ elements 100 and 200 have a planar
shape having long and short sides (e.g., an elliptical shape with
an aspect ratio of 2 or more or an oblong shape with round
corners). The longitudinal direction of the planar shape matches
the direction of the axis e1 or e2 of easy magnetization on the
basis of shape anisotropy.
[0055] The planar shape of the intermediate electrode 10 is, e.g.,
rectangular. The area of the planar shape of the intermediate
electrode 10 is larger than the area of the planar shape of the
first and second MTJ elements 100 and 200.
[1-2] Write Method
[0056] As the write method of the magnetic random access memory
according to the first embodiment of the present invention, a
so-called toggle write method is employed.
[0057] The toggle write method is a current magnetic field write
method. The first write current is supplied to the first write
wiring, and the second write current is supplied to the second
write wiring. A magnetic field generated by these currents is
applied to the MTJ element, thereby writing binary information in
it. One of the first and second write currents is supplied earlier
than the other. Then, the other current is supplied in addition to
the one current. The value of the one current is reduced to the
write threshold value or less earlier than the other current. Then,
the value of the other current is reduced to the write threshold
value or less.
[0058] With this write operation, the state of data of the selected
cell sequentially changes from "1" to "0" to "1" to "0". In other
words, by the write, the relative magnetization direction between
the storage layer (ferromagnetic layer on the side facing the fixed
layer) and the fixed layer (ferromagnetic layer on the side facing
the recording layer when the fixed layer includes a plurality of
ferromagnetic layers divided by nonmagnetic layers) of the MTJ
element changes from the parallel state to the anti-parallel state
or from the anti-parallel state to the parallel state.
[0059] Hence, before arbitrary data is written in a selected cell,
data written in that cell must be read out. If the arbitrary data
has already been written, no write is executed. If data different
from the arbitrary data has been written, the write is executed to
rewrite the data. For example, in writing "0" data in the selected
cell, when data read out from the selected cell is "0" data, no
write is executed. Only when the data is "1" data, the write is
executed. In writing "1" data in the selected cell, when data read
out from the selected cell is "1" data, no write is executed. Only
when the data is "0" data, the write is executed.
[0060] The write method when the above-described confirmation cycle
is performed, and consequently, the write operation is necessary,
i.e., there is necessity of rewriting the data of the selected cell
will be described.
[0061] In this embodiment, the two MTJ elements 100 and 200 are
present between the pair of write wirings W1 and W2. To rewrite
data of only a selected one of the first and second MTJ elements
100 and 200 by the toggle operation, the order of ending or
starting supply of the first and second write currents and the
directions in which the write currents are supplied are changed,
thereby rotating the magnetization of the recording layer of the
selected element in one direction. This write method will be
described below in detail.
[1-2a] Write in First MTJ Element
[0062] The outline of the write method of rewriting only data of
the first MTJ element 100 will be described below.
[0063] One of the first and second write wirings W1 and W2 is
defined as the first selected wiring, and the other is defined as
the second selected wiring. The first selected wiring is turned on
to supply the write current (first cycle).fwdarw.the second
selected wiring is turned on to supply the write current (second
cycle).fwdarw.the first selected wiring is turned off to stop
supplying the write current (third cycle).fwdarw.the second
selected wiring is turned off to stop supplying the write current
(fourth cycle). The direction in which the write current is
supplied is adjusted such that the application direction of the
synthetic field by the write currents in the second cycle matches
the direction of the axis e1 of easy magnetization of the first MTJ
element 100, thereby rotating the magnetization of the recording
layer 113 in one direction (clockwise or counterclockwise). Write
Method Examples 1 to 4 of the first MTJ element 100 will be
described below.
(a) Write Method Example 1 of First MTJ Element
[0064] In Write Method Example 1 of the first MTJ element, the
write current supply direction is adjusted such that the
application direction of the synthetic field by the write currents
in the second cycle matches the direction of the axis e1 of easy
magnetization of the first MTJ element 100, i.e., to the upper
right of the drawing surface (this direction will be defined as a
"45.degree. direction" hereinafter). Data is rewritten while
rotating the magnetization of the recording layer 113
"clockwise".
[0065] FIG. 2 is an explanatory view of the cycles of Write Method
Example 1 of the first MTJ element according to the first
embodiment of the present invention. Write Method Example 1 of the
first MTJ element will be described below.
(Initial State)
[0066] In the initial state, as indicated by (a) in FIG. 2, both
the first and second write wirings W2 are off and set in the no
energized state in which neither write current I1 nor I2 flows to
them.
[0067] In this case, in the recording layer 113 of the first MTJ
element 100, the magnetization of the upper ferromagnetic layer
113c and that of the lower ferromagnetic layer 113a are directed in
180-degree reverse directions because of anti-ferromagnetic
coupling. More specifically, magnetization of the upper
ferromagnetic layer 113c is directed in the 45.degree. direction.
Magnetization of the lower ferromagnetic layer 113a is directed to
the lower left of the drawing surface (this direction will be
defined as a "225.degree. direction" hereinafter). Since the
magnetizations (magnetic moments) of both ferromagnetic layers
balance, composed magnetization (composed magnetic moment) in the
recording layer 113 is almost 0 in the initial state.
[0068] In the recording layer 213 of the second MTJ element 200,
magnetization of the upper ferromagnetic layer 213c and that of the
lower ferromagnetic layer 213a are directed in 180-degree reverse
directions because of anti-ferromagnetic coupling. More
specifically, magnetization of the upper ferromagnetic layer 213c
is directed to the upper left of the drawing surface (this
direction will be defined as a "135.degree. direction"
hereinafter). Magnetization of the lower ferromagnetic layer 213a
is directed to the lower right of the drawing surface (this
direction will be defined as a "315.degree. direction"
hereinafter). Since the magnetizations (magnetic moments) of both
ferromagnetic layers balance, composed magnetization (composed
magnetic moment) in the recording layer 213 is almost 0 in the
initial state.
[0069] In this embodiment, the initial state is defined as a state
in which, e.g., "1" data is written in the first MTJ element 100,
and, e.g., "1" data is written in the second MTJ element 200.
(First Cycle)
[0070] In the first cycle, as indicated by (b) in FIG. 2, only the
first write wiring W1 is turned on to supply the write current I1
to, e.g., the right of the drawing surface (this direction will be
defined as a "0.degree. direction" hereinafter). A magnetic field
is generated to the upper side of the drawing surface (this
direction will be defined as a "90.degree. direction"
hereinafter).
[0071] In this case, composed magnetization (composed magnetic
moment) appears in the recording layer 113 of the first MTJ element
100 due to the magnetic field generated by the write current I1.
The composed magnetization rotates clockwise until it is directed
in the direction (90.degree. direction) of the generated magnetic
field while maintaining the anti-ferromagnetic coupling state
between the upper ferromagnetic layer 113c and the lower
ferromagnetic layer 113a.
[0072] Composed magnetization (composed magnetic moment) appears in
the recording layer 213 of the second MTJ element 200 due to the
magnetic field generated by the write current I1. The composed
magnetization rotates counterclockwise until it is directed in the
direction (90.degree. direction) of the generated magnetic field
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 213c and the lower ferromagnetic layer
213a.
(Second Cycle)
[0073] In the second cycle, as indicated by (c) in FIG. 2, the
first write wiring W1 is kept on to continuously supply the write
current I1 in the 0.degree. direction. The second write wiring W2
is also turned on to start supplying the write current I2 in the
90.degree. direction. A synthetic magnetic field is generated in
the 45.degree. direction.
[0074] In this case, composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100
further rotates clockwise until it is directed in the direction
(45.degree. direction) of the synthetic field generated by the
write currents I1 and I2 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 113c and the
lower ferromagnetic layer 113a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 113
of the first MTJ element 100 is directed in the 45.degree.
direction.
[0075] Composed magnetization (composed magnetic moment) in the
recording layer 213 of the second MTJ element 200 rotates clockwise
this time until it is directed in the direction (45.degree.
direction) of the synthetic field generated by the write currents
I1 and I2 while maintaining the anti-ferromagnetic coupling state
between the upper ferromagnetic layer 213c and the lower
ferromagnetic layer 213a. Consequently, the composed magnetization
(composed magnetic moment) in the recording layer 213 of the second
MTJ element 200 is directed in the 45.degree. direction.
(Third Cycle)
[0076] In the third cycle, as indicated by (d) in FIG. 2, the first
write wiring W1 is turned off to stop supplying the write current
I1. Only the second write wiring W2 is kept on to continuously
supply the write current I2 in the 90.degree. direction. A magnetic
field is generated in the 0.degree. direction.
[0077] In this case, composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100
further rotates clockwise until it is directed in the direction
(0.degree. direction) of the magnetic field generated by the write
current I2 while maintaining the anti-ferromagnetic coupling state
between the upper ferromagnetic layer 113c and the lower
ferromagnetic layer 113a. Consequently, the composed magnetization
(composed magnetic moment) in the recording layer 113 of the first
MTJ element 100 is directed in the 0.degree. direction.
[0078] Composed magnetization (composed magnetic moment) in the
recording layer 213 of the second MTJ element 200 further rotates
clockwise until it is directed in the direction (0.degree.
direction) of the magnetic field generated by the write current I2
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 213c and the lower ferromagnetic layer
213a. Consequently, the composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200 is
directed in the 0.degree. direction.
(Fourth Cycle)
[0079] In the fourth cycle, as indicated by (e) in FIG. 2, both the
first write wiring W1 and second write wiring W2 are turned off to
stop supplying the write currents I1 and I2 to them. Hence, in the
fourth cycle, the applied magnetic fields disappear.
[0080] In this case, the magnetizations of the upper ferromagnetic
layer 113c and lower ferromagnetic layer 113a of the first MTJ
element 100 return to the stable state in the 45.degree. and
225.degree. directions (direction of the axis e1 of easy
magnetization). More specifically, the magnetizations of the upper
ferromagnetic layer 113c and lower ferromagnetic layer 113a further
rotate clockwise. The magnetization of the upper ferromagnetic
layer 113c is directed in the 225.degree. direction. The
magnetization of the lower ferromagnetic layer 113a is directed in
the 45.degree. direction. The magnetization of the upper
ferromagnetic layer 113c and that of the lower ferromagnetic layer
113a are directed in 180-degree reverse directions. Since their
magnetizations (magnetic moments) balance, composed magnetization
(composed magnetic moment) in the recording layer 113 is almost 0.
The magnetization in the recording layer 113 of the first MTJ
element 100 is directed in the direction rotated 180.degree. from
the initial state. Hence, the data of the first MTJ element 100 can
be rewritten from "1" to "0".
[0081] The magnetizations of the upper ferromagnetic layer 213c and
lower ferromagnetic layer 213a of the second MTJ element 200 return
to the stable state in the 135.degree. and 315.degree. directions
(direction of the axis e1 of easy magnetization). More
specifically, the magnetizations of the upper ferromagnetic layer
213c and lower ferromagnetic layer 213a rotate counterclockwise.
The magnetization of the upper ferromagnetic layer 213c is directed
in the 135.degree. direction. The magnetization of the lower
ferromagnetic layer 213a is directed in the 315.degree. direction.
The magnetization of the upper ferromagnetic layer 213c and that of
the lower ferromagnetic layer 213a are directed in 180.degree.
reverse directions. Since their magnetizations (magnetic moments)
balance, composed magnetization (composed magnetic moment) in the
recording layer 213 is almost 0. The magnetization in the recording
layer 213 of the second MTJ element 200 is directed in the same
direction as in the initial state. The data of the second MTJ
element 200 remains "1" and is not rewritten.
(b) Write Method Example 2 of First MTJ Element
[0082] In Write Method Example 2 of the first MTJ element, the
write current supply direction is adjusted such that the
application direction of the synthetic field by the write currents
in the second cycle matches the direction of the axis e1 of easy
magnetization of the first MTJ element 100, i.e., "225.degree.
direction". Data is rewritten while rotating the magnetization of
the recording layer 113 "clockwise".
[0083] FIG. 3 is an explanatory view of the cycles of Write Method
Example 2 of the first MTJ element according to the first
embodiment of the present invention. Write Method Example 2 of the
first MTJ element will be described below.
(Initial State)
[0084] In the initial state, as indicated by (a) in FIG. 3, both
the first and second write wirings W2 are off and set in the no
energized state in which neither write current I1 nor I2 flows to
them.
[0085] In this case, as in (a) in FIG. 2, the magnetizations of the
upper ferromagnetic layer 113c and lower ferromagnetic layer 113a
of the first MTJ element 100 are directed in the 45.degree. and
225.degree. directions. The magnetizations of the upper
ferromagnetic layer 213c and lower ferromagnetic layer 213a of the
second MTJ element 200 are directed in the 135.degree. and
315.degree. directions.
(First Cycle)
[0086] In the first cycle, as indicated by (b) in FIG. 3, only the
first write wiring W1 is turned on to supply the write current I1
in, e.g., the 180.degree. direction. A magnetic field is generated
in the 270.degree. direction.
[0087] In this case, composed magnetization (composed magnetic
moment) appears in the recording layer 113 of the first MTJ element
100 due to the magnetic field generated by the write current I1.
The composed magnetization rotates clockwise until it is directed
in the direction (270.degree. direction) of the generated magnetic
field while maintaining the anti-ferromagnetic coupling state
between the upper ferromagnetic layer 113c and the lower
ferromagnetic layer 113a.
[0088] Composed magnetization (composed magnetic moment) appears in
the recording layer 213 of the second MTJ element 200 due to the
magnetic field generated by the write current I1. The composed
magnetization rotates counterclockwise until it is directed in the
direction (270.degree. direction) of the generated magnetic field
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 213c and the lower ferromagnetic layer
213a.
(Second Cycle)
[0089] In the second cycle, as indicated by (c) in FIG. 3, the
first write wiring W1 is kept on to continuously supply the write
current I1 in the 180.degree. direction. The second write wiring W2
is also turned on to start supplying the write current I2 in the
270.degree. direction. A synthetic magnetic field is generated in
the 225.degree. direction.
[0090] In this case, composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100
further rotates clockwise until it is directed in the direction
(225.degree. direction) of the synthetic field generated by the
write currents I1 and I2 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 113c and the
lower ferromagnetic layer 113a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 113
of the first MTJ element 100 is directed in the 225.degree.
direction.
[0091] Composed magnetization (composed magnetic moment) in the
recording layer 213 of the second MTJ element 200 rotates clockwise
this time until it is directed in the direction (225.degree.
direction) of the synthetic field generated by the write currents
I1 and I2 while maintaining the anti-ferromagnetic coupling state
between the upper ferromagnetic layer 213c and the lower
ferromagnetic layer 213a. Consequently, the composed magnetization
(composed magnetic moment) in the recording layer 213 of the second
MTJ element 200 is directed in the 225.degree. direction.
(Third Cycle)
[0092] In the third cycle, as indicated by (d) in FIG. 3, the first
write wiring W1 is turned off to stop supplying the write current
I1. Only the second write wiring W2 is kept on to continuously
supply the write current I2 in the 270.degree. direction. A
magnetic field is generated in the 180.degree. direction.
[0093] In this case, composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100
further rotates clockwise until it is directed in the direction
(180.degree. direction) of the magnetic field generated by the
write current I2 while maintaining the anti-ferromagnetic coupling
state between the upper ferromagnetic layer 113c and the lower
ferromagnetic layer 113a. Consequently, the composed magnetization
(composed magnetic moment) in the recording layer 113 of the first
MTJ element 100 is directed in the 180.degree. direction.
[0094] Composed magnetization (composed magnetic moment) in the
recording layer 213 of the second MTJ element 200 further rotates
clockwise until it is directed in the direction (180.degree.
direction) of the magnetic field generated by the write current I2
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 213c and the lower ferromagnetic layer
213a. Consequently, the composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200 is
directed in the 180.degree. direction.
(Fourth Cycle)
[0095] In the fourth cycle, as indicated by (e) in FIG. 3, both the
first write wiring W1 and second write wiring W2 are turned off to
stop supplying the write currents I1 and I2 to them. Hence, in the
fourth cycle, the applied magnetic fields disappear.
[0096] In this case, the magnetizations of the upper ferromagnetic
layer 113c and lower ferromagnetic layer 113a of the first MTJ
element 100 return to the stable state in the 45.degree. and
225.degree. directions (direction of the axis e1 of easy
magnetization). More specifically, the magnetizations of the upper
ferromagnetic layer 113c and lower ferromagnetic layer 113a further
rotate clockwise. The magnetization of the upper ferromagnetic
layer 113c is directed in the 225.degree. direction. The
magnetization of the lower ferromagnetic layer 113a is directed in
the 45.degree. direction. The magnetization in the recording layer
113 of the first MTJ element 100 is directed in the direction
rotated 180.degree. from the initial state. Hence, the data of the
first MTJ element 100 can be rewritten from "1" to "0".
[0097] The magnetizations of the upper ferromagnetic layer 213c and
lower ferromagnetic layer 213a of the second MTJ element 200 return
to the stable state in the 135.degree. and 315.degree. directions
(direction of the axis e1 of easy magnetization). More
specifically, the magnetizations of the upper ferromagnetic layer
213c and lower ferromagnetic layer 213a rotate counterclockwise.
The magnetization of the upper ferromagnetic layer 213c is directed
in the 135.degree. direction. The magnetization of the lower
ferromagnetic layer 213a is directed in the 315.degree. direction.
The magnetization in the recording layer 213 of the second MTJ
element 200 is directed in the same direction as in the initial
state. The data of the second MTJ element 200 remains "1" and is
not rewritten.
(c) Write Method Example 3 of First MTJ Element
[0098] In Write Method Example 3 of the first MTJ element, the
write current supply direction is adjusted such that the
application direction of the synthetic field by the write currents
in the second cycle matches the direction of the axis e1 of easy
magnetization of the first MTJ element 100, i.e., "45.degree.
direction". Data is rewritten while rotating the magnetization of
the recording layer 113 "counterclockwise".
[0099] FIG. 4 is an explanatory view of the cycles of Write Method
Example 3 of the first MTJ element according to the first
embodiment of the present invention. Write Method Example 3 of the
first MTJ element will be described below.
(Initial State)
[0100] In the initial state, as indicated by (a) in FIG. 4, both
the first and second write wirings W2 are off and set in the no
energized state in which neither write current I1 nor I2 flows to
them.
[0101] In this case, as in (a) in FIG. 2, the magnetizations of the
upper ferromagnetic layer 113c and lower ferromagnetic layer 113a
of the first MTJ element 100 are directed in the 45.degree. and
225.degree. directions. The magnetizations of the upper
ferromagnetic layer 213c and lower ferromagnetic layer 213a of the
second MTJ element 200 are directed in the 135.degree. and
315.degree. directions.
(First Cycle)
[0102] In the first cycle, as indicated by (b) in FIG. 4, only the
second write wiring W2 is turned on to supply the write current I2
in, e.g., the 90.degree. direction. A magnetic field is generated
in the 0.degree. direction.
[0103] In this case, composed magnetization (composed magnetic
moment) appears in the recording layer 113 of the first MTJ element
100 due to the magnetic field generated by the write current I2.
The composed magnetization rotates counterclockwise until it is
directed in the direction (0.degree. direction) of the generated
magnetic field while maintaining the anti-ferromagnetic coupling
state between the upper ferromagnetic layer 113c and the lower
ferromagnetic layer 113a.
[0104] Composed magnetization (composed magnetic moment) appears in
the recording layer 213 of the second MTJ element 200 due to the
magnetic field generated by the write current I2. The composed
magnetization rotates clockwise until it is directed in the
direction (0.degree. direction) of the generated magnetic field
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 213c and the lower ferromagnetic layer
213a.
(Second Cycle)
[0105] In the second cycle, as indicated by (c) in FIG. 4, the
second write wiring W2 is kept on to continuously supply the write
current I2 in the 90.degree. direction. The first write wiring W1
is also turned on to start supplying the write current I1 in the
0.degree. direction. A synthetic magnetic field is generated in the
45.degree. direction.
[0106] In this case, composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100
rotates counterclockwise until it is directed in the direction
(45.degree. direction) of the synthetic field generated by the
write currents I1 and I2 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 113c and the
lower ferromagnetic layer 113a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 113
of the first MTJ element 100 is directed in the 45.degree.
direction.
[0107] Composed magnetization (composed magnetic moment) in the
recording layer 213 of the second MTJ element 200 rotates
counterclockwise this time until it is directed in the direction
(45.degree. direction) of the synthetic field generated by the
write currents I1 and I2 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 213c and the
lower ferromagnetic layer 213a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 213
of the second MTJ element 200 is directed in the 45.degree.
direction.
(Third Cycle)
[0108] In the third cycle, as indicated by (d) in FIG. 4, the
second write wiring W2 is turned off to stop supplying the write
current I2. Only the first write wiring W1 is kept on to
continuously supply the write current I1 in the 0.degree.
direction. A magnetic field is generated in the 90.degree.
direction.
[0109] In this case, composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100
further rotates counterclockwise until it is directed in the
direction (90.degree. direction) of the magnetic field generated by
the write current I1 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 113c and the
lower ferromagnetic layer 113a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 113
of the first MTJ element 100 is directed in the 90.degree.
direction.
[0110] Composed magnetization (composed magnetic moment) in the
recording layer 213 of the second MTJ element 200 further rotates
counterclockwise until it is directed in the direction (90.degree.
direction) of the magnetic field generated by the write current I1
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 213c and the lower ferromagnetic layer
213a. Consequently, the composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200 is
directed in the 90.degree. direction.
(Fourth Cycle)
[0111] In the fourth cycle, as indicated by (e) in FIG. 4, both the
first write wiring W1 and second write wiring W2 are turned off to
stop supplying the write currents I1 and I2 to them. Hence, in the
fourth cycle, the applied magnetic fields disappear.
[0112] In this case, the magnetizations of the upper ferromagnetic
layer 113c and lower ferromagnetic layer 113a of the first MTJ
element 100 return to the stable state in the 45.degree. and
225.degree. directions (direction of the axis e1 of easy
magnetization). More specifically, the magnetizations of the upper
ferromagnetic layer 113c and lower ferromagnetic layer 113a further
rotate counterclockwise. The magnetization of the upper
ferromagnetic layer 113c is directed in the 45.degree. direction.
The magnetization of the lower ferromagnetic layer 113a is directed
in the 225.degree. direction. The magnetization in the recording
layer 113 of the first MTJ element 100 is directed in the direction
rotated 180.degree. from the initial state. Hence, the data of the
first MTJ element 100 can be rewritten from "1" to "0".
[0113] The magnetizations of the upper ferromagnetic layer 213c and
lower ferromagnetic layer 213a of the second MTJ element 200 return
to the stable state in the 135.degree. and 315.degree. directions
(direction of the axis e1 of easy magnetization). More
specifically, the magnetizations of the upper ferromagnetic layer
213c and lower ferromagnetic layer 213a rotate clockwise. The
magnetization of the upper ferromagnetic layer 213c is directed in
the 315.degree. direction. The magnetization of the lower
ferromagnetic layer 213a is directed in the 135.degree. direction.
The magnetization in the recording layer 213 of the second MTJ
element 200 is directed in the same direction as in the initial
state. The data of the second MTJ element 200 remains "1" and is
not rewritten.
(d) Write Method Example 4 of First MTJ Element
[0114] In Write Method Example 4 of the first MTJ element, the
write current supply direction is adjusted such that the
application direction of the synthetic field by the write currents
in the second cycle matches the direction of the axis e1 of easy
magnetization of the first MTJ element 100, i.e., "225.degree.
direction". Data is rewritten while rotating the magnetization of
the recording layer 113 "counterclockwise".
[0115] FIG. 5 is an explanatory view of the cycles of Write Method
Example 4 of the first MTJ element according to the first
embodiment of the present invention. Write Method Example 4 of the
first MTJ element will be described below.
(Initial State)
[0116] In the initial state, as indicated by (a) in FIG. 5, both
the first and second write wirings W2 are off and set in the no
energized state in which neither write current I1 nor I2 flows to
them.
[0117] In this case, as in (a) in FIG. 2, the magnetizations of the
upper ferromagnetic layer 113c and lower ferromagnetic layer 113a
of the first MTJ element 100 are directed in the 45.degree. and
225.degree. directions. The magnetizations of the upper
ferromagnetic layer 213c and lower ferromagnetic layer 213a of the
second MTJ element 200 are directed in the 135.degree. and
315.degree. directions.
(First Cycle)
[0118] In the first cycle, as indicated by (b) in FIG. 5, only the
second write wiring W2 is turned on to supply the write current I2
in, e.g., the 270.degree. direction. A magnetic field is generated
in the 180.degree. direction.
[0119] In this case, composed magnetization (composed magnetic
moment) appears in the recording layer 113 of the first MTJ element
100 due to the magnetic field generated by the write current I2.
The composed magnetization rotates counterclockwise until it is
directed in the direction (180.degree. direction) of the generated
magnetic field while maintaining the anti-ferromagnetic coupling
state between the upper ferromagnetic layer 113c and the lower
ferromagnetic layer 113a.
[0120] Composed magnetization (composed magnetic moment) appears in
the recording layer 213 of the second MTJ element 200 due to the
magnetic field generated by the write current I2. The composed
magnetization rotates clockwise until it is directed in the
direction (180.degree. direction) of the generated magnetic field
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 213c and the lower ferromagnetic layer
213a.
(Second Cycle)
[0121] In the second cycle, as indicated by (c) in FIG. 5, the
second write wiring W2 is kept on to continuously supply the write
current I2 in the 270.degree. direction. The first write wiring W1
is also turned on to start supplying the write current I1 in the
180.degree. direction. A synthetic magnetic field is generated in
the 225.degree. direction.
[0122] In this case, composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100
further rotates counterclockwise until it is directed in the
direction (225.degree. direction) of the synthetic field generated
by the write currents I1 and I2 while maintaining the
anti-ferromagnetic coupling state between the upper ferromagnetic
layer 113c and the lower ferromagnetic layer 113a. Consequently,
the composed magnetization (composed magnetic moment) in the
recording layer 113 of the first MTJ element 100 is directed in the
225.degree. direction.
[0123] Composed magnetization (composed magnetic moment) in the
recording layer 213 of the second MTJ element 200 rotates
counterclockwise this time until it is directed in the direction
(225.degree. direction) of the synthetic field generated by the
write currents I1 and I2 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 213c and the
lower ferromagnetic layer 213a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 213
of the second MTJ element 200 is directed in the 225.degree.
direction.
(Third Cycle)
[0124] In the third cycle, as indicated by (d) in FIG. 5, the
second write wiring W2 is turned off to stop supplying the write
current I2. Only the first write wiring W1 is kept on to
continuously supply the write current I1 in the 180.degree.
direction. A magnetic field is generated in the 270.degree.
direction.
[0125] In this case, composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100
further rotates counterclockwise until it is directed in the
direction (270.degree. direction) of the magnetic field generated
by the write current I1 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 113c and the
lower ferromagnetic layer 113a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 113
of the first MTJ element 100 is directed in the 270.degree.
direction.
[0126] Composed magnetization (composed magnetic moment) in the
recording layer 213 of the second MTJ element 200 further rotates
counterclockwise until it is directed in the direction (270.degree.
direction) of the magnetic field generated by the write current I1
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 213c and the lower ferromagnetic layer
213a. Consequently, the composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200 is
directed in the 270.degree. direction.
(Fourth Cycle)
[0127] In the fourth cycle, as indicated by (e) in FIG. 5, both the
first write wiring W1 and second write wiring W2 are turned off to
stop supplying the write currents I1 and I2 to them. Hence, in the
fourth cycle, the applied magnetic fields disappear.
[0128] In this case, the magnetizations of the upper ferromagnetic
layer 113c and lower ferromagnetic layer 113a of the first MTJ
element 100 return to the stable state in the 45.degree. and
225.degree. directions (direction of the axis e1 of easy
magnetization). More specifically, the magnetizations of the upper
ferromagnetic layer 113c and lower ferromagnetic layer 113a further
rotate counterclockwise. The magnetization of the upper
ferromagnetic layer 113c is directed in the 225.degree. direction.
The magnetization of the lower ferromagnetic layer 113a is directed
in the 45.degree. direction. The magnetization in the recording
layer 113 of the first MTJ element 100 is directed in the direction
rotated 180.degree. from the initial state. Hence, the data of the
first MTJ element 100 can be rewritten from "1" to "0".
[0129] The magnetizations of the upper ferromagnetic layer 213c and
lower ferromagnetic layer 213a of the second MTJ element 200 return
to the stable state in the 135.degree. and 315.degree. directions
(direction of the axis e1 of easy magnetization). More
specifically, the magnetizations of the upper ferromagnetic layer
213c and lower ferromagnetic layer 213a rotate clockwise. The
magnetization of the upper ferromagnetic layer 213c is directed in
the 135.degree. direction. The magnetization of the lower
ferromagnetic layer 213a is directed in the 315.degree. direction.
The magnetization in the recording layer 213 of the second MTJ
element 200 is directed in the same direction as in the initial
state. The data of the second MTJ element 200 remains "1" and is
not rewritten.
[1-2b] Write in Second MTJ Element
[0130] The outline of the write method of rewriting only data of
the second MTJ element 200 will be described below.
[0131] One of the first and second write wirings W1 and W2 is
defined as the first selected wiring, and the other is defined as
the second selected wiring. The first selected wiring is turned on
to supply the write current (first cycle).fwdarw.the second
selected wiring is turned on to supply the write current (second
cycle).fwdarw.the first selected wiring is turned off to stop
supplying the write current (third cycle).fwdarw.the second
selected wiring is turned off to stop supplying the write current
(fourth cycle). The direction in which the write current is
supplied is adjusted such that the application direction of the
synthetic field by the write currents in the second cycle matches
the direction of the axis e2 of easy magnetization of the second
MTJ element 200, thereby rotating the magnetization of the
recording layer 213 in one direction (clockwise or
counterclockwise). Write Method Examples 1 to 4 of the second MTJ
element 200 will be described below.
(a) Write Method Example 1 of Second MTJ Element
[0132] In Write Method Example 1 of the second MTJ element, the
write current supply direction is adjusted such that the
application direction of the synthetic field by the write currents
in the second cycle matches the direction of the axis e2 of easy
magnetization of the second MTJ element 200, i.e., "315.degree.
direction". Data is rewritten while rotating the magnetization of
the recording layer 213 "clockwise".
[0133] FIG. 6 is an explanatory view of the cycles of Write Method
Example 1 of the second MTJ element according to the first
embodiment of the present invention. Write Method Example 1 of the
second MTJ element will be described below.
(Initial State)
[0134] In the initial state, as indicated by (a) in FIG. 6, both
the first and second write wirings W2 are off and set in the no
energized state in which neither write current I1 nor I2 flows to
them.
[0135] In this case, as in (a) in FIG. 2, the magnetizations of the
upper ferromagnetic layer 113c and lower ferromagnetic layer 113a
of the first MTJ element 100 are directed in the 45.degree. and
225.degree. directions. The magnetizations of the upper
ferromagnetic layer 213c and lower ferromagnetic layer 213a of the
second MTJ element 200 are directed in the 135.degree. and
315.degree. directions.
(First Cycle)
[0136] In the first cycle, as indicated by (b) in FIG. 6, only the
second write wiring W2 is turned on to supply the write current I2
in, e.g., the 90.degree. direction. A magnetic field is generated
in the 0.degree. direction.
[0137] In this case, composed magnetization (composed magnetic
moment) appears in the recording layer 213 of the second MTJ
element 200 due to the magnetic field generated by the write
current I2. The composed magnetization rotates clockwise until it
is directed in the direction (0.degree. direction) of the generated
magnetic field while maintaining the anti-ferromagnetic coupling
state between the upper ferromagnetic layer 213c and the lower
ferromagnetic layer 213a.
[0138] Composed magnetization (composed magnetic moment) appears in
the recording layer 113 of the first MTJ element 100 due to the
magnetic field generated by the write current I2. The composed
magnetization rotates counterclockwise until it is directed in the
direction (0.degree. direction) of the generated magnetic field
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 113c and the lower ferromagnetic layer
113a.
(Second Cycle)
[0139] In the second cycle, as indicated by (c) in FIG. 6, the
second write wiring W2 is kept on to continuously supply the write
current I2 in the 90.degree. direction. The first write wiring W1
is also turned on to start supplying the write current I1 to the
left of the drawing surface (this direction will be defined as a
"180.degree. direction" hereinafter). A synthetic magnetic field is
generated in the 315.degree. direction.
[0140] In this case, composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200
further rotates clockwise until it is directed in the direction
(315.degree. direction) of the synthetic field generated by the
write currents I1 and I2 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 213c and the
lower ferromagnetic layer 213a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 213
of the second MTJ element 200 is directed in the 315.degree.
direction.
[0141] Composed magnetization (composed magnetic moment) in the
recording layer 113 of the first MTJ element 100 rotates clockwise
this time until it is directed in the direction (315.degree.
direction) of the synthetic field generated by the write currents
I1 and I2 while maintaining the anti-ferromagnetic coupling state
between the upper ferromagnetic layer 113c and the lower
ferromagnetic layer 113a. Consequently, the composed magnetization
(composed magnetic moment) in the recording layer 113 of the first
MTJ element 100 is directed in the 315.degree. direction.
(Third Cycle)
[0142] In the third cycle, as indicated by (d) in FIG. 6, the
second write wiring W2 is turned off to stop supplying the write
current I2. Only the first write wiring W1 is kept on to
continuously supply the write current I1 in the 180.degree.
direction. A magnetic field is generated to the lower side of the
drawing surface (this direction will be defined as a "270.degree.
direction" hereinafter).
[0143] In this case, composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200
further rotates clockwise until it is directed in the direction
(270.degree. direction) of the magnetic field generated by the
write current I1 while maintaining the anti-ferromagnetic coupling
state between the upper ferromagnetic layer 213c and the lower
ferromagnetic layer 213a. Consequently, the composed magnetization
(composed magnetic moment) in the recording layer 213 of the second
MTJ element 200 is directed in the 270.degree. direction.
[0144] Composed magnetization (composed magnetic moment) in the
recording layer 113 of the first MTJ element 100 further rotates
clockwise until it is directed in the direction (270.degree.
direction) of the magnetic field generated by the write current I1
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 113c and the lower ferromagnetic layer
113a. Consequently, the composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100 is
directed in the 270.degree. direction.
(Fourth Cycle)
[0145] In the fourth cycle, as indicated by (e) in FIG. 6, both the
first write wiring W1 and second write wiring W2 are turned off to
stop supplying the write currents I1 and I2 to them. Hence, in the
fourth cycle, the applied magnetic fields disappear.
[0146] In this case, the magnetizations of the upper ferromagnetic
layer 213c and lower ferromagnetic layer 213a of the second MTJ
element 200 return to the stable state in the 135.degree. and
315.degree. directions (direction of the axis e2 of easy
magnetization). More specifically, the magnetizations of the upper
ferromagnetic layer 213c and lower ferromagnetic layer 213a further
rotate clockwise. The magnetization of the upper ferromagnetic
layer 213c is directed in the 315.degree. direction. The
magnetization of the lower ferromagnetic layer 213a is directed in
the 135.degree. direction. The magnetization in the recording layer
213 of the second MTJ element 200 is directed in the direction
rotated 180.degree. from the initial state. Hence, the data of the
second MTJ element 200 can be rewritten from "1" to "0".
[0147] The magnetizations of the upper ferromagnetic layer 113c and
lower ferromagnetic layer 113a of the first MTJ element 100 return
to the stable state in the 45.degree. and 225.degree. directions
(direction of the axis e2 of easy magnetization). More
specifically, the magnetizations of the upper ferromagnetic layer
113c and lower ferromagnetic layer 113a rotate counterclockwise.
The magnetization of the upper ferromagnetic layer 113c is directed
in the 45.degree. direction. The magnetization of the lower
ferromagnetic layer 113a is directed in the 225.degree. direction.
The magnetization in the recording layer 113 of the first MTJ
element 100 is directed in the same direction as in the initial
state. The data of the first MTJ element 100 remains "1" and is not
rewritten.
(b) Write Method Example 2 of Second MTJ Element
[0148] In Write Method Example 2 of the second MTJ element, the
write current supply direction is adjusted such that the
application direction of the synthetic field by the write currents
in the second cycle matches the direction of the axis e2 of easy
magnetization of the second MTJ element 200, i.e., "135.degree.
direction". Data is rewritten while rotating the magnetization of
the recording layer 213 "clockwise".
[0149] FIG. 7 is an explanatory view of the cycles of Write Method
Example 2 of the second MTJ element according to the first
embodiment of the present invention. Write Method Example 2 of the
second MTJ element will be described below.
(Initial State)
[0150] In the initial state, as indicated by (a) in FIG. 7, both
the first and second write wirings W2 are off and set in the no
energized state in which neither write current I1 nor I2 flows to
them.
[0151] In this case, as in (a) in FIG. 2, the magnetizations of the
upper ferromagnetic layer 113c and lower ferromagnetic layer 113a
of the first MTJ element 100 are directed in the 45.degree. and
225.degree. directions. The magnetizations of the upper
ferromagnetic layer 213c and lower ferromagnetic layer 213a of the
second MTJ element 200 are directed in the 135.degree. and
315.degree. directions.
(First Cycle)
[0152] In the first cycle, as indicated by (b) in FIG. 7, only the
second write wiring W2 is turned on to supply the write current I2
in, e.g., the 270.degree. direction. A magnetic field is generated
in the 180.degree. direction.
[0153] In this case, composed magnetization (composed magnetic
moment) appears in the recording layer 213 of the second MTJ
element 200 due to the magnetic field generated by the write
current I2. The composed magnetization rotates clockwise until it
is directed in the direction (180.degree. direction) of the
generated magnetic field while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 213c and the
lower ferromagnetic layer 213a.
[0154] Composed magnetization (composed magnetic moment) appears in
the recording layer 113 of the first MTJ element 200 due to the
magnetic field generated by the write current I2. The composed
magnetization rotates counterclockwise until it is directed in the
direction (180.degree. direction) of the generated magnetic field
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 113c and the lower ferromagnetic layer
113a.
(Second Cycle)
[0155] In the second cycle, as indicated by (c) in FIG. 7, the
second write wiring W2 is kept on to continuously supply the write
current I2 in the 270.degree. direction. The first write wiring W1
is also turned on to start supplying the write current I1 in the
0.degree. direction. A synthetic magnetic field is generated in the
135.degree. direction.
[0156] In this case, composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200
further rotates clockwise until it is directed in the direction
(135.degree. direction) of the synthetic field generated by the
write currents I1 and I2 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 213c and the
lower ferromagnetic layer 213a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 213
of the second MTJ element 200 is directed in the 135.degree.
direction.
[0157] Composed magnetization (composed magnetic moment) in the
recording layer 113 of the first MTJ element 100 rotates clockwise
this time until it is directed in the direction (135.degree.
direction) of the synthetic field generated by the write currents
I1 and I2 while maintaining the anti-ferromagnetic coupling state
between the upper ferromagnetic layer 113c and the lower
ferromagnetic layer 113a. Consequently, the composed magnetization
(composed magnetic moment) in the recording layer 113 of the first
MTJ element 100 is directed in the 135.degree. direction.
(Third Cycle)
[0158] In the third cycle, as indicated by (d) in FIG. 7, the
second write wiring W2 is turned off to stop supplying the write
current I2. Only the first write wiring W1 is kept on to
continuously supply the write current I1 in the 0.degree.
direction. A magnetic field is generated in the 90.degree.
direction.
[0159] In this case, composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200
further rotates clockwise until it is directed in the direction
(90.degree. direction) of the magnetic field generated by the write
current I1 while maintaining the anti-ferromagnetic coupling state
between the upper ferromagnetic layer 213c and the lower
ferromagnetic layer 213a. Consequently, the composed magnetization
(composed magnetic moment) in the recording layer 213 of the second
MTJ element 200 is directed in the 90.degree. direction.
[0160] Composed magnetization (composed magnetic moment) in the
recording layer 113 of the first MTJ element 100 further rotates
clockwise until it is directed in the direction (90.degree.
direction) of the magnetic field generated by the write current I1
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 113c and the lower ferromagnetic layer
113a. Consequently, the composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100 is
directed in the 90.degree. direction.
(Fourth Cycle)
[0161] In the fourth cycle, as indicated by (e) in FIG. 7, both the
first write wiring W1 and second write wiring W2 are turned off to
stop supplying the write currents I1 and I2 to them. Hence, in the
fourth cycle, the applied magnetic fields disappear.
[0162] In this case, the magnetizations of the upper ferromagnetic
layer 213c and lower ferromagnetic layer 213a of the second MTJ
element 200 return to the stable state in the 135.degree. and
315.degree. directions (direction of the axis e2 of easy
magnetization). More specifically, the magnetizations of the upper
ferromagnetic layer 213c and lower ferromagnetic layer 213a further
rotate clockwise. The magnetization of the upper ferromagnetic
layer 213c is directed in the 315.degree. direction. The
magnetization of the lower ferromagnetic layer 213a is directed in
the 135.degree. direction. The magnetization in the recording layer
213 of the second MTJ element 200 is directed in the direction
rotated 180.degree. from the initial state. Hence, the data of the
second MTJ element 200 can be rewritten from "1" to "0".
[0163] The magnetizations of the upper ferromagnetic layer 113c and
lower ferromagnetic layer 113a of the first MTJ element 100 return
to the stable state in the 45.degree. and 225.degree. directions
(direction of the axis e2 of easy magnetization). More
specifically, the magnetizations of the upper ferromagnetic layer
113c and lower ferromagnetic layer 113a rotate counterclockwise.
The magnetization of the upper ferromagnetic layer 113c is directed
in the 45.degree. direction. The magnetization of the lower
ferromagnetic layer 113a is directed in the 225.degree. direction.
The magnetization in the recording layer 113 of the first MTJ
element 100 is directed in the same direction as in the initial
state. The data of the first MTJ element 100 remains "1" and is not
rewritten.
(c) Write Method Example 3 of Second MTJ Element
[0164] In Write Method Example 3 of the second MTJ element, the
write current supply direction is adjusted such that the
application direction of the synthetic field by the write currents
in the second cycle matches the direction of the axis e2 of easy
magnetization of the second MTJ element 200, i.e., "315.degree.
direction". Data is rewritten while rotating the magnetization of
the recording layer 213 "counterclockwise".
[0165] FIG. 8 is an explanatory view of the cycles of Write Method
Example 3 of the second MTJ element according to the first
embodiment of the present invention. Write Method Example 3 of the
second MTJ element will be described below.
(Initial State)
[0166] In the initial state, as indicated by (a) in FIG. 8, both
the first and second write wirings W2 are off and set in the no
energized state in which neither write current I1 nor I2 flows to
them.
[0167] In this case, as in (a) in FIG. 2, the magnetizations of the
upper ferromagnetic layer 113c and lower ferromagnetic layer 113a
of the first MTJ element 100 are directed in the 45.degree. and
225.degree. directions. The magnetizations of the upper
ferromagnetic layer 213c and lower ferromagnetic layer 213a of the
second MTJ element 200 are directed in the 135.degree. and
315.degree. directions.
(First Cycle)
[0168] In the first cycle, as indicated by (b) in FIG. 8, only the
first write wiring W1 is turned on to supply the write current I1
in, e.g., the 180.degree. direction. A magnetic field is generated
in the 270.degree. direction.
[0169] In this case, composed magnetization (composed magnetic
moment) appears in the recording layer 213 of the second MTJ
element 200 due to the magnetic field generated by the write
current I1. The composed magnetization rotates counterclockwise
until it is directed in the direction (270.degree. direction) of
the generated magnetic field while maintaining the
anti-ferromagnetic coupling state between the upper ferromagnetic
layer 213c and the lower ferromagnetic layer 213a.
[0170] Composed magnetization (composed magnetic moment) appears in
the recording layer 113 of the first MTJ element 100 due to the
magnetic field generated by the write current I1. The composed
magnetization rotates clockwise until it is directed in the
direction (270.degree. direction) of the generated magnetic field
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 113c and the lower ferromagnetic layer
113a.
(Second Cycle)
[0171] In the second cycle, as indicated by (c) in FIG. 8, the
first write wiring W1 is kept on to continuously supply the write
current I1 in the 180.degree. direction. The second write wiring W2
is also turned on to start supplying the write current I2 in the
90.degree. direction. A synthetic magnetic field is generated in
the 315.degree. direction.
[0172] In this case, composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200
further rotates counterclockwise until it is directed in the
direction (315.degree. direction) of the synthetic field generated
by the write currents I1 and I2 while maintaining the
anti-ferromagnetic coupling state between the upper ferromagnetic
layer 213c and the lower ferromagnetic layer 213a. Consequently,
the composed magnetization (composed magnetic moment) in the
recording layer 213 of the second MTJ element 200 is directed in
the 315.degree. direction.
[0173] Composed magnetization (composed magnetic moment) in the
recording layer 113 of the first MTJ element 100 rotates
counterclockwise this time until it is directed in the direction
(315.degree. direction) of the synthetic field generated by the
write currents I1 and I2 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 113c and the
lower ferromagnetic layer 113a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 113
of the first MTJ element 100 is directed in the 315.degree.
direction.
(Third Cycle)
[0174] In the third cycle, as indicated by (d) in FIG. 8, the first
write wiring W1 is turned off to stop supplying the write current
I1. Only the second write wiring W2 is kept on to continuously
supply the write current I2 in the 90.degree. direction. A magnetic
field is generated in the 0.degree. direction.
[0175] In this case, composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200
further rotates counterclockwise until it is directed in the
direction (0.degree. direction) of the magnetic field generated by
the write current I2 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 213c and the
lower ferromagnetic layer 213a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 213
of the second MTJ element 200 is directed in the 0.degree.
direction.
[0176] Composed magnetization (composed magnetic moment) in the
recording layer 113 of the first MTJ element 100 further rotates
counterclockwise until it is directed in the direction (0.degree.
direction) of the magnetic field generated by the write current I2
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 113c and the lower ferromagnetic layer
113a. Consequently, the composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100 is
directed in the 0.degree. direction.
(Fourth Cycle)
[0177] In the fourth cycle, as indicated by (e) in FIG. 8, both the
first write wiring W1 and second write wiring W2 are turned off to
stop supplying the write currents I1 and I2 to them. Hence, in the
fourth cycle, the applied magnetic fields disappear.
[0178] In this case, the magnetizations of the upper ferromagnetic
layer 213c and lower ferromagnetic layer 213a of the second MTJ
element 200 return to the stable state in the 135.degree. and
315.degree. directions (direction of the axis e2 of easy
magnetization). More specifically, the magnetizations of the upper
ferromagnetic layer 213c and lower ferromagnetic layer 213a rotate
counterclockwise. The magnetization of the upper ferromagnetic
layer 213c is directed in the 315.degree. direction. The
magnetization of the lower ferromagnetic layer 213a is directed in
the 135.degree. direction. The magnetization in the recording layer
213 of the second MTJ element 200 is directed in the direction
rotated 180.degree. from the initial state. Hence, the data of the
second MTJ element 200 can be rewritten from "1" to "0".
[0179] The magnetizations of the upper ferromagnetic layer 113c and
lower ferromagnetic layer 113a of the first MTJ element 100 return
to the stable state in the 45.degree. and 225.degree. directions
(direction of the axis e2 of easy magnetization). More
specifically, the magnetizations of the upper ferromagnetic layer
113c and lower ferromagnetic layer 113a rotate clockwise. The
magnetization of the upper ferromagnetic layer 113c is directed in
the 45.degree. direction. The magnetization of the lower
ferromagnetic layer 113a is directed in the 225.degree. direction.
The magnetization in the recording layer 113 of the first MTJ
element 100 is directed in the same direction as in the initial
state. The data of the first MTJ element 100 remains "1" and is not
rewritten.
(d) Write Method Example 4 of Second MTJ Element
[0180] In Write Method Example 4 of the second MTJ element, the
write current supply direction is adjusted such that the
application direction of the synthetic field by the write currents
in the second cycle matches the direction of the axis e2 of easy
magnetization of the second MTJ element 200, i.e., "135.degree.
direction". Data is rewritten while rotating the magnetization of
the recording layer 213 "counterclockwise".
[0181] FIG. 9 is an explanatory view of the cycles of Write Method
Example 4 of the second MTJ element according to the first
embodiment of the present invention. Write Method Example 4 of the
second MTJ element will be described below.
(Initial State)
[0182] In the initial state, as indicated by (a) in FIG. 9, both
the first and second write wirings W2 are off and set in the no
energized state in which neither write current I1 nor I2 flows to
them.
[0183] In this case, as in (a) in FIG. 2, the magnetizations of the
upper ferromagnetic layer 113c and lower ferromagnetic layer 113a
of the first MTJ element 100 are directed in the 45.degree. and
225.degree. directions. The magnetizations of the upper
ferromagnetic layer 213c and lower ferromagnetic layer 213a of the
second MTJ element 200 are directed in the 135.degree. and
315.degree. directions.
(First Cycle)
[0184] In the first cycle, as indicated by (b) in FIG. 9, only the
first write wiring W1 is turned on to supply the write current I1
in, e.g., the 0.degree. direction. A magnetic field is generated in
the 90.degree. direction.
[0185] In this case, composed magnetization (composed magnetic
moment) appears in the recording layer 213 of the second MTJ
element 200 due to the magnetic field generated by the write
current I1. The composed magnetization rotates counterclockwise
until it is directed in the direction (90.degree. direction) of the
generated magnetic field while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 213c and the
lower ferromagnetic layer 213a.
[0186] Composed magnetization (composed magnetic moment) appears in
the recording layer 113 of the first MTJ element 100 due to the
magnetic field generated by the write current I1. The composed
magnetization rotates clockwise until it is directed in the
direction (90.degree. direction) of the generated magnetic field
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 113c and the lower ferromagnetic layer
113a.
(Second Cycle)
[0187] In the second cycle, as indicated by (c) in FIG. 9, the
first write wiring W1 is kept on to continuously supply the write
current I1 in the 0.degree. direction. The second write wiring W2
is also turned on to start supplying the write current I2 in the
270.degree. direction. A synthetic magnetic field is generated in
the 135.degree. direction.
[0188] In this case, composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200
further rotates counterclockwise until it is directed in the
direction (135.degree. direction) of the synthetic field generated
by the write currents I1 and I2 while maintaining the
anti-ferromagnetic coupling state between the upper ferromagnetic
layer 213c and the lower ferromagnetic layer 213a. Consequently,
the composed magnetization (composed magnetic moment) in the
recording layer 213 of the second MTJ element 200 is directed in
the 135.degree. direction.
[0189] Composed magnetization (composed magnetic moment) in the
recording layer 113 of the first MTJ element 100 rotates
counterclockwise this time until it is directed in the direction
(135.degree. direction) of the synthetic field generated by the
write currents I1 and I2 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 113c and the
lower ferromagnetic layer 113a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 113
of the first MTJ element 100 is directed in the 135.degree.
direction.
(Third Cycle)
[0190] In the third cycle, as indicated by (d) in FIG. 9, the first
write wiring W1 is turned off to stop supplying the write current
I1. Only the second write wiring W2 is kept on to continuously
supply the write current I2 in the 270.degree. direction. A
magnetic field is generated in the 180.degree. direction.
[0191] In this case, composed magnetization (composed magnetic
moment) in the recording layer 213 of the second MTJ element 200
further rotates counterclockwise until it is directed in the
direction (180.degree. direction) of the magnetic field generated
by the write current I2 while maintaining the anti-ferromagnetic
coupling state between the upper ferromagnetic layer 213c and the
lower ferromagnetic layer 213a. Consequently, the composed
magnetization (composed magnetic moment) in the recording layer 213
of the second MTJ element 200 is directed in the 180.degree.
direction.
[0192] Composed magnetization (composed magnetic moment) in the
recording layer 113 of the first MTJ element 100 further rotates
counterclockwise until it is directed in the direction (180.degree.
direction) of the magnetic field generated by the write current I2
while maintaining the anti-ferromagnetic coupling state between the
upper ferromagnetic layer 113c and the lower ferromagnetic layer
113a. Consequently, the composed magnetization (composed magnetic
moment) in the recording layer 113 of the first MTJ element 100 is
directed in the 180.degree. direction.
(Fourth Cycle)
[0193] In the fourth cycle, as indicated by (e) in FIG. 9, both the
first write wiring W1 and second write wiring W2 are turned off to
stop supplying the write currents I1 and I2 to them. Hence, in the
fourth cycle, the applied magnetic fields disappear.
[0194] In this case, the magnetizations of the upper ferromagnetic
layer 213c and lower ferromagnetic layer 213a of the second MTJ
element 200 return to the stable state in the 135.degree. and
315.degree. directions (direction of the axis e2 of easy
magnetization). More specifically, the magnetizations of the upper
ferromagnetic layer 213c and lower ferromagnetic layer 213a rotate
counterclockwise. The magnetization of the upper ferromagnetic
layer 213c is directed in the 315.degree. direction. The
magnetization of the lower ferromagnetic layer 213a is directed in
the 135.degree. direction. The magnetization in the recording layer
213 of the second MTJ element 200 is directed in the direction
rotated 180.degree. from the initial state. Hence, the data of the
second MTJ element 200 can be rewritten from "1" to "0".
[0195] The magnetizations of the upper ferromagnetic layer 113c and
lower ferromagnetic layer 113a of the first MTJ element 100 return
to the stable state in the 45.degree. and 225.degree. directions
(direction of the axis e2 of easy magnetization). More
specifically, the magnetizations of the upper ferromagnetic layer
113c and lower ferromagnetic layer 113a rotate clockwise. The
magnetization of the upper ferromagnetic layer 113c is directed in
the 45.degree. direction. The magnetization of the lower
ferromagnetic layer 113a is directed in the 225.degree. direction.
The magnetization in the recording layer 113 of the first MTJ
element 100 is directed in the same direction as in the initial
state. The data of the first MTJ element 100 remains "1" and is not
rewritten.
[1-3] Read Method
[0196] As the read method of the magnetic random access memory
according to the first embodiment of the present invention, a
normal read method is employed. A voltage (or current) is applied
between the upper electrode 20 and the lower electrode 30, and a
current (or voltage) is detected by the sense amplifier 41, thereby
discriminating the "1" and "0" states of the first and second MTJ
elements 100 and 200.
[0197] When the relative magnetization direction between the
recording layer (ferromagnetic layer on the side facing the fixed
layer) and the fixed layer (ferromagnetic layer on the side facing
the recording layer when the fixed layer includes a plurality of
ferromagnetic layers divided by nonmagnetic layers) of the MTJ
element is in the parallel state (e.g., "1" state), the resistance
is low. In the anti-parallel state (e.g., "0" state), the
resistance is high. The "1" or "0" state of the MTJ element is
determined by reading the difference in resistance value.
[0198] In this embodiment, the two MTJ elements 100 and 200 are
connected in series in one cell. When a voltage (or current) is
applied between the upper electrode 20 and the lower electrode 30,
and a current (or voltage) is read out, the sum of the resistance
values of the two MTJ elements 100 and 200 is read out. In this
embodiment, the total resistance value of one cell is read out,
thereby determining the data of each of the MTJ elements 100 and
200. The read method will be described below in detail.
[0199] FIG. 10 is a schematic circuit diagram of the MTJ element of
one cell according to the first embodiment of the present
invention. FIG. 11 is a view for explaining the difference in
series resistance between logic states in the read according to the
first embodiment of the present invention. FIGS. 12A to 12D are
views for explaining the magnetization arrangements of logic states
according to the first embodiment of the present invention.
[0200] As shown in FIG. 10, in a memory cell MC according to the
first embodiment, the first MTJ element 100 and second MTJ element
200 are connected in series. The resistance values of the first and
second MTJ elements 100 and 200 change between the "1" state and
the "0" state. In the first MTJ element 100, the resistance value
in the "1" state is represented by R1, and the resistance value in
the "0" state is represented by R1+.DELTA.R1. In the second MTJ
element 200, the resistance value in the "1" state is represented
by R2, and the resistance value in the "0" state is represented by
R2+.DELTA.R2. A series resistance R of the memory cell MC equals
the sum of the resistance (R1 or R1+.DELTA.R1) of the first MTJ
element 100 and the resistance (R2 or R2+.DELTA.R2) of the second
MTJ element 200.
[0201] As shown in FIG. 11, the series resistance R of the first
and second MTJ elements 100 and 200 changes to four values Ra, Rb,
Rc, and Rd depending on the logic states of the first and second
MTJ elements 100 and 200.
[0202] For example, assume that "1" data is written in both of the
first and second MTJ elements 100 and 200 (FIG. 12A). The
resistance value of the first MTJ element 100 is R1. The resistance
value of the second MTJ element 200 is R2. The series resistance Ra
of the memory cell MC is R1+R2.
[0203] For example, assume that "0" data is written in the first
MTJ element 100, and "1" data is written in the second MTJ element
200 (FIG. 12B). The resistance value of the first MTJ element 100
is R1+.DELTA.R1. The resistance value of the second MTJ element 200
is R2. The series resistance Rb of the memory cell MC is
R1+.DELTA.R1+R2.
[0204] For example, assume that "1" data is written in the first
MTJ element 100, and "0" data is written in the second MTJ element
200 (FIG. 12C). The resistance value of the first MTJ element 100
is R1. The resistance value of the second MTJ element 200 is
R2+.DELTA.R2. The series resistance Rc of the memory cell MC is
R1+R2+.DELTA.R2.
[0205] For example, assume that "0" data is written in both of the
first and second MTJ elements 100 and 200 (FIG. 12D). The
resistance value of the first MTJ element 100 is R1+.DELTA.R1. The
resistance value of the second MTJ element 200 is R2+.DELTA.R2. The
series resistance Rd of the memory cell MC is
R1+.DELTA.R1+R2+.DELTA.R2.
[0206] Quaternary data can be read out on the basis of the
difference between the resistance values Ra, Rb, Rc, and Rd in the
four states. More specifically, when the series resistance R of the
memory cell MC in the read is, e.g., Ra, "1" data is written in
both of the first and second MTJ elements 100 and 200. When the
series resistance R is, e.g., Rb, "0" data is written in the first
MTJ element 100, and "1" data is written in the second MTJ element
200. When the series resistance R is, e.g., Rc, "1" data is written
in the first MTJ element 100, and "0" data is written in the second
MTJ element 200. When the series resistance R is, e.g., Rd, "0"
data is written in both of the first and second MTJ elements 100
and 200.
[0207] To make the quaternary read possible, the four different
resistance values Ra, Rb, Rc, and Rd must be generated. More
specifically, to obtain the different resistance values Rb and Rc,
the resistance change amounts .DELTA.R1 and .DELTA.R2 must be
different.
[0208] To satisfy this condition, the first and second MTJ elements
100 and 200 are defined as follows.
[0209] For example, the tunnel barrier layer 112 of the first MTJ
element 100 and the tunnel barrier layer 212 of the second MTJ
element 200 are formed in different thicknesses.
[0210] Alternatively, different magnetoresistive (MR) ratios may be
obtained by forming the first MTJ element 100 and second MTJ
element 200 from different materials. For example, when
Co.sub.9--Fe (anti-ferromagnetic layers are made of, e.g., Pt--Mn)
is used for the fixed layers 111 and 211, the MR ratio can be
changed by using following materials for the recording layers 113
and 213. When the material of the recording layers 113 an 213 is
Co--Fe, the MR ratio is 50% or less. When the material of the
recording layers 113 an 213 is Co--Fe--Ni, the MR ratio is 40% to
45%. When the material of the recording layers 113 an 213 is
Ni--Fe, the MR ratio is 35% or less.
[0211] Alternatively, the first MTJ element 100 and second MTJ
element 200 may be formed in different sizes.
[0212] As described above, when the four different resistance
values Ra, Rb, Rc, and Rd are generated, quaternary states can be
obtained. When the resistance values Rb and Rc of the first and
second MTJ elements 100 and 200 almost equal, ternary states can be
obtained.
[1-4] Manufacturing Method
[0213] A method of manufacturing the magnetic random access memory
according to the first embodiment of the present invention will
briefly be described with reference to FIG. 1.
[0214] The second write wiring W2 is formed. An interlayer is
formed on the second write wiring W2. The lower electrode 30 is
formed on the interlayer. A material layer 200a of the second MTJ
element 200 is formed on the lower electrode 30. The second MTJ
element 200 is formed by processing the material layer 200a. The
intermediate electrode 10 is formed on the second MTJ element 200.
A material layer 100a of the first MTJ element 100 is formed on the
intermediate electrode 10. The first MTJ element 100 is formed by
processing the material layer 100a. The upper electrode 20 is
formed on the first MTJ element 100. The first write wiring W1 is
formed above the upper electrode 20.
[0215] The directions of the axes e1 and e2 of easy magnetization
of the first and second MTJ elements 100 and 200 are determined by
magnetic annealing and shape magnetic anisotropy in forming the
fixed layers 111 and 211. For this reason, the MTJ elements can
have stronger anisotropy and stable magnetic characteristic. In
addition, a large output signal can be ensured. Since the
intermediate electrode 10 is provided, the second MTJ element 200
is not affected by the process of the first MTJ element 100.
[1-5] Material
[0216] The layers of the memory cell according to this embodiment
are formed from, e.g., the following materials.
[0217] The following ferromagnetic materials are used for the fixed
layers 111 and 211 and recording layers 113 and 213. For example,
Fe, Co, Ni, a layered film thereof, an alloy thereof, magnetite
having a high spin polarizability, an oxide such as CrO.sub.2 or
RXMnO.sub.3-Y (R: rare earth, X: Ca, Ba, or Sr), or a Heusler alloy
such as NiMnSb or PtMnSb is preferably used. The magnetic materials
may contain a small amount of nonmagnetic element such as Ag, Cu,
Au, Al, Mg, Si, Bi, Ta, B, C, O, N, Pd, Pt, Zr, Ir, W, Mo, or Nb as
long as the ferromagnetism is not lost.
[0218] For the tunnel barrier layers 112 and 212, various
dielectric materials such as Al.sub.2O.sub.3, SiO.sub.2, MgO, AlN,
Bi.sub.2O.sub.3, MgF.sub.2, CaF.sub.2, SrTiO.sub.2, and AlLaO.sub.3
can be used. These dielectric materials may contain oxygen,
nitrogen, or fluorine defects.
[0219] For the intermediate electrode 10, a nonmagnetic material
such as Ru, Ta, or TiN can be used.
[0220] According to the first embodiment, the first and second MTJ
elements 100 and 200 are stacked between the pair of write wirings
W1 and W2. The axes e1 and e2 of easy magnetization of the first
and second MTJ elements 100 and 200 are made to cross
perpendicularly and tilted 45.degree. with respect to the running
directions of the first and second write wirings W1 and W2. To
write data in a selected one of the first and second MTJ elements
100 and 200, a current is supplied to the first selected wiring of
the first and second write wirings W1 and W2 (first cycle).fwdarw.a
current is supplied to the second selected wiring of the first and
second write wirings W1 and W2 (second cycle).fwdarw.current supply
to the first selected wiring is stopped (third
cycle).fwdarw.current supply to the second selected wiring is
stopped (fourth cycle). The direction in which the current is
supplied is adjusted such that the application direction of the
synthetic field generated by the currents in the second cycle
matches the direction of the axis e1 or e2 of easy magnetization of
the selected element.
[0221] In the first to fourth cycles, magnetization in the
recording layer of the selected element rotates in one direction
(clockwise or counterclockwise). After the fourth cycle, the
parallel magnetization arrangement changes to the anti-parallel
magnetization arrangement, or the anti-parallel magnetization
arrangement changes to the parallel magnetization arrangement. On
the other hand, in the first to fourth cycles, magnetization in the
recording layer of the unselected element rotates in two directions
(clockwise and counterclockwise). After the fourth cycle, the
magnetization arrangement returns to the original state. When the
order and directions of the currents I1 and I2 supplied to the
write wirings W1 and W2 are adjusted, data can selectively be
written in the two MTJ elements 100 and 200. In addition, when the
first and second MTJ elements 100 and 200 exhibit different
resistance values for the same data, a quaternary read is
possible.
[0222] As described above, according to the first embodiment,
two-bit information can be stored between the pair of current
magnetic field wirings. For this reason, multilevel storage in
toggle cells is possible, and large-scale integration of the
magnetic random access memory can be implemented.
[2] Second Embodiment
[0223] The second embodiment is a modification to the first
embodiment. The first and second MTJ elements and the intermediate
electrode are processed at once so that they have the same planar
shape. The write method and read method of the second embodiment
are the same as those of the first embodiment, and a description
thereof will be omitted.
[2-1] Structure
[0224] FIG. 13A is a plan view of a magnetic random access memory
according to the second embodiment of the present invention. FIG.
13B is a sectional view of the magnetic random access memory taken
along a line XIIIB-XIIIB in FIG. 13A. The structure of the magnetic
random access memory according to the second embodiment of the
present invention will be described below.
[0225] As shown in FIGS. 13A and 13B, the second embodiment is
different from the first embodiment in that first and second MTJ
elements 100 and 200 and an intermediate electrode 10 have the same
planar shape. The first and second MTJ elements 100 and 200 and
intermediate electrode 10 have, e.g., a circular planar shape.
[0226] As in the first embodiment, the direction of an axis e1 of
easy magnetization of the first MTJ element 100 tilts almost
45.degree. with respect to the X or Y direction. The direction of
an axis e2 of easy magnetization of the second MTJ element 200
tilts almost 45.degree. with respect to the X or Y direction. The
directions of the axes e1 and e2 of easy magnetization of the first
and second MTJ elements 100 and 200 are different by almost
90.degree..
[2-2] Manufacturing Method
[0227] A method of manufacturing the magnetic random access memory
according to the second embodiment of the present invention will
briefly be described.
[0228] A second write wiring W2 is formed. An interlayer is formed
on the second write wiring W2. A lower electrode 30 is formed on
the interlayer. A material layer 200a of the second MTJ element
200, a material layer 10a of the intermediate electrode 10, and a
material layer 100a of the first MTJ element 100 are sequentially
formed on the lower electrode 30. The first and second MTJ elements
100 and 200 and intermediate electrode 10 having the same planar
shape are formed by processing the material layers 100a, 10a, and
200a at once. After an upper electrode 20 is formed on the first
MTJ element 100, a first write wiring W1 is formed above the upper
electrode 20.
[0229] The directions of the axes e1 and e2 of easy magnetization
of the first and second MTJ elements 100 and 200 are determined by
making the MTJ elements 100 and 200 have different magnetic
anisotropies at different magnetization temperatures.
[0230] According to the second embodiment, the same effect as in
the first embodiment can be obtained. Additionally, in the second
embodiment, the material layers 100a, 200a, and 10a of the first
and second MTJ elements 100 and 200 and intermediate electrode 10
are formed at once, and magnetic annealing can be executed in two
steps. For this reason, the effect of shortening the process and
increasing the yield is large. Hence, the process cost can largely
be reduced.
[3] Third Embodiment
[0231] The third embodiment is a modification to the second
embodiment. In the second embodiment, the fixed layer, tunnel
barrier layer, and recording layer are formed in this order from
the lower side (semiconductor substrate side) in both of the first
and second MTJ elements 100 and 200. In the third embodiment,
recording layers 113 and 213 of first and second MTJ elements 100
and 200 are formed close to each other. The write method and read
method of the third embodiment are the same as those of the first
embodiment, and a description thereof will be omitted.
[3-1] Structure
[0232] FIG. 14A is a plan view of a magnetic random access memory
according to the third embodiment of the present invention. FIG.
14B is a sectional view of the magnetic random access memory taken
along a line XIVB-XIVB in FIG. 14A. The structure of the magnetic
random access memory according to the third embodiment of the
present invention will be described below.
[0233] As shown in FIGS. 14A and 14B, the third embodiment is
different from the second embodiment in the order of forming the
fixed layer, tunnel barrier layer, and recording layer in the first
and second MTJ elements 100 and 200.
[0234] More specifically, in the first MTJ element 100, a fixed
layer 111, tunnel barrier layer 112, and recording layer 113 are
formed in this order downward from an upper electrode 20. To the
contrary, in the second MTJ element 200, a fixed layer 211, tunnel
barrier layer 212, and recording layer 213 are formed in this order
upward from a lower electrode 30 (semiconductor substrate side).
Hence, the recording layers 113 and 213 are close to each other.
The recording layers 113 and 213 of the first and second MTJ
elements 100 and 200 are in contact with an intermediate electrode
10. The fixed layer 111 of the first MTJ element 100 is in contact
with the upper electrode 20. The fixed layer 211 of the second MTJ
element 200 is in contact with the lower electrode 30.
[3-2] Manufacturing Method
[0235] A method of manufacturing the magnetic random access memory
according to the third embodiment of the present invention will
briefly be described.
[0236] A second write wiring W2 is formed. An interlayer is formed
on the second write wiring W2. The lower electrode 30 is formed on
the interlayer. A material layer 200a of the second MTJ element
200, a material layer 10a of the intermediate electrode 10, and a
material layer 100a of the first MTJ element 100 are sequentially
formed on the lower electrode 30. In the material layer 200a, the
fixed layer 211, tunnel barrier layer 212, and recording layer 213
are formed in this order from the lower side. In the material layer
100a, the recording layer 113, tunnel barrier layer 112, and fixed
layer 111 are formed in this order from the lower side. The first
and second MTJ elements 100 and 200 and intermediate electrode 10
having the same planar shape are formed by processing the material
layers 100a, 10a, and 200a at once. After the upper electrode 20 is
formed on the first MTJ element 100, a first write wiring W1 is
formed above the upper electrode 20.
[0237] The directions of axes e1 and e2 of easy magnetization of
the first and second MTJ elements 100 and 200 are determined by
making the MTJ elements 100 and 200 have different magnetic
anisotropies at different magnetization temperatures.
[0238] According to the third embodiment, the same effect as in the
second embodiment can be obtained. Additionally, in the third
embodiment, the recording layers 113 and 213 of the first and
second MTJ elements 100 and 200 are close to each other. In the
second embodiment, the recording layer 213 is sandwiched between
two fixed layers 111 and 211. In the third embodiment, however,
only one fixed layer is adjacent to each of the recording layers
113 and 213. Hence, in the third embodiment, the influence of
morphology of the fixed layers 111 and 211 on the delicate
recording layers 113 and 213 can be halved.
[4] Fourth Embodiment
[0239] The fourth embodiment is a modification to the first
embodiment. First and second MTJ elements formed on separate
substrates are stacked by a bonding technique. The write method and
read method of the fourth embodiment are the same as those of the
first embodiment, and a description thereof will be omitted.
[4-1] Structure
[0240] FIG. 15A is a plan view of a magnetic random access memory
according to the fourth embodiment of the present invention. FIG.
15B is a sectional view of the magnetic random access memory taken
along a line XVB-XVB in FIG. 15A. The structure of the magnetic
random access memory according to the fourth embodiment of the
present invention will be described below.
[0241] As shown in FIGS. 15A and 15B, the fourth embodiment is
different from the first embodiment in that first and second MTJ
elements 100 and 200 are stacked by bonding. A contact 40 is
provided between the first and second MTJ elements 100 and 200. The
contact 40 is made of a nonmagnetic material (e.g., Ta, Ru, or
TiN).
[4-2] Manufacturing Method
[0242] A method of manufacturing the magnetic random access memory
according to the fourth embodiment of the present invention will
briefly be described.
[0243] An interlayer dielectric film, switching element 43, contact
31, lower electrode 30, and write wiring W2 are formed on a second
substrate. The second MTJ element 200 is formed and buried with an
interlayer. The contact 40 connected to the second MTJ element 200
is buried in the interlayer.
[0244] On the other hand, an interlayer dielectric film, upper
electrode 20, and write wiring W1 are formed on a first substrate
different from the second substrate. The first MTJ element 100 is
formed and buried with an interlayer. The interlayer is removed by
polishing or etching to expose an end of the first MTJ element 100.
The contact 40 connected to the first MTJ element 100 may be buried
in the interlayer.
[0245] The first and second substrates are bonded. The first and
second MTJ elements 100 and 200 are connected through the contact
40. Then, the unnecessary part of the first substrate is
removed.
[0246] In the fourth embodiment, the directions of axes e1 and e2
of easy magnetization of the first and second MTJ elements 100 and
200 are determined by magnetic annealing and shape magnetic
anisotropy, as in the first embodiment. For this reason, the MTJ
elements can have stronger anisotropy and stable magnetic
characteristic. In addition, a large output signal can be
ensured.
[0247] According to the fourth embodiment, the same effect as in
the first embodiment can be obtained. Additionally, in the fourth
embodiment, the first and second MTJ elements 100 and 200 can
separately be formed. Hence, the materials of the first and second
MTJ elements 100 and 200 can have a wider choice of options.
Process integration is easy. The magnetic characteristic can be
stabilized, and process yield can be increased.
[0248] In the fourth embodiment, the first and second MTJ elements
100 and 200 are bonded such that recording layers 113 and 213 are
arranged close. Instead, the first and second MTJ elements 100 and
200 may be bonded such that the fixed layer, tunnel barrier layer,
and recording layer are stacked in this order from the lower
side.
[5] Fifth Embodiment
[0249] The fifth embodiment is a modification to the first
embodiment. Data of the first and second MTJ elements are read out
separately. The write method of the fifth embodiment is the same as
that of the first embodiment, and a description thereof will be
omitted.
[5-1] Structure
[0250] FIG. 16A is a plan view of a magnetic random access memory
according to the fifth embodiment of the present invention. FIG.
16B is a sectional view of the magnetic random access memory taken
along a line XVIB-XVIB in FIG. 16A. The structure of the magnetic
random access memory according to the fifth embodiment of the
present invention will be described below.
[0251] As shown in FIGS. 16A and 16B, the fifth embodiment is
different from the first embodiment in that a sense amplifier 41 is
connected to an intermediate electrode 10, and a switching element
(e.g., transistor) 44 is connected to an upper electrode 20. With
this structure, each of a first MTJ element 100 and second MTJ
element 200 can be selected in the data read.
[5-2] Read Method
[0252] In the first embodiment, a total series resistance R of the
first and second MTJ elements 100 and 200 is read out, thereby
reading out data of the two MTJ elements 100 and 200
simultaneously. In the read method of the fifth embodiment, a
resistance R100 of the first MTJ element 100 and a resistance R200
of the second MTJ element 200 are read out separately.
[0253] For example, to read out data of the first MTJ element 100,
the switching element 44 is turned on to supply a read current (or
apply a voltage) between the upper electrode 20 and the sense
amplifier 41. With this operation, the resistance R100 of only the
first MTJ element 100 can be read out.
[0254] To read out data of the second MTJ element 200, a switching
element 43 is turned on to supply a read current (or apply a
voltage) between a lower electrode 30 and the sense amplifier 41.
With this operation, the resistance R200 of only the second MTJ
element 200 can be read out.
[0255] According to the fifth embodiment, the same effect as in the
first embodiment can be obtained. Additionally, in the fifth
embodiment, since the resistance value of the first MTJ element 100
and the resistance value of the second MTJ element 200 can be read
out separately, the following effects can also be obtained.
[0256] Since the first and second MTJ elements 100 and 200 can have
the same resistance value in the same write state, the selectivity
of structures and materials of the first and second MTJ elements
100 and 200 can be increased. In addition, since the read signal
amount is doubled, the operation margin can largely be
increased.
[6] Sixth Embodiment
[0257] The sixth embodiment is a modification to the first
embodiment. In the first embodiment, the write wirings (first and
second write wirings W1 and W2) and read wirings (upper electrode
20 and lower electrode 30) are separately provided. In the sixth
embodiment, part (first write wiring) of the write wirings is used
as a read wiring. The write method of the sixth embodiment is the
same as that of the first embodiment, and a description thereof
will be omitted.
[6-1] Structure
[0258] FIG. 17A is a plan view of a magnetic random access memory
according to the sixth embodiment of the present invention. FIG.
17B is a sectional view of the magnetic random access memory taken
along a line XVIIB-XVIIB in FIG. 17A. The structure of the magnetic
random access memory according to the sixth embodiment of the
present invention will be described below.
[0259] As shown in FIGS. 17A and 17B, the sixth embodiment is
different from the first embodiment in that the upper electrode is
omitted, and a first write wiring W1 is connected directly to a
first MTJ element 100. Hence, a sense amplifier 41 is electrically
connected to the first write wiring W1 through a contact 45. The
first MTJ element 100 may be connected to the first write wiring W1
through a contact.
[6-2] Read Method
[0260] In the read method of the first embodiment, a read current
is supplied (or a voltage is applied) between the upper electrode
20 and the lower electrode 30. In the read method of the sixth
embodiment, a read current is supplied (or a voltage is applied)
between the first write wiring W1 and a lower electrode 30.
[0261] The method of discriminating data by reading out a total
series resistance R of the first and second MTJ elements 100 and
200 is the same as in the first embodiment, and a description
thereof will be omitted.
[0262] According to the sixth embodiment, the same effect as in the
first embodiment can be obtained. Additionally, in the sixth
embodiment, the cell area can be reduced by omitting the upper
electrode.
[7] Seventh Embodiment
[0263] The seventh embodiment is a modification to the sixth
embodiment. Data of the first and second MTJ elements are read out
separately. The write method of the seventh embodiment is the same
as that of the first embodiment, and a description thereof will be
omitted.
[7-1] Structure
[0264] FIG. 18A is a plan view of a magnetic random access memory
according to the seventh embodiment of the present invention. FIG.
18B is a sectional view of the magnetic random access memory taken
along a line XVIIIB-XVIIIB in FIG. 18A. The structure of the
magnetic random access memory according to the seventh embodiment
of the present invention will be described below.
[0265] As shown in FIGS. 18A and 18B, the seventh embodiment is
different from the sixth embodiment in that a sense amplifier 41 is
connected to an intermediate electrode 10, and a switching element
(e.g., transistor) 44 is connected to a first write wiring W1. With
this structure, each of a first MTJ element 100 and second MTJ
element 200 can be selected in the data read.
[7-2] Read Method
[0266] In the sixth embodiment, a total series resistance R of the
first and second MTJ elements 100 and 200 is read out, thereby
reading out data of the two MTJ elements 100 and 200
simultaneously. In the read method of the seventh embodiment, a
resistance R100 of the first MTJ element 100 and a resistance R200
of the second MTJ element 200 are read out separately.
[0267] For example, to read out data of the first MTJ element 100,
the switching element 44 is turned on to supply a read current (or
apply a voltage) between the first write wiring W1 and the sense
amplifier 41. With this operation, the resistance R100 of only the
first MTJ element 100 can be read out.
[0268] To read out data of the second MTJ element 200, a switching
element 43 is turned on to supply a read current (or apply a
voltage) between a lower electrode 30 and the sense amplifier 41.
With this operation, the resistance R200 of only the second MTJ
element 200 can be read out.
[0269] According to the seventh embodiment, the same effect as in
the sixth embodiment can be obtained. Additionally, in the seventh
embodiment, the resistance of the first MTJ element 100 and the
resistance of the second MTJ element 200 can be read out
separately. Since the first and second MTJ elements 100 and 200 can
have the same resistance in the same write state, the selectivity
of structures and materials of the first and second MTJ elements
100 and 200 can be increased.
[8] Eighth Embodiment
[0270] In the above-described embodiments, the toggle write is
executed for both of the first and second MTJ elements. In the
eighth embodiment, the toggle write is executed for the first MTJ
element, and the normal one-cycle write is executed for the second
MTJ element. The read method of the eighth embodiment is the same
as that of the above-described embodiments, and a description
thereof will be omitted.
[8-1] Structure
[0271] FIG. 19 is a plan view of a magnetic random access memory
according to the eighth embodiment of the present invention. The
structure of the magnetic random access memory according to the
eighth embodiment of the present invention will be described
below.
[0272] As shown in FIG. 19, the eighth embodiment is different from
the first embodiment in that the direction of an axis e2 of easy
magnetization of a second MTJ element 200 is the same as the
running direction (X direction) of a first write wiring W1.
[8-2] Write Method
[0273] FIG. 20 is a view for explaining quaternary states by the
write method according to the eighth embodiment of the present
invention. The write method according to the eighth embodiment of
the present invention will be described below with reference to
FIG. 20.
[0274] In the first state, the write sequence in, e.g., FIG. 2 is
executed. Magnetization e1 of a first MTJ element 100 is set in a
180.degree. reverse state (e.g., "1" state). Magnetization e2 of
the second MTJ element 200 is set in a right state (e.g., "1"
state).
[0275] In the second state, the write sequence in, e.g., FIG. 3 is
executed. The magnetization e1 of the first MTJ element 100 is set
in the 180.degree. reverse state (e.g., "1" state). The
magnetization e2 of the second MTJ element 200 is set in a left
state (e.g., "0" state).
[0276] In the third state, the write sequence in, e.g., FIG. 8 is
executed. The magnetization e1 of the first MTJ element 100 is set
in an unchanged state without magnetization reversal (e.g., "0"
state). The magnetization e2 of the second MTJ element 200 is set
in the right state (e.g., "1" state).
[0277] In the fourth state, the write sequence in, e.g., FIG. 9 is
executed. The magnetization e1 of the first MTJ element 100 is set
in the unchanged state without magnetization reversal (e.g., "0"
state). The magnetization e2 of the second MTJ element 200 is set
in the left state (e.g., "0" state).
[0278] As described above, according to the eighth embodiment, the
first and second operations can selectively independently be
executed by changing the order of starting supplying the current to
the first and second write wirings W1 and W2 and the write current
supply direction. The first operation is an operation of causing or
not causing the first MTJ element 100 to execute the toggle
operation. The second operation is an operation of reversing
magnetization in a recording layer 213 of the second MTJ element
200. With this write operation, quaternary states can actually be
generated.
[0279] According to the eighth embodiment, two-bit information can
be stored between the pair of current magnetic field wirings, as in
the first embodiment. For this reason, multilevel storage in toggle
cells is possible, and large-scale integration of the magnetic
random access memory can be implemented.
[0280] The present invention is not limited to the above-described
embodiments, and various changes and modifications can be made in
practicing the present invention without departing from its spirit
and scope, as will be described below.
[0281] (a) In the MTJ elements 100 and 200 of the above-described
embodiments, the recording layers 113 and 213 each have an
anti-ferromagnetic coupling structure. The fixed layers 111 and 211
each have a single-layer structure. However, the present invention
is not limited to this. For example, the fixed layers 111 and 211
each may have an anti-ferromagnetic coupling structure or
ferromagnetic coupling structure. More specifically, the fixed
layers 111 and 211 each may have a three-layer structure of first
ferromagnetic layer/nonmagnetic layer/second ferromagnetic layer.
They each may have an anti-ferromagnetic coupling structure in
which magnetic coupling (interlayer exchange coupling) occurs such
that the magnetization directions of the first and second
ferromagnetic layers are anti-parallel. Alternatively, they each
may have a ferromagnetic coupling structure in which magnetic
coupling (interlayer exchange coupling) occurs such that the
magnetization directions of the first and second ferromagnetic
layers are parallel.
[0282] (b) The MTJ elements 100 and 200 of the above-described
embodiments each have a single junction structure having one tunnel
barrier layer. However, the present invention is not limited to
this. For example, the MTJ elements 100 and 200 each may have a
double junction structure having two tunnel barrier layers. More
specifically, the MTJ elements 100 and 200 each having the double
junction structure include a first fixed layer, a second fixed
layer, a recording layer provided between the first and second
fixed layers, a first tunnel barrier layer provided between the
first fixed layer and the recording layer, and a second tunnel
barrier layer provided between the second fixed layer and the
recording layer.
[0283] (c) The planar shape of the MTJ elements 100 and 200 of the
above-described embodiments is illustrated as an ellipse or circle.
However, the present invention is not limited to this. For example,
the planar shape of the MTJ elements 100 and 200 can variously be
changed to a square, rectangle, hexagon, rhombus, parallelogram,
cross, or bean-shape (concave shape).
[0284] In any planar shape, when the toggle write should be
executed in the first and second MTJ elements 100 and 200, the
directions of the axes e1 and e2 of easy magnetization are defined
such that "the direction of the axis e1 of easy magnetization of
the first MTJ element 100 tilts 45.degree. with respect to the
first or second write wiring W1 or W2, the direction of the axis e2
of easy magnetization of the second MTJ element 200 tilts
45.degree. with respect to the first or second write wiring W1 or
W2, and the directions of the axes e1 and e2 of easy magnetization
of the first and second MTJ elements 100 and 200 are different by
90.degree.".
[0285] (d) In the MTJ elements 100 and 200 of the above-described
embodiments, the fixed layer, tunnel barrier layer, and recording
layer are, e.g., processed at once and have the same planar shape.
However, the present invention is not limited to this. For example,
the fixed layer and tunnel barrier layer may be formed into a
rectangular shape, and only the recording layer may be formed into
a cross shape.
[0286] (e) In the magnetic random access memories of the
above-described embodiments, transistors are illustrated as the
switching elements 43 and 44. They may be, e.g., diodes. The
switching elements 43 and 44 need not always be provided.
[0287] (f) In the magnetic random access memories of the
above-described embodiments, the connection portions of the sense
amplifier 41, reference cell 42, and switching element 43 can be
changed if the resistance value of the MTJ element can be detected.
For example, in the structure shown in FIG. 1, the sense amplifier
41 and reference cell 42 may be connected to the lower electrode
30, and the switching element 43 may be connected to the upper
electrode 20. In the structure shown in FIG. 16, the sense
amplifier 41 and reference cell 42 may be connected to the upper
electrode 20 and lower electrode 30, respectively, and the
switching element 43 may be connected to the intermediate electrode
10. In the structure shown in FIG. 17, the sense amplifier 41 and
reference cell 42 may be connected to the lower electrode 30, and
the switching element 43 may be connected to the first write wiring
W1. In the structure shown in FIG. 18, the sense amplifier 41 and
reference cell 42 may be connected to the first write wiring W1 and
lower electrode 30, respectively, and the switching element 43 may
be connected to the intermediate electrode 10.
[0288] (g) Detailed examples of the method of fixing the
magnetization directions of the fixed layers 111 and 211 of the
first and second MTJ elements 100 and 200 in different directions
are as follows.
[0289] The blocking temperature changes depending on the material
of the anti-ferromagnetic layer used for the fixed layers 111 and
211. For example, the blocking temperature is 430.degree. C. when
the material of the anti-ferromagnetic layer is Ni--Mn, 350.degree.
C. when the material is Pt--Mn, 260.degree. C. when the material is
Ir--Mn, and 150.degree. C. when the material is Fe--Mn. By using
the difference in blocking temperature, the magnetization
directions of the fixed layers 111 and 211 of the first and second
MTJ elements 100 and 200 are fixed in different directions.
[0290] First, the second MTJ element 200 is formed. More
specifically, a first layered film including an anti-ferromagnetic
layer (Pt--Mn)/fixed layer 211/tunnel barrier layer 212/recording
layer 213 is deposited on the lower electrode 30. The first layered
film is processed by ion milling such that it becomes long in the
desired magnetization direction of the axis of easy magnetization.
An SiO.sub.X film serving as an interlayer dielectric film is
deposited on the entire surface by, e.g., RF sputtering. The
SiO.sub.X film is planarized to expose the upper surface portion of
the second MTJ element 200.
[0291] Next, the first MTJ element 100 is formed. More
specifically, a second layered film including an anti-ferromagnetic
layer (Ir--Mn)/fixed layer 111/tunnel barrier layer 112/recording
layer 113 is deposited above the second MTJ element 200. The second
layered film is processed by ion milling such that it becomes long
in the desired magnetization direction of the axis of easy
magnetization. The first and second MTJ elements 100 and 200 have
the axes of easy magnetization in different directions.
[0292] After that, the substrate is heated to 350.degree.
C.+.alpha. while applying a magnetic field of several thousand Oe
in the direction of the axis of easy magnetization of the second
MTJ element 200, thereby fixing the magnetization direction of the
fixed layer 211. Subsequently, the substrate is heated to
260.degree. C.+.alpha. while applying a magnetic field of several
thousand Oe in the direction of the axis of easy magnetization of
the first MTJ element 100, thereby fixing the magnetization
direction of the fixed layer 111 in a direction different from that
of the second MTJ element 200.
[0293] When the directions of the axes of easy magnetization of the
recording layers 113 and 213 of the first and second MTJ elements
100 and 200 are set by, e.g., shape anisotropy and magnetic
annealing, the magnetic anisotropy can be made firmer. With this
process, magnetic tunnel junctions with different directions of
axes of easy magnetization can be stacked.
[0294] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *