U.S. patent application number 16/134289 was filed with the patent office on 2019-09-26 for memory device.
This patent application is currently assigned to Toshiba Memory Corporation. The applicant listed for this patent is Toshiba Memory Corporation. Invention is credited to Shoichi Kabuyanagi, Yuuichi Kamimuta, Hiromichi Kuriyama, Masumi Saitoh, Chika Tanaka, Yoko Yoshimura.
Application Number | 20190296234 16/134289 |
Document ID | / |
Family ID | 67985708 |
Filed Date | 2019-09-26 |
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United States Patent
Application |
20190296234 |
Kind Code |
A1 |
Yoshimura; Yoko ; et
al. |
September 26, 2019 |
MEMORY DEVICE
Abstract
A memory device according to an embodiment includes a first
conductive layer extending in a first direction, a second
conductive layer extending in the first direction, a third
conductive layer extending in a second direction intersecting the
first direction, an insulating layer containing aluminum oxide
provided between the first conductive layer and the second
conductive layer, and a first insulating film including a first
region located between the first conductive layer and the third
conductive layer and a second region located between the insulating
layer and the third conductive layer. The first region includes
hafnium oxide mainly formed as an orthorhombic. The second region
includes hafnium oxide mainly formed as crystals other than the
orthorhombic.
Inventors: |
Yoshimura; Yoko; (Yokkaichi,
JP) ; Kuriyama; Hiromichi; (Kuwana, JP) ;
Kabuyanagi; Shoichi; (Yokkaichi, JP) ; Kamimuta;
Yuuichi; (Yokkaichi, JP) ; Tanaka; Chika;
(Fujisawa, JP) ; Saitoh; Masumi; (Yokohama,
JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Toshiba Memory Corporation |
Minato-ku |
|
JP |
|
|
Assignee: |
Toshiba Memory Corporation
Minato-ku
JP
|
Family ID: |
67985708 |
Appl. No.: |
16/134289 |
Filed: |
September 18, 2018 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01L 27/249 20130101;
H01L 27/2463 20130101; H01L 45/1233 20130101; G11C 13/0028
20130101; G11C 13/0007 20130101; H01L 45/1641 20130101; G11C
2213/71 20130101; G11C 2213/77 20130101; H01L 45/04 20130101; G11C
2213/75 20130101; H01L 45/1226 20130101; G11C 13/003 20130101; H01L
27/2481 20130101; H01L 45/146 20130101; H01L 27/11597 20130101;
H01L 27/2418 20130101; H01L 29/40111 20190801; G11C 13/0026
20130101; G11C 11/5685 20130101 |
International
Class: |
H01L 45/00 20060101
H01L045/00; H01L 27/24 20060101 H01L027/24; H01L 27/11597 20060101
H01L027/11597; G11C 13/00 20060101 G11C013/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 23, 2018 |
JP |
2018-055400 |
Claims
1. A memory device comprising: a first conductive layer extending
in a first direction; a second conductive layer extending in the
first direction; a third conductive layer extending in a second
direction intersecting the first direction and including metal; an
insulating layer provided between the first conductive layer and
the second conductive layer, the insulating layer including
aluminum oxide; and a first insulating film including a first
region and a second region, the first region located between the
first conductive layer and the third conductive layer, the first
region including hafnium oxide whose main crystal structure is
orthorhombic, the second region located between the insulating
layer and the third conductive layer, and the second region
including hafnium oxide whose main crystal structure is crystal
structure other than orthorhombic.
2. The memory device according to claim 1, wherein the first
conductive layer and the second conductive layer include metal.
3. The memory device according to claim 2, wherein the first
conductive layer and the second conductive layer include at least
one of titanium nitride, tantalum nitride, or tungsten nitride.
4. (canceled)
5. The memory device according to claim 1, wherein the third
conductive layer includes at least one of tungsten or titanium
nitride.
6. The memory device according to claim 1, wherein a composition of
the first region and a composition of the second region are
substantially the same.
7. The memory device according to claim 1, wherein the first region
includes ferroelectrics and the second region includes
paraelectrics.
8. The memory device according to claim 1, further comprising: a
second insulating film provided between the first insulating film
and the third conductive layer, the second insulating film not
including aluminum oxide.
9. The memory device according to claim 8, wherein the second
insulating film includes at least one of silicon oxide or titanium
oxide.
10. A memory device comprising: a first conductive layer extending
in a first direction; a second conductive layer extending in the
first direction; a third conductive layer extending in a second
direction intersecting the first direction; an insulating layer
provided between the first conductive layer and the second
conductive layer, the insulating layer including aluminum oxide; a
first insulating film including a first region and a second region,
the first region located between the first conductive layer and the
third conductive layer, the first region including hafnium oxide
whose main crystal structure is orthorhombic, the second region
located between the insulating layer and the third conductive
layer, and the second region including hafnium oxide whose main
crystal structure is crystal structure other than orthorhombic; and
a second insulating film provided between the first insulating film
and the third conductive layer, the second insulating film
including paraelectrics and not including aluminum oxide.
11. The memory device according to claim 1, wherein the first
insulating film further includes a third region which is located
between the second conductive layer and the third conductive layer,
and the third region includes hafnium oxide whose main crystal
structure is orthorhombic.
12. A memory device comprising: a first conductive layer extending
in a first direction; a second conductive layer extending in the
first direction; a third conductive layer extending in a second
direction intersecting the first direction; an insulating layer
provided between the first conductive layer and the second
conductive layer, the insulating layer including aluminum oxide; a
first insulating film including a first region and a second region,
the first region located between the first conductive layer and the
third conductive layer, the first region including hafnium oxide
whose main crystal structure is orthorhombic, the second region
located between the insulating layer and the third conductive
layer, and the second region including hafnium oxide whose main
crystal structure is crystal structure other than orthorhombic; a
second insulating film provided between the first insulating film
and the third conductive layer, the second insulating film not
including aluminum oxide; and a multi-layered insulator provided
between the first conductive layer and the first insulating film or
between the second insulating film and the third conductive layer,
wherein the multi-layered insulator has a first layer, a second
layer, and a third layer, the second layer is located between the
first layer and the third layer, electron affinity of the first
layer is larger than electron affinity of the second layer, and the
electron affinity of the second layer is larger than electron
affinity of the third layer.
13. The memory device according to claim 12, wherein a thickness of
the third layer is thinner than a thickness of the first layer and
a thickness of the second layer.
14-20. (canceled)
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2018-055400, filed on
Mar. 23, 2018, the entire contents of which are incorporated herein
by reference.
FIELD
[0002] Embodiments described herein relate generally to a memory
device.
BACKGROUND
[0003] A ferroelectric memory has attracted attention as a
nonvolatile memory. As the ferroelectric memory, for example, a
two-terminal type memory such as a ferroelectric tunnel junction
(FTJ) memory in which a ferroelectric film is provided between two
electrodes or a three-terminal type memory in which a gate
insulating film of a transistor is a ferroelectric film is
used.
[0004] The ferroelectric memory uses polarization inversion of
ferroelectrics to write data into a memory cell and erase data of a
memory cell. When the ferroelectric memory is scaled-down, memory
characteristics may degrade due to an interference between adjacent
memory cells.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIG. 1 is a block diagram of a memory cell array and a
peripheral circuit of a memory device according to a first
embodiment.
[0006] FIGS. 2A, 2B, and 2C are schematic views of a part of the
memory cell array of the memory device of the first embodiment.
[0007] FIGS. 3A, 3B, 3C and 3D are schematic cross-sectional views
showing an example of a method for manufacturing a memory device
according to the first embodiment.
[0008] FIG. 4 is a schematic diagram of a part of a memory cell
array of a memory device of a comparative example.
[0009] FIGS. 5A and 5B are explanatory diagrams of functions and
effects of the memory device according to the first embodiment.
[0010] FIG. 6 is a block diagram of a memory device according to a
second embodiment.
[0011] FIG. 7 is an equivalent circuit diagram of a memory cell
array of the memory device according to the second embodiment.
[0012] FIGS. 8A and 8B are schematic views of a part of the memory
cell array of the memory device according to the second
embodiment.
[0013] FIG. 9 is an equivalent circuit diagram of a memory cell
array of a memory device according to a third embodiment.
[0014] FIGS. 10A and 10B are schematic views of a part of the
memory cell array of the memory device according to the third
embodiment.
[0015] FIG. 11 is a block diagram of a memory cell array and a
peripheral circuit of a memory device according to a fourth
embodiment.
[0016] FIGS. 12A, 12B, and 12C are schematic views of a part of the
memory cell array of the memory device of the fourth
embodiment.
[0017] FIG. 13 is a schematic cross-sectional view of a memory cell
of the memory device according to the fourth embodiment.
[0018] FIG. 14 is a band diagram of a selector layer of the memory
device according to the fourth embodiment.
[0019] FIGS. 15A, 15B, and 15C are explanatory diagrams of
functions and effects of the memory device according to the fourth
embodiment.
[0020] FIG. 16 is an explanatory diagram of functions and effects
of the memory device of the fourth embodiment.
[0021] FIGS. 17A and 17B are schematic views of a part of a memory
cell array of a memory device according to a fifth embodiment.
[0022] FIG. 18 is a schematic cross-sectional view of a memory cell
of the memory device according to the fifth embodiment.
[0023] FIGS. 19A and 19B are schematic views of a part of a memory
cell array of a memory device according to a sixth embodiment.
[0024] FIG. 20 is a schematic cross-sectional view of a memory cell
of the memory device according to the sixth embodiment.
DETAILED DESCRIPTION
[0025] A memory device according to an embodiment includes a first
conductive layer extending in a first direction, a second
conductive layer extending in the first direction, a third
conductive layer extending in a second direction intersecting the
first direction, an insulating layer including aluminum oxide
provided between the first conductive layer and the second
conductive layer, and a first insulating film including a first
region located between the first conductive layer and the third
conductive layer and a second region located between the insulating
layer and the third conductive layer. The first region includes
hafnium oxide whose main crystal structure is orthorhombic. The
second region includes hafnium oxide whose main crystal structure
is crystal structure other than orthorhombic.
[0026] Hereinafter, embodiments of the present disclosure will be
described with reference to the drawings. In the following
description, the same or similar members or the like are denoted by
the same reference numerals, and a description of members and the
like which are once described is omitted as appropriate.
[0027] In addition, in the present specification, the term "above"
or "below" may be used for the sake of convenience. "Above" or
"below" is a term indicating a relative positional relationship
within the drawings and is not a term defining a positional
relationship with respect to gravity.
[0028] Qualitative analysis and quantitative analysis on chemical
compositions of members constituting the memory device in this
specification can be performed, for example, by secondary ion mass
spectroscopy (SIMS), and energy dispersive X-ray spectroscopy
(EDX). In addition, for measuring the thickness of the members
constituting the memory device, the distance between the members,
and the like, for example, it is possible to use a transmission
electron microscope (TEM). For example, X-ray photoelectron
spectroscopy (XPS) can be used for identifying the crystal system
of the members constituting the memory device and comparing the
magnitude of the existence ratio of the crystal system.
[0029] "Ferroelectrics" in the present specification means a
substance which has spontaneous polarization without applying an
electric field from the outside, and inverts polarization when an
electric field is applied from the outside. In addition, in the
present specification, "paraelectrics" means a substance in which
polarization is generated when an electric field is applied and
polarization disappears when an electric field is removed.
[0030] In the present specification, the term "metal" is a generic
term for substances exhibiting metallic properties, and for
example, metal nitrides exhibiting metallic properties are also
included in the range of "metal".
First Embodiment
[0031] A memory device according to a first embodiment includes a
first conductive layer extending in a first direction, a second
conductive layer extending in the first direction, a third
conductive layer extending in a second direction intersecting the
first direction, an insulating layer including aluminum oxide
provided between the first conductive layer and the second
conductive layer, and a first insulating film including a first
region located between the first conductive layer and the third
conductive layer and a second region located between the insulating
layer and the third conductive layer. The first region includes
hafnium oxide whose main crystal structure is orthorhombic. The
second region includes hafnium oxide whose main crystal structure
is crystal structure other than orthorhombic.
[0032] FIG. 1 is a block diagram of a memory cell array 100 and a
peripheral circuit of a memory device according to a first
embodiment. The memory device of the first embodiment is an FTJ
memory. A region indicated by a dotted circle in the memory cell
array 100 of FIG. 1 is one memory cell MC.
[0033] Hereinafter, an x direction shown in FIGS. 1, 2A, 2B, and 2C
is defined as a first direction, a y direction is defined as a
second direction, and a z direction is defined as a third
direction.
[0034] The memory cell array 100 of the memory device according to
the first embodiment includes, for example, a plurality of word
lines WLs and a plurality of bit lines BLs intersecting the word
lines WLs on a semiconductor substrate 101 with an insulating layer
interposed therebetween. The word line WL is provided under the bit
line BL. In addition, a first control circuit 108, a second control
circuit 110, and a sense circuit 112 are provided around the memory
cell array 100 as peripheral circuits.
[0035] A plurality of memory cells MCs are provided in a region
where the word line WL intersects the bit line BL. The memory
device of the first embodiment is an FTJ memory having a cross
point structure. The memory cell MC is a two-terminal element.
[0036] Each of the plurality of word lines WLs is connected to the
first control circuit 108. In addition, each of the plurality of
bit lines BLs is connected to the second control circuit 110. The
sense circuit 112 is connected to the first control circuit 108 and
the second control circuit 110.
[0037] For example, the first control circuit 108 and the second
control circuit 110 select a desired memory cell MC and have a
function of wiring data into the memory cell, reading the data of
the memory cell, erasing the data of the memory cell, and the like.
When data are read out, the data of the memory cell is read out as
the amount of current flowing between the word line WL and the bit
line BL. The sense circuit 112 has a function of determining the
current amount and determining polarity of the data. For example,
the sense circuit 112 determines "0" or "1" of data. The sense
circuit 112 determines the amount of tunnel current flowing in the
memory cell to determine the polarity of the data.
[0038] The first control circuit 108, the second control circuit
110, and the sense circuit 112 are constituted by electronic
circuits using semiconductor devices formed on the semiconductor
substrate 101, for example.
[0039] FIGS. 2A, 2B, and 2C are schematic views of a part of the
memory cell array 100 of a memory device of the first embodiment.
FIG. 2A is a top view, FIG. 2B is a cross-sectional view taken
along the direction A-A' of FIG. 2A, and FIG. 2C is a
cross-sectional view taken along the direction B-B' of FIG. 2A.
[0040] The memory cell array 100 includes a word line WL1 (a first
conductive layer), a word line WL2 (a second conductive layer), a
word line WL3, a word line WL4, a bit line BL1 (a third conductive
layer), a bit line BL2, a bit line BL3, a bit line BL4, a first
insulating film 31, a second insulating film 32, the semiconductor
substrate 101, a first interlayer insulating layer 102, a second
interlayer insulating layer 103 (insulating layer), and a third
interlayer insulating layer 105. Hereinafter, the word line WL1
(the first conductive layer), the word line WL2 (the second
conductive layer), the word line WL3, and the word line WL4 may be
collectively referred to simply as the word line WL. In addition,
the bit line BL1 (the third conductive layer), the bit line BL2,
the bit line BL3, and the bit line BL4 may be collectively referred
to simply as the bit line BL.
[0041] The word line WL extends in the x direction (the first
direction). The word line WL is made of, for example, metal. The
word line WL is made of, for example, metal having high heat
resistance. The word line WL is made of, for example, titanium
nitride (TiN), tungsten nitride (WN), tantalum nitride (TaN),
tungsten (W), tantalum (Ta), niobium (Nb), vanadium (V), iron (Fe),
molybdenum (Mo), cobalt (Co), nickel (Ni), ruthenium (Ru), iridium
(Ir), copper (Cu), palladium (Pd), silver (Ag), or platinum
(Pt).
[0042] The bit line BL extends in the y direction (the second
direction). The y direction (second direction) is orthogonal to the
x direction. The bit line BL is made of, for example, metal. The
bit line BL is made of, for example, metal having high heat
resistance. The bit line BL is made of, for example, tungsten (W),
titanium nitride (TiN), tungsten nitride (WN), tantalum nitride
(TaN), tantalum (Ta), niobium (Nb), vanadium (V), iron (Fe),
molybdenum (Mo), cobalt (Co), nickel (Ni), ruthenium (Ru), iridium
(Ir), copper (Cu), palladium (Pd), silver (Ag), or platinum
(Pt).
[0043] The word line WL1 is an example of a first conductive layer.
The word line WL2 is an example of a second conductive layer. The
bit line BL1 is an example of a third conductive layer.
[0044] The semiconductor substrate 101 is, for example, a silicon
substrate.
[0045] The first interlayer insulating layer 102 is provided on the
semiconductor substrate 101. The first interlayer insulating layer
102 is provided between the semiconductor substrate 101 and the
word line WL. The first interlayer insulating layer 102 includes,
for example, silicon oxide.
[0046] The second interlayer insulating layer 103 is provided
between the word line WL and the word line WL. The second
interlayer insulating layer 103 includes aluminum oxide. The second
interlayer insulating layer 103 is an example of an insulating
layer. The second interlayer insulating layer 103 is located under
the first insulating film 31.
[0047] The third interlayer insulating layer 105 is provided on the
word line WL. The third interlayer insulating layer 105 is provided
between the bit line BL and the bit line BL. The third interlayer
insulating layer 105 includes, for example, silicon oxide.
[0048] The first insulating film 31 is provided between the word
line WL and the bit line BL and between the second interlayer
insulating layer 103 and the bit line BL. The first insulating film
31 includes hafnium oxide. The first insulating film 31 is
segmented between the bit line BL and the bit line BL.
[0049] The first insulating film 31 includes hafnium oxide
including, as an additive element, at least one element selected
from the group consisting of, for example, silicon (Si), titanium
(Ti), zirconium (Zr), aluminum (Al), yttrium (Y), strontium (Sr),
lanthanum (La), cerium (Ce), gadolinium (Gd), and barium (Ba). The
first insulating film 31 may include hafnium oxide not including an
additive element.
[0050] The first insulating film 31 includes a first region 31a
located between the word line WL and the bit line BL and a second
region 31b located between the second interlayer insulating layer
103 and the bit line EL. The first region 31a exists right on the
word line WL, and the second region 31b exists right on the second
interlayer insulating layer 103. The first region 31a and the
second region 31b alternately exist in the y direction in the first
insulating film 31.
[0051] The first region 31a between the word line WL2 (the second
conductive layer) and the bit line BL1 (the third conductive layer)
is an example of the third region.
[0052] A thickness of the first insulating film 31 is, for example,
3 nm or more and 10 nm or less.
[0053] The first region 31a includes hafnium oxide mainly formed as
an orthorhombic. More specifically, the hafnium oxide in the first
region 31a is hafnium oxide mainly formed as orthorhombic III
(space group Pbc2.sub.1, space group number 29). The first region
31a includes hafnium oxide whose main crystal structure is
orthorhombic. The word "main crystal structure" means the crystal
structure occupying the largest ratio among the crystal structures
in the hafnium oxide. Among the crystal structures of the hafnium
oxide included in the first region 31a, a ratio occupied by the
orthorhombic is the largest.
[0054] The first region 31a includes ferroelectrics. The hafnium
oxide exhibiting ferroelectricity is orthorhombic.
[0055] The second region 31b includes hafnium oxide mainly formed
as crystals other than the orthorhombic. The second region 31b
includes hafnium oxide whose main crystal structure is crystal
structure other than orthorhombic. Among the crystal structures of
the hafnium oxide included in the second region 31b, the ratio
occupied by crystal structure other than the orthorhombic is the
largest. In addition to the orthorhombic, there are cubic,
hexagonal, tetragonal, monoclinic, and triclinic.
[0056] The second region 31b includes paraelectrics. The hafnium
oxide formed as crystal structure other than the orthorhombic
exhibits the paraelectricity.
[0057] The first region 31a and the second region 31b are regions
in a film formed at the same time. The compositions of the first
region 31a and the second region 31b are substantially the same.
The compositions of the first region 31a and the second region 31b
are the same within a range of errors in compositions in the film
at the time of the film formation. The compositions are expressed
by atomic percentage of elements included in the first region 31a
and the second region 31b.
[0058] The second insulating film 32 is provided between the first
insulating film 31 and the bit line BL.
[0059] The second insulating film 32 does not contain aluminum
oxide. The second insulating film 32 includes, for example, oxide,
nitride, or oxynitride. The second insulating film 32 includes, for
example, silicon oxide or titanium oxide. The second insulating
film 32 includes, for example, paraelectrics.
[0060] A thickness of the second insulating film 32 is, for
example, 0.5 nm or more and 2 nm or less.
[0061] Next, a method for manufacturing the memory device according
to the first embodiment will be described.
[0062] FIGS. 3A, 3B, 3C and 3D are schematic cross-sectional views
showing an example of a method for manufacturing a memory device
according to the first embodiment. FIGS. 3A, 3B, 3C and 3D show
cross sections corresponding to the sectional view of FIG. 2B. That
is, it shows a cross section including a y direction and a z
direction.
[0063] First, a first interlayer insulating layer 102 is formed on
a semiconductor substrate 101. The first interlayer insulating
layer 102 includes, for example, silicon oxide. The first
interlayer insulating layer 102 is formed by, for example, the film
formation by a chemical vapor deposition (CVD) method. Next, the
plurality of word lines WLs are formed on the first interlayer
insulating layer 102. The word line WL is formed by, for example, a
film formation by the CVD method, and patterning by a lithography
method and a reactive ion etching (RIE) method.
[0064] Next, the second interlayer insulating layer 103 is formed
between the word lines WLs (FIG. 3A). The second interlayer
insulating layer 103 includes aluminum oxide. The second interlayer
insulating layer 103 is formed by, for example, the film formation
by the CVD method and planarization by a chemical mechanical
polishing (CMP) method.
[0065] Next, a first insulating film 31 is formed on the word line
WL and the second interlayer insulating layer 103. The first
insulating film 31 is hafnium oxide. The hafnium oxide is amorphous
just after the film formation. The first insulating film 31 is
formed by, for example, an atomic layer deposition (ALD)
method.
[0066] Next, a second insulating film 32 is formed on the first
insulating film 31 (FIG. 3B). The second insulating film 32 is
formed by, for example, the CVD method. The second insulating film
32 includes, for example, silicon oxide.
[0067] Next, a bit line BL is formed on the second insulating film
32 (FIG. 3C). The bit line BL is formed by, for example, the film
formation by the CVD method, and the patterning by the lithography
method and the RIE method.
[0068] After forming the bit line BL, the second insulating film 32
and the first insulating film 31 between the bit line and the bit
line are removed. The removal of the second insulating film 32 and
the first insulating film 31 is performed by, for example, the RIE
method using the bit line BL as a mask.
[0069] Next, the third interlayer insulating layer 105 is formed on
the word line WL exposed between the bit lines BLs. The third
interlayer insulating layer 105 includes, for example, silicon
oxide. The third interlayer insulating layer 105 is formed by, for
example, the film formation by the CVD method and the planarization
by the CMP method.
[0070] Next, heat treatment is performed to crystallize hafnium
oxide of the first insulating film 31 (FIG. 3D). The heat treatment
is performed, for example, in a nitrogen gas atmosphere at a
temperature of 600.degree. C. or more and 1050.degree. C. or less
for 1 second or more and 30 seconds or less. The heat treatment is
so-called crystallization annealing.
[0071] By the heat treatment, the hafnium oxide between the word
line WL and the bit line BL is crystallized to be orthorhombic. On
the other hand, the hafnium oxide between the second interlayer
insulating layer 103 and the bit line BL is crystallized, but does
not become orthorhombic, but becomes crystals other than the
orthorhombic.
[0072] By the heat treatment, a first region 31a between the word
line WL and the bit line BL and a second region 31b between the
second interlayer insulating layer 103 and the bit line BL are
formed in the first insulating film 31. The first region 31a
includes hafnium oxide mainly formed as the orthorhombic. The
second region 31b includes hafnium oxide mainly formed as crystals
other than the orthorhombic.
[0073] According to the above manufacturing method, the memory
device of the first embodiment shown in FIGS. 2A, 2B, and 2C is
manufactured.
[0074] Next, functions and effects of the memory device according
to the first embodiment will be described.
[0075] First, an operation principle of the FTJ memory will be
briefly described with the memory device of the comparative example
as an example.
[0076] FIG. 4 is a schematic diagram of a part of a memory cell
array of the memory device of the comparative example. FIG. 4 shows
a cross section corresponding to the cross-sectional view of FIG.
2B of the first embodiment. That is, it shows a cross section
including the y direction and the z direction.
[0077] As shown in FIG. 4, the memory cell array of the comparative
example is different from the first embodiment in that the first
insulating film 31 is not segmented into the first region 31a and
the second region 31b. The first insulating film 31 of the
comparative example includes hafnium oxide entirely formed as the
orthorhombic. In addition, the second interlayer insulating layer
103 of the memory cell array of the comparative example is
different from the first embodiment in that it does not contain
aluminum oxide. The second interlayer insulating layer 103 of the
comparative example includes, for example, silicon oxide.
[0078] In the FTJ memory, by changing a voltage applied between the
word line WL and the bit line BL, polarization inversion of the
first insulating film 31 including ferroelectrics is caused. A
shape of a tunnel barrier formed by the first insulating film 31
and the second insulating film 32 is changed by the polarization
state of the first insulating film 31. A tunnel current flowing
between the word line WL and the bit line BL is changed by the
change in the shape of the tunnel barrier.
[0079] For example, when an off state (high resistance state) in
which the tunnel current hardly flows is defined as data "0" and an
on state (low resistance state) in which the tunnel current easily
flows is defined as data "1", a memory cell MC can store 1 bit data
of "0" and "1".
[0080] When the ferroelectric memory is scaled-down, memory
characteristics may degrade due to inter-cell interference between
adjacent memory cells. For example, as an interval between the word
lines WLs is narrow due to the scaling-down, the polarization state
of the first insulating film 31 below adjacent word lines WLs
changes due to the voltage applied to the word line WL, such that
erroneous writing may occur. For example, it is conceivable that
interference occurs between cells in which a size of a polarization
domain of ferroelectrics becomes equal to an interval between the
word lines WLs due to the scaling-down.
[0081] According to the investigation by the inventors, it became
clear that the hafnium oxide in contact with the aluminum oxide
does not form an orthorhombic structure when the crystallization
annealing is performed and does not exhibit ferroelectricity.
[0082] FIGS. 5A and 5B are explanatory diagrams of functions and
effects of the memory device according to the first embodiment.
FIG. 5A is a diagram showing measurement results by XPS. FIG. 5B is
a view showing a cross-sectional structure of a sample used for
measurement.
[0083] As shown in FIG. 5B, the sample has a stacked structure of
polycrystalline silicon (Poly-Si)/aluminum oxide
(AlO)/silicon-added hafnium oxide (HfSiO)/titanium nitride (TiN).
This sample was subjected to the crystallization annealing at
1000.degree. C. for 10 seconds.
[0084] As shown in FIG. 5A, as the measurement result by the XPS, a
peak of cubic hafnium oxide was detected but a peak of orthorhombic
hafnium oxide was not detected. When the same heat treatment was
performed on the sample in which the aluminum oxide was replaced by
the silicon oxide in the same stacked structure, the peak of the
orthorhombic hafnium oxide was detected.
[0085] In the memory device of the first embodiment, the second
interlayer insulating layer 103 between two word lines WLs includes
the aluminum oxide. Therefore, the first insulating film 31 between
the two word lines WLs is in contact with the aluminum oxide during
the crystallization annealing of the hafnium oxide. Therefore, the
second region 31b mainly formed as crystals other than the
orthorhombic is formed in the first insulating film 31 between the
second interlayer insulating layer 103 and the bit line BL.
[0086] On the other hand, the first insulating film 31 between the
word line WL and the bit line BL is not in contact with the second
interlayer insulating layer 103. In addition, the second insulating
film 32 in contact with the first insulating film 31 does not
contain aluminum oxide. Therefore, the first insulating film 31
between the word line WL and the bit line BL is not in contact with
aluminum oxide. Therefore, the first region 31a mainly formed as an
orthorhombic is formed in the first insulating film 31 between the
word line WL and the bit line BL.
[0087] The memory device of the first embodiment has a structure in
which the ferroelectrics under two word lines WLs is physically
segmented by the paraelectrics. Therefore, the degradation of
memory characteristics due to the inter-cell interference is
suppressed.
[0088] From the viewpoint of exhibiting the ferroelectricity in the
hafnium oxide, it is preferable that the word line WL is metal
nitride. For example, it is preferable that the word line WL is
titanium nitride (TiN), tungsten nitride (WN), or tantalum nitride
(TaN). It is preferable that the word line WL is, in particular,
titanium nitride (TiN).
[0089] It is preferable that the bit line BL is metal from the
viewpoint of low resistance. The bit line BL preferably includes
tungsten or titanium nitride because it has the low resistance and
good consistency with the manufacturing process of the existing
semiconductor device.
[0090] It is preferable that the hafnium oxide of the first
insulating film 31 includes least one element selected from the
group consisting of, for example, silicon (Si), titanium (Ti),
zirconium (Zr), aluminum (Al), yttrium (Y), strontium (Sr),
lanthanum (La), cerium (Ce), gadolinium (Gd), and barium (Ba). By
including the above elements, ferroelectricity is easily exhibited
in the hafnium oxide.
[0091] From the viewpoint of exhibiting the ferroelectricity in the
hafnium oxide, it is preferable that the second insulating film 32
includes silicon oxide or titanium oxide.
[0092] The third interlayer insulating layer 105 provided between
the bit line BL and the bit line BL includes, for example, a
material having a dielectric constant lower than that of the
aluminum oxide. The third interlayer insulating layer 105 includes,
for example, silicon oxide. The second interlayer insulating layer
103 provided between the word line WL and the word line WL includes
the aluminum oxide in order to form the second region 31b. The
third interlayer insulating layer 105 between the bit line BL and
the bit line BL includes a material having a low dielectric
constant, such that capacitance between interconnections can be
reduced, and high-speed memory operation and low power consumption
can be realized.
[0093] As described above, according to the first embodiment, the
ferroelectrics under the word line WL is physically segmented from
the ferroelectrics under the adjacent word lines WLs. Therefore,
the memory device in which the degradation of the memory
characteristics due to the inter-cell interference is suppressed
can be realized.
Second Embodiment
[0094] A memory device of a second embodiment is different from the
first embodiment in that the memory cell array has a
three-dimensional structure. Hereinafter, a description of the
contents overlapping with the first embodiment is partially
omitted.
[0095] FIG. 6 is a block diagram of a memory device according to a
second embodiment. FIG. 7 is an equivalent circuit diagram of a
memory cell array of the memory device according to the second
embodiment. FIG. 7 schematically shows a wiring structure in a
memory cell array. A memory cell array 210 of the second embodiment
has a three-dimensional structure in which memory cell MCs are
three-dimensionally arranged.
[0096] As shown in FIG. 6, the memory device includes a memory cell
array 210, a word line driver circuit 212, a row decoder circuit
214, a sense amplifier circuit 215, a column decoder circuit 217,
and a control circuit 221.
[0097] In addition, as shown in FIG. 7, the plurality of memory
cells MCs are three-dimensionally arranged in the memory cell array
210. In FIG. 7, a region surrounded by a dotted line corresponds to
one memory cell MC.
[0098] Hereinafter, as shown in FIGS. 7, 8A, and 8B, an x direction
is defined as a first direction, a y direction is defined as a
second direction, and a z direction is defined as a third
direction.
[0099] The memory cell array 210 includes, for example, a plurality
of word lines WLs (WL11, WL12, WL13, WL21, WL22, and WL23) and a
plurality of bit lines BLs (BL11, BL12, BL21, and BL22). The word
line WL extends in the x direction. The bit line BL extends in the
y direction. The word line WL intersects the bit line BL
vertically. The memory cells MCs are arranged at intersections of
the word lines WLs and the bit lines BLs.
[0100] The plurality of word lines WLs are electrically connected
to the row decoder circuit 214. The plurality of bit lines BLs are
connected to the sense amplifier circuit 215. Selection transistors
STs (ST11, ST21, ST12, and ST22) and global bit lines GBLs (GBL1
and GBL2) are provided between the plurality of bit lines BLs and
the sense amplifier circuit 215.
[0101] The row decoder circuit 214 has a function of selecting the
word line WL according to the input row address signal. The word
line driver circuit 212 has a function of applying a predetermined
voltage to the word line WL selected by the row decoder circuit
214.
[0102] The column decoder circuit 217 has a function of selecting
the bit line BL according to the input column address signal. The
sense amplifier circuit 215 has a function of applying a
predetermined voltage to the bit line BL selected by the column
decoder circuit 217. In addition, the sense amplifier circuit 215
has a function of detecting and amplifying a current flowing
between the selected word line WL and the selected bit line BL.
[0103] The control circuit 221 has a function of controlling the
word line driver circuit 212, the row decoder circuit 214, the
sense amplifier circuit 215, the column decoder circuit 217, and
other circuits (not shown).
[0104] Circuits such as the word line driver circuit 212, the row
decoder circuit 214, the sense amplifier circuit 215, the column
decoder circuit 217, and the control circuit 221 are constituted
by, for example, a transistor using a semiconductor layer (not
shown) and a wiring layer.
[0105] FIGS. 8A and 8B are schematic views of a part of the memory
cell array 210 of the memory device according to the second
embodiment. FIG. 8A is a cross-sectional view taken along xz of the
memory cell array 210. FIG. 8B is a cross-sectional view taken
along yz of the memory cell array 210. FIG. 8A is a cross-sectional
view taken along line BB' of FIG. 8B, and FIG. 8B is a
cross-sectional view taken along line AA' of FIG. 8A.
[0106] The memory cell array 210 includes a plurality of word lines
including the word line WL11 (a first conductive layer) and the
word line WL21 (a second conductive layer), a plurality of bit
lines including the bit line BL11 (a third conductive layer) and
the bit line BL21, a first insulating film 31, a second insulating
film 32, a first interlayer insulating layer 140 (insulating
layer), and a second interlayer insulating layer 150. Hereinafter,
the plurality of word lines including the word line WL11 (the first
conductive layer) and the word line WL1 2 (the second conductive
layer) maybe collectively referred to simply as the word line WL.
In addition, the plurality of bit lines including the bit line BL11
(the third conductive layer) and the bit line BL12 may be
collectively referred to simply as the bit line BL.
[0107] The word lines WLs are alternately stacked in the y
direction (the second direction) with the first interlayer
insulating layer 140. The word line WL extends in the x direction
(the first direction).
[0108] The word line WL is made of, for example, metal. The word
line WL is made of, for example, titanium nitride.
[0109] The first interlayer insulating layer 140 is provided
between the word line WL and the word line WL. The first interlayer
insulating layer 140 includes aluminum oxide. The first interlayer
insulating layer 140 is an example of an insulating layer.
[0110] The bit line BL is provided between the word line WL and the
word line WL. The bit line BL extends in the y direction (the
second direction).
[0111] The bit line BL is made of, for example, metal or
semiconductor. The bit line BL is made of, for example, titanium
nitride or tungsten.
[0112] The second interlayer insulating layer 150 is provided
between the bit line BL and the bit line BL. The second interlayer
insulating layer 150 includes, for example, silicon oxide.
[0113] The first insulating film 31 is provided between the word
line WL and the bit line BL and between the first interlayer
insulating layer 140 and the bit line BL. The first insulating film
31 is provided surrounding the bit line BL. The first insulating
film 31 includes hafnium oxide.
[0114] The first insulating film 31 includes hafnium oxide
including at least one element selected from the group consisting
of, for example, silicon (Si), titanium (Ti), zirconium (Zr),
aluminum (Al), yttrium (Y), strontium (Sr), lanthanum (La), cerium
(Ce), gadolinium (Gd), and barium (Ba). The first insulating film
31 may include hafnium oxide not including an additive element.
[0115] The first insulating film 31 includes a first region 31a
located between the word line WL and the bit line BL and a second
region 31b located between the first interlayer insulating layer
140 and the bit line BL.
[0116] The first region 31a between the word line WL21 (the second
conductive layer) and the bit line BL11 (the third conductive
layer) is an example of the third region.
[0117] A thickness of the first insulating film 31 is, for example,
3 nm or more and 10 nm or less.
[0118] The first region 31a includes hafnium oxide mainly formed as
the orthorhombic. More specifically, the hafnium oxide in the first
region 31a includes hafnium oxide mainly formed as orthorhombic III
(space group Pbc2.sub.1, space group number 29). Among the crystals
of the hafnium oxide included in the first region 31a, a ratio
occupied by the orthorhombic is the largest.
[0119] The first region 31a includes ferroelectrics. The hafnium
oxide exhibiting ferroelectricity is orthorhombic.
[0120] The second region 31b includes hafnium oxide mainly formed
as crystals other than the orthorhombic. Among the crystals of the
hafnium oxide included in the second region 31b, the ratio occupied
by the crystals other than the orthorhombic is the largest. In
addition to the orthorhombic, there are cubic, hexagonal,
tetragonal, monoclinic, and triclinic.
[0121] The second region 31b includes paraelectrics. The hafnium
oxide formed as crystal structure other than the orthorhombic
exhibits the paraelectricity.
[0122] The first region 31a and the second region 31b are regions
in a film formed at the same time. The compositions of the first
region 31a and the second region 31b are substantially the same.
The compositions of the first region 31a and the second region 31b
are the same within a range of errors in compositions in the film
at the time of the film formation.
[0123] The second insulating film 32 is provided between the first
insulating film 31 and the bit line BL. The second insulating film
32 is provided surrounding the bit line BL.
[0124] The second insulating film 32 does not contain aluminum
oxide. The second insulating film 32 includes, for example, oxide,
nitride, or oxynitride. The second insulating film 32 includes, for
example, silicon oxide or titanium oxide. The second insulating
film 32 includes, for example, paraelectrics.
[0125] A thickness of the second insulating film 32 is, for
example, 0.5 nm or more and 2 nm or less.
[0126] The second interlayer insulating layer 150 provided between
the bit line BL and the bit line BL includes, for example, a
material having a dielectric constant lower than that of the
aluminum oxide. The second interlayer insulating layer 150
includes, for example, silicon oxide. The first interlayer
insulating layer 140 provided between the word line WL and the word
line WL includes the aluminum oxide in order to form the second
region 31b. The second interlayer insulating layer 150 between the
bit line BL and the bit line BL is made of a material having a low
dielectric constant, such that capacitance between interconnections
can be reduced, and high-speed memory operation and low power
consumption can be realized.
[0127] Next, an example of a method for manufacturing the memory
device according to the second embodiment will be described.
[0128] First, a laminate in which a conductive layer for forming a
word line WL and the first interlayer insulating layer 140 are
alternately stacked in the y direction (the second direction) is
formed on a substrate (not shown). The conductive layer includes,
for example, titanium nitride. The first interlayer insulating
layer 140 includes, for example, aluminum oxide.
[0129] Next, grooves parallel to an xy plane are formed in the
laminate. A line and space pattern extending in the x direction is
formed on the laminate by the lithography method. The groove is
formed by alternately etching the first interlayer insulating layer
140 and the conductive layer in the space portion by the RIE
method.
[0130] By forming grooves parallel to the xy plane on the laminate,
the word line WL extending in the x direction is formed. The first
interlayer insulating layer 140 is provided between regular word
lines WLs.
[0131] Next, the grooves formed in the laminate are buried with the
second interlayer insulating layer 150. The second interlayer
insulating layer 150 includes, for example, silicon oxide. Next,
holes are formed in the laminate.
[0132] For example, the line and space pattern extending in the z
direction is formed on the laminate by the lithography method. By
selectively etching the second interlayer insulating layer 150 in
the space portion with respect to the word line WL and the first
interlayer insulating layer 140, holes are formed in the
laminate.
[0133] The first insulating film 31 is formed on a side surface of
the hole formed in the laminate. The first insulating film 31
includes, for example, hafnium oxide. The hafnium oxide is
amorphous just after the film formation. The first insulating film
31 is formed by, for example, the ALD method.
[0134] Next, the second insulating film 32 is formed on the first
insulating film 31. The second insulating film 32 is formed by, for
example, the CVD method. The second insulating film 32 includes,
for example, silicon oxide.
[0135] Next, the bit line BL is formed on the second insulating
film 32. The bit line BL is formed, for example, by the CVD method.
The hole is buried by the bit line BL.
[0136] Next, heat treatment is performed to crystallize hafnium
oxide of the first insulating film 31. The heat treatment is
performed, for example, in a nitrogen gas atmosphere at a
temperature of 600.degree. C. or more and 1050.degree. C. or less
for 1 second or more and 30 seconds or less. The heat treatment is
so-called crystallization annealing.
[0137] By the heat treatment, the hafnium oxide between the word
line WL and the bit line BL is crystallized to be orthorhombic. On
the other hand, the hafnium oxide between the first interlayer
insulating layer 140 and the bit line BL is crystallized, but does
not become orthorhombic, but becomes crystals other than the
orthorhombic.
[0138] By the heat treatment, a first region 31a between the word
line WL and the bit line BL and a second region 31b between the
first interlayer insulating layer 140 and the bit line BL are
formed in the first insulating film 31. The first region 31a
includes hafnium oxide mainly formed as the orthorhombic. The
second region 31b includes hafnium oxide mainly formed as crystals
other than the orthorhombic.
[0139] According to the above manufacturing method, the memory
device of the second embodiment shown in FIGS. 8A and 8B is
manufactured.
[0140] As described above, according to the second embodiment, as
in the first embodiment, it is possible to realize a memory device
in which the degradation of the memory characteristics due to the
inter-cell interference is suppressed. In addition, by providing
the three-dimensional structure, it is possible to obtain the
effect that the integration of the memory device is improved.
Third Embodiment
[0141] A memory device of a third embodiment is different from the
first embodiment in that the memory cell array has a
three-dimensional structure. In addition, the third embodiment is
different from the first and second embodiments in that a memory
cell is a three-terminal type memory in which a gate insulating
film of a transistor is a ferroelectric film. A description of the
contents overlapping with the first and second embodiments will
partially omitted.
[0142] The memory device of the third embodiment is a
three-dimensional NAND flash memory in which memory cells are
three-dimensionally arranged. The memory device of the third
embodiment is a ferroelectric memory in which a gate insulating
film of a memory cell transistor MT is a ferroelectric film.
[0143] FIG. 9 is an equivalent circuit diagram of a memory cell
array of the memory device according to the third embodiment. FIG.
9 schematically shows a wiring structure in a memory cell array. A
memory cell array 310 of the third embodiment has a
three-dimensional structure in which memory cell transistors MTs
are three-dimensionally arranged.
[0144] As shown in FIG. 9, the memory cell array 310 includes a
plurality of word lines WLs including a word line WL1 (a first
conductive layer) and a word line WL2 (a second conductive layer),
a plurality of semiconductor pillars SPs including a semiconductor
pillar SP1 (a third conductive layer) and a semiconductor pillar
SP2, a common source line CSL, a source selection gate line SGS, a
plurality of drain selection gate lines SGDs, a plurality of bit
lines BLs, and a plurality of memory strings MSs.
[0145] As shown in FIG. 9, the memory string MS includes source
selection transistors SSTs connected in series between a common
source line CSL and bit line BL, a plurality of memory cell
transistors MTs, and a drain selection transistor SDT.
[0146] Hereinafter, as shown in FIGS. 9, 10A, and 10B, an x
direction is defined as a first direction, a y direction is defined
as a second direction, and a z direction is defined as a third
direction.
[0147] FIGS. 10A and 10B are schematic views of a part of the
memory cell array 310 of the memory device according to the third
embodiment. FIG. 10A is a cross-sectional view taken along xz of
the memory cell array 310. FIG. 10B is a cross-sectional view taken
along yz of the memory cell array 310. FIG. 10A is a
cross-sectional view taken along line BB' of FIG. 10B, and FIG. 10B
is a cross-sectional view taken along line AA' of FIG. 10A.
[0148] The memory cell array 310 includes the plurality of word
lines WLs including the word line WL1 (the first conductive layer)
and the word line WL2 (the second conductive layer), the plurality
of semiconductor pillars SPs including the semiconductor pillar SP1
(the third conductive layer) and the semiconductor pillar SP2, a
first insulating film 31, a second insulating film 32, and an
interlayer insulating layer 160 (insulating layer). Hereinafter,
the plurality of word lines including the word line WL1 (the first
conductive layer) and the word line WL2 (the second conductive
layer) may be collectively referred to simply as the word line WL.
In addition, the plurality of semiconductor pillars including the
semiconductor pillar SP1 (the third conductive layer) and the
semiconductor pillar SP2 maybe collectively referred to simply as
the semiconductor pillar SP.
[0149] The word lines WLs are alternately stacked in the y
direction (the second direction) with the interlayer insulating
layer 160. The word line WL extends in the x direction (the first
direction) and the z direction (the third direction). The word line
WL is on a flat plate.
[0150] The word line WL is made of, for example, metal or
semiconductor. The word line WL is made of, for example, titanium
nitride.
[0151] The interlayer insulating layer 160 is provided between the
word line WL and the word line WL. The interlayer insulating layer
160 includes aluminum oxide. The interlayer insulating layer 160 is
an example of an insulating layer.
[0152] The semiconductor pillar SP is provided penetrating through
the word line WL and the interlayer insulating layer 160. The
semiconductor pillar SP extends in the y direction (the second
direction).
[0153] The semiconductor pillar SP includes semiconductor. The
semiconductor pillar SP includes, for example, polycrystalline
silicon. The semiconductor pillar SP includes, for example, n-type
silicon.
[0154] The first insulating film 31 is provided between the word
line WL and the semiconductor pillar SP and between the interlayer
insulating layer 160 and the semiconductor pillar SP. The first
insulating film 31 is provided surrounding the semiconductor pillar
SP. The first insulating film 31 includes hafnium oxide.
[0155] The first insulating film 31 includes hafnium oxide
including at least one element selected from the group consisting
of, for example, silicon (Si), titanium (Ti), zirconium (Zr),
aluminum (Al), yttrium (Y), strontium (Sr), lanthanum (La), cerium
(Ce), gadolinium (Gd), and barium (Ba). The first insulating film
31 may include hafnium oxide not including an additive element.
[0156] The first insulating film 31 includes a first region 31a
located between the word line WL and the semiconductor pillar SP
and a second region 31b located between the interlayer insulating
layer 160 and the semiconductor pillar SP.
[0157] A thickness of the first insulating film 31 is, for example,
3 nm or more and 10 nm or less.
[0158] The first region 31a includes hafnium oxide mainly formed as
the orthorhombic. More specifically, the hafnium oxide in the first
region 31a includes hafnium oxide mainly formed as orthorhombic III
(space group Pbc2.sub.1, space group number 29). Among the crystals
of the hafnium oxide included in the first region 31a, a ratio
occupied by the orthorhombic is the largest.
[0159] The first region 31a includes ferroelectrics. The hafnium
oxide exhibiting ferroelectricity is orthorhombic.
[0160] The second region 31b includes hafnium oxide mainly formed
as crystals other than the orthorhombic. Among the crystals of the
hafnium oxide included in the second region 31b, the ratio occupied
by the crystals other than the orthorhombic is the largest. In
addition to the orthorhombic, there are cubic, hexagonal,
tetragonal, monoclinic, and triclinic.
[0161] The second region 31b includes paraelectrics. The hafnium
oxide formed as crystals other than the orthorhombic exhibits the
paraelectricity.
[0162] The first region 31a and the second region 31b are regions
in a film formed at the same time. The compositions of the first
region 31a and the second region 31b are substantially the same.
The compositions of the first region 31a and the second region 31b
are the same within a range of errors in compositions in the film
at the time of the film formation.
[0163] The second insulating film 32 is provided between the first
insulating film 31 and the semiconductor pillar SP. The second
insulating film 32 is provided surrounding the semiconductor pillar
SP.
[0164] The second insulating film 32 does not contain aluminum
oxide. The second insulating film 32 includes, for example, oxide,
nitride, or oxynitride. The second insulating film 32 includes, for
example, silicon oxide or titanium oxide. The second insulating
film 32 includes, for example, paraelectrics.
[0165] A thickness of the second insulating film 32 is, for
example, 0.5 nm or more and 2 nm or less.
[0166] The first insulating film 31 and the second insulating film
32 serve as the gate insulating film of the memory cell transistor
MT. Due to the polarization inversion state of the first insulating
film 31, a threshold voltage of the memory cell transistor MT is
changed. As the threshold voltage of the memory cell transistor MT
is changed, anon current of the memory cell transistor MT is
changed. For example, when a state in which an on current having a
high threshold voltage is low is defined as data "0" and a state in
which an on current having a low threshold voltage is high is
defined as data "1", the memory cell transistor MT can store 1 bit
data of "0" and "1".
[0167] The configuration in which the second insulating film 32 is
omitted and only the first insulating film 31 functions as the gate
insulating film of the memory cell transistor MT is possible.
[0168] Next, an example of a method for manufacturing the memory
device according to the third embodiment will be described.
[0169] First, a laminate in which the word line WL and the
interlayer insulating layer 160 are alternately stacked in the y
direction (the second direction) is formed on a substrate (not
shown). The word line WL is made of, for example, titanium nitride.
The interlayer insulating layer 160 includes, for example, aluminum
oxide.
[0170] Next, holes extending in the y direction are formed in the
laminate. The hole penetrates through the laminate in the y
direction. First, a hole pattern is formed on the laminate by a
lithography method. The interlayer insulating layer 160 and the
word line WL are alternately etched by the RIE method to form the
hole.
[0171] Next, the first insulating film 31 is formed on a side
surface of the hole formed in the laminate. The first insulating
film 31 includes, for example, hafnium oxide. The hafnium oxide is
amorphous just after the film formation. The first insulating film
31 is formed by, for example, the ALD method.
[0172] Next, the second insulating film 32 is formed on the first
insulating film 31. The second insulating film 32 is formed by, for
example, the CVD method. The second insulating film 32 includes,
for example, silicon oxide.
[0173] Next, the semiconductor pillar SP is formed by burying the
semiconductor layer on the second insulating film 32 in the hole.
The semiconductor layer includes, for example, polycrystalline
silicon formed by a CVD method.
[0174] Next, heat treatment is performed to crystallize hafnium
oxide of the first insulating film 31. The heat treatment is
performed, for example, in a nitrogen gas atmosphere at a
temperature of 600.degree. C. or more and 1050.degree. C. or less
for 1 second or more and 30 seconds or less. The heat treatment is
so-called crystallization annealing.
[0175] By the heat treatment, the hafnium oxide between the word
line WL and the semiconductor pillar SP is crystallized to be
orthorhombic. On the other hand, the hafnium oxide between the
interlayer insulating layer 160 and the semiconductor pillar SP is
crystallized, but does not become orthorhombic, but becomes
crystals other than the orthorhombic.
[0176] By the heat treatment, a first region 31a between the word
line WL and the semiconductor pillar SP and a second region 31b
between the interlayer insulating layer 160 and the semiconductor
pillar SP are formed in the first insulating film 31. The first
region 31a includes hafnium oxide mainly formed as the
orthorhombic. The second region 31b includes hafnium oxide mainly
formed as crystals other than the orthorhombic.
[0177] According to the above manufacturing method, the memory
device of the third embodiment shown in FIGS. 10A and 10B is
manufactured.
[0178] As described above, according to the third embodiment, as in
the first and second embodiments, it is possible to realize the
memory device in which the degradation of the memory
characteristics due to the inter-cell interference is suppressed.
In addition, a three-dimensional NAND flash memory using
ferroelectrics is realized
Fourth Embodiment
[0179] A memory device of a fourth embodiment includes a first
conductive layer, a second conductive layer, a resistance change
layer provided between the first conductive layer and the second
conductive layer, and a multi-layered insulator provided between
the resistance change layer and a second conductive layer and
including a first layer, a second layer, and a third layer, wherein
the second layer is located between the first layer and the third
layer, electron affinity of the first layer is larger than electron
affinity of the second layer, and electron affinity of the second
layer is larger than electron affinity of the third layer.
[0180] FIG. 11 is a block diagram of a memory cell array 400 and a
peripheral circuit of a memory device according to a fourth
embodiment. The memory device of the fourth embodiment is a
resistive random access memory (ReRAM). A region indicated by a
dotted circle in the memory cell array 400 of FIG. 11 is one memory
cell MC.
[0181] Hereinafter, as shown in FIG. 11, an x direction is defined
as a first direction, a y direction is defined as a second
direction, and a z direction is defined as a third direction.
[0182] The memory cell array 400 of the memory device according to
the fourth embodiment includes, for example, a plurality of word
lines WLs and a plurality of bit lines BLs intersecting the word
lines WLs on a semiconductor substrate 101 with an insulating layer
interposed therebetween. The word line WL is provided under the bit
line BL. In addition, a first control circuit 108, a second control
circuit 110, and a sense circuit 112 are provided around the memory
cell array 400 as peripheral circuits.
[0183] A plurality of memory cells MCs are provided in a region
where the word line WL intersects the bit line BL. The memory
device of the fourth embodiment is the ReRAM including a cross
point structure. The memory cell MC is a two-terminal element.
[0184] Each of the plurality of word lines WLs is connected to the
first control circuit 108. In addition, each of the plurality of
bit lines BLs is connected to a second control circuit 110. The
sense circuit 112 is connected to the first control circuit 108 and
the second control circuit 110.
[0185] For example, the first control circuit 108 and the second
control circuit 110 select a desired memory cell MC and have a
function of wiring data into the memory cell, reading the data of
the memory cell, erasing the data of the memory cell, and the like.
When data are read out, the data of the memory cell is read out as
the amount of current flowing between the word line WL and the bit
line BL. The sense circuit 112 has a function of determining the
current amount and determining polarity of the data. For example,
the sense circuit 112 determines "0" or "1" of data. The sense
circuit 112 determines the amount of tunnel current flowing in the
memory cell to determine the polarity of the data.
[0186] The first control circuit 108, the second control circuit
110, and the sense circuit 112 are constituted by electronic
circuits using semiconductor devices formed on the semiconductor
substrate 101, for example.
[0187] FIGS. 12A, 12B, and 12C are schematic views of a part of the
memory cell array 400 of a memory device of the fourth embodiment.
FIG. 12A is a top view, FIG. 12B is a cross-sectional view taken
along the direction A-A' of FIG. 12A, and FIG. 12C is a
cross-sectional view taken along the direction B-B' of FIG.
12A.
[0188] The memory cell array 400 includes a word line WL1 (a first
conductive layer), a word line WL2, a word line WL3, a word line
WL4, a bit line BL1 (a second conductive layer), a bit line BL2, a
bit line BL3, a bit line BL4, a resistance change layer 250, a
selector layer 260 (a multi-layered insulator), a semiconductor
substrate 101, a first interlayer insulating layer 102, a second
interlayer insulating layer 103, and a third interlayer insulating
layer 105. Hereinafter, the word line WL1 (the first conductive
layer), the word line WL2, the word line WL3, and the word line WL4
may be collectively referred to simply as the word line WL. In
addition, the bit line BL1 (the second conductive layer), the bit
line BL2, the bit line BL3, and the bit line BL4 may be
collectively referred to simply as the bit line BL.
[0189] The word line WL extends in the x direction (the first
direction). The word line WL is made of, for example, metal. The
word line WL is made of, for example, metal having high heat
resistance. The word line WL is made of, for example, titanium
nitride (TiN), tungsten nitride (WN), tantalum nitride (TaN),
tungsten (W), tantalum (Ta), niobium (Nb), vanadium (V), tungsten
(W), iron (Fe), molybdenum (Mo), cobalt (Co), nickel (Ni),
ruthenium (Ru), iridium (Ir), copper (Cu), palladium (Pd), silver
(Ag), or platinum (Pt).
[0190] The bit line BL extends in the y direction (the second
direction). The y direction (second direction) is orthogonal to the
x direction. The bit line BL is made of, for example, metal. The
bit line BL is made of, for example, metal having high heat
resistance. The bit line BL is made of, for example, tungsten (W),
titanium nitride (TiN), tungsten nitride (WN), tantalum nitride
(TaN), tantalum (Ta), niobium (Nb), vanadium (V), iron (Fe),
molybdenum (Mo), cobalt (Co), nickel (Ni), ruthenium (Ru), iridium
(Ir), copper (Cu), palladium (Pd), silver (Ag), or platinum
(Pt).
[0191] The word line WL1 is an example of a first conductive layer.
The bit line BL1 is an example of a second conductive layer.
[0192] The semiconductor substrate 101 is, for example, a silicon
substrate.
[0193] The first interlayer insulating layer 102 is provided on the
semiconductor substrate 101. The first interlayer insulating layer
102 is provided between the semiconductor substrate 101 and the
word line WL. The first interlayer insulating layer 102 includes,
for example, silicon oxide.
[0194] The second interlayer insulating layer 103 is provided
between the word line WL and the word line WL. The second
interlayer insulating layer 103 includes, for example, silicon
oxide.
[0195] The third interlayer insulating layer 105 is provided on the
word line WL. The third interlayer insulating layer 105 is provided
between the bit line BL and the bit line BL. The third interlayer
insulating layer 105 includes, for example, silicon oxide.
[0196] The resistance change layer 250 is provided between the word
line WL and the bit line BL. By applying a current or voltage to
the resistance change layer 250, the resistance change layer 250
changes from a high resistance state to a low resistance state or
from the low resistance state to the high resistance state. The
change from the high resistance state to the low resistance state
is referred to as a set operation, for example. The change from the
low resistance state to the high resistance state is referred to as
the reset operation, for example.
[0197] For example, the high resistance state is defined as data
"0", and the low resistance state is defined as data "1". The
memory cell MC can store 1 bit data of "0" and "1".
[0198] A material of the resistance change layer 250 is not
particularly limited as long as it is a material whose resistance
state changes by application of a current or a voltage. For
example, vacancy modulated conductive oxide is used as the
resistance change layer 250.
[0199] The resistance change layer 250 is in contact with the
selector layer 260.
[0200] The selector layer 260 is provided between the resistance
change layer 250 and the bit line BL. The selector layer 260 is in
contact with the resistance change layer 250 and the bit line
BL.
[0201] In the selector layer 260, voltage-current characteristics
have nonlinearity. The selector layer 260 has a function of
suppressing a current flowing in a non-selected cell in writing,
reading, or erasing a selected cell.
[0202] FIG. 13 is a schematic cross-sectional view of the memory
cell of the memory device according to the fourth embodiment. FIG.
13 shows across section of, for example, one memory cell MC
indicated by a dotted circle in the memory cell array 400 of FIG.
11.
[0203] The selector layer 260 has a multilayered structure. The
selector layer 260 includes a first layer 260a, a second layer
260b, and a third layer 260c. The second layer 260b is provided
between the first layer 260a and the third layer 260c. The first
layer 260a is in contact with the second layer 260b and the second
layer 260b is in contact with the third layer 260c.
[0204] FIG. 14 is a band diagram of the selector layer of the
memory device according to the fourth embodiment. Electron affinity
(EA1) of the first layer 260a is larger than electric affinity
(EA2) of the second layer 260b, and electron affinity of the second
layer 260b is larger than electron affinity (EA3) of the third
layer 260c. That is, the relationship of EA1>EA2>EA3 is
established. The electron affinity is an energy difference between
energy of a lower end of a conductor and a vacuum level.
[0205] In the selector layer 260, the energy of the lower end of
the conductor changes in a stair form from the first layer 260a
toward the third layer 260c.
[0206] The first layer 260a, the second layer 260b, and the third
layer 260c are insulating layers. The first layer 260a, the second
layer 260b, and the third layer 260c are, for example, oxide
layers.
[0207] The first layer 260a includes, for example, titanium oxide.
The second layer 260b includes, for example, tantalum oxide. The
third layer film 260c includes, for example, silicon oxide or
aluminum oxide.
[0208] A thickness of the selector layer 260 is, for example, 1 nm
or more and 5 nm or less. A sum of a thickness (t1) of the first
layer 260a, a thickness (t2) of the second layer 260b, and a
thickness (t3) of the third layer 260c is, for example, 1 nm or
more and 5 nm or less.
[0209] The thickness (t3) of the third layer 260c is, for example,
thinner than the thickness (t1) of the first layer 260a and the
thickness (t2) of the second layer 260b. The thickness (t3) of the
third layer 260c is, for example, 1/2 or less of the thickness (t1)
of the first layer 260a. The thickness (t3) of the third layer 260c
is, for example, 1/2 or less of the thickness (t2) of the second
layer 260b.
[0210] A voltage applied to the selector layer 260 is controlled so
that a side of the first layer 260a becomes a positive voltage with
respect to a side of the third layer 260c. In the memory device of
the fourth embodiment, a voltage applied to the bit line BL (the
second conductive layer) is controlled so that it is relatively
positive with respect to the voltage applied to the word line WL
(the first conductive layer).
[0211] When a positive voltage of a predetermined level or more is
applied to the bit line BL, a direct tunneling current flows from
the bit line BL side to the word line WL side. In other words,
electrons flow in the bit line BL side by tunneling through the
selector layer 260 from the word line WL side.
[0212] Next, functions and effects of the memory device according
to the fourth embodiment will be described.
[0213] In the ReRAM having the cross point structure, it is
necessary to suppress the current flowing in the non-selected cell
when a voltage is applied to the selected cell to write, read, or
erase the selected cell. A large current flowing in the
non-selected cell is a factor of causing malfunctions such as a
data write error, a data read error, and a data erase error.
[0214] In writing, reading, or erasing the selected cell, a voltage
lower than the voltage applied to the selected cell is applied to
the non-selected cell. For example, a half of the voltage applied
to the selected cell is applied to the non-selected cell.
Hereinafter, the voltage applied to the selected cell will be
referred to as anon voltage Von, and the voltage applied to the
non-selected cell will be referred to as an off voltage Voff. The
off voltage Voff is, for example, a half of the on voltage Von.
[0215] The selector layer 260 is provided in each memory cell to
suppress the current flowing in the non-selected cell. In the
selector layer 260, the voltage-current characteristics have
nonlinearity. Hereinafter, a current flowing in the selector layer
260 when the on voltage Von is applied is referred to as an on
current Ion, and a current flowing in the selector layer 260 when
an off voltage Voff is applied is referred to as an off current
Ioff.
[0216] In the selector layer 260, a high on current Ion, a low off
current Ioff, and high nonlinearity (Ion/Ioff) are required. In
particular, when the thickness of the selector layer 260 becomes
thin, it becomes particularly difficult to realize the low off
current Ioff.
[0217] In the memory device of the fourth embodiment, the selector
layer 260 is formed in three layers, and a stair-like band
structure is provided. In this way, even when the thickness of the
selector layer 260 becomes thin, it is possible to realize a high
on current Ion, a low off current Ioff, and large nonlinearity
(Ion/Ioff).
[0218] FIGS. 15A, 15B, and 15C are explanatory diagrams of
functions and effects of the memory device according to the fourth
embodiment. FIGS. 15A, 15B, and 15C are band diagrams of the
selector layer of a comparative example. FIG. 15A shows a case in
which a selector layer is a single layer (Comparative Example 1),
FIG. 15B shows a case in which the selector layer is three layers
but electron affinity of layers at both ends is small (Comparative
Example 2), and FIG. 15C shows a case in which the selector layer
is three layers but the electron affinity at both ends is large
(Comparative Example 3).
[0219] FIG. 16 is an explanatory diagram of functions and effects
of the memory device of the fourth embodiment. FIG. 16 shows
simulation results of the voltage-current characteristics of the
selector layer of Comparative Example 1, Comparative Example 2,
Comparative Example 3, and the fourth embodiment.
[0220] In Comparative Example 1, although the off current Toff is
low, the on current Ion is also low, and the nonlinearity is also
small. In Comparative Example 2, although the on current Ion is
high, the off current Ioff is also high, and the nonlinearity is
also small. In Comparative Example 3, although the on current Ion
is high, the off current Toff is slightly high, and the
nonlinearity is also slightly small.
[0221] On the other hand, in the case of the fourth embodiment, the
high on current Ion, the low off current Ioff, and the large
nonlinearity are realized. It is considered that the third layer
160c having the small electron affinity serves as an electron
barrier and the off current Ioff is reduced. On the other hand, by
making the electron affinity of the first layer 160a larger than
that of the second layer 160b, it is considered that the on current
Ion is suppressed from being lowered
[0222] From the viewpoint of suppressing the on current Ion from
being lowered, the thickness (t3) of the third layer 160c is, for
example, thinner than the thickness (t1) of the first layer 160a
and the thickness (t2) of the second layer 160b.
[0223] From the viewpoint of suppressing the on current Ion from
being lowered, the thickness (t3) of the third layer 260c is
preferably, for example, 1/2 or less of the thickness (t1) of the
first layer 260a, and the thickness (t3) of the third layer 260c is
preferably, for example, 1/2 or less of the thickness (t2) of the
second layer 260b.
[0224] In addition, the thickness of the selector layer 260 is
preferably 1 nm or more and 5 nm or less. Below the above range,
the off current Ioff may increase. When it exceeds the above range,
the on current Ion may decrease.
[0225] As described above, according to the fourth embodiment, by
providing a selector layer having the high on current Ion, the low
off current Ioff, and the high nonlinearity, the memory device with
the suppressed malfunction is realized.
Fifth Embodiment
[0226] A memory device of a fifth embodiment is different from the
memory device of the second embodiment in that the memory device
further includes a multi-layered insulator provided between a first
conductive layer and a first insulating film, wherein the
multi-layered insulator includes a first layer, a second layer, and
a third layer, the second layer is located between the first layer
and the third layer, electron affinity of the first layer is larger
than the electron affinity of the second layer and the electron
affinity of the second layer is larger than the electric affinity
of the third layer. Hereinafter, a description of the contents
overlapping with the second embodiment is partially omitted.
[0227] The memory device of the fifth embodiment includes the
selector layer 260 described in the fourth embodiment with respect
to the memory device of the second embodiment. The structure of the
selector layer 260 is the same as that of the fourth embodiment,
and therefore a description thereof will be omitted.
[0228] FIGS. 17A and 17B are schematic views of a part of a memory
cell array 510 of the memory device according to the fifth
embodiment. FIG. 17A is a cross-sectional view taken along xz of
the memory cell array 510. FIG. 17B is a cross-sectional view taken
along yz of the memory cell array 210. FIG. 17A is a
cross-sectional view taken along line BB' of FIG. 17B, and FIG. 17B
is a cross-sectional view taken along line AA' of FIG. 17A.
[0229] The memory cell array 510 includes a plurality of word lines
including the word line WL11 (a first conductive layer) and the
word line WL21 (a second conductive layer), a plurality of bit
lines including the bit line BL11 (a third conductive layer) and
the bit line BL21, a selector layer 260, a first insulating film
31, a second insulating film 32, a first interlayer insulating
layer 140 (insulating layer), and a second interlayer insulating
layer 150. Hereinafter, the plurality of word lines including the
word line WL11 (the first conductive layer) and the word line WL12
(the second conductive layer) may be collectively referred to
simply as the word line WL. In addition, the plurality of bit lines
including the bit line BL11 (the third conductive layer) and the
bit line BL12 maybe collectively referred to simply as the bit line
BL. The first insulating film 31 and the second insulating film 32
are an example of a resistance change layer.
[0230] The selector layer 260 is provided between the word line
WL11 (the first conductive layer) and the first insulating film 31.
The selector layer 260 is provided between the word line WL and a
first region 31a of the first insulating film 31.
[0231] FIG. 18 is a schematic cross-sectional view of the memory
cell of the memory device according to the fifth embodiment. FIG.
18 shows across section of, for example, one memory cell indicated
by a dotted circle in the memory cell array 510 of FIG. 17B.
[0232] The selector layer 260 has a multilayered structure. The
selector layer 260 includes a first layer 260a, a second layer
260b, and a third layer 260c. The second layer 260b is provided
between the first layer 260a and the third layer 260c. The first
layer 260a is in contact with the second layer 260b and the second
layer 260b is in contact with the third layer 260c.
[0233] Electron affinity (EA1) of the first layer 260a is larger
than electric affinity (EA2) of the second layer 260b, and electron
affinity of the second layer 260b is larger than electron affinity
(EA3) of the third layer 260c. That is, the relationship of
EA1>EA2>EA3 is established.
[0234] A voltage applied to the selector layer 260 is controlled so
that a side of the first layer 260a becomes a positive voltage with
respect to a side of the third layer 260c. In the memory device of
the fifth embodiment, the voltage applied to the word line WL is
controlled to be relatively positive with respect to the voltage
applied to the bit line BL.
[0235] When a positive voltage of a predetermined level or more is
applied to the word line WL, a direct tunneling current flows from
the word line WL side to the bit line BL side. In other words,
electrons flow in the word line WL side by tunneling through the
selector layer 260 from the bit line BL side
[0236] As described above, according to the fifth embodiment, in
addition to the effects of the second embodiment, by providing the
selector layer having the high on current Ion, the low off current
Toff, and the high nonlinearity, the memory device with the
suppressed malfunction is realized.
Sixth Embodiment
[0237] A memory device of a sixth embodiment is different from the
memory device of the second embodiment in that the memory device
further includes a multi-layered insulator provided between a
second insulating film and a third conductive layer, wherein the
multi-layered insulator includes a first layer, a second layer, and
a third layer, the second layer is located between the first layer
and the third layer, electron affinity of the first layer is larger
than the electron affinity of the second layer and the electron
affinity of the second layer is larger than the electric affinity
of the third layer. Hereinafter, a description of the contents
overlapping with the second embodiment is partially omitted. The
memory device of the sixth embodiment is different from the fifth
embodiment in that a multi-layered insulator is provided between
the second insulating film and the third conductive layer.
[0238] The memory device of the sixth embodiment includes the
selector layer 260 described in the fourth embodiment with respect
to the memory device of the second embodiment. The structure of the
selector layer 260 is the same as that of the fourth embodiment,
and therefore a description thereof will be omitted.
[0239] FIGS. 19A and 19B are schematic views of a part of the
memory cell array 610 of the memory device according to the sixth
embodiment. FIG. 19A is a cross-sectional view taken along xz of
the memory cell array 610. FIG. 19B is a cross-sectional view taken
along yz of the memory cell array 610. FIG. 19A is a
cross-sectional view taken along line BB' of FIG. 19B, and FIG. 19B
is a cross-sectional view taken along line AAT of FIG. 19A.
[0240] The memory cell array 610 includes a plurality of word lines
including the word line WL11 (a first conductive layer) and the
word line WL21 (a second conductive layer), a plurality of bit
lines including the bit line BL11 (a third conductive layer) and
the bit line BL21, the selector layer 260, a first insulating film
31, a second insulating film 32, a first interlayer insulating
layer 140 (insulating layer), and a second interlayer insulating
layer 150. Hereinafter, the plurality of word lines including the
word line WL11 (the first conductive layer) and the word line WL12
(the second conductive layer) may be collectively referred to
simply as the word line WL. In addition, the plurality of bit lines
including the bit line BL11 (the third conductive layer) and the
bit line BL12 maybe collectively referred to simply as the bit line
BL. The first insulating film 31 and the second insulating film 32
are an example of a resistance change layer.
[0241] The selector layer 260 is provided between the second
insulating film 32 and the bit line BL (the third conductive
layer).
[0242] FIG. 20 is a schematic cross-sectional view of the memory
cell of the memory device according to the sixth embodiment. FIG.
20 shows across section of, for example, one memory cell indicated
by a dotted circle in the memory cell array 610 of FIG. 19B.
[0243] The selector layer 260 has a multilayered structure. The
selector layer 260 includes a first layer 260a, a second layer
260b, and a third layer 260c. The second layer 260b is provided
between the first layer 260a and the third layer 260c. The first
layer 260a is in contact with the second layer 260b and the second
layer 260b is in contact with the third layer 260c.
[0244] Electron affinity (EA1) of the first layer 260a is larger
than electric affinity (EA2) of the second layer 260b, and electron
affinity of the second layer 260b is larger than electron affinity
(EA3) of the third layer 260c. That is, the relationship of
EA1>EA2>EA3 is established.
[0245] A voltage applied to the selector layer 260 is controlled so
that a side of the first layer 260a becomes a positive voltage with
respect to a side of the third layer 260c. In the memory device of
the sixth embodiment, the voltage applied to the word line WL is
controlled to be relatively positive with respect to the voltage
applied to the bit line BL.
[0246] When a positive voltage of a predetermined level or more is
applied to the word line WL, a direct tunneling current flows from
the word line WL side to the bit line BL side. In other words,
electrons flow in the word line WL side by tunneling through the
selector layer 260 from the bit line BL side.
[0247] As described above, according to the sixth embodiment, in
addition to the effects of the second embodiment, by providing the
selector layer having the high on current Ion, the low off current
Ioff, and the high nonlinearity, the memory device with the
suppressed malfunction is realized.
[0248] In the first and fourth embodiments, the case in which the
cross point structure of the memory cell array is only one layer is
described as an example, but it is also possible to form the
three-dimensional structure in which the plurality of memory cell
arrays of the first and fourth embodiments are stacked.
[0249] In the first embodiment, the case where the selector layer
260 is provided between the resistance change layer 250 and the bit
line BL (second conductive layer) is described as an example, but
the selector layer 260 may be provided between the word line (the
first conductive layer) and the resistance change layer 250.
[0250] In the memory device of the fourth embodiment, the case
where the voltage applied to the bit line BL is controlled to be
relatively positive with respect to the voltage applied to the word
line WL is described as an example, but the voltage applied to the
word line WL can also be controlled to be relatively positive with
respect to the voltage applied to the bit line BL. In this case,
the first layer 260a is disposed on the word line WL side of the
selector layer 260, and the third layer 260c is disposed on the bit
line BL side of the selector layer 260.
[0251] In the memory device of the fifth and sixth embodiments, the
case where the voltage applied to the word line WL is controlled to
be relatively positive with respect to the voltage applied to the
bit line BL is described as an example, but the voltage applied to
the bit line BL can also be controlled to be relatively positive
with respect to the voltage applied to the word line WL. In this
case, the first layer 260a is disposed on the bit line BL side of
the selector layer 260, and the third layer 260c is disposed on the
word line WL side of the selector layer 260.
[0252] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the memory
device described herein may be embodied in a variety of other
forms; furthermore, various omissions, substitutions and changes in
the form of the devices and methods described herein may be made
without departing from the spirit of the inventions. The
accompanying claims and their equivalents are intended to cover
such forms or modifications as would fall within the scope and
spirit of the inventions.
* * * * *