U.S. patent application number 14/778381 was filed with the patent office on 2016-02-11 for two-terminal switching element having bidirectional switching characteristic, resistive memory cross-point array including same, and method for manufacturing two-terminal switching element and cross-point resistive memory array.
The applicant listed for this patent is INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG UNIVERSITY. Invention is credited to Yooncheol BAE, Gwangho BAEK, Jinpyo HONG, Ahrham LEE.
Application Number | 20160043142 14/778381 |
Document ID | / |
Family ID | 51580453 |
Filed Date | 2016-02-11 |
United States Patent
Application |
20160043142 |
Kind Code |
A1 |
HONG; Jinpyo ; et
al. |
February 11, 2016 |
TWO-TERMINAL SWITCHING ELEMENT HAVING BIDIRECTIONAL SWITCHING
CHARACTERISTIC, RESISTIVE MEMORY CROSS-POINT ARRAY INCLUDING SAME,
AND METHOD FOR MANUFACTURING TWO-TERMINAL SWITCHING ELEMENT AND
CROSS-POINT RESISTIVE MEMORY ARRAY
Abstract
Provided are a two-terminal switching element having a
bidirectional switching characteristic, a resistive memory
cross-point array including the same, and methods for manufacturing
the two-terminal switching element and the cross-point resistive
memory array. The two-terminal switching element includes a first
electrode and a second electrode. A pair of first conductive metal
oxide semiconductor layers electrically connected to the first
electrode and the second electrode, respectively, is provided. A
second conductive metal oxide semiconductor layer is disposed
between the first conductive metal oxide semiconductor layers.
Therefore, the two-terminal switching element can show a
symmetrical and bidirectional switching characteristic.
Inventors: |
HONG; Jinpyo; (Seoul,
KR) ; BAE; Yooncheol; (Seoul, KR) ; LEE;
Ahrham; (Gimhae-si, Gyeongsangnam-do, KR) ; BAEK;
Gwangho; (Incheon, KR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INDUSTRY-UNIVERSITY COOPERATION FOUNDATION HANYANG
UNIVERSITY |
Seoul |
|
KR |
|
|
Family ID: |
51580453 |
Appl. No.: |
14/778381 |
Filed: |
March 21, 2014 |
PCT Filed: |
March 21, 2014 |
PCT NO: |
PCT/KR2014/002423 |
371 Date: |
September 19, 2015 |
Current U.S.
Class: |
257/4 ; 257/421;
438/382 |
Current CPC
Class: |
H01L 43/08 20130101;
H01L 43/10 20130101; H01L 43/02 20130101; H01L 29/861 20130101;
H01L 45/1253 20130101; H01L 45/146 20130101; H01L 45/16 20130101;
H01L 27/2409 20130101; H01L 45/1233 20130101; H01L 45/143 20130101;
H01L 27/222 20130101; H01L 27/2463 20130101; H01L 43/12 20130101;
H01L 45/147 20130101; H01L 27/224 20130101; H01L 45/08
20130101 |
International
Class: |
H01L 27/24 20060101
H01L027/24; H01L 27/22 20060101 H01L027/22; H01L 43/12 20060101
H01L043/12; H01L 43/08 20060101 H01L043/08; H01L 43/10 20060101
H01L043/10; H01L 45/00 20060101 H01L045/00; H01L 43/02 20060101
H01L043/02 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 21, 2013 |
KR |
10-2013-0030110 |
Mar 21, 2013 |
KR |
10-2013-0030113 |
Claims
1. A two-terminal switching element comprising: a first electrode;
a second electrode; a pair of first conductivity type metal oxide
semiconductor layers electrically connected to the first electrode
and the second electrode; and a second conductivity type metal
oxide semiconductor layer disposed between the first conductivity
type metal oxide semiconductor layers, wherein any one of the first
conductivity type and the second conductivity type is a P-type and
the other is an N-type.
2-3. (canceled)
4. The element of claim 1, wherein the P-type metal oxide
semiconductor layers each have a band gap of 3 eV or less.
5. The element of claim 1, wherein the P-type metal oxide
semiconductor layer has an atomic ratio of oxygen in a range 30% to
50% greater than a case in which a stoichiometric ratio is
satisfied.
6. The element of claim 1, wherein each P-type metal oxide
semiconductor layer is CuO.sub.x (1.1<x.ltoreq.1.5) or CoO.sub.x
(1.1<x.ltoreq.1.5).
7. The element of claim 1, wherein the N-type metal oxide
semiconductor layer is one metal oxide layer selected from the
group consisting of ZnO, SnO.sub.2, In.sub.2O.sub.3,
Ga.sub.2O.sub.3, InSnO, GaInO, ZnInO, ZnSnO, InGaZnO, TiO.sub.2,
CeO.sub.2, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, LaO.sub.2, NbO.sub.2,
LiNbO.sub.3, BaSrTiO.sub.3, SrTiO.sub.3, ZrO.sub.2, SrZrO.sub.3,
Nb-doped SrTiO.sub.3, Cr-doped SrTiO.sub.3, and Cr-doped
SrZrO.sub.3.
8. A resistive memory cross-point array comprising: a first end
electrode; a second end electrode; a switching layer disposed
between the first end electrode and the second end electrode and
including a pair of first conductivity type metal oxide
semiconductor layers and a second conductivity type metal oxide
semiconductor layer disposed between the first conductivity type
metal oxide semiconductor layers; and a bipolar variable resistive
layer disposed between the switching layer and the second end
electrode, wherein any one of the first conductivity type and the
second conductivity type is a P-type and the other is an
N-type.
9. The array of claim 8, wherein the variable resistive layer is a
magnetic tunnel junction (MTJ) structure or a resistance change
memory layer.
10. The array of claim 8, further comprising an intermediate
electrode located between the switching layer and the variable
resistive layer.
11-13. (canceled)
14. The array of claim 8, wherein the P-type metal oxide
semiconductor layers each have a band gap of 3 eV or less.
15. The array of claim 8, wherein the P-type metal oxide
semiconductor layer has an atomic ratio of oxygen in a range 30% to
50% greater than a case in which a stoichiometric ratio is
satisfied.
16. The array of claim 8, wherein each P-type metal oxide
semiconductor layer is CuO.sub.x (1.1<x.ltoreq.1.5) or CoO.sub.x
(1.1<x.ltoreq.1.5).
17. (canceled)
18. A method of manufacturing a two-terminal switching element,
comprising: forming a first conductivity type lower metal oxide
semiconductor layer on a first electrode; forming a second
conductivity type metal oxide semiconductor layer on the first
conductivity type lower metal oxide semiconductor layer; forming a
first conductivity type upper metal oxide semiconductor layer on
the second conductivity type metal oxide semiconductor layer; and
forming a second electrode on the first conductivity type upper
metal oxide semiconductor layer, wherein any one of the first
conductivity type and the second conductivity type is a P-type and
the other is an N-type.
19. The method of claim 18, further comprising annealing a
resulting structure on which the second electrode is formed.
20-22. (canceled)
23. The method of claim 18, wherein the P-type metal oxide
semiconductor layer has a band gap of 3 eV or less.
24. The method of claim 18, wherein the P-type metal oxide
semiconductor layer has an atomic ratio of oxygen in a range 30% to
50% greater than a case in which a stoichiometric ratio is
satisfied.
25. The method of claim 18, wherein the P-type metal oxide
semiconductor layer is CuO.sub.x (1.1<x.ltoreq.1.5) or CoO.sub.x
(1.1<x.ltoreq.1.5).
26. (canceled)
27. A method of manufacturing a resistive memory cross-point array,
comprising: forming a switching layer including a first
conductivity type lower metal oxide semiconductor layer, a second
conductivity type metal oxide semiconductor layer, and a first
conductivity type upper metal oxide semiconductor layer on a first
end electrode; forming a second end electrode on the switching
layer; and forming a variable resistive layer on the first end
electrode before the switching layer is formed or on the switching
layer before the second end electrode is formed, wherein any one of
the first conductivity type and the second conductivity type is a
P-type and the other is an N-type.
28. The method of claim 27, further comprising annealing a
resulting structure on which the switching layer is formed.
29-31. (canceled)
32. The method of claim 27, further comprising forming an
intermediate electrode between the switching layer and the variable
resistive layer.
33-35. (canceled)
36. The method of claim 27, wherein the P-type metal oxide
semiconductor layer has a band gap of 3 eV or less.
37. The method of claim 27, wherein the P-type metal oxide
semiconductor layer has an atomic ratio of oxygen in a range 30% to
50% greater than a case in which a stoichiometric ratio is
satisfied.
38. The method of claim 27, wherein the P-type metal oxide
semiconductor layer is CuO.sub.x (1.1<x.ltoreq.1.5) or CoO.sub.x
(1.1<x.ltoreq.1.5).
39. (canceled)
Description
TECHNICAL FIELD
[0001] The present invention relates to a switching element, and
more particularly, to a two-terminal switching element having a
bidirectional switching characteristic.
BACKGROUND ART
[0002] Currently, in flash memories commercialized as resistive
random access memories (RRAMs), a change of a threshold voltage
according to storage of charges in a charge storage layer or
removal of charges from the charge storage layer is used. A charge
storage layer may be a floating gate which is a polysilicon layer
or a charge trap layer which is a silicon nitride layer. Recently,
new generation resistive memory elements having lower power
consumption and a higher degree of integration than flash memories
have been studied. For example, the new generation resistive memory
elements include a phase-change random access memory (PRAM), a
magnetoresistive RAM (MRAM), and a resistance change RAM
(ReRAM).
[0003] In order to implement resistive memory elements as an array,
in general, a resistive element having a memory characteristic and
a selective element electrically connected to the resistive element
are provided. The selective element may be a transistor or a diode.
However, transistors have a limitation that the size of the element
is reduced due to a short channel effect such as punch through.
Further, since a general diode makes current flow in one direction,
there is a disadvantage that the diode is not appropriate for a
bipolar element having a resistance change characteristic in a
positive polarity such as the resistive element. Further, in a
transistor, since a gate electrode, source/drain regions, and
source/drain electrodes are formed, there is a disadvantage that
the transistor is not appropriate for a high degree of
integration.
[0004] To solve these problems, Republic of Korea Patent
Application Publication No. 2011-0074354 discloses a memory element
in which a pair of PN diodes are formed at both ends of a bipolar
memory element. However, in this case, it may be difficult for a
characteristic of a PN diode formed at a lower end of the bipolar
memory element and a characteristic of a PN diode formed at an
upper end of the bipolar memory element to be symmetric. Further,
when a forward electric field is applied to any one of the two PN
diodes, a backward electric field is applied to the other. Since a
forward current density is reduced by a backward current density,
the normal memory operation may be difficult.
DISCLOSURE
Technical Problem
[0005] The present invention is directed to providing a
two-terminal switching element having a bidirectional switching
characteristic and a symmetrical element operating characteristic,
a resistive memory cross-point array in which one two-terminal
switching element is included in a unit cell to improve a degree of
integration, and methods of manufacturing the same.
Technical Solution
[0006] One aspect of the present invention provides a two-terminal
switching element. A first electrode and a second electrode are
provided. A pair of first conductivity type metal oxide
semiconductor layers electrically connected to each of the first
electrode and the second electrode are disposed. A second
conductivity type metal oxide semiconductor layer disposed is
disposed between the first conductivity type metal oxide
semiconductor layers.
[0007] The first conductivity type metal oxide semiconductor layers
may be the same material layers.
[0008] Any one of the first conductivity type and the second
conductivity type may be a P-type and the other may be an N-type.
The P-type metal oxide semiconductor layers may each have a band
gap of 3 eV or less. The P-type metal oxide semiconductor layer may
have an atomic ratio of oxygen in a range 30% to 50% greater than a
case in which a stoichiometric ratio is satisfied. The P-type metal
oxide semiconductor layer may be CuO.sub.x (1.1<x.ltoreq.1.5) or
CoO.sub.x (1.1<x.ltoreq.1.5). The N-type metal oxide
semiconductor layer may be one metal oxide layer selected from the
group consisting of ZnO, SnO.sub.2, In.sub.2O.sub.3,
Ga.sub.2O.sub.3, InSnO, GaInO, ZnInO, ZnSnO, InGaZnO, TiO.sub.2,
CeO.sub.2, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, LaO.sub.2, NbO.sub.2,
LiNbO.sub.3, BaSrTiO.sub.3, SrTiO.sub.3, ZrO.sub.2, SrZrO.sub.3,
Nb-doped SrTiO.sub.3, Cr-doped SrTiO.sub.3, and Cr-doped
SrZrO.sub.3.
[0009] Another aspect of the present invention provides a resistive
memory cross-point array. The resistive memory cross-point array
includes a first end electrode and a second end electrode. A
switching layer is disposed between the first end electrode and the
second end electrode. The switching layer includes a pair of first
conductivity type metal oxide semiconductor layers and a second
conductivity type metal oxide semiconductor layer disposed between
the first conductivity type metal oxide semiconductor layers. A
bipolar variable resistive layer is disposed between the switching
layer and the second end electrode.
[0010] The variable resistive layer may be a magnetic tunnel
junction (MTJ) structure or a resistance change memory layer.
[0011] An intermediate electrode may be located between the
switching layer and the variable resistive layer. The first end
electrode and the intermediate electrode may be the same material
layers.
[0012] Still another aspect of the present invention provides a
method of manufacturing a two-terminal switching element. First, a
first conductivity type lower metal oxide semiconductor layer is
formed on a first electrode. A second conductivity type metal oxide
semiconductor layer is formed on the first conductivity type lower
metal oxide semiconductor layer. A first conductivity type upper
metal oxide semiconductor layer is formed on the second
conductivity type metal oxide semiconductor layer. A second
electrode is formed on the first conductivity type upper metal
oxide semiconductor layer.
[0013] Annealing may be performed on a resulting structure on which
the second electrode is formed. The annealing may include heat
treatment or ultraviolet (UV) treatment.
[0014] The first conductivity type metal oxide semiconductor layers
may be the same material layers.
[0015] Any one of the first conductivity type and the second
conductivity type may be a P-type and the other may be an N-type.
The P-type metal oxide semiconductor layer may have a band gap of 3
eV or less. The P-type metal oxide semiconductor layer may have an
atomic ratio of oxygen in a range 30% to 50% greater than a case in
which a stoichiometric ratio is satisfied. The P-type metal oxide
semiconductor layer may be CuO.sub.x (1.1<x.ltoreq.1.5) or
CoO.sub.x (1.1<x.ltoreq.1.5). The N-type metal oxide
semiconductor layer may be one metal oxide layer selected from the
group consisting of ZnO, SnO.sub.2, In.sub.2O.sub.3,
Ga.sub.2O.sub.3, InSnO, GaInO, ZnInO, ZnSnO, InGaZnO, TiO.sub.2,
CeO.sub.2, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, Lath, NbO.sub.2,
LiNbO.sub.3, BaSrTiO.sub.3, SrTiO.sub.3, ZrO.sub.2, SrZrO.sub.3,
Nb-doped SrTiO.sub.3, Cr-doped SrTiO.sub.3, and Cr-doped
SrZrO.sub.3.
[0016] Yet another aspect of the present invention provides a
method of manufacturing a resistive memory cross-point array.
First, a switching layer including a first conductivity type lower
metal oxide semiconductor layer, a second conductivity type metal
oxide semiconductor layer, and a first conductivity type upper
metal oxide semiconductor layer is formed on a first end electrode.
A second end electrode is formed on the switching layer. A variable
resistive layer is formed on the first end electrode before the
switching layer is formed or on the switching layer before the
second end electrode is formed.
[0017] Annealing may be performed on a resulting structure on which
the switching layer is formed. The annealing may include heat
treatment or UV treatment.
[0018] The variable resistive layer may be a bipolar variable
resistive layer, for example, an MTJ structure or a resistance
change memory layer.
[0019] An intermediate electrode may be formed between the
switching layer and the variable resistive layer. The first or
second end electrode and the intermediate electrode, which are
adjacent to the switching layer, may be the same material
layers.
Advantageous Effects
[0020] According to the present invention, a two-terminal switching
element includes a pair of first conductivity type metal oxide
semiconductor layers and a second conductivity type metal oxide
semiconductor layer disposed between the first conductivity type
metal oxide semiconductor layers, and thus can show a symmetrical
and bidirectional switching characteristic. Further, a degree of
integration of a resistive memory cross-point array can be improved
using the two-terminal switching element.
DESCRIPTION OF DRAWINGS
[0021] FIG. 1 is a cross-sectional view illustrating a two-terminal
switching element according to an embodiment of the present
invention.
[0022] FIG. 2 is a cross-sectional view illustrating a unit cell of
a resistive memory cross-point array according to an embodiment of
the present invention.
[0023] FIG. 3 is a cross-sectional view illustrating a unit cell of
a resistive memory cross-point array according to another
embodiment of the present invention.
[0024] FIGS. 4A and 4B are schematic views for describing a writing
method of a resistive memory cross-point array according to an
embodiment of the present invention.
[0025] FIG. 5 is a graph illustrating a Rutherford backscattering
spectroscopy (RBS) peak of a CoO.sub.x layer obtained through
manufacturing of Manufacturing Example 1.
[0026] FIGS. 6A and 6B are graphs illustrating current-voltage
characteristics of P-N-P switching elements manufactured through
Manufacturing Examples 1 to 4.
[0027] FIG. 7 is a graph illustrating current-voltage
characteristics of P-N-P switching elements manufactured through
Manufacturing Examples 1 and 5.
[0028] FIG. 8 is a graph illustrating a current-voltage
characteristic of a variable resistive element manufactured through
Manufacturing Example 6.
[0029] FIGS. 9A and 9B are graphs illustrating a current-voltage
characteristic of an element including a P-N-P switching element
and a variable resistive element, which are connected in
series.
MODES OF THE INVENTION
[0030] Hereinafter, in order to further specifically describe the
invention, exemplary embodiments of the present invention will be
described in more detail with reference to the accompanying
drawings. However, the invention is not limited to the
above-described embodiments, and may be embodied in different
forms.
[0031] In this specification, it will be understood that when a
layer is referred to as being disposed "on" another layer or a
substrate, it can be directly formed on the other layer or the
substrate, or a third layer can be interposed therebetween.
Further, in this specification, it will be understood that
orientational terms such as "upper side," "upper (portion)," or
"upper surface" used herein may also be understood to refer to a
"lower side," "lower (portion)," "lower surface," "side," "side
(portion)," or "side surface." That is, spatially orientational
terms should be understood to refer to relative orientations but
should not be understood to refer to absolute orientations for
purposes of limitation. In addition, in this specification, terms
such as "first" or "second" do not limit components, and will be
understood only as terms distinguishing components.
[0032] Further, thicknesses of layers and areas are exaggerated for
clarity in the drawings of this specification. The same reference
numerals indicate the same components throughout the
specification.
[0033] FIG. 1 is a cross-sectional view illustrating a two-terminal
switching element according to an embodiment of the present
invention.
[0034] Referring to FIG. 1, the two-terminal switching element
includes a first electrode 100, a second electrode 300, a pair of
first conductivity type metal oxide semiconductor layers 210 and
230 electrically connected to the first electrode 100 and the
second electrode 300, respectively, and a second conductivity type
metal oxide semiconductor layer 220 disposed between the first
conductivity type metal oxide semiconductor layers 210 and 230. As
the first conductivity type and the second conductivity type are
opposite conductivity types, one may be a P-type and the other may
be an N-type. Therefore, the two-terminal switching element may
have a structure of P-N-P or N-P-N.
[0035] When a voltage having a predetermined absolute value or more
is applied between the first electrode 100 and the second electrode
300, a depletion layer may be formed throughout the second
conductivity type metal oxide semiconductor layer 220. In this
case, a current may be conducted in a portion to which a reverse
bias is applied among side surfaces of the second conductivity type
metal oxide semiconductor layer 220, which are in contact with the
first conductivity type metal oxide semiconductor layers 210 and
230. As a result, the two-terminal switching element may be turned
on and may have both a threshold voltage having a positive value
and a threshold voltage having a negative value, and thus
bidirectional switching may be implemented.
[0036] Meanwhile, the second conductivity type metal oxide
semiconductor layer 220 may have a smaller thickness than each of
the first conductivity type metal oxide semiconductor layers 210
and 230. In this case, an absolute value of the threshold voltage
may be reduced. Each of the first conductivity type metal oxide
semiconductor layers 210 and 230 may have a thickness in a range of
10 nm to 100 nm, and preferably, a thickness of 30 nm or less.
Further the second conductivity type metal oxide semiconductor
layer 220 may have a thickness in a range of 1 nm to 20 nm, and
preferably a thickness of 5 nm or less.
[0037] The first conductivity type metal oxide semiconductor layers
210 and 230 may be a lower metal oxide semiconductor layer 210
having a first conductivity type and an upper metal oxide
semiconductor layer 230 having a first conductivity type. The lower
and upper metal oxide semiconductor layers 210 and 230 may be the
same material layer, and may have substantially the same thickness.
In this case, the symmetry of the two-terminal switching element
may be improved. However, the lower and upper metal oxide
semiconductor layer 210 and 230 are not limited thereto, and may be
different materials when the lower metal oxide semiconductor layer
210 having a first conductivity type and the upper metal oxide
semiconductor layer 230 having a first conductivity type have the
same conductivity type. Alternatively, the lower metal oxide
semiconductor layer 210 having a first conductivity type and the
upper metal oxide semiconductor layer 230 having a first
conductivity type may have different thicknesses.
[0038] When the first conductivity type metal oxide semiconductor
layers 210 and 230 are P-type metal oxide semiconductor layers, the
second conductivity type metal oxide semiconductor layer 220 may be
an N-type metal oxide semiconductor layer. On the other hand, when
the first conductivity type metal oxide semiconductor layers 210
and 230 are the N-type metal oxide semiconductor layers, the second
conductivity type metal oxide semiconductor layer 220 may be the
P-type metal oxide semiconductor layer. In this case, as an
example, the P-type metal oxide semiconductor layers may each be
one metal oxide layer selected from the group consisting of
NiO.sub.x (1.1<x.ltoreq.1.5), FeO.sub.x (1.1<x.ltoreq.1.5),
CoO.sub.x (1.1<x.ltoreq.1.5), PdO.sub.x (1.1<x.ltoreq.1.5),
CuAlO.sub.x (1.8.ltoreq.x<3), CuGaO.sub.x (1.8.ltoreq.x<3),
SrCu.sub.2O.sub.x (1.ltoreq.x<1.8), RhO.sub.x
(1.1<x.ltoreq.1.5), CrO.sub.x (1.1<x.ltoreq.1.5), CuO.sub.x
(1.1<x.ltoreq.1.5), CuO.sub.x (1.5<x.ltoreq.2), SnO.sub.x
(1.1<x.ltoreq.1.5), Ag.sub.xO (1.5<x.ltoreq.2), LaMnO.sub.x
(2.5<x.ltoreq.3), YBaCu.sub.2O.sub.x (3.5<x.ltoreq.4), PCMO
(PrCaMnO.sub.3), LCMO (LaCaMnO.sub.3), LSMO (LaSrMnO.sub.3), and
PZTO (PbZrTiO.sub.3). Meanwhile, the N-type metal oxide
semiconductor layers may each be one metal oxide layer selected
from the group consisting of ZnO, SnO.sub.2, In.sub.2O.sub.3,
Ga.sub.2O.sub.3, InSnO, GaInO, ZnInO, ZnSnO, InGaZnO, TiO.sub.2,
CeO.sub.2, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, LaO.sub.2, NbO.sub.2,
LiNbO.sub.3, BaSrTiO.sub.3, SrTiO.sub.3, ZrO.sub.2, SrZrO.sub.3,
Nb-doped SrTiO.sub.3, Cr-doped SrTiO.sub.3, and Cr-doped
SrZrO.sub.3.
[0039] In general, it has been very difficult to actually apply the
P-type metal oxide semiconductor to an element due to an extremely
low current density. To solve such difficulty, the P-type metal
oxide semiconductor layer may have a band gap of 3 eV or less, for
example, 2 eV or less. In this case, the current density of the
P-type metal oxide semiconductor layer may be significantly
improved. Alternatively, the P-type metal oxide semiconductor layer
may have a band gap of 1 eV or more. As an example, the P-type
metal oxide semiconductor layer which satisfies this condition may
be CuO.sub.x (1.1<x.ltoreq.1.5, a band gap is in a range of 1.2
eV to 1.4 eV) or CoO.sub.x (1.1<x.ltoreq.1.5, a band gap is in a
range of 1.4 eV to 1.6 eV). Further, the P-type metal oxide
semiconductor layer may have an atomic ratio of oxygen in a range
10% to 50%, specifically, 30% to 50%, greater than a case in which
an atomic ratio of oxygen with respect to a metal satisfies a
stoichiometric ratio. Further, the P-type metal oxide semiconductor
layer which satisfies this condition may be CuO.sub.x
(1.1<x.ltoreq.1.5) or CoO.sub.x (1.1<x.ltoreq.1.5).
[0040] The first electrode 100 and the second electrode 300 may be
formed of materials which may achieve an ohmic contact with the
first conductivity type metal oxide semiconductor layers 210 and
230 connected thereto, respectively. As an example, the first
electrode 100 and the second electrode 300 each may be Al, W, Pt,
Ti, TiN, TaN, WN, or Cu.
[0041] Further, a method of manufacturing a two-terminal switching
element according to an embodiment of the present invention will be
described with reference to FIG. 1.
[0042] The method of manufacturing the two-terminal switching
element according to an embodiment of the present invention may
include forming a first conductivity type lower metal oxide
semiconductor layer 210 on a first electrode 100, forming a second
conductivity type metal oxide semiconductor layer 220 on the first
conductivity type lower metal oxide semiconductor layer 210,
forming a first conductivity type upper metal oxide semiconductor
layer 230 on the second conductivity type metal oxide semiconductor
layer 220, and forming a second electrode 300 on the first
conductivity type upper metal oxide semiconductor layer 230.
[0043] Referring to FIG. 1, the first electrode 100, the lower
metal oxide semiconductor layer 210 having the first conductivity
type, the second conductivity type metal oxide semiconductor layer
220, the upper metal oxide semiconductor layer 230 having the first
conductivity type, and the second electrode 300 are sequentially
formed to form the two-terminal switching element.
[0044] As the first conductivity type and the second conductivity
type are opposite conductivity types, one may be a P-type and the
other may be an N-type. Therefore, the two-terminal switching
element may have a structure of P-N-P or N-P-N.
[0045] The first electrode 100, the lower metal oxide semiconductor
layer 210 having the first conductivity type, the second
conductivity type metal oxide semiconductor layer 220, the upper
metal oxide semiconductor layer 230 having the first conductivity
type, and the second electrode 300 may be formed using a sputtering
method with an appropriate target. Specifically, when the P-type
metal oxide semiconductor layer among the metal oxide semiconductor
layers 210, 220, and 230 is formed, the sputtering method may be
performed in an atmosphere in which inert gas and oxygen are mixed.
As a result, a metal vacancy is formed in the P-type metal oxide
semiconductor layer, and thus a current density of the P-type metal
oxide semiconductor layer may be improved. However, the metal
vacancy is not limited thereto, and may also be formed using a
pulsed laser deposition (PLD) method, a thermal evaporation method,
an electron-beam evaporation method, a physical vapor deposition
(PVD) method, a molecular beam epitaxy (MBE) deposition method, or
a chemical vapor deposition (CVD) method.
[0046] After the second electrode 300 is formed, annealing such as
heat treatment, ultraviolet (UV) treatment, or combination
treatment in which a plurality thereof are applied may be
performed. In this case, an on-current density and an on/off ratio
of the two-terminal selective element may be improved, and a
threshold voltage (a turn-on voltage) may be lowered. The heat
treatment may be heat treatment using rapid thermal annealing (RTA)
or a furnace. The UV treatment may be annealing using a UV lamp and
may be performed using UV-C (UV having a wavelength in a range of
100 nm to 280 nm).
[0047] FIG. 2 is a cross-sectional view illustrating a resistive
memory cross-point array according to an embodiment of the present
invention, and is limited to a unit cell.
[0048] Referring to FIG. 2, the resistive memory cross-point array
includes a first end electrode 150 and a second end electrode 350
crossing an upper portion of the first end electrode 150. A
switching layer 200 and a variable resistive layer 500, which are
sequentially stacked, are disposed at a point at which the end
electrodes 150 and 350 cross. However, these are not limited
thereto, and the switching layer 200 may be stacked on the variable
resistive layer 500. An intermediate electrode 400 may be disposed
between the switching layer 200 and the variable resistive layer
500. The first end electrode 150, the switching layer 200, and the
intermediate electrode 400 may constitute a two-terminal switching
element SD, and the intermediate electrode 400, the variable
resistive layer 500, and the second end electrode 350 may
constitute a variable resistive element RM. Furthermore, the first
end electrode 150 may serve as a word line or an additional word
line may be connected to the first end electrode 150. Further, the
second end electrode 350 may serve as a bit line or an additional
bit line may be connected to the second end electrode 350.
[0049] At least after the switching layer 200 is formed, for
example, before the intermediate electrode 400 is formed after the
switching layer 200 is formed, or before the variable resistive
layer 500 is formed after the switching layer 200 and the
intermediate electrode 400 are formed thereon, annealing may be
performed. The annealing may be heat treatment, UV treatment, or
combination treatment in which a plurality thereof are applied. In
this case, an on-current density and an on/off ratio of the
two-terminal selective element SD may be improved, and a threshold
voltage may be lowered. The heat treatment may be heat treatment
using RTA or a furnace. The UV treatment may be annealing using a
UV lamp and may be performed using UV-C (UV having a wavelength in
a range of 100 nm to 280 nm).
[0050] Each of the end electrodes 150 and 350 and the intermediate
electrode 400 may be an Al, W, Pt, Ti, TiN, TaN, WN, or Cu layer.
However, the end electrodes provided at both sides of the switching
layer 200 and the immediate electrode may be formed with the same
material layer. In this case, the symmetry of the switching element
SD may be improved. However, this is not limited thereto.
[0051] The switching layer 200 includes a pair of the first
conductivity type metal oxide semiconductor layers 210 and 230 and
a second conductivity type metal oxide semiconductor layer 220
disposed between the first conductivity type metal oxide
semiconductor layers 210 and 230. One of the first conductivity
type metal oxide semiconductor layers 210 and 230 may be
electrically connected to one of the end electrodes 150 and 350.
The first conductivity type metal oxide semiconductor layers 210
and 230 may be a lower metal oxide semiconductor layer 210 having a
first conductivity type and an upper metal oxide semiconductor
layer 230 having a first conductivity type. As an example, the
lower metal oxide semiconductor layer 210 is connected to the first
end electrode 150. When the intermediate electrode 400 is disposed,
the upper metal oxide semiconductor layer 230 may be connected to
the intermediate electrode 400. The first conductivity type metal
oxide semiconductor layers 210 and 230 and the second conductivity
type metal oxide semiconductor layer 220 will be described in
detail with reference to the embodiment described with reference to
FIG. 1.
[0052] The variable resistive layer 500 may be electrically
connected to the upper metal oxide semiconductor layer 230. When
the intermediate electrode 400 is disposed, the variable resistive
layer 500 is connected to the intermediate electrode 400. The
variable resistive layer 500 may be a bipolar variable resistive
layer. The variable resistive element RM including the variable
resistive layer 500 may include a magnetoresistive random access
memory (MRAM), specifically a spin transfer torque MRAM. In this
case, the variable resistive layer 500 has a magnetic tunnel
junction (MTJ) structure, and the MTJ structure may have a
ferromagnetic pinned layer 510, a tunnel barrier layer 520, and a
ferromagnetic free layer 530, which are sequentially stacked. The
MTJ structure may further include a pinning layer (nor shown) under
the ferromagnetic pinned layer 510. The ferromagnetic pinned layer
510, which is a layer in which magnetization reversal does not
occur, may be a CoFeB layer or a FePt layer. The tunnel barrier
layer 520 may be an aluminum oxide layer or a magnesium oxide
layer. The ferromagnetic free layer 530, which is a layer in which
magnetization reversal occurs at a critical current density or
more, may be a CoFeB layer or a FePt layer. The ferromagnetic free
layer 530 may have a magnetization direction opposite that of the
pinned layer at a positive critical current density or more, and at
a negative critical current density or less. Therefore, the spin
transfer torque MRAM may operate as a bipolar element.
[0053] Further, a method of manufacturing a resistive memory
cross-point array according to an embodiment of the present
invention will be described with reference to FIG. 2.
[0054] The method of manufacturing the resistive memory cross-point
array according to an embodiment of the present invention may
include forming a switching layer 200 including a first
conductivity type lower metal oxide semiconductor layer 210, a
second conductivity type metal oxide semiconductor layer 220, and a
first conductivity type upper metal oxide semiconductor layer 230
on a first end electrode 150, forming a second end electrode 350 on
the switching layer 200, and forming a variable resistive layer 500
on the first end electrode 150 before the switching layer 200 is
formed or on the switching layer 200 before the second end
electrode 350 is formed.
[0055] Referring to FIG. 2, the first end electrode 150 is formed.
The first end electrode 150 may be formed to extend in one
direction. The switching layer 200 may be formed on the first end
electrode 150. The variable resistive layer 500 may be formed on
the switching layer 200. The second end electrode 350 crossing the
first end electrode 150 may be formed on the variable resistive
layer 500. However, this is not limited thereto, and the variable
resistive layer 500 may be formed on the first end electrode 150
before the switching layer 200 is formed. Thus, a structure in
which the switching layer 200 and the variable resistive layer 500
are stacked may be disposed at a point at which the end electrodes
150 and 350 cross.
[0056] An intermediate electrode 400 may be formed between the
switching layer 200 and the variable resistive layer 500. In this
case, the first end electrode 150, the switching layer 200, and the
intermediate electrode 400 may constitute a two-terminal switching
element SD, and the intermediate electrode 400, the variable
resistive layer 500, and the second end electrode 350 may
constitute a variable resistive element RM. Furthermore, the first
end electrode 150 may serve as a word line and an additional word
line may be connected to the first end electrode 150. Further, the
second end electrode 350 may serve as a bit line and an additional
bit line may be connected to the second end electrode 350.
[0057] At least after the switching layer 200 is formed, for
example, before the intermediate electrode 400 is formed after the
switching layer 200 is formed, or before the variable resistive
layer 500 is formed after the switching layer 200 and the
intermediate electrode 400 are formed thereon, annealing may be
performed. The annealing may be heat treatment, UV treatment, or
combination treatment in which a plurality thereof are applied. In
this case, an on-current density and an on/off ratio of the
two-terminal selective element SD may be improved, and a threshold
voltage (a turn-on voltage) may be lowered. The heat treatment may
be heat treatment using RTA or a furnace. The UV treatment may be
annealing using a UV lamp and may be performed using UV-C (UV
having a wavelength in a range of 100 nm to 280 nm).
[0058] FIG. 3 is a cross-sectional view illustrating a resistive
memory cross-point array according to another embodiment of the
present invention, and is limited to a unit cell. The resistive
memory cross-point array according to the embodiment of the present
invention is similar to the cross-point array described with
reference to FIG. 2 except for the following description.
[0059] Referring to FIG. 3, a variable resistive element RM
including a variable resistive layer 600 may be a resistive RAM
(RRAM). In this case, the variable resistive layer 600 is a bipolar
variable resistive layer, specifically, a RRAM layer having a
bipolar characteristic. As an example, the variable resistive layer
600 may be a metal oxide layer (transition metal oxide layer), a
chalcogenide layer, a perovskite layer, or a metal-doped solid
electrolyte layer. The metal oxide layer may be a SiO.sub.2 layer,
an Al.sub.2O.sub.3 layer, or a transition metal oxide layer. The
transition metal oxide layer may be a HfO.sub.2-x, MnO.sub.2-x,
ZrO.sub.2-x, NiO.sub.1-y, Ta.sub.2O.sub.5-x, CuO.sub.1-y,
Fe.sub.2O.sub.3, (e.g., 0.ltoreq.x.ltoreq.1.5,
0.ltoreq.y.ltoreq.0.5), or a lanthanoid oxide layer. The lanthanoid
may be lanthanum (La), cerium (Ce), praseodymium (Pr), neodymium
(Nd), samarium (Sm), gadolinium (Gd), or dysprosium (Dy). The
chalcogenide layer may be a GeSbTe layer or a GeTeO (e.g.,
Ge.sub.2Te.sub.2O.sub.5) layer, and the perovskite layer may be a
SrTiO.sub.3 layer, a Cr layer, a Nb-doped SrZrO.sub.3 layer, a PCMO
(Pr.sub.1-XCa.sub.XMnO.sub.3, 0<X<1) layer, or an LCMO
(La.sub.1-XCa.sub.XMnO.sub.3, 0<X<1, e.g., X is 0.3) layer.
Further, the metal-doped solid electrolyte layer may be a layer in
which Ag is doped in GeSe, that is, a AgGeSe layer.
[0060] In one embodiment, when a set voltage is applied to the
variable resistive element RM, oxygen ions included in the RRAM
layer 600 may move to the second end electrode 350 to be stored in
the second end electrode 350. In this case, the number of oxygen
vacancies is increased in the RRAM layer 600 and the RRAM layer 600
may be changed to have low resistance. Further, when a reset
voltage is applied to the variable resistive element RM, the oxygen
ions which were moved to the second end electrode 350 may return to
the RRAM layer 600. In this case, the number of oxygen vacancies is
reduced in the RRAM layer 600 and the RRAM layer 600 may be changed
to have high resistance. To this end, the second end electrode 350
may be TiN or WN in which resistance is hardly changed even after
the storing of the oxygen. In this case, each of the first end
electrode 150 and the intermediate electrode 400 may be an Al, W,
Pt, Ti, TaN, WN, or Cu layer.
[0061] FIG. 4A is a schematic view for describing a forward writing
method of a resistive memory cross-point array according to an
embodiment of the present invention.
[0062] Referring to FIG. 4A, a plurality of first data lines, that
is, word lines W.sub.n, W.sub.n+1, W.sub.n+2, and W.sub.n+3, and a
plurality of second data lines, that is, bit lines B.sub.m
B.sub.m-2, and B.sub.m+3 crossing the word lines are disposed. A
two-terminal switching element SD and a variable resistive element
RM, which are connected in series, are disposed at a point at which
each word line and each bit line cross. The two-terminal switching
element SD is connected to the word line and the variable resistive
element RM is connected to the bit line are illustrated, but are
not limited thereto and positions of the two-terminal switching
element SD and the variable resistive element RM may be changed
with each other.
[0063] A 1/2V.sub.write is applied to a bit line B.sub.m+1 selected
from the bit lines and a ground voltage is applied to bit lines
B.sub.m, B.sub.m+2, and B.sub.m+3 not selected from the bit lines.
A -1/2V.sub.write is applied to a word line W.sub.n+1 selected from
the word lines W.sub.n, W.sub.n+1, W.sub.n+2, and W.sub.n+3 and a
ground voltage is applied to word lines W.sub.n, W.sub.n+2,
W.sub.n+3, not selected from the word lines. A V.sub.write may be
applied to a selected unit cell A located at a point at which the
selected bit line B.sub.m+1 and the selected word line W.sub.n+1
cross, and 0 V, 1/2V.sub.write, or -1/2V.sub.write may be applied
to the remaining non-selected unit cells.
[0064] The V.sub.write may have a value of a threshold voltage of
the two-terminal switching element SD or more and a value of a set
voltage of the variable resistive element RM or more, and the
1/2V.sub.write may have a value less than the set voltage of the
resistive memory element RM. Therefore, in the selected unit cell,
only the resistive memory element RM may be selectively changed in
a low resistive state (LRS). Meanwhile, in the non-selected unit
cell, the state of the resistive memory element RM may not be
changed, and the previous state thereof may be maintained.
[0065] FIG. 4B is a schematic view for describing a backward
writing method of a resistive memory cross-point array according to
an embodiment of the present invention. The writing method
according to the embodiment of the present invention is similar to
the forward writing method described with reference to FIG. 4A
except for the following description.
[0066] Referring to FIG. 4B, a -1/2V.sub.write is applied to a bit
line B.sub.m-1 selected from bit lines and a ground voltage is
applied to bit lines B.sub.m, B.sub.m+2, and B.sub.m+3 not selected
from the bit lines. A 1/2V.sub.write is applied to a word line
W.sub.n+1 selected from word lines W.sub.n, W.sub.n+2, and
W.sub.n+3 and a ground voltage is applied to word lines W.sub.n,
W.sub.n+2, W.sub.n+3 not selected from the word lines. A
-V.sub.write may be applied to a selected unit cell A located at a
point at which the selected bit line B.sub.m+1 and the selected
word line W.sub.n+1 cross, and 0 V, 1/2V.sub.write, or
-1/2V.sub.write may be applied to the remaining non-selected unit
cells.
[0067] The -V.sub.write may have a value of a backward threshold
voltage of the two-terminal switching element SD or less and a
reset voltage or less of the resistive memory element RM.
Therefore, in the selected unit cell, only the resistive memory
element RM may be selectively changed in a high resistive state
(HRS). Meanwhile, in the non-selected unit cell, the state of the
resistive memory element RM may not be changed, and a previous
state thereof may be maintained.
[0068] Hereinafter, exemplary experimental examples will be
introduced to help with understanding of the present invention.
However, the experimental examples below are intended only to help
with understanding of the present invention, and the present
invention is not limited thereto.
EXPERIMENTAL EXAMPLES
Manufacturing Example 1
Manufacturing of P-N-P Switching Element, IGZO.sub.--5 nm
[0069] A 30 nm Ti layer was formed on a SiO.sub.2 layer of a Si
substrate including a 200 nm layer of the SiO.sub.2 using a
magnetron sputtering method with a Ti target in a pure argon
atmosphere, and then 100 nm of a Pt layer was formed using a
magnetron sputtering method with a Pt target in the same
atmosphere. Then, a P-type metal oxide semiconductor layer, which
was a 30 nm CoO.sub.x layer, was formed on the Pt layer using a
magnetron sputtering method with a CoO target in an atmosphere in
which 1.1 sccm of oxygen and 10 sccm of argon were mixed. An N-type
metal oxide semiconductor layer, which was a 5 nm IGZO layer, was
formed on the CoO.sub.x layer using a magnetron sputtering method
with an IGZO (InGaZnO) target in a pure argon atmosphere. A P-type
metal oxide semiconductor layer, which was a 30 nm CoO.sub.x layer,
was formed on the IGZO layer using a magnetron sputtering method
with a CoO target in an atmosphere in which 1.1 sccm of oxygen and
10 sccm of argon were mixed. Then, a 100 nm Pt pattern was formed
on the CoO.sub.x layer using a magnetron sputtering method with a
Pt target and using a metal shadow mask in a pure argon atmosphere.
Then, UV treatment in which ultraviolet in a UV-C (UV having a
wavelength in a range of 100 nm to 280 nm) region was emitted for
20 minutes or more was performed in a high vacuum state of
10.sup.-6 Torr or less.
Manufacturing Example 2
Manufacturing of P-N-P Switching Element, IGZO.sub.--10 nm
[0070] A switching element was manufactured using the same method
as Manufacturing Example 1 of the switching element except that a
10 nm IGZO layer was formed.
Manufacturing Example 3
Manufacturing of P-N-P Switching Element, IGZO.sub.--20 nm
[0071] A switching element was manufactured using the same method
as Manufacturing Example 1 of the switching element except that a
20 nm IGZO layer was formed.
Manufacturing Example 4
Manufacturing of P-N-P Switching Element, IGZO.sub.--50 nm
[0072] A switching element was manufactured using the same method
as Manufacturing Example 1 of the switching element except that a
50 nm IGZO layer was formed.
Manufacturing Example 5
Manufacturing of P-N-P Switching Element, Except UV Treatment
[0073] A switching element was manufactured using the same method
as Manufacturing Example 1 except that UV treatment was not
performed.
[0074] FIG. 5 is a graph illustrating a Rutherford backscattering
spectroscopy (RBS) peak with respect to the CoO.sub.x layer
obtained through the manufacturing of Manufacturing Example 1.
[0075] Referring to FIG. 5, it was analyzed that an atomic ratio of
Co and O of the CoO.sub.x layer was 1:1.4, that is, x was 1.4. This
shows that an atomic ratio of O increased more than a case in which
a stoichiometric ratio is satisfied (CoO.sub.x where x=1) and a
content of metal vacancies in the CoO.sub.x (x=1.4) layer
increased.
[0076] FIGS. 6A and 6B are graphs illustrating current-voltage
characteristics of the P-N-P switching elements manufactured
through Manufacturing Examples 1 to 4.
[0077] Referring to FIGS. 6A and 6B, it may be seen that a turn-on
voltage is reduced, and further, an on-current is increased as a
thickness of an IGZO layer is reduced. As an example, it was shown
that the turn-on voltage of the P-N-P the switching element was
about 2 V and the on-current (@4 V) was a very good value such as
about 10.sup.-2 when the IGZO layer was 5 nm. It may be seen that
the increasing of the on-current is a result of the increase in
current density of the CoO.sub.x layer which is a P-type metal
oxide semiconductor layer. The increase in the current density of
the CoO.sub.x layer is considered to have resulted from the
increase in content of metal vacancies according to the increase of
the x value.
[0078] FIG. 7 is a graph illustrating current-voltage
characteristics of the P-N-P switching elements manufactured
through Manufacturing Example 1 and Manufacturing Example 5.
[0079] Referring to FIG. 7, it may be seen that a turn-on voltage
is slightly reduced in the case in which UV treatment was performed
(Manufacturing Example 1) compared to the case in which the UV
treatment was not performed (Manufacturing Example 7), and further,
an on-current is improved. Thus, it may be estimated that the UV
treatment improves an interface characteristic between metal oxide
semiconductor layers and/or between a metal oxide semiconductor
layer and a metal layer.
Manufacturing Example 6
Manufacturing of Variable Resistive Element
[0080] A 30 nm Ti layer was formed on a SiO.sub.2 layer of a Si
substrate including a 200 nm layer of the SiO.sub.2 using a
magnetron sputtering method with a Ti target in a pure argon
atmosphere and then a 100 nm Pt layer was formed using a magnetron
sputtering method with a Pt target in the same atmosphere. Then,
the RRAM layer, which was a 30 nm TiO.sub.x layer (x=1.75), was
formed on the Pt layer using a magnetron sputtering method with a
TiO.sub.2 target in an atmosphere in which 10 sccm of oxygen and 6
sccm of argon were mixed. A 100 nm TiN pattern was formed on the
TiO.sub.x layer using a magnetron sputtering method with a Ti
target and using a metal shadow mask in an atmosphere in which 1.5
sccm of nitrogen and 8 sccm of argon were mixed.
[0081] FIG. 8 is a graph illustrating a current-voltage
characteristic of the variable resistive element manufactured
through Manufacturing Example 6.
[0082] Referring to FIG. 8, it may be seen that the variable
resistive element manufactured through Manufacturing Example 6
shows a bipolar characteristic having a set voltage of about 2 V
and a reset voltage of about -2 V.
[0083] FIGS. 9A and 9B are graphs illustrating a current-voltage
characteristic of an element including a P-N-P switching element
and a variable resistive element, which are connected in series.
Specifically, Pt which is an upper electrode of the P-N-P switching
element manufactured through Manufacturing Example 1 and Pt which
is a lower electrode of the variable resistive element manufactured
through Manufacturing Example 6 are connected through a wire
bonding.
[0084] Referring to FIGS. 9A and 9B, it may be seen that a forward
threshold voltage V.sub.th1 of the switching element is about 1 V,
and a backward threshold voltage V.sub.th2 is about -1 V. Further,
it may be seen that a set voltage of the variable resistive element
is about 4 V and a reset voltage thereof is about -4 V.
Accordingly, the V.sub.write described with reference to FIGS. 4A
and 4B may be set to about 4 V which is the set voltage, and the
-V.sub.write may be set to about -4 V which is the reset voltage.
Further, when a voltage V.sub.read applied to the selected unit
cell is set to about 3 V in order to read data of the selected unit
cell, a ratio of an on-current with respect to an off-current may
be about 4.
[0085] Although the invention has been described in detail with
reference to exemplary embodiments, the invention is not limited
thereto. Those skilled in the art may make various modifications
and changes without departing from the spirit and scope of the
present invention.
* * * * *