KR102146419B1 - Selector including two dimensional materials - Google Patents

Abstract

The present application includes a graphene layer formed on a substrate, a two-dimensional insulating layer formed on the graphene layer, and a first electrode formed on the two-dimensional insulating layer, and the dielectric strength of the two-dimensional insulating layer is It relates to a selection device that is 5 MV/cm or more.

Description

Selection elements including 2D materials {SELECTOR INCLUDING TWO DIMENSIONAL MATERIALS}

The present application relates to a selection device comprising a two-dimensional material.

Volatile memories are pursuing high-density integration, but they are reaching their technical limits. Accordingly, research on new memories to replace the existing volatile memory is being actively conducted. Unlike volatile memory, non-volatile memory is of great interest to both academia and industry because it does not store charge as a basic principle for storing information.

Nonvolatile memories that are emerging as the next-generation memory are PRAM (phase change RAM), NFGM (nanofloating gate memory), RRAM (resistive RAM), PoRAM (polymer RAM), MRAM (magnetic RAM), and molecular electronic devices. Among them, RRAM (resistive memory) is attracting the most attention as a next-generation nonvolatile memory due to its easy manufacturing process, fast switching speed, and excellent durability compared to other devices.

The RRAM has an advantage in that it is possible to implement a crossbar structure capable of maximizing the degree of integration of the device, since the device can be implemented with only two access lines. However, in the crossbar structure, several cells are connected to one access line, thereby generating a leakage current. When a transistor is connected to solve this leakage current, the advantage of the RRAM is lost, and thus the problem of solving the leakage current in the RRAM is very important.

In order to solve this problem, a device made of a material having a large current on/off ratio is required, and a device that performs this role is called a selection device. However, it has been difficult for the conventional selection device to stably implement an on/off ratio required for driving an integrated device of 10 ¹⁰ .

The technology behind the present application, Chengbin Pan., et al., Coexistence of Grain-Boundaries-Assisted Bipolar and Threshold Resistive Switching in Multilayer Hexagonal Boron Nitride, Adv. Funct. Mater. , 2017, 27, 1604811 The paper relates to the resistance change of multilayer hexagonal boron nitride. However, the resistance-changing device implemented in the above paper has a current flash ratio of at most 10 ⁶ , and a commercially available selection device is required to have a higher current flash ratio.

The present application is to solve the above-described problems of the prior art, and an object thereof is to provide a selection element including a two-dimensional material.

In addition, an object of the present application is to provide a resistive memory device including the selection device.

However, the technical problem to be achieved by the embodiments of the present application is not limited to the technical problems as described above, and other technical problems may exist.

As a technical means for achieving the above technical problem, the first aspect of the present application is a graphene layer formed on a substrate, a two-dimensional insulating layer formed on the graphene layer, and a first electrode formed on the two-dimensional insulating layer Including, and the dielectric strength (dielectric strength) of the two-dimensional insulating layer is 5 MV / cm or more to provide a selection device.

According to the exemplary embodiment of the present disclosure, the thickness of the two-dimensional insulating layer may be 5 nm to 30 nm, but is not limited thereto.

According to one embodiment of the present application, the two-dimensional insulating layer, hexagonal boron nitride (hBN), a transition metal chalcogen compound, Ca(OH) ₂ , Mg(OH) ₂ , SiO ₂ , HfO ₂ , Al ₂ O ₃ and may be selected from the group consisting of combinations thereof, but is not limited thereto.

According to the exemplary embodiment of the present disclosure, the 2D insulating layer may be formed by laminating a 2D hBN material, but is not limited thereto.

According to one embodiment of the present application, the transition metal chalcogen compound may be selected from the group consisting of MoS ₂ , MnO ₂ , MoO ₃ , MoSe ₂ , MoTe ₂ , WS ₂ , WSe ₂ and combinations thereof, It is not limited thereto.

According to the exemplary embodiment of the present disclosure, the graphene layer may have a thickness of 10 nm or less, but is not limited thereto.

According to the exemplary embodiment of the present disclosure, the graphene layer may be selected from the group consisting of graphene, graphene oxide, reduced graphene oxide, and combinations thereof, but is not limited thereto.

According to the exemplary embodiment of the present disclosure, the on/off ratio of the selection device may be 10 ^{10 or} more, but is not limited thereto.

According to the exemplary embodiment of the present disclosure, the first electrode may be selected from the group consisting of gold, silver, platinum, titanium, nickel, iron, cobalt, copper, chromium, aluminum, palladium, and combinations thereof, but is limited thereto. It does not become.

According to one embodiment of the present application, the substrate is silicon, silicon carbide, germanium, silicon germanium, silicon carbide, InAs, AlAs, GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, and combinations thereof It may be selected from the group consisting of, but is not limited thereto.

According to the exemplary embodiment of the present disclosure, the selection device may further include an oxide insulating layer formed on the substrate, but is not limited thereto.

According to the exemplary embodiment of the present disclosure, even when a voltage is applied to the selection device, the metal filament formed from the first electrode may not be in contact with the graphene layer, but is not limited thereto.

According to the exemplary embodiment of the present disclosure, the selection device may include a second electrode formed on the graphene layer, but is not limited thereto.

According to the exemplary embodiment of the present application, the second electrode may be selected from the group consisting of gold, silver, platinum, titanium, nickel, iron, cobalt, copper, chromium, aluminum, palladium, and combinations thereof, but is limited thereto. It does not become.

A second aspect of the present application provides a resistive memory element including the selection element according to the first aspect of the present application.

The above-described problem solving means are merely exemplary and should not be construed as limiting the present application. In addition to the above-described exemplary embodiments, additional embodiments may exist in the drawings and detailed description of the invention.

According to the above-described problem solving means of the present application, the selection element according to the present application utilizes a two-dimensional insulating layer, and the current on/off ratio is 10 ¹⁰ It can have the above characteristics.

In addition, the selection device according to the present disclosure has a large current flash ratio, so that a leakage current is reduced, which may lead to a reduction in power consumption of the resistive memory device including the selection device.

Furthermore, since the current change according to the voltage change of the selection device according to the present application reaches 10 ¹⁰ , the reaction speed is fast, and thus it can be applied to a next-generation memory device.

In addition, the selection device according to the present application utilizes a two-dimensional material, and various methods of high-density integration methods such as a vertical stack structure are allowed.

However, the effect obtainable in the present application is not limited to the effects as described above, and other effects may exist.

1 is a schematic diagram of a selection device according to an embodiment of the present application.
2 is a graph showing a current-voltage curve of a resistive memory device according to an exemplary embodiment of the present disclosure.
3 is a graph showing a current-voltage curve of a selection device according to an embodiment of the present disclosure.
4 is a graph showing a current-voltage curve of a selection device according to a voltage direction according to an exemplary embodiment of the present disclosure.
5 is a graph showing a current-voltage curve of a selection device according to a voltage direction according to an exemplary embodiment of the present disclosure.
6 is a graph showing a current-voltage curve of a selection device according to an embodiment of the present disclosure.

Hereinafter, exemplary embodiments of the present application will be described in detail with reference to the accompanying drawings so that those of ordinary skill in the art may easily implement the present application.

However, the present application may be implemented in various different forms and is not limited to the embodiments described herein. In addition, in the drawings, parts not related to the description are omitted in order to clearly describe the present application, and similar reference numerals are attached to similar parts throughout the specification.

Throughout the present specification, when a part is said to be "connected" with another part, this includes not only the case that it is "directly connected", but also the case that it is "electrically connected" with another element interposed therebetween. do

Throughout this specification, when a member is positioned "on", "upper", "upper", "under", "lower", and "lower" another member, this means that a member is located on another member. This includes not only the case where they are in contact, but also the case where another member exists between the two members.

In the entire specification of the present application, when a certain part "includes" a certain component, it means that other components may be further included rather than excluding other components unless specifically stated to the contrary.

As used herein, the terms "about", "substantially" and the like are used at or close to the numerical value when manufacturing and material tolerances specific to the stated meaning are presented, and to aid understanding of the present application In order to prevent unreasonable use by unscrupulous infringers of the stated disclosures, either exact or absolute figures are used. In addition, throughout the specification of the present application, "step to" or "step of" does not mean "step for".

In the entire specification of the present application, the term "combination of these" included in the expression of the Makushi format refers to one or more mixtures or combinations selected from the group consisting of the components described in the expression of the Makushi format, and the component It means to include one or more selected from the group consisting of.

Throughout this specification, the description of "A and/or B" means "A, or B, or, A and B".

Hereinafter, the selection device of the present application will be described in detail with reference to embodiments and embodiments and drawings. However, the present application is not limited to these embodiments and examples and drawings.

As a technical means for achieving the above technical problem, the first aspect of the present application includes a graphene layer formed on a substrate, a two-dimensional insulating layer formed on the graphene layer, and a first electrode formed on the two-dimensional insulating layer. Including, and the dielectric strength of the two-dimensional insulating layer (dielectric strength) is 5 MV / cm or more to provide a selection device.

1 is a schematic diagram of a selection device according to an embodiment of the present application.

Referring to FIG. 1, the selection device according to an embodiment of the present disclosure includes a graphene layer 200 formed on a substrate 100, a two-dimensional insulating layer 300 formed on the graphene layer 200, and the 2 And a first electrode 400 formed on the dimensional insulating layer 300.

The selection element according to the present invention performs a different function from the resistive memory element (RRAM). If the voltage applied to the resistive memory element is reduced to '0 V', the RRAM maintains the'high resistance' or'low resistance' state, but in the case of the selection element, only the'high resistance' state is obtained from '0 V'.

When the resistive memory device has a structure including a substrate, a graphene layer, an insulating layer, and a metal electrode like the selection device of the present application, the structure may be similar, but the internal operating principle is different.

Specifically, when a voltage is applied to a general resistive memory device having a structure including a substrate, a graphene layer, an insulating layer, and a metal electrode (on state), the filament generated from the metal electrode penetrates into a defect inside the insulating layer, Eventually, it comes into contact with the graphene layer. Accordingly, even if the voltage is changed to 0 V after applying the voltage (off state), a low resistance state in which a predetermined current can flow through the resistive memory element is maintained (see FIG. 2).

On the other hand, in the case of the selection device according to the present application, the dielectric strength of the two-dimensional insulating layer 300 has a value of 5 MV/cm or more. That is, the two-dimensional insulating layer 300 according to the present application has a very small defect density. Therefore, even when a voltage is applied to the selection device according to the present application (on state), the filament generated from the first electrode 400 becomes unstable at a low voltage (0 V), and the graphene layer 200 and the filament connection are not It becomes impossible to maintain. Therefore, if the voltage is changed to 0 V after applying the voltage (off state), no current flows on the selection element (see FIG. 3).

The dielectric strength is also referred to as dielectric strength, and refers to the highest voltage that can be used without causing dielectric breakdown of the insulator. The dielectric strength can be measured by applying a constant voltage to the insulator and checking whether the current flows due to the breakdown of insulation at about several volts.

In one embodiment of the present application, the thickness of the two-dimensional insulating layer 300 may be 5 nm to 30 nm, but is not limited thereto. The selection element according to the present application is required to prevent the filament generated from the first electrode 400 from penetrating the two-dimensional insulating layer 300 when a voltage is applied. Therefore, it is preferable that the thickness of the two-dimensional insulating layer 300 is thick, for example, 5 nm or more. However, when the thickness of the 2D insulating layer 300 is too thick, for example, when the thickness is greater than 30 nm, the filament made of electrode atoms may be easily broken.

The thickness of the two-dimensional insulating layer 300 is, for example, 5 nm to 30 nm, 6 nm to 30 nm, 7 nm to 30 nm, 8 nm to 30 nm, 9 nm to 30 nm, 10 nm to 30 nm, 11 nm to 30 nm, 12 nm to 30 nm, 13 nm to 30 nm, 14 nm to 30 nm, 15 nm to 30 nm, 16 nm to 30 nm, 17 nm to 30 nm, 18 nm to 30 nm, 19 nm to 30 nm, 20 nm to 30 nm, 21 nm to 30 nm, 22 nm to 30 nm, 23 nm to 30 nm, 24 nm to 30 nm, 25 nm to 30 nm, 26 nm to 30 nm, 27 nm To 30 nm, 28 nm to 30 nm, 29 nm to 30 nm, 5 nm to 29 nm, 5 nm to 28 nm, 5 nm to 27 nm, 5 nm to 26 nm, 5 nm to 25 nm, 5 nm to 24 nm, 5 nm to 23 nm, 5 nm to 22 nm, 5 nm to 21 nm, 5 nm to 20 nm, 5 nm to 19 nm, 5 nm to 18 nm, 5 nm to 17 nm, 5 nm to 16 nm, 5 nm to 15 nm, 5 nm to 14 nm, 5 nm to 13 nm, 5 nm to 12 nm, 5 nm to 11 nm, 5 nm to 10 nm, 5 nm to 9 nm, 5 nm to 8 nm, 5 nm To 7 nm, or 5 nm to 6 nm, but is not limited thereto.

According to one embodiment of the present application, the two-dimensional insulating layer 300 is, hexagonal boron nitride (hBN), a transition metal chalcogen compound, Ca(OH) ₂ , Mg(OH) ₂ , SiO ₂ , HfO ₂ , Al ₂ O ₃ and may be selected from the group consisting of combinations thereof, but is not limited thereto.

Preferably, the two-dimensional insulating layer 300 may be formed by stacking a two-dimensional hexagonal boron nitride (hBN) material, which is currently known to have the lowest defect density, but is not limited thereto.

Since the hexagonal boron nitride (hBN) has a hexagonal structure similar in chemical and physical properties to graphite, it has excellent properties such as thermal conductivity, heat resistance, corrosion resistance, chemical stability, high temperature lubricity, and non-adhesion. In addition, the hexagonal boron nitride (hBN) has electrical insulation and can be used as an insulating layer, but is not limited thereto. For example, hBN is used in electrical insulating materials, electronic materials, and materials for electronic parts.

According to one embodiment of the present application, the transition metal chalcogen compound may be selected from the group consisting of MoS ₂ , MnO ₂ , MoO ₃ , MoSe ₂ , MoTe ₂ , WS ₂ , WSe ₂ and combinations thereof, It is not limited thereto.

The graphene layer 200 is known to have the most physically and/or chemically stable surface among two-dimensional metals, so that the surface of the graphene layer 200 allows filament connection only at a high voltage, so that the filament due to surface tension Breaking can be induced very easily.

According to the exemplary embodiment of the present disclosure, the graphene layer 200 may be selected from the group consisting of graphene, graphene oxide, reduced graphene oxide, and combinations thereof, but is not limited thereto.

The graphene means that a plurality of carbon atoms are covalently linked to each other to form a polycyclic aromatic molecule, and the carbon atoms connected by the covalent bond form a 6-membered ring as a basic repeating unit, but a 5-membered ring And/or it is also possible to further include a 7-membered ring. Accordingly, the sheet formed by the graphene may be viewed as a single layer of carbon atoms covalently bonded to each other. The sheet formed by the graphene may have various structures, and such a structure may vary depending on the content of the 5-membered ring and/or the 7-membered ring that may be included in the graphene. In addition, when the sheet formed by the graphene is made of a single layer, they may be stacked on each other to form a plurality of layers, and the side ends of the graphene sheet may be saturated with hydrogen atoms.

The graphene oxide is also called graphene oxide, and may be abbreviated as "GO". It may include a structure in which a carboxyl group, a hydroxy group, an epoxy group, and a functional group containing oxygen are bonded on the single layer graphene. Graphene oxide has properties such as excellent water solubility, amphiphilicity, easy surface functionalization, and fluorescence quenching ability, so it can be used in biological applications.

The reduced graphene oxide refers to graphene oxide whose oxygen ratio is reduced through a reduction process, and may be abbreviated as "rGO". Compared to graphene oxide (GO), it has superior fluorescence quenching ability and can be used as a biosensor through fluorescence signal conversion.

According to the exemplary embodiment of the present disclosure, the graphene layer 200 may have a thickness of 10 nm or less, but is not limited thereto. For example, the thickness of the graphene layer 200 may be 10 nm or less, 9 nm or less, 8 nm or less, 7 nm or less, or 6 nm or less, but is not limited thereto.

According to the exemplary embodiment of the present disclosure, the first electrode 400 may be selected from the group consisting of gold, silver, platinum, titanium, nickel, iron, cobalt, copper, chromium, aluminum, palladium, and combinations thereof. , But is not limited thereto.

Preferably, the first electrode 400 may be formed of silver, but is not limited thereto.

Specifically, the silver electrode is a metal electrode capable of well forming a filament through diffusion. Silver atoms can easily pass through insulating layers including oxide layers to form filaments. However, like the selection device according to the present application, the filament cannot be easily formed in an insulating layer having an insulation strength of 5 MV/cm or more and a very low defect density.

Accordingly, in the selection device according to the present application, the filament formed from the first electrode 400 may not be in contact with the graphene layer 200, but is not limited thereto.

According to one embodiment of the present application, the substrate 100 is, for example, silicon, silicon carbide, germanium, silicon germanium, silicon carbide, InAs, AlAs, GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, and may be selected from the group consisting of combinations thereof, but is not limited thereto.

According to the exemplary embodiment of the present disclosure, the selection device according to the present disclosure may further include an oxide insulating layer 110 formed on the substrate 100, but is not limited thereto.

According to one embodiment of the present application, the oxide insulating layer 110 is, for example, SiO ₂ , Al ₂ O ₃ , TiO ₂ , Ta ₂ O ₅ , HfO ₂ , ZrO ₂ , BST, PZT, and combinations thereof It may include a material selected from the group consisting of, but is not limited thereto.

According to the exemplary embodiment of the present disclosure, the selection device according to the present disclosure may include the second electrode 500 formed on the graphene layer 200, but is not limited thereto.

Specifically, the second electrode 500 may be formed on the graphene layer and spaced apart from the two-dimensional insulating layer, but is not limited thereto.

According to the exemplary embodiment of the present disclosure, the second electrode 500 may be selected from the group consisting of gold, silver, platinum, titanium, nickel, iron, cobalt, copper, chromium, aluminum, palladium, and combinations thereof. , But is not limited thereto

According to the exemplary embodiment of the present disclosure, the selection device according to the present disclosure may have an on/off ratio of 10 ^{10 or} more, but is not limited thereto.

The current flashing ratio means a ratio of a current flowing below a specific voltage and a current flowing above a specific voltage.

A second aspect of the present application relates to a resistive memory element including the selection element according to the first aspect of the present application.

Specifically, by introducing the selection device according to an embodiment of the present application to a resistive memory device, a sneak current according to a high degree of integration of the resistive memory device can be drastically reduced, and through this, the next-generation memory can achieve a high degree of integration. It becomes possible to have.

Resistive memory devices have emerged as promising candidates for next-generation electronic data storage due to their simple structure and CMOS logic compatibility process. A resistive RAM (RRAM) cell that has hitherto been confined entirely between two vertically neighboring metal interconnect layers includes a conductive bottom electrode separated from a conductive top electrode by a dielectric data storage layer. During operation of the RRAM cell, the data storage layer has a variable resistance representing a unit of data, such as a bit of data or multiple bits of data. The resistance of the data storage layer can be thought of as based on the extent to which oxygen vacancy is present in the so-called "filament" in the data storage layer.

For example, to set the logic to "1", the data storage layer is set to a low-resistance state by applying a first bias across the bottom and top electrodes to strip oxygen ions from the filaments in the data storage layer. Thus, the first data state can be written to the RRAM cell. Conversely, in order to reset the logic to "0", a second different bias is applied across the bottom and top electrodes to refill oxygen ions back into the filament, thereby setting the data storage layer to a high-resistance state for a second Data states can be written to RRAM cells. In addition, through application of the third bias condition across the bottom and top electrodes, the resistance of the data storage layer may be measured to determine the stored resistance in the RRAM cell.

[Example]

First, 300 nm of silicon oxide 110 is grown on the silicon 100. The graphene 200 is transferred thereon to be connected to the electrode 500. Hexagonal boron nitride (hBN) 300 is transferred onto graphene, and a silver (Ag) electrode 400 is deposited thereon to fabricate a two-terminal device. After that, a two-terminal element is patterned through an e-beam lithography technique.

[Experimental Example 1]

3 is a graph showing a current-voltage curve of a selection device according to an embodiment of the present disclosure.

Specifically, when a high voltage is applied to the selection element according to an embodiment of the present application, a high current flows due to the formation of a filament crossing hBN. When the voltage is reduced to 0 V and the current is measured, the low current is Flowing, hysteresis is visible. This means that the Ag filament generated in hBN is unstable at low voltage and thus the selection element is implemented in a way that the connection is disconnected. 4 and 5 are graphs showing the current-voltage curve of the selection element according to an embodiment of the present application, showing that the operation of the selection element is effective at voltages of negative and positive signs, and the current-voltage characteristic is Indicates that it repeats stably.

[Experimental Example 2]

6 shows a current-voltage curve of a selection device according to an embodiment of the present disclosure, and shows a high on/off ratio and a high on current, which are essential conditions of a high-performance selection device. It can be seen that the selection device according to the exemplary embodiment of the present disclosure exhibits the best performance among the selection devices reported so far. The foregoing description of the present application is for illustrative purposes only, and those of ordinary skill in the art to which the present application pertains will be able to understand that it can be easily modified into other specific forms without changing the technical spirit or essential features of the present application. Therefore, it should be understood that the embodiments described above are illustrative in all respects and not limiting. For example, each component described as a single type may be implemented in a distributed manner, and similarly, components described as being distributed may also be implemented in a combined form.

The scope of the present application is indicated by the claims to be described later rather than the detailed description, and all changes or modified forms derived from the meaning and scope of the claims and their equivalent concepts should be construed as being included in the scope of the present application.

100: substrate
110: oxide insulating layer.
200: graphene layer.
300: two-dimensional insulating layer.
400: first electrode.
500: second electrode.

Claims (15)

A graphene layer formed on the substrate;
A two-dimensional insulating layer formed on the graphene layer; And
A first electrode formed on the two-dimensional insulating layer;
Including,
The dielectric strength of the two-dimensional insulating layer is 5 MV/cm or more,
The thickness of the two-dimensional insulating layer is 10 nm to 30 nm,
Even when a voltage is applied, the filament formed from the first electrode is cut off by the surface tension of the graphene layer, so that it does not contact on the graphene layer,
The current flashing ratio (on/off ratio) is 10 ¹⁰ or more,
Optional element.
delete The method of claim 1,
The two-dimensional insulating layer is hexagonal boron nitride (hBN), a transition metal chalcogen compound, Ca(OH) ₂ , Mg(OH) ₂ , SiO ₂ , HfO ₂ , Al ₂ O ₃ and combinations thereof One selected from the group consisting of, a selection element.
The method of claim 3,
The 2D insulating layer is formed by stacking a 2D hBN material.
The method of claim 3,
The transition metal chalcogen compound is selected from the group consisting of MoS ₂ , MnO ₂ , MoO ₃ , MoSe ₂ , MoTe ₂ , WS ₂ , WSe ₂ and combinations thereof.
The method of claim 1,
The graphene layer will have a thickness of 10 nm or less.
The method of claim 1,
The graphene layer is selected from the group consisting of graphene, graphene oxide, reduced graphene oxide, and combinations thereof.
delete The method of claim 1,
The first electrode is selected from the group consisting of gold, silver, platinum, titanium, nickel, iron, cobalt, copper, chromium, aluminum, palladium, and combinations thereof.
The method of claim 1,
The substrate is selected from the group consisting of silicon, silicon carbide, germanium, silicon germanium, silicon carbide, InAs, AlAs, GaAs, InP, GaN, InGaAs, InAlAs, GaSb, AlSb, AlP, GaP, and combinations thereof, Optional element.
The method of claim 1,
The selection device further comprises an oxide insulating layer formed on the substrate.
delete The method of claim 1,
The selection device comprising a second electrode formed on the graphene layer.
The method of claim 13,
The second electrode is selected from the group consisting of gold, silver, platinum, titanium, nickel, iron, cobalt, copper, chromium, aluminum, palladium, and combinations thereof.
A resistive memory device comprising the selection element according to any one of claims 1, 3 to 7, 9 to 11, 13, and 14.

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