SPHERICAL COMPLEMENTARY RESISTANCE SWITCHABLE FILLER AND NONVOLATILE COMPLEMENTARY RESISTANCE SWITCHABLE MEMORY COMPRISING THE SAME

Abstract

A resistance-switchable material containing: an insulating support; and a complementary resistance switchable filler dispersed in the insulating support, wherein the complementary resistance switchable filler has a spherical core-shell structure containing: a spherical conductive core containing a conductive material; and an insulating shell formed on the surface of the core and containing an insulating material. The resistance-switchable material is capable of exhibiting complementary resistive switching characteristics with improved reliability and stability as symmetrical uniform filament current paths are formed in respective resistive layers adjacent to two electrodes with the conductive core of the complementary resistance-switchable filler at the center due to the electric field control effect by the spherical complementary resistance-switchable filler

Claims

1. A resistance-switchable material comprising: an insulating support; and a complementary resistance switchable filler dispersed in the insulating support, wherein the complementary resistance switchable filler has a spherical core-shell structure comprising: a spherical conductive core comprising a conductive material; and an insulating shell formed on the surface of the core and comprising an insulating material.

2. The resistance-switchable material according to claim 1, wherein the spherical conductive core comprises one or more selected from a spherical carbon particle, a spherical gold particle, a spherical platinum particle, a spherical silver particle and a spherical copper particle.

3. The resistance-switchable material according to claim 1, wherein the spherical conductive core has a diameter of 20-100 nm.

4. The resistance-switchable material according to claim 1, wherein the insulating shell has a thickness of 10-50 nm.

5. The resistance-switchable material according to claim 1, wherein the insulating shell comprises one or more selected from NiO, SiO.sub.2, TiO.sub.2, ZnO, HfO.sub.2, Nb.sub.2O.sub.5, MgO, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, La.sub.2O, Cu.sub.2O, ZrO.sub.2, Fe.sub.2O.sub.3, SrTiO.sub.3, Cr-doped SrZrO.sub.3, Pr.sub.0.7Ca.sub.0.3MnO.sub.3, Ag.sub.2S, Ag.sub.2Se, CuS, AgI, Ag.sub.2Te, Ag.sub.2HgI.sub.4 and Ag.sub.3SI.

6. The resistance-switchable material according to claim 1, wherein the insulating support comprises one or more selected from an acrylic resin, a urethane-based resin, an epoxy-based resin, a polyester-based resin, a phenol-based resin, polyvinyl chloride, polyacetal and polyvinyl alcohol.

7. A nonvolatile complementary resistance switchable memory comprising: a substrate; a bottom electrode disposed on the substrate; a resistance-switchable material disposed on the bottom electrode; and a top electrode disposed on the resistance-switchable material, wherein the resistance-switchable material comprises: an insulating support; and a complementary resistance switchable filler dispersed in the insulating support, the complementary resistance switchable filler has a spherical core-shell structure comprising: a spherical conductive core comprising a conductive material; and an insulating shell formed on the surface of the core and comprising an insulating material, and the bottom electrode and the top electrode respectively form two different resistive layers by contacting different surfaces of the complementary resistance switchable filler.

8. The nonvolatile complementary resistance switchable memory according to claim 7, wherein symmetric electric fields are formed on the two resistive layers.

9. The nonvolatile complementary resistance switchable memory according to claim 7, wherein the symmetric electric fields are generated by filament current paths formed on both sides of the spherical conductive core.

10. The nonvolatile complementary resistance switchable memory according to claim 9, wherein the filament current paths are formed with symmetrical conical shapes.

11. The nonvolatile complementary resistance switchable memory according to claim 10, wherein the size of the filament current path is controlled by one or more selected from the diameter of the spherical conductive core and the coating thickness of the insulating shell.

12. The nonvolatile complementary resistance switchable memory according to claim 10, wherein the size of the filament current path is controlled by a compliance current set when the filament current path is formed first.

13. A method for preparing a complementary resistance switchable filler, comprising: (1) preparing a core dispersion by dispersing a spherical conductive core in a solvent; and (2) coating an insulating layer on the surface of the spherical conductive core by adding a precursor of an insulating polymer to the core dispersion.

14. A method for preparing a nonvolatile complementary resistance switchable memory, comprising: (a) preparing a paste comprising the resistance-switchable material according to claim 1; (b) forming a bottom electrode on a substrate; (c) forming a resistance-switchable material layer by coating the paste on the bottom electrode and then curing the same; and (d) forming a top electrode on the resistance-switchable material layer.

15. The method for preparing a nonvolatile complementary resistance switchable memory according to claim 14, wherein (a) comprises: (a-1) preparing a complementary resistance switchable filler of a core-shell structure by coating an insulating material on the surface of a spherical conductive nanoparticle; and (a-2) preparing the paste by mixing the complementary resistance switchable filler with an insulating supporting material.

16. The method for preparing a nonvolatile complementary resistance switchable memory according to claim 15, wherein, in (a-1), the insulating material is coated by dispersing the spherical conductive nanoparticle in a solvent and then adding a precursor of the insulating material.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0041] FIG. 1 shows the voltage distribution of a nonvolatile complementary resistance switchable memory according to the present disclosure prepared in Example 1.

[0042] FIG. 2 shows the electric field distribution of a nonvolatile complementary resistance switchable memory according to the present disclosure prepared in Example 1.

[0043] FIG. 3 shows a filament current path formed in a nonvolatile complementary resistance switchable memory according to the present disclosure prepared in Example 1.

[0044] FIG. 4 is an image showing the shape and flexibility of complementary resistance switchable memory prepared in Example 1.

[0045] FIG. 5 shows images of a complementary resistance switchable memory layer prepared in Example 1.

[0046] FIG. 6 shows electric fields formed in two resistive layers of a memory prepared in Comparative Example 1.

DETAILED DESCRIPTION OF EMBODIMENTS

[0047] Hereinafter, various aspects and exemplary embodiments of the present disclosure are described in more detail.

[0048] Hereinafter, the exemplary embodiments of the present disclosure are described in more detail referring to the attached drawings so that those of ordinary skill in the art to which the present disclosure belongs can easily carry out the present disclosure.

[0049] However, the following description is not intended to limit the present disclosure to specific exemplary embodiments and description of well-known techniques is omitted to avoid unnecessarily obscuring the present disclosure.

[0050] The terms used in the present disclosure are intended to describe specific exemplary embodiments, not to limit the present disclosure. Singular expressions include plural expressions unless they have definitely opposite meanings in the context. In the present disclosure, the terms contain, include, have, etc. indicate that a feature, a number, a step, an operation, an element or a combination thereof described in the specification is present, but does not preclude the possibility of presence or addition of one or more other features, numbers, steps, operations, elements or combinations thereof.

[0051] Hereinafter, a resistance-switchable material of the present disclosure is described in detail.

[0052] The resistance-switchable material of the present disclosure may contain: an insulating support; and a complementary resistance switchable filler dispersed in the insulating support.

[0053] The complementary resistance switchable filler may have a spherical core-shell structure containing: a spherical conductive core containing a conductive material; and an insulating shell formed on the surface of the core and containing an insulating material.

[0054] The spherical conductive core may contain a spherical carbon particle, a spherical gold particle, a spherical platinum particle, a spherical silver particle, a spherical copper particle, etc.

[0055] The spherical conductive core may have a diameter of specifically 20-100 nm, more specifically 20-40 nm.

[0056] The insulating shell may contain NiO, SiO.sub.2, TiO.sub.2, ZnO, HfO.sub.2, Nb.sub.2O.sub.5, MgO, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, La.sub.2O, Cu.sub.2O, ZrO.sub.2, Fe.sub.2O.sub.3, SrTiO.sub.3, Cr-doped SrZrO.sub.3, Pr.sub.0.7Ca.sub.0.3MnO.sub.3, Ag.sub.2S, Ag.sub.2Se, CuS, AgI, Ag.sub.2Te, Ag.sub.2HgI.sub.4, Ag.sub.3SI, etc.

[0057] The insulating shell coated on the spherical conductive core may have a thickness of specifically 10-50 nm, more specifically 10-20 nm.

[0058] The insulating support may contain an acrylic resin, a urethane-based resin, an epoxy-based resin, a polyester-based resin, a phenol-based resin, polyvinyl chloride, polyacetal, polyvinyl alcohol, etc.

[0059] Hereinafter, a nonvolatile complementary resistance switchable memory of the present disclosure is described in detail.

[0060] The nonvolatile complementary resistance switchable memory of the present disclosure may have a structure in which a substrate, a bottom electrode, a resistance-switchable material and a top electrode are stacked sequentially.

[0061] The resistance-switchable material may contain: an insulating support; and a complementary resistance switchable filler dispersed in the insulating support, and the complementary resistance switchable filler may have a spherical core-shell structure containing: a spherical conductive core containing a conductive material; and an insulating shell formed on the surface of the core and containing an insulating material.

[0062] The substrate may be glass, a silicon wafer, a metal foil, etc.

[0063] The conductive material contained in the spherical conductive core may be a spherical carbon particle, a spherical gold particle, a spherical platinum particle, a spherical silver particle, a spherical copper particle, etc.

[0064] The insulating material contained in the insulating shell may include NiO, SiO.sub.2, TiO.sub.2, ZnO, HfO.sub.2, Nb.sub.2O.sub.5, MgO, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, La.sub.2O, Cu.sub.2O, ZrO.sub.2, Fe.sub.2O.sub.3, SrTiO.sub.3, Cr-doped SrZrO.sub.3, Pr.sub.0.7Ca.sub.0.3MnO.sub.3, Ag.sub.2S, Ag.sub.2Se, CuS, AgI, Ag.sub.2Te, Ag.sub.2HgI.sub.4, Ag.sub.3SI, etc.

[0065] The top electrode is disposed on the resistance-switchable material.

[0066] The bottom electrode and the top electrode may respectively form two different resistive layers by contacting different surfaces of the complementary resistance switchable filler.

[0067] Symmetric electric fields may be formed on the two resistive layers. The symmetric electric fields may be generated by filament current paths formed on both sides of the spherical conductive core. The filament current paths may be formed with symmetrical conical shapes.

[0068] The spherical conductive core contained in the complementary resistance switchable filler may have a diameter of specifically 20-100 nm, more specifically 20-40 nm, and the insulating shell coated on the spherical conductive core may have a thickness of specifically 10-50 nm, more specifically 10-20 nm. However, the scope of the present disclosure is not limited thereto.

[0069] The size of the filament current path may be controlled by controlling the diameter of the spherical conductive core or the coating thickness of the insulating shell.

[0070] The size of the filament current path may also be controlled by a compliance current set when the filament current path is formed first.

[0071] The bottom electrode or the top electrode may be made of a metal, a conductive carbon material or a conductive polymer material.

[0072] The metal may be Ag, Au, Cu, Ni, Cr, Pt, Pb, Ru, Pd, TiN, W, Co, Mn, Ti, Fe, etc.

[0073] The conductive carbon material may be graphene, a carbon nanotube, a fullerene, etc.

[0074] The conductive polymer material may be polypyrrole, polythiophene, poly(p-phenylene vinylene), polyaniline, polyacetylene, PEDOT:PSS (poly(3,4-ethylenedioxythiophene) polystyrene sulfonate), etc.

[0075] Hereinafter, a method for preparing a complementary resistance switchable filler of the present disclosure is described.

[0076] First, a core dispersion is prepared by dispersing a spherical conductive core in a solvent (step 1).

[0077] Reference can be made to the foregoing description for details about the spherical conductive core.

[0078] Specifically, the solvent may be an alcohol solvent.

[0079] Next, an insulating layer is coated on the surface of the spherical conductive core by adding a precursor of an insulating polymer to the core dispersion (step 2).

[0080] The precursor of the insulating material may be tetraethoxysilane (TEOS), tetramethyl orthosilicate (TMOS), titanium tetrachloride (TiCl.sub.4), titanium(IV) propoxide (Ti(OH).sub.4), aluminum sulfate (Al.sub.2(SO.sub.4).sub.3), zinc nitrate (Zn(NO.sub.3).sub.2), zirconium nitrate (Zr(NO.sub.3).sub.4), silver nitrate (AgNO.sub.3), etc.

[0081] As a result of the reaction, an insulating material such as NiO, SiO.sub.2, TiO.sub.2, ZnO, HfO.sub.2, Nb.sub.2O.sub.5, MgO, Al.sub.2O.sub.3, Ta.sub.2O.sub.5, La.sub.2O, Cu.sub.2O, ZrO.sub.2, Fe.sub.2O.sub.3, SrTiO.sub.3, Cr-doped SrZrO.sub.3, Pr.sub.0.7Ca.sub.0.3MnO.sub.3, Ag.sub.2S, Ag.sub.2Se, CuS, AgI, Ag.sub.2Te, Ag.sub.2HgI.sub.4, Ag.sub.3SI, etc. may be coated on the surface of the spherical conductive material.

[0082] Hereinafter, a method for preparing a complementary resistance switchable memory of the present disclosure is described.

[0083] First, a paste containing the resistance-switchable material of the present disclosure is prepared (step a).

[0084] A complementary resistance switchable filler of a core-shell structure is prepared by coating an insulating material on the surface of a spherical conductive nanoparticle (step a-1).

[0085] The insulating material may be coated by dispersing the spherical conductive nanoparticle in a solvent and then adding the precursor of the insulating material.

[0086] The spherical conductive nanoparticle may be a spherical carbon particle, a spherical gold particle, a spherical platinum particle, a spherical silver particle, a spherical copper particle, etc.

[0087] Reference can be made to the foregoing description about the method for preparing a complementary resistance switchable filler for details about the precursor of the insulating material.

[0088] As a result of the reaction, the insulating material may be coated on the surface of the spherical conductive material, and reference can be made to the foregoing description about the method for preparing a complementary resistance switchable filler for details about the insulating material.

[0089] Next, a paste is prepared by mixing the complementary resistance switchable filler with an insulating supporting material (step a-2).

[0090] The insulating supporting material may be an acrylic resin, a urethane-based resin, an epoxy-based resin, a polyester-based resin, a phenol-based resin, polyvinyl chloride, polyacetal, polyvinyl alcohol, etc.

[0091] Then, a bottom electrode is formed on a substrate (step b).

[0092] The bottom electrode may be formed by sputtering, chemical vapor deposition, atomic layer deposition, pulsed laser deposition, molecular beam epitaxy, vacuum thermal deposition, vacuum electron beam deposition, etc.

[0093] The bottom electrode may be made of a metal, a conductive carbon material, a conductive polymer material, etc. and reference can be made to the foregoing description for details.

[0094] Next, a resistance-switchable material layer is formed by coating the paste on the bottom electrode and then curing the same (step c).

[0095] The paste may be coated by spin coating, blade casting, inkjet printing, etc., although the scope of the present disclosure is not limited thereto.

[0096] The curing may be performed by thermal curing or photocuring. Specifically, it may be performed by thermal curing.

[0097] Finally, a top electrode is formed on the resistance-switchable material layer (step d).

[0098] The top electrode may be formed by sputtering, chemical vapor deposition, atomic layer deposition, pulsed laser deposition, molecular beam epitaxy, vacuum thermal deposition, vacuum electron beam deposition, etc.

[0099] The top electrode may be made of a metal, a conductive carbon material, a conductive polymer material, etc. and reference can be made to the foregoing description for details.

[0100] Hereinafter, the present disclosure is described in more detail through examples.

EXAMPLES

Example 1

[0101] (1) Preparation of Silver Nanopowder

[0102] A silver nanopowder (AgNP) with a diameter of 45 nm was prepared. First, 30 g of an aqueous solution was prepared by dissolving 0.151 g of polyvinylpyrrolidone (M.sub.w: 55000, Sigma Aldrich), 0.048 g of trisodium citrate (Sigma Aldrich) and glucose (Daejung Chemicals & Metals) in 29.719 g of water. After heating to 100 C., a solution prepared by mixing 0.027 g of silver nitrate (Sigma Aldrich) and 0.5 g of ammonium hydroxide (1 mol/L, Junsei) in 5 g of water was added at a constant speed for 10 minutes, a total of 3 times over 30 minutes. A silver nanopowder was prepared by terminating the reaction when the color of the solution turned jade green.

[0103] (2) Preparation of Paste

[0104] A complementary resistance-switchable filler was prepared by coating SiO.sub.2 on the surface of the Ag nanopowder (diameter: 45 nm). First, after dispersing the prepared AgNP in 40 mL of an ethanol solvent, a SiO.sub.2 insulating shell was formed on the surface of the AgNP by adding 0.2 g of TEOS (tetraethyl orthosilicate, Sigma Aldrich) and 2 mL of ammonium hydroxide (28%, Junsei) and performing reaction at 40 C. for 2 hours. The coating thickness of SiO.sub.2 was set to 17 nm by controlling the reaction temperature and the amount of TEOS. Then, a paste was prepared by mixing 10 mg of the prepared complementary resistance-switchable filler (SiO.sub.2@AgNP) with 1 g of PVA (M.sub.w: 85000-124000, Sigma Aldrich) and 9 g of water.

[0105] (3) Preparation of Nonvolatile Complementary Resistance Switchable Memory

[0106] A resistance-switchable material layer was formed by spin-coating the paste on a Pt/TiO.sub.2/SiO.sub.2/Si bottom substrate having a bottom electrode formed and then curing the same at 70 C. for 24 hours. A patterned Ag top electrode was formed on the resistance-switchable material layer by thermal deposition using a mask.

Comparative Example 1

[0107] A nonvolatile complementary resistance switchable memory was prepared in the same manner as in Example 1 except that a silver nanowire (average particle diameter: 100 nm) was used instead of the silver nanopowder.

Test Examples

Test Example 1: Analysis of Electric Field Distribution of Memory

[0108] The voltage distribution, electric field distribution and filament current path formation of the nonvolatile complementary resistance switchable memory according to the present disclosure prepared in Example 1 are shown in FIGS. 1-3, respectively.

[0109] From FIGS. 1-3, it can be seen that resistance switching layers were formed on two parts of the insulating shell of the complementary resistance switchable filler contacting the top electrode or the bottom electrode, symmetric electric fields were formed and a strong electric field was formed around the conductive core.

[0110] The nonvolatile complementary resistance switchable memory of Example 1 has a structure in which the two resistance switching layers are surrounded by the insulating support. Because the electric field is oriented toward the conductive core, only two filaments are formed per memory. Therefore, stable operation is possible despite repeated resistance switching. In addition, the reliability of the memory can be ensured because the operation voltage and current ranges are constant during the cell-to-cell operation.

Test Example 2: Physical Properties of Complementary Resistance Switchable Memory

[0111] FIG. 4 is an image showing the shape and flexibility of the complementary resistance switchable memory prepared in Example 1 and FIG. 5 shows images showing the transparency of the complementary resistance switchable memory layer prepared in Example 1.

[0112] From FIG. 4 and FIG. 5, it can be seen that the memory device of Example 1 is bendable and transparent.

Test Example 3

[0113] FIG. 6 shows electric fields formed from unsymmetrical contact with the electrode for the nanowire-based complementary resistance switchable memory prepared in Comparative Example 1. From FIG. 6, it can be seen that unsymmetrical electric fields may be formed in two resistive layers of the memory of Comparative Example 1, unlike the memory of Example 1.

[0114] While the present disclosure has been described with respect to the specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the disclosure as defined in the following claims.