KR102184039B1 - Memristor and non-valatile memory device having the memristor - Google Patents

Abstract

A memristor element is disclosed. The memristor element includes: a first electrode and a second electrode disposed to face each other; And a resistance varying layer disposed between the first electrode and the second electrode and formed of an organic-inorganic halogen compound represented by Chemical Formula 1 and having a hexagonal crystal structure. These memristor devices can implement performance such as low driving voltage, fast speed, and high on/off ratio.

Description

A memristor device and a nonvolatile memory device including the same

The present invention relates to a memristor device capable of nonvolatilely storing information through a resistance change, and a nonvolatile memory device including the same.

A memristor is a nano-unit passive element that connects a magnetic flux and an electric charge, and has a characteristic that the resistance changes according to the electric charge amount by storing an electric charge amount. Even when the power supply is cut off, the current amount and direction are memorized, and the existing state can be restored when power is supplied. This memristor is one of the basic components of an electric circuit along with a resistor, a capacitor and an inductor.

Oxide, nitride, and organic materials have been studied as memristor materials that have been mainly used, but recently, organic/inorganic perovskite materials with a high driving voltage and relatively low on/off ratio of 10 ⁵ or more have been used. Memristor research is ongoing.

However, existing organic/inorganic materials have problems that need to be improved, such as a relatively unstable switching operation and a requirement for a forming process, and a new technology capable of solving these problems is required.

One object of the present invention is a memristor having a low driving voltage, a high on/off ratio, long retention, multilevel storage capacity, etc. by having a resistance change layer formed of an organic/inorganic halogen compound having a hexagonal crystal structure. It is to provide the device.

Another object of the present invention is to provide a nonvolatile memory device including the memristor element.

A memristor device according to an embodiment of the present invention includes: a first electrode and a second electrode disposed to face each other; And a resistance changing layer disposed between the first electrode and the second electrode, represented by Formula 1 below, and formed of an organic-inorganic halogen compound having a hexagonal crystal structure.

[Formula 1]

In Formula 1, R represents an organic cation, M represents a metal cation, X represents a halogen anion, and x, y and z independently represent real numbers of -0.5 or more and +0.5 or less.

In one embodiment, the organic cation (R) may include at least one selected from the group consisting of CH(NH ₂ ) ₂ ⁺ , CH ₃ NH ₃ ⁺ , and N ₂ H ₅ ⁺ .

In one embodiment, the metal cation (M) is a copper ion (Cu ²⁺ ), a nickel ion (Ni ²⁺ ), a cobalt ion (Co ²⁺ ), an iron ion (Fe ²⁺ ), a manganese ion (Mn ^{2 +} ), chromium ion (Cr ²⁺ ), palladium ion (Pd ²⁺ ), cadmium ion (Cd ²⁺ ), ytterbium ion (Yb ²⁺ ), lead ion (Pb ²⁺ ), tin ion (Sn ²⁺ ) , Germanium ion (Ge ²⁺ ), bismuth ion (Bi ³⁺ ), and antimony ion (Sb ³⁺ ) may include one or more selected from the group consisting of.

In one embodiment, the halogen anion (X) is a fluoride ion (F ^-) include at least one selected from the group consisting of chlorine ion (Cl ^-), bromide ion (Br ^{- -)} and an iodine ion (I) I can.

In one embodiment, in the hexagonal crystal structure of the organic-inorganic halogen compound, 6 X ions surround one M ion to form an octahedral unit, and the octahedral units are arranged adjacently along the c-axis of the crystal. Two octahedral units can be arranged to share one side to form a linear structure.

In one embodiment, the ab-plane of the hexagonal crystal structure may be disposed parallel to one surface of the first electrode or the second electrode.

In one embodiment, the organic-inorganic halogen compound contains halogen vacancy, and the energy level of the halogen vacancy is higher than the valence band energy level of the organic-inorganic halogen compound and lower than the conduction band energy level. I can.

A nonvolatile memory device according to an embodiment of the present invention includes: a first signal line and a second signal line extending in a direction crossing each other; And a memory cell and a selection element disposed therebetween in a region where the first signal line and the second signal line overlap, and connected in series to each other, wherein the memory cell comprises the first signal line and the second signal A first electrode electrically connected to one of the lines, a second electrode electrically connected to the selection element, and a resistance change layer disposed between the first electrode and the second electrode, wherein the resistance change layer is represented by Formula 1 below. It is represented by and is formed of an organic-inorganic halogen compound having a hexagonal crystal structure.

[Formula 1]

In Formula 1, R represents an organic cation, M represents a metal cation, X represents a halogen anion, and x, y and z independently represent real numbers of -0.5 or more and +0.5 or less.

In an embodiment, the memory cell may have a bipolar switching characteristic.

In one embodiment, the memory cell may have multilevel storage capability.

According to the memristor device and the nonvolatile memory device of the present invention, since the resistance change layer of the memory cell is formed of the organic-inorganic halogen compound of Formula 1 having a hexagonal crystal structure, a high on/off ratio of 10 ⁵ or more, and a long-term retention capacity It has (retention), multilevel storage capability, etc., and can operate even at high temperatures.

1 is a cross-sectional view illustrating a memristor device according to an embodiment of the present invention.
2A to 2C are diagrams for explaining a crystal structure of the material of the resistance change layer shown in FIG. 1.
3 is a perspective view illustrating a nonvolatile memory device according to an embodiment of the present invention.
4A is a plan view and cross-sectional SEM images of FAPbI ₃ thin films after annealing formed in the memristor elements of Examples 1 (a, f), 2 (b, g) and 3 (c, h). 4B are planar SEM images and cross-sectional SEM images of the FAPbI ₃ thin film after annealing formed in the memristor devices of Comparative Examples 1 (d, i) and 2 (e, j).
5 shows XRD patterns (a) measured for the FAPbI ₃ thin films of Examples 1 to 3 and Comparative Examples 1 and 2, and XRD peaks (b, C) calculated for α-FAPbI ₃ and δ-FAPbI ₃ Show.
6A is a graph showing a current-voltage (IV) relationship measured in response to a first sweep of the memristor elements of Examples 1 to 3, and FIG. 6B is a first diagram for the memristor elements of Comparative Examples 1 and 2. These are graphs showing the current-voltage (IV) relationship measured in response to the sweep.
7 is a diagram showing two different migration paths of iodine vacancies (V _I ^* ) in δ-FAPbI ₃ and a relative energy profile according to the two migration paths.
FIG. 8A is a diagram showing the electromagnetic density of states (a) of α-FAPbI ₃ and the density of states of α-FAPbI3 with one iodine pore (b), and FIG. 8B is the electromagnetic density of states of δ-FAPbI ₃ (c ) And the density of state (d) of δ-FAPbI ₃ having one iodine vacancy.
9 is a voltage-current graph showing the result of performing 20 resistance switching sweeps on the memristor device of Example 3. FIG.
10A and 10B are graphs showing resistance switching results using voltage pulses for the memristor device of Example 3. FIG.
11 is a voltage-current graph showing the multilevel storage capability measured at four different compliance currents for the memristor device of Example 3. FIG.
12 is an IV curve (a) measured at 80° C. for the memristor device of Example 3 and an IV curve (b) measured after cooling to room temperature after aging at 100° C. for 1 minute.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the present invention, various modifications may be made and various forms may be applied, and specific embodiments will be illustrated in the drawings and described in detail in the text. However, this is not intended to limit the present invention to a specific form of disclosure, it is to be understood as including all changes, equivalents, or substitutes included in the spirit and scope of the present invention.

The terms used in the present application are only used to describe specific embodiments and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly indicates otherwise. In the present application, terms such as "comprise" or "have" are intended to designate the existence of features, steps, actions, components, parts, or a combination thereof described in the specification, but one or more other features or steps It is to be understood that it does not preclude the possibility of addition or presence of, operations, components, parts, or combinations thereof.

Unless otherwise defined, all terms, including technical and scientific terms, used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs. Terms as defined in a commonly used dictionary should be interpreted as having a meaning consistent with the meaning in the context of the related technology, and should not be interpreted as an ideal or excessively formal meaning unless explicitly defined in this application. Does not.

1 is a cross-sectional view illustrating a memristor device according to an exemplary embodiment of the present invention, and FIGS. 2A to 2C are diagrams illustrating a crystal structure of a material of a resistance change layer shown in FIG. 1.

1 and 2A to 2C, the memristor device 100 according to an embodiment of the present invention includes a first electrode 110, a second electrode 120, and a resistance change layer 130.

The first electrode 110 and the second electrode 120 are disposed to face each other while being spaced apart from each other, and may be formed of an electrically conductive material. For example, each of the first electrode 110 and the second electrode 120 may be formed of a conductive oxide, a conductive metal, a conductive nitride, a conductive polymer, a conductive carbon-based material, or the like. The conductive oxide may include at least one selected from indium tin oxide (ITO), fluorine tin oxide (FTO), ZnO-Ga ₂ O ₃ , ZnO-Al ₂ O ₃ , tin oxide, zinc oxide, and the like. The conductive metal is aluminum (Al), molybdenum (Mo), tungsten (W), titanium (Ti), platinum (Pt), chromium (Cr), silicon (Si), gold (Au), nickel (Ni), and copper. It may contain one or more selected from (Cu), silver (Ag), indium (In), ruthenium (Ru), palladium (Pd), rhodium (Rh), iridium (Ir), osmium (Os), and the like.

In one embodiment, one of the first electrode 110 and the second electrode 120 is an active electrode formed of a metal material having low ionization energy such as copper (Cu), silver (Ag), and aluminum (Al) And the other one may be an inert electrode formed of a conductive material having higher ionization energy than a material forming the active electrode. For example, the inactive electrode may be formed of one or more metals selected from platinum (Pt), gold (Au), palladium (Pd), and the like.

The resistance change layer 130 is disposed between the first electrode 110 and the second electrode 120 and is high according to the voltage applied to the first electrode 110 and the second electrode 120. The resistance may reversibly change from a high resistance state to a low resistance state and from a low resistance state to a high resistance state.

In one embodiment, the resistance change layer 130 may be formed of an organic-inorganic halogen compound represented by Formula 1 below.

[Formula 1]

In Formula 1, R represents an organic cation, M represents a metal cation, and X represents a halogen anion. And x, y, and z represent real numbers of -0.5 or more and +0.5 or less independently of each other.

In one embodiment, the organic cation (R) may include at least one selected from CH(NH ₂ ) ₂ ⁺ , CH ₃ NH ₃ ⁺ , N ₂ H ₅ ⁺ , and the like. The metal cations (M) are copper ions (Cu ²⁺ ), nickel ions (Ni ²⁺ ), cobalt ions (Co ²⁺ ), iron ions (Fe ²⁺ ), manganese ions (Mn ²⁺ ), chromium ions ( Cr ²⁺ ), palladium ion (Pd ²⁺ ), cadmium ion (Cd ²⁺ ), ytterbium ion (Yb ²⁺ ), lead ion (Pb ²⁺ ), tin ion (Sn ²⁺ ), germanium ion (Ge ^{2 +} ), bismuth ions (Bi ³⁺ ), antimony ions (Sb ³⁺ ), and the like. The halogen anion (X) is a fluoride ion (F ^-) can include one or more selected from, such as chloride ion (Cl ^-), bromide ion (Br ^{- -),} iodide (I).

In an embodiment, as shown in FIGS. 2A and 2B, the organic-inorganic halogen compound of Formula 1 may have a hexagonal crystal structure. For example, in the organic-inorganic halogen compound of the resistance change layer 130 having the hexagonal crystal structure, 6 X ions surround one M ion to form an octahedral unit, and the octahedral units are c -Two octahedral units arranged adjacent to each other along the axis are arranged to share one side to form a linear structure, and the linear structures are arranged in a triangular shape, and the corresponding three units included in each of three different linear structures One R ion may be placed between octahedral units.

When the resistance change layer 130 is formed of an organic-inorganic halogen compound of Formula 1 having a hexagonal crystal structure, a resistance switching operation by formation and destruction of a conductive filament inside the resistance change layer 130, for example, Switching from a high resistance state to a low resistance state through the formation of a conductive filament ("and switching from a low resistance state to a high resistance state due to destruction of the conductive filament" may occur. The formation and destruction of the conductive filaments in the resistance change layer 130 formed of an organic/inorganic halide material is greatly influenced by migration of point defects such as halogen vacancy in the lattice.

On the other hand, when the resistance change layer 130 is formed of an organic-inorganic halogen compound of Formula 1 having a hexagonal crystal structure, two paths through which halogen vacancy can migrate in the crystal, for example, ab-plane There is a path along the [010] direction parallel to and a path along the [123] direction slightly inclined with the c-axis, but the migration barrier energy of the path along the [123] direction is the migration of the path along the [010] direction. Since it is smaller than the barrier energy, most of the halogen vacancy is migrated to a path along the [123] direction, and thus switching characteristics of the resistance change layer 130 may be improved. Therefore, in the resistance change layer 130, the ab-plane of the hexagonal crystal structure is disposed parallel to one of the upper surface of the first electrode 110 or the lower surface of the second electrode 120. In this case, more excellent switching characteristics can be expressed.

In addition, in the case of the organic-inorganic halogen compound of Formula 1 having the hexagonal crystal structure, the energy level of the halogen vacancy may be located within the band gap of the organic-inorganic halogen compound. That is, the energy level of the halogen vacancy may be higher than the valence band energy level of the organic-inorganic halogen compound and lower than the conduction band energy level. In this case, since the interaction between the halogen vacancies is limited within a short distance, the halogen vacancies can be easily separated from the cluster through migration, and thus switching from a low resistance state to a high resistance state (``characteristic can be improved. .

3 is a perspective view illustrating a nonvolatile memory device according to an embodiment of the present invention.

Referring to FIG. 3, a nonvolatile memory device 1000 according to an embodiment of the present invention includes a memory cell 1100, a selection element 1200, a first signal line 1300 and a second signal line 1400. do.

The memory cell 1100 may be disposed between the first signal line 1300 and the second signal line 1400, and one of the first signal line 1300 and the second signal line 1400 And can be electrically connected.

The memory cell 1100 may include a first electrode 1110, a second electrode 1120, and a resistance change layer 1130. Since the memory cell 1100 is the same as the memristor device 100 described with reference to FIG. 1, a redundant detailed description thereof will be omitted.

Meanwhile, in FIG. 3, it is shown that the second electrode 1120 is electrically connected to the fourth signal line 1400 and the first electrode 1110 is electrically connected to the selection element 1200. The first electrode 1110 may be electrically connected to the first signal line 1300 and the second electrode 1120 may be electrically connected to the selection element 1200.

The selection element 1200 is connected in series with one of the first signal line 1300 and the second signal line 1400 and the memory cell 1100, and leakage from another neighboring memory cell disposed adjacent thereto. By suppressing a sneak current, it is prevented from affecting a sensing current of the memory cell 1100. The selection element 1200 exhibits a nonlinear current-voltage characteristic having a small resistance value at a sensing voltage such as read or write applied to a selected memory cell, and a very large resistance value at a low voltage applied to a non-selected memory cell. The device is not particularly limited, and a known selection device may be applied without limitation.

The first signal line 1300 and the second signal line 1400 may extend in a direction crossing each other. For example, the first signal line 1300 may extend in a first direction (X), and the second signal line 1400 may extend in a second direction (Y) orthogonal to the first direction. I can.

Meanwhile, in FIG. 3, the first signal line 1300 and the second signal line 1400 are shown to be electrically connected to one memory cell 1100, but the first signal line 1300 is The second signal line 1400 may be electrically connected to a plurality of memory cells arranged in a row along the second direction Y, and the second signal line 1400 may be connected to a plurality of other memory cells arranged in a row along the first direction X. Can be electrically connected.

According to the memristor device and the nonvolatile memory device of the present invention, since the resistance change layer of the memory cell is formed of an organic-inorganic halogen compound of Formula 1 having a hexagonal crystal structure, a high on/off ratio of 10 ⁵ or more, and a long time retention It has retention time, multilevel storage capability, etc., and can operate at high temperatures.

Hereinafter, some examples and comparative examples will be described in detail to aid understanding of the present invention. However, the following examples are only some embodiments of the present invention, and the scope of the present invention is not limited to the following examples.

<Examples 1 to 3>

After forming a 100 nm-thick platinum (Pt) thin film on a silicon wafer, a FAPbI ₃ (HC(NH ₂ ) ₂ PbI ₃ ) thin film was formed thereon, and a 150 nm thick film was formed on the FAPbI ₃ thin film by vacuum deposition. A silver (Ag) thin film was formed. The FAPbI ₃ thin film was prepared by dissolving 1 mmol of FAI powder (172.0 mg), 1 mmol of PbI ₂ (461.0 mg), and 1 mmol of DMSO (dimethylsulfoxide) (78.1 mg) in 1.48 mL of DMF (dimethylformamide) to obtain 30 wt% of 30 wt% After preparing the FAPbI ₃ precursor solution, it was formed by spin coating on the platinum thin film at a speed of 4000 rpm for 30 seconds, and 0.2 mL of diethyl ether was added dropwise during the spin coating.

Then, the FAPbI ₃ thin film was crystallized by annealing at 75° C. (Example 1), 100° C. (Example 2), and 125° C. (Example 3) for 10 minutes, thereby manufacturing the memristor devices of Examples 1 to 3 I did.

<Comparative Examples 1 and 2>

Platinum on a silicon wafer in the same manner as in Example (Pt) thin film, FAPbI ₃ thin film and the silver (Ag) thin films after the FAPbI ₃ thin film for 10 minutes 150 ℃ (Comparative Example 1) and 175 ℃ (comparative example for forming the By annealing in 2) to crystallize, the memristor devices of Comparative Examples 1 and 2 were manufactured.

[Experimental Example]

4A is a plan view and cross-sectional SEM images of FAPbI ₃ thin films after annealing formed in the memristor elements of Examples 1 (a, f), 2 (b, g) and 3 (c, h). 4B are planar SEM images and cross-sectional SEM images of the FAPbI ₃ thin film after annealing formed in the memristor devices of Comparative Examples 1 (d, i) and 2 (e, j).

4A and 4B, the color of the FAPbI ₃ thin film was brown in Examples 1 to 3, but black in Comparative Examples 1 and 2, and was found to be different from each other. This indicates that a structural change occurs for the FAPbI ₃ thin film based on the sintering temperature of about 150°C. That is, it is determined that δ-FAPbI ₃ having a hexagonal crystal structure is formed at a low temperature of about 75°C to 125°C, and α-FAPbI ₃ having a trigonal crystal structure is formed at a high temperature of 150°C or higher. Meanwhile, as a result of measuring the average grain size from the plane and cross-sectional SEM images of FIGS. 4A and 4B, about 110 nm (75° C.), 170 nm (100° C.), 190 nm (125° C.), 380 nm (150° C.), and 500 nm ( 175℃), and in the temperature range below 150℃, the grain size increased relatively slowly as the annealing temperature increased, but in the temperature range above 150℃, the grain size increased relatively rapidly as the annealing temperature increased. Started to change from 150°C. This is believed to be due to the change in the crystal structure of the FAPbI ₃ thin film based on the annealing temperature of about 150°C.

Meanwhile, the thickness of the FAPbI ₃ thin film was measured to be 170 nm (75° C.), 190 nm (100° C.), 190 nm (125° C.), 170 nm (150° C.), and 170 nm (175° C.), and Comparative Example 1 annealed at 150° C. Except for the memristor element of, the surface of the FAPbI ₃ thin film after annealing was found to be smooth. In the case of the FAPbI ₃ thin film annealed at 150°C, it is believed that this is due to the accompanying phase change and shape change.

5 shows XRD patterns (a) measured for the FAPbI ₃ thin films of Examples 1 to 3 and Comparative Examples 1 and 2, and XRD peaks (b, C) calculated for α-FAPbI ₃ and δ-FAPbI ₃ Show.

Referring to FIG. 5, it can be seen that the FAPbI3 thin films of Examples 1 to 3 annealed at a low temperature of less than 150°C are δ-FAPbI ₃ having a hexagonal crystal structure, and Comparative Examples 1 and 2 annealed at a high temperature of 150°C or higher. It can be seen that the FAPbI ₃ thin film of is α-FAPbI ₃ having a trigonal crystal structure.

On the other hand, the PbI ₂ peak appeared at 100° C., and it was found to become stronger as the annealing temperature increased. This indicates that the unreacted PbI2 increases as the annealing temperature increases.

6A is a graph showing a current-voltage (IV) relationship measured in response to a first sweep of the memristor elements of Examples 1 to 3, and FIG. 6B is a first diagram for the memristor elements of Comparative Examples 1 and 2. These are graphs showing the current-voltage (IV) relationship measured in response to the sweep. The compliance currents for the positive and negative voltage sweeps were 1 mA and 10 mA, respectively.

6A and 6B, for all devices, resistance switching from a high resistance state to a low resistance state called SET process in a positive voltage sweep (0V->0.25V->0V) is related to the annealing temperature. It occurred around 0.22V without. However, in a negative voltage sweep (0V->-0.7V->0V), the resistance switching from the low resistance state to the high resistance state, called the RESET process, appeared differently depending on the annealing temperature. Specifically, in the case of the memristor devices of Examples 1 to 3, it was found that the width of the RESET voltage decreases when the annealing temperature increases from 75°C to 125°C, as shown in FIG. 5A. That is, in the memristor device of Example 1, the RESET voltage was in a wide range of -0.1V to -0.6V, but in the memristor device of Example 3, the RESET voltage was about -0.15V.

On the other hand, as shown in FIG. 6B, RESET occurred randomly in the memristor device of Comparative Example 1, and the RESET process did not appear in the memristor device of Comparative Example 2.

From this, FAPbI _third conductive filament formed into a thin film has a relatively low temperature, in particular the other hand, which can be more easily disconnected 125 ℃ the δ-FAPbI ₃ annealed at the, the α-FAPbI annealed at above 150 ℃ relative high temperature _3, almost It can be seen that it does not break.

On the other hand, in FAPbI ₃ based memristor devices, the electric field required for formation of the conductive filament by migration of the active metal Ag is required to be 1.0X10 ⁷ V/m or more, which is greater than the SET electric field (1.38X10 ⁶ V/m), The resistance switching of FAPbI ₃ is thought to be related to the migration of point defects such as iodine vacancies rather than the migration of Ag. To confirm this, the result of measuring the SET voltage and RESET voltage after fabricating a memristor element with a δ-FAPbI ₃ (125°C) thin film disposed between the electrode and the Pt electrode, the SET stood up around 0.4V. And RESET occurred around -0.3V. From this, it can be seen that the formation of conductive filaments in the FAPbI ₃ based memristor device is more affected by migration of iodine vacancy than by Ag migration.

7 is a diagram showing two different migration paths of iodine vacancies (V _I ^* ) in δ-FAPbI ₃ and a relative energy profile according to the two migration paths. Nudged Elastic Band calculation was applied to understand the migration energy of iodine vacancies (V _I ^* ).

Referring to FIG. 7, in the δ-FAPbI ₃ lattice, iodine vacancies (V _I ^* ) migrate to a path along the [010] direction parallel to the ab-plane or in the [123] direction slightly inclined to the c-axis. It can be migrated to the following path. When the ab-plane of δ-FAPbI ₃ is perpendicular to the electrode, a conductive filament must be generated through migration of iodine vacancy (V _I ^* ) along the [010] direction, whereas when the ab-plane is parallel to the electrode, [ 123] A conductive filament must be formed through migration of iodine vacancies (V _I ^* ) along the direction.

And the barrier energy for migration of iodine public (V _I ^*) of iodine public (V _I ^*) according to, while the [123] direction of the path barrier energy for migration is 0.9 eV in accordance with the [010] direction of the path is 0.48 eV Was calculated to be. It is believed that the difference in migration barrier energy according to this path is due to preferential orientation of FA molecules along a direction parallel to the ab-plane. When FA molecules are preferentially oriented along a direction parallel to the ab-plane, the rotation of the FA molecule is required before moving to the next lattice site in order for iodine vacancy (V _I ^* ) to migrate to the [010] direction path. The migration barrier energy is imparted, whereas the migration of iodine vacancies (V _I ^* ) along the [123] direction path is not disturbed by FA molecules, and thus a low migration barrier energy is imparted. Therefore, in the δ-FAPbI ₃ lattice, the iodine vacancies (V _I ^* ) mainly migrate along the [123] direction rather than the [010] direction, and as a result, better resistance switching than when the ab-plane is parallel to the electrode. Characteristics can be implemented.

In the mechanisms involved in the formation and destruction of filaments by iodine vacancies (V _I ^* ) within FAPbI ₃ , RESET is closely related to the separation of iodine vacancies (V _I ^* ) clusters. Therefore, to understand the separation of the iodine vacancy (V _I ^* ) cluster, the interaction energy of the two iodine vacancy was investigated.

As α-FAPbI ₃ and _δ-3 FAPbI public iodine (V ^* _I) result, α-FAPbI ₃ and each 0.35eV and 0.39eV for the δ-FAPbI ₃ calculates a defect formation energy, were similar to one another. Further, by calculating an energy difference between the two iodine public (V _I ^*) on the density functional theory (DFT) of two independent iodine public (V _I ^*) most closely arranged in the manner of the two iodine public (V _I ^* ) Was calculated, and the iodine vacancies (V _I ^* ) interaction energies were all equal to 0.14 eV for both α-FAPbI ₃ and δ-FAPbI ₃ .

However, a significant difference was found in the interaction distance of the iodine vacancies (V _I ^* ) in α-FAPbI ₃ and δ-FAPbI ₃ by the density function theory (DFT) method. for δ-FAPbI _3, iodine public (V _I ^*) interactions between the two iodine public (V _I ^*) and determined that the rapidly disappears as the distance increases between the I, α-FAPbI ₃ in the The interactions of the iodine vacancies (V _I ^* ) in the were found to extend over relatively long distances.

As a result of the density function theory (DFT) calculation, as the iodine vacancies (V _I ^* ) from the first site to the nearest second site within δ-FAPbI ₃ migrate, the interaction energy decreased to less than 0.02 eV. , As a result, it was found that the iodine vacancies (V _I ^* ) in δ-FAPbI ₃ interact with each other only within a short distance. In contrast, in α-FAPbI ₃ , even if one of the two iodine vacancies (V _I ^* ) located at a long distance (14.2 Å) migrate to the nearest neighboring site, the interaction energy between them did not decrease.

To understand the physical origin of the difference in the interaction distance of iodine vacancies (V _I ^* ) within α-FAPbI ₃ and δ-FAPbI ₃ , the electromagnetic density of states was investigated, and the results Is shown in Figures 8a and 8b.

FIG. 8A is a diagram showing the electromagnetic density of states (a) of α-FAPbI ₃ and the density of states of α-FAPbI3 with one iodine pore (b), and FIG. 8B is the electromagnetic density of states of δ-FAPbI ₃ (c ) And the density of state (d) of δ-FAPbI ₃ having one iodine vacancy.

When FIG. 8a and FIG. 8b, δ-FAPbI and the _third band gap is 2.85eV, the band gap of the α-FAPbI ₃ is a 1.47eV, the band gap of the δ-FAPbI ₃ is larger than the band gap of the α-FAPbI ₃ Appeared.

In the case of α-FAPbI _3, the electromagnetic state of the iodine vacancy (V _I ^* ) overlaps with the conduction band due to the small band gap, so it can diffuse through the entire conduction band, and as a result, two iodine vacancy ( V _I ^*) does not decrease even if increasing the physical distance between the interaction via the conduction band, and the public iodine _(I ^* V) interaction energies between the public iodine (V _I ^*). In contrast, the conduction band of δ-FAPbI ₃ is sufficiently larger than the energy level of the iodine vacancies (V _I ^* ), and as a result, the two iodine vacancies (V _I ^* ) interact only through their physical location, so that the iodine vacancies ( As the distance between V _I ^* ) increases, the energy of interaction between iodine vacancies (V _I ^* ) decreases rapidly.

It is believed that this difference in the interaction behavior of iodine vacancies (V _I ^* ) makes a difference in the RESET characteristic. For example, in the case of δ-FAPbI ₃ is therefore limited to within a short distance interaction iodine public (V _I ^*), RESET is iodine public (V _I ^*) the migration suppression to take place easily in accordance with the distance from the cluster It is judged to be there. On the other hand, in α-FAPbI ₃ , since the interaction distance of iodine vacancy (V _I ^* ) is extended, long-distance migration of iodine vacancy (V _I ^* ) is required to be separated from the cluster. As a result, α-FAPbI Within ₃ , it is judged that the conductive filament is not easily destroyed, resulting in poor reset characteristics.

Additionally, the on/off ratio, endurance, and multilevel capability of the memristor device of Example 3, which was annealed at 125°C, were investigated.

9 is a voltage-current graph showing the result of performing 20 resistance switching sweeps on the memristor device of Example 3. FIG.

Referring to FIG. 9, in a positive voltage sweep (0V->0.25V->0V), SET switching of the memristor element of Example 3 occurs around 0.2 V, and a negative voltage sweep (0V->-0.75V) ->0V), the RESET switching took place around -0.2V. And the current in the high resistance state was about 10 ^-8 A to 10 ^-9 A, the current in the low resistance state was 1.0X10 ^-3 A, and as a result, the on/off ratio of the memristor element of Example 3 was about It was 10 ⁵ to 10 ⁶ .

On the other hand, when comparing the first sweep with the subsequent sweeps, it was found that there was little difference in the SET process, and from this, it can be seen that the memristor element of Example 3 does not require initial forming.

10A and 10B are graphs showing resistance switching results using voltage pulses for the memristor device of Example 3. FIG. In the above voltage pulse, in the case of the SET process, the pulse voltage (pulse width is 45ms) is 0.28V, the read voltage is 0.028V, in the case of the RESET process, the pulse voltage (pulse width of 230ms) is -0.6V, and the read voltage is It was -0.06V. And the positive/negative voltage sweep was repeated 1200 cycles.

Referring to FIG. 10A, it can be seen that the memristor device of Example 3 is capable of reversibly switching bipolar resistance for 1200 cycles.

Referring to FIG. 10B, the retention of the low storage state (LRS) and the high resistance state (HRS) was maintained for 3000 s while maintaining a constant on/off ratio of 10 ⁵ or more.

On the other hand, the on/off ratio of 10 ⁵ or more of the memristor device of Example 3 is 3 orders of magnitude greater than the previously reported V-doped SrZrO ₃ or Pr _0.7 Ca _0.3 MnO ₃ . As described above, since the memristor device of the third embodiment has an On/off ratio of 10 ⁵ or more, the memristor device of the third embodiment may have a multilevel storage capability. The multilevel storage capability for the memristor element of Example 3 can be measured by lowering the compliance current in a positive voltage sweep, which is shown in FIG. 11.

11 is a voltage-current graph showing the multilevel storage capability measured at four different compliance currents for the memristor device of Example 3. FIG.

Referring to FIG. 11, when the compliance current was reduced from 10 ^-2 A to 10 ^-5 A in a positive voltage sweep, reversible resistance switching without damage to the SET voltage was observed. The energy for RESET decreased with the decrease in the compliance current, because it is affected by the amount of iodine vacancies forming the filament for the compliance current. The number of iodine vacancies for filament formation was reduced at low compliance currents. From these results, it can be confirmed that δ-FAPbI ₃ not only has excellent resistance switching characteristics, but also has a multilevel storage capability.

On the other hand, since thermal stability is important from an actual point of view, temperature-dependent switching characteristics were investigated. 12 is an I-V curve (a) measured at 80°C for the memristor device of Example 3 and an I-V curve (b) measured after cooling to room temperature after aging at 100°C for 1 minute.

Referring to FIG. 12, comparing the IV curve measured at 80°C for the memristor device of Example 3 with the results measured at room temperature, the current for both the high resistance state (HRS) and the low resistance state (LRS) is However, the SET voltage and the on/off ratio decreased. It is believed that the decrease in SET voltage is due to a decrease in active energy for migration of iodine vacancies at an elevated temperature. And ambient temperature and has appeared to have a different profile, RESET, which is determined to be related to the temperature-dependent migration of public _δ-3 FAPbI side effects of structural changes and / or δ-FAPbI ₃ at a high temperature. For example, due to partial dissolution of the filaments at high temperatures, the conductive filaments can be partially broken.

Meanwhile, the resistance switching profile measured after cooling to room temperature after thermal shock at 100°C shows a stable switching operation. It is believed that this is because the crystalline phase of δ-FAPbI ₃ can change reversibly with the heating and cooling cycles.

Although the above has been described with reference to the preferred embodiments of the present invention, those skilled in the art will be able to variously modify and change the present invention without departing from the spirit and scope of the present invention described in the following claims. You will understand that you can.

100: memristor element 110: first electrode
120: second electrode 130: resistance change layer
1000: nonvolatile memory device 1100: memory cell
1200: selection element 1300: first signal line
1400: second signal line

Claims (11)

A first electrode and a second electrode disposed to face each other; And
It is disposed between the first electrode and the second electrode, and is represented by the following formula (1) and includes a resistance change layer formed of an organic-inorganic halogen compound having a hexagonal crystal structure,
In the hexagonal crystal structure of the organic-inorganic halogen compound, six X ions surround one M ion to form an octahedral unit, and the octahedral units are one of two octahedral units arranged adjacent to each other along the c-axis of the crystal. Memristor element, characterized in that it is arranged to share the faces of the linear structure :
[Formula 1]

In Formula 1, R represents an organic cation, M represents a metal cation, X represents a halogen anion, and x, y and z independently represent real numbers of -0.5 or more and +0.5 or less. The method of claim 1,
The organic cation (R) is characterized in that it comprises at least one selected from the group consisting of CH(NH ₂ ) ₂ ⁺ , CH ₃ NH ₃ ⁺ and N ₂ H ₅ ⁺ . The method of claim 1,
The metal cations (M) are copper ions (Cu ²⁺ ), nickel ions (Ni ²⁺ ), cobalt ions (Co ²⁺ ), iron ions (Fe ²⁺ ), manganese ions (Mn ²⁺ ), chromium ions ( Cr ²⁺ ), palladium ion (Pd ²⁺ ), cadmium ion (Cd ²⁺ ), ytterbium ion (Yb ²⁺ ), lead ion (Pb ²⁺ ), tin ion (Sn ²⁺ ), germanium ion (Ge ^{2 +} ), bismuth ions (Bi ³⁺ ) and antimony ions (Sb ³⁺ ), characterized in that it comprises at least one selected from the group consisting of, memristor device. The method of claim 1,
The halogen anion (X) is a fluoride ion (F ^-), chloride ion (Cl ^-), bromide ion (Br ^-) and an iodine ion (I ^-), characterized in that it comprises at least one selected from the group consisting of, MEM Lister element. delete The method of claim 1,
The memristor element, characterized in that the ab-plane of the hexagonal crystal structure is disposed parallel to one surface of the first electrode or the second electrode. A first electrode and a second electrode disposed to face each other; And
It is disposed between the first electrode and the second electrode, and is represented by the following formula (1) and includes a resistance change layer formed of an organic-inorganic halogen compound having a hexagonal crystal structure,
The organic-inorganic halogen compound contains halogen vacancy,
The energy level of the halogen vacancy is higher than the valence band energy level of the organic-inorganic halogen compound and lower than the conduction band energy level, the memristor element:
[Formula 1]

In Formula 1, R represents an organic cation, M represents a metal cation, X represents a halogen anion, and x, y and z independently represent real numbers of -0.5 or more and +0.5 or less.
A first signal line and a second signal line extending in a direction crossing each other; And
A memory cell and a selection element disposed therebetween in a region where the first signal line and the second signal line overlap, and connected in series with each other,
The memory cell includes a first electrode electrically connected to one of the first signal line and the second signal line, a second electrode electrically connected to the selection element, and a resistor disposed between the first electrode and the second electrode. Including the layer of change,
The resistance change layer is represented by the following formula (1) and is formed of an organic-inorganic halogen compound having a hexagonal crystal structure,
In the hexagonal crystal structure of the organic-inorganic halogen compound, six X ions surround one M ion to form an octahedral unit, and the octahedral units are one of two octahedral units arranged adjacent to each other along the c-axis of the crystal. A non-volatile memory device, characterized in that it is arranged to share the faces of to form a linear structure :
[Formula 1]

In Formula 1, R represents an organic cation, M represents a metal cation, X represents a halogen anion, and x, y and z independently represent real numbers of -0.5 or more and +0.5 or less. The method of claim 8,
The nonvolatile memory device, characterized in that the memory cell has a bipolar switching characteristic. The method of claim 8,
The nonvolatile memory device, characterized in that the memory cell has a multilevel storage capability.
A first signal line and a second signal line extending in a direction crossing each other; And
A memory cell and a selection element disposed therebetween in a region where the first signal line and the second signal line overlap, and connected in series with each other,
The memory cell includes a first electrode electrically connected to one of the first signal line and the second signal line, a second electrode electrically connected to the selection element, and a resistor disposed between the first electrode and the second electrode. Including the layer of change,
The resistance change layer is represented by the following formula (1) and is formed of an organic-inorganic halogen compound having a hexagonal crystal structure,
The organic-inorganic halogen compound contains halogen vacancy,
The energy level of the halogen vacancy is higher than the valence band energy level of the organic-inorganic halogen compound and lower than the conduction band energy level, the nonvolatile memory device:
[Formula 1]

In Formula 1, R represents an organic cation, M represents a metal cation, X represents a halogen anion, and x, y and z independently represent real numbers of -0.5 or more and +0.5 or less.

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