Light-mediated multi-level flexible copper iodide resistive random access memory device for ultra-low power data storage application without formation process, and method for manufacturing same

Abstract

According to an embodiment of the present invention, provided is a multi-level resistive random access memory device comprising: a base substrate; a lower electrode disposed on the base substrate; a resistance change layer disposed on the lower electrode; and an upper electrode disposed on the resistance change layer, wherein the resistance change layer includes a copper iodide (CuI) which is a binary halide.

Description

Optically-parametric multilevel flexible copper iodide resistive random access memory device for ultra-low-power data storage applications without formation process and method for manufacturing the same

[0001] The present invention relates to an optical parametric multilevel flexible copper iodide resistive random access memory device for ultra-low power data storage applications without a formation process and a method for manufacturing the same.

[0002] Recently, there has been a surge in interest in emerging applications such as virtual reality (VR), metaverse, and autonomous driving, and the demand for invisible and flexible on-chip memory storage technology with appropriate power efficiency is increasing significantly to address issues such as data security, continuously increasing data, and flexible form factors. To meet the challenging aspects of the key requirements for the aforementioned applications, multi-level non-volatile memory (NVM) with novel form factors coupled with complementary circuits with ultra-low power consumption efficiency has been considered as an essential individual component. Metal oxide (TaO) x , HfO x , TiO x , ZrO2, IGZO), perovskite oxides (Pr x Ca 1-x Various candidates using perovskites (MnO3, SrTiO3, BaTiO3, BiFeO3), metal halide perovskites (Cs2Cu3I5) and other materials are being investigated with great anticipation for invisible complementary circuits and emerging NVMs.

[0003] Among them, metal oxides have been mainly studied and applied in contemporary electronic systems. Despite the attractive properties of metal oxides, including CMOS process compatibility and desirable multilayer stacking characteristics of NVMs, the development of metal oxide-based complementary circuit systems integrated with NVMs has been limited by challenges such as the lack of promising p-type candidates, low field-effect mobility, and unstable electrical properties under light illumination. Therefore, halide materials (γ-CuI) have been developed due to their optical transparency (~direct bandgap 3.1 eV), low electrical resistivity (~72 mΩ cm), and low resistivity (~51.6 cm). 2 V -1 s -1 It has been investigated as an alternative p-type semiconductor in flat panel displays due to its essential properties including high hole mobility. Moreover, the remarkable properties of CuI have led to its use in various other applications such as thermoelectric devices, flexible transparent pn diodes, hole transport layers in solar cells, and self-powered photodetectors.

[0004] On the other hand, there have been few reports on the stable operation or switching mechanisms of multi-level CuI resistive random access memory (RRAM), which could lead to the aforementioned core electronic applications. One possible reason is that, despite considerable effort, an ideal deposition method for NVM applications to control the CuI film texture and reduce defect density has not been established. Therefore, a thorough understanding of CuI film properties for memory applications has not been achieved to date. Various CuI synthesis methods have been used for electronic applications, including reactive sputtering, spin coating of CuI solutions, dip coating, and thermal evaporation of CuI.

[0005] Furthermore, CuI NVMs have rarely been reported, and further in-depth studies, including long-term durability and charge transfer mechanisms, are limited, likely due to the poor stability of the films. This poor stability is caused by the flat surface and morphology of CuI films, which vary depending on the synthesis route. Recently, a solid-state iodination method has been shown to effectively contribute to high performance of resistive switching (RS) by yielding high-quality CuI films with columnar particle morphology and nanohole-free surfaces due to vacuum-driven processing conditions. Interestingly, operationally stable CuI RRAMs with multilevel structures based on the solid-state iodination technique have not been reported, despite the compatibility of the proposed CuI synthesis process with optimal NVM compositions, which should open up tremendous research opportunities.

[0006] The present invention relates to an optical parametric multilevel flexible copper iodide resistive random access memory device for ultra-low power data storage applications without a formation process and a method for manufacturing the same.

[0007] The purpose of the present invention is not limited to the purposes mentioned above. The purpose of the present invention will become clearer from the following description, and can be realized by the means and combinations thereof described in the claims.

[0008] The present invention first reports a reliable CuI RRAM device based on solid iodization technology. (i) Excellent durability (10 3 (ii) low-voltage resistive switching of less than ± 0.5 V with a constant On / Off ratio (~10 4 ) with adequate maintenance performance (5Х10 4s), (iii) reproducible optical response in the high resistance state (HRS) suitable for optically assisted multilevel memory storage, (iv) flexible CuI RRAMs on PET substrates exhibiting performance similar to that on rigid substrates, and (v) stable operation of CuI RRAMs through optimized PMMA encapsulation that can maintain RS performance in air for 15 days. In addition, the CuI RRAM presented in the present invention is highly reliable, and a comprehensive study on temperature-dependent IV characteristics was performed in the range of 200 K to 343 K. This was confirmed by the activation energy, Schottky barrier height (φ b ) and other electrical characteristics that are helpful in understanding the conduction and resistive switching characteristics of CuI RRAM devices. The binary halide CuI proposed in the present invention exhibits excellent properties and adequate reliability for nonvolatile RRAM, and provides significant contributions to invisible, flexible, and multi-value NVM storage applications.

[0009] According to one embodiment of the present invention, a photoreactive multi-level resistive random access memory device is provided, which includes a base substrate, a lower electrode disposed on the base substrate, a resistance change layer disposed on the lower electrode, and an upper electrode disposed on the resistance change layer, wherein the resistance change layer includes copper iodide (CuI), which is a binary halide.

[0010] The above copper iodide (CuI) has a zinc blende, Marshite crystal structure and can be a multi-level resistive random access memory element due to its photoreactivity.

[0011] The above base substrate may be a flexible substrate.

[0012] The upper electrode may include silver (Ag).

[0013] The lower electrode may include at least one selected from the group consisting of indium oxide (ITO), gold (Au), platinum (Pt), nickel (Ni), and molybdenum (Mo).

[0014] The upper electrode and the resistance change layer are characterized by making Schottky contact at the interface.

[0015] The metal cations of the upper electrode can reduce the Schottky barrier height.

[0016] A passive layer including any one of poly(methyl metacrylate) (PMMA), CYTOP, SU-8, silicon oxide (SiO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), hafnium oxide (HfO2), yttrium oxide (Y2O3), zirconium oxide (ZrO2), polyvinyl pyridine (PVP), polyvinyl alcohol (PVA), polyvinyl phenol (PVP), polydimethyl siloxane (PDMS), polystyrene (PS), BCB, and polyvinyl naphthylene (PVN) may be further disposed on the multi-level resistive random access memory element.

[0017] According to another embodiment of the present invention, a method for manufacturing a photoreactive multi-level resistive random access memory device is provided, comprising: providing a base substrate having a lower electrode formed thereon; depositing a copper (Cu) film on the lower electrode; reacting the copper (Cu) film with iodine (I) to form a resistance-switching layer including copper iodide (CuI) on the lower electrode; and forming an upper electrode on the resistance-switching layer, wherein the step of forming the resistance-switching layer including copper iodide (CuI) on the lower electrode is performed by vacuum-driven iodine evaporation at room temperature.

[0018] The present invention demonstrates the effectiveness of a novel p-type copper iodide (CuI) semiconductor in flexible low-voltage resistive random access memory (RRAM) that can be readily integrated with its metal oxide n-type counterpart for complementary circuit systems.

[0019] Here, the CuI RRAM device is implemented through a room-temperature solid-state iodination process, and has an ultra-low bias range (±0.5 V) and a constant on / off ratio (~10 4 ), long retention period (>5X10 4 ~10 with s) 3 It exhibits excellent durability beyond cycles.

[0020] Furthermore, we demonstrate a photoparametric multilevel data storage scheme using blue illumination (λ = 455 nm) to exploit the photomemory capability enabled by the remarkable optical response of CuI.

[0021] Additionally, the current conduction and resistive switching (RS) behaviors are systematically studied through low-temperature measurements from 203 K to 343 K to verify the thermal stability and dominant key switching mechanism of CuI RRAM devices.

[0022] The long-standing problem of CuI device lifetime is effectively solved by PMMA encapsulation, which improves device lifetime in air by a factor of 15 compared to non-passivated devices.

[0023] The results of the present invention suggest that flexible optoelectronic systems can be combined with reliable ultra-low-power CuI RRAM devices with photo-memory resistance functionality to enhance multifunctional selectors required for synaptic elements in Process-in-Memory (PIM) and neuromorphic applications.

[0024] Figure 1 shows (a) a schematic diagram of the synthesis of CuI films on ITO-glass by a room-temperature, vacuum-driven iodination method, (b) XRD pattern and JCPDS file of the prepared CuI film (inset; γ-phase (Marschitite) zincblende-type crystal structure of CuI), (c, d) Cu 2p and I 3d core-level XPS spectra of the CuI film, (e) surface FE-SEM image of the CuI thin film, (f) EDS elemental mapping of Cu and I elements in the CuI film, and (g) cross-sectional SEM image of the assembled ITO / CuI vertical structure on the ITO-glass (inset: low-magnification image of the cross-section of the CuI / ITO-glass).

[0025] Figure 2 shows (a) the UV-visible absorption spectrum showing the absorption in the visible wavelength range of a CuI thin film deposited on a glass substrate (inset: CuI film deposited on ITO-glass), and (b) the full XPS survey spectrum of the CuI film surface.

[0026] Figure 3 shows (a) a surface SEM image of a CuI film on an ITO / glass substrate, (b) a cross-sectional EDS elemental mapping of CuI confirming the uniform distribution of constituent elements (Cu and I), (c) a graph of atomic weight (%) versus CuI film thickness of the synthesized CuI film, (d) an average particle size distribution of the CuI film on an ITO-glass substrate, (e) an XRD spectrum of the synthesized CuI and an EDS spectrum of the CuI film after 1 month, and (f) an EDS spectrum of the CuI film.

[0027] Figure 4 shows (a) typical IV characteristics of an ITO / CuI / Ag device (inset; vertical stacking diagram of an ITO / CuI / Ag device), (b) HRS and LRS for 1000 RS cycles of an ITO / CuI / Ag device, (c) set and reset voltage distributions for 1000 RS cycles represented by box-and-whisker plots (inset; showing cumulative set and reset voltages of an ITO / CuI / Ag device), (d) V for On and Off states. read 5Х10 at ± 0.05 V 4 Data retention characteristics measured over a period of seconds, (e) for ITO / CuI / Ag devices at various allowable currents (I) of 1 μA, 10 μA, 100 μA, and 1 mA Cc ) multi-stage IV characteristics, (f) different current tolerance (I Cc ), HRS and LRS graphs at 1 μA, 10 μA, 100 μA and 1 mA.

[0028] Figure 5 is a typical IV characteristic graph of an ITO / CuI / Ag based memory device for (a) 1000 cycles.

[0029] Figure 6 is a graph showing typical IV characteristics, set and reset voltage distributions, HRS and LRS values ​​for 50 cells of (ac) ITO / CuI / Ag devices.

[0030] Figure 7 shows (a) a double log plot of the IV characteristics of the ITO / CuI / Ag device, (b) an IV plot for LRS and ln IV for HRS. 1 / 2 Schematic diagrams of energy levels for ohmic contacts between Ag or (ITO) and CuI before (c) and after (d) contact, illustrating current conduction via thermally activated ion hopping in the HRS (straight lines are linear fits), and (e) schematic diagram of the proposed switching model showing the filament-based electrochemical metallization type in CuI-based RRAM.

[0031] Figure 8 shows typical IV characteristics of (a,b) ITO / CuI / Ag devices and ITO / CuI / Au devices, (c) typical IV characteristics of CuI with ITO as the bottom electrode and different top metal electrodes of silver (Ag), nickel (Ni), and aluminum (Al), and (d) typical IV characteristics graphs of various bottom electrode materials such as indium oxide (ITO), gold (Au), nickel (Ni), and molybdenum (Mo) and Ag as the top electrode.

[0032] Figure 9 shows a) temperature-dependent I-V characteristics in the temperature range of 203 K-343 K, b) temperature-dependent HRS states in the voltage range of 0.02 V-0.1 V of the ITO / CuI / Ag device, c) set and reset voltage distributions with respect to temperature, d) Arrhenius plot (ln I vs. 1 / T), e, f) energy band diagrams for low-temperature and high-temperature regimes of the ITO / CuI / Ag device.

[0033] Figure 10 is a graph showing a) typical IV characteristics of CuI films in the temperature range of 203 K-343 K, and b) extracted values ​​of conductivity versus temperature.

[0034] Figure 11 shows a) the extracted activation energy values, b) the Richardson plot (ln I / T 2 Graph showing the Schottky barrier height for the low-temperature and high-temperature regions (a) and (b) (1000 / T).

[0035] Figure 12: a) Schematic diagram of the experimental setup for optical memory characterization of ITO / CuI / Ag devices, b) dark conditions and 3.3 mW cm -2 6.6 mW cm -2 a) Typical I-V characteristics of ITO / CuI / Ag devices measured under blue light (optical wavelength: 455 nm) with various irradiances, c) HRS and LRS under dark condition, 50% and 100% power illumination with 455 nm (blue light), d) Light-dependent I-V characteristics of ITO / CuI / Ag devices under continuous dark-blue-dark condition, e,f) Set and reset voltage distributions of ITO / CuI / Ag devices under dark and illuminated conditions, g) Photoresponse of CuI RRAM under different illumination power (455 nm) at 10%, 50% and 100%, h,i) Schematic energy band diagrams of ITO / CuI / Ag devices under dark and bright conditions.

[0036] Figure 13 is a graph showing a) typical IV characteristics of ITO / CuI / Ag memory devices tested at different wavelength excitations of dark, 455 nm (blue), 540 nm (green), 656 nm (red), 740 nm, 850 nm and 940 nm, and b) HRS values ​​at different wavelengths showing a distinct effect for 455 nm (blue) irradiation compared to other wavelength illumination.

[0037] Figure 14 shows a) It characteristics of ITO / CuI / Ag devices at different powers under 455 nm illumination, and b) long-term photoexcitation graphs at different light powers for calculating decay time.

[0038] Figure 15 shows a,b) schematic diagrams and optical images of flexible ITO / CuI / Ag devices fabricated on PET substrates, c) typical IV characteristics of PET / ITO / CuI / Ag devices, and d) reversible HRS and LRS graphs of ITO / CuI / Ag devices on flexible PET substrates for 100 cycles at different bending radii of 10.8 mm, 6.6 mm, and 4.5 mm.

[0039] Figure 16 is a photo of a flexible device demonstration of a PET-ITO / CuI / Ag device at various bending radii (10.8 mm, 6.6 mm, 5.7 mm, 4.5 mm).

[0040] Figure 17 is a graph showing typical IV characteristics, HRS and LRS, set and reset voltage distributions of an unpassivated ITO / CuI / Ag device for ac) 6 days, and typical IV characteristics, HRS and LRS, set and reset voltage distributions of a PMMA-encapsulated ITO / CuI / Ag / PMMA device for df) 15 days.

[0041] The above-described purposes, other objectives, features, and advantages of the present invention will be readily understood through the following preferred embodiments, which are described in conjunction with the attached materials. However, the present invention is not limited to the embodiments described herein and may be embodied in other forms. Rather, the embodiments introduced herein are provided to ensure that the disclosure is thorough and complete, and to sufficiently convey the spirit of the present invention to those skilled in the art.

[0042] In this specification, terms such as “include” or “have” are intended to specify the presence of a feature, number, step, operation, component, part, or combination thereof described in the specification, but should be understood not to exclude in advance the possibility of the presence or addition of one or more other features, numbers, steps, operations, components, parts, or combinations thereof.

[0043] Unless otherwise specified, all numbers, values, and / or expressions expressing components and reaction conditions used herein are approximations that inherently reflect, among other things, the various uncertainties of measurement that arise in obtaining such values, and therefore should be understood as being modified in all instances by the term "about." Furthermore, whenever a numerical range is disclosed herein, such range is continuous and includes every value from the minimum value to the maximum value inclusive, unless otherwise indicated. Furthermore, whenever such a range refers to integers, every integer from the minimum value to the maximum value inclusive, unless otherwise indicated, is included.

[0044]

[0045] According to one embodiment of the present invention, a photoreactive multi-level resistive random access memory device is provided, which includes a base substrate, a lower electrode disposed on the base substrate, a resistance change layer disposed on the lower electrode, and an upper electrode disposed on the resistance change layer, wherein the resistance change layer includes copper iodide (CuI), which is a binary halide.

[0046] The above copper iodide (CuI) has a zinc blende, Marshite crystal structure and can be a multi-level resistive random access memory element due to its photoreactivity.

[0047] The above base substrate may be a flexible substrate.

[0048] The upper electrode may include silver (Ag).

[0049] The lower electrode may include at least one selected from the group consisting of indium oxide (ITO), gold (Au), platinum (Pt), nickel (Ni), and molybdenum (Mo).

[0050] The upper electrode and the resistance change layer are characterized by making Schottky contact at the interface.

[0051] The metal cations of the upper electrode can reduce the Schottky barrier height.

[0052] A passive layer including any one of poly(methyl metacrylate) (PMMA), CYTOP, SU-8, silicon oxide (SiO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), hafnium oxide (HfO2), yttrium oxide (Y2O3), zirconium oxide (ZrO2), polyvinyl pyridine (PVP), polyvinyl alcohol (PVA), polyvinyl phenol (PVP), polydimethyl siloxane (PDMS), polystyrene (PS), BCB, and polyvinyl naphthylene (PVN) may be further disposed on the multi-level resistive random access memory element.

[0053] According to another embodiment of the present invention, a method for manufacturing a photoreactive multi-level resistive random access memory device is provided, comprising: providing a base substrate having a lower electrode formed thereon; depositing a copper (Cu) film on the lower electrode; reacting the copper (Cu) film with iodine (I) to form a resistance-switching layer including copper iodide (CuI) on the lower electrode; and forming an upper electrode on the resistance-switching layer, wherein the step of forming the resistance-switching layer including copper iodide (CuI) on the lower electrode is performed by vacuum-driven iodine evaporation at room temperature.

[0054]

[0055] Hereinafter, the present invention will be described in detail using examples. However, the examples according to the present invention may be modified in various ways, and the scope of the present invention is not limited to the examples described below. The examples in this specification are provided to more fully explain the present invention to those of ordinary skill in the art.

[0056]

[0057] 1. Experiment

[0058] 1.1. Film formation and device fabrication

[0059] An ITO-coated glass substrate (sheet resistance 10 ohm / sq, thickness 0.7 mm, purchased from Omniscience Korea) was used as the lower electrode. The ITO-coated substrate was ultrasonically rinsed with acetone, isopropanol, and deionized water, and then dried with N2 gas before synthesizing the CuI film.

[0060] CuI films were synthesized on cleaned ITO-glass substrates by converting copper (Cu) to copper iodide at room temperature. First, the Cu film was synthesized under vacuum (1x10 -6 0.15 Å s under 1 Torr -1 was deposited on an ITO-glass substrate cleaned by thermal evaporation at a rate of . The evaporated copper film was set in an iodine atmosphere according to a vacuum-driven iodine evaporation technique known as the iodination process.

[0061] The reaction between copper and solid iodine takes place in a vacuum desiccator under moderate vacuum. The vacuum level not only prevents oxidation of copper and iodine, but also drives the rate of iodine evaporation.

[0062] Under high-temperature growth conditions, agglomeration of CuI films results in non-uniform growth of CuI. Therefore, the room-temperature vacuum-driven iodination process outperforms the film quality obtained through the high-temperature process.

[0063] The iodization time directly affects the thickness and roughness of the CuI film. However, as the thickness increases, the epitaxial growth of the CuI film may be shortened due to strain effects, even though the RRAM device exhibits a wider memory window. A shadow mask is then used to deposit the top electrode (90 nm thick silver) by thermal evaporation.

[0064]

[0065] 1.2. Device stability

[0066] The device stability of CuI-based RRAM was improved by coating with a poly(methyl metacrylate) (PMMA) encapsulation layer. A 2 wt.% PMMA solution (weight / volume ratio, d 1.17 g / ml, purchased from Sigma Aldrich) was spin-coated onto the ITO / CuI / Ag device configuration and then calcined at 110 °C for 1 h in air. The passivated device was stored in ambient air to evaluate the effects of humid air and humidity. In the case of unpassivated ITO / CuI / Ag-based devices, degradation is accelerated due to the catalytic effect of moisture resulting from the reaction between the CuI film and the Ag top electrode.

[0067]

[0068] 1.3. Film Characterization

[0069] CuI films were grown on ITO-glass substrates and then vacuum annealed at 120°C. X-ray diffraction (XRD) measurements in a RIGAku Smart Lab with Cu Kα radiation (λ = 1.54Å) characterized the phase and crystal structure. XRD peak data were obtained at room temperature in the 2θ range of 20°–80° with a step size of 0.03° and a peak frequency of 3° min. -1The surface and cross-sectional images were examined using Field Emission Scanning Electron Microscopy (FE-SEM) (JEOL / JSM-7800F). Elemental mapping and images were obtained at an acceleration voltage of 10.0 kV. XPS elemental studies were performed at an incident energy of 600 eV at 10 -8 It was performed on the ULVAC-PHI 5000 Versa Probe PHI in Pa.

[0070]

[0071] 1.4. Device Characterization

[0072] The electrical properties were characterized by a semiconductor parameter analyzer (Agilent 4155B) in ambient air. For low-temperature measurements, the IV characteristics were measured using a semiconductor analyzer (4200-SCS, Keithley) at 6X10 -2 The measurements were performed using a low-temperature cryogenic vacuum chamber (CRX-6.5K, Lake Shore) at a vacuum level of 10 Torr. The photoconductive effect on the RS of the CuI RRAM device was studied under a laser light source by a multi-wavelength fiber-coupled LED source (Mightex) with various wavelengths, including 455 nm (blue), 540 nm (green), 656 nm (red), 740 nm, 850 nm, and 940 nm. The calibrated power intensity of the 455 nm laser was 6.60 mW cm -2 am.

[0073]

[0074] 2. Results and Discussion

[0075] 2.1. Synthesis and properties of CuI films

[0076] 2.1.1. Synthesis, crystal structure, phase, and morphology of CuI

[0077] Figure 1a illustrates the process flow for synthesizing a CuI film. First, Cu (60 nm) was deposited on a cleaned ITO / glass substrate via thermal evaporation at room temperature (Figure 1a(i)). The Cu film was then exposed to solid iodine under vacuum in an iodine-equipped vacuum dryer for 30 min and then annealed at 120°C, resulting in a transparent CuI film, as schematically illustrated in Figure 1a(ii-iv). The iodination process significantly influences the surface morphology of the CuI film, particularly the particle size and roughness.

[0078] Accordingly, in the present invention, iodine sublimation was performed under vacuum (~1 mtorr) at room temperature to precisely control the iodination rate of Cu films depending on vacuum conditions. Relatively speaking, vapor iodination of Cu at room temperature produces CuI films with a rough surface and narrow particle size. In contrast, vacuum-driven solid-state iodination, due to room-temperature conditions, produces CuI films with very transparent and fine particles, a broad particle size distribution, and a smoother film (Fig. 2).

[0079] Figure 1b shows an X-ray diffraction (XRD) pattern, showing diffraction peaks at 25.5°, 42.21°, and 49.9° corresponding to the assigned (111), (220), and (311) planes, respectively. These are consistent with γ-phase CuI as reported in JCPDS No. 06-0246. The inset of Figure 1b shows the zinc blende, Marshite crystal structure of CuI.

[0080] The scanning electron microscopy (XPS) spectrum confirmed that there were no additional peaks other than Cu and I in the CuI film (Fig. 2b). The core-level Cu 2p and I 3d orbitals due to spin-orbit interaction were at 932.1 eV (Cu 2p 5 / 2 ) and 951.9 eV (Cu 3d 3 / 2)(Fig. 1c) was divided into two peaks, and the I 3d core level spectrum was I 3d 5 / 2 Wow I 3d 3 / 2 It was divided into two peaks at 619.3 and 631.4 eV corresponding to Cu. In addition, there was no shake-up peak or satellite peak in the XPS peak spectrum. The above data consistently indicate that the oxidation state of Cu is +1, which means that Cu 2+ It was reconfirmed that no oxidation state was formed.

[0081] Figure 1(e) shows a planar scanning electron microscope (SEM) image, EDS element mapping, and a cross-sectional SEM image of a CuI film formed on ITO / glass. The planar FE-SEM images (Figs. 1e, 3a) and EDS element mapping (Fig. 1f) of the CuI film confirm uniform, pinhole-free, transparent crystalline CuI throughout the film and a uniform distribution of both Cu and I throughout the film. The EDS mapping confirms the uniform distribution of Cu and I throughout the thickness of the CuI film. The average particle size of the CuI film calculated from the FE-SEM images is 120 nm, which is consistent with the literature report.

[0082] The cross-sectional SEM image (Fig. 1g) shows the formation of a uniform, columnar, and broadly grained CuI film. This confirms that the deposited 60 nm thick Cu film was converted to a 270 nm thick CuI film, which is consistent with the theoretical volume ratio of Cu to CuI (~4.5–5) within the range reported in the literature (Fig. 3).

[0083]

[0084] 2.2. Resistance switching characteristics

[0085] 2.2.1. RRAM Characteristics

[0086] Figure 4a shows typical IV characteristics in a semi-logarithmic scale over an applied bias range of ±0.5 V for an ITO / CuI / Ag-based RRAM device (inset: Figure 4a shows the vertical stacking structure of the ITO / CuI / Ag-based RRAM device).

[0087] The ITO / CuI / Ag device has a current compliance (I) of 100 μA with the ITO grounded. cc ) exhibits bipolar switching behavior with a positive bias at the upper electrode (Ag). Initially, it is in a high resistance state (HRS), and when the positive voltage sweep is from 0 V to 0.5 V, it decreases to about + 0.3 V (V set ) showed a phenomenon of abrupt transition to low resistance state (LRS) at voltage of 0 V. On the other hand, negative voltage sweep (0 V ~ -0.5) showed an ultra-low reset voltage (V reset )(~ -0.15 ± 0.02 V) to return the device to HRS.

[0088] Forming-free RS prevents chemical and thermal decomposition of the active layer, which is common during the electroplating process, resulting in damage-free operation and V set or V reset leads to negligible fluctuations in Ag. Perhaps, the switching behavior without formation process is + It can be recognized as an easy migration of cations.

[0089] As a result, Ag + Cations could induce uniform RS behavior by overcoming the barrier height through the CuI film and establishing a conduction path through the active layer.

[0090] Figure 4b shows the IV characteristics of 1000 consecutive cycles. read~ ± 0.05 V. The inferred HRS and LRS are shown. Remarkable RS cycling by ITO / CuI / Ag devices is achieved with consistent On / Off current ratio (~10) without significant degradation over 1000 consecutive cycles. 4 ) showed excellent durability (Fig. 5).

[0091] Additionally, Fig. 4c shows statistically analyzed box-and-whisker plots for set or reset voltage (Vset / reset), realizing excellent operating uniformity. V set / reset The distributions are approximately 0.29 V ± 0.03 V (or -0.12 V ± 0.07 V), respectively, as clearly visualized in the cumulative probability plot in Fig. 4c. CuI RRAMs are expected to be attractive for memory applications because of their very low power consumption. For example, the average power consumption for set (or reset) is P set = V set x I cc (or V reset x I cc ) was estimated to be 2.7 pW (or 16 pW) based on the relationship.

[0092] Data retention can be a very important parameter when evaluating RRAM from a practical application perspective. Also, for ITO / CuI / Ag devices, V read The data retention characteristics measured at ~ ± 0.05 V are shown in Fig. 4d. The ITO / CuI / Ag device has a 5Х10 5 HRS and LRS were maintained for a sufficiently long period of time without any discernible degradation.

[0093] The multi-level IV characteristics and their corresponding resistance states are illustrated in Fig. 4(e,f). I cc By controlling the abrupt switching and high On / Off ratio, multi-level data storage of CuI-based RRAM devices can be achieved.

[0094] Figure 4e shows different current limits I cc The IV characteristics of the ITO / CuI / Ag device at (1 μA, 10 μA, 100 μA, 1 mA) are shown, showing four different LRS states with similar HRS (Fig. 4f).

[0095] Also, I cc Even under different conditions, CuI RRAM devices have similar voltage V set It shows the ability to switch from HRS to LRS. Similar V set These multilevel IV characteristics imply that RS is independent of the current limit. This observation demonstrates that the applied electric field dominantly directs RS in memory devices.

[0096] I from 1 μA to 100 μA cc V for set is I cc = No significant change except for the limit change for 1 mA. However, during reversible RS, V reset showed some fluctuations in the negative bias sweep.

[0097] At the low current limit (~1 μA and 10 μA), the transition from LRS to HRS is observed at about 0 V, which is due to the formation of weak conducting filaments. On the other hand, the high current limit (1 mA) requires a higher reset voltage due to the formation of stronger filaments. This is due to the required high I cc This is because more cations accumulate near the ITO bottom electrode of the CuI active layer.

[0098] Also I cc Reset for the (~100 μA) condition occurs at ultra-low voltages (-0.02 V to -0.1 V), making it very attractive for low-power memristor applications.

[0099] Here, CuI RRAM demonstrates a practical four-level storage capability that enhances data storage density and improves the usability of analog memristors. To evaluate the reproducibility of RS, cell-to-cell variations for ITO / CuI / Ag-based memory devices were evaluated using 50 assemblies under identical physical conditions (Fig. 6(a)). The HRS / LRS values ​​and V set / reset The distribution showed high uniformity for 50 cell-to-cell measurements, demonstrating operational consistency and overall device yield.

[0100]

[0101] 2.3. Current conduction and resistance switching mechanisms

[0102] The current conduction mechanism and switching mechanism are presented in Fig. 7. The abrupt switching from HRS to LRS (set) and vice versa (reset) is attributed to filamentary switching induced by electrochemical reactions and thermal cracking. To better understand the current conduction mechanisms for HRS and LRS, the IV characteristics are plotted on a double logarithmic scale, as shown in Fig. 7a. The dominant current transport mechanisms of HRS and LRS have distinct characteristics. The difference in electrical conduction over the same voltage range (0 V to 0.5 V) suggests that different mechanisms are involved in the current conduction of HRS and LRS.

[0103] In the on state, i.e., the LRS region, the LRS is linearly fit to ln I versus ln V with a slope of 1.04 during the positive sweep (0 V to +0.5 V to 0 V), which means that the LRS state follows ohmic conduction behavior.

[0104] On the other hand, the off state, i.e., the HRS region, follows a nonlinear path with a slope of 0.51, which closely matches the Schottky conduction mechanism. To explain the current conduction mechanism, the IV curves are rearranged in Fig. 7b to show Ohmic conduction in the LRS and Schottky emission in the HRS.

[0105]

[0106] *Figure 7b(i) is an I vs. V plot of the LRS region, confirming the ohmic conduction mechanism. This is interpreted as a result of the formation of conductive filaments between the upper and lower electrodes through the CuI resistive layer, resulting in rapid switching. However, for the evaluation of the nonlinear HRS region, the IV characteristics are plotted as the logarithmic current vs. voltage square root (ln I vs. V) as in Figure 7b(ii). 1 / 2 ) was replaced by the relationship. This region (HRS) is ln I vs. V 1 / 2 A linear fit to the plot demonstrates that Schottky emission dominates in the off state.

[0107] According to equation (1), the cations (Ag) diffused from the upper electrode + ) is governed by the conduction mechanism of thermionic Schottky emission.

[0108] [Equation (1)]

[0109]

[0110] Here, I is the current, ε is the dielectric constant, q is the charge, d is the thickness of the CuI film, and V is the applied voltage. During the current conduction in the HRS, the applied electric field passes through the Schottky barrier at the interface of the top electrode, Ag, and CuI film. + It facilitates the easy transport of ions. The dominant Schottky conduction in HRS is based on equation (2):

[0111] [Equation (2)]

[0112]

[0113] Here A* is the effective Richardson constant, q is the charge, φ b is the Schottky barrier height, ε o is the vacuum permittivity, ε r is the relative permittivity.

[0114]

[0115] The energy band diagrams of Ag and ITO before forming physical contact with CuI are shown in Fig. 7c, providing information on the band diagrams required for Ag / CuI and CuI / ITO bonding.

[0116] Overall, the switching behavior is quite consistent with electrochemical metallization (ECM) type switching, so the proposed switching model is evaluated by energy band diagram after physical contact formation for CuI sandwiched between Ag and ITO (Fig. 7(d,e)).

[0117] Additionally, the above-described electro-physical reaction kinetics is schematically illustrated in Fig. 7e and explained in relation to the energy band diagram in Fig. 7d.

[0118]

[0119] The switching process starts with the oxidation of Ag when a positive bias of 0 V to 0.5 V is applied to the upper electrode.

[0120] This is the generated Ag + After the cations gradually diffuse into CuI, Ag + The formation of ions begins. After that, the ions move toward the ITO electrode through the CuI resistive layers. In the CuI layer, cations (Ag + ) is thought to be related to thermally assisted ion hopping as one of the main transport mechanisms for the HRS state, as depicted in the energy band diagram (Fig. 7d, e(ii)).

[0121] Therefore, the main HRS conduction is strongly related to trap-state mediated conduction in the switching medium of CuI, which is consistent with previously reported results based on thermally excited electrons.

[0122] Also, Ag + When the ions reach the lower electrode (Fig. 7e(iii)), Ag + The ions are reduced to Ag, which tends to form conductive filaments. This causes an abrupt transition from HRS to LRS. During the reset process, i.e., the transition from LRS to HRS, the conductive path is expected to be destroyed due to Joule heating decomposition of the Ag filament electrode (Fig. 7e(iv)).

[0123] Therefore, the switching behavior and capability of CuI can be achieved at ultra-low bias voltages, strongly suggesting that the conducting filaments are very narrow and thermally unstable.

[0124]

[0125] The choice of electrode pairs plays a crucial role in achieving these remarkable and reproducible switching characteristics.

[0126] The top and bottom electrodes were made of various metals with different work functions to understand the switching mechanism during RS. The ITO / CuI / Au device exhibited different IV characteristics from the ITO / CuI / Ag device (Fig. 8(a,b)), which may be due to the absence of electrochemical inertness of Au as the top electrode. This was analyzed to be due to the high stability of the Au top electrode, which suppresses the formation of conductive filaments. This suggests that the Au in the top electrode of the CuI film did not participate in the RS behavior.

[0127] In CuI with Au-top electrode, very low on / off switching behavior below 1st order was observed. This is due to vacancy defects (V cu , V I ) or interstitial defects present in CuI films (Cu i, I i ) may be due to point defects associated with possible candidates such as filament switching, reaffirming that ECM type filament switching mainly dominates the speed of ITO / CuI / Ag devices. Detailed studies on the top and bottom electrodes are presented in Fig. 8(c,d).

[0128]

[0129] The thermal stability of ITO / CuI / Ag devices was investigated over the temperature range of 203 K to 343 K to investigate the correlation between charge transfer of carriers, RS mechanism, and operational stability over the specified temperature range. Temperature-dependent IV characteristics during RS confirmed the operational stability of ITO / CuI / Ag devices from 203 K to 343 K with a step size of 20 K (Fig. 9a).

[0130] For analytical understanding, it was shown that the HRS current value increased steadily with temperature in the voltage range of 0.02 V to 0.1 V according to the temperature in Fig. 9b. This is because the metal cation (Ag) from the upper electrode + ) may be due to the synergistic effect of point defects present in the moving and switching medium (CuI). Ag + The transport rate of cations probably dominates the current level in the high-temperature region, whereas trap states in the CuI film mainly contribute to the HRS current variation in the low-temperature region.

[0131] The predominance of point defects in the low-temperature range is experimentally verified by the temperature-dependent electrical conductivity, indicating that heat-assisted transport of charge carriers is widespread in the CuI film (Fig. 10).

[0132]

[0133] Figure 9c shows (i) the oxidation and nucleation rates of the upper electrode (Ag), (ii) the cations (Ag) in the switching layer + ) and (iii) indirect temperature effects due to various factors such as reduction at the lower electrode (ITO). set or (Vreset ) shows a gradual decreasing trend with increasing temperature.

[0134] Temperature rise occurs due to Ag through CuI resistive layer + Facilitates easy movement of cations and Ag + It helps to reduce Ag to V, which results in V set is lowered. However, V reset is associated with the destruction of the filament through the assisted melting of the line.

[0135] As a result, the conductive filament becomes narrower at high temperatures and exhibits poor thermal stability, resulting in V reset is reduced. The temperature-dependent V observed during switching set or (V reset ) values ​​demonstrate that the ECM mechanism is dominant in the ITO / CuI / Ag device, which is consistent with previously reported literature.

[0136]

[0137] The Arrhenius plot for the HRS state shows two distinct regions, suggesting that different charge transfer mechanisms may be involved in the measured temperature range (Fig. 9d). Kaushik et al. reported that thermally evaporated CuI exhibited distinct charge transfer behaviors in the temperature range from 150 K to 300 K. The estimated activation energies (E) at different voltages from 0.02 V to 0.1 V for the high- and low-temperature regions of the HRS a ) is shown in Fig. 9d.

[0138] The extracted activation energies for the high temperature (or low temperature) region were found to be 0.38 eV (or 0.18 eV), respectively (Fig. 11a). In particular, the trap state is a vacancy (V cu , V I ), intrusive defects (Cu i , I i) and point defects such as substitution defects are located in specific energy states within the optical band gap of CuI films. According to density functional theory calculations, V in CuI films I (or V cu ) The activation enthalpy (ΔH) for the defect is V I For each ΔH = 0.5-0.1 eV (or V cu The range is 0.005-0.03 eV.

[0139] E extracted for charge transfer a This implies that Ag cation migration and Cu vacancies act as trap sites for ion hopping conduction associated with local states and transitions through them in the low-temperature region. However, the difference in activation energy observed in different temperature ranges (i.e., regions I and II) is due to the difference in the Ag cation mobility in the CuI film. + This may be due to the complex influence on the transport behavior associated with cations and trap states.

[0140] Therefore, one of the possible causes of the temperature-dependent conductivity change is speculated to be related to the point defects and non-chemical measurements present in the CuI film, which require further study. This leads to a decrease in V in the low-temperature range (203 K to 273 K). I and V cu It is likely that defects contribute significantly to charge transfer.

[0141]

[0142] ln(I / T) at applied voltages of 0.02 V, 0.04 V, 0.06 V, and 0.1 V 2 ) versus 1000 / T, the Richardson plot shows two distinct linear regions for high and low temperatures, respectively, and the calculated barrier height φ b can be extracted for each bias from the slope of these linear plots. In this way, the trend of the Schottky emission distance was evaluated from the slope of the Richardson plot (Fig. 11b).

[0143] For the ITO / CuI / Ag device, the obtained barrier height at the junction of CuI / Ag, φ b were calculated to be 210 meV (or 80 meV) for low (and high) temperatures, respectively. This suggests that the HRS current level occurs because of different Schottky barrier heights for the low-temperature and high-temperature regions (Fig. 11c).

[0144] A possible scenario is as follows: a Schottky contact is formed at the interface of the Ag and CuI layers, then Ag metal cations dissolved in the CuI layer act as charge carriers from the top electrode. In addition, Ag metal cations reduce the Schottky barrier height between Ag and CuI. Experimentally obtained E a The values ​​suggest that the HRS current in the low-temperature region is contributed only by traps and defect states (copper and iodine deficiency) present in the CuI active layer. Therefore, V I and V cu Defects are a major contributor to charge transfer in the low-temperature range (203 K to 273 K).

[0145]

[0146] The energy band diagram for low temperature (Fig. 9e) is V I and V cu It is shown that defects contribute significantly to charge transfer in the HRS state.

[0147] In addition, charge transfer in the high temperature region (273 K to 343 K) is carried out via hopping conduction in Ag as shown in the energy band diagram (Fig. 9f). + Controlled by the movement of cations and point defects.

[0148] That is, the HRS current in the high temperature region is distributed along with the Ag trap sites within the CuI film. + The tendency for cations to increase is due to increased mobility and increased hopping. These results are consistent with the Schottky emission-based mechanism reported in the literature for the HRS region.

[0149]

[0150] 2.4. Evaluation of the optically activated CuI memristor and demonstration as a flexible device

[0151] In particular, the capabilities of CuI as a photosensitive material have been actively reported in the literature. To confirm the photo-assisted multilevel states in CuI-based devices, the IV characteristics were evaluated under blue light (l = 455 nm) illumination (Fig. 12).

[0152] Figure 12a is a schematic diagram of the electrical and optical analyzer used to evaluate the optoelectronic characteristics of the ITO / CuI / Ag RRAM device.

[0153] The IV characteristics of the ITO / CuI / Ag-based device were evaluated for different power intensities under blue light irradiation (Fig. 12b), showing discrete HRS currents corresponding to the dark state and distinct illumination powers of blue light from 10% to 100%.

[0154] This demonstrates the practical sensitivity of CuI-based memory devices to a wavelength of 455 nm for light-assisted multilevel data storage. These results suggest that reproducible discrete current levels and multilevel HRS can be achieved by controlling both the illumination power intensity and wavelength of optoelectronic devices in an engineering mode.

[0155] Figure 12c shows the corresponding LRS and HRS under dark conditions with illumination levels of 50% and 100%. The LRS exhibits consistent behavior, with no change in both dark and bright conditions. However, the HRS current level exhibits three distinct steps under light exposure, ranging from 20 nA to 56 nA at a read voltage of 0.05 V, enabling light-assisted multilevel data storage.

[0156] Wavelength-dependent tests again highlight the response of CuI to blue light due to its direct band gap properties and various trap states (Fig. 13). In particular, illumination at different excitation wavelengths (λ = 355 nm, 540 nm, 656 nm, 740 nm, 850 nm, and 940 nm) did not induce repetitive RS (λ = 355 nm) or distinguishable HRS currents in ITO / CuI / Ag devices.

[0157] The IV characteristics of the ITO / CuI / Ag device showed almost complete recovery after successive cycling under dark, blue light, and dark conditions, as shown in Fig. 12d. In particular, the average V for dark and bright conditions set / reset was evaluated by measuring more than 50 assemblies (i.e., ITO / CuI / Ag device cells) as shown in Fig. 12(e, f).

[0158] V in both dark and light conditions set showed a normal distribution, with an average value of 0.313 V for dark conditions and 0.29 V for light conditions. However, the average V reset The V tended to decrease from -0.20 V to -0.13 V under blue light conditions, which shows that the uniformity of the reset behavior under lighting conditions increased. In conclusion, V set / reset The change in distribution was noticeably reduced under blue light, improving the device operability.

[0159] Figure 12g shows the time-dependent photoresponse of CuI for various illumination powers of 10%, 50%, and 100%.

[0160] The off current was 8 nA and increased to 13.9 nA, 22.04 nA, and 28 nA, respectively, corresponding to 10%, 50%, and 100% illumination in 0.2 s. The decay time to reach the off-state current level (8 nA), defined as 10% of the on-state current level in illumination, was consistently observed within 0.02 s, demonstrating the excellent optical properties of CuI.

[0161] However, a 10-15% decrease in photocurrent was observed during the light-on time, and the time constants for this were estimated to be 12.8 s, 13.4 s, and 13.9 s, corresponding to 10%, 50%, and 100% power illumination levels (Fig. 14).

[0162] V set or (V reset ) photocurrent decay and change (Fig. 12g) reaffirm the photo-assisted transport of point defects, suggesting charge carrier transport. However, a negligible persistent photocurrent effect was observed, suggesting that RRAM under illumination may be attractive for practical applications.

[0163] The changes in HRS current levels under blue light (455 nm) illumination were studied in detail with the help of band diagrams (Fig. 12(h, i)) for dark and light conditions, respectively.

[0164] During dark conditions, the HRS current level is Ag + attributed to the movement of ions and point defects. In contrast, photogenerated charge carriers, defects and trap states (i.e., V) present in CuI under illumination Cu , V I , Cu I and I Cu ) contributes to the current level of HRS.

[0165] As shown in Fig. 12i, a possible mechanism related to blue illumination is V located near the valence band. Cu It matches well with the interband transition and transition-related trap levels near the conduction band edge.

[0166]

[0167] To address the practical aspects of CuI RRAM, we successfully demonstrated a flexible ITO / CuI / Ag RRAM device fabricated on a PET / ITO substrate.

[0168] Figures 15(a, b) show schematic and schematic images of a flexible configuration of CuI-based RRAM. Figure 15(c) shows the IV characteristics of an ITO / CuI / Ag device on a flexible substrate for 100 cycles at various bending radii: 10.8 mm, 6.6 mm, and 4.5 mm.

[0169] Effective RS performance was observed without noticeable degradation even after bending the substrate at a high bending radius corresponding to 4.55 and tensile strain δ = 0.83% (Fig. 16(ad)).

[0170] As shown in Fig. 15d, continuous RS cycling was evaluated for 30 cycles at different bending radii of 10.8 mm and 6.6 mm, and 40 cycles at extreme bending of 4.5 mm. The ITO / CuI / Ag device exhibited excellent flexible performance, with no noticeable degradation in RS performance such as HRS, LRS, On / Off ratio, or set or reset voltage. Despite extreme bending over the past 40 cycles at a radius of 4.5 mm, only marginal changes in LRS were observed, although other RS ​​characteristics were successfully maintained.

[0171] Long-term stability is crucial for the successful operation of non-volatile memories in practical applications. Ag is a well-known electrochemically active metal that readily reacts with CuI to form AgX, which degrades device performance over time. Therefore, the IV characteristics of ITO / CuI / Ag devices were investigated for up to 15 days to evaluate the short-term lifetime associated with device lifespan with PMMA encapsulation without passivation (Fig. 17). In the non-passive configuration, the ITO / CuI / Ag device completely lost its RS performance within 5 days (Fig. 17(a-c)).

[0172] The IV characteristics of the ITO / CuI / Ag devices began to show significant degradation on the second day of device fabrication. However, the encapsulated ITO / CuI / Ag / PMMA devices successfully maintained their RS performance for more than 15 days without significant changes in HRS and LRS values ​​even in ambient conditions.

[0173] Furthermore, CuI is highly sensitive to humidity, causing rapid degradation of the CuI film when exposed to ambient air. Moisture in the air can accelerate degradation by triggering a reaction between CuI and Ag. Apparently, the rapid degradation of the memory device is a result of the top Ag metal electrode reacting with the CuI layer, ultimately leading to overactivation in the presence of moisture under ambient conditions. This can hinder the reliable performance of CuI in ambient conditions.

[0174] Among various encapsulation methods, PMMA overcoating followed by further annealing is widely used as a convenient method to block moisture diffusion and improve short-term device lifetime in various applications.

[0175] Therefore, in the present invention, a similar PMMA encapsulation method was adopted for CuI RRAM, and the encapsulated device with the ITO / CuI / Ag / PMMA configuration showed better operational durability.

[0176] Figure 17(df) shows the IV characteristics of a PMMA passive ITO / CuI / Ag device in air, confirming the long-term operational stability of the RRAM device even after 15 days. PMMA encapsulation, frequently used in low-dimensional carbon nanotube (or air-sensitive thin film) transistors, effectively prevents moisture penetration onto the CuI / Ag film surface.

[0177] The PMMA encapsulated devices consequently exhibited stable RS, which ensured a decrease in the reaction rate of the CuI layer with the upper Ag electrode.

[0178] In conclusion, PMMA encapsulation can effectively minimize device performance degradation, allowing device characterization at low temperatures and preserving RS performance CuI-based memory devices for long lifetimes.

[0179]

[0180] 3. Conclusion

[0181] We have developed photo-mediated two-component halide CuI RRAMs with an operating voltage of less than 0.5 V using CuI films developed through a solid-state iodization process, without a formation process. This device system for CuI RRAMs is expected to open up photo-mediated multifunctional analog (and / or digital) circuit systems and further support desirable increases in NVM memory density.

[0182] The present invention contributes to the development of planned applications requiring ultra-low power and extreme memory density, such as autonomous driving and neuromorphic (or security) systems with embedded PIM. The CuI RRAMs were encapsulated using conventional PMMA to allow low-temperature characterization. The results revealed key parameters (e.g., activation energy, Schottky barrier height, etc.) and elucidated the fundamental mechanisms of current conduction related to point defects and the RS mechanism.

[0183] These results are consistent with the mobility and mobility of silver ions, device lifetime, and other characteristics. Furthermore, the present invention successfully demonstrated the photomemory effect for flexible RRAM and RRAM by utilizing the optoelectronic properties of CuI. These results open the way for applications in various Internet of Things (IoT) devices, including flexible, wearable, and smart electronic devices.

[0184] The present invention is expected to advance the understanding of CuI and other halide-based RRAMs for low-voltage RS and to demonstrate their potential wide-ranging applications in memory technologies requiring ultra-low power consumption for next-generation computing systems.

[0185]

[0186] The present invention described above is not limited to the above-described embodiments, as various substitutions and changes can be made within the scope of the technical idea of ​​the present invention by a person having ordinary skill in the art to which the present invention pertains.

Claims

1. Base board; A lower electrode disposed on the base substrate; a resistance change layer disposed on the lower electrode; and An upper electrode disposed on the resistance change layer; The above resistance change layer includes copper iodide (CuI), which is a binary halide. Multilevel resistive random access memory device based on photoreactivity.

2. In paragraph 1, The above copper iodide (CuI) has a zinc blende, Marshite crystal structure, and is a multi-level resistive random access memory element due to its photoreactivity.

3. In paragraph 1, A multi-level resistive random access memory device based on photoreactivity, wherein the base substrate is a flexible substrate.

4. In paragraph 1, The upper electrode is a multi-level resistive random access memory element due to photoreactivity, which includes silver (Ag).

5. In paragraph 1, A photoreactive multi-level resistive random access memory device, wherein the lower electrode comprises at least one selected from the group consisting of indium oxide (ITO), gold (Au), platinum (Pt), nickel (Ni), and molybdenum (Mo).

6. In paragraph 1, A multi-level resistive random access memory device based on photoreactivity, wherein the upper electrode and the resistance change layer make Schottky contact at the interface.

7. In paragraph 6, A multi-level resistive random access memory device due to photoreactivity, wherein the metal cations of the upper electrode reduce the Schottky barrier height.

8. In paragraph 1, A photoreactive multi-level resistive random access memory device further comprising a passive layer comprising any one of poly(methyl metacrylate) (PMMA), CYTOP, SU-8, silicon oxide (SiO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), hafnium oxide (HfO2), yttrium oxide (Y2O3), zirconium oxide (ZrO2), polyvinyl pyridine (PVP), polyvinyl alcohol (PVA), polyvinyl phenol (PVP), polydimethyl siloxane (PDMS), polystyrene (PS), BCB, and polyvinyl naphthylene (PVN).

9. Step of preparing a base substrate with a lower electrode formed on the upper side; A step of depositing a copper (Cu) film on the lower electrode; A step of forming a resistance change layer containing copper iodide (CuI) on the lower electrode by reacting the copper (Cu) film with iodine (I); and A step of forming an upper electrode on the resistance change layer; The step of forming a resistance change layer containing copper iodide (CuI) on the lower electrode is performed by vacuum-driven iodine evaporation at room temperature. A method for fabricating a multi-level resistive random access memory device based on photoreactivity.

10. In paragraph 9, The above copper iodide (CuI) has a zinc blende, Marshite crystal structure, and a method for manufacturing a multi-level resistive random access memory device due to photoreactivity.

11. In paragraph 9, A method for manufacturing a multi-level resistive random access memory device due to photoreactivity, wherein the base substrate is a flexible substrate.

12. In paragraph 9, A method for manufacturing a multi-level resistive random access memory device due to photoreactivity, wherein the upper electrode comprises silver (Ag).

13. In paragraph 9, A method for manufacturing a multi-level resistive random access memory device due to photoreactivity, wherein the lower electrode comprises at least one selected from the group consisting of indium oxide (ITO), gold (Au), platinum (Pt), nickel (Ni), and molybdenum (Mo).

14. In paragraph 9, A method for manufacturing a multi-level resistive random access memory device based on photoreactivity, wherein the upper electrode and the resistance change layer make Schottky contact at the interface.

15. In paragraph 14, A method for manufacturing a multi-level resistive random access memory device due to photoreactivity, wherein the metal cations of the upper electrode reduce the Schottky barrier height.

16. In paragraph 9, After the step of forming an upper electrode on the resistance change layer, a photoreactive multi-level resistive random access memory element is further provided with a passive layer comprising any one of poly(methyl methacrylate) (PMMA), CYTOP, SU-8, silicon oxide (SiO2), tantalum oxide (Ta2O5), titanium oxide (TiO2), hafnium oxide (HfO2), yttrium oxide (Y2O3), zirconium oxide (ZrO2), polyvinyl pyridine (PVP), polyvinyl alcohol (PVA), polyvinyl phenol (PVP), polydimethyl siloxane (PDMS), polystyrene (PS), BCB, and polyvinyl naphthylene (PVN). Memory device.

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