Ag Top Electrode Research Articles

GeTe/MoTe2 Van der Waals Heterostructures: Enabling Ultralow Voltage Memristors for Nonvolatile Memory and Neuromorphic Computing Applications.

Advanced electronic semiconducting Van der Waals heterostructures (HSs) are promising candidates for exploring next-generation nanoelectronics owing to their exceptional electronic properties, which present the possibility of extending their functionalities to diverse potential applications. In this study, GeTe/MoTe2 HS are explored for nonvolatile memory and neuromorphic-computing applications. Sputter-deposited Ag/GeTe/MoTe2/Pt HS cross-point devices are fabricated, and they demonstrate memristor behavior at ultralow switching voltages (VSET: 0.15V and VRESET: -0.14V) with very low energy consumption (≈30 nJ), high memory window, long retention time (104 s), and excellent endurance (105 cycles). Resistive switching is achieved by adjusting the interface between the Ag top electrode and the heterojunction switching layer. Cross-sectional transmission electron microscope images and conductive atomic force microscopy analysis confirm the presence of a conducting filament in the heterojunction switching layer. Further, emulating various synaptic functions of a biological synapse reveals that GeTe/MoTe2 HS can be utilized for energy-efficient neuromorphic-computing applications. A multilayer perceptron is implemented using the synaptic weights of the Ag/GeTe/MoTe2/Pt HS device, revealing high pattern accuracy (81.3%). These results indicate that HS devices can be considered a potential solution for high-density memory and artificial intelligence applications.

Tunable distributed Bragg reflector developed by magnetron sputtering to improve the power conversion efficiency of transparent IR cells for solar energy harvesting applications

Transparent organic photovoltaic (TOPV) cells integrated into windows are key to reducing the carbon dioxide emissions associated with the building sector. However, TOPV cells that reach a compromise between efficiency and transparency must still be developed. In addition, to implement this technology in glass production companies, the materials and processes used in TOPV cell development must be compatible with producing these devices on an industrial scale. Here, an infrared (IR) cell combining a PC60BM-based active material, ITO/ZnO as the back transparent electrode, PEDOT:PSS and ITO or Ag as the top transparent electrode, and a DBR as an antireflective coating was developed and applied on 625 mm2 glass samples. The structure of the DBR based on titanium dioxide (TiO2) and silicon dioxide (SiO2) monolayers was adjusted to the IR cell absorption spectra to reach a power conversion efficiency (PCE) of 5 and 4.3, and an average visible transmission (AVT) of 41 % and 51 % for ITO and Ag top electrodes, respectively. The manufacturing route of these devices involved commercial polymers and coatings that can be deposited by technologies already applied in the glass industry, such as magnetron sputtering or thermal evaporation. Therefore, the IR cells developed here showed a good compromise between efficiency, transparency, and large-scale production manufacturability.

Investigations on structural, morphological and UV light detection characteristics in p- ZrO2/ n-Si Heterostructure based devices

The development of hetero-structured based UV photodiode is a rapidly growing interest in the area of optoelectronic applications. In recent years, one of the next generation semiconductor material zirconium dioxide (ZrO2), has attracted much attention for UV photodiode applications. The curent research work focuses on the fabrication of ultraviolet (UV) photodetectors using ZrO2 nanocrystals with different molar concentrations. Using the co-precipitation method, ZrO2 nanocrystals were formed onto n-Si substrate. The prepared ZrO2 nanocrystals were characterized by XRD, UV–visible spectroscopy, FeSEM, HRTEM, PL spectroscopic analysis. The structural analysis of ZrO2 nanoparticles shows the cubic space groups with ((Fm-3m, Z = 4) and (Im-3m, Z = 1) respectively. The morphological analysis reveals the irregular shape and highly agglomerated. The TEM and HR-TEM images, and SAED pattern of ZrO2 NPs were obtained at higher mole concentration. The optical energy band gap of ZrO2 nanocrystals were determined in between 3.12 and 2.86 eV. The PL emission spectrum of ZrO2 nanoparticles shows highly intensive emission bands between 360 nm and 520 nm. The optimum ZrO2 (0.3 M) nanocrystal layers were formed onto n-Si substrate which was stacked between top and bottom Ag electrodes. The current-voltage measurements (I–V) plots and ln J-V plots characteristics of the fabricated Ag/p-ZrO2/n-Si/Ag devices were investigated under dark and UV illumination. The p-ZrO2/n-Si junction diodes exhibit the ideal rectifying function at higher molar concentration of ZrO2 diode, and the reverse saturation with maximum photo sensitivity was investigated.

Stable and repeatable ZrO2 RRAM achieved by NiO barrier layer for negative set phenomenon elimination

Resistive random-access memory (RRAM) is a promising non-volatile memory technology due to its fast operation, low power consumption, and high reliability. However, the negative set phenomenon remains a challenge for RRAM, which can lead to the deterioration of device switching parameters. In this study, we successfully addressed this issue by inserting a NiO blocking layer between the ZrO2 and Ag top electrodes in ZrO2-based RRAM. In addition, the resistive switching characteristics of the device are significantly enhanced by the incorporation of a p-type oxide NiO layer. Compared to single-layer ZrO2 devices, the double-layer Ag/NiO/ZrO2/ITO RRAM exhibits improved cycling durability (>500 cycles) and good retention time (3 × 104s). Our analysis of the device conduction mechanism and proposed resistive switching model suggest that oxygen vacancies play a connecting role in the reset process, leading to failed reset behavior. Through the incorporation of a p-type semiconductor NiO layer into ZrO2-based RRAMs, the interference of oxygen vacancies on the reset process can be effectively impeded. This approach not only provides an effective resolution to the unforeseen negative set phenomenon in RRAM devices, but it also holds paramount significance for the advancement of high-performance RRAMs.

Effect of Electrochemically Active Top Electrode Materials on Nanoionic Conductive Bridge Y2O3 Random-Access Memory.

Herein, sol-gel-processed Y2O3 resistive random-access memory (RRAM) devices were fabricated. The top electrodes (TEs), such as Ag or Cu, affect the electrical characteristics of the Y2O3 RRAM devices. The oxidation process, mobile ion migration speed, and reduction process all impact the conductive filament formation of the indium-tin-oxide (ITO)/Y2O3/Ag and ITO/Y2O3/Cu RRAM devices. Between Ag and Cu, Cu can easily be oxidized due to its standard redox potential values. However, the conductive filament is easily formed using Ag TEs. After triggering the oxidation process, the formed Ag mobile metal ions can migrate faster inside Y2O3 active channel materials when compared to the formed Cu mobile metal ions. The fast migration inside the Y2O3 active channel materials successfully reduces the SET voltage and improves the number of programming-erasing cycles, i.e., endurance, which is one of the nonvolatile memory parameters. These results elucidate the importance of the electrochemical properties of TEs, providing a deeper understanding of how these factors influence the resistive switching characteristics of metal oxide-based atomic switches and conductive-metal-bridge-filament-based cells.

All-printed organic photodetectors with metal electrodes enabled by one-step solvent-mediated transfer printing technology.

A one-step solvent-mediated transfer printing technology (sTPT) is proposed to fabricate printable silver (Ag) electrodes. This simple approach can realize the residuals in the active layer serving as the mediator due to the capillary action without the use of any additional solvent. The as-cast polydimethylsiloxane (PDMS) was used as the stamp in the fabrication process. The residual solvent and the as-cast PDMS stamps simplified the fabrication process, while the transfer-printed Ag electrodes presented favorable conductivity and improved hydrophobicity due to the presence of residual PDMS on the surface of Ag, indicating the superiority as the top electrode for organic photodetectors (OPDs). Compared to the devices with the top Ag electrodes fabricated by the conventional evaporation method, we demonstrated that the OPDs with transfer-printed Ag electrodes presented better performance than that of the reference devices, including suppressed dark current, enlarged linear dynamic range, shortened response time, and optimized durability. These improved performances can be attributed to the fewer traps at the interface between the active layer and Ag electrodes. The sTPT may be a promising method for the fabrication of OPDs owing to the simplified fabrication process and enhanced device performance.

Improving the Uniformity of Top Emitting Organic Light Emitting Diodes Using a Hybrid Electrode Structure

AbstractSome applications of organic light‐emitting diodes (OLEDs) require large area, high light output, and high uniformity. It is difficult to achieve these attributes simultaneously because of voltage drops in the contacts, which cannot easily satisfy high optical transparency and electrical conductivity simultaneously. In large area OLEDs, thin electrodes with high sheet resistance induce voltage drops across the devices, leading to non‐uniform distribution of light. However, thick electrodes with low sheet resistance decrease the light output due to low transmittance. To overcome this trade‐off, a multilayer hybrid electrode based on Ag (20 nm)/WO3/Ag (20 nm)/WO3 is designed to obtain high electrical conductance with low optical loss. Compared to conventional devices using a single Ag (40 nm) top electrode, there is a considerable increase in the external quantum efficiency (EQE) of the device using this electrode (from 11.5% to 25.5% at 1000 cd m−2), while maintaining similar sheet resistance. In addition, a large area (≈57 cm2) OLED with the hybrid electrode demonstrates a luminance uniformity of 77% as compared to a device using single silver electrode with uniformity of 66%. Therefore, the proposed Ag/WO3/Ag/WO3 hybrid electrode is a promising choice for the fabrication of efficient and uniform large‐area OLEDs.

Impact of Top Electrodes (Cu, Ag, and Al) on Resistive Switching behaviour of Cu-rich Cu2ZnSnS4 (CZTS) Ideal Kesterite.

Cu2ZnSnS4 (CZTS) active material-based resistive random-access memory (RRAM) devices are investigated to understand the impact of three different Cu, Ag, and Al top electrodes. The dual resistance switching (RS) behaviour of spin coated CZTS on ITO /Glass is investigated up to 102 cycles. The stability for all the devices (Cu/CZTS/ITO, Ag/CZTS/ITO, and Al/CZTS/ITO) is investigated up to 103 s in low- (LRS) and high- (HRS) resistance states at 0.2 V read voltage. The endurance up to 102 cycles with 30 ms switching width is showing the stable write and erase current. Weibull cumulative distribution plots suggest that Ag top electrode is relatively more stable for set and reset state with 33.61 and 25.02 shape factors, respectively. The charge carrier transportation is explained by double logarithmic plots, Schottky emission plots, and band diagrams, substantiating that at lower applied electric field intrinsic copper ions dominate in Cu/CZTS/ITO, whereas, at higher electric filed, top electrodes (Cu and Ag) dominate over intrinsic copper ions. Intrinsic Cu+ in CZTS plays a decisive role in resistive switching with Al electrode. Further the impedance spectroscopy measurements suggest that Cu+ and Ag+ diffusion is the main source for the resistive switching with Cu, and Ag electrodes.

Electrical properties and defect analysis of MAPbI3 thin films grown on TiO2 layer through a two-step drying process

We studied the electrical properties and defect states of methylammonium lead iodide perovskite (MAPbI3) thin film grown onto the TiO2 layer at a temperature of 120 °C via a two-step drying process. The TiO2 layer with thickness of 20 nm were formed on fluorine doped tin oxide/glass at 120 °C via atomic layer deposition. The MAPbI3 thin film showed α-phase structure with band gap energy of about 1.61 eV. For the MAPbI3/TiO2 with Ag top and bottom electrodes, the resistance switching phenomena were enhanced compared to the MAPbI3 film without the TiO2 layer. In the MAPbI3/TiO2, two deep level states of E1(Ec-0.38 eV) and H2 (Ev+0.82 eV) appeared from deep level transient spectroscopy measurements. The defect states of E1 and H2 are related to iodine interstitial (Ii) and iodine antisite (IPb), respectively. In the MAPbI3/TiO2, the defect of Ii appeared as the ionized states of Ii+ or Ii−, so that it was found that the defect state of Ii caused the MAPbI3/TiO2 to have the resistance random access memory property by the migration of the ionized states.

Stable resistive switching behavior of polyvinyl alcohol coating film-based memristor under multiple operating voltages by doping AgNWs

The integration of memristive effect devices for both information storage and computation can enhance the efficiency and performance of artificial intelligence (AI) systems，the memristors based on various polymers as functional layers show high application prospects. This research introduces 5 wt% silver nanowires (AgNWs) doping into the polyvinyl alcohol (PVA) memristor device, which enables stable resistive switching (RS) behavior across multiple operating voltages. Defects from PVA and AgNWs are counterbalanced by Ag ions stimulated by AgNWs and Ag top electrode, thus reducing conductive path randomness. The device demonstrates excellent cycle durability for 300 cycles and data retention for up to 104 s. Analysis of the I-V characteristic curve reveals that the current conduction mechanism is mainly related to Ohmic conduction, Space-charge-limited conduction (SCLC), and Schottky emission mechanisms. The AgNWs simplify the structure of conductive filaments (CFs) and facilitate the formation and breakage of CFs dominated by Ag atoms, leading to the conversion between HRS and LRS of the device.

A Novel Anthracene Derivative Used as Cathode Interlayer for Efficient Inverted Perovskite Solar Cell

Metal halide hybrid perovskite solar cells have recently emerged as a highly cost‐effective photovoltaic technology. The cathode interlayer plays a critical role in aligning energy levels and promoting charge extraction in inverted perovskite solar cells. Herein, a novel multinitrogen derivative interlayer, Anth‐hpp2, is designed and synthesized consisting of 1,1'‐(4‐(9,10‐di(naphthalen‐2‐yl)anthracen‐2‐yl)pyridine‐2,6‐diyl)bis(1,3,4,6,7,8‐hexahydro‐2H‐pyrimido[1,2‐a] pyrimidine), between the PCBM and top Ag electrode. The superbase group in Anth‐hpp2 effectively contacts the silver electrode, reducing the work function of Ag. Consequently, the power conversion efficiency of the Anth‐hpp2‐based device improved from 16.05% to 20.37%, along with enhancements in short‐circuit current and fill factor. The stabilities of perovskite solar cells are measured with Anth‐hpp2 under N2 storage, and the device efficiency with Anth‐hpp2 decayed by only 5% after fabrication for approximately 2500 h, which is five times that of the control device. This study provides original insights into designing new cathode interlayer materials.

Stopping Voltage‐Dependent PCM and RRAM‐Based Neuromorphic Characteristics of Germanium Telluride

AbstractRecently, phase change chalcogenides, such as monochalcogenides, are reported as switching materials for conduction‐bridge‐based memristors. However, the switching mechanism focused on the formation and rupture of an Ag filament during the SET and RESET, neglecting the contributions of the phase change phenomenon and the distribution and re‐distribution of germanium vacancies defects. The different thicknesses of germanium telluride (GeTe)‐based Ag/GeTe/Pt devices are investigated and the effectiveness of phase loops and defect loops future application in neuromorphic computing are explored. GeTe‐based devices with thicknesses of 70, 100, and 200 nm, are fabricated and their electrical characteristics are investigated. Highly reproducible phase change and defect‐based characteristics for a 100 nm‐thick GeTe device are obtained. However, 70 and 200 nm‐thick devices are unfavorable for the reliable memory characteristics. Upon further analysis of the Ag/GeTe/Pt device with 100 nm of GeTe, it is discovered that a state‐of‐the‐art dependency of phase loops and defect loops exists on the starting and stopping voltage sweeps applied on the top Ag electrode. These findings allow for a deeper understanding of the switching mechanism of monochalcogenide‐based conduction‐bridge memristors.

Evaluation of Cellulose-MXene Composite Hydrogel Based Bio-Resistive Random Access Memory Material as Mimics for Biological Synapses.

We report a memory device based on organic-inorganic hybrid cellulose-Ti3C2TX MXene composite hydrogel (CMCH) as a switching layer sandwiched between Ag top and FTO bottom electrodes. The device (Ag/CMCH/FTO) was fabricated by a simple, solution-processed route and exhibits reliable and reproducible bipolar resistive switching. Multilevel switching behavior was observed at low operating voltages (±0.5 to ±1 V). Furthermore, the capacitive-coupled memristive characteristics of the device were corroborated with electrochemical impedance spectroscopy and this affirmed the filamentary conduction switching mechanism (LRS-HRS). The synaptic functions of the CMCH-based memory device were evaluated, wherein potentiation/depression properties over 8 × 103 electric pulses were observed. The device also exhibited spike time-dependent plasticity-based symmetric Hebbian learning rule of a biological synapse. This hybrid hydrogel is expected to be a potential switching material for low-cost, sustainable, and biocompatible memory storage devices and artificial synaptic applications.

Systematic Investigation of Core and Endcap Selection on the Development of Functional π-Conjugated Materials

We investigate the optoelectronic properties of four new π-conjugated materials, which feature either a 3,4-ethylenedioxythiophene (EDOT) or an EDOT-flanked benzothiadiazole aryl core with two N-annulated perylene diimide (NPDI) or theobromine endcaps. Endcap selection was an important factor for the preferred molecular geometry, where the use of NPDI endcaps induced a dragonfly-type conformation and the use of theobromine endcaps promoted a corkscrew-like conformation. Electrochemically, the choice of aryl π-conjugated core was found to have a strong influence on the molecule’s highest occupied molecular orbital (HOMO) energy level, while the choice of endcap had a more profound effect on the lowest unoccupied molecular orbital (LUMO) energy level. Although the optical absorption profiles were generally dominated by endcap contributions, using the larger EDOT-flanked benzothiadiazole aryl core was found to decrease the optical energy band gap. Proof-of-concept organic photovoltaic (OPV) devices, using a PM6:Y6 bulk heterojunction (BHJ) photoactive layer, were fabricated using the four new π-conjugated materials as the cathode interlayer (CIL). The molecules featuring the EDOT aryl core (A and B) enabled OPV device power conversion efficiencies (PCEs) by around 12%, comparable to control devices using PDINN as the CIL, while those featuring the EDOT-flanked benzothiadiazole aryl core (C and D) obtained PCEs of 10.5%. The observed differences in OPV device performance were attributed to superior solubility and subsequent CIL film formation in the case of A and B, compared to C and D, which, in turn, led to improved contact between the Ag top electrode and the BHJ photoactive layer.

Flexible Memristor Devices Using Hybrid Polymer/Electrodeposited GeSbTe Nanoscale Thin Films.

We report on the development of hybrid organic-inorganic material-based flexible memristor devices made by a fast and simple electrochemical fabrication method. The devices consist of a bilayer of poly(methyl methacrylate) (PMMA) and Te-rich GeSbTe chalcogenide nanoscale thin films sandwiched between Ag top and TiN bottom electrodes on both Si and flexible polyimide substrates. These hybrid memristors require no electroforming process and exhibit reliable and reproducible bipolar resistive switching at low switching voltages under both flat and bending conditions. Multistate switching behavior can also be achieved by controlling the compliance current (CC). We attribute the switching between the high resistance state (HRS) and low resistance state (LRS) in the devices to the formation and rupture of conductive Ag filaments within the hybrid PMMA/GeSbTe matrix. This work provides a promising route to fabricate flexible memory devices through an electrodeposition process for application in flexible electronics.

(Digital Presentation) Oxide Memristors Based on SiO2 with Cu/Ag Alloy Metallization for Neuromorphic Computing

By mimicking biomimetic synaptic processes, the success of artificial intelligence (AI) has been astounding with various applications such as driving automation, big data analysis, and natural-language processing.[1-4] Due to a large quantity of data transmission between the separated memory unit and the logic unit, the classical computing system with von Neumann architecture consumes excessive energy and has a significant processing delay.[5] Furthermore, the speed difference between the two units also causes extra delay, which is referred to as the "memory wall".[6, 7] To keep pace with the rapid growth of AI applications, enhanced hardware systems that particularly feature an energy-efficient and high-speed hardware system need to be secured. The novel neuromorphic computing system, an in-memory architecture with low power consumption, has been suggested as an alternative to the conventional system. Memristors with analog-type resistive switching behavior are a promising candidate for implementing the neuromorphic computing system since the devices can modulate the conductance with cycles that act as synaptic weights to process input signals and store information.[8, 9]The memristor has sparked tremendous interest due to its simple two-terminal structure, including top electrode (TE), bottom electrode (BE), and an intermediate resistive switching (RS) layer. Many oxide materials, including HfO2, Ta2O5, and IGZO, have extensively been studied as an RS layer of memristors. Silicon dioxide (SiO2) features 3D structural conformity with the conventional CMOS technology and high wafer-scale homogeneity, which has benefited modern microelectronic devices as dielectric and/or passivation layers. Therefore, the use of SiO2 as a memristor RS layer for neuromorphic computing is expected to be compatible with current Si technology with minimal processing and material-related complexities.In this work, we proposed SiO2-based memristor and investigated switching behaviors metallized with different reduction potentials by applying pure Cu and Ag, and their alloys with varied ratios. Heavily doped p-type silicon was chosen as BE in order to exclude any effects of the BE ions on the memristor performance. We previously reported that the selection of TE is crucial for achieving a high memory window and stable switching performance. According to the study which compares the roles of Cu (switching stabilizer) and Ag (large switching window performer) TEs for oxide memristors, we have selected the TE materials and their alloys to engineer the SiO2-based memristor characteristics. The Ag TE leads to a larger memory window of the SiO2 memristor, but the device shows relatively large variation and less reliability. On the other hand, the Cu TE device presents uniform gradual switching behavior which is in line with our previous report that Cu can be served as a stabilizer, but with small on/off ratio.[9] These distinct performances with Cu and Ag metallization leads us to utilize a Cu/Ag alloy as the TE. Various compositions of Cu/Ag were examined for the optimization of the memristor TEs. With a Cu/Ag alloying TE with optimized ratio, our SiO2 based memristor demonstrates uniform switching behavior and memory window for analog switching applications. Also, it shows ideal potentiation and depression synaptic behavior under the positive/negative spikes (pulse train).In conclusion, the SiO2 memristors with different metallization were established. To tune the property of RS layer, the sputtering conditions of RS were varied. To investigate the influence of TE selections on switching performance of memristor, we integrated Cu, Ag and Cu/Ag alloy as TEs and compared the switch characteristics. Our encouraging results clearly demonstrate that SiO2 with Cu/Ag is a promising memristor device with synaptic switching behavior in neuromorphic computing applications. Acknowledgement This work was supported by the U.S. National Science Foundation (NSF) Award No. ECCS-1931088. S.L. and H.W.S. acknowledge the support from the Improvement of Measurement Standards and Technology for Mechanical Metrology (Grant No. 22011044) by KRISS.

Improved Environment Stability of Y2O3 RRAM Devices with Au Passivated Ag Top Electrodes.

In this study, we fabricated sol-gel-processed Y2O3-based resistive random-access memory (RRAM) devices. The fabricated Y2O3 RRAM devices exhibited conventional bipolar RRAM device characteristics and did not require the forming process. The long-term stability of the RRAM devices was investigated. The Y2O3 RRAM devices with a 20 nm thick Ag top electrode showed an increase in the low resistance state (LRS) and high resistance state (HRS) and a decrease in the HRS/LRS ratio after 30 days owing to oxidation and corrosion of the Ag electrodes. However, Y2O3 RRAM devices with inert Au-passivated Ag electrodes showed a constant RRAM device performance after 30 days. The 150 nm-thick Au passivation layer successfully suppressed the oxidation and corrosion of the Ag electrode by minimizing the chance of contact between water or oxygen molecules and Ag electrodes. The Au/Ag/Y2O3/ITO RRAM devices exhibited more than 300 switching cycles with a decent resistive window (>103). They maintained constant LRS and HRS resistances for up to 104 s, without significant degradation of nonvolatile memory properties for 30 days while stored in air.

A synaptic memristor based on natural organic honey with neural facilitation

Neural facilitation is an essential activity-dependent synaptic plasticity in most chemically transmitting synapses. Emerging artificial synaptic devices need to be capable of emulating this function in order to be used in brain-inspired neuromorphic computing systems. In this paper, neural facilitation in natural organic honey based synaptic memristor was investigated. The memristive layer was fabricated by commercially purchased honey via a solution-based process and sandwiched in between Al top electrode and ITO bottom electrode. Two process conditions, 90 °C/8 h and 140 °C/2 h were applied to dry the honey thin film for comparison. Test results show that both devices demonstrated bipolar resistive switching and neural facilitation behaviors, while the memristor with the honey film dried by 90 °C/8 h demonstrated a larger on/off ratio and read memory window, lower current at high-resistant state, and larger facilitation index. The index is also larger than our previously reported honey-memristor with same drying conditions but Ag top electrode, and memristors based on other natural organic materials such as chicken albumen and lignin. The index decayed following two exponential phases as a function of the interval time of the two stimulation voltage pulses, which is similar to biological synapses. Besides shorter pulse interval time, the response of facilitation also enhanced by larger magnitude and width of the stimulation voltage pulses. • Synaptic neural facilitation of honey-based memristor was investigated. • Largest facilitation gain in natural organic memristors was achieved. • The gains decay with pulse interval time, similar to biological synapses. • Larger pulse magnitude and pulse width, short interval of stimuli enhance the gain.

Robust resistive switching in MoS2-based memristor with Ti top electrode

Nonvolatile memories based on two-dimensional nanomaterials are of significant interest to researchers attempting to achieve robust resistive switching (RS) with simple device integration and low energy consumption. In this study, the RS behavior of a MoS2-based memristor was investigated using Ti and Ag as top electrodes (TEs). Compared with the memristor using the Ag TE, that employing the Ti TE not only exhibited substantially enhanced and reproducible endurance performance for up to 104 cycles, but also showed excellent operational uniformity with a coefficient of variation limited to 3.5% and 4.0% for SET and RESET voltages, respectively. Moreover, the Ti TE memristor demonstrated RS behavior after 1 month of storage under ambient conditions. The formation of a TixSy layer at the Ti/MoS2 interface and the presence of an abundant 1T phase MoS2 (or S vacancy, VS) in the initial state of the MoS2 film contribute to its distinctive properties. This work indicates that suitable TE selection can enable the fabrication of high-performance nonvolatile MoS2-based memristors.

Multi-Level Resistive Switching in SnSe/SrTiO3 Heterostructure Based Memristor Device.

Multilevel resistive switching in memristive devices is vital for applications in non-volatile memory and neuromorphic computing. In this study, we report on the multilevel resistive switching characteristics in SnSe/SrTiO3(STO) heterojunction-based memory devices with silver (Ag) and copper (Cu) top electrodes. The SnSe/STO-based memory devices present bipolar resistive switching (RS) with two orders of magnitude on/off ratio, which is reliable and stable. Moreover, multilevel state switching is achieved in the devices by sweeping voltage with current compliance to SET the device from high resistance state (HRS) to low resistance state (LRS) and RESET from LRS to HRS by voltage pulses without compliance current. With Ag and Cu top electrodes, respectively, eight and six levels of resistance switching were demonstrated in the SnSe/SrTiO3 heterostructures with a Pt bottom electrode. These results suggest that a SnSe/STO heterojunction-based memristor is promising for applications in neuromorphic computing as a synaptic device.