Non-volatile Resistive Switching Device Research Articles

A Singlet-Diradical Co(III)-Dimer as a Nonvolatile Resistive Switching Device: Synthesis, Redox-Induced Interconversion, and Current-Voltage Characteristics.

Herein we report a ligand-centered redox-controlled strategy for the synthesis of an unusual binuclear diradical cobalt(III) complex, [Co2III(L•3-)2] (1), featuring two three-electron reduced trianionic monoradical 2,9-bis(phenyldiazo)-1,10-phenanthroline ligands (L•3-) and two intermediate-spin cobalt(III) centers having a Co-Co bond. Controlled ligand-centered oxidation of 1 afforded two mononuclear complexes, [CoII(L•-)(L0)]+ ([3])+ and [CoII(L0)2]2+ ([2]2+), which upon further ligand-centered reduction yielded a di-azo-anion diradical complex, [CoII(L•-)2] (4). In complex 1, two three-electron reduced di-azo-anion monoradical ligands (L•3-) bridge two intermediate Co(III) centers at a distance of 2.387(2) Å, while upon oxidation, one of the coordinating azo-arms of L becomes pendent, and in complexes [2]2+, [3]+, and 4, two tetradentate ligands coordinate a single Co(II) center in a tridentate meridional fashion with one uncoordinated azo-arm from each of the ligands. In the presence of reducing agents, the monomers [2]2+, [3]+, and 4 undergo ligand-centered reduction to form azo-anion radicals, and the otherwise pendent azo-arms in the presence of cobalt(II)-salts like Co(ClO4)2 or CoCl2 bind the second Co(II)-ion; further internal electron transfer from the cobalt center to the arylazo backbone produces the binuclear complex 1. Spectroscopic analysis, DFT studies, and control experiments were performed to understand the electronic structures and the ligand-centered redox-controlled interconversion. The application of complex 1 as a molecular memory device (memristor) was also explored. Complex 1 showed encouraging results as a memristor with a current ON/OFF ratio > 104 and is highly promising for resistive RAM/ROM applications.

Stable Resistive Switching in ZnO/PVA:MoS2 Bilayer Memristor.

Reliability of nonvolatile resistive switching devices is the key point for practical applications of next-generation nonvolatile memories. Nowadays, nanostructured organic/inorganic heterojunction composites have gained wide attention due to their application potential in terms of large scalability and low-cost fabrication technique. In this study, the interaction between polyvinyl alcohol (PVA) and two-dimensional material molybdenum disulfide (MoS2) with different mixing ratios was investigated. The result confirms that the optimal ratio of PVA:MoS2 is 4:1, which presents an excellent resistive switching behavior. Moreover, we propose a resistive switching model of Ag/ZnO/PVA:MoS2/ITO bilayer structure, which inserts the ZnO as the protective layer between the electrode and the composite film. Compared with the device without ZnO layer structure, the resistive switching performance of Ag/ZnO/PVA:MoS2/ITO was improved greatly. Furthermore, a large resistive memory window up to 104 was observed in the Ag/ZnO/PVA:MoS2/ITO device, which enhanced at least three orders of magnitude more than the Ag/PVA:MoS2/ITO device. The proposed nanostructured Ag/ZnO/PVA:MoS2/ITO device has shown great application potential for the nonvolatile multilevel data storage memory.

Multi-level characteristics of TiOx transparent non-volatile resistive switching device by embedding SiO2 nanoparticles

TiOx-based resistive switching devices have recently attracted attention as a promising candidate for next-generation non-volatile memory devices. A number of studies have attempted to increase the structural density of resistive switching devices. The fabrication of a multi-level switching device is a feasible method for increasing the density of the memory cell. Herein, we attempt to obtain a non-volatile multi-level switching memory device that is highly transparent by embedding SiO2 nanoparticles (NPs) into the TiOx matrix (TiOx@SiO2 NPs). The fully transparent resistive switching device is fabricated with an ITO/TiOx@SiO2 NPs/ITO structure on glass substrate, and it shows transmittance over 95% in the visible range. The TiOx@SiO2 NPs device shows outstanding switching characteristics, such as a high on/off ratio, long retention time, good endurance, and distinguishable multi-level switching. To understand multi-level switching characteristics by adjusting the set voltages, we analyze the switching mechanism in each resistive state. This method represents a promising approach for high-performance non-volatile multi-level memory applications.

Conductive filament evolution dynamics revealed by cryogenic (1.5 K) multilevel switching of CMOS-compatible Al2O3/TiO2 resistive memories

Non-volatile resistive switching devices are considered as prime candidates for next-generation memory applications operating at room temperature and above, such as resistive random-access memories or brain-inspired in-memory computing. However, their operability in cryogenic conditions remains to be mastered to adopt these devices as building blocks enabling large-scale quantum technologies via quantum–classical electronics co-integration. This study demonstrates multilevel switching at 1.5 K of Al2O3/TiO2-x resistive memory devices fabricated with complementary metal-oxide-semiconducto-compatible processes and materials. The I–V characteristics exhibit a negative differential resistance (NDR) effect due to a Joule-heating-induced metal-insulator transition of the Ti4O7 conductive filament. Carrier transport analysis of all multilevel switching I–V curves show that while the insulating regime follows the space charge limited current (SCLC) model for all resistance states, the conduction in the metallic regime is dominated by SCLC and trap-assisted tunneling for low- and high-resistance states respectively. A non-monotonic conductance evolution is observed in the insulating regime, as opposed to the continuous and gradual conductance increase and decrease obtained in the metallic regime during the multilevel SET and RESET operations. Cryogenic transport analysis coupled to an analytical model accounting for the metal-insulator-transition-induced NDR effects and the resistance states of the device provide new insights on the conductive filament evolution dynamics and resistive switching mechanisms. Our findings suggest that the non-monotonic conductance evolution in the insulating regime is due to the combined effects of longitudinal and radial variations of the Ti4O7 conductive filament during the switching. This behavior results from the interplay between temperature- and field-dependent geometrical and physical characteristics of the filament.

Water and air friendly alkali metals synthesis of the h-BN-C QDTs and the utilization in the non-volatile resistive switching memory devices

A novel and facile hydrothermal route was designed to produce h-BN-C quantum dots (h-BN-C QDTs) using h-BN powder as a precursor and Potassium Sodium Tartare as an intercalant. The resulting yellow solution possessed mono or few-layers of quantum dots with an average size of ~2.5 nm. Due to the incorporation of functional groups (carbon, oxygen) on the surface of h-BN, an enhancement of photo luminescent magnitude and a blue shift were observed in photoluminescence spectra from h-BN-C QDTs solution. Further, h-BN-C QDTs exhibits a bright blue fluorescence under the irradiation by a 365 nm UV light. Next, h-BN QDTs was utilized as the dielectric active layer by using simple drop casting method between the electrodes and fabricated the nonvolatile resistive switching devices. The fabricated devices exhibited the nonvolatile bipolar resistive switching characteristics with 103 ON/OFF ratio and turned ON and OFF threshold voltages of −1.9 V and +1.4 V, respectively. Further, the switching mechanisms of h-BN-C QDTs were found to be space charged trapping. It provides a route toward tailoring the optical and electrical properties of the h-BN materials and can be utilized in the future potential applications.

Oxide 2D electron gases as a reservoir of defects for resistive switching

A non-volatile resistive switching device is demonstrated, utilizing a 2D electron gas (2DEG) between a SrTiO3 substrate and an amorphous Al2O3 layer. A large resistance window is observed, and its origin is discussed. We pinpoint the role of the oxide interface in enabling the resistive switching behavior. The switching mechanism is proposed to be of filamentary type that is formed inside the Al2O3 layer, the result of oxygen vacancies that are driven from the interface into the insulating Al2O3 under high electric fields. These results highlight the concept of memristive devices where the 2DEG serves both as the back electrode and as the source of defects necessary for resistive switching, providing a simple and scalable process for future devices.

Robust and Transient Write‐Once‐Read‐Many‐Times Memory Device Based on Hybrid Perovskite Film with Novel Room Temperature Molten Salt Solvent

AbstractOrganic–inorganic hybrid perovskites (OIHPs) have emerged as a novel class of functional materials with applications in solar cells, photodetectors, light‐emitting diodes, and resistive switching memories. Generally, perovskite films are fabricated with toxic solvents and antisolvent technique under inert atmosphere, which limits the commercial applications of OIHP‐based devices. To address this issue, uniform CH3NH3PbBr3 (MAPbBr3) film is fabricated through a facile one‐step spin‐coating method by directly dissolving perovskite precursor in a room‐temperature molten salt methylammonium acetate under air ambient condition. The nonvolatile resistive switching devices based on MAPbBr3 exhibit robust and reproducible write‐once‐read‐many‐times (WORM) memory properties with a large ON/OFF ratio (106), reliable retention properties (104 s), and somewhat ternary resistive characteristic. The conductive filaments in the perovskite thin film are proposed to induce the electrical conductivity switching. Additionally, the MAPbBr3 films can be dissolved rapidly in deionized water within 5 s, showing the transient characteristics. This work demonstrates a new perspective on the perovskite film fabrication and shows the potential application of MAPbBr3 in transient WORM devices.

Threshold switching of non-stoichiometric CuO nanowire for selector application

Tunable volatile and non-volatile resistive switching devices were demonstrated with non-stoichiometric CuO nanowire. These resistive switching modes were controlled by the stability of hole-based conductive filaments via the compliance current in the SET process. The CuO-nanowire based volatile threshold switching selector exhibited a bidirectional operation with high selectivity (104), ultra-low OFF-current (<100 pA), and good reliability with the endurance over 105 cycles under the pulse operation. The present study demonstrates the nanowire-based threshold switching selector with the bottom-up method for future cross-point memory, logic application, and neuromorphic computing.

Resistance state evolution under constant electric stress on a MoS2 non-volatile resistive switching device.

MoS2 has been reported to exhibit a resistive switching phenomenon in a vertical metal–insulator–metal (MIM) structure and has attracted much attention due to its ultra-thin active layer thickness. Here, the resistance evolutions in the high resistance state (HRS) and low resistance state (LRS) are investigated under constant voltage stress (CVS) or constant current stress (CCS) on MoS2 resistive switching devices. Interestingly, compared with bulk transition metal oxides (TMO), MoS2 exhibits an opposite characteristic in the fresh or pre-RESET device in the “HRS” wherein the resistance will increase to an even higher resistance after applying CVS, a unique phenomenon only accessible in 2D-based resistive switching devices. It is inferred that instead of in the highest resistance state, the fresh or pre-RESET devices are in an intermediate state with a small amount of Au embedded in the MoS2 film. Inspired by the capability of both bipolar and unipolar operation, positive and negative CVS measurements are performed and show similar characteristics. In addition, it is observed that the resistance state transition is faster when using higher electric stress. Numerical simulations have been performed to study the temperature effect with small-area integration capability. These results can be explained by a modified conductive-bridge-like model based on Au migration, uncovering the switching mechanisms in the ultrathin 2D materials and inspiring future studies in this area.

Air-Stable Lead-Free Perovskite Thin Film Based on CsBi3I10 and Its Application in Resistive Switching Devices.

The development of organic-inorganic hybrid perovskite materials has been rapid in recent years; but their applications are limited by the toxicity and stability of the materials. To address these issues in the context of resistive switching devices, an inorganic lead-free perovskite namely CsBi3I10 is developed. Uniform and pinhole-free CsBi3I10 thin films can be fabricated by using CsI-rich precursor solution via a facile antisolvent-assisted spin-coating method. The nonvolatile resistive switching devices based on CsBi3I10 demonstrate a large on/off ratio (103), reliable retention properties (104 s), and endurance (150 cycles). Conductive atomic force microscopy reveals that the high- and low-resistance states are formed by breaking and formation of conductive filaments in the perovskite thin film. Because of the excellent stability of the CsBi3I10 perovskite, the devices exhibit no obvious change in resistive switching behavior even after over 2 month storage in an ambient (60% relative humidity) environment. Our work suggests that the all-inorganic lead-free CsBi3I10 perovskite has great potential in resistive switching memory as well as in other optoelectronic devices where toxicity and stability are a concern.

Non-volatile resistive switching based on zirconium dioxide: poly (4-vinylphenol) nano-composite

Recently, resistive switching devices are getting tremendous attention since they can be used for data storage in future. In this paper, we propose a non-volatile resistive switching device based on inorganic and organic nano-composite of zirconium dioxide (ZrO2) and poly (4-vinylphenol) (PVP), respectively. The nano-composite active layer ZrO2:PVP is fabricated on indium tin oxide (ITO) coated polyethylene terephthalate (PET) substrate through a spin coater technology and the top electrodes are fabricated by using silver (Ag) epoxy. The proposed device demonstrates a bipolar resistive switching at low operating voltage of ± 1.5 V with high resistance state and low resistance state of 11.438 kΩ and 262.25 Ω, respectively. To verify the non-volatility and long-term stability, the retention time is checked for more than 30 days and Roff/Ron resistance ratio is ~ 44. The proposed device is analyzed electrically and mechanically to analyze the effect of PVP in ZrO2 for better memory application and FESEM is used for the morphological characteristics of the device. These results ensure that the ZrO2:PVP nano-composite-based resistive switching device can be a possible candidate for the forthcoming flexible and low-power non-volatile resistive switching memory device.

Electrical properties of pulsed laser deposited BaBiO3−δ thin films and their non-volatile resistive switching

Thin films (50 nm, 100 nm and 300 nm) of multifunctional BaBiO3-δ (BBO) are grown in Au/BBO/Pt architecture using pulsed laser deposition (PLD) technique. Temperature dependent resistivity and dielectric measurements show a first order transformation with a thermal hysteresis of ∼40 K (between ∼150 K and ∼190 K) in Au/BBO300/Pt device. Non-volatile resistive switching (RS) with a resistance window of ∼8.5X is observed in Au/BBO300/Pt device at room temperature. The hysteretic J-V behavior exists in I2/m phase only. The application of a magnetic field (∼0.5 T) doubles the J-V hysteresis area. Thus, we demonstrate that the Au/BBO300/Pt is a non-volatile RS device and J-V hysteresis area of this device can be appreciably improved by applied magnetic field.

Solution-processed flexible non-volatile resistive switching device based on poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4, 8-diyl)]: polyvinylpyrrolidone composite and its conduction mechanism

Recently, solution-processed resistive switches for wearable electronics have got tremendous attention and are required for different applications due to their easy process and fabrication. Hence, this paper proposes the solution-processed resistive switching memory device based on two polymers, poly[(9,9-di-n-octylfluorenyl-2,7-diyl)-alt-(benzo[2,1,3]thiadiazol-4, 8-diyl)] (F8BT) and polyvinylpyrrolidone (PVP) composite, which is fabricated on a flexible indium–tin–oxide (ITO)-coated polyethylene terephthalate (PET) substrate through spin coating technology. The fabricated device demonstrates a perfect non-volatile bipolar resistive switching through small operating voltage sweeping of ± 1.5 V, and its high-resistance state (HRS) and low-resistance state (LRS) are 92678.89 Ω and 337.85 Ω, respectively. To verify the non-volatility and long-term stability, the device is checked for more than 700 endurance cycles. During these cycles, the variations of HRS and LRS are 48 Ω and 37.35 Ω, respectively. The retention time is checked for more than 60 days, and the ROFF/RON ratio is 274.31. The bendability is carried out up to bending diameters < 10 mm, and FESEM is used for the morphological characteristics of the device. Conduction mechanism of the proposed device is supported by space charge-limited conduction (SCLC) which is explained by the log–log I–V slope-fitting curve. The results insure that the F8BT:PVP composite-based resistive switching device is to be a potential candidate for the future flexible and low-power non-volatile resistive switching memory device.

(Invited) Oxide Interface Is the Device: Properties of Two-Dimensional Electron Gas

Transition metal oxides exhibit rich phase diagrams and exotic physical properties as a result of strong correlations between charge, spin, orbital and lattice. The recent advances of thin film technology allow the synthesis of high-quality epitaxial oxide heterostructures with control at the unit cell level, which enables exploring rich physics and opportunities for future technologies. As a notable example, interesting transport phenomena like 2D electron conduction and orbital reconstruction were discovered at the polar-nonpolar LaAlO3/SrTiO3 (LAO/STO)interface. In this talk, I will first discuss our results of Kondo effect and two-dimensional insulator-to-metal transition obtained on interface-based field effect device with double layer ionic electrolyte as the top gate. Then I will introduce an interface-based nonvolatile resistive switching device, where the ionic drift and alteration of electronic configuration underpin the memory operation. Finally, I will discuss the possible routes to achieving higher electron mobility in such oxide interfaces and the perspective of constructing interface-based photodetectors.

Current Induced Non-Volatile Resistive Switching Effect in Silicon Devices with Large Magnetoresistance

We develop a non-volatile resistive switching device in a Si—SiO2—Mg structure with an on/of ratio of about 4.5 at a certain transition voltage after being stimulated by a large current. It is observed that the resistance transition voltage Vt shifts reproducibly under a reversed large current. By applying a reading voltage in the range of Vt, non-volatile resistive switching phenomena with an endurance of more than 80 cycles are observed. Moreover, it is also found that the magnetic field could shift Vt to higher values, yielding a voltage dependent room-temperature magnetoresistance in the range of 103 % at 1 T. The multifunctional properties of the silicon device suggested by this work may be beneficial to the silicon based industry.

Unipolar Resistive Switch Based on Silicon Monoxide Realized by CMOS Technology

In this letter, a reliable nonvolatile resistive switching device based on silicon monoxide (SiO) is demonstrated. The device was fabricated with a low-temperature process that can be compatible with a CMOS back-end process and attractive for 3-D memory integration. The fabricated Cu/SiO/W device was found to have a repeatable unipolar resistive switching behavior. The results show excellent on/off resistance ratio (over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> ) and good retention performance. The switching mechanism of the device is analyzed by experimental data and probably can be attributed to the behaviors of copper ions in the bulk of SiO under different voltages.