Search

In this study, a two-dimensional electron gas (2DEG), which is a conductive layer formed at the interface of Al2O3 and TiO2, was used as an electrode for resistive random access memory (RRAM) and implemented in a cell size down to 30 nm. For an RRAM device comprising W/2DEG/TiO2/W, we confirmed that the dominant switching mechanism changed from interfacial to filamentary as the cell size decreased from 500 nm to 30 nm. Through analyses of changes in forming characteristics and conduction mechanisms in the low resistive state depending on the cell size, it was identified that the 2DEG acted as an oxygen-scavenging layer of TiO2 during the resistive switching process. By comparing the switching characteristics of RRAM devices with and without 2DEG for a 30 nm cell size, we confirmed that a high-performance 2DEG RRAM was realized, with highly uniform current–voltage characteristics, a low operating voltage (∼1 V), and a high on/off ratio (>102). Finally, the applicability of the proposed device to a crossbar array was validated by evaluating 1S1R operation with an NbO2-based selector. Considering the improved switching uniformity, the 2DEG RRAM shows promise for high-density memory applications. [ABSTRACT FROM AUTHOR]

Herein, a digital–analog hybrid resistive random‐access memory (RRAM) is prepared by integrating the structurally similar SiNx‐based digital‐type RRAM with analog‐type RRAM by heterogeneous integration method. The Pt/SiNx/Ta/Ru is a digital RRAM due to the formation and breakage of the internal silicon dangling bonds conductive filaments, and the TiN/SiNx/Ta/Ru structure is an analog RRAM due to the traps‐filled limit region of the space‐charge limited current. The heterogeneously integrated digital RRAM has good cycling stability and endurance characteristics, and the heterogeneously integrated analog RRAM has high linearity and multistate counting characteristics. This heterogeneous integration approach is useful for the implementation of hybrid digital–analog RRAM. [ABSTRACT FROM AUTHOR]

A novel benzothiadiazole-based donor-acceptor type polymer, resistive random access memory (RRAM) material, poly{[4,4'-(2,7-diphenyl-9H-fluorene-9,9-diyl)bis(N,N-diphenylaniline)]-alt-[4,7-bis(4-dodecyl-5-vinylthiophen-2- yl)benzo[c][1,2,5] thiadiazole]} (PFVT) was synthesized. By using PFVT as the active layer, the as-fabricated electronic device with a configuration of Al/PFVT/ITO (ITO: indium tin oxides) exhibites a nonvolatile RRAM performance. During 50 consecutive cycle-to-cycle measurements, the observed average switch-on voltage, switch-off voltage and ON/OFF current ratio are (−0.54 ± 0.01) V, (2.42 ± 0.05) V, and 1.5×10³, respectively. The cycle-to-cycle variation for the programming voltage is less than 2.1%, suggesting excellent reliability. After thermal annealing at 200 ℃, the switch-on and switch-off voltages decrease to (−0.49±0.01) V and (2.27±0.02) V, respectively, due to the enhanced material crystallinity. The switching mechanism can be assigned to the intramolecular charge-transfer occurred in the materials system. The ON and OFF-state currents can be fitted by the Ohmic current model and space-charge-limited current model, respectively. The switchon voltage is highly associated with the bandgap of the materials. For comparison purpose, 4,4′-(2,7-diphenyl-9H-fluorene-9,9- diyl)bis(N,N-diphenylaniline) was replaced with phenyl group to synthesize poly[4-(4-dodecyl-5-((E)-4- methylstyryl)thiophen-2-yl)-7-(4-dodecyl-5-((E)-prop-1-en-1-yl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole](PPVT). In contrast to PFVT, PPVT also shows the similar RRAM performance, with a bigger switch-on voltage and a smaller ON/OFF current ratio. Replacement of bulky fluorene unit with phenyl unit leads to a sharp decrease in the thermal stability of the material and an increase in the bandgap. [ABSTRACT FROM AUTHOR]

Covalent organic polymers (COPs) memristors with multilevel memory behavior in harsh environments and photoelectric regulation are crucial for high‐density storage and high‐efficiency neuromorphic computing. Here, a donor–acceptor (D–A)‐type COP film (Py‐COP‐3), which is initiated by keto–enol tautomerism, is proposed for high‐performance memristors. Satisfactorily, the indium tin oxide (ITO)/Py‐COP‐3/Ag device demonstrates multilevel memory performance, even in high temperatures, acid‐base corrosion, and various organic solvents. Moreover, the performance can be modulated by the photoelectric effect to maintain a great switching behavior. By contrast, Py‐COP‐0, with similar structure and chemical composition to Py‐COP‐3 but without keto–enol tautomerism, exhibits binary storage performance. Further studies unravel that both the formation of conductive filaments and charge transfer within D‐A Py‐COP‐3 film contribute to the resistive switching behavior of memory devices. [ABSTRACT FROM AUTHOR]

The coming big‐data era has created a huge demand for next‐generation memory technologies with characters of higher data‐storage densities, faster access speeds, lower power consumption and better environmental compatibility. In this field, the design of resistive switching active materials is pivotal but challengeable. Polyoxometalates (POMs) are promising candidates for next‐generation molecular memristors due to their versatile redox characters, excellent electron reservoirs and good compatibility/convenience in microelectronics processing. In this review, five kinds of POM‐based active materials in nonvolatile memories (inorganic POMs, crystalline organic‐inorganic hybrid POMOFs, polymer modified POMs, POM/transition metal oxides composites and the deposition of POM on metal surfaces) were described. The components of POMs active materials, device fabrications, device parameters, and resistive switching mechanisms relative to their structures were summarized. Finally, challenges and future perspectives of POMs‐based memristors were also presented. [ABSTRACT FROM AUTHOR]

Activation energy, bipolar resistance switching behavior, and the electrical conduction transport properties of ITOX:SiO2 thin film resistive random access memory (RRAM) devices were observed and discussed. The ITOX:SiO2 thin films were prepared using a co-sputtering deposition method on the TiN/Si substrate. For the RRAM device structure fabrication, an Al/ITOX:SiO2/TiN/Si structure was prepared by using aluminum for the top electrode and a TiN material for the bottom electrode. In addition, grain growth, defect reduction, and RRAM device performance of the ITOX:SiO2 thin film for the various oxygen gas flow conditions were observed and described. Based on the I-V curve measurements of the RRAM devices, the turn on-off ratio and the bipolar resistance switching properties of the Al/ITOX:SiO2/TiN/Si RRAM devices in the set and reset states were also obtained. At low operating voltages and high resistance values, the conductance mechanism exhibits hopping conduction mechanisms for set states. Moreover, at high operating voltages, the conductance mechanism behaves as an ohmic conduction current mechanism. Finally, the Al/ITOX:SiO2/TiN/Si RRAM devices demonstrated memory window properties, bipolar resistance switching behavior, and nonvolatile characteristics for next-generation nonvolatile memory applications. [ABSTRACT FROM AUTHOR]

Variability is an inherent property of memristive devices based on the switching of resistance in a simple metal–oxide–metal structure compatible with the standard complementary metal–oxide–semiconductor fabrication process. For each specific structure, the variability should be measured and assessed as both the negative and positive factors for different applications of memristive devices. In this report, it is shown how this variability can be extracted and analyzed for such main parameters of resistive switching as the set and reset voltages/currents and how it depends on the methodology used and experimental conditions. The obtained results should be taken into account in the design and predictive simulation of memristive devices and circuits. [ABSTRACT FROM AUTHOR]

The electrode-dependent resistive random access memories (ReRAM) with aluminum, silver, platinum, and indium tin oxide (ITO) judiciously selected as a pair of electrodes, and the bismuth ferrite (BiFeO3 or BFO) as the active dielectric layer, are fabricated for elaborate characterizations. The Ag/BFO/Pt and Ag/BFO/ITO ReRAMs have reflected excellent electrical properties, notably for the Ag/BFO/ITO combination. The Ag/BFO/ITO endures more than 1200 switching cycles and an excellent (> 102) on/off current or resistance ratio. The retention time in both high and low resistance states could reach 104 s and beyond. It has been found that the electrochemical metallization mechanism dominated by metal ion migration and the valence change mechanism dictated by oxygen vacancy conduction are inseparable from the establishment and destruction of the conductive filament. Moreover, a ReRAM with a dual dielectric layer of BFO/α-Fe2O3) is also prepared for comparison. A special "two-step reset" phenomenon is observed which could be explained with filament theory. [ABSTRACT FROM AUTHOR]

One of the most effective methods for improving the storage density of resistive random access memories (RRAMs) is to fabricate 3D vertical stacking devices. By using BP-DDAT(DDAT: S-1-dodecyl-S ′-(α,α′-dimethyl-α′ ′- aceticacid)trithiocarbonate) as a key 2D template and reversible addition-fragmentation chain transfer (RAFT) reagent, a novel poly(N-vinylcarbazole) covalently functionalized black phosphorus derivative (BP-PVK) is successfully synthesized and well-characterized by infrared spectroscopy, X-ray electron spectroscopy and UV-Vis absorption spectroscopy. The environmental stability and solubility of BP nanosheets are greatly improved. Using BP-PVK as active layer, a double-layer vertically stacked RRAM memory device (17×17 stripe array) with a configuration of Al/BP-PVK/Al/BP-PVK/Al is fabricated. The as-fabricated device shows good bistable electrical switching and non-volatile rewritable performance at room temperature, with an ON/OFF current ratio exceeding 10³, higher production yield of the memory devices and structural uniformity. [ABSTRACT FROM AUTHOR]

According to Moore's Law's development law, traditional floating gate memory is constrained by charge tunneling, and its size is approaching the physical limit, which is insufficient to meet the requirements of large data storage. The introduction of new information storage devices may be the key to overcoming the bottleneck. Resistive random access memory (RRAM) has garnered interest due to its fast switching speed, low power consumption, and high integration density. The resistive switching (RS) behaviors can be demonstrated in many materials, including transition metal oxides, perovskite oxides and organic matter, etc. Among these materials, graphene oxide (GO) with its unique physical, chemical properties and excellent mechanical properties is attracting significant attention for use in RRAM owing to its RS operation and potential for integration with other graphene-based electronics. However, there is unacceptable variability in RS reliability, including retention and endurance, which is the key factor that affects the development of memristors. In addition, the RS mechanism of GO-based RRAM has not been systematically discussed. In this article, we discuss systematically several typical models of the switching mechanism of GO-based RRAM and a summary of methods for improving the device's RS performance. This article concludes by discussing the applications of GO-RRAM in artificial neural networks, flexible devices, and biological monitoring. [ABSTRACT FROM AUTHOR]

According to Moore's Law's development law, traditional floating gate memory is constrained by charge tunneling, and its size is approaching the physical limit, which is insufficient to meet the requirements of large data storage. The introduction of new information storage devices may be the key to overcoming the bottleneck. Resistive random access memory (RRAM) has garnered interest due to its fast switching speed, low power consumption, and high integration density. The resistive switching (RS) behaviors can be demonstrated in many materials, including transition metal oxides, perovskite oxides and organic matter, etc. Among these materials, graphene oxide (GO) with its unique physical, chemical properties and excellent mechanical properties is attracting significant attention for use in RRAM owing to its RS operation and potential for integration with other graphene-based electronics. However, there is unacceptable variability in RS reliability, including retention and endurance, which is the key factor that affects the development of memristors. In addition, the RS mechanism of GO-based RRAM has not been systematically discussed. In this article, we discuss systematically several typical models of the switching mechanism of GO-based RRAM and a summary of methods for improving the device's RS performance. This article concludes by discussing the applications of GO-RRAM in artificial neural networks, flexible devices, and biological monitoring. [ABSTRACT FROM AUTHOR]

With the increase in data-driven frameworks, the demand for non-volatile memory has increased and resistive switching-based memory is one of them. In this study, the structural, charge transport and the current vs. voltage (I-V) behaviour of (1-x)La 0.7 Sr 0.3 MnO 3 .(x)ZnO composite systems were investigated and observed that, they exhibit bipolar resistive switching behaviour. The oxygen vacancy, oxygen ions and interfacial layers play an important role in the resistive switching behaviour. From the XPS analysis, it is observed that the oxygen-deficient region increases with the increasing concentration of ZnO. The sample with x = 0.050 shows better resistive switching behaviour and high ON/OFF current ratio as compared with the x = 0.005 and 0.010 samples. The Ohmic and Schottky emissions are found to be responsible for the conduction mechanism. The shifting in the metal–insulator transition temperature (TMI) towards the low temperature is observed from the resistivity vs. temperature plot with the increasing concentration of the ZnO. [ABSTRACT FROM AUTHOR]

Processing-In-Memory(PIM) has emerged as a high-performance and energy-efficient computing paradigm for accelerating convolutional neural network (CNN) applications. Resistive random access memory (ReRAM) has been widely used in PIM architectures due to its extremely high efficiency for accelerating matrix-vector multiplications through analog computing. However, because CNN training usually requires high-precision computation in the backward propagation (BP) stage, the limited precision of analog PIM accelerators impedes their adoption in CNN training. In this article, we propose ReHy, a hybrid PIM accelerator to support CNN training in ReRAM arrays. It is composed of Analog PIM (APIM) and Digital PIM (DPIM) modules. ReHy uses APIM to accelerate the feed-forward propagation (FP) stage for high performance, and DPIM to process the BP stage for high accuracy. We exploit the capability of ReRAM for Boolean logic operations to design the DPIM architecture. Particularly, we design floating-point multiplication and addition operators to support matrix multiplications in ReRAM arrays. We also propose a performance model to offload high-precision matrix multiplications to DPIM according to the data parallelism. Experimental results show that ReHy can speed up CNN training by 48.8× and 2.4×, and reduce energy consumption by 35.1× and 2.33×, compared with CPU/GPU architectures (baseline) and the state-of-the-art FloatPIM, respectively. [ABSTRACT FROM AUTHOR]

This work explores the phenomenon of HfO2 resistive random access memory (RRAM) postprogramming resistance relaxation using experimental data and kinetic Monte Carlo (KMC) physical simulation. This issue has become an important limitation for multilevel cell (MLC) applications. The physical KMC simulation replicates the RRAM cell‐to‐cell intrinsic resistance variability due to the conductive filament (CF) morphology fluctuations and the weak correlation between the number of oxygen vacancies and the resulting resistance. It furthermore accurately simulates the vacancies' microscopic dynamics within the CF that are responsible for the RRAM resistance relaxation. A link between programming current, CF size/configuration, and relaxation amplitude is clarified and shows the ensuing benefits and limitations of smart programming techniques (read & verify) for MLC applications. Coupled with experimental data obtained on HfO2‐based RRAM arrays, this simulation paves the way to a better understanding of the physics at stake in the RRAM relaxation process and provides guidelines to potential technological solutions for MLC reliability prediction. [ABSTRACT FROM AUTHOR]

Reset-first resistive random access memory (RRAM) devices were demonstrated for off-stoichiometric Ni1−xO thin films deposited using reactive sputtering with a high oxygen partial pressure. The Ni1−xO based RRAM devices exhibited both unipolar and bipolar resistive switching characteristics without an electroforming step. Auger electron spectroscopy showed nickel deficiency in the Ni1−xO films, and X-ray photoemission spectroscopy showed that the Ni3+ valence state in the Ni1−xO films increased with increasing oxygen partial pressure. Conductive atomic force microscopy showed that the conductivity of the Ni1−xO films increased with increasing oxygen partial pressure during deposition, possibly contributing to the reset-first switching of the Ni1−xO films. [ABSTRACT FROM AUTHOR]

This article investigates the spatial tailoring of nitrogen vacancies by atomic layer annealing (ALA) on resistive random access memory (RRAM) devices with an AlN resistive switching layer. The ALA technique involves the in-situ layer-by-layer He/Ar plasma treatment in the cycle of atomic layer deposition for AlN. The AlN RRAM devices prepared with the ALA treatment near the TiN electrode have significantly superior uniformity of the operation voltages and the switching resistances, along with a lower cycle-to-cycle variation in endurance. This enhancement could be attributed to the relatively stable location of rupture and formation of conductive filaments, as a result of the film densification and the suppression of nitrogen vacancies in the AlN region treated with the ALA process. The AlN RRAM devices also demonstrate excellent retention of more than 106 seconds at 125°C. In addition, the ultra-thin 3.3 nm AlN switching layer contributes to low operation voltages of AlN RRAM. The outcomes manifest that the ALA technique could effectively improve the properties of nanoscale materials through precise spatial tailoring, with an accuracy up to atomic scale. [Display omitted] • ALA involves in-situ, layer-by-layer plasma treatment during AlN deposition by ALD. • ALA contributes to film densification and suppression of nitrogen vacancies in AlN. • The uniformity of AlN RRAM properties is improved by ALA near the TiN electrode. • Stable rupture and formation of conductive filaments due to ALA near TiN electrode. • Ultrathin (3.3 nm) AlN in RRAM exhibits low operation voltages and good retention. [ABSTRACT FROM AUTHOR]

Interest in resistive random access memory (RRAM) has grown rapidly in recent years for realizing ultrahigh density data storage devices. However, sneak currents in these devices can result in misreading of the data, thus limiting the applicability of RRAM. Complementary resistive switching (CRS) memory consisting of two antiserial RRAMs can considerably reduce sneak currents; however, complicated device architectures and manufacturing processes still remain as challenges. Herein, an effective and simple approach for fabricating CRS memory devices using self‐assembled block copolymer micelles is reported. Cu ions are selectively placed in the core of polystyrene‐block‐poly(2‐vinylpyridine) spherical micelles, and a hexagonally packed micelle monolayer is prepared through spin‐coating. The micelle monolayer can be a symmetrical resistive switching layer, because the micelles and Cu act as dielectric and active metals in memory devices, respectively. The locally enhanced electric field and Joule heating achieved by the structured Cu atoms inside the micelles promote metal ionization and ion migration in a controlled manner, thus allowing for position selectivity during resistive switching. The micelle‐based memory device exhibits stable and reliable CRS behavior, with a nonoverlapping and narrow distribution of threshold voltages. Therefore, this approach is promising for fabricating CRS memory devices for high‐performance and ultrahigh‐density RRAM applications. [ABSTRACT FROM AUTHOR]

Despite the great promises that the resistive random access memory (ReRAM) has shown as the next generation of non-volatile memory technology, its crossbar array structure leads to a severe sneak path interference to the signal read back from the memory cell. In this paper, we first propose a novel belief propagation (BP) based detector for the sneak path interference in ReRAM. Based on the conditions for a sneak path to occur and the dependence of the states of the memory cells that are involved in the sneak path, a Tanner graph for the ReRAM channel is constructed, inside which specific messages are updated iteratively to get a better estimation of the sneak path affected cells. We further combine the graph of the designed BP detector with that of the BP decoder of the polar codes to form a joint detector and decoder. Tailored for the joint detector and decoder over the ReRAM channel, effective polar codes are constructed using the genetic algorithm. Simulation results show that the BP detector can effectively detect the cells affected by the sneak path, and the proposed polar codes and the joint detector and decoder can significantly improve the error rate performance of ReRAM. [ABSTRACT FROM AUTHOR]

Dielectric breakdown (DB) controls the failure, and increasingly the function, of microelectronic devices. Standard imaging techniques, which generate contrast based on physical structure, struggle to visualize this electronic process. Here in situ scanning transmission electron microscopy (STEM) electron beam‐induced current (EBIC) imaging of DB in Pt/HfO2/Ti valence change memory devices is reported. STEM EBIC imaging directly visualizes the electronic signatures of DB, namely local changes in the conductivity and in the electric field, with high spatial resolution and good contrast. DB is observed to proceed through two distinct structures arranged in series: a volatile, "soft" filament created by electron injection; and a non‐volatile, "hard" filament created by oxygen‐vacancy aggregation. This picture makes a physical distinction between "soft" and "hard" DB, while at the same time accommodating "progressive" DB, where the relative lengths of the hard and soft filaments can change on a continuum. [ABSTRACT FROM AUTHOR]

Resistive random access memory (RRAM) based on ultrathin 2D materials is considered to be a very feasible solution for future data storage and neuromorphic computing technologies. However, controllability and stability are the problems that need to be solved for practical applications. Here, by introducing a damage‐less ion implantation technology using ultralow‐energy plasma, the transport mechanisms of space charge limited current and Schottky emission are successfully realized and controlled in RRAM based on 2D Bi2Se3 nanosheets. The memristors exhibit stable resistive switching behavior with a high resistive switching ratio (>104), excellent cycling endurances (300 cycles), and great retention performance (>104 s). The reliability and controllability of Bi2Se3 memory endowed by oxygen plasma injection demonstrate the great potential of this ultralow‐energy ion implantation technology in the application of 2D RRAM. [ABSTRACT FROM AUTHOR]

This study demonstrates a hyper‐level control of metal‐ion migration through vacancy‐induced‐percolation (VIP) path to maximize the steep‐slope performance of the threshold selector with excellent selectivity and endurance. Highly efficient control over metal‐ion migration through VIP is achieved with sophisticated stack engineering through the material evolution process and refined electrical operation. A thorough analysis of the energetics of metal‐ion‐ and vacancy‐based hybrid filament is performed using density functional theory calculations, which leads to a proper tuning of the biasing scheme. Command over bias‐induced ion migration to control the atomic‐scale filament is the key to maximize the threshold switching (TS) performance. The devices are designed with different diffusive materials and alloys. Precise atomic‐level control is realized with optimized device structure and alloy electrode, which indicates that the TS is safe within the vicinity of quantum contact. Owing to the synergistic impact of localized metal‐ion injection through VIP, alloy electrode material, and atomic‐level filament, the devices exhibit meticulous control of a highly stable TS with a high steep‐slope of <2 mV dec−1, extremely high selectivity of >4 × 1010 with an exceptional endurance >109 cycles, and device yield of 100%, which suggest the applicability of these devices in 1S1R and 1T1R platforms. [ABSTRACT FROM AUTHOR]

Highly repeatable, photosensitive nonvolatile resistive random access memory (ReRAM) made of a Si/SiO2/Cu/PRPC/Ta stack with a photoresponsive polymer composite (PRPC) as the active medium is presented. The device shows errorless bipolar resistive switching with more than 100 cycles repeatability and stable SET and RESET voltages. It changes its resistive states in response to white light and recovers completely after removal of the light source. It also changes its state in response to heat and recovers randomly after the removal of the heat source. The phenomenon is explained by valance charge transfer along with a space‐charge‐limited conduction (SCLC) mechanism. The initial state of the device is low resistance state (LRS) because of electric‐field‐induced formation of valance charge transfer states. It switches to a high resistance state (HRS) due to electric‐field‐induced dissociation of the charge transfer states. [ABSTRACT FROM AUTHOR]

Resistive random access memory (RRAM) is viewed as the next-generation memory model, surpassing the constraints of traditional random access memory. Given its non-volatile nature, which lessens static power consumption, RRAM boasts significant computing-in-memory (CIM) potential. We herein present a four-transistor/two-resistor cross-coupling structure based on RRAM. In this structure, two RRAMs are situated in opposite directions, a configuration referred to as reverse coding. This structure provides the flexibility and reconfigurability to adjust the RRAM connections, facilitating various CIM operations in fewer cycles. A full adder design was developed and its feasibility was validated through simulations. Monte Carlo analysis ensures the accuracy of logic operations, even while encountering significant resistance fluctuations. This approach effectively mitigates the resistance crossover observed in existing RRAM CIMs. Compared with previous methodologies, the proposed structure achieves greater robustness with fewer cycle counts and RRAM numbers, The comparison of our approach with state-of-the-art Boolean logic circuits for RRAM architecture shows significant improvement in both delay (1.4–4.1 ×) and the number of RRAM (1.2–6.6 ×). [ABSTRACT FROM AUTHOR]

Artificial synapse devices are currently the subjects of great attention as next-generation hardware for data processing to overcome the problem of data explosion due to the rapid advances in artificial intelligence and cloud computing technology. Nanocomposite-based devices enable unique applications and have several advantages that cannot be achieved in single material-based devices. This study presents binary electrical synapses with digital data storing and analog data processing through a nanocomposite-based active layer composed of poly(methyl methacrylate) (PMMA) with embedded chlorine-functionalized graphene quantum dots (fGQDs) on an indium tin oxide (ITO) substrate. The Al/PMMA-fGQD/ITO devices with an fGQD concentrations of 5 wt% exhibited excellent memory performance with R ON /R OFF ratio of 103. Moreover, we demonstrated that our device can successfully emulate biological synaptic functions such as potentiation/depression, short-term/long-term memory, paired-pulse facilitation, learning experience, and spike-timing-dependent plasticity. Furthermore, on the basis of the synaptic behaviors of the devices, they achieved about a 90 % recognition capability when a learning algorithm was used in a single-layer neural network. [Display omitted] • A chlorine-functionalized graphene quantum dots (fGQDs) was introduced as tapping centers of an active layer in an artificial synapse. • The Al/PMMA-fGQDs/ITO device showed excellent electrical characteristics and successfully mimicked various synaptic functions. • Based on the conductance of the Al/PMMA-fGQDs/ITO device, the MNIST pattern recognition algorithm achieved about a 90 % recognition rate. [ABSTRACT FROM AUTHOR]

We report an ReRAM-based pseudo-true random number generator (RNG) which can significantly improve the security feature of e-ReRAM chips at a very low cost. Combining the true randomness from stochastic behavior of ReRAM and the high output speed from a modified linear feedback shift register (LFSR), the proposed architecture can provide ultrahigh throughput random sequence following system clocks from several Mbit/sec to tens of Gbit/sec. The highly reliable, unpredictable, and unrepeatable ReRAM-based pseudo-true RNG circuit can pass NIST SP800-22 randomness tests at a high score. It is suitable for secure IoT and 5G applications. [ABSTRACT FROM AUTHOR]

Herein, we characterize resistive random access memory (RRAM) devices containing an oxygen-deficient layer. The RRAM devices consist of multiple layered NiO thin films that consist of an oxygen-deficient NiO 0.95 layer, within a NiO/NiO 0.95 /NiO layer structure. The NiO thin-film layers were deposited on Pt/Ta/SiO 2 /Si substrates by radio frequency magnetron sputtering. The stoichiometry and thickness of the NiO triple-layer thin films were determined by Auger electron spectroscopy. We fabricated RRAM capacitors with a structure of Pt/NiO/NiO 0.95 /NiO/Pt to investigate the resistive switching characteristics. The presence of an oxygen-deficient layer significantly lowers the forming and SET/RESET voltages compared to a Pt/NiO/Pt RRAM capacitor. This reduces the energy required to form conducting filaments in the oxygen-deficient layer. Moreover, the forming and SET/RESET voltages exhibit reduced dispersion due to the relatively high oxygen vacancy density in the oxygen-deficient NiO 0.95 layer. [ABSTRACT FROM AUTHOR]

Photograph response in transparent devices has been a hot area of investigation, with several material systems being used to generate a response to illumination. In this study, we propose an ITO/MgO/HfO2/ITO bilayer (BL) transparent resistive switching (RS) device that exhibits a photograph response through defect engineering in the switching layer, which resulted in a subsurface active RS location in the formed conductive filament, thus reducing the loss of oxygen through the polycrystalline electrode. We observe that the switching performance is enhanced in the ITO/MgO/HfO2/ITO BL device as compared to the ITO/HfO2/ITO single-layer device with the insertion of MgO layer between the ITO top electrode and HfO2 RS layer. The device shows excellent ON/ OFF ratio (~107), high and stable dc electrical set and optical reset endurance (>1000 cycles without degradation), excellent retention (>104 s at 85 °C), high transparency (>85% transmittance in the visible spectrum), and a response time of 30 μs for the optical reset. This study lays the foundation for future work involving oxide defect-based optical functionalization in RS devices with the possibility for being used in photograph sensing. [ABSTRACT FROM AUTHOR]

The methods of the theory of the functional of electron density and pseudopotential from the first principles obtained the characteristics of an electronic subsystem of the working layer of RRAM (Resistive Random Access Memory) which is based on the HfO2 It is calculated how the introduction of vacancies into the crystal and the introduction of silver atoms affects the properties of the object. The spatial distributions of the density of valence electrons and their cross sections within the cell, the distribution of the density of electronic states, and electric charges in the vicinity of the Hafnium atoms in different atomic environments are calculated. It is investigated how changes in material structure affect conductive properties. [ABSTRACT FROM AUTHOR]

In this article, the development history and the technical hurdles of phase-change memory (PCM) are reviewed and recent progress and future directions are discussed. Prospects of PCM for storage-class memory (SCM) are discussed in terms of the technical challenges to satisfy the market requirements, mainly for the performance and cost effectiveness. For a more in-depth discussion, PCM is segmented into the memory part, the access device part, and the sensing scheme part. In the memory part, Set (crystallization)–Reset (amorphization) write characteristics and thermal disturbance (TDB) will be reinterpreted in terms of power consumption and performance of SCM. In the access device part, the application history of various devices, such as the transistor, the diode, and the two-terminal selector, will be reviewed and explained based on the process integration issues and area efficiency. In the next part, various sensing schemes used to make a lower read latency, multilevel cell (MLC), and cross point (X-point) are summarized. Thereafter, future directions and possible evolution pathways of 3-D structures, including X-point and vertical X-point (VXP), will be discussed for the first time. Finally, the feasibility of PCM for neuromorphic application will be followed. [ABSTRACT FROM AUTHOR]

Adding the two-dimensional (2D) material into the metal/oxide interface is a novel method to tune the property of the interface and the interface-controlled device. Compared to the widely studied influence of the interfacial 2D-material on the kinetic diffusion of the atom across the interface, the effect of the interfacial 2D layer on the energetic behavior of the point defect at the interface viewed at the electronic-/atomic-scale is less focused. In this work, the influence of graphene on the Au/HfO 2 interface is studied using a first-principles calculation. It is found that graphene can eliminate the Au-induced insulator-metal-transition of the HfO 2 layer at the interface, by screening the strong interaction between Au and HfO 2. At the atomic scale, graphene significantly increases the formation energy of the oxygen vacancy and vacancy pair in HfO 2 at the Au/HfO 2 interface, making the interfacial HfO 2 -layer surface-like. Also graphene alleviates the valence-electron-number dependent segregation of the alloying elements Ag, Cu and Ta at the Au/HfO 2 interface. The significant impact of graphene at the metal/oxide interface unraveled from the energetic point of view provides an alternative insight into the interface engineering of the electronic device such as the oxide-based resistive random access memory. Unlabelled Image • Graphene significantly screens the strong electronic interaction at interface Au/HfO 2. • Graphene increases the formation energy of the oxygen vacancy (pair) in HfO 2. • Graphene alleviates the segregation of the alloying elements at interface Au/HfO 2. • Graphene makes the HfO 2 -layer at the interface more surface-like or bulk-like. [ABSTRACT FROM AUTHOR]

Resistive random access memory (RRAM) has been developed as a next-generation nonvolatile memory because of its fast operation speed, low power consumption, high density, and simple structure. Non-oxide materials such as AlN-based RRAM also exhibit low operation energy and large on/off ratios. However, AlN-based RRAM may deteriorate upon oxidation when exposed to air/moisture. In addition, chemical reactivity between the electrode and the switching layer material affects device stability. In this study, four kinds of top electrode materials (Al, Ti, TiN, and Pt) were used in an AlN/TiN stack and a water-resistant encapsulation layer was used to prevent the degradation of AlN-based RRAM. The electrical properties of the device were measured at weekly intervals for 7 weeks. The devices containing Al and Ti top electrodes showed degradation of resistance states despite being encapsulated in a thin Al2O3 layer. In contrast, the devices with TiN and Pt electrodes maintained their resistance states and switching properties regardless of the encapsulation layer. These trends in degradation can be explained by the electrode and AlN reactivity with moisture based on fundamental thermodynamics. [ABSTRACT FROM AUTHOR]

Abstract In this study, a glass/indium tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS)/CH 3 NH 3 PbI 3 (MAPbI 3)/poly(methyl methacrylate) (PMMA)/Al nonvolatile memory device is demonstrated. The MAPbI 3 film is prepared on top of the PEDOT:PSS by a two-step process, showing a bipolar resistive switching character. Because PEDOT:PSS is widely used as a hole transporting layer for a planar heterojunction perovskite solar cell, the demonstrated memory property of PEDOT:PSS/MAPbI 3 combination opens up the application potential for multifunctional optoelectronic memory. The device is improved by introducing potassium iodide (KI) as an additive to ameliorate the quality of MAPbI 3 material and PEDOT:PSS/MAPbI 3 interface. As compared with the pristine MAPbI 3 , the KI-doped perovskite device exhibits a resistive switching ON/OFF ratio of 103, better endurance and more stable retention. The KI additive is helpful for forming uniform crystalline grain, high-compact structure and passivation of defect states for MAPbI 3 film and interface, which are the main reasons to the improved memory properties. Finally, we suggest that KI has great potential to be used as an additive for constructing a high performance perovskite memory device. Highlights • A MAPbI 3 film was fabricated by the two-step process on the PEDOT:PSS layer. • The PEDOT:PSS/MAPbI 3 -based device shows a bipolar resistive switching behavior. • The KI-doped MAPbI 3 exhibited a uniform and high compact structure with few defects. • The KI-doped device behaved an improved resistive switching property. [ABSTRACT FROM AUTHOR]

This article, titled "Cover Feature: The Old Polyoxometalates in New Application as Molecular Resistive Switching Memristors," explores the use of polyoxometalates (POMs) in molecular resistive switching memristors. The article discusses five different types of POM-based active materials and their potential as next-generation molecular memristors. It provides information on the components of these materials, device fabrication, device parameters, and resistive switching mechanisms. The article is authored by Hailong Yang, Guoli Yue, Tao Li, Lingling Du, Haohong Li, Zhirong Chen, and Shoutian Zheng. [Extracted from the article]

Abstract A forming-free sol-gel derived ZrO x resistive switching random access memory (RRAM) is demonstrated in this paper. The ZrO x layer after annealing at 400 °C in air shows a condensed poly-crystalline structure with a significant reduction in interstitial oxygen content. The ZrO x RRAM exhibits a remarkable memory window of 103 for 500 dc switching cycles. Retention characteristic is examined to confirm the non-volatile property. The carrier conduction and resistive switching mechanisms are explored. The ZrO x RRAMs are detailedly investigated by XRD, XPS, FTIR, and SEM. Highlights • Simplified and low-cost fabrication of a forming-free ZrO x RRAM. • Resistive switching mechanism of sol-gel ZrO x films. • Demonstration of an ZrO x RRAM with an indium ball top electrode. • Effect of post-annealing on sol-gel ZrO x RRAM performance. [ABSTRACT FROM AUTHOR]

Abstract Resistive random access memory has emerged as a promising next-generation non-volatile memory. AgInZnS (AIZS) semiconductor nanoparticles are demonstrated due to their large abundance, non-toxicity and the simplicity of synthesis. Herein, AIZS nanoparticles are synthesized as the switching layer in the sandwich structure of Al/AIZS/ITO via a hot-injection method and show excellent optical and electronic properties. By means of the electrical characterization, the memory device shows bipolar resistive switching behavior and exhibits the ON/OFF current ratio of about 18 with the good endurance performance over 75 cycles. This study reveals that the obtained AIZS nanoparticles have a great potential to be used in non-volatile resistive switching memory application. [ABSTRACT FROM AUTHOR]

Abstract Flexible resistive random access memory devices based on polymer films embedded with nanoparticles have attracted great attention. The electrode has been considered to play a key role in affecting switching performance, making its elucidation a vital issue. In the present study, the effect of various electrode materials, such as Ag, Al, Cu, indium tin oxide and Au on the resistive switching of a poly(N-vinylcarbazole) film embedded with TiO 2 nanoparticles spin-coated on flexible substrate was investigated. Switching was found to depend on the interface between the electrode and functional layer. Using numerical simulations based on finite element analyses, it was demonstrated that the delamination at the electrode/active-layer interface limits the formation of conduction paths. The present results well-explains the reason of the conduction mechanism transition observed for samples with Au or Cu electrodes before and after bending, which may provide useful information for the electrode-dependent switching performance in future flexible resistive random access memory devices. [ABSTRACT FROM AUTHOR]

We proposed a PbS-buffered method to fabricate the (110)-textured CH 3 NH 3 PbI 3 (MAPbI 3 ) film by three-step conversion (PbS → PbI 2  → MAPbI 3 ). The PbS buffer layer comprised numerous polyhedron particles was prepared on top of the Glass/indium tin oxide (ITO) via a chemical bath deposition process. Firstly, the PbS was converted to PbI 2 by I 2 gas annealing that caused a dense and (001)-preferred PbI 2 . Secondly, the PbI 2 was turned into a MAPbI 3 film by MAI vapor annealing, of which the degree of preferring orientation of the (110) face was higher and the micrometer grains was more compact than that was prepared by the conventional two-step (PbI 2  → MAPbI 3 ) spin-coated MAPbI 3 . The dense and (001)-textured PbI 2 , which was converted from the PbS with an appropriate condition, was the key to obtain the (110)-preferred MAPbI3 with a good quality. For comparative study, the memory devices (Glass/ITO/MAPbI 3 /poly methyl methacrylate (PMMA)/Al) made by the PbS-buffered MAPbI 3 and the spin-coated MAPbI 3 were both studied. As a result, both of them showed bipolar resistive switching behaviors with an ON/OFF ratio of ~10 2 ; whereas the leakage current of the PbS-buffered MAPbI 3 sample was 3 orders lower than that of the spin-coated one. The large crystalline grain, high-compact structure and (110) preferred texture of the PbS-buffered MAPbI 3 were believed to contribute to such a low leakage current, which is beneficial for the memory application. [ABSTRACT FROM AUTHOR]

Abstract: In recent years, numerous organic molecules and polymers carrying various functional groups were synthesized and used in fabrication of wearable electronic devices. Compared to previous materials that suffer from poisonousness, stiffness and complex film fabrication, we circumvent above matters by taking advantage of mussel‐inspired polydopamine as our active material to realize resistive random access memories (RRAMs). Polydopamine thin films were grown on indium tin oxide glass catalyzed by Cu2SO4/H2O2 and characterized by Fourier infrared spectroscopy (FT‐IR), UV/Vis spectroscopy and scanning electron microscopy. The Al/Polydopamine film/ITO devices possess ternary memory behavior with good ternary device yield with two threshold voltages around 1.50 V and 3.50 V, long data retention over 104 s of continuous reading or 104 pulse reading. The two resistance switchings are attributed to defects functioning as charge traps and the formation of conductive filaments. A flexible device based on Al/polydopamine film/ITO/polyethylene terephthalate retains its ternary memory behavior after being bent with a bending radius of 1.54 cm and bending cycles up to 5000, demonstrating good compatibility and flexibility of polydopamine. [ABSTRACT FROM AUTHOR]

In this study, indium tin oxide (ITO), zinc oxide (ZnO), tungsten oxide (WO x ), and aluminum nitride (AlN) were employed to fabricate and investigate four transparent resistive random access memory (ReRAMs) structures: ITO/ZnO/ITO (structure 1), ITO/WO 3 /ZnO/ITO (structure 2), ITO/WO x (x < 3)/WO 3 /ZnO/ITO (structure 3), and ITO/WO x (x < 3)/WO 3 /ZnO/AlN/ITO (structure 4). Structure 4 exhibited less variation in low-resistance states, lower operating voltages, and higher endurance compared with other structures. This phenomenon was attributed to the oxygen-deficient WO x layer in structure 4, which acted as an oxygen ion reservoir for efficient resistive changes, and the WO 3 layer limited the filament rupture and formation region. Moreover, the high thermal conductivity of the AlN layer alleviated the thermally activated ion movement of the ReRAM and strengthened the high-resistance state. Structure 4 was found to be the optimal structure, with median operating voltages 1.6 V for SET operations and − 1.0 V for RESET operations, retention of > 10 4 s at 200 °C, and endurance of 10 4 cycles with a resistance ratio of over 20. Structure 4 exhibited extremely high stability in both low- and high-resistance states during cycling. The transmittance of structure 4 was 85.49%, which is suitable for optoelectronic applications. [ABSTRACT FROM AUTHOR]

Resistive switching (RS) effect has attracted enormous attention due to its potential for application of resistive random access memory with fast speed, good scalability and high endurance. NiO is a model system of RS effect, in which the formation/rupture of nickel filaments is directly related to the RS effect. In fact, it is still controversial that the RS effect in NiO films should be attributed to whether a single filament or multi-filaments. In this work, we demonstrate that multi-filaments are involved in the RS process by means of conventional I-V measurements, conductive atomic force microscopy and transmission electron microscopy. Furthermore, we observed the interesting tunneling magnetoresistance in this system for the first time, which not only reveals the mechanism of multi-filaments, but also provides a new way for multifunctional devices. [ABSTRACT FROM AUTHOR]

Two different displacement damage experiments were performed on CBRAM cells. In one experiment, conductive bridging random access memory (CBRAM) cells were exposed to 14 MeV neutrons to a total fluence of 3.19 \times 10^13 n/cm2. In the second test, CBRAM cells were bombarded with 200 keV Si2+ ions. In both the experiments, the high resistance and low resistance states (LRSs) of the cells were observed to converge with increasing particle fluence. After reaching a 14 MeV neutron fluence of $2.93 \times 10^{{{13}}}$ n/cm2, the CBRAM cells became irrecoverably locked into their final resistance state. In situ testing during heavy ion exposure showed a steady decrease in the resistance state of each cell with each successive exposure to the beam. The devices eventually became locked in an LRS. [ABSTRACT FROM PUBLISHER]

In this paper, the Ni/VOx/Al resistive random access memory (RRAM) device is constructed and it shows bipolar resistive switching behavior, low resistive state (LRS) nonlinearity, and good retention. The set and reset processes are likely induced by the electron trapping and detrapping of trapping centers in the VOx films, respectively. The conduction mechanism in negative/positive region are controlled by space charge limited current mechanism (SCLC)/Schottky emission. The temperature dependence of I–V curves for HRS is measured to confirm the defects trapping and detrapping electrons model. activation energy was calculated to analyze the endurance performance of the device. The detailed analysis of the switching behavior with SCLC mechanism and Schottky emission mechanism could provide useful information for electronic bipolar resistive switching (eBRS) characteristics. [ABSTRACT FROM AUTHOR]

Nonvolatile resistive random-access memory devices based on graphene-oxide-wrapped gold nanospheres (AuNS@GO) are fabricated following a one-step room-temperature solution-process approach reported herein for the first time. The effect of the thickness of the GO layer (2, 5, and 7 nm) and the size of the synthesized AuNS (15 and 55 nm) are inspected. Reliable bistable switching is observed in the devices made from a flexible substrate and incorporating 5 and 7 nm thick GO-wrapped AuNS, sandwiched between two metal electrodes. Current-voltage measurements show bipolar switching behavior with an ON/OFF ratio of 103 and relatively low operating voltage (−2.5 V). The aforementioned devices unveil remarkable robustness over 100 endurance cycles and a retention of 103 s. Conversely, a 2 nm thick GO layer is shown to be insufficient to allow current passage from the bottom to the top electrodes. The resistive switching mechanism is demonstrated by space charge trapped limited current due to the AuNS in AuNS@GO matrix. The proposed device and methodology herein applied are expected to be attractive candidates for future generation flexible memory devices. [ABSTRACT FROM AUTHOR]

Amorphous SrMoO 4 (SMO) thin films were deposited on Pt/Ti/SiO 2 /Si substrates at room temperature by pulsed laser deposition and the resistive switching (RS) behavior of the Au/SMO/Pt devices was investigated. The Au/SMO/Pt devices exhibit typical unipolar RS behavior with excellent switching parameters as follows: high resistance ratio (~10 5 ) between the low resistance state (LRS) and high resistance state (HRS), non-overlapping switching voltages, and good endurance and retention characteristics. Detailed analysis of their current-voltage characteristics reveals that the conduction mechanisms are Ohmic conduction in the LRS and lower voltage region of HRS, and Poole-Frenkel emission in the higher voltage region of the HRS. Temperature dependent resistance measurements, combined with x-ray photoelectron spectroscopy and model analysis indicate that the unipolar RS behavior of the Au/SMO/Pt devices could be understood by a conical conducting filaments (CFs) model in which the conical CFs are composed of oxygen vacancies. The conical CFs extend from the cathode to anode during the forming process and the observed RS behavior occurs in the localized region near the anode. These results suggest that the room-temperature- deposited amorphous SMO thin films could find potential application in nonvolatile RS memory. [ABSTRACT FROM AUTHOR]

Graphene-based resistive random access memory devices is a promising non-volatile memory technology that combines low operation voltage and power, extremely fast write/erase speeds, excellent reliability and storage capacity of RRAM with low-cost, large area and flexibility of carbon-based technologies. However, low-cost single-step synthesis of high-quality graphene remains a challenge. In this paper, high quality graphene synthesized directly from sustainable carbon source ( M. alternifolia oil) was used as electrode and pentacene/C 60 as active layers in carbon-based RRAM. I-V measurements were used to demonstrate reproducible switching (rapid increase in current) at certain voltage which was reversible. Charge transport and accumulation was visualized using electric field induced optical second harmonic generation and charge modulation spectroscopy. Hole transport from graphene layer to the organic layer was the primary cause of the observed switching behavior. [ABSTRACT FROM AUTHOR]

We have performed the fabrication and characterization of resistive random access memory devices based on Au/ZnO nanowires/Ag capacitor structure. First, vertically aligned ZnO nanowires were grown on Ag electrode layer. The poly 4-vinyl phenol (PVP) was then spin-coated on nanowires as a support and isolation layer. After appropriate etching of PVP in oxygen plasma to expose ZnO nanowire tips, a layer of Au was sputtered onto the tips of ZnO nanowires forming the top electrode. The resulting ZnO nanowire array devices were found to exhibit bipolar resistive switching characteristics. Switching between high resistance state (HRS) and low resistance state (LRS) could be achieved at a very low threshold voltage of 0.3 V for a long conducting channel of 500 nm, exhibiting a very low electric field, without electrical forming. The resistance ratios of HRS to LRS were higher than two orders of magnitude. The results indicate the application potentials of Au/ZnO nanowires/Ag devices for nonvolatile memory devices. [ABSTRACT FROM AUTHOR]

The demand for flexible resistive random access memories (ReRAM) has increased because wearable devices, such as smart watches, e-paper, and flexible displays, have become a trend. These devices have advantages such as portability, light weight, and user-friendly interfaces, which are better than the currently available rigid electronic systems. A flexible nonvolatile memory is an essential part of electronic systems. In this study, zinc oxide (ZnO) thin films were used for fabricating ReRAM devices. The fabrication was achieved by a simple solution processing method and low temperature annealing (approximately 100 °C) on a hot plate. In addition, the devices fabricated on polyimide substrates showed excellent operational characteristics with a high ratio (≥ 10 4 ) of the high resistance state to the low resistance state. The operational voltage of the ZnO ReRAM devices was < 2 V, and the reset operational voltage was less than − 1 V. [ABSTRACT FROM AUTHOR]