Stable Bipolar Resistive Switching Research Articles

A sub-500 mV monolayer hexagonal boron nitride based memory device

The recent discovery of memristive devices based on two-dimensional materials have attracted much interest for emerging applications on flexible memory, neuromorphic computing, and so forth. Reducing the thickness to a single-layer level would prompt the scaling limit to sub-nanometer. However, monolayer materials based vertical memristive devices generally suffer inferior performance with high operating voltage, large leakage currents, and poor reliability. In this study, an interfacial polymer layer is inserted between the monolayer hexagonal boron nitride (h-BN) and top electrodes, which not only helps to constrain the conducting filament size but also block the formation of excess filaments from the bottom Cu foil. Therefore, the device shows stable bipolar resistive switching behavior with low operating voltage (< 500 mV), large on/off ratio (up to 105), long retention time (> 105 s), and excellent flexibility. It is demonstrated that tunneling conduction is shown in off-state and on-state current conducts via metallic conducting filaments, which are formed by the substitute of metal ions for lattice vacancies in h-BN. This work presents a scalable interface engineering strategy to control the interactions between metal ions and defects in monolayer h-BN films and sheds light on their promising application for large-scale integrated ultrathin flexible memory.

Enhancement of Resistive Switching Characteristics of Sol–Gel TiO x RRAM Using Ag Conductive Bridges

In this article, the effects of active Ag electrodes on the ROFF/RON ratio, SET/RESET voltages, and endurance characteristics of a sol-gel TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> resistive memory are investigated. Stable bipolar resistive switching (RS) behavior with a large R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> /R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> ratio of 105 is observed in an Ag/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -Si resistive memory. The SET and RESET processes can only be triggered by positive and negative voltages, respectively. Nonpolar RS behavior is found when directly using a tungsten probe to measure the I-V curves of a TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> -Si device. A high voltage of ~+40 V is needed to induce the SET process. In addition, the RS behavior is not stable and can only repeat few times. When the top and bottom electrodes are both Ag (Ag/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> /Ag), the SET process can be easily triggered by a low voltage regardless of the voltage polarity. However, the RESET process does not happen in the following voltage cycles. Dramatic differences in the RS characteristics of these devices verify the impact of the Ag electrode on the RS characteristics of the sol-gel TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</sub> layer.

Abnormal volatile and normal stable bipolar resistive switching characteristics of hybrid nanocomposites: Morphology–defects–property ‘Relationship

The characteristics of nano-fillers in a polymer matrix have a significant influence on the microstructural, thermo-mechanical, optical, and conductivity properties of organic-inorganic nanocomposites. In this study, we investigated the influence of inorganic component – ZnO nanoparticles (NPs) on the characteristics and properties of PVA-ZnO nanocomposites which have been applied as an insulation layer in a resistive switching (RS) device. Three nanocomposites originating from three different types of ZnO NPs exhibit different RS characteristics: Abnormal volatile RS is observed with the ∼20-nm-sized spherical-like NPs (Z1) and 15–20-nm-sized mixed shaped NPs (Z2), whereas normal nonvolatile bipolar RS is observed with the 50–150-nm-sized hexagonal rod-like NPs (Z3). The concentration and size of the intrinsic defects of the ZnO NPs as well as the thickness of the PVA-ZnO interface are responsible for the different charge transport paths, operating voltage ranges, and ON/OFF switching ratios of the memory devices. Simultaneously, the distinct sizes and morphologies of the ZnO NPs can affect the nanoholes among the PVA chains and induce various fractional free volumes in the nanocomposites. It may modify the conductivity of the nanocomposite layer or the resistance ratio of the memory devices. Understanding the influence of ZnO NPs size, morphology, and defects on the characteristics of RS of PVA-ZnO nanocomposites can help in the selection and management of functional applications, especially in the data storage field.

Temperature dependence of resistive switching characteristics in NiO(111) films on metal layer

Dense and uniform NiO(111) films are deposited on a Pt layer via magnetron sputtering. At temperatures of up to 80 °C, the Ag/NiO(111)/Pt memory cells exhibit a stable bipolar resistive switching behaviour with a switching time of <40 µs and a retention time of >104 s. Both the Arrhenius-type and Schottky-type current-temperature plots are well fitted by linear relationships, revealing that the electron transport in the high resistance state is governed by the Schottky tunnelling mechanism. The x-ray photoelectron spectroscopy depth profiles demonstrate that the NiO(111) films are highly oxygen deficient, and that oxygen-vacancy conductive filaments are responsible for the temperature-dependent resistive switching behaviour of the NiO(111) films.

Li-Doping Effect on Characteristics of ZnO Thin Films Resistive Random Access Memory.

In this study, a Pt/Ag/LZO/Pt resistive random access memory (RRAM), doped by different Li-doping concentrations was designed and fabricated by using a magnetron sputtering method. To determine how the Li-doping concentration affects the crystal lattice structure in the composite ZnO thin films, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) tests were carried out. The resistive switching behaviors of the resulting Pt/Ag/LZO/Pt devices, with different Li-doping contents, were studied under direct current (DC) and pulse voltages. The experimental results showed that compared with the devices doped with Li-8% and -10%, the ZnO based RRAM device doped by 5% Li-doping presented stable bipolar resistive switching behaviors with DC voltage, including a low switching voltage (<1.0 V), a high endurance (>103 cycles), long retention time (>104 s), and a large resistive switching window. In addition, quick switching between a high-resistance state (HRS) and a low-resistance state (LRS) was achieved at a pulse voltage. To investigate the resistive switching mechanism of the device, a conduction model was installed based on Ag conducting filament transmission. The study of the resulting Pt/Ag/LZO/Pt devices makes it possible to further improve the performance of RRAM devices.

A New Approach to the Fabrication of Memristive Neuromorphic Devices: Compositionally Graded Films.

Energy-efficient computing paradigms beyond conventional von-Neumann architecture, such as neuromorphic computing, require novel devices that enable information storage at nanoscale in an analogue way and in-memory computing. Memristive devices with long-/short-term synaptic plasticity are expected to provide a more capable neuromorphic system compared to traditional Si-based complementary metal-oxide-semiconductor circuits. Here, compositionally graded oxide films of Al-doped MgxZn1−xO (g-Al:MgZnO) are studied to fabricate a memristive device, in which the composition of the film changes continuously through the film thickness. Compositional grading in the films should give rise to asymmetry of Schottky barrier heights at the film-electrode interfaces. The g-Al:MgZnO films are grown by using aerosol-assisted chemical vapor deposition. The current-voltage (I-V) and capacitance-voltage (C-V) characteristics of the films show self-rectifying memristive behaviors which are dependent on maximum applied voltage and repeated application of electrical pulses. Endurance and retention performance tests of the device show stable bipolar resistance switching (BRS) with a short-term memory effect. The short-term memory effects are ascribed to the thermally activated release of the trapped electrons near/at the g-Al:MgZnO film-electrode interface of the device. The volatile resistive switching can be used as a potential selector device in a crossbar memory array and a short-term synapse in neuromorphic computing.

Bipolar resistive switching in HoCrO3 thin films

We report on the resistive switching characteristics of an HoCrO3 (HCO) based memristor device. The device comprising Ag/HCO/fluorine doped tin oxide shows stable bipolar resistive switching with a good ON/OFF resistance ratio between high resistance state (HRS) and low resistance state (LRS). Furthermore, the device is capable to show excellent endurance and retentivity characteristics over a period of 30 days. The statistical distribution of the switching parameters (voltage and resistance) show a narrow distribution, hinting reliable memory performance and stability of the device. Impedance spectroscopy analysis of the HRS and LRS illustrates a bulk resistance effect, which is due to formation of multiple ionic conductive channels in the film with oxygen vacancies. Indeed, conducting channels formed by oxygen vacancies are further confirmed by calculating the temperature coefficient of resistance through resistance vs temperature measurements. We believe that these results will be helpful in developing future memory devices based on resistive switching.

Flexibility of Fluorinated Graphene-Based Materials.

The resistivity of different films and structures containing fluorinated graphene (FG) flakes and chemical vapor deposition (CVD)-grown graphene of various fluorination degrees under tensile and compressive strains due to bending deformations was studied. Graphene and multilayer graphene films grown by means of the chemical vapor deposition (CVD) method were transferred onto the flexible substrate by laminating and were subjected to fluorination. They demonstrated a weak fluorination degree (F/C lower 20%). Compressive strains led to a strong (one-two orders of magnitude) decrease in the resistivity in both cases, which was most likely connected with the formation of additional conductive paths through fluorinated graphene. Tensile strain up to 3% caused by the bending of both types of CVD-grown FG led to a constant value of the resistivity or to an irreversible increase in the resistivity under repeated strain cycles. FG films created from the suspension of the fluorinated graphene with a fluorination degree of 20–25%, after the exclusion of design details of the used structures, demonstrated a stable resistivity at least up to 2–3% of tensile and compressive strain. The scale of resistance changes ΔR/R0 was found to be in the range of 14–28% with a different sign at the 10% tensile strain (bending radius 1 mm). In the case of the structures with the FG thin film printed on polyvinyl alcohol, a stable bipolar resistive switching was observed up to 6.5% of the tensile strain (bending radius was 2 mm). A further increase in strain (6.5–8%) leads to a decrease in ON/OFF current ratio from 5 down to 2 orders of magnitude. The current ratio decrease is connected with an increase under the tensile strain in distances between conductive agents (graphene islands and traps at the interface with polyvinyl alcohol) and thickness of fluorinated barriers within the active layer. The excellent performance of the crossbar memristor structures under tensile strain shows that the FG films and structures created from suspension are especially promising for flexible electronics.

High-Performance TiN/Al2O3/ZnO/Al2O3/TiN Flexible RRAM Device With High Bending Condition

The bipolar resistive switching (RS) characteristics of the ZnO-based TiN/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /ZnO/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /TiN structure are investigated for flexible nonvolatile memory applications. Using a thin Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> buffer layer on both sides of the ZnO device shows uniform and eminently stable bipolar resistance switching characteristics. The device exhibits good RS with more than two orders of resistance ON-OFF ratio, retention of >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> s at 120 °C, good dc endurance >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> cycles, and high ac endurance of >10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">8</sup> cycles with 40-ns pulsewidth without any degradation. The device shows high mechanical stability when under 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> continuous repetitive flexible bendings, indicating that high endurance with a very small bending radius of up to 3 mm. The lower Gibbs free energy of the Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (-1676 kJ/mol) film compared with the ZnO (-320.4 kJ/mol) and TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> (-994 kJ/mol) films can improve the RS properties of the TiN/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /ZnO/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /TiN device. The significant improvement in the TiN/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /ZnO/Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> /TiN device is due to the reason that thin Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> layers on both sides of ZnO would help stabilize the local oxygen migrations for the formation and rupture of the conductive filament during the continuous switching cycles, resulting in high memory switching characteristics.

Flexible resistive switching device based on the TiO2 nanorod arrays for non-volatile memory application

In this article, a flexible resistive switching memory is developed based on TiO2 nanorod arrays with interstice between the nanorods to release the bending stress/strain. The device shows a stable forming-free bipolar resistive switching behavior with low operating voltage of below 3 V, high ON/OFF ratio of above 102, good retention for more than 105 s, good endurance of 107 cycles, and good thermal stability of the high resistance and low resistance state at 85 °C during the retention and fatigue tests. Moreover, under the different bending radius from 12 mm to 5 mm, the electrical performances referring to operating voltage and ON/OFF ratio of the device show few changes, and under the bending cycles of 400 times with the bending radius of 12 mm, all of the devices show no interfacial crack or delamination as well as keep the bipolar resistive switching behavior with the low operating voltage and high ON/OFF ratio. The good performances of the devices suggest that the TiO2 nanorod arrays resistive switching device may open up new possibilities in realizing high-performance flexible memory.

Improved air stability and low voltage resistive switching behaviors of NiO-buffered CH3NH3PbI3 films prepared by a solution method

Electric field-induced drift of ions or charged defects in organic–inorganic hybrid perovskite materials generally results in distinct current–voltage hysteresis, opening up a new era in the development of low-cost resistive switching memory and neural synapse devices. Here, a new type of resistive switching memory cell based on NiO-buffered CH3NH3PbI3 films is prepared by a solution method. It exhibits stable and low voltage bipolar resistive switching behaviors: switching voltages lower than ±0.5 V, an ON/OFF ratio higher than 103, and a reversible current–voltage loop of more than 400 cycles in air ambient. Both ‘iodine-vacancy conductive filaments’ and the ‘interfacial p–n junction effect’ are responsible for the improved resistive switching properties. This work establishes the potential for application in low operation voltage organic–inorganic hybrid perovskite resistive switching devices.

Flexible and Waterproof Resistive Random‐Access Memory Based on Nitrocellulose for Skin‐Attachable Wearable Devices

AbstractMemory for skin‐attachable wearable devices for healthcare monitoring must meet a number of requirements, including flexibility and stability in external environments. Among various memory technologies, organic‐based resistive random‐access memory (RRAM) devices are an attractive candidate for skin‐attachable wearable devices due to the high flexibility of organic materials. However, organic‐based RRAMs are particularly vulnerable to external moisture, making them difficult to apply as skin‐attachable wearable devices. In this research, RRAMs are fabricated that meet the requirements for skin‐attachable wearable devices using a novel organic material, nitrocellulose (NC), which is biocompatible with high water‐resistance and high flexibility. The fabricated NC‐based RRAMs show a stable bipolar resistive switching characteristic. In addition, the formation of a native Al oxide between Al and NC is verified, which is the source of the bipolar switching characteristic of NC‐based RRAMs. Furthermore, electrical and chemical analysis is conducted after dipping and submersion into various solutions as well as deionized water to confirm the water‐resistance of the NC‐based RRAMs. Finally, it is also confirmed that NC‐based RRAMs are suitable for use in skin‐attachable wearable devices through a flexibility test. In conclusion, this study suggests that NC‐based RRAMs can be applied in skin‐attachable wearable devices, simplifying healthcare in the future.

Electro-optical dual modulation on resistive switching behavior in BaTiO3/BiFeO3/TiO2 heterojunction**Project supported by the Scientific Research Program of Hunan Provincial Education Department, China (Grant No. 18C0232) and the International Cooperative Extension Program of Changsha University of Science and Technology, China (Grant No. 2019IC35).

The novel BaTiO3/BiFeO3/TiO2 multilayer heterojunction is prepared on a fluorine-doped tinoxide (FTO) substrate by the sol–gel method. The results indicate that the Pt/BaTiO3/BiFeO3/TiO2/FTO heterojunction exhibits stable bipolar resistive switching characteristic, good retention performance, and reversal characteristic. Under different pulse voltages and light fields, four stable resistance states can also be realized. The analysis shows that the main conduction mechanism of the resistive switching characteristic of the heterojunction is space charge limited current (SCLC) effect. After the comprehensive analysis of the band diagram and the P–E ferroelectric property of the multilayer heterojunction, we can deduce that the SCLC is formed by the effect of the oxygen vacancy which is controlled by ferroelectric polarization-modulated change of interfacial barrier. And the effective photo-generated carrier also plays a regulatory role in resistance state (RS), which is formed by the double ferroelectric layer BaTiO3/BiFeO3 under different light fields. This research is of potential application values for developing the multi-state non-volatile resistance random access memory (RRAM) devices based on ferroelectric materials.

Zn vacancy complex-determined filamentary resistive switching characteristics in Au/ZnSe/ITO chalcogenide-based memory cells

ZnSe films with a sphalerite structure and about 100nm grain size were deposited on ITO substrate. 200 stable bipolar resistive switching (RS) cycles were obtained in Au/ZnSe/ITO chalcogenide-based memory cells and it shows an ON/OFF ratio of 10 and retention time of 104 seconds. The conduction mechanism is Ohmic in both low resistance state (LRS) and low voltage region in high resistance state (HRS) while thermionic emission limited conduction (TELC) at high voltage region in HRS. The top electrode (TE) size independence of low resistance implies a filamentary resistive switching mechanism. Photoluminescence (PL) spectroscopy shows a double difference of relative intensity between shallow zinc vacancy state and deep zinc vacancy complex state in HRS and LRS. The explanation for HRS is the dissociation of zinc vacancy complex and the formation of zinc vacancy. Then the shallow acceptor zinc vacancy compensates for the shallow donor contributing the HRS. It is deduced from linear relation of reset voltage and reset power versus temperature that the thermal activation energy of ZnSe film is 0.19 eV, which indicates an over 20nm intertrap distance and the critical temperature for conductive filament (CF) rupture is 305.6K with 0.2mV/s sweep rate, respectively. The component of CF is metal-like shallow donor such as Al or Ga with the help of deep zinc vacancy complex to depress the compensation of shallow zinc vacancy acceptor.

Strategic extended air stability of organolead halide perovskite nonvolatile memory devices

In this study, we demonstrated long-term stability in the resistive switching (RS) properties of MAPbI3 films, coated via a one-step chemical vapor deposition (CVD) method using no additives or polymers. The RS behavior of the CVD-fabricated memory devices compares favorably to that of spin-coated films; these devices exhibited reliably stable bipolar resistive switching properties for 30 days under ambient conditions, while spin-coated devices were stable for only 10 days. For further enhancement of air stability, a 20 nm-thick ZnO passivation layer was deposited on MAPbI3via on-axis and facing-target sputtered (FTS) techniques. The resistive random-access memory (ReRAM) devices with a ZnO passivation layer deposited via FTS technique exhibited extended air stability for 3 months under ambient conditions, whereas in the case of memory devices fabricated with an on-axis sputtered passivation layer, air stability was limited to 60 days. This extended air stability can be attributed to excellent step coverage and free of plasma damage during deposition. Memory devices fabricated via the CVD and FTS methods showed no significant variations at either set or reset levels of voltage and showed favorable levels in terms of both data retention and endurance performance with storage time.

Resistive Switching Effect with ON/OFF Current Relation up to 109 in 2D Printed Composite Films of Fluorinated Graphene with V2O5 Nanoparticles

AbstractComposite films consisting of fluorinated graphene flakes with vanadium oxide (V2O5) nanoparticles exhibit a stable bipolar resistive switching effect that depends on the size of the composite particles, on the proportion between the film components, on the heat‐treatment conditions of the films (or on the hydration degree of V2O5 nanoparticles), and on the area of the structures. The ON/OFF current ratio of printed crossbar structures reaches 106–109 for films 20–50 nm thick, with the switching voltage varying in the range from 1.5 to 3.7 V, 30 ns time for structure switching, and endurance characteristics up to 1.3 × 103 switching cycles without any changes in ON/OFF current ratio. A mechanism to describe the resistive switching effect implying the formation of sign‐alternating electric fields in a multibarrier structure is proposed. The investigated structures are of interest for the fabrication of nonvolatile memory cells, including memory cells for flexible and printed electronics.

Programmable Multilevel Memtransistors Based on van der Waals Heterostructures

AbstractNeuromorphic computing that mimics the energy‐efficient cortical neural network in the human brain is attractive because of its possibility to process complex and massive data sets and achieve fast computing capability. Herein, a heterosynaptic and programmable memtransistor architecture with high computing functionality is reported by monolithically integrating a hexagonal boron nitride (h‐BN) memristor with a molybdenum disulfide (MoS2) transistor. Memristors consisting of a vertically stacked van der Waals materials (multilayer graphene (MLG) and h‐BN) exhibit a stable bipolar resistive switching behavior with a memory window more than three orders of magnitude due to the formation and rupture of the metallic filament within the h‐BN layer. By controlling the resistance state of the h‐BN memristor, the behaviors of the memtransistor can be programmed with a high switching ratio of ≈104, showing ≈16 pW standby power consumption. A multistate computing window and tunable current on/off ratio can be achieved by controlling the synaptic weight of the memristor, demonstrating that the presented 2D architecture can be exploited as a logic inverter device. The results pave the way toward the development of highly functional neuromorphic systems for the next‐generation in‐memory computing.

Bipolar resistive switching characteristics of tungsten-doped indium–zinc oxide conductive-bridging random access memory

The purpose of this work is to develop a reliable amorphous tungsten-doped indium-zinc oxide based conductive-bridging random access memory (CBRAM). The device with Cu/TiW/InWZnO/Pt structure exhibits stable bipolar resistive switching behavior. The device also shows good non-volatile memory characteristics, such as low operation voltage, on/off resistance ratio (∼102), high switching endurance (more than 5×102 cycles). The temperature coefficient of resistance in the conductive filament confirms that an electro-chemical metallization (ECM) based conduction is observed in the InWZnO device. Furthermore, the temperature retention characteristics and the current transport mechanisms are also investigated. According to our experiments, we propose a model to explain the resistive switching phenomenon observed in our devices. These results have given a great potential for the transparent amorphous oxide semiconductor (TAOS)-based material utilizing in CBRAM stacks and integrating into the display circuits for future memory-in-pixel applications.

Bipolar resistive switching characteristics of samarium oxide solid electrolyte thin films for non-volatile memory applications

In this paper, we report the bipolar resistive switching behaviors in Ag/Sm2O3/Pt structures where the Sm2O3 thin films act as solid electrolyte layer of electrochemical metallization memory (ECM) devices. The memory devices show reproducible and stable bipolar resistive switching over 1000 cycles with a resistance ratio (high-resistance state to low-resistance state) of over 4 orders of magnitude and stable retention for over 104[Formula: see text]s at room temperature. Moreover, the benefits of high yield and multilevel storage possibility make the device promising in the next generation non-volatile memory application.

Flexible Pyrene/Phenanthro[9,10‐d]imidazole‐Based Memristive Devices for Mimicking Synaptic Plasticity

Emulation of memory and learning functionalities of biological synapses using a two‐terminal electronic device with bidirectional progressive conductance modulation is an indispensable move toward the development of bio‐inspired neuromorphic networks. Herein, a small molecule 1‐phenyl‐2‐(4‐(pyren‐1‐yl)phenyl)‐1H‐phenanthro[9,10‐d]imidazole (pPPI) is synthesized, and an organic synaptic device is investigated with bipolar resistive switching characteristics and bidirectional gradual conductance regulation for the first time. A facile solution‐processing approach can be used to deposit a uniform active layer on flexible substrates. Our pPPI‐based nonvolatile memory presents a superior electrical performance, such as relatively stable and reproducible bipolar resistive switching phenomena and a robust data retention capability. In particular, our device displays a remarkably large switching window of around 7.0 × 107, which is a record ON/OFF ratio compared with other small molecule‐based memories up to now. In addition, comprehensive cognitive functions of chemical synapses, for example, the excitatory postsynaptic current (EPSC), paired‐pulse facilitation/depression (PPF/PPD), spike‐rate‐dependent plasticity (SRDP), and spike‐time‐dependent plasticity (STDP) are successfully achieved. Our achievement of a synaptic device based on small molecules may boost the development of bio‐inspired neuromorphic systems using organic electronics.