Memristive devices are able to store and process information, which offers several key advantages over the transistor-based architectures. However, most of the two-terminal memristive devices have fixed functions once made and cannot be reconfigured for other situations. Here, we propose and demonstrate a memristive device “memlogic” (memory logic) as a nonvolatile switch of logic operations integrated with memory function in a single light-gated memristor. Based on nonvolatile light-modulated memristive switching behavior, a single memlogic cell is able to achieve optical and electrical mixed basic Boolean logic of reconfigurable “AND”, “OR”, and “NOT” operations. Furthermore, the single memlogic cell is also capable of functioning as an optical adder and digital-to-analog converter. All the memlogic outputs are memristive for in situ data storage due to the nonvolatile resistive switching and persistent photoconductivity effects. Thus, as a memdevice, the memlogic has potential for not only simplifying the programmable logic circuits but also building memristive multifunctional optoelectronics.Keywords: light-gated memristor; memcomputing; memlogic; memristive switching; persistent photoconductance;

Flexible and transparent resistive switching memories are highly desired for the construction of portable and even wearable electronics. Upon optimization of the microstructure wherein an amorphous-nanocrystalline hafnium oxide thin film is fabricated, an all-oxide based transparent RRAM device with stable resistive switching behavior that can withstand a mechanical tensile stress of up to 2.12% is obtained. It is demonstrated that the superior electrical, thermal and mechanical performance of the ITO/HfOx/ITO device can be ascribed to the formation of pseudo-straight metallic hafnium conductive filaments in the switching layer, and is only limited by the choice of electrode materials. When the ITO bottom electrode is replaced with platinum metal, the mechanical failure threshold of the device can be further extended.

AbstractNanoscale manipulation of materials' physicochemical properties offers distinguished possibility to the development of novel electronic devices with ultrasmall dimension, fast operation speed, and low energy consumption characteristics. This is especially important as the present semiconductor manufacturing technique is approaching the end of miniaturization campaign in the near future. Here, a superior metal–insulator transition (MIT) of a 1D VO2 nanochannel constructed through an electric-field-induced oxygen ion migration process in V2O5 thin film is reported for the first time. A sharp and reliable MIT transition with a steep turn-on voltage slope of <0.5 mV dec−1, fast switching speed of 17 ns, low energy consumption of 8 pJ, and low variability of <4.3% is demonstrated in the VO2 nanochannel device. High-resolution transmission electron microscopy observation and theoretical computation verify that the superior electrical properties of the present device can be ascribed to the electroformation of nanoscale VO2 nanochannel in V2O5 thin films. More importantly, the incorporation of the present device into a Pt/HfO2/Pt/VO2/Pt 1S1R unit can ensure the correct reading of the HfO2 memory continuously for 107 cycles, therefore demonstrating its great possibility as a reliable selector in high-density crossbar memory arrays.

The present study is primarily designed to develop an environmentally-benign approach for the recovery of precious metals, especially gold, from the ever increasingly-discarded electronic wastes (e-waste). By coupling the metal reduction process with an increase in the intrinsic oxidation state of the aniline polymers, and the subsequent re-protonation and reduction of the intrinsically oxidized polymer to the protonated emeraldine (EM) salt, polyaniline (PANi) films and polyaniline coated cotton fibers are able to recover metallic gold from acid/halide leaching solutions of electronic wastes spontaneously and sustainably. The current technique, which does not require the use of extensive extracting reagents or external energy input, can recover as much as 90% of gold from the leaching acidic solutions. The regeneration of polyaniline after gold recovery, as confirmed by the X-ray photoelectron spectroscopy measurements, promises the continuous operation using the current approach. The as-recovered elemental gold can be further concentrated and purified by incineration in air.By coupling the metal reduction process with an increase in the intrinsic oxidation state of the polymers, polyaniline (PANi) films and polyaniline coated cotton fibers are able to recover metallic gold from acid/halide leaching solutions of electronic wastes spontaneously and sustainably. The current technique, which does not require the use of extensive extracting reagents or external energy input, can recover as much as 90% of gold from the leaching acidic solutions.Download high-res image (210KB)Download full-size image

In this study, an artificial synapse with a sandwich structure of Ta/ethyl viologen diperchlorate [EV(ClO4)2]/triphenylamine-based polyimide (TPA-PI)/Pt is fabricated directly on a flexible PET substrate and exhibits distinctive history-dependent memristive behaviour, which meets the basic requirements for synapse emulation. Essential synaptic plasticity (including long-term plasticity and short-term plasticity) and some memory and learning behaviours of human beings (including the conversion from short-term memory to long-term memory and the “learning–forgetting–relearning”) have been demonstrated in our device. More importantly, the device still exhibits the synaptic performance when the surface strain of the device reaches 0.64% (or, the bending radius reaches 10 mm). Moreover, the device was able to endure 100 bending cycles. Our findings strongly demonstrate that the organic artificial synapse is not only promising for constructing a neuromorphic information storage and processing system, but is also interesting for the realization of wearable neuromorphic computing systems.

A bio-memristor fabricated with ferritin exhibits novel resistive switching characteristics wherein memory switching and threshold switching are made steadily coexistent and inter-convertible through controlling the magnitude of compliance current presets.

Switching luminescence of lanthanide-based molecules through an external electric field is considered as a promising approach toward novel functional molecule-based devices. Classic routes use casted films and liquid electrolyte as media for redox reactions. Such protocol, even if efficient, is relatively hard to turn into an effective solid-state device. In this work, we explicitly synthesize lanthanide-based dimers whose luminescent behavior is affected by the presence of Cu2+ ions. Excellent evaporability of the dimers and utilization of Cu2+-based solid-state electrolyte makes it possible to reproduce solution behavior at the solid state. Reversible modulation of Cu2+ ions transport can be achieved by an electric field in a solid-state device, where lanthanide-related luminescence is driven by an electric field. These findings provide a proof-of-concept alternative approach for electrically driven modulation of solid-state luminescence and show promising potential for information storage media in the future.

Memristors have been extensively studied for nonvolatile memory storage, neuromorphic computing, and logic applications. Particularly, synapse emulation is viewed as a key step to realizing neuromorphic computing, because the biological synapse is the basic unit for learning and memory. In this study, a memristor with the simple structure of Ta/viologen diperchlorate [EV(ClO4)2]/terpyridyl-iron polymer (TPy-Fe)/ITO is fabricated to simulate the functions of the synapse. Essential synaptic plasticity and learning behaviours are emulated by using this memristor, such as spike-timing-dependent plasticity and spike-rate-dependent plasticity. It is demonstrated that the redox between a terpyridyl-iron polymer and viologen species leads to our memristor behavior. Furthermore, the learning behavior depending on different amplitudes of voltage pulses is investigated as well. These demonstrations help pave the way for building bioinspired neuromorphic systems based on memristors.

Reversible nanoscale magnetization reversal controlled merely by electric fields is still challenging at the moment. In this report, first-principles calculation indicates that electric field-induced magnetization reversal can be achieved by the appearance of unidirectional magnetic anisotropy along the (110) direction in Fe-deficient cobalt ferrite (CoFe2–xO4, CFO), as a result of the migration and local redistribution of the Co2+ ions adjacent to the B-site Fe vacancies. In good agreement with the theoretical model, we experimentally observed that in the CFO thin films the nanoscale magnetization can be reversibly and nonvolatilely reversed at room temperature via an electrical ion-manipulation approach, wherein the application of electric fields with appropriate polarity and amplitude can modulate the size of magnetic domains with different magnetizations up to 70%. With the low power consumption (subpicojoule) characteristics and the elimination of external magnetic field, the observed electric field-induced magnetization reversal can be used for the construction of energy-efficient spintronic devices, e.g., low-power electric-write and magnetic-read memories.Keywords: cobalt ferrite thin films; electric field control of magnetism; ion migration and redistribution; reversible magnetization reversal;

Linear and hyperbranched poly(azomethine)s (PAMs)-based on triphenylamine moieties are synthesized and used as the functioning layers in the Ta/PAM/Pt resistive switching memory devices. Comparably, the hyperbranched PAM with isotropic architecture and semi-crystalline nature shows enhanced memory behaviors with more uniform distribution of the HRS and LRS resistances.

Thermally stable poly(triphenylamine) (PTPA) synthesized by an oxidative coupling reaction is used as the functional layer in memory devices, which exhibit non-volatile bistable resistive switching behavior with a large ON/OFF ratio over 5 × 108, a long retention time exceeding 8 × 103 s and a wide working temperature range of 30–390 K.

•A series of copolymers containing different ratio of electron-donor and acceptor moieties were prepared and characterized.•The memory behaviors of organic devices depend on the ratios of donor/acceptor in the polymers.•All polymers blending by donor- and acceptor-homopolymers do not show memory effects.•Controllable resistive memory switching effects have been established in donor–acceptor polymer systems.Controllable bistable electrical conductivity switching behavior and resistive memory effects have been demonstrated in Al/polymer/indium-tin oxide (ITO) sandwich structure devices, constructed from non-conjugated vinyl copolymers of PTPAnOXDm with pendant donor–acceptor chromophores. The observed electrical bistability can be attributed to the field-induced intra- and intermolecular charge transfer interaction between triphenylamine electron donor (D) and oxadiazole electron acceptor (A) entities, and is highly dependent on the chemical structure of the copolymers. The vinyl copolymers showed different memory behaviors, which depended on the loading of D/A ratios. The polymers containing only donor or acceptor moieties showed as insulators, the polymers containing both donor and acceptor moieties showed as WORM, flash and DRAM as D/A ratio increased. The structural effect on the physicochemical and electronic properties of the PTPAnOXDm copolymers, viz surface morphology, thermal stability, optical absorbance and photoluminescence, and molecular orbital energy levels, were investigated systematically to study the factors that influence the memory characteristics of the devices.Graphical abstractControllable resistive memory switching effects have been established in donor–acceptor polymer systems with triphenylamine (TPA) as the electron donor and (2,5-biphenyl)-1,3,4-oxadiazole (OXD) moiety as the acceptor. The devices fabricated from the vinyl copolymers showed as insulators, WORM, flash and DRAM memory depending on the ratios of TPA/OXD (D/A) in the polymers. The structural effects on the origin of the electrical bistability, which are arising from the intra- and intermolecular charge transfer interaction, have been investigated by exploring the chemical structure–memory characteristics relationships.

Resistive switching memories based on ion transport and related electrochemical reactions have been extensively studied for years. To utilize the resistive switching memories for high-performance information storage applications, a thorough understanding of the key information of ion transport process, including the mobile ion species, the ion transport paths, as well as the electrochemical reaction behaviors of these ions should be provided for material and device optimization. Moreover, ion transport is usually accompanied by processes of microstructure modification, phase transition, and energy band structure variation that lead to further modulation of other physical properties, e.g., magnetism, optical emission/absorbance, etc., in the resistive switching materials. Therefore, novel resistive switching memories that are controlled through additional means of magnetic or optical stimulus, or demonstrate extra functionalities beyond information storage, can be made possible via well-defined ion transportation in various switching materials and devices. In this contribution, the mechanism of ion transport and related resistive switching phenomena in thin film sandwich structures is discussed first, followed by a glance at the recent progress in the development of high-performance and multifunctional resistive switching memories. A brief perspective of the ion transport-based resistive switching memories is addressed at the end of this review.

Two donor–acceptor (D–A) polyazothines (PAs), incorporating the oxadiazole entity either acting as an electron acceptor (A) to form D–A structured PA-1 with the triphenylamine donor (D), or acting as a donor to form D–A structured PA-2 with the 3,3′-dinitro-diphenylsulfone acceptor, have been successfully synthesized via a polycondensation reaction. The variation in the role of the oxadiazole moiety in the D–A polymers, together with the use of different top electrode metals, leads to interesting electronic transport properties and various resistive switching behaviors of the present polyazothines. Pt-electrode devices based on a PA-1 active layer show a rewritable memory effect with poor endurance (less than 20 cycles), whereas the PA-2 based Pt devices exhibit write-once read-many-times (WORM) memory behavior. For the Al-electrode devices, both PAs demonstrate a much improved resistive switching effect, and the endurance of the PA-2 devices is better than that of the PA-1 devices. The difference in the electronic transport and memory properties of the four devices may originate from the different charge injection/extraction and electron transfer processes of the sandwich systems, and will provide guidelines for selecting both the proper D and A moieties in D–A polymers and electrode metals for high-performance resistance random access memories (RRAMs).

Two donor–acceptor (D–A) polyazothines (PAs), incorporating the oxadiazole entity either acting as an electron acceptor (A) to form D–A structured PA-1 with the triphenylamine donor (D), or acting as a donor to form D–A structured PA-2 with the 3,3′-dinitro-diphenylsulfone acceptor, have been successfully synthesized via a polycondensation reaction. The variation in the role of the oxadiazole moiety in the D–A polymers, together with the use of different top electrode metals, leads to interesting electronic transport properties and various resistive switching behaviors of the present polyazothines. Pt-electrode devices based on a PA-1 active layer show a rewritable memory effect with poor endurance (less than 20 cycles), whereas the PA-2 based Pt devices exhibit write-once read-many-times (WORM) memory behavior. For the Al-electrode devices, both PAs demonstrate a much improved resistive switching effect, and the endurance of the PA-2 devices is better than that of the PA-1 devices. The difference in the electronic transport and memory properties of the four devices may originate from the different charge injection/extraction and electron transfer processes of the sandwich systems, and will provide guidelines for selecting both the proper D and A moieties in D–A polymers and electrode metals for high-performance resistance random access memories (RRAMs).

Linear and hyperbranched poly(azomethine)s (PAMs)-based on triphenylamine moieties are synthesized and used as the functioning layers in the Ta/PAM/Pt resistive switching memory devices. Comparably, the hyperbranched PAM with isotropic architecture and semi-crystalline nature shows enhanced memory behaviors with more uniform distribution of the HRS and LRS resistances.

A bio-memristor fabricated with ferritin exhibits novel resistive switching characteristics wherein memory switching and threshold switching are made steadily coexistent and inter-convertible through controlling the magnitude of compliance current presets.

In this study, an artificial synapse with a sandwich structure of Ta/ethyl viologen diperchlorate [EV(ClO4)2]/triphenylamine-based polyimide (TPA-PI)/Pt is fabricated directly on a flexible PET substrate and exhibits distinctive history-dependent memristive behaviour, which meets the basic requirements for synapse emulation. Essential synaptic plasticity (including long-term plasticity and short-term plasticity) and some memory and learning behaviours of human beings (including the conversion from short-term memory to long-term memory and the “learning–forgetting–relearning”) have been demonstrated in our device. More importantly, the device still exhibits the synaptic performance when the surface strain of the device reaches 0.64% (or, the bending radius reaches 10 mm). Moreover, the device was able to endure 100 bending cycles. Our findings strongly demonstrate that the organic artificial synapse is not only promising for constructing a neuromorphic information storage and processing system, but is also interesting for the realization of wearable neuromorphic computing systems.

Thermally stable poly(triphenylamine) (PTPA) synthesized by an oxidative coupling reaction is used as the functional layer in memory devices, which exhibit non-volatile bistable resistive switching behavior with a large ON/OFF ratio over 5 × 108, a long retention time exceeding 8 × 103 s and a wide working temperature range of 30–390 K.