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Emerging optoelectronic memristors are promising candidates to develop neuromorphic computing, owing to the combined advantages of photonics and electronics. However, the reversible modulation on device conductance usually requires complicated operations involving hybrid optical/electrical signals. Herein, we design a fully light-modulated memristor based on ZnO/MoOx heterojunction, which exhibits potentiation and depression behaviors under the irradiation of ultraviolet and visible light, respectively. Several basic synaptic functions have been emulated by utilizing optical signals, including short-term/long-term plasticity and spike-number-dependent plasticity. Based on the all-optical modulation characteristics, low-level image pre-processing (including contrast enhancement and noise reduction) is demonstrated. Furthermore, logic operations ("AND," "NOTq," and "NIMP") can be performed by combining various optical signals in the same device. The memristive switching mechanism under optical stimulus can be attributed to barrier change at the heterojunction interface. This work proposes a fully light-modulated memristor based on ZnO/MoOx heterojunction that may promote the development of neuromorphic computing with high efficiency. [ABSTRACT FROM AUTHOR]

An optoelectronic memristor can respond to both electrical and optical stimuli, which has tremendous potential to realize light-involved operations. Here, N-doped carbon dots (NCDs)-based optoelectronic memristor devices with reliable resistive switching (RS) characteristics are demonstrated. The devices possess reproducible bipolar RS behavior, good endurance, long retention time, and fast switching speed (<28 ns). Based on the light-controlled charge trapping, the SET voltage can be modulated from 1.5 to 0.2 V by varying the ultraviolet (UV) light intensity. Furthermore, the switching process can be completely triggered by external light when the intensity is more than 10 mW/cm2. The mechanism of charge trapping of the NCDs is verified via Kelvin probe force microscopy measurements. The stateful reconfigurable logic of NAND and AND operations can be achieved through the control of UV light. The results show the feasibility of light-controlled stateful logic based on NCDs memristors for in-memory computing applications. [ABSTRACT FROM AUTHOR]

In this work, we demonstrate the coexistence of nonvolatile memory (NVM) and volatile threshold switching (VTS) behaviors in an Ag-embedded sodium-alginate-based memristor using the current pulse mode. High and low compliance currents allow the device to present stable and reliable NVM and VTS behaviors, respectively. Specifically, NVM and VTS behaviors randomly occur under a compliance current of 40 μA. On this basis, four polygon Boolean operations (AND, OR, NOT, and XOR) and physical unclonable functions (PUFs) with an inter-class Hamming distance of 50.75% are demonstrated simultaneously in memristive devices. Adopting PUF keys, image encryption and decryption are implemented by executing the XOR logic operation. Our memristive devices have the ability of in-memory computing and providing PUFs simultaneously and thus great potential for hardware security applications. [ABSTRACT FROM AUTHOR]

True random number generator (TRNG) that cannot be arbitrary attacked with predictable software algorithm is a promising data security solution. Memristors, possessing specific intrinsic stochasticity, are just appropriate to be the random sources for encryption applications. In this work, a TRNG system based on the stochastic duration time of double threshold-switching (TS) memristors is proposed. The reliable stochasticity of this system is mainly attributed to the gradual dissolution of Ag conductive channels and the synergistic effect of these two TS memristors. A digital circuit system based on the micro-controller unit is designed to produce stable random "0" and "1" bitstreams. The random data key generated by this double TS memristor TRNG passed the National Institute of Standards and Technology randomness tests without post-processing procedure. Taking advantage of the true random data key, the binary image can be encrypted and decrypted by executing the XNOR logic operation. In addition, the Gaussian noise effect on the decryption stability of image information secure communication is also analyzed. Although 90% Gaussian noise was applied to the original image, the pristine binary image still can be roughly recognized. This work demonstrates that the double TS memristors-based TRNG system has great potential for hardware security applications. [ABSTRACT FROM AUTHOR]

Temperature is known as an important factor in biological synaptic transmission. In this study, temperature-modulated switching behaviors are reported in an amorphous carbon (a-C) diffusive memristor device to emulate biorealistic synaptic plasticity. The devices exhibit memory switching and threshold switching behaviors depending on the compliance current and ambient temperature. As confirmed by conducting atomic force microscopy, the thermal effect can promote the electrochemical formation of a stable metallic conductive filament. A series of timing-controlled pulse experiments are carried out to study the temperature effect on the switching characteristics, and the device shows second-order memristive behaviors. Frequency-dependent synaptic plasticity and timing-controlled spike-time-dependent plasticity are demonstrated in the device, which are analogous to the synaptic strength in a biological synapse at elevated temperatures. As a proof of concept, the forgetting behavior of numerical images learned at different temperatures and different pulse durations is conceptually emulated with synaptic device arrays. It is expected the present device with second order memristive behaviors provides alternatives for biorealistic synaptic applications. [ABSTRACT FROM AUTHOR]

Optoelectronic synapses are considered to be important cornerstones in the construction of neuromorphic computing systems because of their low power consumption, high operating speeds, and high scalability. In this work, we demonstrate an optoelectronic synaptic device based on a ZnO/HfOx heterojunction in which optical potentiation/electrical depression behaviors and nonvolatile high current state can be implemented. The heterojunction device exhibits conductance evolution with high linearity. The excellent optoelectronic memristive behavior of the device can be attributed to the interface barrier between ZnO and HfOx, which hinders the recombination of photo-excited electron–hole pairs to increase the carrier lifetime, and realizes the nonvolatile high current state. More importantly, the artificial vision system based on optoelectronic synaptic devices can achieved a high recognition accuracy of 96.1%. Our work provides a feasible pathway toward the development of optoelectronic synaptic devices for use in high-performance neuromorphic vision systems. [ABSTRACT FROM AUTHOR]

In this Letter, we report a complementary resistive switch (CRS) with good thermal stability and low ON current. The device is constructed with a bilayer structure composed of sputtered amorphous carbon (a-C) and thermal annealed Cu doped a-C (a-C:Cu). The Cu atoms in a-C:Cu can agglomerate to form nanosized active electrodes by thermal annealing. The Cu species can migrate and redistribute to form conductive filaments within the a-C and a-C:Cu layer through an electrochemical redox reaction. The depletion of Cu species in the a-C:Cu or a-C layer produces complementary resistive switching behaviors. Benefiting from the high thermal stability of a-C and a-C:Cu, the device works stable at a high temperature of up to 300 °C with an endurance of 104 switching cycle and narrow cycle-to-cycle distribution of threshold voltages. Furthermore, the effects of the Cu content in the a-C:Cu layer and the thickness ratio of a-C:Cu/a-C on the ON state current were studied. By limiting the content of Cu in the a-C:Cu layer, a low ON state current of 5 μA was obtained, which is among the lowest in the reported CRSs. Furthermore, a "stateful" material implication logic with the "0" and "1" states represented by a distinct combination of the resistance of each layer was implemented. The CRS is a potential and promising device for low power memory/computing applications and harsh electronics. [ABSTRACT FROM AUTHOR]

Mimicking Pavlovian conditioning by memristive synapse is significant to implement neuromorphic computing at the hardware level. In this work, we demonstrated the Pavlovian conditioning based on the artificial synapse architecture of one-transistor/one-resistor (1T1R), which included an AgInSbTe/α-C-based memristor as a variable resistance and an N-MOS transistor. Thanks to stable resistance switching behavior of memristor and outstanding controllability of device conductance by transistor gating of 1T1R, the experimental demonstration of the acquisition and extinction of Pavlovian conditioning were realized. Moreover, the temporal relation between the conditioned and unconditioned stimuli was also established in which the memory time of associative learning decreased with the increase in the interval of two stimuli. This work provided an idea to biorealistically mimic the Pavlovian conditioning, paving the way for memristive neuromorphic computing. [ABSTRACT FROM AUTHOR]

A thermal-assisted electroforming (TAE) method is proposed to address the current overshoot issue and improve the resistive switching (RS) performance of electrochemical metallization (ECM) memory with a Cu/amorphous carbon (a-C)/Pt structure. In the initial electroforming process, thermal treatment can promote the electrochemical formation of metallic conductive filament (CF). The required electroforming voltage is reduced, and the undesirable overshoot current is suppressed. As a result, the RS performance of the cell is improved, including reduced RS parameter fluctuations, enlarged off/on ratio, and enhanced cycling endurance. The cell can be operated with a low compliance current (ICC) of 50 μA, which is among the lowest value of reported a-C-based ECM memories. Benefit from the low ICC, multilevel memory with five nonvolatile resistance states in a single cell is obtained. The main role of the TAE method is interpreted as to avoid the extreme high-temperature caused by the overshoot current. Conductive-atomic force microscopy mapping implies that the suppression of overshoot current can avoid over-injection of Cu cations into the a-C layer, facilitating CF with a simple structure and low randomness. The present work offers a feasible approach for addressing the current overshoot issue and improving the performance of ECM memory. [ABSTRACT FROM AUTHOR]

In this work, we demonstrated the high switching uniformity and 50 fJ/bit energy consumption in an amorphous silicon-based resistive switching (RS) device by inserting the AgInSbTe (AIST) layer between the silicon insulating layer and Ag top electrodes. The improved RS performance is attributed to the introduction of an Ag ion reservoir layer, which helps to suppress conducting filament overgrowth. After insertion of the AIST layer, the cumulative probability of low/high resistance states decreased from 176.8%/46.2% to 3.1%/11.9%, respectively. The advantages of promoting Ag dissolution enable the realization of fast switching speed (<50 ns) and low set voltage (∼70 mV), which gives our device low energy consumption (∼50 fJ/bit). Moreover, the multi-step of set/reset analytical model of our dual-layer RS device was developed based on the formation and dissolution of the Ag-ion-based conductive filaments. Our work presents an effective method for obtaining high-performance Si-based memory for practical applications. [ABSTRACT FROM AUTHOR]

An energy-efficient memristive synapse is highly desired for the development of brain-like neurosynaptic chips. In this work, a ZnO-based memristive synapse with ultralow-power consumption was achieved by simple N-doping. The introduction of N atoms, as the acceptor, reduces the carrier concentration and greatly increases the resistance of the ZnO film. The low energy consumption, which is as low as 60 fJ per synaptic event, can be achieved in our device. Essential synaptic learning functions have been demonstrated, including excitatory postsynaptic current, paired-pulse facilitation, and experience-dependent learning behaviors. Furthermore, the device can still exhibit the synaptic performance in the bent state or even after 100 bending cycles. Our memristive synapse is not only promising for energy-efficient neuromorphic computing systems but also suitable for the development of wearable neuromorphic electronics. [ABSTRACT FROM AUTHOR]

Current stressing treatment on amorphous carbon (a-C)-based electrochemical metallization (ECM) memory cells before the electroforming process is proposed. The resistive switching (RS) performance of a Cu/a-C/Pt ECM cell after low current (10 μA) stressing treatment is improved, including reduced forming voltages, improved switching uniformity, enhanced cycling endurance, and enhanced switching speed. MicroRaman mapping and conductive-atomic force microscopy measurements reveal that current stressing can cause clustering of sp2 sites in a-C and the conductive filament (CF) randomness is reduced. The reduction of CF nucleation site randomness and enhancement of the local electric field through sp2-clustering are assumed to be responsible for the observed RS performance improvement. The results demonstrate that current stressing is a feasible approach for optimizing the RS performance of a-C-based ECM memory, and it can also be extended to the development of carbon-based electronic devices. [ABSTRACT FROM AUTHOR]

We developed an intensity-modulated light-emitting device (LED) by integrating a p-GaN/n-ZnO heterojunction with multilevel resistive random access memory (RRAM). In this device, the luminous intensity of LED can be adjusted through regulating the injection current according to the variable resistance state of RRAM. As one critical foundation of device fabrication, uniform operation of multilevel RRAM was achieved by inserting carbon quantum dots into HfO2−x RRAM as a local-electric-field regulator. Eventually, the reversible regulation of electroluminescence intensity was demonstrated by tuning the compliance current in the modulated LED. Thanks to the simple structure and nanoscale switching region, this modulated LED may offer a feasible method to replace traditional thin film transistors or CMOSs with complicated structures and techniques, enabling the potential application of low-cost and high-density LED displays. [ABSTRACT FROM AUTHOR]