Guangsheng Tang

Synaptic plasticity and learning behaviours mimicked through Ag interface movement in an Ag/conducting polymer/Ta memristive system

In this study, a memristor with the simple structure Ag/poly(3,4-ethylenedioxythiophene):poly (styrenesulphonate) (PEDOT:PSS)/Ta was fabricated. Essential synaptic plasticity and learning behaviours were emulated using this memristor, including short-term plasticity, long-term plasticity, spike-timing-dependent plasticity and spike-rate-dependent plasticity. Important time constants were extracted from these synaptic modifications, which are associated with brain learning and memory functions. It was clearly demonstrated that the movement of the Ag interface upon the initiation of a redox reaction accounts for the resistive switching mechanism of our memristor. The conducting path in the polymer layer and the elastic effect of the polymer matrix were suggested to be considered in the memory and learning processes. Moreover, the energy band diagram of our memristor was drawn after the cross-sectional transmission electron microscopy images were analysed. It was found that a natural p–n junction in the PEDOT:PSS/Ta compound was formed. This resulted in rectifying, high resistance and low power consumption. Our device structure may be considered a feasible prototype for integrating memristors into a large-scale neuromorphic circuit.

Migration of interfacial oxygen ions modulated resistive switching in oxide-based memory devices

Oxides-based resistive switching memory induced by oxygen ions migration is attractive for future nonvolatile memories. Numerous works had focused their attentions on the sandwiched oxide materials for depressing the characteristic variations, but the comprehensive studies of the dependence of electrodes on the migration behavior of oxygen ions are overshadowed. Here, we investigated the interaction of various metals (Ni, Co, Al, Ti, Zr, and Hf) with oxygen atoms at the metal/Ta2O5 interface under electric stress and explored the effect of top electrode on the characteristic variations of Ta2O5-based memory device. It is demonstrated that chemically inert electrodes (Ni and Co) lead to the scattering switching characteristics and destructive gas bubbles, while the highly chemically active metals (Hf and Zr) formed a thick and dense interfacial intermediate oxide layer at the metal/Ta2O5 interface, which also degraded the resistive switching behavior. The relatively chemically active metals (Al and Ti) can...

Conductance quantization in a Ag filament-based polymer resistive memory

Resistive switching and conductance quantization are systematically studied in a Ag/poly(3-hexylthiophene):[6,6]-phenyl-C61-butyric acid methyl ester/indium-tin oxide sandwich structure. The observed bipolar switching behavior can be attributed to the formation and dissolution of Ag filaments during positive and negative voltage sweeps, respectively. More importantly, conductance quantization with both integer and half integer multiples of single atomic point contact can be realized by slowing down the voltage sweep speed as well as by pulse measurement. The former may reflect the formed Ag filaments with different atomic point contacts, while the latter probably originates from the interaction between the Ag filaments and the elemental hydrogen provided by the organic storage medium. With appropriate current compliances, low resistance states with desired quantized conductance values are successfully achieved, thus showing the potential for ultrahigh density memory applications. Besides, 100 successive switching cycles with densely distributed resistance values of each resistance state and extrapolated retention properties over ten years are also demonstrated.

Effect of Electrode Materials on AlN-Based Bipolar and Complementary Resistive Switching

We report the complementary resistive switching (CRS) behaviors in aluminum nitride (AlN)-based memory devices as the promising new material system for large-scale integration of passive crossbar arrays. By utilizing different electrodes (Cu, Pt, and TiN), CRS characteristics are demonstrated in both TiN/AlN/Cu/AlN/TiN electrochemical metallization cells and Pt/AlN/TiN/AlN/Pt ionic resistive switching systems. The instability of Pt/AlN/Cu/AlN/Pt based CRS is explained by the relatively small reset voltage caused by the thermal effects enhanced reset process in the corresponding bipolar resistive switching element. It is concluded that the prerequisite for reliable and stable CRS is that the reset voltage of the bipolar resistive switching element must be much larger than half of the set voltage.

Cu-Embedded AlN-Based Nonpolar Nonvolatile Resistive Switching Memory

This letter covers the fabrication of a nonpolar resistive switching (RS) random access memory device using Cu-embedded AlN and its reproducible RS characteristics. The AlN-based memory device shows endurance of >; 103, reliable retention time (ten years extrapolation at both room temperature and 85°C), and fast programming speed under 100-ns pulses in unipolar operation mode. The switching mechanism is believed to be mediated by the formation and rupture of conductive Cu filaments.

Resistive switching with self-rectifying behavior in Cu/SiOx/Si structure fabricated by plasma-oxidation

We report a resistive switching memory structure based on silicon wafers by employing both materials and processing fully compatible with complementary metal-oxide semiconductor technology. A SiOx nanolayer was fabricated by direct plasma-oxidation of silicon wafers at room-temperature. Resistive switching behaviors were investigated on both p- and n-Si wafers, whereas self-rectifying effect was obtained in the Cu/SiOx/n-Si structure at low-resistance state. The self-rectifying effect was explained by formation of the Schottky barrier between the as-formed Cu filament and the n-Si. These results suggest a convenient and cost-efficient technical-route to develop high-density resistive switching memory for nowadays Si-based semiconductor industry.

Structure and ferromagnetism in vanadium-doped LiNbO3

Doping into LiNbO3 (LN) and studying its magnetism might provide an alternative way for fabricating diluted magnetic compounds with potential application in the field of spintronics. Room-temperature ferromagnetic V-doped LN with V contents of 1–3 at. % was prepared by ion-beam implantation. The samples exhibit a maximum atomic magnetic moment of 3.82 μB/V at a V doping concentration of 2 at. %. Structural characterization and first principle calculation suggest that the magnetism most likely arises from the oxygen vacancy around the V dopant. X-ray absorption near-edge spectroscopy reveals that the V atom principally substituted for the Nb atom in the LN lattice and that the V is octahedrally coordinated but with a large distortion. It also showed that oxygen vacancies are present in the third shell of the doped V atoms. With the aid of first-principle calculations, we constructed the electronic structure of this system and demonstrated that the O vacancies play an important role in modulating the magnet...