Tunable threshold resistive switching characteristics of Pt-Fe2O3 core-shell nanoparticle assembly by space charge effect

A Facile Hydrothermal Synthesis and Resistive Switching Behavior of α-Fe2O3 Nanowire Arrays

A facile hydrothermal process has been developed to synthesize the α-Fe₂O₃ nanowire arrays with a preferential growth orientation along the [110] direction. The W/α-Fe₂O₃/FTO memory device with the nonvolatile resistive switching behavior has been achieved. The resistance ratio (R_HRS/R_LRS) of the W/α-Fe₂O₃/FTO memory device exceeds two orders of magnitude, which can be preserved for more than 10³s without obvious decline. Furthermore, the carrier transport properties of the W/α-Fe₂O₃/FTO memory device are dominated by the Ohmic conduction mechanism in the low resistance state and trap-controlled space-charge-limited current conduction mechanism in the high resistance state, respectively. The partial formation and rupture of conducting nanofilaments modified by the intrinsic oxygen vacancies have been suggested to be responsible for the nonvolatile resistive switching behavior of the W/α-Fe₂O₃/FTO memory device. This work suggests that the as-prepared α-Fe₂O₃ nanowire-based W/α-Fe₂O₃/FTO memory device may be a potential candidate for applications in the next-generation nonvolatile memory devices.

Analog Memristive Characteristics of Square Shaped Lanthanum Oxide Nanoplates Layered Device

Square-shaped or rectangular nanoparticles (NPs) of lanthanum oxide (LaO_x) were synthesized and layered by convective self-assembly to demonstrate an analog memristive device in this study. Along with non-volatile analog memory effect, selection diode property could be co-existent without any implementation of heterogeneous multiple stacks with ~1 μm thick LaO_x NPs layer. Current–voltage (I–V) behavior of the LaO_x NPs resistive switching (RS) device has shown an evolved current level with memristive behavior and additional rectification functionality with threshold voltage. The concurrent memristor and diode type selector characteristics were examined with electrical stimuli or spikes for the duration of 10–50 ms pulse biases. The pulsed spike increased current levels at a read voltage of +0.2 V sequentially along with ±7 V biases, which have emulated neuromorphic operation of long-term potentiation (LTP). This study can open a new application of rare-earth LaO_x NPs as a component of neuromorphic synaptic device.

Investigation on Threshold Voltage Adjustment of Threshold Switching Devices with HfO2/Al2O3 Superlattice on Transparent ITO/Glass Substrate

Threshold voltage adjustment in threshold switching (TS) devices with HfO₂/Al₂O₃ superlattice (by means of changing the cycle ratio of HfO₂ to Al₂O₃ in atomic layer deposition) is investigated to implement a transparent cross-point array. TS devices with different cycle ratios (i.e., 3:1, 3:2, and 3:3) were fabricated and studied. The threshold voltage of the devices was increased from 0.9 V to 3.2 V, as the relative contents of Al₂O₃ layer in the superlattice were increased. At the same time, it is demonstrated that the off-resistance values of the devices were enhanced from 2.6 10⁹ to 6 10¹⁰ as the atomic layer deposition (ALD) cycle ratio of HfO₂ to Al₂O₃ layer was adjusted from 3:1 to 3:3. However, the hold voltage and the on-current values were almost identical for the three devices. These results can be understood using the larger barrier height of Al₂O₃ layer than that of HfO₂ layer.

Analog Memristive Characteristics of Mesoporous Silica-Titania Nanocomposite Device Concurrent with Selection Diode Property

A threshold resistive switching (RS) device concurrently demonstrating analog memristive property with mesoporous silica-titania (m-ST) nanocomposites is introduced in this study. The nanostructured m-ST layer in an Al/m-ST/Pt device was constructed by facile soft templating of evaporation-induced self-assembly (EISA) method to demonstrate nonlinear threshold RS behaviors accompanying with discrete synaptic characteristics along with adaptive motions. The EISA layer was composed of well-ordered mesopores (∼10 nm), where paths of electrical currents could be controllably guided and sequentially activated by repeated voltage sweeps. The combinational memristive behavior accompanying the shift of threshold voltage (V_th) could implicate concurrent performances of threshold RS and selection diode devices. In addition, synaptic functionalities of long-term potentiation and depression were characterized by variations of pulse timing width (7-100 ms). Physical and chemical features of the m-ST were analyzed with Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, high-resolution transmission electron microscopy, and optical microscopy to investigate the unique origin of dual operation modes of the device. The m-ST synaptic device could have potential for further development of a hybrid selection diode having both a low sneaky current loss and memristive characteristics accomplishing low level of cross-talk between RS devices.

Effect of Mn doping on electroforming and threshold voltages of bipolar resistive switching in Al/Mn : NiO/ITO

We investigated the bipolar resistive switching (BRS) properties of Mn-doped NiO thin films by sol-gel spin-coating. As the Mn doping concentration increased, lattice constant, grain size and band gap were found to decrease simultaneously. Moreover, the electroforming voltages and threshold voltages were gradually reduced. It can be ascribed to the increase in the density of grain boundaries, and the defects caused by doping Mn and lower formation energy of Mn-O. They would be helpful for the formation of oxygen vacancies and conductive filaments. It is worth mentioning that excellent BRS behaviors can be obtained at a low Mn-doped concentration including enlarged ON/OFF ratio, good uniformity and stability. Compared with other samples, the 1% Mn-doped NiO showed the highest ON/OFF ratio (>106), stable endurance of >100 cycles and a retention time of >104 s. The mechanism should be determined by bulk properties rather than the dual-oxygen reservoir structure. These results indicate that appropriate Mn doping can be applied to improve the BRS characteristics of NiO thin films, and provide stable, low-power-consumption memory devices.

Resistive Switching of Sub-10 nm TiO₂ Nanoparticle Self-Assembled Monolayers

Resistively switching devices are promising candidates for the next generation of non-volatile data memories. Such devices are up to now fabricated mainly by means of top-down approaches that apply thin films sandwiched between electrodes. Recent works have demonstrated that resistive switching (RS) is also feasible on chemically synthesized nanoparticles (NPs) in the 50 nm range. Following this concept, we developed this approach further to the sub-10 nm range. In this work, we report RS of sub-10 nm TiO₂ NPs that were self-assembled into monolayers and transferred onto metallic substrates. We electrically characterized these monolayers in regard to their RS properties by means of a nanorobotics system in a scanning electron microscope, and found features typical of bipolar resistive switching.

Dual-functional Memory and Threshold Resistive Switching Based on the Push-Pull Mechanism of Oxygen Ions

The combination of nonvolatile memory switching and volatile threshold switching functions of transition metal oxides in crossbar memory arrays is of great potential for replacing charge-based flash memory in very-large-scale integration. Here, we show that the resistive switching material structure, (amorphous TiOx)/(Ag nanoparticles)/(polycrystalline TiOx), fabricated on the textured-FTO substrate with ITO as the top electrode exhibits both the memory switching and threshold switching functions. When the device is used for resistive switching, it is forming-free for resistive memory applications with low operation voltage (<± 1 V) and self-compliance to current up to 50 μA. When it is used for threshold switching, the low threshold current is beneficial for improving the device selectivity. The variation of oxygen distribution measured by energy dispersive X-ray spectroscopy and scanning transmission electron microscopy indicates the formation or rupture of conducting filaments in the device at different resistance states. It is therefore suggested that the push and pull actions of oxygen ions in the amorphous TiOx and polycrystalline TiOx films during the voltage sweep account for the memory switching and threshold switching properties in the device.

Convertible resistive switching characteristics between memory switching and threshold switching in a single ferritin-based memristor

The coexistence and inter-conversion between threshold and memory resistance switching in a ferritin memristor makes it a promising candidate for physiological applications.

Noble metal@metal oxide semiconductor core@shell nano-architectures as a new platform for gas sensor applications

This feature article focuses on recent research progress in noble metal@metal oxides core@shell NPs for gas sensor applications.

Architecture controlled PtNi@mSiO2 and Pt–NiO@mSiO2 mesoporous core–shell nanocatalysts for enhanced p-chloronitrobenzene hydrogenation selectivity

The p-CAN selectivity over Pt–NiO@mSiO₂ and PtNi@mSiO₂ is significantly enhanced while maintaining the high activity of the Pt catalysts.