Sol-Gel Processed ZrO2 Based Forming-Free Resistive Switching Memory Devices

In this work, we fabricated ZrO2 based resistive random access memory by sol-gel spin coating technique and investigated its structural, optical and resistive switching properties. The X-ray diffraction pattern revealed that 400 °C annealed ZrO2 thin film has tetragonal structure. The optical band gap value of ZrO2 thin film obtained was 5.51 eV. The resistive switching behaviour of W/ZrO2/ITO capacitor like structure was studied. It was found that no initial electroforming process required for the device. The fabricated devices show a self-compliance bipolar resistive switching behaviour and have high on off ratio (>102). Our result suggests that solution processed ZrO2 has great potential to develop transparent and flexible resistive random access memory devices.

Multi-Level Resistive Switching of Pt/HfO2/TaN Memory Device

This work characterizes resistive switching and neuromorphic simulation of Pt/HfO2/TaN stack as an artificial synaptic device. A stable bipolar resistive switching operation is performed by repetitive DC sweep cycles. Furthermore, endurance (DC 100 cycles) and retention (5000 s) are demonstrated for reliable resistive operation. Low-resistance and high-resistance states follow the Ohmic conduction and Poole–Frenkel emission, respectively, which is verified through the fitting process. For practical operation, the set and reset processes are performed through pulses. Further, potentiation and depression are demonstrated for neuromorphic application. Finally, neuromorphic system simulation is performed through a neural network for pattern recognition accuracy of the Fashion Modified National Institute of Standards and Technology dataset.

Chitosan-Based Flexible Memristors with Embedded Carbon Nanotubes for Neuromorphic Electronics

In this study, we propose high-performance chitosan-based flexible memristors with embedded single-walled carbon nanotubes (SWCNTs) for neuromorphic electronics. These flexible transparent memristors were applied to a polyethylene naphthalate (PEN) substrate using low-temperature solution processing. The chitosan-based flexible memristors have a bipolar resistive switching (BRS) behavior due to the cation-based electrochemical reaction between a polymeric chitosan electrolyte and mobile ions. The effect of SWCNT addition on the BRS characteristics was analyzed. It was observed that the embedded SWCNTs absorb more metal ions and trigger the conductive filament in the chitosan electrolyte, resulting in a more stable and wider BRS window compared to the device with no SWCNTs. The memory window of the chitosan nanocomposite memristors with SWCNTs was 14.98, which was approximately double that of devices without SWCNTs (6.39). Furthermore, the proposed SWCNT-embedded chitosan-based memristors had memristive properties, such as short-term and long-term plasticity via paired-pulse facilitation and spike-timing-dependent plasticity, respectively. In addition, the conductivity modulation was evaluated with 300 synaptic pulses. These findings suggest that memristors featuring SWCNT-embedded chitosan are a promising building block for future artificial synaptic electronics applications.

Excellent Bipolar Resistive Switching Characteristics of Bi4Ti3O12 Thin Films Prepared via Sol-Gel Process

Herein, Bi4Ti3O12 (BIT) ferroelectric thin films were fabricated into Au/BIT/LaNiO3/Si structures to demonstrate their memristor properties. Repeatable and stable bipolar resistive switching (RS) characteristics of the device are first reported in this work. The switching ratio of the device annealed in air reached approximately 102 at 0.1 and −0.1 V. The RS performance was not significantly degraded after 100 consecutive cycles of testing. We also explored the factors affecting the RS behavior of the device. By investigating the RS characteristics of the devices annealed in O2, and in combination with XPS analysis, we found that the RS properties were closely related to the presence of oxygen vacancies. The devices annealed in air exhibited a markedly improved RS effect over those annealed in O2. According to the slope fitting, the conduction mechanism of the device was the ohmic conduction and space charge limited current (SCLC). This study is the first to successfully apply BIT ferroelectric films to the RS layers of memristors. Additionally, a theory of conductive filaments is proposed to adequately explain the relationship between RS behavior and oxygen vacancies, providing meaningful inspiration for designing high-quality resistive random access memory devices.

Demonstration of Threshold Switching and Bipolar Resistive Switching in Ag/SnOx/TiN Memory Device

In this work, we observed the duality of threshold switching and non-volatile memory switching of Ag/SnOx/TiN memory devices by controlling the compliance current (CC) or pulse amplitude. The insulator thickness and chemical analysis of the device stack were confirmed by transmission electron microscope (TEM) images of the Ag/SnOx/TiN stack and X-ray photoelectron spectroscopy (XPS) of the SnOx film. The threshold switching was achieved at low CC (50 μA), showing volatile resistive switching. Optimal CC (5 mA) for bipolar resistive switching conditions with a gradual transition was also found. An unstable low-resistance state (LRS) and negative-set behavior were observed at CCs of 1 mA and 30 mA, respectively. We also demonstrated the pulse operation for volatile switching, set, reset processes, and negative-set behaviors by controlling pulse amplitude and polarity. Finally, the potentiation and depression characteristics were mimicked by multiple pulses, and MNIST pattern recognition was calculated using a neural network, including the conductance update for a hardware-based neuromorphic system.

Conduction and Resistive Switching Memory in Al/MoS2+PVP/Ag Devices Fabricated using Drop cast Method

Resistive switching in MoS2 embedded PVP composite-based ReRAM with Al and Ag electrodes is reported. A cost-free drop cast method was used to deposit active layers consisting of 30 wt%, 40 wt%, and 70 wt% of MoS2 in PVP. Each system exhibited unique electroforming and switching mode. Asymmetrical bipolar resistive switching occurring only in the positive voltage bias, a typical bipolar resistive switching and a typical ‘O-type’ resistive switching were observed for the 30 wt%, 40 wt%, and 70 wt% systems, respectively. Furthermore, injection of charge carriers at the electrode/active layer interface and electrochemical metalization mechanisms drove the formation of a nanoscale conductive filament in the device A and B. On the other hand, we attributed the conduction mechanism of device C to hopping conduction. Our results demonstrate the behaviour of MoS2 embedded PVP composite-based ReRAM has a strong dependence on the amount of MoS2 and that both the switching and conduction mechanism can be exploited by controlling the amount of MoS2 in the composite.