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The introduction of metal nanocrystals (NCs) has been confirmed to improve electrical uniformity of oxide-based resistive random access memory (RRAM) devices significantly; however, the current reports do not systematically elucidate the relationship between the size/distribution of NCs and the electrical uniformity of RRAM devices. In this paper, we focused on the impact of metal NCs size and areal density on the resistive switching (RS) performances of oxide RRAM by atomic layer deposition (ALD) based on the experimental results and theoretical calculation. The dependence of ALD cycles of 50–130 during Pt or CoPtx NCs growth on the RS parameters of Al2O3 or HfO2 memory units has been evaluated systematically. The RRAM embedded Pt or CoPtx NCs shows the trends: with increasing ALD cycles, the forming voltage, set/reset voltage, the resistance in off and on state, and ${R}_{ \mathrm{\scriptscriptstyle OFF}}/{R}_{ \mathrm{\scriptscriptstyle ON}}$ ratio entirely first decrease, then flatten, and increase later with a minimum value at about 100 cycles. Although all metal NCs with various sizes enhance the electric field strength compared to at the planar region, only metal NCs with proper NCs size and areal density (9 nm/6– $10\times 10^{\textsf {11}}$ /cm2 in this paper) can effectively produce stronger localized electric field at the tip of metal NCs, leading to optimal RS behavior. [ABSTRACT FROM AUTHOR]

In this paper, the transition rate (TR) from the high-resistance state to the low-resistance state of a HfO2-based resistive random access memory (RRAM) is investigated. The TR is statistically characterized by applying constant voltage stresses in the range from 0.45 to 0.65 V. It is found that TR follows a voltage dependence which closely resembles the one exhibited by metal-insulator-semiconductor / metal-insulator-metal structures when subjected to constant voltage stress, but with remarkably different fitting parameters. This result suggests a common underlying mechanism in both evolutionary behaviors. Furthermore, the investigation provides additional evidence supporting the micro-structural changes in the oxide after the forming step as well as the role played by the atomic species during the SET event. [ABSTRACT FROM AUTHOR]

This paper investigates the issues of oxygen accumulation and variation in the high-resistance state of HfO2-based resistive random access memory (RRAM), with improvement attained by inserting a thin oxygen-vacancy-rich layer of indium-tin-oxide (ITO) film. By acting as the oxygen ion reservoir, this ITO thin film on the TiN electrode can further stabilize resistance switching (RS) characteristics. In terms of reliability, ac endurance, and retention tests confirm stable RS characteristics for the Pt/HfO2/ITO/TiN device. Finally, a conducting model was proposed to explain the influence of the ITO thin layer and clarify the physical mechanism of electrical improvements. [ABSTRACT FROM AUTHOR]

In the study of resistive random access memory using GeTeOx film as the switching layer, the device performed excellent property of bipolar resistive switching (BRS), which could be gradually transformed to the complementary resistive switching (CRS) by varying SET process current compliance. The conductive filament conduction mechanism of BRS could be verified by electrical characteristics and reliable data fitting. Through increasing current compliance of the SET process, CRS could be achieved due to higher activity of oxygen vacancies originated from the intensified thermal effect. This paper was beneficial to understand the switching mechanisms of BRS and CRS and provide a method to realize interconversion. Moreover, it was also a potential and promising device to be applied in the neurosynaptic biomimetic field. [ABSTRACT FROM AUTHOR]

An intentionally introduced interface layer in the resistive random-access memory (RRAM) devices play an important role in the improvement of resistive switching characteristics. In this paper, the resistive switching characteristics of ZrO2-based RRAM devices by inserting a thin TiO2 interface layer between electrodes and ZrO2 resistive switching layer were investigated. Compared with the Cu/ZrO2/Pt and Cu/ZrO2/TiO2/Pt devices, the Cu/TiO2/ZrO2/Pt and Cu/TiO2/ZrO2/TiO2/Pt devices showed much improved programing voltages, including lower forming voltage and lower set voltage. Moreover, the reset current was also improved. These results indicate that the TiO2 interface layer between the anode electrode and the resistive switching layer plays an important role in improving device performance. [ABSTRACT FROM AUTHOR]

The switching properties of Te and TeTiW top electrodes (TEs) on TiW/SiN/TiN resistive switching memory devices are explored in this paper. The TeTiW TE device exhibits more favorable bipolar resistive switching behavior because of the decrease in binding energy after its use. This finding is confirmed through X-ray photoelectron spectroscopy analyses. The filament of the TeTiW TE device is metal like after forming, and the reset process corresponds with the thermal-dissolution mechanism. A physical model based on a Te filament is constructed to explain such phenomena. The TeTiW TE device provides the excellent endurance of more than 104 cycles, with an ON/OFF ratio of 500. The improvement can be attributed to the filament’s robustness during the forming and set processes, which prevent its diffusion even at high temperature. The device also features long retention for up to 104 s at 225 °C without stress, and 104 s at 85 °C with stress of −0.3 V. Therefore, it has high potential for high-density nonvolatile memory applications. [ABSTRACT FROM AUTHOR]

Resistive switching memory (RRAM) is among the most mature technologies for next generation storage class memory with low power, high density, and improved performance. The biggest challenge toward industrialization of RRAM is the large variability and noise issues, causing distribution broadening which affects retention even at room temperature. Noise and variability can be addressed by enlarging the resistance window between low-resistance state and high-resistance state, which requires a proper engineering of device materials and electrodes. This paper presents an RRAM device technology based on silicon oxide (SiOx), showing high resistance window thanks to the high bandgap in the silicon oxide. Endurance, retention, and variability show excellent performance, thus supporting SiOx as a strong active material for developing future generation RRAMs. [ABSTRACT FROM AUTHOR]

A comprehensive physical model on the resistive switching (RS) behaviors of bilayered TaOx-based RS access memory [resistive random access memory (RRAM)] is presented. In the model, the effects of the generation and recombination (G-R) of oxygen vacancies ( $V_{{\rm{O}}}$ ), phase transition (P-T) between Ta2O5 and TaO2, and the interaction (I-A) between Ta2O5 and TaOx layers are involved to explain the RS behaviors based on ab initio calculations. An atomistic Monte Carlo simulation method based on the model is developed to investigate the dynamic physical processes and reproduce the experimental phenomena. The impacts of G-R and P-T as well as the I-A effects on the RS behaviors of a bilayered Ta2O5/TaOx structure and the device performances are identified. This paper indicates that the G-R effect dominates the RS behaviors, and self-compliance is due to the I-A effect. Based on the simulations, the optimization guidance of a bilayered TaOx-based RRAM is presented. [ABSTRACT FROM AUTHOR]

A highly transparent resistive random access memory with a configuration of multilayer graphene (MLG)/ Dy2O3 /indium tin oxide (ITO) structure is demonstrated in this paper. The fabricated device is transparent, with 80% transmittance at 550 nm. The MLG/ Dy2O3 /ITO device shows unipolar resistance switching with a low operation current (<100~\muA) , low operation voltage (<1~V) , low power consumption (<100~\muW) , high resistance ratio (>10^4) , fast switching speed (<60~ns) , reliable data retention, and promising cycle endurance properties (>200~cycles) , which makes a step toward the realization of low-power transparent electronics for next-generation nonvolatile memory application. The MLG/ Dy2O3 /ITO device exhibited typical filamentary-conduction-type resistive random access memory behavior and no forming process is required. High resistance state (HRS) increases with a reduced device area while low resistance state (LRS) is insensitive to the device sizes. Moreover, Raman spectra obtained in pristine state, HRS, and LRS indicate that the lower power consumption of MLG/ Dy2O3 /ITO device is attributable to the formation of oxygen graphene layers. [ABSTRACT FROM AUTHOR]