Yingtao Li

Real‐Time Observation on Dynamic Growth/Dissolution of Conductive Filaments in Oxide‐Electrolyte‐Based ReRAM

Evolution of growth/dissolution conductive filaments (CFs) in oxide-electrolyte-based resistive switching memories are studied by in situ transmission electron microscopy. Contrary to what is commonly believed, CFs are found to start growing from the anode (Ag or Cu) rather than having to reach the cathode (Pt) and grow backwards. A new mechanism based on local redox reactions inside the oxide-electrolyte is proposed.

Investigation of resistive switching in Cu-doped HfO2 thin film for multilevel non-volatile memory applications

In this paper, the resistive switching characteristics in a Cu/HfO(2):Cu/Pt sandwiched structure is investigated for multilevel non-volatile memory applications. The device shows excellent resistive switching performance, including good endurance, long retention time, fast operation speed and a large storage window (R(OFF)/R(ON)>10(7)). Based on the temperature-dependent test results, the formation of Cu conducting filaments is believed to be the reason for the resistance switching from the OFF state to the ON state. By integrating the resistive switching mechanism study and the device fabrication, different resistance values are achieved using different compliance currents in the program process. These resistance values can be easily distinguished in a large temperature range, and can be maintained over 10 years by extrapolating retention data at room temperature. The integrated experiment and mechanism studies set up the foundation for the development of high-performance multilevel RRAM.

Resistive Switching Properties of

The reliable resistive switching properties of Au/ZrO2/ Ag structure fabricated with full room temperature process are demonstrated in this letter. The tested devices show low operation voltages (< 1 V), high resistance ratio (about 104), fast switching speed (50 ns), and reliable data retention (ten years extrapolation at both RT and 85 °C). Moreover, the benefits of high yield and multilevel storage possibility make them promising in the next generation nonvolatile memory applications.

\hbox{Au}/ \hbox{ZrO}_{2}/\hbox{Ag}

The ZrO2 films with Au nanocrystals embedded (ZrO2:nc-Au) are fabricated by e-beam evaporation, and the self-rectifying effect in the Au/ZrO2:nc-Au/n+ Si sandwich structure is investigated. Self-rectifying resistive switching characteristics are obtained when the resistive memory is switched to low-resistance state (LRS). It is found that the Schottky contact at the Au/ZrO2 interface limits charge injection under reverse bias, while under forward bias the current is limited by space charge, resulting in a rectification of 7×102 under ±0.5 V at LRS, which enables the resistive memory to alleviate the cross-talk effect without additional switching elements in crossbar structure arrays. This self-rectifying resistive switching is believed to occur at a localized region and explained by a proposed model.

Structure for Low-Voltage Nonvolatile Memory Applications

In this letter, the insertion of a Cu nanocrystal (NC) layer between the Pt electrode and ZrO2 film is proposed as an effective method to improve resistive switching properties in the ZrO2-based resistive switching memory. This Cu/ZrO2:Cu/Cu NC/Pt memory exhibits asymmetric nonpolar resistive switching behavior, low operating voltage (<; 1.2 V), low Reset current (<; 50 μA), and high uniformity of resistance switching. The switching mechanism is believed to be related with the formation and rupture of conductive filament. The NC-induced electrical field enhancement has the benefit to accelerate and control the CF formation process, thus leading to low-switching threshold voltage and high uniformity.

Self-rectifying effect in gold nanocrystal-embedded zirconium oxide resistive memory

In this letter, we dynamically investigate the resistive switching characteristics and physical mechanism of the Ni/ZrO2/Pt device. The device shows stable bipolar resistive switching behaviors after forming process, which is similar to the Ag/ZrO2/Pt and Cu/ZrO2/Pt devices. Using in situ transmission electron microscopy, we observe in real time that several conductive filaments are formed across the ZrO2 layer between Ni and Pt electrodes after forming. Energy-dispersive X-ray spectroscopy results confirm that Ni is the main composition of the conductive filaments. The ON-state resistance increases with increasing temperature, exhibiting the feature of metallic conduction. In addition, the calculated resistance temperature coefficient is equal to that of the 10–30 nm diameter Ni nanowire, further indicating that the nanoscale Ni conductive bridge is the physical origin of the observed conductive filaments. The resistive switching characteristics and the conductive filaments component of Ni/ZrO2/Pt device are consistent with the characteristics of the typical solid-electrolyte-based resistive random access memory. Therefore, aside from Cu and Ag, Ni can also be used as an oxidizable electrode material for resistive random access memory applications.

Low-Power and Highly Uniform Switching in

In this letter, the resistive random access memory (RRAM) with metal-insulator-metal structure is investigated for the first time under radiation conditions. The fabricated Cu-doped HfO₂-based RRAM devices are found to have immunity from ⁶⁰Co γ ray of various dose ranges. The basic RRAM parameters such as high-resistance state, low-resistance state, SET/RESET voltages, operation speed, and endurance have nearly no degradation after ⁶⁰Co γ ray treatment with a total dose as high as 3.6 × 10⁵ rad (Si). Furthermore, a retention characteristic of 10⁵ s is also achieved during radiation. The highly stable characteristics of Cu-doped HfO₂ -based RRAM devices under radiation provide RRAM a great potential for aerospace and nuclear applications.

\hbox{ZrO}_{2}

The stabilization of the resistive switching characteristics is important to resistive random access memory (RRAM) device development. In this paper, an alternative approach for improving resistive switching characteristics in ZrO(2)-based resistive memory devices has been investigated. Compared with the Cu/ZrO(2)/Pt structure device, by embedding a thin TiO(x) layer between the ZrO(2) and the Cu top electrode, the Cu/TiO(x)-ZrO(2)/Pt structure device exhibits much better resistive switching characteristics. The improvement of the resistive switching characteristics in the Cu/TiO(x)-ZrO(2)/Pt structure device might be attributed to the modulation of the barrier height at the electrode/oxide interfaces.

-Based ReRAM With a Cu Nanocrystal Insertion Layer

Resistive switching with a self-rectifying feature is one of the most effective solutions to overcome the sneaking current issue in a crossbar structure. In this letter, we have successfully demonstrated a prototype device with inherent rectifying property with a-Si/WO3 bilayer structure. After a forming process, the devices exhibit obvious rectifying property with forward/reverse current ratio of 102 at ±0.75 V and excellent reproducibility. The formation of localized conductive filaments (CFs) in the WO3 layer and the corresponding CF/a-Si Schottky contact are suggested to explain the rectifying behavior. The results in this letter demonstrate a possible way to realize selector-free crossbar structure.

In situ observation of nickel as an oxidizable electrode material for the solid-electrolyte-based resistive random access memory

The effect of nitrogen doping by the NH3 plasma treatment approach on the resistive switching properties of a HfO2-based resistive random access memory (RRAM) device is investigated. Test results demonstrate that significantly improved performances are achieved in the HfO2-based RRAM device by nitrogen doping, including low operating voltages, improved uniformity of switching parameters, satisfactory endurance and long retention characteristics. Doping by nitrogen is proposed to suppress the stochastic formation of conducting filaments in the HfO2 matrix and thus improve the performances of the Pt/Ti/HfO2/Pt device.