Switching Random Access Memory Devices Research Articles

Improved Resistive Switching Behaviors of Al/Ag-Doped Fe2O3 Film/ITO Devices Fabricated with a Radio-Frequency Co-Sputtering System

We fabricated Fe2O3−x and Ag-doped Fe2O3−x devices with resistive switching behavior by using a radiofrequency cosputtering system. Our results indicated that doping Ag into Fe2O3−x can effectively improve device performance, increasing the data retention test time to beyond 104 s and resulting in switching cycles of approximately ∼3 × 102 times; resistance on/off ratios of approximately ∼103; and mean setting and reset voltages of 0.94 V and −1.35 V, respectively. The improvement in performance had several possible reasons. In our case, conductive filament formation was mainly induced by oxygen vacancies and Ag atoms. X-ray photoelectron spectroscopy showed that oxygen vacancies increased significantly with Ag doping. This phenomenon can improve device performance. Ag atoms served as trap centers, allowing for the easy trapping and release of charges. This effect facilitated the formation of conductive filaments. Ag-doped Fe2O3−x has significant potential for application in resistive switching random access memory devices.

Sustainable resistance switching performance from composite-type ReRAM device based on carbon Nanotube@Titania core\u2013shell wires

A novel nanocomposite-based non-volatile resistance switching random access memory device introducing single-walled carbon nanotube (SWCNT)@TiO2 core–shell wires was proposed for flexible electronics. The SWCNT was de-bundled by ultrasonication with sodium dodecylbenzene sulfonate (SDBS), and then the TiO2 skin layer on the SWCNT surface was successfully introduced by adding benzyl alcohol as a weak surfactant. The nanocomposite resistance switching layer was composed of the SWCNT@TiO2 core–shell wires and poly(vinyl alcohol) (PVA) matrix by a simple spin-coating method. The device exhibited reproducible resistance switching performance with a remarkably narrow distribution of operating parameters (VSET and VRESET were 2.63 ± 0.16 and 0.95 ± 0.11 V, respectively) with a large RON/ROFF ratio of 105 for 200 consecutive switching cycles. Furthermore, the excellent resistance switching behavior in our device was maintained against mechanical stress up to 105 bending test. We believe that the nanocomposite memory device with SWCNT@TiO2 core–shell wires would be a critical asset to realize practical application for a flexible non-volatile memory field.

Nickel oxide thin films grown by chemical deposition techniques: Potential and challenges in next‐generation rigid and flexible device applications

AbstractNickel oxide (NiOx), a p‐type oxide semiconductor, has gained significant attention due to its versatile and tunable properties. It has become one of the critical materials in wide range of electronics applications, including resistive switching random access memory devices and highly sensitive and selective sensor applications. In addition, the wide band gap and high work function, coupled with the low electron affinity, have made NiOx widely used in emerging optoelectronics and p‐n heterojunctions. The properties of NiOx thin films depend strongly on the deposition method and conditions. Efficient implementation of NiOx in next‐generation devices will require controllable growth and processing methods that can tailor the morphological and electronic properties of the material, but which are also compatible with flexible substrates. In this review, we link together the fundamental properties of NiOx with the chemical processing methods that have been developed to grow the material as thin films, and with its application in electronic devices. We focus solely on thin films, rather than NiOx incorporated with one‐dimensional or two‐dimensional materials. This review starts by discussing how the p‐type nature of NiOx arises and how its stoichiometry affects its electronic and magnetic properties. We discuss the chemical deposition techniques for growing NiOx thin films, including chemical vapor deposition, atomic layer deposition, and a selection of solution processing approaches, and present examples of recent progress made in the implementation of NiOx thin films in devices, both on rigid and flexible substrates. Furthermore, we discuss the remaining challenges and limitations in the deposition of device‐quality NiOx thin films with chemical growth methods.image

Extremely Low Program Current Memory Based on Self-Assembled All-Inorganic Perovskite Single Crystals.

Memory devices based on lead halide perovskite have attracted great interests because of their unique current-voltage hysteresis. However, current memory devices based on polycrystalline perovskites usually suffer from large intrinsic electronic current and parasitic leakage current due to the existence of grain boundaries, which further leads to high power consumption. Here, a low-power resistance switching random-access memory device is demonstrated by assembling single-crystalline CsPbBr3 on Ag electrodes. The assembled structure serves as a bipolar nonvolatile resistance switching memory device with a low program current (∼10 nA), good endurance, long data retention (>103 S), and big on/off ratio of ∼103. The low program current results in a power of ∼3 × 10-8 W, which is much lower than that of polycrystalline perovskite-based devices (10-1-10-6 W). It is found that the formation and annihilation of Ag and bromide vacancy conductive filaments contribute to the significant resistive switching effect. At a low resistive state, the conductive filaments originate from the accumulation of Br- ions at the drain. Furthermore, the conductive filaments are proved to be a cone shape, shrinking from the drain to the source.

The impact of TiW barrier layer thickness dependent transition from electro-chemical metallization memory to valence change memory in ZrO2-based resistive switching random access memory devices

The effect of TiW metal barrier layer thickness on voltage-current characteristics of the Cu/TiW/ZrO2/TiN conductive bridge random access memory device was systematically investigated. The change of reset behavior from abrupt decrease to gradual decrease with increasing TiW thickness was observed. Electronic conduction during the forming process was also analyzed to obtain detailed information about the effect of TiW layer thickness on the nature of the conduction phenomenon. The temperature coefficient of resistance of the conductive filament confirms that an electro-chemical metallization (ECM) based conduction was observed in the devices made with a thinner TiW layer. On the other hand, valence change memory (VCM) based conduction was observed with a thick TiW layer. A conduction mechanism is proposed to explain the ECM to VCM conduction transformation phenomenon.

High-performance flexible resistive memory devices based on Al2O3:GeOx composite

In this study a resistive switching random access memory device using Al2O3:GeOx composite thin films on flexible substrate is presented. A bipolar switching characteristic was observed for the co-sputter deposited Al2O3:GeOx composite thin films. Al/Al2O3:GeOx/ITO/PET memory device shows excellent ON/OFF ratio (∼104) and endurance (>500 cycles). GeOx nanocrystals embedded in the Al2O3 matrix have been found to play a significant role in enhancing the switching characteristics by facilitating oxygen vacancy formation. Mechanical endurance was retained even after several bending. The conduction mechanism of the device was qualitatively discussed by considering Ohmic and SCLC conduction. This flexible device is a potential candidate for next-generation electronics device.

Recovery of failed resistive switching random access memory devices by a low-temperature supercritical treatment

The successful recovery of resistive switching random access memory (RRAM) devices that have undergone switching failure is achieved by introducing a low-temperature supercritical-fluid process that passivates the switching layer. These failed RRAM devices, which are incapable of switching between high- and low-resistance states, were treated with supercritical carbon dioxide with pure water at 120 °C for 1 h. After the treatment, the devices became operational again and showed excellent current–voltage (I–V) characteristics and reliability as before. On the basis of the current conduction mechanism fitting results, we propose a model to explain the phenomenon.

Validation and Extension of Local Temperature Evaluation of Conductive Filaments in RRAM Devices

Local temperature plays a key role in resistive switching random access memory devices. We have previously presented a method for measuring the local filament temperature on a nanometric scale using an MIS bipolar transistor structure. Here, a more detailed analysis of the method is presented. A new calibration technique improves the accuracy of the extracted temperature. Alternative device structures allow validation of the method by the extraction of temperature that equals the ambient temperature when no self-heating occurs as well as extension of the obtained temperature range. The accuracy, prospects, and limitations of the method are discussed.

Study of Multilevel High-Resistance States in HfO<sub><italic>x</italic></sub>-Based Resistive Switching Random Access Memory by Impedance Spectroscopy

Multilevel high-resistance states are achieved in TiN/HfO x /Pt resistive switching random access memory device by controlling the reset stop voltage. Impedance spectroscopy is used to study the multilevel high-resistance states. It is shown that the high-resistance states can be described with an equivalent circuit consisting of the major components $R_{s}$ , $R$ , and $C$ corresponding to the series resistance of the TiON interfacial layer, the equivalent parallel resistance, and capacitance of the leakage gap between the TiON layer and the residual conductive filament, respectively. These components show a strong dependence on the stop voltage, which can be explained in the framework of oxygen vacancy model and conductive filament concept. On the other hand, $R$ is observed to decrease with dc bias, which can be attributed to the barrier lowering effect of the Coulombic trap well in the Poole–Frenkel emission model.

Al-doped ZnO as a switching layer for transparent bipolar resistive switching memory

In this report, we employ an Al-doped ZnO (AZO) layer as a resistive switching layer for transparent resistive switching random access memory devices. An Indium-Tin-Oxide (ITO)/AZO/ITO/glass device exhibits a transmittance of ∼80% (including a glass substrate) in the visible wavelength region and demonstrates reliable bipolar resistive switching behavior over d.c. 300 sweeping cycles with a low operation voltage and a very low variation in the switching threshold voltage. These results indicate that the AZO film is a promising transparent resistive switching layer.

An Indium-Free Transparent Resistive Switching Random Access Memory

We report an indium-free transparent resistive switching random access memory device based on GZO-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -ZnO-Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -GZO structure by metal-organic chemical vapor deposition. The memory device shows good transmittance in the visible region and bipolar resistive switching behavior with good cycling characteristics and retention time under room temperature. The conduction and resistive switching mechanism was discussed based on filament theory.