Resistive Switching Performance Research Articles

Enhancement of DC/AC resistive switching performance in AlOx memristor by two-technique bilayer approach

In this work, we enhance the DC/AC resistive switching performance in AlOx memristors by using a two-technique bilayer approach. Compared to the single-layer memristors (W/AlOx or Al2O3/Pt), the dual-layer memristor (W/AlOx/AlOy/Pt) shows high uniformity in DC cycling (σ/μ < 0.12), large memory window in AC cycling (>100), fast switching speed (20 ns), high endurance (107 cycles), and high-temperature stability (104 s at 125 °C). These performance enhancements are attributed to the localization of the conductive region after using a dual layer with different defect concentrations. Moreover, the W/AlOx/AlOy/Pt memristor exhibits stable III-bit multilevel storage capability by varying the amplitude of negative pulses. Our results provide an effective strategy to develop high-performance memristors for future memory and computing applications.

Optimized Resistive Switching in TiO2 Nanotubes by Modulation of Oxygen Vacancy Through Chemical Reduction

The resistive switching behavior of 1-D TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanotube-based resistive random access memory (ReRAM) is discussed in this article. Highly oriented TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanotubes were synthesized by anodic oxidation method on a Ti substrate, which was used as the bottom electrode. To modulate the oxygen vacancy (VO) in TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanotubes, hydrazine hydrate reduction was employed in the temperature range 60 °C-100 °C. After charactering the morphological, elemental, and crystallographic properties, the level of reduction in different TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanotubes array was estimated by Raman, photoluminescence, and X-ray photoelectron spectroscopies. Au/TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanotubes/Ti devices were fabricated by using TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanotubes with various levels of reductions where thin and porous Au top electrode was used to make the resistive switching faster. TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> Nanotubes array, reduced at 80 °C showed promising resistive switching performance with SET/RESET voltages of 2 V/1.8 V, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OFF</sub> /R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">ON</sub> of 19 at a read voltage of 0.5 V (25 °C) and stable endurance behavior after the 100th cycle. Interestingly, reduction temperature at 60 °C and 100°C, offered degraded resistive switching within the same voltage range. All the devices showed electroforming free bipolar resistive switching. Efforts were devoted to establish the role of V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">O</sub> and its tuning to improve the resistive switching behavior in 1-D TiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanotubes. This article systematically showcases the efficacy of 1-D metal oxide for potential ReRAM application and establishes an easy but efficient approach to improve the resistive switching by modulating oxygen vacancy in it.

Exploiting Flexible Memristors Based on Solution‐Processed Colloidal CuInSe2 Nanocrystals

AbstractCompared to analogous bulk materials, colloidal nanocrystals have presented a powerful platform for building up electronic devices on the nano/micrometer scale and flexible portable electronic apparatus with the benefits of solution‐based processing approach at room temperature. Herein, memristors based on CuInSe2 (CISe) colloidal nanocrystals prepared using a solution‐based process at room temperature are constructed. The memristors exhibit obvious bipolar resistive switching performance with a high–low resistance ratio larger than 5.7 and a steady retention time over 104 s. This is attributed to the copper ion redox reaction and the migration of these ions under an applied electric field. When the SET voltage is reached, the ions are separated from one of the electrodes, and the memristor changes from a low‐resistance state (LRS) to a high‐resistance state (HRS). Conversely, when the voltage reaches the RESET voltage, the memristor switches from a HRS to a LRS. In addition, the flexible memristor can be fabricated by spincoating nanocrystal solution onto polyethylene terephthalate (PET) at room temperature, showing excellent reproducibility of the performance including 100 times of continuous operation, 104 s of reproducible reading, 600 times of antifatigue testing, and thermal stability up to 95 °C. The flexible devices demonstrate promising applications for portable electronic devices.

Controlling Cu Migration on Resistive Switching, Artificial Synapse, and Glucose/Saliva Detection by Using an Optimized AlO x Interfacial Layer in a-CO x -Based Conductive Bridge Random Access Memory.

The Cu migration is controlled by using an optimized AlOx interfacial layer, and effects on resistive switching performance, artificial synapse, and human saliva detection in an amorphous-oxygenated-carbon (a-COx)-based CBRAM platform have been investigated for the first time. The 4 nm-thick AlOx layer in the Cu/AlOx/a-COx/TiNxOy/TiN structure shows consecutive >2000 DC switching, tight distribution of SET/RESET voltages, a long program/erase (P/E) endurance of >109 cycles at a low operation current of 300 μA, and artificial synaptic characteristics under a small pulse width of 100 ns. After a P/E endurance of >108 cycles, the Cu migration is observed by both ex situ high-resolution transmission electron microscopy and energy-dispersive X-ray spectroscopy mapping images. Furthermore, the optimized Cu/AlOx/a-COx/TiNxOy/TiN CBRAM detects glucose with a low concentration of 1 pM, and real-time measurement of human saliva with a small sample volume of 1 μL is also detected repeatedly in vitro. This is owing to oxidation–reduction of Cu electrode, and the switching mechanism is explored. Therefore, this CBRAM device is beneficial for future artificial intelligence application.

Endurance degradation of solution-processed ZnO polycrystalline film-based resistive switching memory

Metal oxide-based resistive switching memory cell has potential applications in the next generation of nonvolatile memory devices due to its simple structure, fast reading/writing speed, and good endurance. Zinc oxide (ZnO) is one of excellent resistive switching candidate materials owing to its low-cost, simple preparation process and significant resistive switching characteristics. In this work, homogeneous ZnO precursor solution is spin-coated on indium tin oxide (ITO)-coated glass substrate to deposit a smooth and dense film composed by ZnO nanoparticles with the hexagonal wurtzite structure. Atomic force microscopy images reveal the average grain size of ZnO polycrystalline nanoparticle is about 23.7 nm. An optical band gap of about 3.3 eV is derivate from the ultraviolet-visible light absorption spectra. Current-voltage ( I - V ) curves of Ag/ZnO/ITO memory cells exhibit reversible low-voltage bipolar resistive switching characteristics. Their switching voltages ( V Set/ V Reset) are lower than ± 0.4 V, and the ON/OFF resistance ratio is 103–104 at the read voltage of −0.1 V, which are superior to resistive switching performance of other ZnO polycrystalline films prepared via similar solution methods. However, the memory cell can only maintain 60 stable I - V cycles. After that, the low resistance state gradually degrades to the high resistance state, and the resistive switching memory window completely disappears after 100 I - V cycles. X-ray photoelectron spectra of Zn 2p and O 1s core-levels for ZnO film before and after I - V measurement demonstrate that as-grown film is oxygen-defective ZnO x I - V measurement. Under sustained electric field stress, some drifted oxygen ions combine with oxygen vacancies and change to localized lattice oxygen atoms, this partially remedies the oxygen-deficiency of as-grown non-stoichiometric ZnO x

Photoassisted Electroforming Method for Reliable Low‐Power Organic–Inorganic Perovskite Memristors

AbstractOrganic–inorganic hybrid perovskite memristors with high resistive‐switching (RS) reliability and low power consumption are crucial for high‐density storage and high‐efficiency neuromorphic computing. However, the current overshoot in the electroforming process generally induces overgrowth of conductive filaments (CFs) and degrades the RS performance. Here, a simple photo‐assisted electroforming (PAE) method to suppress the current overshoot, in which the visible light irradiation is introduced into the initial electroforming process, is proposed for the first time. As a result, a reliable memristor with reduced RS fluctuation and enhanced cycling endurance is obtained, and also, the low operating current of 0.06 mA and low powerconsumption of 0.12 mW are achieved, which are about one order of magnitude lower than those of most reported hybrid perovskite‐based memristors. Further experimental evidence indicates that light irradiation plays dual roles: 1) the light‐induced lowering of iodide migration barrier leads to a significant reduction of overshoot current and forming voltage; 2) the enhanced local photoconductivity of the perovskite film shares the overshoot current through the CFs. Both factors limit the total quantity of vacancy defects generated in the electroforming process, thus preventing undesirable overgrowth of the CFs. The present PAE strategy has promise for developing high‐performance memristors.

Resistive switching performance improvement of InGaZnO-based memory device by nitrogen plasma treatment

With the demand of flat panel display development, utilizing the non-volatile memory devices based on indium-gallium-zinc-oxide (IGZO) film may be integrated with IGZO thin film transistors (TFTs) to accomplish system-on-panel applications. In this work, 1 × 1 μm2 via hole structure IGZO based memory device was fabricated and the resistive switching (RS) behavior was investigated. By inserting a nitrogen doping layer IGZO:N by plasma treatment in Pt/IGZO/TiN device, highly improved RS performance including lower forming voltage, remarkable uniformity, large memory window of 102, retention property of 104 s at 125 °C, excellent pulse endurance of 107 cycles were achieved. The X-ray photoelectron spectroscopy analysis indicates that plasma doping method can evenly dope nitrogen and induce more non-lattice oxygen in the IGZO film. It is deduced that the N atoms of the inserting layer can influence the random formation of oxygen vacancy type conducting filaments, which results in more stable and uniform performance.

Synaptic learning and memory functions in SiO2:Ag/TiO2 based memristor devices

In this study, a TiO2 thin layer is deliberately inserted in the Pt–Ag/SiO2:Ag/p++-Si memristor to achieve enhanced resistive switching performance in terms of retention and cyclic endurance characteristics. The memristor device exhibits a bidirectional analog switching behavior corresponding to a wide dynamic range of synaptic weight modulation as potentiation and depression under the consecutive positive or negative DC bias sweeps and pulse trains. Moreover, the learning and memory functions, including paired-pulse facilitation and pulse repetition-induced short-term memory to long-term memory transition, are also demonstrated. The relation of the memory stability to the repeated input pulse stimulus and the device conductance with time have also been revealed by the stretched exponential relaxation model. It is shown that the conductance of our newly fabricated Pt–Ag/SiO2:Ag/TiO2/p++-Si memristor device can be modulated by successive Ag-filament growth and dissolution in the SiO2:Ag/TiO2 bilayer oxide structure, which is essential for potential applications in memory devices and artificial neural systems.

Artificial Synapse Based on van der Waals Heterostructures with Tunable Synaptic Functions for Neuromorphic Computing.

Two-dimensional (2D) materials and van der Waals heterostructures have attracted tremendous attention because of their appealing electronic, mechanical, and optoelectronic properties, which offer the possibility to extend the range of functionalities for diverse potential applications. Here, we fabricate a novel multiterminal device with dual-gate based on 2D material van der Waals heterostructures. Such a multiterminal device exhibited excellent nonvolatile multilevel resistance switching performance controlled by the source-drain voltage and back-gate voltage. Based on these features, heterosynaptic plasticity, in which the synaptic weight can be tuned by another modulatory interneuron, has been mimicked. A tunable analogue weight update (both on/off ratio and update nonlinearity) of synapse with high speed (50 ns) and low energy (∼7.3 fJ) programming has been achieved. These results demonstrate the great potential of the artificial synapse based on van der Waals heterostructures for neuromorphic computing.

Toward a Reliable Synaptic Simulation Using Al-Doped HfO2 RRAM

The potential in a synaptic simulation for neuromorphic computation has revived the research interest of resistive random access memory (RRAM). However, novel applications require reliable multilevel resistive switching (RS), which still represents a challenge. We demonstrate in this work the achievement of reliable HfO2-based RRAM devices for synaptic simulation by performing the Al doping and the postdeposition annealing (PDA). Transmission electron microscopy and operando hard X-ray photoelectron spectroscopy results reveal the positive impact of Al doping on the formation of oxygen vacancies. Detailed I-V characterizations demonstrate that the 16.5% Al doping concentration leads to better RS properties of the device. In comparison with the other reported results based on HfO2 RRAM, our devices with 16.5% Al-doping and PDA at 450 °C show better reliable multilevel RS (∼20 levels) performance and an increased on/off ratio. The 16.5% Al:HfO2 sample with PDA at 450 °C shows good potentiation/depression characteristics with low pulse width (10 μs) along with a good On/Off ratio (>1000), good data retention at room temperature, and high temperature and good program/erase endurance characteristics with a pulse width of 50 ns. The synapse features including potentiation, depression, and spike time-dependent plasticity were successfully achieved using optimized Al-HfO2 RRAM devices. Our results demonstrate the beneficial effects of Al doping and PDA on the enhancement of the performances of RRAM devices for the synaptic simulation in neuromorphic computing applications.

Resistive switching memory performance in oxide hetero-nanocrystals with well-controlled interfaces

ABSTRACT For realization of new informative systems, the memristor working like synapse has drawn much attention. We developed isolated high-density Fe3O4 nanocrystals on Ge nuclei/Si with uniform and high resistive switching performance using low-temperature growth. The Fe3O4 nanocrystals on Ge nuclei had a well-controlled interface (Fe3O4/GeOx/Ge) composed of high-crystallinity Fe3O4 and high-quality GeOx layers. The nanocrystals showed uniform resistive switching characteristics (high switching probability of ~90%) and relatively high Off/On resistance ratio (~58). The high-quality interface enables electric field application to Fe3O4 and GeOx near the interface, which leads to effective positively charged oxygen vacancy movement, resulting in high-performance resistive switching. Furthermore, we successfully observed memory effect in nanocrystals with well-controlled interface. The experimental confirmation of the memory effect existence even in ultrasmall nanocrystals is significant for realizing non-volatile nanocrystal memory leading to neuromorphic devices.

Logic Function and Random Number Generator Build Based on Perovskite Resistive Switching Memory and Performance Conversion via Flexible Bending

Perovskite CH3NH3SnCl3 thin films serving as the active layer are used for preparing flexible memory devices with the structure of Al/CH3NH3SnCl3/poly(vinyl alcohol)/ITO/PET. This memory device sho...

Resistive switching and synaptic learning performance of a TiO2 thin film based device prepared by sol–gel and spin coating techniques

A resistance random access memory device based on TiO2 thin films was fabricated using a sol–gel spin and coating techniques. The composition, surface morphology, and microstructure of the TiO2 films were characterized using x-ray diffraction, Raman spectroscopy, scanning electronic microscopy, and transmission electron microscopy, respectively. The fabricated Al/TiO2 film/fluorine-doped tin oxide device exhibited electroforming-free bipolar resistive switching characteristics with a stable ON/OFF ratio higher than 300. The performance of the endurance cycling was still good after 100 direct sweeping cycles. A retention time of no less than 104 s was confirmed. A switching mechanism is systematically discussed based on the test results, and space-charge-limited current was found to be responsible for the switching behavior. Multilevel memory performance was realized in the as-fabricated devices. The synaptic performance was investigated by applying consecutive positive (0–2 V) and negative (0 to −1.6 V) voltage sweeps. The fabricated devices were found to exhibit ‘learning-experience’ behavior.

Introducing a thin MnO2 layer in Co3O4-based memory to enhance resistive switching and magnetization modulation behaviors

Nanocrystalline bilayer composite MnO2/Co3O4 thin films were fabricated by a simple chemical solution deposition method to investigate the resistive and magnetization switching properties. Compared with pure Co3O4 thin films device, bilayer MnO2/Co3O4 thin films device exhibits enhancement in resistive switching (RS) and magnetization modulation, such as uniform SET and RESET voltages, stable cycle-to-cycle switching endurance (>2 × 103 cycles), good data retention time (>104 s), and RS induced magnetization switching (∼63%). Through the analysis of fitting current-voltage (I–V) curves and temperature-dependent resistance, it demonstrated that Schottky emission conduction is dominated at high resistance state of the devices. Enhancement in RS performance can be attributed to the growth and dissolution of confined conductive filaments which are composed of Mn atoms and oxygen vacancies, evidenced by temperature dependence and magnetization switching at different resistance states. The physical relevancy between RS and magnetic switching involves in the creation and annihilation of conductive filaments, associated with the reversible conversion of cation valence state (Co2+ and Co3+, Mn ions and Mn atoms). Results suggest that by introducing a thin MnO2 inserting layer, Co3O4 based device shows promising applications for nonvolatile RS memory and multifunctional electromagnetic coupling device.

Unipolar resistive switching behavior in Al2O3/HfO2 multilayer dielectric stacks: fabrication, characterization and simulation

In this work, the impact of different HfO2/Al2O3-based multilayer dielectric stack (DS) configurations on the electrical characteristics and on the resistive switching (RS) performance of Ni/Insulator/Silicon devices has been systematically investigated. Significant differences are observed in the electrical characteristics of the fabricated bilayer, trilayer and pentalayer stacks compared to a single HfO2 layer of the same physical thickness. The RS analysis has shown similar low resistance state currents and set voltages for all the DS combinations whereas currents at the high resistance state and reset voltages depend on the DS. The shift of the reset voltage to lower values for HfO2 and Al2O3/HfO2/Al2O3 cases is explained by the results from thermal simulations that reveal that these differences could be associated to the different temperature distributions at the narrowest part of the conductive filament immediately before the thermally triggered reset process occurs.

Ammonium phosphomolybdate: a material for dielectric crossover and resistive switching performance.

The yellow ammonium phosphomolybdate [(NH4)3PMo12O40] (YAPM) is a robust and elegant compound that has found innumerable field applications. Herein, we have shown that this inorganic polymer serves as a novel dielectric material and a compound for memory device fabrication. It displays changeable dielectric performance and ac conductivity under UV (∼365 nm) irradiation. Drastic lowering of the dielectric constant (ε′) was observed with the increase in dielectric loss factor, which was ascertained due to electron accumulation under UV exposure producing green APM (GAPM). The contributions of the Maxwell–Wagner polarization and the dipolar relaxation are correlated with the charge transfer and dielectric contribution of the material. Interestingly, the pressure-induced reduction of Mo(vi) to Mo(v) is reported for the first time and is similar to UV-exposed mixed-valence GAPM, which was corroborated by EPR spectra. In the ac signal, the crossover from quantum mechanical tunneling to hopping conduction is an adequate explanation for YAPM under UV irradiation. The fabricated device Au‖YAPM‖Au on a flexible paper substrate shows a resistive memory behavior that is modeled as a Schottky-type emission (SE) and Poole–Frenkel (PF) carrier transport for the OFF and ON states, respectively. The device exhibited a constant ON–OFF current ratio of 2 × 102 for YAPM. The OFF state endurance of the device (with 3 V pulses having 1 s time-period) under UV showed a steady increment current strength with time. After 100 s of UV exposure, the Au‖YAPM‖Au device became Au‖GAPM‖Au, and the conductivity completely shifted to a stable ON-state (at 300 s).

The strategies of filament control for improving the resistive switching performance

The recent developments of filament control in resistive switching devices including electrode optimization, switching layer optimization and channel design are reviewed.

A carbon-based memristor design for associative learning activities and neuromorphic computing.

Carbon quantum dots (QDs) have attracted significant interest due to their excellent electronic properties and wide application prospects. However, the application of carbon QDs has been rarely reported in memristors. Here, a memristor model with carbon conductive filaments (CFs) is proposed for the first time based on carbon quantum dots. The CF-based devices exhibited excellent resistive switching performance, in particular a narrow range of SET and RESET voltages and good power efficiency and retention properties. These devices could also emulate important biological synapse performances, such as the transition from short-term plasticity (STP) to long-term potentiation (LTP) behaviors, long-term depression (LTD) behavior, and four types of spike-timing-dependent plasticity (STDP) learning rules. Interestingly, Pavlovian associative learning functions were also reliably demonstrated in the memristor device (MD). The digit recognition ability of the MDs was evaluated though a single-layer perceptron model, in which the recognition accuracy of digits reached 92.63% after 250 training iterations. The transmission electron microscopy (TEM) results evidenced that the carbon CF was found in the MD at the "ON" state. Thus, this new carbon CF-based mechanism for memristors provides a new idea for achieving better neuromorphic MDs and applications.

Resistive switching performance of fibrous crosspoint memories based on an organic–inorganic halide perovskite

Fiber-shaped RRAMs with an ON/OFF ratio of approximately 106 have been presented via a MAPbI3 perovskite for flexible wearable electronic textiles.

Improved resistive switching behavior of multiwalled carbon nanotube/TiO2 nanorods composite film by increased oxygen vacancy reservoir

The non-linear nature in the current-voltage relationship and good resistive switching characteristics were demonstrated with the help of TiO2 nanorods-functionalized multiwalled carbon nanotube (fMWCNT) composite grown by the low-cost hydrothermal method. The composites were characterized by X-ray diffraction, scanning electron microscopy, Raman, photoluminescence, and X-ray photoelectron spectroscopy to investigate the structural, morphological, and chemical composition of composite films. The resistive switching characteristics of the TiO2-fMWCNT nanocomposites were found to be strongly dependent on the fMWCNT concentration. The enhanced switching performance is associated with the surface nanostructure and chemical composition of the nanocomposites. Owing to the hierarchical rutile TiO2 nanorods and opportune fMWCNT content, the nanocomposite based device with 0.03 wt % fMWCNT exhibited the best resistive switching performance with good endurance and retention non-volatile memory properties. Interestingly, with the optimized stoichiometric composition and operation conditions, forming-free, low operational voltage, self-rectifying like properties have been simultaneously achieved, which are some of the prerequisites for next-generation memory devices. In addition to this, the double-valued charge-magnetic flux nature of the developed devices was demonstrated. The experimental current-voltage characteristics are well-matched with the Ohmic and Schottky conduction mechanisms.