Typical Bipolar Resistive Switching Behavior Research Articles

Lead-free CsCu2Br3 perovskite for multilevel resistive switching memory

Organic–inorganic metal halide perovskites have recently attracted enormous interest in the field of resistive switching memories owing to their unique electrical properties. Unfortunately, two challenges, the inadequate long-term stability and the toxicity of lead, largely hinder their further practical application. Herein, a 1D all-inorganic lead-free CsCu2Br3 perovskite is proposed for resistive switching devices to resolve these issues. The CsCu2Br3-based resistive switching devices exhibit typical bipolar resistive switching behavior with low set voltage, high on/off ratio (103), stable retention properties (>2 × 104 s), and endurance (200 cycles) in air. The unencapsulated CsCu2Br3-based device still maintains resistive switching characteristics while stored in ambient environment for over 2 months. Moreover, four on-state multilevel information storage behavior has been observed by regulating the value of compliance current during set process. The resistive switching behavior is dominated by the formation and fracture of conductive filaments, which are induced by the movement of Br− ions under electrical bias. This work offers the opportunity and strategy for the design of air-stable and environment-friendly metal halide perovskite-based memory devices.

Dimer-type Cs3Sb2I9: An efficient perovskite material for low operating voltage and high stability flexible resistive switching memory

All-inorganic perovskites have been taken as the promising functional materials in non-volatile resistive switching (RS) memory. Herein, the lead-free all-inorganic Cs3Sb2I9 perovskites with high stability are fabricated via hydrochloric acid (HCl) assisted solution method at low-temperature. The devices with a structure of Ag/polymethyl methacrylate (PMMA)/HCl-modified dimer-Cs3Sb2I9/ITO take on typical bipolar RS behavior and remarkable characteristics such as high ON/OFF ratio (≈66), low operating voltage (≈ −0.34 V/+0.25 V), excellent endurance property (≥120 cycles) and long data retention (≥104 s). Moreover, outstanding mechanical stability of the Cs3Sb2I9-based flexible memory devices are demonstrated under different bending angles and over consecutive 103 bending cycles. In addition, the Cs3Sb2I9-based memory devices show no obvious change in the RS behavior after over 10 days storage under an ambient atmosphere. This work will contribute to understanding the characteristics of low operating voltage and high stability RS behavior of the all-inorganic perovskites, and illuminate the great application potential of the lead-free antimony-based perovskite materials in next generation low power consumption non-volatile flexible memory devices.

Transparent, Flexible, and Low-Operating-Voltage Resistive Switching Memory Based on Al2O3/IZO Multilayer.

In this study, a different number of indium zinc oxide (IZO) interlayers are fabricated into Al2O3‐based transparent resistive switching memory on a transparent indium tin oxide (ITO)/glass substrate at room temperature. Al2O3/IZO multilayer transparent memory has a transmittance of at least 65% in the wavelength range of 400–900 nm. In addition, the Al2O3/IZO multilayer transparent memory can achieve an electroforming voltage that is 35.7% lower than that of ITO/pure‐Al2O3/IZO transparent memory. The fabricated Al2O3/IZO multilayer transparent memory exhibits typical bipolar resistive switching behavior, regardless of the number of IZO interlayers. Also, the fabricated Al2O3/IZO multilayer transparent memory has a low operating voltage within ±1.5 V. In addition, a flexible Al2O3/IZO multilayer transparent memory is fabricated using the same process on ITO‐coated polyethylene terephthalate. The fabricated flexible transparent memory also maintains the resistive switching characteristics during the bending state.

Sputtering-deposited amorphous SrVOx-based memristor for use in neuromorphic computing

The development of brain-inspired neuromorphic computing, including artificial intelligence (AI) and machine learning, is of considerable importance because of the rapid growth in hardware and software capacities, which allows for the efficient handling of big data. Devices for neuromorphic computing must satisfy basic requirements such as multilevel states, high operating speeds, low energy consumption, and sufficient endurance, retention and linearity. In this study, inorganic perovskite-type amorphous strontium vanadate (a-SrVOx: a-SVO) synthesized at room temperature is utilized to produce a high-performance memristor that demonstrates nonvolatile multilevel resistive switching and synaptic characteristics. Analysis of the electrical characteristics indicates that the a-SVO memristor illustrates typical bipolar resistive switching behavior. Multilevel resistance states are also observed in the off-to-on and on-to-off transition processes. The retention resistance of the a-SVO memristor is shown to not significantly change for a period of 2 × 104 s. The conduction mechanism operating within the Ag/a-SVO/Pt memristor is ascribed to the formation of Ag-based filaments. Nonlinear neural network simulations are also conducted to evaluate the synaptic behavior. These results demonstrate that a-SVO-based memristors hold great promise for use in high-performance neuromorphic computing devices.

Resistive switching behaviors and mechanisms of HfS2 film memory devices studied by experiments and density functional theory calculations

Energy band diagrams are widely utilized to explain the switching mechanism of resistance random access memory (RRAM). However, a precise and quantitative band theory is still lacking in this field. Although HfS2 has good applications in many fields because of its good electrical and optical properties, its applications in RRAM have seldom been reported. In this work, the exfoliated nanosheets of HfS2 were utilized to fabricate memory devices with a structure of Pt/Al/HfS2/p+-Si, which show typical bipolar resistive switching behavior with high switching voltage and a small ratio of high and low resistive states (R-ratio). According to the density functional theory (DFT) calculation results of energy band diagrams, instead of conductive filament formation in other resistive switching materials, the doping of sulfur vacancy (VS) of 3.8% is already enough to change the whole HfS2 layer from the semiconductor to the metal. The transition is caused by the change in the VS doping concentration from low to high, which is the result of the generation and movement of VS under an electric field. The DFT also calculated that HfS2 devices utilizing Indium Tin Oxide as the bottom electrode can show bipolar resistive switching behavior with lower switching voltage and a higher R-ratio than those utilizing p+-Si, which is confirmed by the experimental results. The DFT calculation can be utilized for both explaining the switching mechanism and designing the device structure to optimize the switching characteristics.

Morphological regulation of all-inorganic perovskites for multilevel resistive switching

Enormous attention has been paid to all-inorganic cesium lead halide perovskites in various photoelectronic fields for their remarkable performances. However, comparing to their analogue organic-inorganic hybrid perovskites, the film morphology of such all-inorganic lead halide perovskites is difficult to control due to the low solubility of cesium salt. Here, we propose a new fabrication routine to control the film morphology of CsPbBr3. A series of CsPbBr3 thin films with big grains (≈800 nm) were successfully prepared. The memristors based on such CsPbBr3 thin films take on typical bipolar resistive switching behavior and remarkable characteristics such as high Ron/Roff ratio (≈105), very low working voltage (≈±1 V), and long data retention (≥104 s). Furthermore, through modulating the film morphology, memristors with multilevel resistive switching behavior can be easily prepared. These advantages demonstrate that the all-inorganic cesium lead halide memristors possess great potential for future application.

Control the switching mode of Pt/HfO2/TiN RRAM devices by tuning the crystalline state of TiN electrode

In order to increase the resistive switching performance of memory devices based on TiN electrode, it is desirable to fabricate TiN with good oxygen reservoir ability. In the present paper, we report that the crystallized (200) textured TiN electrode were achieved by epitaxial grown on CrRu intermediate layer, which had better oxygen reservoir ability than the amorphous TiN. It is found that the Pt/HfO2/TiN devices with crystallized TiN electrode exhibited a typical bipolar resistive switching behavior, while the I-V curves of the Pt/HfO2/TiN devices with amorphous TiN electrode showed the unipolar resistive switching behavior regardless of voltage polarity, which is similar to the Pt/HfO2/Pt devices. It is believed that this originates from the different oxygen reservoir ability of TiN with different fabricating process. Moreover, the RRAM device with the new structure of TiN (amorphous)/HfO2/TiN (crystallized) exhibited the bipolar resistive switching behavior. This further proved the amorphous TiN electrode had poorer ability of oxygen reservoir than crystallized TiN, which was similar to a noble electrode like Pt electrode. Tuning the resistive switching behaviors of RRAM devices by controlling the crystalline state of TiN electrode may offer a method for fabrication of transition metal oxides based RRAM device with good performances.

Bipolar Resistive Switching Properties of Hf0.5Zr0.5O2 Thin Film for Flexible Memory Applications

An Au/Ni/Hf0.5Zr0.5O2/Au flexible memory device fabricated on a polyethylene terephthalate substrate was studied for flexible resistive random access memory applications. A typical bipolar resistive switching behavior was revealed with an OFF/ON ratio of approximately 15. The reproducibility and uniformity were investigated using 100 repetitive write/erase cycles. The retention property did not degrade for up to 5 × 104 s, and the resistive switching properties did not degrade even under bending conditions, which indicated good mechanical flexibility. The current–voltage characteristics of the memory device show a Poole–Frenkel emission conduction mechanism in the high‐voltage region in the high‐resistance state, while in the low‐voltage region, the Ohmic contact and space charge limit current responded to the low‐resistance state and high‐resistance state, respectively. Combined with the conductance mechanism, the resistive switching behavior is attributed to conductive filaments forming and rupturing due to oxygen vacancies migrating under the external driving electric field.

Ultrathin Cs3Bi2I9 Nanosheets as an Electronic Memory Material for Flexible Memristors

Methylammonium lead halide (MAPbX3) perovskites have attracted tremendous attention due to their remarkable performances in solar cells, light‐emitting diodes, photodetectors, lasers, and electronic memories. However, the issue of toxicity still greatly restricts their further large‐scale applications. Here, this study presents a series of nontoxic and stable methylammonium (or cesium) bismuth halides A3Bi2I9 (A = Cs+ and MA+) nanosheets for using in flexible memories. The ultrathin A3Bi2I9 nanosheets can be easily prepared by a dissolution–recrystallization process. This is the first attempt that reports the ultrathin bismuth halides and explores their potential applications in flexible electronic devices. The flexible memristors based on such ultrathin Cs3Bi2I9 nanosheets exhibit typical bipolar resistive switching behavior and remarkable characteristics such as high Ron/Roff ratio (≈103), very low working voltage (≈0.3 V), and long data retention (>104 s), as well as excellent endurability, reproducibility, environmental stability, and flexibility. With such appealing characteristics, the cesium bismuth halide memristors have great potential for practical applications. The results of this work demonstrate that cesium bismuth halide ultrathin nanosheets will be promising candidates for more emerging applications in electronics and optoelectronics such as memories, photodetectors, photovoltaics, and light‐emitting diodes.

Nitrogen concentration and temperature dependence of Ag/SiN/p +-Si resistive switching structure

In this study, resistive switching behaviors of Ag/SiN/p+-Si device were investigated by adjusting nitrogen concentration and layer thickness. The device with a nitrogen concentration of 50% and a thickness of 10 nm has a typical bipolar resistive switching behavior with a low forming voltage (~4 V), a high on/off ratio (~102), an excellent endurance (>102) and a long retention time (>105 s). According to I–V characteristics analyses, electric transports in both a high resistance state and a low resistance state are dominated by hot electron emission which is caused by the electron trapping and detrapping through immovable nitrogenrelated traps. The temperature dependence of a resistive switching behavior not only illustrates the existence and importance of the traps, but also discovers a new phenomenon of the transition about the polar of a resistive switching method. Surely, more efforts need to be made for deeper understanding of the carrier transport in SiN thin films.

Bipolar resistive switching behavior of an amorphous Ge₂Sb₂Te₅ thin films with a Te layer.

The mechanism of bipolar resistive switching (BRS) of amorphous Ge2Sb2Te5 (GST) thin films sandwiched between inert electrodes (Ti and Pt) was examined. Typical bipolar resistive switching behavior with a high resistance ratio (∼10(3)) and reliable switching characteristics was achieved. High-resolution transmission electron microscopy revealed the presence of a conductive Te-filament bridging between the top and bottom electrodes through an amorphous GST matrix. The conduction mechanism analysis showed that the low-resistance state was semiconducting and dominated by band transport, whereas Poole-Frenkel conduction governed the carrier transport in the high-resistance state. Thus, the BRS behavior can be attributed to the formation and rupture of the semiconducting conductive Te bridge through the migration of the Te ions in the amorphous GST matrix under a high electric field. The Te ions are provided by the thin (∼5 nm) Te-rich layer formed at the bottom electrode interface.

Multilayered Barium Titanate Thin Films by Sol-Gel Method for Nonvolatile Memory Application

The modification of multispin casting multilayered barium titanate (BTO) thin films on indium tin oxide (ITO)/glass substrate without doping other elements is adopted to improve the memory performance. The X-ray photoelectron spectroscopy analysis reveals the concentration of oxygen vacancies can be reduced by the increasing number of the BTO layer. Mechanisms of conducting paths relating to the concentration of oxygen vacancies will also be explicated. The memory devices showed typical bipolar resistive switching behavior and an ON/OFF ratio of over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> . The memory devices also exhibited outstanding uniformity. A retention time of over 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> s without fluctuation at room temperature and 85 °C can be achieved.

Modulation of surface trap induced resistive switching by electrode annealing in individual PbS micro/nanowire-based devices for resistance random access memory.

Bipolar resistive switching (RS) devices are commonly believed as a promising candidate for next generation nonvolatile resistance random access memory (RRAM). Here, two-terminal devices based on individual PbS micro/nanowires with Ag electrodes are constructed, whose electrical transport depends strongly on the abundant surface and bulk trap states in micro/nanostructures. The surface trap states can be filled/emptied effectively at negative/positive bias voltage, respectively, and the corresponding rise/fall of the Fermi level induces a variation in a degenerate/nondegenerate state, resulting in low/high resistance. Moreover, the filling/emptying of trap states can be utilized as RRAM. After annealing, the surface trap state can almost be eliminated completely; while most of the bulk trap states can still remain. In the devices unannealed and annealed at both ends, therefore, the symmetrical back-to-back Fowler-Nordheim tunneling with large ON/OFF resistance ratio and Poole-Frenkel emission with poor hysteresis can be observed under cyclic sweep voltage, respectively. However, a typical bipolar RS behavior can be observed effectively in the devices annealed at one end. The acquirement of bipolar RS and nonvolatile RRAM by the modulation of electrode annealing demonstrates the abundant trap states in micro/nanomaterials will be advantageous to the development of new type electronic components.

Resistive Switching Behavior in Amorphous Aluminum Oxide Film Grown by Chemical Vapor Deposition

The repeatable bipolar resistive switching phenomenon is observed in amorphous Al2O3 prepared by metal-organic chemical vapor deposition on ITO glass, with ITO as the bottom electrode and Ag as the top electrode. The crystal structure, morphology, composition and optical properties of Al2O3 thin films are investigated by x-ray diffraction, x-ray photoelectron spectroscopy, atomic force microscopy and ultraviolet-visible-infrared spectroscopy, respectively. The electronic character of Ag/Al2O3/ITO structure is tested by an Agilent B1500A. The device shows a typical bipolar resistive switching behavior under the dc voltage sweep mode at room temperature. The variation ratio between HRS and LRS is larger than nearly three orders of magnitude, which indicates the good potential of this structure in future resistive random access memory (ReRAM) applications. Based on the conductive filament model, the high electric field is considered the main reason for the resistive switching according to our measurements.

Investigating bipolar resistive switching characteristics in filament type and interface type BON-based resistive switching memory

This paper studies the effect of doping on BON-based resistive switching characteristics. Typical bipolar resistive switching behavior can be observed in Pt/BON/TiN and Pt/BON:Gd/TiN devices. The conductive path(s) of the Pt/BON/TiN is vacancy-dominated while the Pt/BON:Gd/TiN is metal-dominated. Additionally, there is an atypical bipolar resistive switching in the Gd-doping device. This atypical characteristic has not only a size effect, but also a lower operating current. The resistance transitions are due to the variation in conductance of the switching layer, which is clearly influenced by the different area size. A mechanism is proposed to explain this atypical characteristic.