Flexible Resistive Switching Device Research Articles

A flexible resistive switching device for logical operation applications in wearable systems

As an emerging micro/nano device, memristor integrates functions, such as memory, sensing, and computing, and has similar internal dynamics to synapses, showing great potential in neuromorphic computing and logical operations. In this work, a flexible memristor with Al/TiOx/Al/polyethylene terephthalate structure was developed to investigate the synergistic effect from the oxygen vacancy, H2O molecule, and NaCl. A forming-free resistive switching (RS) behavior observed in the flexible memristor can be ascribed to the migration and accumulation of the oxygen vacancy and Schottky emission of the interfaces. This forming-free RS is sensitive to the NaCl and H2O molecule because the Na+ migration disturbs the oxygen vacancy filament and interplay between oxygen vacancy and H2O molecules. The variation conductance modulated by the concentration of NaCl and H2O molecules can represent the weight update incrementally that the online learning required. Therefore, the memristor has the potential to be used as a biosensor in human tissues or to realize the brain-like chip, which points out the research direction for the extension function of the memristor in wearable systems.

Flexible resistive switching device based on air-stable lead-free Cu3SbI6 perovskite film for nonvolatile memory application

Resistive switching (RS) behavior of lead-free rudorffite perovskite Cu3SbI6 is explored for developing high performance flexible resistive switching random access memory (ReRAM) devices. The Cu3SbI6 based devices exhibit reproducible bipolar nonvolatile RS behaviors with low operating voltage (≤±0.6 V), stable endurance (≥400 cycles), and long data retention time (≥104 s). Moreover, the devices fabricated on flexible substrates show good electrical reliability and mechanical stability under different bending angles and consecutive bending cycles (103 times). A computational study method is used to reveal the mechanical stability of the Cu3SbI6 and the RS properties of the memory devices. More importantly, the Cu3SbI6 based devices exhibit no significant changes in RS behaviors after stored in ambient conditions for over 60 days. The results suggest that devices based on all-inorganic lead-free rudorffite perovskite materials have great potential for high performance, stable, and flexible ReRAM.

Flexible Memory Device Composed of Metal-Oxide and Two-Dimensional Material (SnO2/WTe2) Exhibiting Stable Resistive Switching.

Two-terminal, non-volatile memory devices are the fundamental building blocks of memory-storage devices to store the required information, but their lack of flexibility limits their potential for biological applications. After the discovery of two-dimensional (2D) materials, flexible memory devices are easy to build, because of their flexible nature. Here, we report on our flexible resistive-switching devices, composed of a bilayer tin-oxide/tungsten-ditelluride (SnO2/WTe2) heterostructure sandwiched between Ag (top) and Au (bottom) metal electrodes over a flexible PET substrate. The Ag/SnO2/WTe2/Au flexible devices exhibited highly stable resistive switching along with an excellent retention time. Triggering the device from a high-resistance state (HRS) to a low-resistance state (LRS) is attributed to Ag filament formation because of its diffusion. The conductive filament begins its development from the anode to the cathode, contrary to the formal electrochemical metallization theory. The bilayer structure of SnO2/WTe2 improved the endurance of the devices and reduced the switching voltage by up to 0.2 V compared to the single SnO2 stacked devices. These flexible and low-power-consumption features may lead to the construction of a wearable memory device for data-storage purposes.

Flexible resistive switching device based on the TiO2 nanorod arrays for non-volatile memory application

In this article, a flexible resistive switching memory is developed based on TiO2 nanorod arrays with interstice between the nanorods to release the bending stress/strain. The device shows a stable forming-free bipolar resistive switching behavior with low operating voltage of below 3 V, high ON/OFF ratio of above 102, good retention for more than 105 s, good endurance of 107 cycles, and good thermal stability of the high resistance and low resistance state at 85 °C during the retention and fatigue tests. Moreover, under the different bending radius from 12 mm to 5 mm, the electrical performances referring to operating voltage and ON/OFF ratio of the device show few changes, and under the bending cycles of 400 times with the bending radius of 12 mm, all of the devices show no interfacial crack or delamination as well as keep the bipolar resistive switching behavior with the low operating voltage and high ON/OFF ratio. The good performances of the devices suggest that the TiO2 nanorod arrays resistive switching device may open up new possibilities in realizing high-performance flexible memory.

Highly flexible and stable resistive switching devices based on WS2 nanosheets:poly(methylmethacrylate) nanocomposites

This paper reports data for the electrical characteristics and the operating mechanisms of flexible resistive switching devices based on WS2 nanosheets (NSs) dispersed in a poly(methyl methacrylate) (PMMA) layer. The ON/OFF ratio of the memristive device based on an Al/WS2 NSs:PMMA/indium tin oxides (ITO) structure was approximately 5.9 × 104. The memristive device based on the WS2 NSs also exhibited the bipolar switching characteristics with low power consumption and great performance in the bent state with radii of the curvatures of 20 and 10 mm. Especially, the results obtained after bending the device were similar to those observed before bending. The device showed nearly the same ON/OFF ratio for a retention time of 1 × 104 sec, and the number of endurance cycles was greater than 1 × 102. The set voltage and the reset voltage probability distributions for the setting and the resetting processes indicated bipolar switching characteristics. The operating and the carrier transport mechanisms of the Al/WS2 NSs:PMMA/ITO device could be explained based on the current-voltage results with the aid of an energy band diagram.

Ultrathin silver telluride nanowire films and gold nanosheet electrodes for a flexible resistive switching device.

We demonstrated a flexible resistive switching device based on ultrathin Ag2Te nanowire (NW) films and Au nanosheet (NS) electrodes by exploiting a monolayer assembly on the water surface for macroscale two-dimensional structures. Firstly, ultrathin TeNWs (diameter ≈ 10 nm) are rapidly assembled on the water surface as a form of monolayer and transferred to fabricate TeNW films on various substrates with any available size. An assembled TeNW film was used as a template to produce a Ag2TeNW film through chemical transformation. A well-aligned Ag2TeNW film device showed reversible resistive switching properties when the Ag composition of the silver telluride NW becomes stoichiometric Ag2Te. Additionally, a non-stoichiometric Ag2+δTeNW film shows an increased On/Off ratio. For a flexible memory device, ultrathin AuNSs (thickness ≤20 nm) were adopted as working electrodes, since thermally deposited gold electrodes tend to crack under strain, which can fail to maintain the electrical properties. A paper-like flexibility of AuNS proved its capability as optimal electrodes of ultrathin Ag2TeNW film-based resistive memory devices.

Flexible resistive switching device based on poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/poly(4-vinylphenol) (PVP) composite and methyl red heterojunction

To obtain a desired performance of non-volatile memory applications, heterojunction-based resistive switching devices have tremendous attractions. In this paper, we demonstrate resistive switching characteristics for heterojunction of poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/poly(4-vinylphenol) (PVP) composite and methyl red sandwiched in between bottom and top silver (Ag) electrodes. The proposed heterojunction layers are fabricated through spin coater at 3000 rpm for 60 s each, and the Ag electrodes are deposited through a commercialized inkjet printer DMP-3000 on polyethyleneterephthalate (PET) substrate. To verify the proposed device, the resistive switching on dual polarity voltage of ±10.2 V is measured over more than 500 endurance cycles. The paper also presents an Roff/Ron ratio which can adjust through an active layer’s area and a blending ratio of the PEDOT:PSS and PVP. By applying the area of 100 μm2 and the blending ratio of 3:1, we achieve the higher Roff/Ron ratio of 121, and its high resistance state (HRS) and low resistance state (LRS) are observed as 3000 kΩ and 24.7 kΩ, respectively. To maintain a long retention time, the device is encapsulated with PDMS, which changes a little variations of 52 Ω for HRS 498 Ω for LRS over 60 days. For the flexible realization to be utilized in wearable applications, it can be easily applied on a plastic substrate using printed technologies.

A two-dimensional hexagonal boron nitride/polymer nanocomposite for flexible resistive switching devices

Organic–inorganic hybrid nanocomposites are an attractive choice for various electronic device applications.

Fabrication of graphene-nanoflake/poly(4-vinylphenol) polymer nanocomposite thin film by electrohydrodynamic atomization and its application as flexible resistive switching device

This paper describes synthesis of graphene/poly(4-vinylphenol) (PVP) nanocomposite and deposition of thin film by electrohydrodynamic atomization (EHDA) for fabrication flexible resistive switching device. EHDA technique proved its viability for thin film deposition after surface morphology analyses by field emission scanning electron microscope (FESEM) and non-destructive 3D Nano-profilometry, as the deposited films were, devoid of abnormalities. The commercially available graphene micro-flakes were exfoliated and broken down to ultra-small (20nm–200nm) nano-flakes by ultra-sonication in presence of N-methyl-pyrrolidone (NMP). These graphene nanoflakes with PVP nanocomposite, were successfully deposited as thin films (thickness ~140±7nm, Ra=2.59nm) on indium–tin-oxide (ITO) coated polyethylene terephthalate (PET) substrate. Transmittance data revealed that thin films are up to ~87% transparent in visible and NIR region. Resistive switching behaviour of graphene/PVP nanocomposite thin film was studied by using the nanocomposite as active layer in Ag/active layer/ITO sandwich structure. The resistive switching devices thus fabricated, showed characteristic OFF to ON (high resistance to low resistance) transition at low voltages, when operated between ±3V, characterized at 10nA compliance currents. The devices fabricated by this approach exhibited a stable room temperature, low power current–voltage hysteresis and well over 1h retentivity, and ROFF/RON≈35:1. The device showed stable flexibility up to a minimum bending diameter of 1.8cm.

Excellent resistive switching property and physical mechanism of amorphous TiO2 thin films fabricated by a low-temperature photochemical solution deposition method

Abstract High-performance resistive switching Pt/TiO2/Pt memory cells were fabricated. The amorphous TiO2 active layer was prepared by using a low-temperature photochemical solution deposition method—a simple preparation process combining first chemical solution deposition of the TiO2 film layer and subsequent ultraviolet (UV) irradiation treatment. The obtained Pt/TiO2/Pt memory cells exhibited excellent resistive switching parameters, such as centralized distribution of set and reset voltages, stable current values at high and low resistance states, and long retention time. The conductive mechanisms of high resistance state and low resistance state were Schottky emission and Ohmic conduction, respectively. The X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, and scanning electron microscopy characterization of the TiO2 thin films indicated that the UV irradiation treatment can lead to decomposition of the residual organics and the formation of enhanced metal-oxide bonds in the thin films. On the basis of the analysis of current–voltage characteristics and the temperature dependence of resistance, we explained the resistive switching phenomenon for Pt/TiO2/Pt devices by using the model of formation/rupture of conductive filaments. Our study also suggested that the simple photochemical solution deposition method can be used for preparing some other oxide thin films with good resistive switching properties at low processing temperature which is promising to be extended to flexible resistive switching devices.

Resistive switching characteristics of thin NiO film based flexible nonvolatile memory devices

Flexible resistive switching device consisting of thin NiO film sandwiched between a flexible Cu foil substrate and Ti top electrode is proposed in this work. The Ti/NiO/Cu structure was fabricated by radio frequency magnetron sputtering deposition of a NiO film on the flexible Cu foil substrate. The fabricated device showed stable bipolar resistive switching behavior and its performance was not degraded upon different bending states. The Ti/NiO/Cu flexible device presented in our work has potential applications in the field of resistive switching random access memory (RRAM) devices.