Resistive Switching Effect Research Articles

Resistive switching effects in fluorinated graphene films with graphene quantum dots enhanced by polyvinyl alcohol

Two-layer films of partially fluorinated graphene (PFG) with graphene quantum dots and polyvinyl alcohol (PVA) were prepared by means of 2D printing technology. A stable resistive switching effect with the ON/OFF current ratio amounting from one to 4–5 orders of magnitude is found. The decrease in the PVA thickness leads to a change of the unipolar threshold switchings to the bipolar resistive switchings. The crossbar Ag/PFG/PVA/Ag structures retain their performance up to 6.5% deformation. The switching phenomenon is observed for a period about a year. The traps with characteristic activation energies ∼0.05 eV are suggested to be responsible for resistive switching. The time of charge-carrier emission from the localized states was found to be ∼5 μs. A quality model to describe the resistive switching effect in two-layer films implying the conduction over quantum dots proceeding with the participation of active traps at the PFG/PVA interface is proposed. The structures with the design demonstrated threshold resistive switching have their high potential for development of selector devices integrated to sensor or memristors circuits, for information storage and data processing, for flexible and wearable electronics. The structures with lower PVA thickness and the bipolar threshold switching are perspective for non-volatile memory cells for printed and flexible electronics.

Resistive switching effect enhanced by light irradiation in C/BaTiO3/C memory structure

The Ta/[C/BaTiO3/C]/Si device was obtained. The resistive switching (RS) behaviors of the Ta/[C/BaTiO3/C]/Si device are studied in the dark and under white-light illumination with various power densities. The results show that the device displays bipolar RS effect, which can be modulated by the white light. And the RS memory device shows biggish resistance ratio, which is more than 105 under white-light irradiation with a power density of 40[Formula: see text]mW/cm2, and the ratio can stabilize at nearly 71 cycles. This work is helpful for the optical control non-volatile memory.

Tunable thermal conductivity in aluminum oxide resistive based switching structures by conducting filament diffusion

Nanoscale oxide resistive switching structures have attracted widespread attention in connection with future logic, memory, neuromorphic computing, and storage structure applications. Resistive switching effects are usually assumed to be caused by conducting filaments (CFs), which are formed by metal diffusion, and their breaking across the insulating oxide between the metal electrodes. Understanding thermal transport in CF containing metal/oxide based structures is critical to determine whether these filaments exist. This paper reports phonon transport in Cu diffused aluminum oxide (AO) in a Cu/AO/Si resistive switching structure where Cu based CFs have formed locally as a result of electric breakdown. This was studied by measuring cross-plane thermal conductivity on CF containing AO layers from 100 to 500 K. Our results suggest that conferring thermal properties upon non-thermoelectric materials as a result of CF formation enables thermal conductivity to be controlled by CF density. Therefore, the proposed methodology, including a local probing method, will also help understand other physical properties of metal/oxide based resistive switching structures in the future.

Electroforming and resistive reversible switching effect in polycrystalline fullerene C60 films

It has been found that the conductivity of a polycrystalline fullerene C60 thin film increases by several orders of magnitude after lengthy exposure to an electric field of ∼ 106 V/cm. This effect is called electroforming. After electroforming, the current-voltage characteristic shows high current stability and reproducibility of results. An increase in capacitance and a decrease in resistance by 4 orders is observed in a narrow voltage range of 0.1-1 V, which is the effect of reversible resistive switching. In fields with a strength of 105-106 V/cm, the I-V characteristic of molded films is determined by the current with a limited space charge. Trap concentrations are defined as Nt-1 ≈ 2.3· 1021 m−3 and Nt-2 ≈ 5.8·1020 m−3 and their depth Et ≈ 0.17 eV for polycrystalline C60 films with thicknesses of 250 and 500 nm, respectively.

Thermal stability of resistive switching effect in ZnO/BiFeO3 bilayer structure

Superior thermal stability of resistive switching performance is essential for resistive random access memory (R-RAM) device with high reliability. Thermal stable resistive switching performance can be achieved in ZnO/BiFeO3 bilayer structure by modifying the interface. The bilayer structure with a distinct interface is fabricated with an optimized annealing process in chemical solution deposition method. This bilayer structure shows a better thermal stability compared to the case with an indistinct interface. Attempt has been made to explain such effects based on conductive filament mechanism. We propose that the confinement of the oxygen vacancies migration at distinct interface could be the reason for the thermal stability. Our results indicate that morphology of interface is an important factor to improve the thermal stability of R-RAM.

The effect of post-process annealing on optical and electrical properties of mixed HfO2\u2013TiO2 thin film coatings

In this paper a comparison of electrical and optical properties of mixed hafnium-titanium oxides is described. Thin films were deposited with the use of the magnetron co-sputtering method. For further analysis (Hf0.52Ti0.48)Ox and (Hf0.29Ti0.71)Ox coatings, which were amorphous directly after the deposition process, were chosen,. Moreover, post-process annealing was also performed in order to compare the electrical and optical properties of amorphous and nanocrystalline thin films with the same material composition. It was found that the phase transition from amorphous to orthorhombic HfTiO4 occurred in the case of (Hf0.52Ti0.48)Ox coating at 650 °C. In turn, the phase transition to TiO2-anatase was observed at the temperature of 600 °C in the case of (Hf0.29Ti0.71)Ox thin film. The leakage current for both amorphous coatings was in the range of 10−7–10−8 A/cm2. After additional annealing and phase transition, the leakage current slightly decreased for (Hf0.29Ti0.71)Ox thin film, while in the case of (Hf0.52Ti0.48)Ox sample the resistance switching effect was observed. The dielectric constant was equal to 24 and 25 for amorphous (Hf0.52Ti0.48)Ox and (Hf0.29Ti0.71)Ox films, respectively. However, after the phase transition it decreased to 15 for (Hf0.52Ti0.48)Ox and increased to 51 for (Hf0.29Ti0.71)Ox film. The results of optical studies showed that amorphous thin films were well transparent in a visible light range with an average transparency of ca. 85%. After the phase transition to HfTiO4-orthorhombic and TiO2-anatase, a slight decrease in the transparency level by 3% and a redshift of the cut-off wavelength was observed. Moreover, additional annealing caused small changes of the optical band gap energy, refractive index and extinction coefficient.

Current channeling along extended defects during electroreduction of SrTiO3

Electroreduction experiments on metal oxides are well established for investigating the nature of the material change in memresistive devices, whose basic working principle is an electrically-induced reduction. While numerous research studies on this topic have been conducted, the influence of extended defects such as dislocations has not been addressed in detail hitherto. Here, we show by employing thermal microscopy to detect local Joule heating effects in the first stage of electroreduction of SrTiO3 that the current is channelled along extended defects such as dislocations which were introduced mechanically by scratching or sawing. After prolonged degradation, the matrix of the crystal is also electroreduced and the influence of the initially present dislocations diminished. At this stage, a hotspot at the anode develops due to stoichiometry polarisation leading not only to the gliding of existing dislocations, but also to the evolution of new dislocations. Such a formation is caused by electrical and thermal stress showing dislocations may play a significant role in resistive switching effects.

Resistive Switching Behavior in Ferroelectric Heterostructures

Resistive random-access memory (RRAM) is a promising candidate for next-generation nonvolatile random-access memory protocols. The information storage in RRAM is realized by the resistive switching (RS) effect. The RS behavior of ferroelectric heterostructures is mainly controlled by polarization-dominated and defect-dominated mechanisms. Under certain conditions, these two mechanisms can have synergistic effects on RS behavior. Therefore, RS performance can be effectively improved by optimizing ferroelectricity, conductivity, and interfacial structures. Many methods have been studied to improve the RS performance of ferroelectric heterostructures. Typical approaches include doping elements into the ferroelectric layer, controlling the oxygen vacancy concentration and optimizing the thickness of the ferroelectric layer, and constructing an insertion layer at the interface. Here, the mechanism of RS behavior in ferroelectric heterostructures is briefly introduced, and the methods used to improve RS performance in recent years are summarized. Finally, existing problems in this field are identified, and future development trends are highlighted.

Back-to-back Interface diodes induced symmetrical negative differential resistance and reversible bipolar resistive switching in β-CuSCN trigonal pyramid micro/nanoarray

As a superior p-type wide bandgap semiconductor, β-CuSCN has a huge potential in optoelectronic device application, and however its conduction could intensively be affected by externally applied bias. Here, we demonstrate electrodeposited individual β-CuSCN trigonal micro/nanopyramids and their array films can show Cu+ trap-controlled bias dependence of electron transport. Before being subjected to a large reverse bias or a unidirectional bias, their cyclic IV curves are coincident resulted from bulk-trap related carrier hopping. At relatively large bidirectional operation bias, they can symmetrically present two large hysteresis loops with negative differential resistance (NDR), and meanwhile accompany with nonvolatile negative resistive switching (RS) feature. After being applied respectively a relatively large fixed bias in two opposite directions, more importantly, switchable classic asymmetrical bipolar RS can successfully be realized at a relatively low operation bias. The switchable formation of reversion and depletion layer, resulted from the minority carriers (electrons) injection into the traps of surface connected with negative electrode, plays a crucial role. Under relatively large bias, the synergistic effect of two surface trap-related back-to-back connected bipolar RS devices results in symmetrical negative RS with NDR. After being applied a relatively large fixed bias, the bipolar RS effect can be enhanced at the surface connected with negative electrode due to the presence of electron injection induced high and narrow barrier, and conversely it disappears at the surface connected with positive electrode due to hole injection-induced ohmic contact. Then, the devices can be set and reset by the filling and emptying of holes in the thin reversion and depletion layer at low reverse and forward voltages, respectively, showing switchable bipolar RS behavior. Due to superior stability, reversibility, nondestructive readout, and low operation bias as well as remarkable cycle performance, the bias-governed conduction with negative RS and switchable bipolar RS makes it a potential candidate in next-generation erasable nonvolatile RRAM devices.

Effects of Monopolar Resistive Switching in Thin Diamond-Like Carbon Layers

The current-voltage characteristics have been studied for Pt/diamond-like C/Pt structures based on thin (20 nm) diamond-like carbon layers, in which the ratio between carbon phases with sp2 and sp3 hybridization is controlled by the growth conditions of the layers by the high-frequency diode sputtering method. The effects of resistive switching from the initial high-resistive state to a low-resistive one at an applied voltage of V ~ 3 V and reverse switching at V ~ 0 V are detected. These effects are symmetric with respect to change in voltage polarity and are explained by the change in the hybridization type of local carbon regions, which causes switching from the high- to low-resistive state in strong (~106 V/cm) fields because of sp3 → sp2 transitions and reverse switching in the absence of the field. The high-to-low resistance ratio reaches ~50.

Conductive filaments controlled ferromagnetism in Co-doped ZnO resistive switching memory device

Both the bipolar resistive switching (RS) behavior and the ferromagnetism (FM) of a Co-doped ZnO device were investigated in this study. The magnetic hysteresis curves of the device with RS behavior in the high-resistance state (HRS) and low-resistance state (LRS) were analyzed, both of which showed ferromagnetic behavior. Interestingly, the intensity of the saturation magnetization in the device in HRS and LRS were observed to be the smallest and largest, respectively. X-ray photoelectron spectra demonstrated the existence of oxygen vacancies in the device, the concentration of which in LRS was larger than that in HRS. Especially, depth-profiling X-ray photoelectron spectra showed that a change in the conductive filaments was consistent with the resistance states and FM. The results clearly demonstrate that the RS effect and FM could be attributable to film defects.

Oxygen vacancy dynamics in redox-based interfaces: tailoring the memristive response

Redox-based memristive devices are among the alternatives for the next generation of non-volatile memories, but are also candidates for emulating the behavior of synapses in neuromorphic computing devices. Nowadays it is well established that the motion of oxygen vacancies at the nanoscale is the key mechanism for reversible switching of metal/insulator/metal structures from insulating to conducting, i.e. to accomplish the resistive switching effect. The control of oxygen vacancy dynamics has a direct effect on the resistance changes, and therefore on different properties of memristive devices such as switching speed, retention, endurance and energy consumption. Advances in this direction demand not only experimental techniques that allow the measurement of oxygen vacancy profiles but also theoretical studies that shed light on the mechanisms involved. With these goals in mind we analyze the oxygen vacancy dynamics in redox interfaces formed when an oxidizable metallic electrode is in contact with the insulating oxide. We show how the transfer of oxygen vacancies can be manipulated by the use of different electrical stimulus protocols that allow optimization of device figures such as the ON/OFF ratio or writing energy dissipation. Analytical expressions for both high- and low-resistance states are derived in terms of total oxygen vacancies transferred at the interface. Our predictions are validated with experiments performed in Ti/La1/3Ca2/3MnO3 redox memristive devices.

Механизмы токопереноса и резистивного переключения в конденсаторах со слоями стабилизированного иттрием диоксида гафния

AbstractThe peculiarities of resistive switching in capacitors with yttria-stabilized hafnia layers were studied. The characteristics of current transport in the initial state and after electroforming and resistive switching at different temperatures were examined. The parameters of a small-signal equivalent circuit of a capacitor were determined for switching into low- and high-resistance states. These parameters suggest that the resistance of filaments changes after each successive switching. This provides an opportunity to use such measurements to determine the nature of resistive switching and verify the reproducibility of its parameters. The contribution of electron traps to switching was revealed. Ion migration polarization was observed at temperatures above 500 K, and the activation energy of ion migration and the ion concentration were determined. The effect of resistive switching under the influence of temperature was observed and interpreted for the first time.

Improvement of the performance in Cr-doped ZnO memory devices via control of oxygen defects.

The defect-enhanced resistive switching behavior of Cr-doped ZnO films was investigated in this study, and evidence that the switching effect can be attributed to defects was found. X-ray photoelectron spectroscopy demonstrated the existence of oxygen vacancies in the ZnO-based films, and the concentration of oxygen vacancies in the Cr-doped ZnO film was larger than that in the undoped ZnO film, which can be attributed to Cr doping. We concluded that the defects in Cr-doped ZnO were due to the Cr dopant, leading to excellent performance of Cr-doped ZnO films. In particular, depth-profiling analysis of the X-ray photoelectron spectra demonstrated that the resistive switching effects corresponded to variations in the concentration of the defects. The results confirmed that oxygen vacancies are crucial for the entire class of resistive switching effects in Cr-doped ZnO films. In particular, the Cr-doped ZnO films not only show bipolar resistive switching behavior but also excellent reliability and stability, which should be beneficial for next-generation memory device applications.

Transport Properties in Co-doped ZnO/YMnO3 n-p Heterojunctions

Abstract N-p heterojunctions have been the focus of research due to their broad range of applications. We studied the transport properties in Co-doped ZnO/YMnO3 n-p heterojunctions. Samples were grown at two different numbers of laser pulses and at different at. % Co concentration. Current-voltage characterization showed diode behavior, along with dependence of electrical properties on growth parameters and Co doping concentration. In fact, samples grown at 2500 laser pulses at 2.0 and 5.0 atom percent exhibited hysteretic and asymmetric I-V curves, indicating a possible resistive switching effect with a relation between low-resistance state and high-resistance state of around 9.8.

Magnetic properties and oxygen migration induced resistive switching effect in Y substituted multiferroic bismuth ferrite

Multiferroic Y-doped BiFeO3 (BY10FO) thin films were deposited on FTO coated glass substrate using sol-gel spin coating technique. Y-doping causes structural distortion without changing the structure of the parent BiFeO3 (rhombohedral: R3c). The M-H hysteresis curve reveals that the BY10FO film exhibits saturation magnetization at a low-coercive field by suppressing the spiral spin modulated structure. The bipolar resistive switching behavior has been investigated on a Ag/BY10FO/FTO hetero-structure through conventional I-V curve measurements and the device can produce an ON/OFF ratio of around 12 over 30 complete testing cycles. The space charge limited current and Schottky barrier emission conduction mechanism play a crucial role in switching the states between HRS and LRS. The impedance spectroscopy analysis at HRS and LRS confirms the significant degradation of resistance from MΩ to kΩ. The switching mechanism in the hetero-structure is due to migration and recombination of oxygen vacancies present in the film. The non-degradation of the Ag/BY10FO/FTO device after several testing cycles confirms that the switching of resistance between ON and OFF states is reproducible, reversible and controllable to be used for possible future non-volatile resistive random access memory application.

Nanoscale mechanical control of surface electrical properties of manganite films with magnetic nanoparticles.

Mechanical control of electrical properties in complex heterostructures, consisting of magnetic FeOx nanoparticles on top of manganite films, is achieved using atomic force microscope (AFM) based methods. Under applied pressure of the AFM tip, drop of the electrical conductivity is observed inducing an electrically insulating state upon a critical normal load. Current and surface potential maps suggest that the switching process is mainly governed by the flexoelectric field induced at the sample surface. The relaxation process of the electrical surface potential indicates that the diffusion of oxygen vacancies from the bulk of the manganite films towards the sample surface is the dominant relaxation mechanism. The magnetic FeOx nanoparticles, staying attached to the sample surface after the rubbing, protect the underlying manganite films and provide stability of the observed resistive switching effect. The employed mechanical control gives a new freedom in the design of resistive switching devices since it does not depend on the film thickness, and biasing is not needed.

Study of the resistive switching effect in In/HfO2/Ptdevices

Abstract HfO2 thin films were grown on Pt/TiO2/SiO2/Si substrates via RF magnetron sputtering technique at pure oxygen atmosphere with a substrate temperature of 550 °C. We studied the structural and electrical properties on HfO2 thin films, varying the thickness (tHfO2) from 23 to 155 nm. Grazing-incident x-ray diffraction shows a polycrystalline composition, some peaks are shifted when the tHfO2 increase, that is, a relaxation occur on the film. We fabricated In/HfO2/Ptlike a capacitor structurefor perform the electrical property measurements. The current-voltage curves display a resistive switching behavior for all thicknesses, and the resistance dependence with time, displays retention states with Low and High resistance in all samples. The percentage of change on resistance ([(RON-ROFF)/ROFF]×100) scale with HfO2 thickness and reach a saturation value ∼ 30% at tHfO2>120 nm.

Solution-Processable ZnO Thin Film Memristive Device for Resistive Random Access Memory Application

The memristive device is a fourth fundamental circuit element with inherent memory, nonlinearity, and passivity properties. Herein, we report on a cost-effective and rapidly produced ZnO thin film memristive device using the doctor blade method. The active layer of the developed device (ZnO) was composed of compact microrods. Furthermore, ZnO microrods were well spread horizontally and covered the entire surface of the fluorine-doped tin oxide substrate. X-ray diffraction (XRD) results confirmed that the synthesized ZnO was oriented along the c-axis and possessed a hexagonal crystal structure. The device showed bipolar resistive switching characteristics and required a very low resistive switching voltage (±0.8 V) for its operation. Two distinct and well-resolved resistance states with a remarkable 103 memory window were achieved at 0.2-V read voltage. The developed device switched successfully in consecutive 102 switching cycles and was stable over 102 seconds without any observable degradation in the resistive switching states. In addition to this, the charge–magnetic flux curve was observed to be a single-valued function at a higher magnitude of the flux and became double valued at a lower magnitude of the flux. The conduction mechanism of the ZnO thin film memristive device followed the space charge limited current, and resistive switching was due to the filamentary resistive switching effect.

An atomic switch using oxygenated amorphous carbon as solid electrolyte

Atomic switches based on carbon films as electrolyte have received great attention due to the many advantages of carbon, but their low high-resistance state and poor thermal stability of the device have greatly limited their further development. Here, we have constructed an atomic switch in which we use an oxygenated amorphous carbon (a-COx) film as a solid electrolyte through introducing O2 gas during the sputtering of a graphite target. The reversible and steady resistive switching effect with a resistance ratio over two orders of magnitude was achieved. While the sputtered pure C film has a low resistivity, which is not suitable for an atomic switch, the resistance of a-COx increases substantially with the partial pressure of O2. More importantly, we found that the higher the partial pressure of O2, the better the high temperature retention. In combination with the two-step reset process in which the heat and electric fields respectively act and mutable forming voltage with temperature, the achieved high temperature retention for more oxidized carbon films is most likely due to the more reduction of structural defects caused by the greater addition of oxygen during the deposition process and the chemical inertness of a-COx.