Current Bistability Research Articles

Ultra-sensitive current bistability and light switching in a resonant tunneling superlattice transistor

Bistability in the current–voltage characteristics of semiconductor superlattices and quantum cascade laser structures has the potential for wide-ranging applications, particularly in sensing systems. However, the interdependency of applied bias and current injection in conventional two-terminal structures has led to complications in analysis and rendered the bistability phenomenon difficult to implement in practical applications. Here, we report a new kind of electronic bistability coupled to optical switching in a resonant tunneling bipolar superlattice transistor. This bistability manifests as sharp discontinuities in the collector current with extremely small variations of the applied voltage, which arise from unstable tunneling transmission across the hetero-barrier between the two-dimensional electron gas (2DEG) at the edge of the transistor base and the collector superlattice structure. The electronic transitions between high and low quantum mechanical transmissions are demonstrated to be caused by self-consistent variations of the internal electric field at the heterointerface between the 2DEG and the superlattice. They are also present in the base current of the three-terminal device and result in sharp switching of near-infrared spontaneous light emission output from an interband radiative recombination process with a peak emission wavelength of 1.58 μm. A comprehensive quantum mechanical theoretical model accounting for the self-consistent bistable tunneling transmission is in quantitative agreement with the experimental data. The measured peak transconductance sensitivity value of 6000 mS can be used in the highly sensitive detector and non-linear device applications.

Mathematical Estimation Methods and Models for Industrial Companies

The collateralized debt obligations and credit default swaps applications are shown in this paper. The industry obligations secondary market risk estimation methods are considered in this work. The new methods taking into account statistically significant parameters for industrial credit derivatives portfolio are offered for single-name investment risks numerical experiments realization. The mathematical estimation of tranche were shown. The single and multiple name default obligations necessary mathematical modeling methods and formulae for the industrial materials manufacturers derivative credit tools market are shown. It is determined that the portfolio of synthetic debt tools is made of the given parameters. The task of a loss derivative tranches mathematical estimation is solved. Late defaults raise the equity tranches payment required sums with high spreads, early defaults reduce. Also the functional characteristics required for an estimation huge debts problem solving are partly considered in this paper. The problem of the default modeling for market tools and numerical simulation of the obligations influence on conditions of current bistability mode are shown here. Some credit derivatives of industrial manufacturers are demonstrated in the modeling process of default as an example. It is found that the model is an additional factor help us to estimate the default opportunity.

Mass transport and dynamical instabilities in a model electrocatalytic process with a preceding chemical reaction

The influence of mass transport on the occurrence of periodic current oscillations and bistability in a model electrocatalytic process with a preceding homogeneous first-order chemical reaction in the Nernst diffusion layer for different diffusion coefficients of species involved in the chemical reaction is shown. The impacts of the diffusion coefficients of electrochemically active and inactive species, as well as the preceding chemical reaction rate constants on the emergence of these dynamical instabilities are uncovered. The effect of the aforementioned parameters on frequency of oscillations is determined. The peculiarities of the system behavior at the bifurcation points are demonstrated in the Nyquist and Bode plots. For the first time, the role of diffusion coefficient of inactive species in these nonlinear processes is presented theoretically.

Tungsten oxide nonvolatile memory devices using photothermal in-situ oxidation method

The tungsten oxide nonvolatile memory devices were fabricated using the photothermal in-situ oxidation method. The photothermal in-situ oxidation method can monitor the oxidation process in real time. Raman spectra revealed that tungsten oxides were formed by thermal oxidation. The ON/OFF ratio of the current bistability for the device was as large as ~ 102 at a 2 V reading voltage, and the cycling endurance of the ON/OFF switching for the devices was stable without noticeable degradation. Memory mechanisms for device are described using fitted the I–V curves.

Printed memory devices using electrohydrodynamic deposition technique

This research utilizes electrohydrodynamic printing to fabricate a transparent memristor device having active film of zinc-oxide sandwiched between two silver cross-bar electrodes. It is a unique structure and never been reported in the literature before. The bipolar memristor device demonstrates current bistability as a result of the breakdown of zinc oxide layer into distinct doped and un-doped regions, thus resulting into swift charge transfer. The oxygen vacancies are created in the zinc-oxide layer upon receiving a minimum bias voltage (+ve/−ve) known as forming voltage. The maximum ON/OFF ratio of the current bi-stability for the fabricated memristor was as large as 1 × 103 which is considered satisfactory. The memristor device demonstrated a robust performance of up to 1000 read/write cycles. The printed device was characterized for the structural confirmation using x-ray diffraction analysis and it showed hexagonal wurtzite structure for ZnO active layer and typical face-centred cubic structure for the silver electrodes. The morphological uniformity was confirmed by scanning electron microscopy whereas > 90% transparency was reported by the optical characterization of the zinc-oxide active layer.

Influence of blending ratio on resistive switching effect in donor-acceptor type composite of PCBM and PVK-based memory devices

Abstract The influence of blending ratio on resistive switching effect in donor-acceptor type composite of [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and poly(N-vinylcarbazole) (PVK)-based memory devices are investigated. Current-voltage (I-V) curves for the ITO/PCBM + PVK/Al devices with 9 wt.% of PCBM showed a current bistability with a maximum OFF/ON resistance ratio of 9 × 104, which was 100 times larger than that of the device with 23 wt.% of PCBM and was 2000 times larger than that of the device with 41 wt.% of PCBM. Furthermore, the threshold voltage obviously decreased as the PCBM concentration increases. The retention time was above 105 s indicative of the memory stability of the as-fabricated devices. The I-V characteristics at OFF state dominantly comply with the rules of space-charge-limited-current behaviors, and I-V curve at ON state obey Ohmic laws. The proposed device suggests a promising approach for adjustale OFF/ON resistance ratio and threshold voltage in electronic memory devices.

Enlarged memory margins for resistive switching devices based on polyurethane film due to embedded Ag nanoparticles

Current-voltage (I-V) properties of indium-tin-oxide/Ag nanoparticles embedded in polyurethane film/Al devices exhibited a current bistability with ON/OFF ratio within the range of 105–103 with the variation of voltage from −0.85 to 3.95 V, which was nearly 102 larger than that for the device without Ag nanoparticles. The memory margin was obviously enlarged due to the existence of the Ag nanoparticles embedded in the polyurethane layer. I-V properties and write-read-erase-read voltage cycles test indicated the flash resistive switching properties. The data retention time reach up to 1.8 × 104 s, which manifested the stability of the memory devices. I-V property at ON state was attributed to the drift mechanism, and the property at OFF state was related to the space-charge-limited-current behaviors.

Highly-stable memristive devices based on poly(methylmethacrylate): CsPbCl3 perovskite quantum dot hybrid nanocomposites

Abstract Memristive devices based on cesium-lead-chlorine (CsPbCl3) perovskite quantum dots (PQDs) embedded in a poly(methyl methacrylate) (PMMA) layer were fabricated to enhance their memory stability. Current-voltage (I-V) measurements on Al/PQDs embedded in PMMA layer/indium-tin-oxide devices at 300 K showed nonvolatile rewritable memristive behaviors. The maximum ON/OFF ratio of the current bistability for the devices was as large as 2 × 104. The retention time for the devices was above 1 × 104 s, indicative of high stability of the device. The operating mechanisms of the devices related to the interaction between the PQDs and the PMMA matrix could be explained by adjusting the thickness of the active layer. Furthermore, the carrier transport mechanisms of the devices are described on the basis of the I-V results with the aid of the energy-band diagram. The carrier transport could be attributed to the space-charge-limited-current mechanism in the high resistance state and to Ohmic conduction in the low resistance state.

Highly-reproducible nonvolatile memristive devices based on polyvinylpyrrolidone: Graphene quantum-dot nanocomposites

Abstract The properties of nonvolatile memristive devices (NMD) fabricated utilizing organic/inorganic hybrid nanocomposites were investigated due to their superior advantages such as mechanical flexibility, low cost, low-power consumption, simple technological process in fabrication and high reproducibility. The current-voltage (I-V) curves for the Al/polyvinylpyrrolidone (PVP): graphene quantum-dot (GQD)/indium-tin-oxide (ITO) memristive devices showed current bistability characteristics at 300 K. The window margins corresponding to the high-conductivity (ON) state and the low-conductivity (OFF) state of the devices increased with increasing concentration of the GQDs. The ON/OFF ratio of the optimized device was 1 × 104, which was the largest memory margin among the devices fabricated in this research. The endurance number of ON/OFF switching was above 1 × 102 cycles, and the retention time was relatively constant, maintaining a value above 104 s. The devices showed high reproducibility with the writing voltage being distributed between −0.5 and −1.5 V and the erasing voltage being distributed between 2 and 3 V. The ON state currents remained between 0.02 and 0.03 A, and the OFF state currents stayed between 10−6 and 10−4 A. The carrier transport mechanisms are illustrated by using both the results obtained by fitting the I-V curves and the energy band diagrams of the devices.

Reduced graphene oxide preparation and its applications in solution-processed write-once-read-many-times graphene-based memory device

We fabricated graphene-based non-volatile memory device by solution-processed route in this work. Thermally reduced graphene oxide (rGO) on quartz substrate prepared in the ambient of acetylene/hydrogen plasma treatment was used as bottom conductive electrode to replace the commonly-used bottom conductive indium-tin-oxide layer. The morphology of the rGO film was characterized and used for device fabrication. The device was fabricated in the simple structure of silver nanowires/nanocomposite/rGO/quartz and the nanocomposite was prepared by mixing the graphene quantum dots and graphene oxide in ethanol. Current-voltage (I–V) measurement of the fabricated device shows current bistablity with the similar behavior as write-once-read-many-times (WORM) memory device. The ON/OFF ratio of the current bistability for the devices was as large as 1 × 103 with retention stability up to 1 × 104 s. The direct tunnelling, trapped-charge limited-current, and Ohmic conduction were proposed as dominant conduction mechanisms through the fabricated NVM devices based on the obtained I–V characteristics.

Enhancements of the memory margin and the stability of an organic bistable device due to a graphene oxide:mica nanocomposite sandwiched between two polymer (9-vinylcarbazole) buffer layers

Current-voltage (I–V) curves for the Al/polymer (9-vinylcarbazole) (PVK)/graphene oxide (GO):mica/PVK/indium-tin oxide (ITO) devices at 300K showed a current bistability with a maximum high conductivity (ON)/low conductivity (OFF) ratio of 2×104, which was approximately 10 times larger than that of the device without a PVK layer. The endurance number of ON/OFF switchings for the Al/PVK/GO:mica/PVK/ITO device was 1×102 cycles, which was 20 times larger than that for the Al/GO:mica/ITO device. The “erase” voltages were distributed between 2.3 and 3V, and the “write” voltages were distributed between −1.2 and −0.5V. The retention time for the Al/PVK/GO:mica/PVK/ITO device was above 1×104s, indicative of the memory stability of the device. The carrier transport mechanisms occurring in the Al/PVK/GO:mica/PVK/ITO and the Al/GO:mica/ITO devices are described on the basis of the I–V results and the energy band diagrams.

Peculiarities of tunneling current in w-AlN/GaN(0001) two-barrier structures induced by deep-level defects

The influence of deep-level defects localized in spacer layers on the tunneling current in a w-AlN/GaN (0001) double-barrier structure is studied. It is shown that the current value essentially depends on the nature and spatial distribution of defects. New effects (screening of built-in fields, negative feedback, fixing of current peaks at high temperature) and a new mechanism of formation of resonances and tunneling current hysteresis caused by deep centers are established. The results of calculation agree with a number of experimental data on the position and temperature dependence of the current peak. It is noted that the current bistability can be caused by multicharged deep centers localized near the heteroboundaries of a double-barrier structure. Due to the defects, electric field in the barriers can reach values, at which the Poole-Frenkel effect should be taken into account.

Indium-tin-oxide, free, flexible, nonvolatile memory devices based on graphene quantum dots sandwiched between polymethylsilsesquioxane layers

Indium-tin-oxide (ITO) free, nonvolatile memory (NVM) devices based on graphene quantum dots (GQDs) sandwiched between polymethylsilsesquioxane (PMSSQ) layers were fabricated directly on polyethylene terephthalate (PET) substrates by using a solution process technique. Current-voltage (I-V) curves for the silver nanowire/PMSSQ/GQD/PMSSQ/poly(3,4-ethylenethiophene):poly(styrene sulfonate)/PET devices at 300 K showed a current bistability. The ON/OFF ratio of the current bistability for the NVM devices was as large as 1 × 104, and the cycling endurance time of the ON/OFF switching for the NVM devices was above 1 × 104 s. The Schottky emission, Poole-Frenkel emission, trapped-charge limited-current, and space-charge-limited current were dominantly attributed to the conduction mechanisms for the fabricated NVM devices based on the obtained I-V characteristics, and energy band diagrams illustrating the “writing” and the “erasing” processes of the devices.

Carrier transport and memory mechanisms of multilevel resistive memory devices with an intermediate state based on double-stacked organic/inorganic nanocomposites

Multilevel resistive memory devices with an intermediate state were fabricated utilizing a poly(methylmethacrylate) (PMMA) layer sandwiched between double-stacked PMMA layers containing CdSe/ZnS core–shell quantum dots (QDs). The current–voltage (I–V) curves on a Al/[PMMA:CdSe/ZnS QD]/PMMA/[PMMA:CdSe/ZnS QD]/indium-tin-oxide/glass device at low applied voltages showed current bistabilities with three states, indicative of multilevel characteristics. A reliable intermediate state was realized under positive and negative applied voltages. The carrier transport and the memory mechanisms of the devices were described on the basis of the I–V curves and energy band diagrams, respectively. The write-read-erase-read-erase-read sequence of the devices showed rewritable, nonvolatile, multilevel, and memory behaviors. The currents as functions of the retention time showed that three current states were maintained for retention times larger than 1 × 104 s, indicative of the good stability of the devices.

Memory stabilities and mechanisms of organic bistable devices with giant memory margins based on Cu2ZnSnS4 nanoparticles/PMMA nanocomposites

Organic bistable devices (OBDs) were fabricated utilizing nanocomposites made from a blend of Cu2ZnSnS4 (CZTS) nanoparticles within a polymethyl methacrylate (PMMA) matrix on a polyethylene terephthalate substrate. Energy dispersive X-ray spectroscopy profiles, X-ray diffraction patterns, and high-resolution transmission electron microscopy images showed that the polycrystalline CZTS nanoparticles were randomly distributed in the PMMA layer. The current–voltage (I–V) curves at 300K for the fabricated OBDs showed bidirectional switchable and current hysteresis behaviors, indicative of the removal of sneak current paths without an additional layer with characteristics of diode or selector. The removal of the sneak current paths prevented the leakage current of the OBDs, resulting in an increase of the current of high conduction (ON) level. The maximum ON/low-conduction (OFF) ratio of the current bistability for the fabricated OBDs was as large as 1×109. The write–read–erase–read sequences of the OBDs showed rewritable nonvolatile memory behaviors. The ON or the OFF states could be retained for 1×105 cycles, indicative of excellent memory stability. The ON/OFF ratio of 109 was maintained after 105 cycles. The memory mechanisms of the fabricated OBDs are described on the basis of the I–V results.

Nonvolatile memory devices based on Au/graphene oxide nanocomposites with bilateral multilevel characteristics

Current–voltage measurements on the Al/self-assembled Au nanoparticles inserted in graphene-oxide (GO) layer/indium-tin-oxide/glass devices at 300K showed bilateral current bistabilities with four current states in a cell. The multilevel behaviors with four current states were obtained by applying different erasing voltages of −6, −12, and −18V with a writing voltage of 3V or different erasing voltages of 8, 14, and 18V with a writing voltage of −5V. The resistive memory devices demonstrated bilateral multilevel characteristics due to a nanocomposite consisting of Au nanoparticles inserted in a GO layer. The stabilities of the four current states with 1×10−1, 1×10−4, 1×10−6, and 1×10−8A achieved for the devices by using different erasing voltages were maintained for retention cycles larger than 1×104s under a continuous reading test. Memory operating mechanisms and multilevel characteristics based on the I–V curves were described by using the carrier-capture in the self-assembled Au nanoparticles and the local filament-path on the surface between the electrode and the GO layer.

Bistable electrical switching and nonvolatile memory effect in carbon nanotube-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) composite films.

PSS and single-wall carbon nanotubes (SWCNTs) composite thin films have been investigated. The effect of doping level on electrical conductance switching behavior of an indium tin oxide/ PSS + SWCNTs/aluminum (ITO/PEDOT:PSS + SWCNTs/Al) sandwich structure has been reported. The ITO/(PEDOT:PSS + SWCNTs)/Al devices show current bistability. Moreover, the ON/OFF state current ratio is in an extent of 10(2)-10(4). The OFF state current increased with the decreasing SWCNTs content in the composite film, and the ON/OFF state current ratio of the device increases with the increase in SWCNTs content of the composite film. Thus, by varying the doping level of SWCNTs in PSS composite thin films, the electrical conductance switching behavior of ITO/PEDOT:PSS + SWCNTs/Al can be modulated in a controlled manner.

Role of dual nuclear baths on spin blockade leakage current bistabilities

Spin-blockaded electronic transport across a double quantum dot (DQD) system represents an important advancement in the area of spin-based quantum information. The basic mechanism underlying the blockade is the formation of a blocking triplet state. The bistability of the leakage current as a function of the applied magnetic field in this regime is believed to arise from the effect of nuclear Overhauser fields on spin-flip transitions between the blocking triplet and the conducting singlet states. The objective of this paper is to present the nuances of considering a two bath model on the experimentally observed current bistability by employing a self consistent simulation of the nuclear spin dynamics coupled with the electronic transport of the DQD set up. In doing so, we first discuss the important subtleties involved in the microscopic derivation of the hyperfine mediated spin flip rates. We then give insights as to how the differences between the two nuclear baths and the resulting difference Overhauser field affect the two-electron states of the DQD and their connection with the experimentally observed current hysteresis curve.

Enhancement of memory margins for stable organic bistable devices based on graphene-oxide layers due to embedded CuInS2 quantum dots

Current–voltage (I–V) curves for Al/CuInS2 (CIS) quantum dots (QDs) embedded in graphene-oxide layer/indium-tin-oxide devices at 300K showed a current bistability with a maximum high conductivity (ON)/low conductivity (OFF) ratio of 1×104, which was 100 times larger than the ON/OFF ratio of the device without CIS QDs. I–V curves and write-read-erase-read voltage cycles demonstrated the rewritable nonvolatile memory properties of the organic bistable devices (OBDs) with ON and OFF current states at the same voltage. The retention time was above 1×105s, indicative of the memory stability of the OBDs. I–V curve at lower voltages up to 0.05V was attributed to the thermionic emission mechanism, and the curve in the applied voltage range from 0.06 to 0.17V was related to an ohmic mechanism. The I–V characteristics in the applied voltage above 0.18V dominantly followed the space-charge-limited-current behaviors.

Electrical Bistability of Organic Bistable Devices Based on Colloidal CuInS2 Quantum Dots Embedded in a Poly(N-vinylcarbazole) Layer

Organic bistable devices (OBDs) with CuInS2 (CIS) quantum dots (QDs) embedded in a poly(N-vinylcarbazole) (PVK) layer were fabricated by spin coating. Current–voltage (I–V) curves of Al/colloidal hybrid CIS QD-PVK/indium tin oxide devices at 300 K showed that the current bistability with an ON/OFF ratio of 1×103 is larger than that of OBDs without CIS QDs. The number of retention cycles of the ON and OFF states for the OBDs was above 1×105. The carrier transport mechanisms of the OBDs were described on the basis of the I–V results.