Stable Switching Research Articles

Combined feature of enhanced stability and multi-level switching observed in TiN/Ta2O5/Ag-NPs/ITO/PET structure.

Both stability and multi-level switching are crucial performance aspects for resistive random-access memory (RRAM), each playing a significant role in improving overall device performance. In this study, we successfully integrate these two features into a single RRAM configuration by embedding Ag-nanoparticles (Ag-NPs) into the TiN/Ta2O5/ITO structure. The device exhibits substantially lower switching voltages, a larger switching ratio, and multi-level switching phenomena compared to many other nanoparticle-embedded devices. We attribute it to the embedded Ag-NPs effectively switching the mechanism of conductive filaments and the controlled distribution of Ag-NPs facilitates the occurrence of multi-level switching. Additionally, the fabricated structure demonstrated an impressive optical transmittance of nearly 85%. Undoubtedly, this combined feature of RRAM not only enhances stability but also enables multi-level switching, thereby demonstrating an approach to fabricating versatile and practical electronic devices aimed at boosting storage capacity and speed.&#xD.

Bifurcation and stability analysis of within host HIV dynamics with multiple infections and intracellular delay.

Human immunodeficiency virus (HIV) manifests multiple infections in CD4+ T cells, by binding its envelope proteins to CD4 receptors. Understanding these biological processes is crucial for effective interventions against HIV/AIDS. Here, we propose a mathematical model that accounts for the multiple infections of CD4+ T cells and an intracellular delay in the dynamics of HIV infection. We study the model system and establish the conditions under which the disease-free equilibrium point and the endemic equilibrium point are locally and globally asymptotically stable. We further provide the conditions under which these equilibrium points undergo forward or backward transcritical bifurcations for the autonomous model and Hopf bifurcation for both the delay model and autonomous models. Our simulation results show that an increase in the rate of multiple infections of CD4+ T cells stabilizes the endemic equilibrium point through Hopf bifurcation. However, in the presence of an intracellular delay, the model system evinces three types of stability scenarios at the endemic equilibrium point-instability switch, stability switch, and stability invariance and is demonstrated using bi-parameter diagrams. One of the novel aspects of this study is exhibiting all these interesting nonlinear dynamical results within a single model incorporating a single time delay.

Organic Manganese Halides with Near-Unity Quantum Efficiency for High-Resolution and Flexible X-Ray Detection and Imaging.

In this paper, two new organic manganese halides (pe-ted)2MnX4 (pe-ted+ = ethylphenyltriethylenediamine cation, X = Cl, Br) are synthesized, exhibiting green luminescence with near-unity photoluminescence quantum efficiency. (pe-ted)2MnBr4 shows good linear response to X-ray dose rate, with a high light yield of ≈62 000photonsMeV-1 and low detection limit of 1.376µGys-1. Flexible scintillator film is prepared by blending with polydimethylsiloxane for high-resolution imaging, with a low detection limit (5.173µGys-1), an excellent X-ray imaging spatial resolution (18.0lpmm-1) and an impressive X-ray irradiation switching stability (3.6mGys-1). WLED of high color rendering index hasalso been fabricated. These findings represent an example of shapeable X-ray scintillators, providing new possibilities for curved and 3D X-ray imaging.

Stability switch of tumor-immune system driven by delayed response in cell-to-cell contact

Stability switch of tumor-immune system driven by delayed response in cell-to-cell contact

Abnormal widening of the domain touching the electrode during in-plane local switching in lithium niobate

The qualitatively different domain evolution scenarios for different polarities of applied voltage pulses have been studied. For positive pulse, the domain demonstrates only slight width increase during further switching and high stability during subsequent domain imaging. For negative pulse, faster domain widening at the electrode as compared to the domain base leads to change in the type of charged domain wall (CDW) from tail-to-tail (t2t) to head-to-head (h2h) as well as formation of the domain teeth at CDW and an array of wedge-like domains. Additional domain imaging leads to reconstruction of the wedge-like domain with t2t CDW. It was demonstrated by numerical simulation that the switching field is above the threshold for step generation in wide region along the electrode. This field stimulates the formation of above-mentioned domain structure. The absence of this effect for positive pulse has been attributed to the huge difference in conductivity of t2t and h2h CDWs. The current along conductive h2h CDW after domain touching results in decrease in the tip bias due to voltage drop on the series resistance. The stability of the domains growing from the tip was attributed to effective screening of depolarization field by the injected charge. The ineffective screening at the electrode due to absence of charge injection stimulates domain backswitching. The obtained knowledge is useful for further development of domain engineering methods in thin films for the fabrication of periodically poled waveguides.

Transparent Zinc Oxide Memristor Structures: Magnetron Sputtering of Thin Films, Resistive Switching Investigation, and Crossbar Array Fabrication.

This paper presents the results of experimental studies of the influence of high-frequency magnetron sputtering power on the structural and electrophysical properties of nanocrystalline ZnO films. It is shown that at a magnetron sputtering power of 75 W in an argon atmosphere at room temperature, ZnO films have a relatively smooth surface and a uniform nanocrystalline structure. Based on the results obtained, the formation and study of resistive switching of transparent ITO/ZnO/ITO memristor structures as well as a crossbar array based on them were performed. It is demonstrated that memristor structures based on ZnO films obtained at a magnetron sputtering power of 75 W exhibit stable resistive switching for 1000 cycles between high resistance states (HRS = 537.4 ± 26.7 Ω) and low resistance states (LRS = 291.4 ± 38.5 Ω), while the resistance ratio in HRS/LRS is ~1.8. On the basis of the experimental findings, we carried out mathematical modeling of the resistive switching of this structure, and it demonstrated that the regions with an increase in the electric field strength along the edge of the upper electrode become the main sources of oxygen vacancy generation in ZnO film. A crossbar array of 16 transparent ITO/ZnO/ITO memristor structures was also fabricated, demonstrating 20,000 resistive switching cycles between LRS = 13.8 ± 1.4 kΩ and HRS = 34.8 ± 2.6 kΩ for all devices, with a resistance ratio of HRS/LRS of ~2.5. The obtained results can be used in the development of technological processes for the manufacturing of transparent memristor crossbars for neuromorphic structures of machine vision, robotics, and artificial intelligence systems.

Facile Hydrothermal Synthesis and Resistive Switching Mechanism of the α-Fe2O3 Memristor.

Among the transition metal oxides, hematite (α-Fe2O3) has been widely used in the preparation of memristors because of its excellent physical and chemical properties. In this paper, α-Fe2O3 nanowire arrays with a preferred orientation along the [110] direction were prepared by a facile hydrothermal method and annealing treatment on the FTO substrate, and then α-Fe2O3 nanowire array-based Au/α-Fe2O3/FTO memristors were obtained by plating the Au electrodes on the as-prepared α-Fe2O3 nanowire arrays. The as-prepared α-Fe2O3 nanowire array-based Au/α-Fe2O3/FTO memristors have demonstrated stable nonvolatile bipolar resistive switching behaviors with a high resistive switching ratio of about two orders of magnitude, good resistance retention (up to 103 s), and ultralow set voltage (Vset = +2.63 V) and reset voltage (Vreset = -2 V). In addition, the space charge-limited conduction (SCLC) mechanism has been proposed to be in the high resistance state, and the formation and destruction of the conductive channels modulated by oxygen vacancies have been suggested to be responsible for the nonvolatile resistive switching behaviors of the Au/α-Fe2O3/FTO memristors. Our results show the potential of the Au/α-Fe2O3/FTO memristors in nonvolatile memory applications.

Space-Confined Vertical Growth of Large-Size Organic Semiconductor Single Crystals.

Organic semiconductor single crystals (OSSCs) have garnered considerable attention because of their high charge mobility and atomic-scale smooth surface. However, their large-size high-quality preparation remains challenging due to the inevitable defects and limited growth speed brought by traditional epitaxial growth. Here, we demonstrate a space-confined strategy, named out-of-plane microspacing in-air sublimation (OPMAS), for growing vertically millimeter-sized OSSCs in several minutes by revolutionizing the heterogeneous epitaxial growth mode severely depending on substrates into a spontaneous homogeneous growth mode free from substrates. The intrinsic driven force of this transformation is proved to be the change of surface energy, and the maximum size of crystals is thermodynamically dependent on the distance of the microspace. OPMAS has been proven to be suitable for preparing single crystals of various typical organic semiconductors. Numerous characterizations have been conducted to prove the high quality and uniformity of the thus-produced OSSCs. In addition, the photoresponse of the prepared OSSCs is highly dependent on the illumination intensities, making it suitable for high-contrast Morse coding process, demonstrating a stable switch ratio of about 3.3. This work provides a universal platform for preparing large-sized OSSCs, advancing both fundamental (opto)electronic studies and a wide range of practical applications.

Formation of vanadium dioxide nanocrystal arrays via post-growth annealing for stable and energy-efficient switches

The abrupt and reversible semiconductor-metal phase transition in vanadium dioxide nanocrystals has attracted considerable attention for potential applications in oxide electronics, including neuromorphic systems. This study presents a systematic investigation of post-growth annealing conditions for the formation of single VO2 M-phase nanocrystals arrays from VOx films synthesized by atomic layer deposition. The composition of the initial VOx films and the annealing parameters were found to significantly affect the morphology, phase composition and electrical properties of the obtained single nanocrystal arrays. Our results demonstrate that the formation of VO2 M-phase nanocrystal arrays occurs at annealing temperatures of 650 °C and above, irrespective of the initial film composition. More homogeneous in size nanocrystals are formed from initial VOx films with higher V+4 content. The structures with the initial V+4 content of 60 % annealed at 650 °C for 2 h demonstrates the resistive switching with an energy less than 150 fJ, and a total number of stable switching cycles more than 101⁰. Our results pave the way for the novel energy-efficient nanoelectronic and nanophotonic devices based on VO₂ nanoparticles.

(Invited) Large-Area Flexible and Stretchable Electrochromic Devices with Viologen Derivatives

Electrochromic devices (ECDs) demonstrate reversible color switchings through electron and ion exchanges during redox reactions. Viologen derivatives are commonly utilized in ECD fabrication due to their electron-accepting properties and straightforward synthesis pathways. However, viologens often present issues like slow switching speeds, limited long-term stability, and low coloration efficiency. Indium tin oxide (ITO), among various transparent conducting oxide electrodes, plays a crucial role in ECD performance. Nevertheless, ECDs, particularly those employing ITO-PET films, frequently encounter low conductivity and poor uniformity. This study focuses on the development and performance evaluation of large-area flexible and stretchable ECDs incorporating viologen derivatives. The versatility of viologen derivatives in synthesis was utilized, and the active layer, formed using ion gels through various solution processing methods, exhibited high ionic mobility and good long-term stability. Electrochromic behaviors were examined and compared with traditional viologen-based ECDs. Additionally, highly stretchable ECDs were fabricated utilizing self-healing and self-adhesive polymer electrolytes, showcasing significant transmittance contrast at extended states and stable switching throughout stretching cycles. These findings present viable strategies for producing large-area flexible and stretchable ECDs at cost-effective rates, leveraging viologen derivatives, modified electrodes, and solution coating techniques.

Highly Flexible Electrochromic Devices Containing Photo-Curable Acrylated Viologens

Electrochromic technology enables colorimetric modulation via external voltage control, driven by electron movement and reversible redox reactions. Although inorganic metal oxides provide stability, they exhibit restricted color changes confined to single-layer arrangements. Organic materials, particularly viologens, have garnered attention for their multi-color capabilities and ease of preparation. In this study, we synthesized photo-curable viologen derivatives displaying red, green, and blue hues with enhanced adhesion from acrylate end groups. We fabricated single-layer electrochromic devices (ECDs) by combining these viologens with polymer-based electrolytes. All three colors exhibited large optical contrast (over 80%), high cyclic stability (300 cycles), and moderate switching (within 20 s). Furthermore, the electrode modification was carried out by applying a coating layer of fluorinated carbon nanotubes (FCNTs). The performances of flexible ECDs were significantly improved by incorporating FCNT-modified electrodes, which led to excellent cycling stability (>300 cycles) and swift switching. We also obtained flexible and even stretchable electrodes made up of PDMS substrates with silver nanowires and PEDOT:PSS. By spray-coating FCNT to enhance flexibility and performance, the prepared flexible ECDs demonstrated a large transmittance difference, stability for extended cycles, and consistent operation. The current studies suggest promising applications in smart windows and cutting-edge wearable electrochromic devices.

Outstanding Stability and Resistive Switching Performance through Octa-Amino-Polyhedral Oligomeric Silsesquioxane Modification in Flexible Perovskite Resistive Random-Access Memories.

Resistive random access memory (RRAM) has emerged as a promising candidate for next-generation storage technologies due to its simple structure, high running speed, excellent durability, high integration density, and low power consumption. This paper focuses on the application of organic-inorganic hybrid perovskite (OIHP) materials in RRAM by introducing an innovative three-dimensional POPA modification strategy, which is realized by binding octa-amine-polyhedral oligomeric silsesquioxanes (8NH2-POSS) onto the side chains of poly(acrylic acid) (PAA), thereby enhancing the material's resilience under elevated temperatures and humidity conditions. POPA cross-links with perovskite grains at crystalline boundaries through multiple -NH3+ and -C═O chemical anchoring sites on its branch chain, enhancing the grain adhesion, optimizing the film quality, and improving the cage structure distribution at the perovskite grain boundaries. The experimental results demonstrate that the POPA-modified OIHP RRAM exhibits an excellent resistance switching performance, with an optimal ON/OFF ratio of 5.0 × 105 and a data retention time of 104 s. After 150 days of environmental exposure, the ON/OFF ratio remains at 1.0 × 105, indicating good stability. Furthermore, the POPA modification endows the perovskite film with considerable flexibility, maintaining stable resistance switching performance under various bending radii. This study provides a vital reference for flexible, high-performance, and long-lifespan perovskite memory devices.

Anion-substituted Hybrid Zinc Halides with Remarkable Dielectric Switches.

Thermo-responsive dielectric switching hybrid halides, displaying reversible dielectric bistability, have recently made them highly versatile and attractive for their structural tunability and rich functional properties. However, the substantial improvement of the dielectric switching operating range is limited near room temperature, and obtaining ultra-wide dielectric switching temperature region is a major challenge. Herein, a remarkable dielectric switching effect is reported with ultra-wide dielectric switching temperature region in a hybrid halide system, caused by dipolar orientational polarization ascribing order-disorder phase transitions. The new A2BX4 hybrid halide [C6H5(CH2)4NH3]2ZnBr4 (4PBA-ZnBr4) with an ultra-wide dielectric hysteresis loop of about 55 K near room temperature is designed successfully through halogen substitution. Meanwhile, structurally similar hybrid materials 4PBA-ZnI4 were designed as controls. More interestingly, the crystal structure, phase transition temperature (Tc), dielectric and semiconductor properties exhibit significant discrepancies as the halogen atoms vary from Br to I. This discovery provides an efficiently regulated anionic framework to construct hybrid halides with ultra-wide high dielectric switching and reliable cycling stability by assembling with various cations, making them potentially excellent candidates for highly responsive room temperature smart switches or transducer devices.

Second Generation Zwitterionic Aza‐Diarylethene: Photoreversible CN Bond Formation, Three‐State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization

AbstractDiarylethenes are a well‐studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza‐diarylethenes have been developed in which carbon‐carbon bond connections are replaced by carbon‐nitrogen connections. This structural elaboration opens up an entire new structure and property space expanding the versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza‐diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High‐yielding photoswitching between the neutral open form and a zwitterionic Z isomer is achieved with two different wavelengths of light. The third zwitterionic E isomeric state can be reached in up to 87 % upon irradiation with a third wavelength. Its high energy content of >10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza‐diarylethenes into interesting candidates for molecular solar thermal energy storage (MOST) applications. The third state also serves as locking state, allowing to toggle light‐responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA), directly harnessing the unleashed chemical reactivity of our aza‐diarylethene in a materials application.

Second Generation Zwitterionic Aza-Diarylethene: Photoreversible CN Bond Formation, Three-State Photoswitching, Thermal Energy Release, and Facile Photoinitiation of Polymerization.

Diarylethenes are a well-studied and optimized class of photoswitches with a wide range of applications, including data storage, smart materials, or photocontrolled catalysis and biological processes. Most recently, aza-diarylethenes have been developed in which carbon-carbon bond connections are replaced by carbon-nitrogen connections. This structural elaboration opens an entire new structure and property space expanding versatility and applicability of diarylethenes. In this work, we present the second generation of zwitterionic aza-diarylethenes, which finally allows for fully reversible photoswitching and precise control over all three switching states. High-yielding photoswitching between the neutral open form and a zwitterionicZisomer is achieved with two different wavelengths of light. The third zwitterionicEisomeric state can be reached up to 87% upon irradiation with a third wavelength. Its high energy content of >10 kcal/mol can be released thermally by deliberate solvent change as trigger mechanism, rendering aza-diarylethenes into interesting candidates for molecular solar thermal energystorage (MOST) applications. The third state further serves as locking state, allowing to toggle light-responsiveness reversibly between thermally labile and thermally stable switching. Further, irradiation of the zwitterionic states leads to highly efficient photopolymerization of methyl acrylate (MA),directly harnessing the unleashed chemical reactivity of aza-diarylethene in materials applications.

Nonlinear and linear conductance modulation and synaptic plasticity in stable tin-zinc oxide based-memristor for neuro-inspired computing

Inducing post-transition metals in an oxide semiconductor system has a high potential for use in storage for neuromorphic computing. It is challenging to find a material that can be switched stably between multiple resistance states. This research explores the memristive properties of Sn (post-transition metal)-doped ZnO (SZO) thin films, emphasizing their application in memristor devices. The (magnetron sputtered) synthesized SZO thin films in the form of Ag/SZO/Au/Ti/SiO₂ device demonstrated a clear bipolar resistive switching (BRS) behavior with VSET and VRESET of 1.0 V and −0.75 V, respectively. The memristor could change between a high resistance state and a low resistance state with a high RON/OFF rate of 104, mimicking synaptic behaviors such as potentiation and depression. This switching is attributed to the formation and dissolution of Ag filaments within the SZO layer, influenced by the migration of Ag⁺ ions and the presence of oxygen vacancies. These vacancies facilitate the formation of conductive filaments under positive bias and their dissolution under negative bias. The endurance and retention tests showed stable switching characteristics, with the memristor maintaining distinct HRS and LRS over 100 cycles and retaining these states for over 5K seconds without significant degradation. Finally, the nonlinearity values for potentiation and depression were αp∼1.6 and αd ∼ -0.14, suggesting that the memristor may be more responsive to increasing synaptic weights in biological systems. The linearity response at a very small pulse width showed the device is more applicable for neuromorphic applications. The observed memristor combined with stable endurance and retention performance, suggests that this memristor structure could play a crucial role in the development of artificial synapses and memory technologies.

Stable Millivolt Range Resistive Switching in Percolating Molybdenum Nanoparticle Networks.

To overcome the limitations of the conventional Von Neumann architecture, inspiration from the mammalian brain has led to the development of nanoscale neuromorphic networks. In the present research, molybdenum nanoparticles (NPs), which were produced by means of gas phase condensation based on magnetron sputtering, are shown to be the constituents of electrically percolating networks that exhibit stable, complex, neuron-like spiking behavior at low potentials in the millivolt range, satisfying well the requirement of low energy consumption. Characterization of the NPs using both scanning electron microscopy and scanning transmission electron microscopy revealed not only pristine shape, size, and density control of Mo NPs but also a preliminary proof of the working mechanism behind the spiking behavior due to filament formations. Furthermore, electrostatics COMSOL Multiphysics simulations of the morphology of the NPs provided evidence that the stable switching is due to the as-deposited stellate Mo NPs creating high electric field strengths, while keeping them separated, not seen before in other percolating networks based on spherical NPs. Hence, our results show the working mechanism behind switching in percolating Mo NP networks and show that they are very promising for realistic neuromorphic systems.

Dynamics of a single population model with memory and nonlinear boundary condition

In this paper, a heterogeneous single population model with memory effect and nonlinear boundary condition is investigated. By virtue of the implicit function theorem and Lyapunov-Schmidt reduction, spatially nonconstant positive steady state solutions appear from two trivial solutions, respectively. Through the distribution of the eigenvalues and bifurcation analysis, sufficient conditions for the occurrence of the Hopf bifurcation associated with one spatially nonconstant positive steady state are obtained. Results about the stability associated with the other one are also yielded. It is found that with the interaction of memory delay, spatial heterogeneity and nonlinear boundary condition, the Hopf bifurcation will happen in such diffusive model. To be specific, the memory delay could induce a single stability switch from stability to instability. As contrast to the diffusive model only with memory effect, the stability switch is independent of memory delay. The obtained results are applied to some specific models, from which we can find that the theoretical analysis is verified and the results enrich the existing ones.

Hopf bifurcation control of memristor-based fractional delayed tri-diagonal bidirectional associative memory neural networks under various controllers

In this paper, authors present a memristor-based fractional order system of tri-diagonal bidirectional associative memory neural networks (TdBAMNNs) incorporating leakage and communication delays. The existence and uniqueness theorem is established for the memristor-based fractional-order TdBAMNNs system. Analysis of Hopf bifurcation anti-control is conducted using various feedback controllers by exploring single-parameter and double-parameter approaches. A study of the stability switching curves is undertaken to determine the direction of stability transitions in the system. The theoretical results and graphical illustrations are validated through numerical simulations to exhibit their feasibility. Comparative analysis of the system’s dynamical behavior under different controllers is performed. This paper comprehensively explores the proposed memristor-based system, proving its theoretical underpinnings, and analyzing stability through bifurcation control strategies and comparative assessments under different control scenarios.

Solution-Processed TiO2/ZnFe2O4 Heterostructure for Stable Multilevel Memristor with Room-Temperature Reactive Gas Selectivity.

Solution-processed oxide-based heterojunctions that work in diverse directions will be ideal alternatives for cost-effective, stable, and multifunctional devices. Here, we have reported a stable multilevel resistive switching (RS) at the solution-processed TiO2/ZnFe2O4 heterointerface with endurance stability over 104 cycles and retention over 105 s. It can maintain the switching after dripping water onto the device, followed by drying at 100 °C and at an operating temperature of up to 200 °C. As the switching mechanism is governed by filamentary and interface-dominated charge conduction, our device shows additional tunability in the low resistance state (LRS) by changing environmental conditions. The inability to form filaments results in almost negligible switching under a vacuum or inert environment with an LRS loss. Meanwhile, the presence of reducing gas leads to a depletion layer lowering at the TiO2/ZnFe2O4 heterointerface by removing the surface-adsorbed oxygen molecules that help filament conduction through the interface and, hence, a change in LRS. Furthermore, different reaction capacities of different reactive gas environments with the surface-adsorbed oxygen molecule lead to discrete ON-OFF ratios, presenting a pathway to identify several reactive vapors like ammonia, formaldehyde, and acetone at room temperature and presenting a new approach for integrating RS and room temperature gas sensing in the multifunctional device technology.