Memristive devices based on single ZnO nanowires - from material synthesis to neuromorphic functionalities

Memristive and resistive switching devices are considered promising building blocks for the realization of artificial neural networks and neuromorphic systems. Besides conventional top-down memristive devices based on thin films, resistive switching devices based on nanowires (NWs) have attracted great attention, not only for the possibility of going beyond current scaling limitations of the top-down approach, but also as model systems for the localization and investigation of the physical mechanism of switching. This work reports on the fabrication of memristive devices based on ZnO NWs, from NW synthesis to single NW-based memristive cell fabrication and characterization. The bottom-up synthesis of ZnO NWs was performed by low-pressure Chemical Vapor Deposition (LPCVD) according to a self-seeding Vapor-Solid (VS) mechanism on a Pt substrate over large scale (∼ cm2), without the requirement of previous seed deposition. The grown ZnO NWs are single crystalline with wurtzite crystal structure and are vertically aligned respect to the growth substrate. Single NWs were then contacted by means of asymmetric contacts, with an electrochemically active and an electrochemically inert electrode, to form NW-based electrochemical metallization memory (ECM) cells that show reproducible resistive switching behaviour and neuromorphic functionalities including short-term synaptic plasticity and Paired Pulse Facilitation (PPF). Besides representing building blocks for NW-based memristive and neuromorphic systems, these single crystalline devices can be exploited as model systems to study physicochemical processing underlaying memristive functionalities thanks to the high localization of switching events on the ZnO crystalline surface.

Electro-Thermal Model-Based Design of Bidirectional On-Board Chargers in Hybrid and Full Electric Vehicles

In this paper, a model-based approach for the design of a bidirectional onboard charger (OBC) device for modern hybrid and fully electrified vehicles is proposed. The main objective and contribution of our study is to incorporate in the same simulation environment both modelling of electrical and thermal behaviour of switching devices. This is because most (if not all) of the studies in the literature present analyses of thermal behaviour based on the use of FEM (Finite Element Method) SWs, which in fact require the definition of complicated models based on partial derivative equations. The simulation of such accurate models is computationally expensive and, therefore, cannot be incorporated into the same virtual environment in which the circuit equations are solved. This requires long waiting times and also means that electrical and thermal models do not interact with each other, limiting the completeness of the analysis in the design phase. As a case study, we take as reference the architecture of a modular bidirectional single-phase OBC, consisting of a Totem Pole-type AC/DC converter with Power Factor Correction (PFC) followed by a Dual Active Bridge (DAB) type DC/DC converter. Specifically, we consider a 7 kW OBC, for which its modules consist of switching devices made with modern 900 V GaN (Gallium Nitrade) and 1200 V SiC (Silicon Carbide) technologies, to achieve maximum performance and efficiency. We present a procedure for sizing and selecting electronic devices based on the analysis of behaviour through circuit models of the Totem Pole PFC and DAB converter in order to perform validation by using simulations that are as realistic as possible. The developed models are tested under various operating conditions of practical interest in order to validate the robustness of the implemented control algorithms under varying operating conditions. The validation of the models and control loops is also enhanced by an exhaustive robustness analysis of the parametric variations of the model with respect to the nominal case. All simulations obtained respect the operating limits of the selected devices and components, for which its characteristics are reported in data sheets both in terms of electrical and thermal behaviour.

Evolution and modulation of Ag filament dynamics within memristive devices based on necklace-like Ag@TiO2 nanowire networks

Random nanowire networks (NWNs) are regarded as promising memristive materials for applications in information storage, selectors, and neuromorphic computing. The further insight to understand their resistive switching properties and conduction mechanisms is crucial to realize the full potential of random NWNs. Here, a novel planar memristive device based on necklace-like structure Ag@TiO2 NWN is reported, in which a strategy only using water to tailor the TiO2 shell on Ag core for necklace-like core-shell structure is developed to achieve uniform topology connectivity. With analyzing the influence of compliance current on resistive switching characteristics and further tracing evolution trends of resistance state during the repetitive switching cycles, two distinctive evolution trends of low resistance state failure and high resistance state failure are revealed, which bear resemblance to memory loss and consolidation in biological systems. The underlying conduction mechanisms are related to the modulation of the Ag accumulation dynamics inside the filaments at cross-point junctions within conductive paths of NWNs. An optimizing principle is then proposed to design reproducible and reliable threshold switching devices by tuning the NWN density and electrical stimulation. The optimized threshold switching devices have a high ON/OFF ratio of ~107 with threshold voltage as low as 0.35 V. This work will provide insights into engineering random NWNs for diverse functions by modulating external excitation and optimizing NWN parameters to satisfy specific applications, transforming from neuromorphic systems to threshold switching devices as selectors.

Inverter design with positive feedback field-effect transistors

As the physical size of semiconductor devices continues to be aggressively scaled down, feedback field-effect transistors (FBFET) with a positive feedback mechanism among a few promising steep switching devices have received attention as next-generation switching devices. Conventional FBFETs have been studied to explore their device performance. However, this has been restricted to the case of single FBFET; basic circuit designs with FBFETs have not been investigated extensively. In this work, we propose an inverter circuit design with silicon-on-insulator (SOI) FBFETs; we verified this inverter design with mixed-mode technology computer-aided design simulation. The basic principles and mechanisms for designing FBFET inverter circuits are explained because their configuration is different from conventional inverters. In addition, the device parameters necessary to optimize circuit construction are introduced for logic device applications.

A multiphysics model of processes in electromagnets and actuators of vacuum switching devices taking into ac-count contact interaction of structural elements

The purpose of the work is to improve mathematical models and algorithms of computer modeling of multiphysics processes in electromagnets and actuators of vacuum switching devices by taking into account the contact interaction of structural elements when changing their stress-strain state. In the design of modern vacuum circuit breakers and contactors, there is a significant use of electromagnetic actuators based on high-coercive hard magnetic rare earth composite materials NdFeB and SmCo. The most promising for use as drives of circuit breakers and contactors are polarized electromagnets based on the use of these high-coercive permanent magnets. However, the existing serial designs of electromagnets and actuators need to be significantly improved in order to increase reliability and service life, reduce weight and cost, further reduce energy consumption, improve the manufacturability of the mass production process. Computer simulation is proposed to be performed by the Finite Element Method in 2D formulation using commercial software products and/or software created directly for these investigations. One of the priority areas for improving mathematical models and algorithms for computer modeling of processes in the mechanical circuit of vacuum switching devices of medium and high voltage is to take into account the contact interaction of the structural elements of the devices under consideration. The next step, thanks to the use of an advanced mathematical model, is to perform a set of computational research and based on the obtained numerical results to develop recommendations aimed at creating designs of electromagnets and actuators that would meet world standards and be competitive in the world market.

Electrical and thermal analysis of Symmetric and Asymmetric metal contacts in Resistive Switching Devices

The full text of this preprint has been withdrawn by the authors due to author disagreement with the posting of the preprint. Therefore, the authors do not wish this work to be cited as a reference. Questions should be directed to the corresponding author.

A single-phase simplified DC-AC converter using DC-link capacitors and an H-bridge

This paper introduces a simplified inverter circuit using a single dc source and an H-bridge with a least possible number of “switching devices”. This topology does not employ multiple “dc sources”, which enhances the reliability of the configuration. The topology consists of two parts, namely: “Level generation parts” as well as “Polarity generation parts”, it is the mixture of some of the switching devices, DC-link capacitor and a single DC source completes the part of level generation. The H-bridge in the proposed structure produces the polarity generation part. A detailed explanation of the modulation system and operating modes of the proposed framework are discussed. Finally, in the MATLAB/SIMULINK platform, the projected network topology is simulated and the outcomes are presented.