Resistive switching effect in metal/insulator/metal heterostructures and its application for non‐volatile memory

This paper presents two types of resistive switching effects observed in metal/insulator/metal heterostructures: one is the forced‐switch type, and the other is the memory‐switch type. The former was observed in metal/semi‐insulating GaAs hybrid structures. The nonlinear resistive switch showed a strong magnetic field dependence at room temperature. The latter, described in this report, appears in the Pt/Co oxide/Pt capacitor structures. The resistive switch showed bistability, which is certainly a phenomenon with great promise of application to nonvolatile solid state electronic memory. For both cases, the recent experimental evidences show that the electronic state of the interface between the metal electrode and the insulator plays a crucial role in the resistive switching effect. © 2007 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Resistive switching characteristics and conducting nanobits of polycrystalline NiO thin films

Thin films of NiO were deposited on Pt/Ta/glass sub-strates using a radio frequency (RF) sputtering method. The NiO thin films showed polycrystalline nature, indicating preferentially (111)-oriented structure. The resistive random access memory (RRAM) capacitor of a Pt/NiO/Pt structure exhibited unipolar switching characteristics and bistable resistivities for 200 repeated switching cycles. Furthermore, RRAM nanobits array was formed on the NiO thin films by applying a bias. The RRAM nanobits had a diameter of approximately 8 nm and were observed via a conducting atomic force microscope (CAFM). The density of the RRAM nanobits array was estimated to be approximately 0.64 Tbit/cm².     

Building structured biomaterials using AC electrokinetics

In this article, the application of alternating current (ac) electrokinetics in the formation of multicellular structured biomaterials from cells is reviewed. The formation of bacterial biofilms with defined internal architectures is investigated. Investigating such interactions could not only help in understanding how biofilms operate, but biofilms could also be used as a primitive model for cell interactions and development in higher organisms such as animals and plants. A discussion on how the same techniques can be used to create multicellular systems from animal and plant cells is presented.     

HVDC tapping using soft switching techniques

Contents  Soft switching techniques have been applied to develop a novel dc/dc power converter for feeding small loads (under 5 MW) with low cost and high reliability, from HVDC transmission lines. This dc/dc converter is connected in series with a pole of the HVDC transmission line. It drains energy to a dc capacitor through an air-core transformer. From this dc capacitor, a voltage-source converter may be directly connected to supply ac loads. This HVDC tap can supply high quality ac power to isolated areas, with or without ac power generation. The controller of the HVDC tap is independent from the master control of the HVDC link. It does not need any communication channel to the control of the main HVDC converter stations. Simulation results have revealed that the proposed HVDC tap can be a very good option for feeding small loads along the HVDC transmission line. It generates high quality ac voltage and is extremely robust. Received: 26 July 2000     

静止同步补偿器的开关函数建模与仿真

针对目前静止同步补偿器(Static Synchronous Compensator,STATCOM)输出建模和拓扑建模等方法的不足,通过引入单极性二值逻辑开关函数,建立了基于变换器物理特性和拓扑结构的开关函数模型.该模型的参数都是装置实际的物理参数,易于确定,更具一般性.对380V两机系统进行的仿真计算证明了所提模型和方法的正确性和有效性,并验证了STATCOM对系统无功补偿和电压稳定具有重要作用.     

Ceramic Based Resistive Sensors

This paper reviews the current status and research trends of two types of ceramic based resistive sensors, thermistors and gas sensors. The issues and challenges associated with their development for high temperature applications are examined and discussed. Worldwide research efforts in ceramic based resistive sensors, devoted mostly to resolve the issues of selectivity and stability, are also reviewed. These efforts tend to integrate the results obtained from both empirical and basic science approaches, and focus on various stages of sensor development, including development of new material systems, sensor fabrication and manufacturing techniques, and smart sensor arrays.     

Physics-based modeling approaches of resistive switching devices for memory and in-memory computing applications

The semiconductor industry is currently challenged by the emergence of Internet of Things, Big data, and deep-learning techniques to enable object recognition and inference in portable computers. These revolutions demand new technologies for memory and computation going beyond the standard CMOS-based platform. In this scenario, resistive switching memory (RRAM) is extremely promising in the frame of storage technology, memory devices, and in-memory computing circuits, such as memristive logic or neuromorphic machines. To serve as enabling technology for these new fields, however, there is still a lack of industrial tools to predict the device behavior under certain operation schemes and to allow for optimization of the device properties based on materials and stack engineering. This work provides an overview of modeling approaches for RRAM simulation, at the level of technology computer aided design and high-level compact models for circuit simulations. Finite element method modeling, kinetic Monte Carlo models, and physics-based analytical models will be reviewed. The adaptation of modeling schemes to various RRAM concepts, such as filamentary switching and interface switching, will be discussed. Finally, application cases of compact modeling to simulate simple RRAM circuits for computing will be shown.     

Stochastic modeling of bipolar resistive switching in metal-oxide based memory by Monte Carlo technique

A stochastic model of the resistive switching mechanism in bipolar metal-oxide based resistive random access memory (RRAM) is presented. The distribution of electron occupation probabilities obtained is in agreement with previous work. In particular, a low occupation region is formed near the cathode. Our simulations of the temperature dependence of the electron occupation probability near the anode and the cathode demonstrate a high robustness of the low occupation region. This result indicates that a decrease of the switching time with increasing temperature cannot be explained only by reduced occupations of the vacancies in the low occupation region, but is related to an increase of the mobility of the oxide ions. A hysteresis cycle of RRAM switching simulated with the stochastic model including the ion dynamics is in good agreement with experimental results.     

Ignition Criteria for Resistive Circuits

The criterion of no ignition is stated in general. The relation between the electrical power output and the discharge voltage, and the power output and time are discussed for resistive circuits with source voltages ranging from 24-60 V, tested by the German breakflash. Shadow photographs of the electrode area with the incipient kernel and the relevant oscillograms of the discharge voltage are recorded. From the oscillograms a general discharge voltage pattern emerges. The theoretical considerations as well as the experimental results suggest that the critical section when ignition is likely to occur under minimum igniting conditions coincides with the peak of the power transfer function. Suggestions are made about the practical application of these results to monitor the sensitivity of the breakflash or forecast the probable value of minimum igniting current or power for a given circuit.     

Envelope tracking using transient waveform switching shaping supply modulation

A novel supply modulation scheme for envelope tracking for a power amplifier in a transmitter is proposed, which follows a control principle that is fundamentally different from the existing ones. Instead of regulating the supply modulator's output in accordance with a given reference signal, the system utilizes a look‐ahead window and synthesizes pulses for the supply modulator such that its output tracks the envelope of the radio frequency signal amplified by the power amplifier, while minimizing its switching rate. Simulation results for a 5 MHz Long Term Evolution signal with 16 quadrature amplitude modulation indicates that the proposed technique provides very high average efficiency (84%) while maintaining a very low ratio between the switching frequency and the envelope bandwidth. Copyright © 2013 John Wiley & Sons, Ltd.     

Optimized switching scheme of cascaded H-bridge multilevel inverter using PSO

The paper uses particle swarm optimization (PSO) to determine the optimum switching angles of cascaded H-bridge multilevel inverter (CH-MLI) so as to produce the required fundamental voltage and reduce the harmonic content. This is done by solving the transcendental equations characterizing the harmonic content. The validity of the proposed method is verified through simulation studies for three-phase, five-level CH-MLI. To compare the results obtained using PSO, the simulation studies have been extended for three-phase, five-level CH-MLI using sinusoidal pulse width modulation (SPWM). The results obtained using PSO are found superior as compared to SPWM in terms of total harmonic distortion at different modulation indices.     

Reduction of harmonics in grid-connected inverters using variable switching frequency

The increasing application of distributed power generation into the power system makes grid interconnection requirements of power quality more and more stringent. The reduction of current total harmonic distortion (THD) of grid-connected inverters to achieve the grid code by increasing of switching frequency in PWM of inverters is one of the popular methods, but this increases the switching loss. The aim of this paper is to propose a PWM technique with the function of variable switching cycle to reduce the current harmonics in grid-connected inverters. The weights of this function are determined by using a genetic algorithm under the constraint of constant switching loss. The simulation and experimental results of the proposed technique as well as the conventional constant technique are given and compared, which validate the performance of the proposed technique.     

邻周期采样的数字控制DC-DC开关变换器

针对高频DC-DC开关变换器,提出了数字控制DC-DC开关变换器的邻周期采样(adjacent cycle sampling,ACS)控制方法,缓解硬件处理速度与系统瞬态性能之间的矛盾。依据纹波控制方法,ACS控制算法利用硬件空闲阶段采样数据,增大环路预留时间,消除占空比的影响。采用ACS控制算法,推导出适用于后缘调制降压型DC-DC开关变换器的数字V2控制律和电流控制律,并且研究了次谐振荡现象及其数字斜坡补偿消除方法。仿真结果表明,在相同的硬件条件,对于负载的瞬间扰动,数字V2控制较数字电流控制具有更快的瞬态响应速度;与现有技术相比,ACS控制方法可有效提高系统的瞬态响应性能。     

电阻式电压互感器的研究

介绍了电阻分压器传感电压的电阻式电压互感器;它在整个测量范围内无饱和畸变、线性好而且体积小、结构紧凑,便于测量和控制系统小型化。分析表明分布电容和温度变化是它最主要的误差源。通过分压电阻的选择及结构设计研制成10 kV电阻式电压互感器,型式试验验证达到0.2级准确度。     

Impedance Measurement by a Resistive Bridge

The possibility of measuring an unknown impedance Z=R+jX by including it in one arm of a Wheatstone bridge, whose other arms are purely resistive, is examined. It is shown that by adjusting the variable resistance for minimum bridge output and measuring this output, one can calculate the magnitude ?Z?, the resistive part R, and the magnitude of the reactive part ?X? of the unknown impedance. Using a fixed auxiliary capacitor whose reactance is less than 2?X?, the sign of the reactive part can also be determined. The sensitivity of the bridge decreases as the ratio ?X?/R increases; this can be remedied by adding a suitable series resistance to Z and/or by measuring the bridge output when its rate of variation with the adjustable resistance is maximum. An alternative method not involving voltage measurements, but requiring a suitable fixed, standard inductor or capacitor, has also been discussed. The theory involved in these measurements is pretty well within the reach of a sophomore student of electrical engineering and as such, this may constitute a simple, but interesting, laboratory exercise at that level.     

Novel polyphosphazene-hydroxyapatite composites as biomaterials

Evaluating a polymer-ceramic biomaterial as a candidate for bone tissue engineering. The objective of the present work was to develop novel composites of biodegradable polyphosphazenes and HA as candidate materials for bone tissue engineering. The mechanical and degradation properties of novel PPHOS/HA composites were compared to PLAGA/HA composites as PLAGA being the most extensively investigated polymer for bone tissue engineering application.     

Estimation of multiphase currents using DC bus current and switching state

The voltage of solar cell strings can be controlled in residential photovoltaic systems using a multiphase convertor. However, multiphase convertors require a few current sensors. The authors examined how to reduce the current sensor for each phase of a multiphase convertor. This paper presents the analysis of a multiphase convertor based on DC bus current, phase currents, and switching state, and it proposes an estimation method for multiphase currents. The estimation method can be implemented with constant sampling frequency. Experimental results demonstrate the validity of the estimation method of multiphase currents for current-controlled three-phase convertor.     

Resistive random access memory (RRAM) technology: From material,device, selector, 3D integration to bottom-up fabrication

Emerging non-volatile memory technologies are promising due to their anticipated capacity benefits, non-volatility, and zero idle energy. One of the most promising candidates is resistive random access memory (RRAM) based on resistive switching (RS). This paper reviews the development of RS device technology including the fundamental physics, material engineering, three-dimension (3D) integration, and bottom-up fabrication. The device operation, physical mechanisms for resistive switching, reliability metrics, and memory cell selector candidates are summarized from the recent advancement in both industry and academia. Options for 3D memory array architectures are presented for the mass storage application. Finally, the potential application of bottom-up fabrication approaches for effective manufacturing is introduced.     

TCSC allocation in power systems considering switching loss using MOABC algorithm

This paper is dedicated to investigate the influence of switching losses on Thyristor Controlled Series Compensator (TCSC) optimum allocation in power systems by using a Multi-Objective optimization technique. This allocation is performed with respect to minimization in system cost and voltage deviation as the objectives. For this purpose, cost of active power losses, investment cost of devices and active power generation cost in the peak load are considered to constitute the cost function as the economical objective. In addition, the paper considers interest rate in cost calculations to avoid impractical allocation results and imprecise solutions. The operational, technical and controlling constraints as well as load constraints are regarded in the allocation procedure. Also, the simulations are utilizing three unequal annual load levels to find optimum location and size of TCSC. The IEEE-14 Bus test system is used to validate the proposed method and show the importance of TCSC switching loss. Here, a novel optimization algorithm, Multi-Objective Artificial Bee Colony, is presented to provide Pareto optimal solutions. Also, an approach based on the goal attainment method combined with Genetic Algorithm is used to compromise between contradictory objectives and approach to the global optimum.     

氧化锌避雷器阻性电流的在线监测

介绍了避雷器在线监测的几种常用方法,对阻性电流在线监测的原理和具体操作方法进行了详细的阐述,对可能出现的误差和干扰进行了解释并提出了解决的办法。