Nonlinear Switching Research Articles

Built-In Nonlinear Characteristics of Low Power Operating One-Resistor Selector-Less RRAM by Stacking Engineering

The sneak-path leakage current issue is one of the severe hindrances for the application of high density resistive random access memory (RRAM) array design. In this work, we demonstrate nonlinear (NL) resistive switching characteristics of HfOx/SiOx-based stacking structure as a realization for selector-less RRAM devices. The NL characteristic was obtained and designed by optimizing internal filament location with low effective dielectric constant intending in HfOx/SiOx structure. The stacking HfOx/SiOx-based RRAM device as the one-resistor-only memory cell is applicable without additional selector device to solve the sneak-path issue with switching voltage ~1 V, which is desirable for low power operating in built-in nonlinearity crossbar array configuration.

High nonlinearity in WOx film prepared by hydrazine hydrate reduction method

In this work, we fabricate the sandwich structure based on WOx film which exhibits remarkable nonlinear electrical characteristics. The WOx film is deposited on FTO substrate by using a simple chemical reductionmethod. The hydrazine hydrate used as reductant is added into precursor. Asa result, the nonlinearity of this single-layer device is greatly improved and is as high as 104. The XPS analyses indicate that the nonlinear switching behavior can be attributed to the suboxides in WOx film. This work not only enhances the nonlinear electrical characteristics of metal oxide, but also provides a new way for nonlinear devices.

Structurally Engineered Nanoporous Ta2O5-x Selector-Less Memristor for High Uniformity and Low Power Consumption.

A memristor architecture based on metal-oxide materials would have great promise in achieving exceptional energy efficiency and higher scalability in next-generation electronic memory systems. Here, we propose a facile method for fabricating selector-less memristor arrays using an engineered nanoporous Ta2O5-x architecture. The device was fabricated in the form of crossbar arrays, and it functions as a switchable rectifier with a self-embedded nonlinear switching behavior and ultralow power consumption (∼2.7 × 10-6 W), which results in effective suppression of crosstalk interference. In addition, we determined that the essential switching elements, such as the programming power, the sneak current, the nonlinearity value, and the device-to-device uniformity, could be enhanced by in-depth structural engineering of the pores in the Ta2O5-x layer. Our results, on the basis of the structural engineering of metal-oxide materials, could provide an attractive approach for fabricating simple and cost-efficient memristor arrays with acceptable device uniformity and low power consumption without the need for additional addressing selectors.

Built-in Nonlinear Characteristics of Low Power Operating One-Resistor Selector-Less RRAM By Stacking Engineering

Resistive random access memory (RRAM) using various metal oxides (i.e., SiO2[1], HfO2, NiO[2], Al2O3, NbO) have attracted much attentions since the current nonvolatile memory (NVM) has been approaching the scaling limit. Meanwhile, selector devices are essential to address the sneak path issue which causes reading errors and hinders the implementation of RRAM in high-density cross-bar array architecture [3-4]. However, additional selector devices, e.g. a commonly proposed one selector-one resistor (1S-1R) design, increases the process complexity and cost. In this work, selectorless 1R RRAM devices have been demonstrated by utilizing the nonlinear (NL) resistive switching (RS) characteristics. Pulse operation voltage variation tolerance on SiOx-based stacking structures has also been characterized. The starting substrates are heavily-doped N+ Si wafers, and titanium nitride of 200 nm thickness was deposited on N+ Si substrate as bottom electrode. Then, 9 nm of SiOx and 4 nm of HfOx were deposited as RS dielectric layers for bilayer (HfOx/SiOx) structures by RF sputtering method. Pt (165nm) was deposited as top electrodes for RRAM devices (Fig. 1). Fig. 2 shows bipolar RS I-V characteristics during DC voltage sweeps for single-layer HfOx and bilayer devices. Both SET and RESET voltages are lower in single-layer HfOx devices than in bilayer devices possibly due to higher oxygen concentration. The SET voltage of single-layer HfOx devices is about 0.2 V lower than of single-layer SiOx devices, and RESET voltage is reduced to half (~ 0.5 V) with inserting a HfOx stack layer, which is potentially beneficial for low voltage operating applications. Also, the RESET current is critical for overall switching power in RRAM applications, is ~1 mA and has been found to be independent of the thickness ratio of stacks. Comparing the bilayer structure to the single-layer HfOxstructure, the current at -0.2 V is reduced from ~10-4 to ~10-6 A. It depicts that there was significantly increased resistance at low voltage region, which is proposed as a solution for sneak path issue in crossbar array applications. Nonlinearity (NL) is defined as the ratio of the current at full read voltage (i.e. -0.6 V) to the current at 1/3 read voltage (-0.2 V). The higher nonlinearity, the better ability is to avoid the sneak current interference. The NL characteristics in ILRS of all the devices are showed in Fig. 3. With a thin SiOx layer (2 nm) on the bottom of HfOx (11 nm) layer, the NL is ~3x in comparison to the single-layer HfOx layer devices. Based on our results, the bilayer RRAM device has been found to show the highest NL among the SiOx-based stacking structures. This makes SiOx-based bilayer devices a potential candidate for 1R selectorless RRAMs. To evaluate the voltage variation tolerance in pulse operation, the reset stop voltage effect has been studied. The RS I-V was characterized with increasing RESET stop voltage from -1.4 to -2.6 V for the bilayer and trilayer devices (Fig. 4). For bilayer devices, the high resistance state (HRS) resistance and memory window increase with increasing RESET stop voltage (Fig. 5). The bilayer devices with higher SET/RESET voltage variation tolerance (less variation below stop voltage of 2.2 V) and have been found to exhibit better NL characteristics (~10) than the trilayer devices, which shows larger switching voltage variation with changing reset stop voltage (Fig.6). In this study, build-in nonlinear characteristics have been realized for the SiOx-based one-resistor (1R) device without an additional diode or a selector. The highly nonlinear characteristics observed in SiOx-based bilayer devices are desirable in avoiding the read error and preventing sneak-path currents in crossbar arrays. Our results show that SiOx-based bilayer devices are promising for high-density, low-power, selectorless RRAM applications. Figure 1

In-plane nonlinear multiple equilibria and switches of equilibria of pinned–fixed arches under an arbitrary radial concentrated load

Nonlinear in-plane multiple equilibria and buckling of pinned–fixed shallow circular arches under an arbitrary radial concentrated load are investigated. Analytical solutions for the multiple nonlinear equilibria, buckling and limit points are derived. New findings are: (1) pinned–fixed shallow arches under the arbitrary concentrated load have multiple stable and unstable equilibria; (2) the position of the arbitrary concentrated load and the modified slenderness of the arch influence the number of multiple equilibria and limit points as well as the first buckling load significantly; (3) a pinned–fixed arch under the arbitrary concentrated load can buckle in a limit point instability mode, but not in a bifurcation mode; (4) when the load is located between the crown and the pinned end, the buckling load is lower than that when the load is located between the crown and the fixed end, and (5) in addition to limit points, the nonlinear equilibria of pinned–fixed arches under the arbitrary concentrated load have inflexion points, which corresponds to specific modified slenderness switching the number of equilibria and limit points or switching buckling and no buckling behaviour. The analytical solutions for inflexion points and specific modified slenderness, and for the corresponding load, axial force and displacement are also derived for the first time in the literature. Comparisons with the finite element results have shown that the analytical solutions can accurately predict the multiple equilibria, limit points, inflexion points, and buckling load of shallow pinned–fixed arches under the arbitrary concentrated load.

Optical scheme of conversion of a positionally encoded decimal digit to frequency encoded Boolean form using Mach–Zehnder interferometer‐based semiconductor optical amplifier

The conversion of decimal number to its equivalent binary one and vice-versa is very important in the field of electronic/optical computing and data processing system. There are so many well established methods for this conversion. In this study, the authors propose a new scheme for optical conversion of a decimal number to its frequency encoded binary equivalent using tree architecture-based system and frequency-encoding principle. To implement the above conversion, some optical non-linear switches, such as Mach–Zehnder interferometer-based semiconductor optical amplifier (SOA), reflecting SOA based on SOA, have been used to get frequency encoded response.

Nonresonant and Resonant Nonlinear Absorption of CdSe-Based Nanoplatelets**Supported by the National Natural Science Foundation of China under Grant Nos 61234005 and 11304197.

We present a comprehensive understanding of the nonlinear absorption characteristics of CdSe-based nanoplatelets (NPLs) synthesized by the solution-phase method and the colloidal atomic layer deposition approach through Z-scan techniques at 532 nm with picosecond pulses. The CdSe NPLs exhibit strong two-photon induced free carrier absorption (effective three-photon absorption) upon the nonresonant excitation, resulting in a remarkable optical limiting behavior with the limiting threshold of approximately 75 GW/cm2. A nonlinear optical switching from saturable absorption (SA) to reverse saturable absorption (RSA) with increasing the laser intensity is observed when coating CdSe NPLs with a monolayer of CdS shell to realize the resonant absorption. The SA behavior originates from the ground state bleaching and the RSA behavior is attributed to the free carrier absorption. These findings explicitly demonstrate the potential applications of CdSe-based NPLs in nonlinear optoelectronics such as optical limiting devices, optical pulse compressors and optical switching devices.

Saturation‐aware control design for micro–nano positioning systems

This study proposes a non-linear saturation-aware controller for dual-stage micro–nano actuators. Dual-stage motion systems use two actuators in series in order to achieve an improved performance: a micro actuator responsible for a large range of actuation, and a nano actuator (NA) able to achieve a high bandwidth. The NA is commonly driven by flexure-based piezoelectric actuators subject to a limited range which presents large oscillations in the presence of output saturation. In order to avoid these oscillations, a non-linear smooth switching function that limits the actuation of the NA to only track references within its range is proposed. Experimental results demonstrate the effectiveness of the proposed approach, which is able to reduce oscillations and energy consumption without compromising settling time performance.

State/Model-Free Variable-Gain Discrete Sliding Mode Control for an Ultraprecision Wafer Stage

Wafer stage is an important mechatronic unit of industrial lithography tool for manufacturing integrated circuits. This paper presents a novel state/model-free variable-gain discrete sliding mode control (DSMC) to suppress the unmolded position-dependent dynamics and disturbances in the nanopositioning wafer stage. The proposed DSMC is essentially composed of feedforward control term, linear feedback control term, and nonlinear switching control term, which can be designed separately. The gain of the switching control term is meaningfully designed to be variable to balance the tradeoff between the robustness and the chattering. Data-driven parameter optimization approach is employed to achieve the optimal controller parameters of the typically nonlinear controller, where off-line parameter updating is iteratively carried out based on the input/output data to minimize a predefined objective function. This scheme facilitates a rapid implementation without either a parameter model or a state observer, and excellent tracking performance with the optimal controller parameters. Moreover, the closed-loop stability is analyzed, and the proposed DSMC is finally implemented on an ultraprecision wafer stage developed in our lab. Comparative experimental results demonstrate that it not only achieves nanoscale tracking accuracy but also possesses promising robustness to position-dependent dynamics and disturbances.

Stochastic economic model predictive control for Markovian switching systems

The optimization of process economics within the model predictive control (MPC) formulation has given rise to a new control paradigm known as economic MPC (EMPC). Several authors have discussed the closed-loop properties of EMPC-controlled deterministic systems, however, little have uncertain systems been studied. In this paper we propose EMPC formulations for nonlinear Markovian switching systems which guarantee recursive feasibility, asymptotic performance bounds and constrained mean square (MS) stability.

A Variable Structure System Control and its Application in Underwater Vehicles

The paper proposes a new Variable Structure System (VSS) control algorithm and its application in underwater robotics. The main features of the proposed approach consist on the usage of coupled switching surfaces, and on the usage of an adaptive adjustment method for their parameters in order to accelerate the transient processes. The adaptive algorithm of linear and nonlinear switching surfaces coefficients, is based on the stabilization of the sliding mode parameter close to the reference value. In this paper, it is shown how the proposed approach improves the system transient processes and the energy efficiency in comparison with conventional VSS, neutralizing also some drawbacks. The proposed adaptive VSS algorithm is applied to control a Remotely Operated Vehicle (ROV), and simulation results confirm the advantages to apply it.

Design of frequency-encoded data-based optical master-slave-JK flip-flop using polarization switch

An optical data processing and communication system provides enormous potential bandwidth and a very high processing speed, and it can fulfill the demands of the present generation. For an optical computing system, several data processing units that work in the optical domain are essential. Memory elements are undoubtedly essential to storing any information. Optical flip-flops can store one bit of optical information. From these flip-flop registers, counters can be developed. Here, the authors proposed an optical master-slave (MS)-JK flip-flop with the help of two-input and three-input optical NAND gates. Optical NAND gates have been developed using semiconductor optical amplifiers (SOAs). The nonlinear polarization switching property of an SOA has been exploited here, and it acts as a polarization switch in the proposed scheme. A frequency encoding technique is adopted for representing data. A specific frequency of an optical signal represents a binary data bit. This technique of data representation is helpful because frequency is the fundamental property of a signal, and it remains unaltered during reflection, refraction, absorption, etc. throughout the data propagation. The simulated results enhance the admissibility of the scheme.

A nonlinear switching control strategy of regulation and safety protection for aero-engines based on the equilibrium manifold expansion model

This article proposes a nonlinear switching control strategy to solve the regulation control problem with safety constraint for aero-engines based on the equilibrium manifold expansion model. That is a kind of nonlinear model with satisfactory accuracy. The design procedure includes design of sub-controllers such as the nonlinear high-pressure spool speed tracking controller, high pressure turbine outlet temperature safety protection controller and the nonlinear dynamic feedback recovery controller. Also, switching law and dynamic controller state reset law are properly designed. Under the proposed strategy, system trajectory starting from temperature safety boundary will never return to the safety boundary. The designed reset law ensures a smooth switching from protection mode to recovery mode. Switch-off moment of the protection controller can be arbitrarily selected according to the tracking performance requirement. Freedom degree of selection is enlarged. The sub-controllers corresponding to objectives of regulation and safety protection are designed separately with more freedom degree and less conservatism. The effectiveness and the robustness of the proposed strategy are verified through a case study for a two-spool turbofan engine.

Visualization of a nonlinear conducting path in an organic molecular ferroelectric by using emission of terahertz radiation

Nonlinear electric transport and switching to a negative resistance state are typical electric-field-induced phenomena in correlated electron materials, while their mechanisms are generally difficult to solve. In the present study, we apply the terahertz-radiation imaging method to an organic molecular ferroelectric, \ensuremath{\alpha}-type bis(ethylenedithio)tetrathiafulvalene iodide salt, and investigate the nature of its negative resistance phenomenon. When the negative resistance state is produced, the ferroelectric order is melted in an elongated region with the width of \ensuremath{\sim}100 \ensuremath{\mu}m and that region grows along the direction inclined by about 40\ifmmode^\circ\else\textdegree\fi{} from the $b$ axis with the increase of nonlinear current. A comparison of the terahertz radiation intensity with the current magnitude revealed that the melted region forms a conducting path. We interpreted the diagonal growth of the conduction path by taking into account the anisotropy of the intermolecular transfer integrals.

Nonlinear optical switching properties of dye-doped inorganic/organic nanocomposite films

The sol–gel method has been employed in the fabrication of composite films consisting of nanometer size self-assembled organic mesostructures surrounded by a silica framework. The hydrophobic domains within the mesostructures make these films an excellent host matrix for the donor/acceptor energy transfer complexes. Time-resolved fluorescence and transient absorption studies revealed that these complexes exhibit ultrafast nonlinear optical responses as a result of the energy transfer process. The optical properties of these composite films may make them suitable for use as the photonic film in future all-optical switching devices.

Perpendicular magnetic tunneling junction switching dynamic modes, extreme events, and performance scaling

The performance of the state-of-the-art perpendicular magnetic tunneling junction (pMTJ) device is fundamentally determined by the physics of material “extreme events.” A dynamic mode approach is used to study “extreme events” of stochastic nonlinear magnetization switching, including magnetic interactions and non-uniform magnetization dynamics. Our theory and experiment show that the magnetization switching “extreme events” are well characterized by the dynamic modes of interacting magnetic systems. The dynamic modes provide a clear understanding of the physical processes of the magnetization switching “extreme events.” We predict markedly different pMTJ scaling behaviors for spin transfer torque, spin-orbit-interaction torque, and thermal fluctuations at different operation speeds and bit error rate conditions. Understanding these scaling behaviors is critical for existing and emerging pMTJ device applications.

Self-Selecting Resistive Switching Scheme Using TiO2 Nanorod Arrays

In this study, the resistive switching scheme using TiO2 nanorod arrays synthesized by a large-scale and low-cost hydrothermal process was reported. Especially, the nonlinear I–V characteristics of TiO2 nanorod arrays with a nonlinearity of up to ~10, which suppress the leakage current less than 10−4 Acm−2, were demonstrated, exhibiting a self-selecting resistive switching behavior. It provides a simple pathway for integration of RRAM crossbar arrays without additional stacking of active devices. The mechanisms of the nonlinear resistive switching behaviors were discussed in detail. In addition, the maximum array numbers of 79 for self-selecting RRAM cells were estimated. The results demonstrate an opportunity of using the concept of self-selecting resistive switching characteristics in a single material, which offers a new strategy to tackle the sneak path issue of RRAM in the crossbar arrays structure.

Jaya, harmony search and water cycle algorithms for solving large-scale real-life urban traffic light scheduling problem

Abstract This paper studies a large-scale urban traffic light scheduling problem (LUTLSP). A centralized model is developed to describe the LUTLSP, where each outgoing flow rate is described as a nonlinear mixed logical switching function over the source link’s density, the destination link’s density and capacity, and the driver’s potential psychological response to the past traffic light signals. The objective is to minimize the total network-wise delay time of all vehicles in a time window. Three metaheuristic optimization algorithms, named as Jaya algorithm, harmony search (HS) and water cycle algorithm (WCA) are implemented to solve the LUTLSP. Since we adopt a discrete-time formulation of LUTLSP, we firstly develop a discrete version of Jaya and WCA. Secondly, some improvement strategies are proposed to speed up the convergence of applied optimizers. Thirdly, a feature based search operator is utilized to improve the search performance of reported optimization methods. Finally, experiments are carried out based on the real traffic data in Singapore. The HS, WCA, Jaya, and their variants are evaluated by solving 11 cases of traffic networks. The comparisons and discussions verify that the considered metaheuristic optimization methods can effectively solve the LUTLSP considerably surpassing the existing traffic light control strategy.

Study of all-optical switching properties of zinc phthalocyanine thin film by pump-probe technique

The nonlinear optical absorption, refraction and switching behavior of Zinc phthalocyanine (Zn(II)Pc) thin films are reported. Z-scan technique is employed to study the nonlinear absorption and nonlinear refraction behavior of the thin films with nanosecond pulses of Nd:YAG laser at ∼532nm. Optical switching behavior of the dye is studied using pump-probe technique with ∼5ns pulses of Nd:YAG at ∼532nm as the pump beam and ∼632.8nm cw He-Ne laser as the probe beam. The switching behavior of the dye is attributed to excited state absorption (ESA) of the probe beam by the dye molecules. Probe beam modulation with increasing pump intensity is also investigated.

Instantaneous Power Quality Indices Based on Single-Sideband Modulation and Wavelet Packet-Hilbert Transform

Diverse conditions in power systems, such as massive use of nonlinear loads, continuous switching and operation of large electrical loads, and the integration of renewable energies, among others, have adversely affected the power quality (PQ) because they produce undesirable distortions in the waveforms of voltage and current. The conventional way to quantify the PQ is using the PQ indices (PQIs). Yet, the nonstationary properties of voltage and current signals degrade the PQIs estimation whenever classical techniques are used. In this paper, a methodology based on single-sideband modulation method and the Wavelet and Hilbert transforms for the estimation of instantaneous PQIs is proposed. It is shown that the proposal yields better tracking of transitory changes in the voltage/current signals than classical techniques such as the short-time Fourier transform. The PQIs used are the root-mean-square values, frequency, total harmonic distortion, active power, reactive power, apparent power, distortion power, power factor, and total power factor. PQIs performance is validated using synthetic and real signals.