An accurate model of domain-wall-based spintronic memristor

Spintronic memristors are promising devices that can be used in various applications such as memory chips and neuromorphic systems. The spintronic memristor combines the non-volatility advantage of resistive memristors, and the good scalability, and radiation hardness of spin-transfer torque magnetic devices. In addition, spintronic memristors can benefit from the maturity of integrating magnetic devices on top of CMOS devices. Current models of spintronic memristor only provide a similar version of the linear ion drift model of resistive memristors, which offers a simplified model, but with low accuracy and without enough linking to the device's physical parameters. In this paper, an accurate model of domain-wall- based spintronic memristor based on Landau-Lifshitz-Gilbert-Slonczewski (LLGS) equation is proposed. The proposed model provides a more accurate dynamical behavior by using the LLGS equation, and better relation to the device's physical parameters. It also uses the required equations that cover different types and geometries of spintronic memristors. The effect of the thermal fluctuations on device's parameters is also included into the model. The model uses the theory of domain-wall motion to explain the behavior of the device. Furthermore, a Verilog-A model is developed in order be compatible with IC CAD tools.     

A compact,low‐frequency,memristor‐based oscillator

A relaxation oscillator using a memristor is hereby presented. The memristor is used to substitute the function of a capacitor in an equivalent RC oscillator. The voltage across the memristor changes according to the quantity and polarity of the current passing through, thus substituting the changing voltage across a capacitor in the equivalent RC oscillator. The memristor has the advantage of occupying much less area than the equivalent capacitor, which may be important when trying to build on‐chip oscillators for portable or medical applications. Copyright © 2014 John Wiley & Sons, Ltd.     

Dynamics analysis of chaotic circuit with two memristors

Based on Chua’s chaotic oscillation circuit, a fifth-order chaotic circuit with two memristors is designed and its corresponding dimensionless mathematic model is established. By using conventional dynamical analysis methods, stability analysis of the equilibrium set of the circuit is performed, the distribution of stable and unstable regions corresponding to the memristor initial states is achieved, and the complex dynamical behaviors of the circuit depending on the circuit parameters and the memristor ini...     

Window functions and sigmoidal behaviour of memristive systems

A common approach to model memristive systems is to include empirical window functions to describe edge effects and nonlinearities in the change of the memristance. We demonstrate that under quite general conditions, each window function can be associated with a sigmoidal curve relating the normalised time‐dependent memristance to the time integral of the input. Conversely, this explicit relation allows us to derive window functions suitable for the mesoscopic modelling of memristive systems from a variety of well‐known sigmoidals. Such sigmoidal curves are defined in terms of measured variables and can thus be extracted from input and output signals of a device and then transformed to its corresponding window. We also introduce a new generalised window function that allows the flexible modelling of asymmetric edge effects in a simple manner. Copyright © 2016 John Wiley & Sons, Ltd.     

Review and comparative study of I-V characteristics of different memristor models with sinusoidal input

ABSTRACT

Memory-resistor (Memristor) has drawn considerable attention of the researchers in the last decade due to its remarkable properties. After the first concept of memristor, proposed by Leon Chua in 1971, almost no research work was conducted in this field for a long time. However, since the revolutionary discovery of the physical structure of memristor and its model of the HP lab in 2008, a tremendous amount of research work has been going on. Researchers are focusing on improving the models for the analysis of the memristor. Different researchers have come up with their model to improve the existing ones. These models can be linear, nonlinear or exponential. To overcome the boundary problem, many window functions have been proposed. Different models have their explanations of voltage-current relationship and state variable derivatives. This paper presents a detailed review and a comparative study of the existing memristor models based on their I-V characteristic curve. Original experimental I–V curve from the HP lab has been used as the reference for comparison.     

Memristive Switching Characteristics in Biomaterial Chitosan-Based Solid Polymer Electrolyte for Artificial Synapse

This study evaluated the memristive switching characteristics of a biomaterial solid polymer electrolyte (SPE) chitosan-based memristor and confirmed its artificial synaptic behavior with analog switching. Despite the potential advantages of organic memristors for high-end electronics, the unstable multilevel states and poor reliability of organic devices must be overcome. The fabricated Ti/SPE-chitosan/Pt-structured memristor has stable bipolar resistive switching (BRS) behavior due to a cation-based electrochemical reaction between a polymeric electrolyte and metal ions and exhibits excellent endurance in 5 × 10² DC cycles. In addition, we achieved multilevel per cell (MLC) BRS I-V characteristics by adjusting the set compliance current (I_cc) for analog switching. The multilevel states demonstrated uniform resistance distributions and nonvolatile retention characteristics over 10⁴ s. These stable MLC properties are explained by the laterally intensified conductive filaments in SPE-chitosan, based on the linear relationship between operating voltage margin (ΔV_switching) and I_cc. In addition, the multilevel resistance dependence on I_cc suggests the capability of continuous analog resistance switching. Chitosan-based SPE artificial synapses ensure the emulation of short- and long-term plasticity of biological synapses, including excitatory postsynaptic current, inhibitory postsynaptic current, paired-pulse facilitation, and paired-pulse depression. Furthermore, the gradual conductance modulations upon repeated stimulation by 10⁴ electric pulses were evaluated in high stability.     

A unified cubic flux‐controlled memristor: theoretical analysis,simulation and circuit experiment

In this paper, a unified cubic flux‐controlled memristor is proposed, and how to choose its parameters to obtain an appropriate memristor is investigated. The relevant frequency band of the exciting source that enables the memristor to keep its characteristics (call it mem‐frequency band) is analyzed, and the matter of high mem‐frequency is also clinched. Based on the trend of their i–v curves versus time, the memristors are divided into two types: P and N. The design, simulations and experiments of the circuits for the presented memristor model are given to describe its dynamical behaviors. The results from simulations and experiments are in good agreement with the theoretical analysis, which are of special guidance for designing such device to satisfy the requirements in practical engineering. Copyright © 2014 John Wiley & Sons, Ltd.     

Novel chaotic behavior in the Muthuswamy–Chua system using Chebyshev Polynomials

In this paper, three kinds of memristors with memristance functions obtained from the Chebyshev polynomials are used in the Muthuswamy–Chua system, which has only three circuit elements: a linear passive inductor, a linear passive capacitor and a nonlinear active memristor. We use multivariable second‐order polynomial functions of current and memristor state for the internal state function of the memristor. This enables our system to generate not only double‐scroll but also four‐scroll attractors. Systematic studies of chaotic behavior in these systems are performed using phase portraits, bifurcation diagrams and Lyapunov exponents. Simulation results show that all these systems exhibit chaotic behavior over a range of control parameters. Copyright © 2014 John Wiley & Sons, Ltd.