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In this paper the implementation of maximum power point tracking (MPPT) schemes by the ripple correlation control (RCC) algorithm is discussed in case of multiple ripple harmonics. As an example, a single-phase single-stage grid-connected photovoltaic (PV) system based on H-bridge inverter and level doubling network (LDN) is considered, leading to a multilevel inverter having the double of output...
A new algorithm has been designed and implemented, that allows for the automatic generation of an optimum 2D and 3D grid for device simulation from the information available at the circuit-layout level. The tool fills a gap in the top-down design chain of integrated circuits, easing the task of circuit designers who are often unaware of specific features of device-modeling tools.
A general expression is worked out for the trap-to-trap transition probability per unit time, applicable to amorphous materials where charge conduction is dominated by localized states. The outcome is a closed-form expression involving temperature and local electric potential. It is suitable for inclusion into hydrodynamic or energy-balance numerical solvers to be used for simulating devices based...
This paper presents a computational analysis, by means of a compact model, of the electric response of an Ovonic Threshold-Switch device embedded in a circuit subjected to an oscillatory bias.
A method for directly measuring the inverse screening length in semiconductors in terms of ionized-impurity concentration and lattice temperature is demonstrated, based on a first-principle calculation of the effect of ionized-impurity scattering. No fitting parameters are involved in the derivation, which covers a wide range of doping concentrations and intrinsically complies with the Mathiessen...
Recent papers on advanced semiconductor devices adopt a model called density-gradient correction, in which the standard electric potential acting on the carriers is modified by a non-linear term involving the carrier concentration and its second derivatives. When applied to cases where quantum effects are not negligible, the modified model improves the results with respect to the standard approach...
The time evolution of current and voltage in Ovonic-switching devices is affected, on one side, by parasitic elements due to contacts and connectors and, on the other one, by the internal-relaxation mechanisms of the material itself. The two aspects, respectively termed here “extrinsic” and “intrinsic” dynamics, are investigated in this paper on the basis of the time-dependent, trap-limited conduction...
The numerical approach to quantum transport in nanowires and nanotubes in the ballistic regime requires an accurate numerical solution of the coupled Schrödinger and Poisson equations. Here the feasibility of a 5th-order method is proved for the longitudinal part of the wave equation. The effectiveness of the method is demonstrated on a ballistic device.
The hydrodynamic model for the trap-limited conduction regime in amorphous materials, used in the description of phase-change memory devices, is re-examined from the viewpoint of numerical efficiency. Among other features, the approach presented here avoids the calculation of integrals involving the distribution function during the iterative solution, and makes the proposed solution scheme suitable...
The so-called Numerov process provides a three-point interpolation with an ∼η5 accuracy in grid's size η, much better than the standard finite-difference scheme that keeps the ∼η2 terms. Such a substantial improvement is achieved with a negligible increase in computational cost. As the method is applicable to second-order differential equations in one dimension, it is an ideal tool for solving, e...
An important contribution to charge transport in amorphous-chalcogenide materials used for manufacturing memory devices is due to the trap-to-trap transitions. Here the physics of the phenomenon is worked out as a combination of energy and space transitions, and its probability is expressed in closed form in terms of microscopic parameters. The results are useful for setting up the macroscopic master...
The dynamic scheme for extracting parameters of the phase-change memories is examined. The experimentally-observed behavior due to the heating and quenching of the material is modeled by a set of differential and algebraic equations. The method allows one to extract important design parameters of the PCM, along with their temperature dependence.
A sound physical model for electric conduction in Ovonic materials is presented. Trap-limited conduction is assumed to determine the part of the I(V) curve below the characteristic threshold of these materials. Band transport comes into play at and above threshold, where the cooperative electron-electron interactions couple the conduction band with the traps. The model can be implemented into numerical...
Charge transport in amorphous-chalcogenide materials used for manufacturing memory devices is determined by two mechanisms: hopping of trapped electrons and motion of band electrons. Electron-electron interaction is investigated here as one of the mechanisms mainly responsible for the trap-to-band transitions. The problem is tackled using a fully quantum-mechanical approach by numerically solving...
Charge transport in amorphous chalcogenide-GST used for memory devices is modeled by means of two contributions: hopping of trapped electrons and motion of band electrons. Field-induced emission is accounted for as the mechanism mainly responsible for the trap-to-band transitions. The experimental snap-back behavior of the I(V) curves is reproduced even in the simple case of one-dimensional, uniform...
The Schrödinger equation, or the coupled Schrödinger and Poisson equations, are transformed into an integral equation. Back-substituting from the original equations allows one to approximate the numerical corrections to any order without the need of calculating derivatives of the unknown function of order larger than one. Typical applications are in the numerical analysis of quantum transport in...
Chalcogenide compounds (GST) are extensively being investigated as active materials in phase change memories (PCM). Experimental structural data and charge transport features of GST devices suggest that electrical conduction in the amorphous phase is controlled by defects and trapped carriers. A M1-3D, self-consistent Monte Carlo code has been implemented to the purpose of calculating carrier transport...
Chalcogenide GST materials can suitably be exploited for manufacturing phase-change memory devices. In this paper a transport model for the amorphous phase of GST is investigated, based on the variable-range hopping model. The model is implemented into a Monte Carlo current-driven simulation of a test device made of a layer of amorphous Ge2Sb2Te5 in contact with two planar metallic electrodes. The...
In this work we propose a unified model for the low-field effective electron mobility in SOI and DG-MOSFETs with ultrathin SiO2/HfO2 gate stacks, different substrate and channel orientations and uniaxial stress conditions.The model accounts for quantum-confinement effects in the MOSFET channel. Next, we apply this mobility model to a 1D quantum drift-diffusion (QDD) transport model in order to investigate...
The paper addresses the calculation of the band structure for different phases of the chalcogenide Ge2Sb2Te5 compound, which is raising considerable interest in view of the applications to the nonvolatile-memory technology. The band structure is necessary for determining the charge- and heat-transport properties of the material. The band diagram of the face-centered cubic phase, which is the most...
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