Quantum mechanical effects on noise properties of nanoelectronic devices: application to Monte Carlo simulation

A discussion about the quantum mechanical effects on noise properties of ballistic (phase-coherent) nanoscale devices is presented. It is shown that quantum noise can be understood in terms of quantum trajectories. This interpretation provides a simple and intuitive explanation of the origin of quantum noise that can be very salutary for nanoelectronic engineers. In particular, an injection model is presented that, coupled with a standard Monte Carlo algorithm, provides an accurate modeling of quantum noise. As a test, the standard results of noise in tunneling junction devices are reproduced within this approach.     

Comparison of distributed and lumped element models for analysis of filtering properties of nonlinear transmission lines

The filtering properties of periodic loaded lossy transmission lines are studied from the point of view of microwave network theory. Under the condition that the per‐section capacitance of the line is small compared to that of the loading capacitors, it is shown that the distributed circuit can be described accurately by means of a lumped element ladder network. The effects of transmission line losses on this approximation are also analyzed. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12, 503–507, 2002. Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mmce.10050     

Optimization of Nonlinear Transmission Lines for Harmonic Generation: The Role of the Capacitance-Voltage Characteristic and the Area Effect

In this paper, nonlinear transmission lines (NLTLs) periodically loaded with symmetric voltage dependent capacitances are investigated by means of computer simulation. Specifically, we have studied the role that the C-V characteristic plays on the performance of NLTLs as frequency multipliers. The main conclusion of the work is that the area under the C(V) curve is a key parameter for the optimization of conversion efficiency. This result is interpreted on the basis of soliton like propagation in NLTLs.     

Boundary conditions with Pauli exclusion and charge neutrality: application to the Monte Carlo simulation of ballistic nanoscale devices

Electron transport becomes (quasi-) ballistic for nanoscale devices with active regions smaller than 20 nm. Under these conditions, the current and the noise are mainly determined by the electron injection process. Thus, the numerical simulation of these small devices can be very sensible to the boundary conditions (BC). In this work, we present a novel BC for (time-dependent) particle simulators that fulfill Fermi statistics and charge neutrality at the contacts. Monte Carlo simulations of a nanometric two-terminal device using a traditional injection model and the novel model presented in this work are compared.     

Understanding Soliton Wave Propagation in Nonlinear Transmission Lines for Millimeter Wave Multiplication

In this paper, soliton propagation in nonlinear transmission lines (NLTLs) periodically loaded with symmetric voltage dependent capacitances is studied. From the lumped element equivalent circuit of the line we have analyzed the influence of nonlinear shunt reactances on soliton propagation characteristics. It is shown that by increasing the non linearity of the C–V characteristic, a faster separation of input signal into solitons is achieved. The fact that frequency multiplication in NLTLs is governed by soliton formation makes the results of this work relevant to understand the influence of nonlinear loading devices on multiplier performance. Since a heterostructure barrier varactor (HBV)-like voltage dependent capacitance has been considered for the nonlinear devices, this study can be of interest for the design of millimeter wave frequency multipliers loaded with HBVs.     

Effects of Line Parameters on Soliton-Like Propagation in Nonlinear Transmission Lines: Application to the Optimization of Frequency Triplers

In this paper, soliton propagation in nonlinear transmission lines (NLTLs) periodically loaded with heterostructure barrier varactors is studied. From the lumped element equivalent circuit of the line we have analyzed the influence of transmission line parameters (i.e, per-section inductance and capacitance) on soliton propagation characteristics. It is shown that by increasing these parameters, a faster separation of input signals into solitons is achieved. From the point of view of NLTL harmonic generation, this gives additional flexibility to optimize multiplier performance by appropriate circuit design. These conclusions are supported from the analysis of a frequency tripler, where device losses are included.     

Quantum transport beyond DC

This introductory paper for the special issue on Quantum transport beyond DC has two main goals. First, we discuss the reasons why such a special issue is timely and relevant. Second, we present a brief summary of the subsequent papers included in it. Along the paper, we emphasize didactic explanations in front of formal mathematical developments.     

Study of Noise Properties in Nanoscale Electronic Devices Using Quantum Trajectories

Noise properties in nanoscale devices are studied extending, via quantum trajectories, the classical particle Monte Carlo techniques to devices in which quantum non-local effects are important. This approach can be used to study noise in a wide range of frequencies and can also be easily coupled to a Poisson solver to study long range Coulomb effects in noise characteristics. As a numerical example, we have studied noise in a tunneling barrier showing that the results obtained within our approach exactly reproduce those of the standard Landauer-Buttiker formalism in the zero frequency limit.     

Monte Carlo simulations of nanometric devices beyond the “mean-field” approximation

For nanoscale electron devices, the role of a single-electron (or a single-impurity) can have a large impact on their electrical characteristics. A new method for introducing the long-range and short-range Coulomb interaction in semiconductor semi-classical Monte Carlo simulations is presented. The method is based on directly dealing with a many-particle system by solving a different Poisson equation for each electron. The present work shows the numerical viability of this alternative approach for nanoscale devices with few (<100) electrons. The method is compared with the traditional “mean-field” Monte Carlo simulations. It is shown, numerically, that the “mean-field” approximation produces important errors for aggressively-scaled devices.