Abstract-A detailed full-wave time-domain simulation model for the analysis of electromagnetic effects on the behavior of the suhmicrometer-gate field-effect transistor (FET's) is presented. The full wave simulation model couples a three-dimensional (3-D) time-domain solution of Maxwell's equations to the active device model. The active device model is based on the moments of the Boltzmann's transport equation obtained by integration over the momentum space. The coupling between the two models is established by using fields obtained from the solution of Maxwell's equations in the active device model to calculate the current densities inside the device. These current densities are used to update the electric and magnetic fields. Numerical results are generated using the coupled model to investigate the effects of electron-wave interaction on the behavior of microwave FET's. The results show that the voltage gain increases along the device width. While the amplitude of the input-voltage wave decays along the device width, due to the electromagnetic energy loss to the conducting electrons, the amplitude of the output-voltage wave increases as more and more energy is transferred from the electrons to the propagating wave along the device width. The simulation confirms that there is an optimum device width for highest voltage gain for a given device structure. Fourier analysis is performed on the device output characteristics to obtain the gain-frequency and phase-frequency dependencies. The analysis shows a nonlinear energy build-up and wave dispersion at higher frequencies. E H

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Abstract-Thiswork presents a comprehensive characterization of the frequency dependence of the effective complex permittivity of bundled carbon nanotubes considering different densities over a broadband of frequencies from 10 MHz to 50 GHz using only one measurement setup. The extraction technique is based on rigorous modeling of coaxial and circular discontinuities using mode matching technique in conjunction with inverse optimization method to map the simulated scattering parameters to those measured by vector network analyzer. The dramatic values of complex permittivity obtained at low frequencies are physically explained by the percolation theory. The effective permittivity of a mixture of nano-particles of alumina and carbon nanotubes versus frequency and packing density is studied to verify the previously obtained phenomenon.

This paper presents a new approach for the simulation and optimization of microwave devices using a genetic algorithm (GA). The proposed technique solves the equations that describe the semiconductor transport physics in conjunction with Poisson's equation, employing an adaptive real-coded GA. An objective function is formulated, and most of the GA parameters are recommended to change during the simulation. In addition, different methods for describing the way the GA parameters change are developed and studied. The effect of GA parameters including the mutation value, number of crossover points, selection criteria, size of population, and probability of mutation is analyzed. The technique is validated by simulating a submicrometer field-effect transistor, and then compared to successive over relaxation, showing the same degree of accuracy along with a moderate speed of convergence. The purpose of this paper is to introduce a new vision for a GA capable of optimizing real value functions with a considerably large number of variables. This paper also represents a fundamental step toward applying GAs to Maxwell's equations in conjunction with the hydrodynamic model, aiming to develop an optimized and unconditionally stable global-modeling simulator.

Silicon has many advantages as a microwave substrate material including low cost and a mature technology. The lower resistivity of Si (=lo k R-cm) compared to GaAs (=lo M R-cm) is perceived as a major disadvantage. In this paper, we present measured and simulated results demonstrating that the losses of a coplanar transmission line (CPW) realized on silicon substrates are comparable to the losses of a CPW realized on a GaAs substrate with insulators. The loss mechanisms of Si and GaAs substrates used for microwave applications are analyzed using both microwave and semiconductor physics theory. A high resistivity Si substrate can be used both as a microwave substrate and an active element carrier permitting futher integration at low cost.

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