The BICMOS technology which integrates the CMOS technology with bipolar technology has drawn considerable attention as an attractive VLSI technology because of the high speed performance and low power consumption of the BICMOS. However, continued down scaling of CMOS devices has caused increased concerns with problems such as latch up, hot carriers and short channel effect. Most of the above mentioned problems can be avoided by operating the CMOS at liquid-nitrogen temperature(LNT). At low-temperatures, the CMOS exhibits lower sub threshold leakage, higher carrier mobility (which yields improved speed performance), and a steeper logarithmic currentvoltage slope. On the other hand, the low-temperature operation of conventional silicon bipolar circuits has been generally dismissed as impractical because of the well known decrease in the current gain at low temperature. The present interest in integrated bipolarCMOS circuits, plus the prospect of increased reliability, lower wiring delay, and lower noise, has revised interest in low-temperature bipolar devices. In this context, it is therefore important to acquire accurate knowledge of the transistor properties at liquid nitrogen temperature. This can be done in two ways. One is through experimental lowtemperature measurements and the other by low-temperature device simulations. Existing room temperature numerical simulators are typically not useful for low temperature conditions. This is because the physical assumptions such as complete ionization, the parameter models and implementation methods for room temperature condition do not hold at low temperature. Therefore, we used BiLow - a steady state onedimensional Bipolar Low Temperature Simulator for the temperature range of 77K- 300K. This simulator, originally written in FORTRAN, was converted to C for the dual purpose of proper memory management and making further modifications easier. The focus of this research has been to model bandgap narrowing, incomplete ionization and Mott Transition at room and at low-temperature, evaluate the performance of the new BiLow and to derive conclusions on the BIT performance at LNT. It was observed that the bandgap narrowing was independent of temperature for the entire range of majority carrier concentration. The effect of Mott transition on the abrupt decrease in the electron concentration in emitter has been taken care of by smoothing out the concentration profile in the emitter thereby providing a continuity in the region of Mott transition. Both the current gain(~) and the frequency(ft) values obtained from simulating the two new profiles were found to be smaller than those obtained using the original BiLow simulator, as the doping in the base is higher and the device sizes were smaller. Most of the degradation in 13 and ft was found to occur below 150K. From the plots of the charge characteristics, we found that the total charge which is a strong function of temperature is more in the case of the profiles studied for this work than the total charge from the original BiLow simulator.

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A simulation program has been developed to facilitate the investigation and analysis of power semiconductor devices under the reverse-bias condition. The electrostatic potential distribution is solved by using Poisson's equation alone, with particular attention to the neighborhood of avalanche breakdown. Because of its generality and efficiency, the program emerges as a powerful engineering tool for the design of power devices incorporating special junction termination techniques. Results are presented for a DMOS structure to illustrate the improvement in breakdown voltage when a field plate is applied. Numerical solution techniques for solving elliptic partial differential equations in a multi-material domain are discussed. The discretization of this domain is nonuniform in general due to its highly nonuniform physical parameters. By careful selection of grid lines near interfaces, the difference equation coefficients are considerably simplified. The resultant matrix of coefficients is symmetric even though Neumann boundary conditions are specified.

The effects of ionizing radiation on the breakdown-voltage degradation of power-MOSFET termination structures were examined through two-dimensional simulation. A wide variety of sensitivity to surface-charge density was found for various devices employing floating field rings and/or equipotential field plates. Termination structures that were both insensitive to surface charge and possessed a high breakdown voltage were identified. The results were compared with measurements made on selected structures. The principal ionizing radiation damaging mechanisms in MOS devices are discussed. Modifications made to an existing simulation program in order to simulate these complex field ring and field plate structures are described. Background information into how these termination structures improve the breakdown voltage and their sensitivities to positive interface charge buildup is investigated.

The objective of this thesis was to model the Fuzz Face , a transistor-based guitar distortion effect, digitally at the circuit level, and explore how changes in the discrete analog components change the digital model. The circuit was first simulated using SPICE simulation software. Typically outputs and how they changed based on transistor gains were documented. A test circuit was then constructed in lab to determine true transistor gains. An analog Fuzz Face circuit was then constructed, and physical parameters were recorded. A digital model was then created using MATLAB. Capacitive filtering effects were found to be negligible in terms of the guitar signal and were not modeled. The transistors were modeled using the Ebers-Moll equations. A MATLAB algorithm was written to produce Fuzz Face type distortion given an input guitar signal. The algorithm used numerical techniques to solve the nonlinear equations and stored them in a look-up table. This table was used to process the input clips. The sound of the Fuzz Face was not perfectly modeled, but the equations were found to provide a reasonable approximation of the circuit. Further study is needed to determine a more complete modeling equation for the circuit.

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A new quantum transport simulator -- Schrödinger Equation Monte Carlo in Three Dimensions (SEMC-3D) -- has been developed for simulating the carrier transport in nanoscale 3D MOSFET geometries. SEMC-3D self-consistently solves: (1) the 1D quantum transport equations derived from the SEMC method with open boundary conditions and rigorous treatment of various scattering processes including phonon and surface roughness scattering, (2) the 2D Schrödinger equations of the device cross sections with close boundary conditions to obtain the spatially varying subband structure along the conduction channel, and (3) the 3D Poisson equation of the whole device. Therefore, SEMC-3D can provide a physically accurate and electrostatically selfconsistent approach to the quantum transport in the subbands of 3D nanoscale MOSFETs. SEMC-3D has been used to simulate Si nanowire (NW) nMOSFETs to both demonstrate the capabilities of SEMC-3D, itself, and to provide new insight into transport phenomena in nanoscale MOSFETs, particularly with regards to interplay among scattering, quantum confinement and transport, and strain. / text

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