Development of a multisubband Monte Carlo simualtor for nanometric transistors

Abstract

The ultimate objective of this PhD Thesis is the study of the performance of nanometric transistors, and the importance that quantum effects have on the determination of their behavior. To do so, this work presents a description of the new architectures which are postulated as an alternative for future technological nodes, and the simulation tools employed to achieve an accurate determination of the electrostatic and transport properties of such devices, accounting for the dominant quantum effects which they undergo. We start with a summary of several technological architectures which are proposed to overcome the downscaling limitations of conventional planar devices. They are required to keep under control the short-channel effects (SCEs), that is, the loss of the control of the channel charge by the gate terminal. The starting point of the simulation frame which is a Multisubband Ensemble Monte Carlo (MS-EMC) scheme is analyzed. This tool is based on the mode-space approach of quantum transport where the system is decoupled in the confinement direction and the transport plane, where the 1D Schrödinger equation and the 2D Boltzmann Transport Equation (BTE) are solved, respectively. Both equations are coupled to the 2D Poisson Equation to keep the self-consistency of the solution. It has already demonstrated its capabilities in different scenarios keeping a reasonable computational effort with respect to the full-quantum approach. However, this code has been parallelized in order to allow for the study of more complex devices in a reasonable simulation time. Other techniques for statistical enhancement are included in order to reduce the stochastic noise. Furthermore, the appearance of the leakage currents modifies the stable performance of the conventional MOSFETs. Accordingly, a deep study of each physical mechanisms responsible for these leakage currents was carried out. One of the main advantages of considering this MS-EMC simulator is that quantum effects can be included in a separate way because of the decoupled approximation allowing for an independent inquiry.