| The study of energy transport in electronic devices with sub-micron features has been the focus of increased research efforts during the past years. Most published studies simplify the phonon physics by considering a gray approach, in which a single phonon propagation speed is defined according to the Debye model. Although some efforts have recently been made to account for phonon dispersion and polarization effects, the treatment of optical phonons has been simplified in most studies by assigning them zero propagation speed and purely capacitive characteristics, in an assumption consistent with the Einstein model. Additionally, many of the problems that have been addressed in the literature correspond to steady state conditions.; The objective of this thesis is, therefore, to develop a phonon transport model, considering dispersion and polarization effects, without the usual simplifying assumptions made with regard to the treatment of optical phonons. The phonon transport model is then applied to the study of thin film heat conduction in silicon, and to the study of the transient thermal response of Silicon-on-Insulator (SOI) transistors under Joule heating conditions.; The main results from this thesis are the characterization of the transition from diffusive to ballistic transport in thin film heat conduction that occurs as the phonon mean free path becomes larger than the film thickness. This transition to ballistic transport is also found in the context of SOI simulations, and it is characterized by three main phenomena: first, the thermal energy transport takes place in the form of phonon traveling waves. Second, temperature slip conditions develop at the boundaries with prescribed temperature levels, and third, phonon confinement effects result in higher hotspot peak temperatures than what is predicted by the Fourier equation.; It is found that the gray LBM is inexpensive in terms of computational effort needed, which compensates for the simplified description of the phonon physics (Debye model) that it uses. In contrast, the dispersion LBM, although physically accurate, results in orders of magnitude increases on the computational effort required to solve nanoscale heat conduction, which makes it unsuitable for simulating realistic geometries. (Abstract shortened by UMI.)... |
