Thesis (B.A.(Hons.))--University of Adelaide. Dept. of History, 1973.

Thesis (Ph. D.)--Bob Jones University, 2006. / Includes bibliographical references (leaves 245-252).

Thesis (Ph. D.)--Bob Jones University, 2006. / Includes bibliographical references (leaves 245-252).

Thesis (M.S.)--University of Michigan, 1976.

La conception des dispositifs nanométriques CMOS apporte de nouveaux défis à la communauté TCAD. En effet, de nos jours, les améliorations des performances des transistors ne sont plus simplement dû à une simple diminution des dimensions des dispositifs, mais aussi à l'introduction de boosters de technologies tels que des nouvelles architectures (FDSOI, trigate), des oxydes de grille à forte permittivité, l'ingénierie de la contrainte ou de nouveaux matériaux de canal (Ge, III-V). Pour faire face à tous ces nouveaux défis technologiques, la modélisation TCAD (Technology Computer Aided Design) est un outil puissant pour guider le développement mais aussi pour réduire les coûts. Dans ce contexte, ce travail de thèse vise à améliorer la modélisation TCAD pour les technologies 28/14 et 10FDSOI, avec une attention particulière sur les impacts des contraintes mécaniques sur leurs performances. Dans un premier temps, les différents mécanismes impactant la mobilité des technologies FDSOI ont été étudiés en détail. Les modèles implémentés dans des outils de simulations avancés (NEGF, Multi subbands Monte Carlo, Kubo-Greenwood) sont étudiés, comparés et des développements du logiciel interne à STMicroelectronics (UTOXPP) sont proposés. Dans un second temps, une approche « top down » a été mis en place. Elle consiste à calibrer les modèles TCAD empiriques non pas sur des mesures mais sur des outils de simulations avancés (Kubo-Greenwood). Les modèles TCAD calibrés montrent de très bons accords avec les mesures de mobilité (split-CV) en variant la température, la polarisation du substrat et l’épaisseur de l’IL (Interfacial layer). Dans un troisième temps, les méthodes utilisées lors de cette thèse pour modéliser les contraintes induites par le procédé de fabrications sont décrites. Enfin, la dernière partie concerne la modélisation TCAD des technologies 28 et 14FDSOI. Des simulations mécaniques sont effectuées pour modéliser les profils de contraintes dans les transistors. Des solutions pour optimiser la configuration des contraintes dans le canal pour ces technologies sont proposées. / The design of nanoscale CMOS devices brings new challenges to TCAD community. Indeed, nowadays, CMOS performances improvements are not simply due to device scaling but also to the introduction of new technology “boosters” such as new transistors architectures (FDSOI, trigate), high-k dielectric gate stacks, stress engineering or new channel material (Ge, III-V). To face all these new technological challenges, Technology Computer Aided Design (TCAD) is a powerful tool to guide the development of advanced technologies but also to reduce development time and cost. In this context, this PhD work aimed at improving the modeling for 28/14 and 10FDSOI technologies, with a particular attention on mechanical strain impacts. In the first section, a summary of the main models implemented in state of the art device simulators is performed. The limitations and assumptions of these models are highlighted and developments of the in-house STMicroelectronics KG solvers are discussed. In the second section, a “top down” approach has been set-up. It has consisted in using advanced physical-based solvers as a reference for TCAD empirical models calibration. Calibrated TCAD reproduced accurately split-CV mobility measurements varying the temperature, the back bias and the Interfacial Layer (IL) thickness. The third section deals with a description of the methodologies used during this thesis to model stress induced by the process flow. Simulations are compared to nanobeam diffraction (NBD) strain measurements. The use and calibration of available TCAD models to efficiently model the impact of stress on mobility in a large range of stress (up to 2GPa) is also discussed in this section. The last part deals with TCAD modeling of advanced CMOS devices for 28/14 and 10FDSOI technology development. Mechanical simulations are performed to model the stress profile in transistors and several solutions to optimize the stress configuration in sSOI and SiGe-based devices have been presented.

Die zuverlässige Berechnung der elektrischen Leitfähigkeit vieler Materialien aus ersten Prinzipien erfordert die Berücksichtigung der anharmonischen Gitterdynamik. Der ab initio Kubo-Greenwood (KG)-Ansatz, der die KG-Leitfähigkeitsformel und die ab initio-Molekulardynamik kombiniert, scheint vielversprechend zu sein, da er die Anharmonizität des Gitters auf natürliche Weise berücksichtigt. Seine Anwendung auf kristalline Materialien hat jedoch bisher nur wenig Beachtung gefunden. Diese Arbeit beschreibt den KG-Ansatz und stellt eine numerische Implementierung dieses Ansatzes für den harmonischen Kristall Si und den anharmonischen Kristall SnSe vor. Die Fallstudie für Si zeigt erhebliche numerische Schwierigkeiten bei den KG-Berechnungen auf. Insbesondere behindert die erforderliche dichte k-Punkt-Abtastung die Konvergenz in Superzellengröße und macht die Berechnungen nur innerhalb der (semi-)lokalen Dichtefunktionaltheorie (DFT) durchführbar. Außerdem führt die notwendige Einführung eines Verbreiterungsparameters (η) zu einer erheblichen Unsicherheit bei der Bestimmung der Leitfähigkeit. Um diese Probleme zu lösen, werden rechnerisch effiziente Strategien diskutiert, darunter: (i) der "Scherenoperator"-Ansatz zur Korrektur des DFT-Bandlückenproblems; (ii) das "Optimal-η-Schema" zur Wahl eines geeigneten Wertes von η; und (iii) die Finite-Size-Scaling-Methode zur Ableitung der Leitfähigkeit in der thermodynamischen Grenze. Es wird festgestellt, dass die KG-Berechnungen mit diesen Strategien Leitfähigkeiten in angemessener Übereinstimmung mit den Experimenten ergeben. Der Vergleich mit früheren ab initio Boltzmann-Transportberechnungen zeigt jedoch, dass das η-Problem und die Frage der Konvergenz in Superzellengröße weiter verbesserte Konzepte erfordern. Die Fallstudie für SnSe zeigt sehr ähnliche numerische Schwierigkeiten wie im Fall von Si. Es werden Einblicke in die Auswirkung der Anharmonizität auf die Konvergenz der Superzellengröße gegeben. / Reliable first-principles calculation of the electrical conductivity in many materials requires accounting for the anharmonic lattice dynamics. The ab initio Kubo-Greenwood (KG) approach, which combines the KG conductivity formula and ab initio molecular dynamics, appears to be promising because it naturally includes lattice anharmonicity. However, its application to crystalline materials has so far received very little attention. This thesis describes the KG approach and presents a numerical implementation of this approach for the harmonic crystal Si and the anharmonic crystal SnSe. The case study for Si identifies considerable numerical difficulties in the KG calculations. In particular, the dense k-point sampling required hinders supercell-size convergence and makes the calculations only feasible within (semi)local density-functional theory (DFT). Besides, the necessary introduction of a broadening parameter (η) introduces a significant uncertainty in determining the conductivity. To address these issues, computationally efficient strategies are discussed, including: (i) the "scissor operator" approach to correct the DFT band-gap problem; (ii) the "optimal-η scheme" to choose an appropriate value of η; and (iii) the finite-size scaling method to deduce the conductivity in the thermodynamic limit. It is found that with these strategies, the KG calculations yield conductivities in reasonable agreement with experiment. Yet, comparison with previous ab initio Boltzmann transport calculations shows that the η problem and the issue of supercell-size convergence still require improved concepts. The case study for SnSe shows very similar numerical difficulties as in the case of Si. Insights into the effect of anharmonicity on the supercell-size convergence are provided.

Thesis (D. Min.)--Covenant Theological Seminary, 2005. / Abstract. Includes bibliographical references (leaves 154-160).

Thesis (D. Min.)--Covenant Theological Seminary, 2005. / Abstract. Includes bibliographical references (leaves 154-160).

As the foundation for a new computational implementation, we survey the calculation of the complex electrical conductivity tensor based on the Kubo-Greenwood (KG) formalism (Kubo, 1957; Greenwood, 1958), with emphasis on derivations and technical aspects pertinent to use of projector augmented wave datasets with plane wave basis sets (BIlichl, 1994). New analytical results and a full implementation of the KG approach in an open-source Fortran 90 post-processing code for use with Quantum Espresso (Giannozzi et al., 2009) are presented. Named KGEC ([K]ubo [G]reenwood [E]lectronic [C]onductivity), the code calculates the full complex conductivity tensor (not just the average trace). It supports use of either the original KG formula or the popular one approximated in terms of a Dirac delta function. It provides both Gaussian and Lorentzian representations of the Dirac delta function (though the Lorentzian is preferable on basic grounds). KGEC provides decomposition of the conductivity into intra- and inter band contributions as well as degenerate state contributions. It calculates the dc conductivity tensor directly. It is MPI parallelized over k-points, bands, and plane waves, with an option to recover the plane wave processes for their use in band parallelization as well. It is designed to provide rapid convergence with respect to k-point density. Examples of its use are given.

This paper investigates the effect of financial development on income inequality in 20 African countries. Theory and a growing number of empirical studies suggest that the former exerts a negative impact on the latter by enabling low-income holders to undertake income-enhancing education and business investments, thereby promoting a tighter income distribution. However, using the share of GDP constituted by domestic credit to the private sector and broad money respectively as proxies for financial development, the results of this study fail to give significant evidence of this income-equalising effect. Given the heterogeneous nature of the economies studied here and the fact that data quality and quantity improve over time, it is believed that country-specific studies and future research can offer more conclusive results on how financial development influences income distribution in the African context. This would also provide a stronger foundation for policy recommendations in the continent’s plight to address the persistent high levels of income inequality.