I would like to express my deep gratitude to a number of people and organizations who supported me during my work on this dissertation which would not have been possible - at least not on this level - without their help and challenge.
Prof. Siegfried Selberherr has not only provided me with one of the best working environments a student can ever dream of, he also knew to ensure the right combination of guidance and freedom. I am also indebted to Prof. Erich Gornik who agreed to take part in the examining commitee at a very short notice.
I would like to thank the people of AMS, Austria, for their collaboration and support at many occasions. Furthermore, I want to thank Prof. Christer Svensson of the IFM of the University of Linköping, Sweden, and Dake Liu for sharing their extensive knowledge about VLSI circuits and ultra-low-power techniques with me, and I want to express my appreciation to Hiroo Masuda of the Hitachi Device Development Center in Tokyo, Japan, and to his group not only for the opportunity to learn a lot about semiconductors, but also for cultural engagement and for their friendship. I am also very grateful to Vivek De and his group and to Richard Green of Intel, who made it possible for me to learn a lot about high-performance device structures, and to appreciate the American type of working environment.
I also wish to thank my colleagues at the Institute for Microelectronics for their support and patience. And I want to thank ``my'' master's students for delivering useful products, most notably Andi Stach, the author of MINISIM.
Last, but certainly not least I want to thank my family and my friends, among them Stefan Halama and Horst Steiner, without whom I would never have been able to achieve so much. Their encouragement, wit, and sense of humor let me always attain more than I had anticipated.