TABLE OF CONTENTS Alexander A. Demkov,
Department of Physics, The University of Texas at Austin,
Austin, TX 78712, . USA e-mail: demkov@physics.utexas.edu
Abstract Density functional theory has proved to be a useful tool in device engineering, particularly at nanoscale and when novel materials are involved. In this chapter we briefly introduce the theoretical background necessary for understanding the modern theory of solid state and review recent theoretical results in the area of advanced gate stack materials engineering.
As scaling of the complementary metal oxide semiconductor (CMOS) technology takes us below 65 nm many new materials, traditionally not associated with the semiconductor process, are being introduced into manufacturing. Notably, transition metal (TM) oxides or more generally dielectrics with a high dielectric constant or high-fc dielectrics are being considered for the gate stack applications instead of SiO 2. The gate stack is a multilayer structure in place of the metal oxide semiconductor capacitor (see Fig. 7.1). Its capacitance controls the saturation current and has been traditionally maintained by reducing its thickness in accord with the gate length reduction (the so-called scalin at the heart of Moor's law). However, after reaching the oxide thickness of 12 A the scaling has more or less stopped due to the prohibitively large gate leakage current caused by direct tunneling across the gate oxide. Thus a new dielectric with a larger dielectric constant has to be introduced. After the introduction of Cu this is arguably the most drastic departure from the traditional CMOS process. The...
