1. Introduction

The International Technology Roadmap for Semiconductors [6] is an indicator, where the industry is now and where it should go to keep up in the race for technological progress. Now, after four decades of constant improvement, predicted by the ITRS, we are at the introduction of the $32\,\mathrm{nm}$ node[7,8]. The development for the following $22\,\mathrm{nm}$ node has started and will be even more demanding than the nodes before [6,9].

Depending on the gate stack of the field-effect transistor many different applications can be realized, for instance, the well known transducer which amplifies electrical signals (starting with silicon dioxide as gate oxide due to its excellent interface properties [10] and shifting now to high-k dielectric materials due to scaling issues [8,11]). However, today's probably most important application as a switch enables incredible complex digital devices like modern CPUs [12,13], PDAs, mobile phones, mp3-players, cameras etc. By storing charge in the gate stack one is able to facilitate cheap, robust, high density, commodity storage like memory cards (CF^TM, SD^TM, Memory Stick^TM, XD^TM etc.) or solid-state disk for all kinds of portable devices, thus, enabling application areas and designs which were impossible some years ago. Even though the concept of flash memory is very popular today, in future due to scaling limits alternative concepts will be needed (FeRAM,MRAM,PCRAM,RRAM [14,15]). There are new applications emerging, extending the field of established electrical engineering. Exchanging the polysilicon/metal gate structure with a biofunctionalized gate oxide surface, the realization of various biochemical sensors is feasible, starting with a simple pH sensor [16] for a native gate oxide, spanning over to detecting DNA snippets with DNAFETs [17].

In this work I study some selected gate stacks with emphasis on the engineering and modeling point of view. In Chapter $2$ there is a general overview regarding the different types of gate stacks in use. Also the working principle and the most important properties of these devices are examined. Chapter $3$ reviews strain-influenced gate stacks and how they can be exploited to change the band structure in order to boost the transport. The k.p method is used for this purpose. Chapter $4$ specializes on the electrolytic gate stacks and their mathematical description combined with simulation results. Chapter $5$ provides a summary and a conclusion.