TABLE OF CONTENTS The metal-oxide-semiconductor (MOS) structure is the basis of CMOS technology. The Si-SiO 2 MOS system has been studied extensively (Nicollian and Brews, 1982) because it is directly related to most planar devices and integrated circuits. In this section, we review the fundamental properties of MOS capacitors and the basic equations that govern their operation. The effects of charges in the oxide layer and at the oxide-silicon interface are discussed in Section 2.3.6.
The cross section of an MOS capacitor is shown in Fig. 2.21. It consists of a conducting gate electrode (metal or heavily doped polysilicon) on top of a thin layer of silicon dioxide grown on a silicon substrate. The energy-band diagrams of the three components are shown in Fig. 2.22. Silicon dioxide is an insulator with a large energy gap in the range of 8 9 eV. It is convenient to relate the band structures of all three materials to a common reference potential, the vacuum level. The vacuum level is defined as the energy level at which the electron is free, i.e., no longer bonded to the lattice. In silicon, the vacuum level is 4.05 eV above the conduction band, as shown in Fig. 2.22. In other words, an electron at the conduction-band edge must gain a kinetic energy of 4.05 eV (called the electron affinity, ?) in order to break loose from the crystal...
