83
3
Metal-Oxide-Semiconductor System
3.1 Introduction
The metal-oxide-semiconductor (MOS) structure, commonly referred to as
the MOS capacitor, is a two-terminal device with one electrode connected
to the metal and the other electrode connected to the semiconductor, forming a voltage-dependent capacitor. The acronym MOS is used even if the top
electrode is not a metal and the insulator is not an oxide. An MOS capacitor is a very useful device both for evaluating the MOS integrated circuit
(IC)–fabrication process and for predicting the MOS transistor performance.
Therefore, MOS capacitors are included in the test chip for IC process and
device characterization.
The MOS capacitor systems have been the subject of numerous investigations and the detailed description of the early development can be found in
the literature [1]. The major objective of this chapter is to build the foundation
for the development of MOS transistor theory and models that will be used
in Chapters 4, 5, and 9. In order to achieve our objective, we first discuss the
behavior of an MOS capacitor system and then develop the charge-voltage
(Q–V) and capacitance-voltage (C–V) relationships, which will be used later
in the development of MOS transistor model.
3.2 MOS Capacitor at Equilibrium
In order to describe the basic performance of MOS capacitor system, let us
consider the two-dimensional (2D) cross section of an ideal MOS capacitor shown in Figure 3.1. The structure includes a p- or n-type semiconductor substrate such as silicon, a dielectric layer such as silicon dioxide
(SiO 2 ), a metal or polysilicon gate, a gate electrode (G), and a body (back or
bulk) electrode (B) for operating the MOS capacitor system at the intended
applied bias V g and V b . Typically, the SiO 2 layer is thermally grown on silicon substrate with a typical thickness between 10 and 100 nm. The gate
3
Metal-Oxide-Semiconductor System
3.1 Introduction
The metal-oxide-semiconductor (MOS) structure, commonly referred to as
the MOS capacitor, is a two-terminal device with one electrode connected
to the metal and the other electrode connected to the semiconductor, forming a voltage-dependent capacitor. The acronym MOS is used even if the top
electrode is not a metal and the insulator is not an oxide. An MOS capacitor is a very useful device both for evaluating the MOS integrated circuit
(IC)–fabrication process and for predicting the MOS transistor performance.
Therefore, MOS capacitors are included in the test chip for IC process and
device characterization.
The MOS capacitor systems have been the subject of numerous investigations and the detailed description of the early development can be found in
the literature [1]. The major objective of this chapter is to build the foundation
for the development of MOS transistor theory and models that will be used
in Chapters 4, 5, and 9. In order to achieve our objective, we first discuss the
behavior of an MOS capacitor system and then develop the charge-voltage
(Q–V) and capacitance-voltage (C–V) relationships, which will be used later
in the development of MOS transistor model.
3.2 MOS Capacitor at Equilibrium
In order to describe the basic performance of MOS capacitor system, let us
consider the two-dimensional (2D) cross section of an ideal MOS capacitor shown in Figure 3.1. The structure includes a p- or n-type semiconductor substrate such as silicon, a dielectric layer such as silicon dioxide
(SiO 2 ), a metal or polysilicon gate, a gate electrode (G), and a body (back or
bulk) electrode (B) for operating the MOS capacitor system at the intended
applied bias V g and V b . Typically, the SiO 2 layer is thermally grown on silicon substrate with a typical thickness between 10 and 100 nm. The gate