TABLE OF CONTENTS The metal-oxide-semiconductor (MOS) structure is the core of the MOS technology. The two-terminal structure is called the MOS capacitor and as a stand-alone device it plays a fundamental role in technology characterization and parameter extraction. Also, it is sometimes used as a circuit element to implement a varactor. Important as they are, these uses are not the subject of this chapter. Here, we will focus on the operation of the MOS capacitor as the core of the transistor (four-terminal device). The two- and three-terminal MOS structures are presented.
Because it forms the basis of MOS compact models, the equivalent capacitive circuit of the MOS structure is carefully derived. A rigorous definition of pinch-off based on charge is given. This chapter includes a thorough treatment of the unified charge control model (UCCM), which is at the center of the so-called charge-based models.
The first step in the development of a model for the current or the charges in a semiconductor device is the calculation of the carrier concentrations in the device. The interest in the equilibrium condition derives from the fact that it not only serves as a reference state, but often semiconductor devices can be considered to be operating in a quasi-equilibrium regime.
In equilibrium (also referred to as thermal or thermodynamic equilibrium) electrons and holes in an ideal crystalline semiconductor behave as ideal gases if the doping concentrations are not too high (typically of the order of 10 19 cm -3
