TABLE OF CONTENTS A complete MOS transistor is formed by adding two more terminals to the basic MOS structure of Chap. 2 to contact two opposite ends of the inversion layer. Through these terminals a potential difference can be applied across the inversion layer and a current can be caused to flow in it. A number of phenomena can then be observed, some directly associated with the current flow, some not. It is not convenient to introduce all these phenomena when they are present simultaneously. Some of these, specifically the ones not directly associated with current flow, can best be isolated and studied by themselves by means of a structure simpler than the MOS transistor, which we call a three-terminal MOS structure. This structure is formed by contacting the inversion layer of the basic MOS structure at only one end. We will study the changes that take place in the charges and the potential distribution of the three-terminal structure, caused by the application of an external voltage between this new terminal and the substrate. By the end of this short chapter, we will have all the facts necessary for a careful and convenient look at the MOS transistor, which will be the subject of all succeeding chapters.
Assume that an n + region is added to the basic MOS two-terminal structure, so that the structure shown in Fig. 3.1a is obtained; a constant V GB will be assumed until further notice. Consider the
