1. Basic principle and structures of MOS transistors

1.1 Field effect

• The operating principle of a MOS (Metal-Oxide-Semiconductor) transistor is based on the "field effect", which consists in electrostatically modulating a density of mobile charges in a semiconductor. This modulation is caused by an electric field perpendicular to the direction of movement of these charges, and acting between two electrodes separated by a dielectric, as in a planar capacitor.

Figure 1 illustrates the field effect in a schematic MOS transistor:

• One of the electrodes (grid G) controls the intensity of the electric field and consequently the density of mobile...