ABSTRACT
This chapter reviews the structure and characteristics of MOSFETs. The dc current-voltage characteristics of planar long-channel MOSFETs are derived by considering the device physics of MOS capacitors, three-terminal MOS structures (i.e., gated diodes), and finally, four-terminal MOSFETs. The surface conditions on the semiconductor side of a MOS capacitor are classified as accumulation, flat band, depletion, weak inversion, and strong inversion. The channel of a MOSFET is an inversion layer formed on the surface of the semiconductor substrate by applying gate voltage. The degree of inversion at the substrate surface increases as the gate voltage is increased, whereas the degree of inversion decreases as the channel potential is increased. In the nonsaturation region, the entire channel between the source and drain is strongly inverted, but in the saturation region, the channel near the drain is pinched off and weakly inverted. The MOSFET scaling law served as a powerful guiding principle for the development of MOSFETs and integrated circuits.
