MOS Device Physics.pdf

MOS device physics is reviewed, focusing on aspects relevant to analog circuit designers, with an emphasis on separating first-order from higher-order phenomena. The history of field-effect transistors is discussed, including early attempts by Julius Lilienfeld and William Shockley, and the development of the first practical semiconductor amplifier, the point-contact bipolar transistor. The junction FET (JFET) and MOSFET are described, with the MOSFET being the preferred device for integrated circuits due to its simple fabrication and high density potential. The basic idea of a FET is to modulate the resistance between two terminals using a third terminal, the gate. The operation of JFETs and MOSFETs is explained, including the concept of depletion-mode and enhancement-mode devices. The long channel approximation is introduced, assuming a low electric field, and the behavior of short channel devices is discussed. The physics of MOSFETs is described, including the formation of an inversion layer and the creation of a conductive path between the source and drain.