Fundamentals of Microelectronics, 2nd Edition

Physics of MOS Transistors

Today’s field of microelectronics is dominated by a type of device called the metal-oxide-semiconductor field-effect transistor (MOSFET). Conceived in the 1930s but first realized in the 1960s, MOSFETs (also called MOS devices) offer unique properties that have led to the revolution of the semiconductor industry. This revolution has culminated in microprocessors having 100 million transistors, memory chips containing billions of transistors, and sophisticated communication circuits providing tremendous signal processing capability.

Our treatment of MOS devices and circuits follows the same procedure as that taken in Chapters 2 and 3 for pn junctions. In this chapter, we analyze the structure and operation of MOSFETs, seeking models that prove useful in circuit design. In Chapter 7, we utilize the models to study MOS amplifier topologies. The outline below illustrates the sequence of concepts covered in this chapter.

6.1   STRUCTURE OF MOSFET

Recall from Chapter 5 that any voltage-controlled current source can provide signal amplification. MOSFETs also behave as such controlled sources but their characteristics are different from those of bipolar transistors.

In order to arrive at the structure of the MOSFET, we begin with a simple geometry consisting of ...