Compact models, which describe the electrical behavior of the passive and active devices on a chip, are the fundamental link between circuit designers and foundries. Compact models allow simulation of the circuit functionality before its fabrication, thus saving time and money. In CMOS technologies, the MOS transistor is the principal component; consequently, its model plays a decisive role in the analysis and design of integrated circuits.

Early compact MOSFET models rely on approximate solutions that are valid only in particular regions of operation, which are connected mathematically by smoothing functions. Because the threshold of strong inversion VT is the key parameter in these regional models, they are also called VT-based models. This regional approach leads to inaccuracy between regions and, consequently, this class of models is not accurate enough to represent the moderate-inversion region. To overcome the limitations of VT-based MOSFET models, a new class of models emerged, namely inversion-charge-based and surface-potential-based models.

This chapter provides an overview of the approaches taken by the developers of MOSFET models. After a brief review of VT-based MOSFET models, we present a summary of some fundamental properties of advanced MOSFET models.

The accuracy of the transistor characteristics depends not only on an appropriate device model but also on the accuracy of its fundamental parameters. To complete the chapter we describe some procedures to extract fundamental parameters of MOSFET models, in particular those used in this textbook as design parameters.