Modeling of the MOSFET inversion charge and drain current, in moderate inversion

The widespread use of MOS technology in analog circuit design demands a precise and efficient circuit simulation model of the MOS transistor valid in all regions of inversion. Currently available circuit simulation models fail in the intermediate range of gate voltages, known as the moderate inversion region. Expressions characterizing the large-signal behavior of the long-channel MOS transistor in the moderate inversion region are derived. The correct dependencies on all the physical and process parameters are preserved by a careful approximation to the physical equations, based on the charge sheet assumption. Another goal is to develop expressions that treat the moderate inversion as a small, voltage-dependent correction to currently existing simplified models. This approach should allow a simple modification of the existing circuit simulation models to improve the accuracy in moderate inversion. The model was compared with a numerical charge sheet model and with experimental measurements of a long-channel, ion-implanted NMOS transistor. The expressions could serve as a basis for a comprehensive MOSFET circuit simulation model