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. Circuit simulation models currently available fail in the intermediate range of gate voltages, known as the moderate inversion region, which becomes increasingly important with the reduction of power supply voltages. New expressions characterizing the large-signal behavior of the long-channel MOS transistor in the moderate inversion region are derived in this work. We attempt to preserve the correct dependencies on all the physical and process parameters 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. It seems that the new expressions could serve as a basis for a comprehensive MOSFET circuit simulation model. © 1990 IEEE