New Fundamental Insights Into Capacitance Modeling of Laterally Nonuniform MOS Devices

Abstract—In compact transistor modeling for circuit simula-tion, the capacitances of conventional MOS devices are commonly determined as the derivatives of terminal charges, which in their turn are obtained from the so-called Ward–Dutton charge partitioning scheme. For devices with a laterally nonuniform channel doping profile, however, it is shown in this paper that no terminal charges exist from which the capacitances can be derived. Instead, for such devices, a new model is presented for the capacitances themselves. Furthermore, a method is given to incor-porate such a capacitance model into circuit simulators, which are traditionally based on terminal charge models. Comparison with two-dimensional device simulations and a segmentation model shows that for a constant mobility, the new capacitance model provides an accurate description for a MOSFET with a laterally diffused channel doping profile. Through a comparison with high-frequency measurements, the agreement between model and experimental results is discussed. Index Terms—Charge partitioning, diffused doping, integrated circuit design, lateral double-diffused MOS (LDMOS), modeling. I