Compact Modeling of Lateral Nonuniform Doping in High-Voltage MOSFETs

This paper reports on the detailed analysis and modeling of lateral nonuniform doping present in intrinsic MOS channel of high-voltage (HV) MOSFETs, e.g., vertical (VDMOS) and lateral diffused MOS (LDMOS). It is shown that conventional long-channel MOSFET models using uniform lateral doping can never correctly model the capacitance behavior of these devices. A new analytical compact model for lateral nonuniformly doped MOSFET is reported. The intrinsic nonuniformly doped MOS model is first validated on numerical simulation and then on measured characteristics of VDMOS and LDMOS transistors including the drift region. The model shows good results in the dc and, most importantly, in the ac regime, especially in simulating the peaks on C_GD, C_GS, and C_GG capacitances. This new model improves the accuracy of HV MOS models, especially output characteristics and during transient response (i.e., amplitude and position of peaks, as well as slope of capacitances).