Modeling of the Impurity-Gradient Effect in High-Voltage Laterally Diffused MOSFETs

MOSFET capacitance values in high-voltage laterally diffused MOSFETs, including the channel impurity concentration, which tails off along the channel from the source side to the drain side, are investigated. This pertinent doping inhomogeneity of the intrinsic MOSFET channel induces an additional electrostatic contribution to the amount of internal charges. With an emphasis on the deviations from homogeneous impurity-profile settings, the additional contribution was formulated within the framework of compact MOSFET models based on the surface-potential description. The developed capacitance-model enhancement requires a solution for the drain-side potentials at two uniform impurity concentrations, each of which corresponds to the source-side and the drain-side concentration of the impurity profile with gradient, respectively. The developed approach is found successful for all drain-source voltages, where the resulting high-voltage MOSFET-specific features are observed.