Characterization and modeling of frequency dispersion in RF LDMOS transistors

This paper characterises the effects of frequency dispersion in laterally diffused metal-oxide semiconductor (LDMOS) from pulsed-S-parameter measurements. Using the calculated high-frequency drain current from measured data, we demonstrate that length of the lightly doped drain extension is directly proportional to the amount of current collapse at high frequency. To capture the frequency dispersion in a nonlinear model, a frequency-domain mapping is proposed to augment quasi-static nonlinear electrothermal models. The importance of including the dispersiveness is demonstrated through comparing a standard quasi-static model, the newly augmented model, and on-wafer load-pull measurements. For a 5-mm, 500 μm unit-gate-width transistor, we demonstrate that the quasi-static model over predicts the drain efficiency during large signal drive at P
_3dB
by 9%. The new augmented model is able to predict the efficiency within 2% of the measured value.