Frequency-dependent resistive and capacitive components in RF MOSFETs

It is found from measured high frequency (HF) s-parameter data that the ext racted effective gate sheet resistance (R-gsh), effective gate unit-area ca pacitance (C-gg,C-unit), and transconductance (G(m)) in radio-frequency (RF ) MOSFETs show strong frequency dependency when the device operates at freq uencies higher than some critical frequency. As frequency increases, R-gsh increases but C-gg,C-unit and G(m) decrease. This behavior is different fro m what we have observed in low or medium frequencies, at which these compon ents are constant over a frequency range, This phenomenon has been observed in MOSFETs with L-f longer than 0.35 mum at frequency higher than 1 GHz, a nd becomes more serious as L-f is longer and frequency is higher. This beha vior can be explained by a MOSFET model considering Non-Quasi-Static (NQS) effect. Simulation results show that a RF model based on BSIM3v3 with NQS e ffect describes well the behaviors of both real and imaginary parts of Y-21 of the device with strong NQS effect even though its fitting to Y-11 needs to be improved further.