Frequency-dependent resistive and capacitive components in RF MOSFETs

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