Scaling of characteristic frequencies in RF CMOS

Device simulation of the 180-, 90-, and 65-nm CMOS generations shows that in NMOSTs, the cut-off frequency f_T and the maximum oscillation frequency f_max are roughly inversely proportional to the gate length. The voltage-gain bandwidth f_A depends only weakly on the gate length. At 40-nm gate length, f_T values of 300 GHz are predicted. For small values of the drain and source contact resistance (<10^-8 Ω·cm²), f_T can only be improved by a further reduction of the gate length. The f_max values (for zero gate resistance higher than f_T) degrade strongly with increasing gate resistance. Simple approximate formulas for the dependence of f_T and f_A on the contact resistances are presented.