Characterization and Modeling of RF-Performance $(f_{T})$ Fluctuation in MOSFETs

The fluctuation of RF performance (particularly for f_T: cutoff frequency) in the transistors fabricated by 90-nm CMOS technology has been investigated. The modeling for f_T fluctuation is well fitted with the measurement data within approximately 1% error. Low-V_t transistors (fabricated by lower doping concentration in the channel) show higher f_T fluctuation than normal transistors. Such a higher f_T fluctuation results from C_gg (total gate capacitance) variation rather than g_m variation. More detailed analysis shows that C_gs + C_gb (charges in the channel and the bulk) are predominant factors over C_gd (charges in LDD/halo region) to determine C_gg fluctuation.