0.13-μm RF CMOS and varactors performance optimization by multiple gate layouts

0.13-μm radio frequency (RF) CMOS devices with multifinger gate structure have been fabricated by the standard logic process, and the measured effective gate-length is 80 nm. Extensive RF characterization has been done to obtain cutoff frequency (f_T), associated power gain cutoff frequency (f_max), minimum noise figure (NF_min), output power (P_out), and power added efficiency (PAE) for RF circuit design and to explore the optimized gate layout in terms of the extracted RF device parameters. Our important finding to be reported in this paper is that an optimized unit finger width (W_F) exists by trade-off among f_T, f_max, NF_min, P_out, and PAE. Under fixed total width to achieve the same current drivability (I_ds), the smaller W_F and the larger finger number (N_F) leads to higher f_max but lower f_T due to trade-off between gate resistance (R_g) and parasitic gate capacitance. As for NF_min complicated by f_T and R_g, counter-balance between parasitic gate capacitance and R_g leads to nearly constant NF_min w.r.t. various splits of (W_F,N_F). Regarding P_out and PAE, W_F of 4 μm and N_F of 18 is the optimized layout parameter, which offers the maximum P_out of around 11 dBm and PAE of 30.5% at 5.8 GHz. The performances of accumulation-mode MOS varactors with different gate layout structures are also investigated in this report. Since the same area varactors with different gate layout may result in different parasitic resistance and fringing capacitance, which will affect the capacitance tuning range and the associated Q-factor. The maximum Q-factor is about 59 of the 120 μm² gate area varactor, and its tuning range is from 210 fF to 1.64 pF, where the maximum C_max/C_min ratio is about 7.8.