A Study of Gate/Source-terminated Field-Plate NMOS Transistors and Its application in Switch Design

We have systematically studied the microwave noise, power, and linearity characteristics of field-plate (FP) 0.13-mum CMOS transistors in which the field-plate are separately connected to the gate and source terminals. The gate-terminated FP NMOS (FP-G NMOS) provided the best minimum noise figure (NF_min) at 6 GHz compared to standard device and source- terminated FP device (FP-S NMOS) owing to the lowest gate resistance (R_g) can be obtained in this structure. By adopting FP metal in NMOS, both FP-S and FP-G devices achieved higher current density at high gate bias voltages; besides, they also demonstrated higher efficiency under high drain-to-source voltages at high input power swing. The third-order inter- modulation product (IM3) is -39.4 dB for FP-S NMOS for P_in=-20 dBm; the corresponding values for FP-G and standard devices are -34.9 and -37.3 dB, respectively. These experimental results indicated that the FP-G architecture is suitable for low noise applications and FP-S is more effective at high power and high linearity operation. Finally, a 24 GHz T/R switch was designed and fabricated by using FP-S NMOSs for achieving good ability of isolation and harmonics rejection ratio.