Highly Tunable High-Q Inversion-Mode MOS Varactor in the 1–325-GHz Band

This article presents the design, experimental results, and modeling of an inversion-mode CMOS varactor integrated in the STMicroelectronics 55-nm BiCMOS technology. The device was characterized from 1 to 325 GHz, demonstrating high-quality factor at millimeter-waves. For instance, a quality factor of 7 at around 190 GHz for a tuning ratio (C_max/C_min) greater than 4 was measured. This performance overpasses that of accumulation-mode varactors usually provided in CMOS technologies design kits, for frequencies beyond about 100 GHz. In addition, a smallsignal electrical model is provided from 100 to 250 GHz.