Characterization of MOS Varactors in 40 nm CMOS Technology at 77 K and 4 K

In this work the characterization of MOS varactors are performed by using three testkeys fabricated in tsmc 40-nm CMOS technology. We investigate the characteristics of MOS varactors at cryogenic temperatures as well as at room temperature for comparisons. The comparisons of varactor capacitances and Q factors at 300 K, 77 K, and 4 K are given. The capacitance of varactors and other parasitic parameters were extracted by using on-wafer de-embedding skill. Based on the observations from the simulation and the measurement data, equivalent circuit models are also proposed. These equivalent circuit models aim to properly represent the RF behavior of varactors at cryogenic temperatures for RF oscillator design applications.