Compact Modeling and Circuit Impact of a Novel Frequency Dependence of Capacitance in RF MOSFETs

The exploration and modeling of high-frequency MOSFET phenomena are vitally important because MOSFETs are emerging as candidates for active devices in front-end RF circuits operating at more than 1GHz [1-2]. In this work we present a novel frequency-dependecnce of MOSFET capacitance, predicted in numerical device simulation and observed in measurements. Hitherto unobserved and unexplained, the phenomenon includes a drop in CBG (and CGG) with frequency in the accumulation regime, and changes in the weak-inversion regime. This behaviour is explained with the help of finite substrate resistance and non-quasi-static effects. Conventional quasi-static MOSFET compact models do not replicate the frequency dependence; a non-quasi-static MOSFET model developed in Motorola successfully models the frequency dependence of capacitance components. This model is used to demonstrate the impact of the novel frequency-dependence in simple RF-circuits