Frequency-Independent Asymmetric Double- pi Equivalent Circuit for On-Chip Spiral Inductors: Physics-Based Modeling and Parameter Extraction

We present a frequency-independent compact model for silicon on-chip spiral inductors with an asymmetric double-pi equivalent circuit incorporating high-order parasitics such as skin effect and proximity effect. A set of partition factors for parameter ratios between the input and output segments has been introduced and derived from physical analysis to characterize the non-symmetrical feature of the inductor. A novel approach to extracting the model parameters is also developed based on measured S-parameters. As demonstrated for a series of inductors with different geometries fabricated by 0.18-mum CMOS process, the partition factors derived from the physical model are consistent with the extracted parameters, and the model can simulate precisely the inductor characteristics including the asymmetric admittances over a wide frequency rang beyond the self-resonant frequency without fitting parameters