Modeling and Characterization of Spiral Inductors based on a Standard Silicon Technology

In this paper a new design approach for silicon, on-chip spiral inductors is proposed, which extensively uses the results of an electromagnetic simulator. To this purpose, a numerical solver of the Maxwell's equations, based on the Finite Difference Time Domain (FDTD) method, has been adopted. Exploiting the geometrical flexibility of the solver, very complicated structures can be modeled such as: single- and multi-layer windings as well as inductors with grounded shields of different shapes. Moreover, the proposed approach accounts for a rigorous treatment of metal and substrate losses. To check the accuracy of the simulator, several test structures of different geometries have actually been fabricated, adopting a standard, 0.35um CMOS silicon technology. The comparison between experiments and simulated results shows that the inductor performance are correctly predicted by the proposed methodology. Finally, an automatic procedure has been developed for the extraction of equivalent-circuit models that easily plug into the RF IC design flow.