Multi-layer spiral inductor design for monolithic DC-DC converters

This paper discusses ideas for integrating inductors using standard CMOS process to be used in monolithic DC-DC converters. A circuit model for single-layer planar, spiral inductor is presented. Expressions to compute each element in this model are described. Estimates of performance from these expressions and from the simulation results using a field solver is compared to validate the circuit model of the single-layer spiral. Selection of the geometric parameters of the spiral, based on the simulation results, is discussed. Further, the single-layer circuit model is extended to model the multilayer spiral inductor by using valid approximations. Feasibility of multi-layer spiral inductor is discussed. Better alternatives for single-layer spiral inductor are identified.