RF Planar Ferromagnetic Inductors on Silicon

Abstract

Two-port coplanar ferromagnetic inductors using solid magnetic planes were fabricated on silicon. L, R, and Q measurements are presented. Cutoff frequencies exceed 10 GHz, indicating no capacitance limitation. The increase in L over the air-core value is /spl sim/15%, and the quality factor Q is of /spl sim/10 up to 1.5 GHz. The inductance scales with HA-alignment and spiral excitation ratio. Agreement with High-Frequency Structure Simulator simulations including ferromagnetic resonance led to a better understanding in terms of L and Q. Current increase in L is limited by the film thickness (0.2 /spl mu/m). Thicker films (0.5-1 /spl mu/m) would lead to larger gain over L (23% to 31%) with similar Q (/spl sim/10). The restriction in Q from the air-core inductor consists in magnetic losses but not only. Another contribution would come from anomalous ohmic losses from the spiral itself enhanced by the proximity of the magnetic planes.