Comparison of microwave inductors fabricated on silicon-on-sapphire and bulk silicon

Inductors are important elements of microwave circuits that frequently require high self-resonant frequencies and high quality factors. In this work, circular spiral inductors fabricated on silicon-on-sapphire (SOS) and bulk silicon are compared. Due to the low-loss dielectric substrate, SOS inductors showed both higher self-resonant frequencies and higher quality factors than those fabricated on bulk silicon. Small-signal models extracted for the inductors confirm that the degradation of the inductor characteristics in bulk silicon stems from losses in the substrate.