Design of Components and Circuits Underneath Integrated Inductors

In this paper, we present a study of the eddy current effect of devices placed underneath and inside an on-chip inductor. We verified the performance of such area-saving structures through electromagnetic (EM) simulations and measurement of test structures. We used layout techniques to minimize eddy current loss and magnetic coupling between the devices and the inductor, and constructed a complete voltage-controlled oscillator (VCO) inside an inductor. Measurement results show that this compact VCO has an equal performance in phase noise and output power as compared to a traditional VCO while reducing the area by about 50%. The techniques presented in this paper are general and can be implemented in most layouts without extra post-processing steps.