High- ${Q}$ Inductors Utilizing Thick Metals and Dense-Tapered Spirals

Ultra-thick metals are known to be counter productive for quality factor (Q) improvement at high frequencies in multiturn inductors. From the experimental results, assisted by electromagnetic simulations, it is first shown that Q improvement with ultra-thick metals can be pushed to higher frequencies using variable width and spaced (tapered) spirals. Furthermore, it is also shown that the extent of tapering is proportional to the metal thickness for the highest performance. Second, dense-tapered layouts are shown to be good candidates for higher Q rather than hollow ones for a given inductance density.