Design of Novel High-$Q$-Factor Multipath Stacked On-Chip Spiral Inductors

High-
$Q$
-factor and small-occupying-area inductors are prerequisite for monolithic-microwave integrated-circuit applications. This paper presents a novel multipath crossover-interconnection octagon stacked spiral inductor which is fabricated with the 0.13-
$\mu\hbox{m}$
SiGe BiCMOS process. The metal wire of the spiral inductor is divided into multiple paths according to the process rule and the depth of the skin effects at the response frequency. The width of a single path is typically less than or equal to the skin depth. This so-called multipath technique effectively depresses the proximity and skin effects, therefore contributing to the high
$Q$
-factor of the inductors and reducing the occupying area. The crossover-interconnection method can make the total path lengths approximately equal to each other. This connected way lowers the current-crowding effect, which also enhances the
$Q$
-factor. Using the proposed technique, we have observed up to 63.8% improvement in the
$Q$
-peak (2.3 GHz) as compared to conventional stacked inductors (1.5 GHz) and about 44% improvement in the occupying area as compared to conventional single inductors fabricated on silicon substrates.