Analysis on the effect of parallel current path on the quality factor of CMOS spiral inductors for 1-10 GHz

A structure of spiral inductor having a parallel current path through the branch of the metal strip was designed to achieve a quality (Q) factor enhancement compatible with conventional CMOS and/or established SiGe process in RF and microwave arena. The Q factor enhanced by 12% was quantitatively analyzed with a lumped-element model and its origin was investigated at a structural point of view. As a result we noted that the parallel-branching structure greatly reduced the series resistance of the inductor at a high frequency range of GHz by suppressing current crowding and in turn enhanced the Q factor beyond the additional parasitic capacitance.