Q-enhancement of spiral inductor with N/sup +/-diffusion patterned ground shields

This paper discusses the quality factor enhancement by employing different patterned ground shields underneath the simple spiral inductor in a commercial BiCMOS technology. The effectiveness of the patterned ground shield technique depends heavily on the counter-effects between the reduction of substrate loss and the increase of parasitic capacitance. With proper choice of the shielding layer, the quality factor can achieve 21% enhancement for a 5-nH spiral inductor. The n/sup +/-diffusion layer is found to be the most effective layer for the patterned ground shield technique due to less associated parasitic capacitance.