Design and simulation of digitally tunable high-Q on-chip inductor

This paper presents a practical architecture for a 2-bit digitally tunable high-Q spiral inductor on standard CMOS substrate utilizing surface-micromachined electrostatically actuated microrelays. The design is based on the use of two microrelays to reconfigure the effective magnetic area of the spiral inductor. This is achieved by introducing additional interconnecting lines together with two microrelays within the hollow area of the spiral inductor. The high-Q performance of the inductor is mainly due to employing a thick isolating oxide layer between the spiral and the substrate, and a thick copper layer for the spiral inductor and interconnects. A tuning range from 2.29 to 3.73 nH is achieved for 1.5-turns spiral inductor with peak Q factor above 15 for the four switching configurations. The design concept can be easily extended to achieve higher inductance tuning ranges.