Multilevel-spiral inductors using VLSI interconnect technology

A multilevel-spiral (MLS) inductor structure for implementation in VLSI interconnect technology is presented. Inductances of 8.8 and 32 nH and maximum quality-factors (Q) of ∼6.8 and 3.0, respectively, are achieved in a four-level metal BiCMOS technology, with four turns at each of the two or four stacked spiral coils and with an area of 226 × 226 μm2. The comparison of the MLS inductors to different single-level-spiral (SLS) control devices shows that a MLS inductor provides the same inductance at ∼50% de resistance, but the maximum Q is typically measured at a lower frequency and the self-resonance frequency is reduced due to a high inter-wire capacitance.