A practical suspended spiral inductor for MMIC application

In this paper, we propose an air-bridge based on-chip suspended inductor for MMIC application. The quality factor of suspended inductor on sapphire is 10.6 at 4.0 GHz, which is improved by almost 50%, comparing with traditional air-bridge based inductor of the same size. The self-resonance frequency is also improved from 9 GHz to 10 GHz. Several key fabrication processes of this suspended inductor will be presented to illustrate that our method is exactly the same as general air-bridge inductor fabrication processes in MMIC. By analyzing the equivalent circuits of RF inductors, it is shown that the suspended inductor yields lower parasitic capacitance and suffers smaller substrate loss.