High Frequency Monolithic Inductor with Air-Gaps

In this paper, we evaluate the possible implementation of air-gaps for extending the operating range of an RF on-chip inductor, without affecting the inductance. To determine where air-gaps should be placed, the dominant parasitic capacitance component of an inductor is first identified, using an equivalent circuit model to extract their values from numerical simulation data. An air-gap fabrication in the back-end of line technology is given to illustrate for the feasibility of the integration. Based on the fabricated array of air-gaps at a 2:1 void-to-dielectric interval, we show that the capacitance is reduced by 40%, which translates to an increase in the inductor self-resonance frequency by 20% to 27 GHz, while having a large value inductance at 1.5 nH range.