A novel Ni capped high Q copper air gap spiral inductor

A high Q on-chip spiral inductor has been fabricated by 0.13 μm CMOS copper technology with air gap structure. The copper wires were capped with electroless Ni plating to prevent the copper from oxidizing. A Si3N4/SiO2 X-beam was designed to increase the mechanical strength of the inductor in air gap. The enhancement of maximum mechanical strength (MMS) of a spiral inductor with X-beams is more than 4500 times. The measured maximum quality factor (Q) of the suspending inductor and frequency at maximum Q are improved from 5.2 and 1.6 GHz of conventional spiral inductor to 7.3 and 2.1 GHz, respectively.