Design and fabrication of the suspended high-Q spiral inductors with X-beams

In this paper, deep sub-micron CMOS process compatible high Q on-chip spiral inductors with air gap structure were designed and fabricated. In the design the electromagnetic solver, SONNET, and the finite element program, ANSYS, were used for electrical-characteristics and maximum mechanical strength, respectively. 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 of a spiral inductor with X-beams is more than 4,500 times. Among these structures, 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.