Fabrication and Characterization of Microscaled On-Chip Toroidal Inductors

Microscaled on-chip toroidal inductors with ultrahigh quality factor (Q-factor) at tens of gigahertz have been successfully fabricated and characterized. The toroidal inductors with various diameters and dielectric layer thickness were designed and fabricated with two sets of inclined metal bars with a ring-shaped core of SiO₂ inserted in-between. The frequency-dependent Q-factor and inductance were investigated using a 50-GHz S-parameter measurement system with standard two terminal ground-signal-ground microprobes on a radio-frequency (RF) probe station. The maximum inductance increases with increasing diameter of the inductor due to the enlargement of total magnetic flux. The highest Q-factor of 183 at a frequency of 28.8 GHz was realized in the inductor with diameter of 960 mum and dielectric layers thickness of 5000 nm. In addition, the resonance frequency increases with increasing the dielectric layer thickness owing to a reduction of the parasitic capacitance.