Fabrication of high-performance on-chip suspended spiral inductors by micromachining and electroless copper plating

摘要

Polysilicon spiral inductors encapsulated with copper (Cu) were suspended over 30-μm-deep cavities in the silicon substrate beneath. The metallization process simultaneously coated the inner surfaces of the cavities with Cu to form both good radio-frequency (RF) ground and electromagnetic shield. Quality factor (Q) up to 30 and self-resonance frequency (f{sub}(res)) higher than 10 GHz were achieved for a 10.4-nH inductor. Simulation showed that the Cu-lined cavities reduced the mutual inductance between two adjacent inductors by a factor of 5, compared with that without the cavities. This proves that good shielding was provided by the cavities.