A UNIVERSAL MEMS FABRICATION PROCESS FOR HIGH-PERFORMANCE ON-CHIP RF PASSIVE COMPONENTS AND CIRCUITS
We have developed a fabrication approach that allows us to integrate monolithically on silicon high-performance on-chip radio-frequency (RF) passive components, such as inductors, transformers and fixed and tunable capacitors. We applied two- layer polysilicon surface micromachining to construct the devices, which were suspended over 30-pm-deep cavities formed into the silicon substrate. We also performed electroless copper (Cu) plating to metallize the polysilicon structures for high conductivity. The inner surfaces of the cavities were Cu coated too, providing good RF ground and electromagnetic shielding. The deep cavities dramatically reduce the electric and magnetic couplings and parasitic capacitances between the devices and the substrate. High quality factors over 30 and resonant frequencies over 10 GHz have been achieved for inductors. We have designed and fabricated high-performance varactors, transformers and LC-