Fig. 3

Fabrication process of the proposed VCO integrated with a MEMS tunable inductor. a The bottom metal layer was deposited and patterned by a lift-off process on a thermally-oxidized, 4-inch silicon wafer. b Polyimide as a sacrificial layer was coated on a silicon substrate, and the contact metal was deposited and patterned. c The dielectric layer was deposited and patterned using plasma-enhanced chemical vapor deposition (PECVD) and reaction ion etching (RIE), respectively. Polyimide was patterned using RIE for forming anchors. d Cu metal was formed using an electroplating process. e The sacrificial layer was removed using an O₂ plasma etching process, and the MEMS tunable inductor was released from the substrate. f CMOS VCO was bonded on bottom pads that were connected to a tunable inductor using the flip-chip bonding process