Embedded conductor technology for micromachined RF elements

A surface-micromachined, multilayer, embedded conductor fabrication process is presented. The process is based on high-aspect-ratio MEMS via formation and subsequent conformal/plate-through-mold metallization. Using this process, the fabrication of epoxy-embedded, high-Q electroplated RF inductors is demonstrated. This process has two attractive features. First, the embedded nature of these interconnects and inductors allows conventional handling and packaging of inductor/interconnect/chip systems without additional mechanical consideration for the inductor structure and without its significant electrical degradation after further packaging. Second, since the embedding material forms a permanent structural feature of the device, embedding materials that would otherwise be difficult to remove during the fabrication process are instead very appropriate for this technology. The epoxy-based implementation of this technology is low temperature and compatible with post-processing on CMOS foundry-fabricated chips or wafers. Multiple solenoid-type inductors with varying numbers of turns and core-widths are fabricated on a silicon substrate using this technology. A six-turn solenoid type inductor shows an inductance of 2.6 nH and a peak Q-factor of 20.5 at 4.5 GHz.