A low-loss silicon-on-silicon DC-110-GHz resonance-free package

This paper reports on the design and fabrication of a hermetic-compatible wafer-scale package for microwave and millimeter-wave devices. Coplanar waveguide (CPW) lines on a high-resistivity silicon wafer are covered with another silicon wafer using gold-to-gold thermo-compression bonding. Oxide is used as a dielectric inter-layer for CPW feed-throughs underneath the gold sealing ring. A 130-μm-high cavity is etched in the cap wafer to remove an impact of capping wafer on CPW lines or RF devices. The designed feed-through has an insertion loss of 0.05-0.26 dB at dc-110 GHz with a return loss of <-20 dB (per transition). The gold sealing ring is connected to the CPW ground to eliminate any parasitic resonance and leakage of the package. The whole packaged CPW line has a measured insertion loss of 0.2-0.7 dB and return loss of <-20 dB at dc-110 GHz.