W-band low-loss wafer-scale package for RF MEMS

This paper reports on the design and fabrication of a wafer-scale package for RF MEMS devices at W-band. 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 feedthroughs 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 MEMS components. The designed feedthrough has an insertion loss of 0.19-0.26 dB at 75-110 GHz with a return loss of < -20 dB (per transition). The gold sealing ring is connected to the CPW ground to eliminate any parasitic ring effect of the gold sealing ring. The whole package has a measured insertion loss of 0.6-0.8 dB and return loss of < -20 dB at 75-110 GHz.