A novel grounded coplanar waveguide with cavity structure

This paper presents a grounded coplanar waveguide (GCPW), which is useful in RF-MEMS devices in order to effectively reduce noise from neighboring transmission lines. The GCPW structures demonstrated here were fabricated by front-surface-only processes on a single silicon wafer. A silicon nitride membrane supports the coplanar waveguide, which is located above a ground plane formed on an etched silicon cavity We found that the insertion losses of the 50-Ω GCPW´s with a 26-μm-wide signal line and a 6-μm-deep cavity do not exceed 0.4 dB/mm up to 20 GHz, which agreed with the simulated loss. The demonstrated maximum depth of metallized cavity is 30 μm, which enables the GCPW´s loss to be as low as 0.08 dB/mm at 20 GHz.