A hollow-GCPW (HGCPW) as low-loss and wafer-conductivity-free structure on a single silicon wafer

A low-loss hollow grounded co-planar waveguide (HGCPW) suitable for a transmission line on a low-resistivity silicon wafer is presented. The HGCPW is disposed in a newly developed dielectric-air-metal (DAM) cavity, which consists of an SiN membrane above a fully metallized cavity made by a micromachining process. Low-loss property is achieved by removing substrate between a signal line and grounds. Existence of a bottom ground metal realizes wafer-conductivity-free structure on a low-resistivity silicon wafer by isolating the line from the substrate completely. Also, the bottom ground enables the impedance to be 50 ohm with narrow line width. HGCPWs on the 6-,μm and 30-μm DAM cavities were fabricated and tested. The measured losses were about 0.3 dB/mm and 0.1 dB/mm respectively at 12 GHz.