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-conducthity-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.