Silicon Micromachined CPW Transmission Lines

MEMS technology with its three-dimensional (3D) treatment of substrates allows realization of CPWs with lower attenuation. This is achieved by removing the substrate material in the gap between signal and ground metalizations of the CPW transmission lines. A series of different removing/underetching schemes was investigated and processed and compared with common CPW lines. This paper explains the idea as well as the micromachining process steps used. Lowest measured attenuation was 0.081 dB/mm at 40 GHz for CPW lines with ground to ground spacing of 300 μm and substrate removal of 60 μm in depth. This corresponds to an improvement in attenuation of more than 20% compared to common CPW lines.