Fabrication of 3-dimensional Cu coplanar waveguide using porous silicon MEMS technology

A 3-dimensional Cu coplanar waveguide(CPW) transmission line, been fabricated on 10-mum-thick oxidized porous silicon(OPS) using surface micromachining technology. The fabricated 3-dimensional Cu CPW with the dimensions of S-W-S = 30-80-30 mum has insertion loss of -0.25 dB and return loss of -28.9 dB at 4 GHz. The line dimensions of the CPW phase shifter were designed with S-W-Sg = 100-30-400 mum. The width and length of the air-bridge with "subset of" shape were 100 mum and 400-460-400 mum, respectively. The insertion loss of the stepped air-bridge CPW phase shift has improved characteristics from that of no stepped air-bridge CPW phase shift. The measured phase shift characteristics of the fabricated CPW phase shifter are close to 180degrees over a very broad frequency range of 28 GHz. The results indicate that the thick OPS can be used for high performance low cost microwave and millimeter wave circuits using silicon-based process technology.