Characteristics of trenched coplanar waveguide for SiMMIC applications

A novel low loss trenched aluminium CPW transmission line structure, fabricated on a selection of high, medium and low resistivity silicon substrate materials, is reported. In comparison with conventional aluminium conductor CPW line structures, RF losses are reduced. For 10 K/spl Omega/ cm high resistivity material, this reduction may be as much as 0.5 dB/cm at 30 GHz, achieved by etching longitudinal trenches in the silicon substrate material. For medium resistivity substrates (700-1000 /spl Omega/ cm,) a 13 /spl mu/m deep trench reduces measured line loss from 3.9 dB/cm to 3.4 dB/cm at 30 GHz. For low resistivity silicon substrate material (10-20 /spl Omega/ cm), RF losses can be improved by 36 dB/cm at 30 GHz with 80 /spl mu/m deep trenches. The effect of the trench depth on the characteristic impedance of these CPW lines is reported.