Impact of light illumination and passivation layer on silicon finite-ground coplanar-waveguide transmission-line properties

Modeling of silicon finite-gronnd coplanar-waveguide (FGCPW) transmission l ines is presented in this paper. It is shown that the effective substrate c onductivity increases in the presence of illumination and in the presence o f a passivation layer in the slot regions independently. As a result, the l osses of trenched FGCPW are lower than conventional FGCPW transmission line s. The strong dependence of the substrate conductivity on illumination sugg ests that optically controlled attenuators can be implemented with FGCPW tr ansmission lines exhibiting practically no phase change between the differe nt attenuation states. A new contrast ratio for optically controlled transm ission lines is derived.