Abstract
Low-loss amorphous-silicon (a-Si) waveguides comprising three vertically stacked layers prepared on silicon-on-insulator substrates are demonstrated. We have fabricated multilayer a-Si waveguides and investigated their loss characteristics; this is the first such investigation to our knowledge. All the process temperatures were regulated below 400 °C for the complementary metal oxide semiconductor (CMOS) backend process compatibility. When the surface roughness and sidewall roughness were decreased, the propagation loss decreased to 3.7 dB/cm even in the case of the third layer a-Si waveguide. Such low-loss waveguides can be effectively applied to realize multilayer stacked optical devices.