Exploration of waveguide fabrication from thermally evaporated Ge–Sb–S glass films

Abstract

Waveguides from thermally evaporated Ge23Sb7S70 films have been fabricated using both plasma etching and lift-off techniques. The two methods have been compared in their ability to provide high quality, low-loss waveguides for microphotonics applications. We have demonstrated in this paper that low-loss 3μm and 4μm wide channel waveguides can be fabricated using CHF3 and SF6 plasma etching, and lift-off, respectively. Additionally, lift-off does not change the structure of the waveguide during the fabrication whereas the structure of the plasma etched waveguide differs slightly from that of the films. Finally, channel waveguides fabricated using lift-off leads to a low RMS roughness of 10±2nm, compared to those fabricated by a plasma etching process which lead to a higher RMS roughness of 17–20nm. As-fabricated waveguides have been found to exhibit optical propagation losses of 3–5dB/cm at 1550nm. These high losses are attributed to scattering by sidewall roughness and defects arising from the fabrication process.