ALUMINA THIN-FILMS AS OPTICAL WAVE-GUIDES

Amorphous Al2O3, fabricated by reactive rf magnetron sputtering, has b een evaluated as a planar waveguide material, The microstructure and o ptical properties of planar waveguides were examined as a function of deposition (substrate temperature, O-2 how rate) and annealing conditi ons, X-ray and electron diffraction verified that as-deposited films w ere amorphous for substrate temperatures up to 500 degrees C and for a wide range of O-2 flow rates. This amorphous phase was stable through anneals up to 800 degrees C, but crystallized to gamma-Al2O3 at 1000 degrees C and to alpha-Al2O3 at 1200 degrees C. The amorphous films ha d transmission windows that extended from 200 nm to 7 mu m with an ave rage refractive index of 1.65 and reproducible losses as low as simila r to 1 dB/cm at 632.8 nm. The refractive index increased with substrat e temperature, but was independent of O-2 flow rate. The losses decrea sed with substrate temperature and increased as a function of O-2, flo w rate, As a final check on the amorphous structure, Cr-doped films we re prepared by codeposition. Fluoresence was detected only in annealed crystalline films.