Ion beam sputtering of Ta2O5 films on thermoplast substrates as waveguides for biosensors

Tantalum pentoxide thin films have been deposited at room temperature by (dual) ion beam sputtering for applications as waveguides in biosensors. The oxygen partial pressure and the energy of the substrate ion beam were the major parameters varied in ion beam sputtering and dual ion beam sputtering experiments, respectively. For sufficiently high oxygen partial pressures, the films were stoichiometric, free of contaminants, amorphous, and extremely smooth. Ion bombardment of the growing films with Ar(+) ions up to 200 eV had no significant influence on these properties. The refractive index of stoichiometric films was 2.1 +/- 0.1 and the extinction coefficient well below the resolution limit of ellipsometry and UV/visible measurements. By coupling a laser beam via an optical grating into a 150 nm thick Ta(2)O(5) layer, the optical losses could be estimated to be below 3 dB/cm. A series of experiments has been carried out to prove that this deposition process is compatible with the use of thermoplast substrates which are sensitive not only to high temperatures but also to ion bombardment and UV radiation. Finally, first experiments are presented to functionalize the surfaces of Ta(2)O(5) films with amine and epoxy groups.