The study of optical and microstructural evolution of Ta2O5 and SiO2 thin films by plasma ion assisted deposition method

Microstructural examination indicated that nanocrystallized structures and few voids existed in Ta2O5 thin films at temperatures above 375 °C. The nanocrystallized structures will increase the refractive index of Ta2O5 thin films, while voids may reduce the refractive index. For the Ta2O5 and SiO2 single layers, optical measurements indicated that the refractive index were about 2.13-2.16 and 1.47-1.485, respectively, and that the extinction coefficient was approximately equal to 10−4. The deposition rate attributed no evident effects to the optical characteristics, while changes in the annealing temperature resulted in the surface roughness and optical evolution. The annealed single Ta2O5 and SiO2 thin films possessed the lowest surface roughness at 325-375 °C. The optical measurement showed Ta2O5 single thin film samples had better optical characteristics at 325 °C that is consistent with atomic force microscopy (AFM) results. The designed (HL)6H6LH(LH)6 multilayers indicated higher insertion loss than the designed (HL)68H(LH)6 multilayers. Therefore, using the high refractive index as spacer material represented lower insertion loss.