Effects of composition variables on optical properties of sodium borosilicate glass films fabricated by aerosol flame deposition

Sodium borosilicate glass (SBSG) films were fabricated on silicon substrates as waveguide layers of planar optical waveguide devices. The aerosol flame deposition (AFD) method was employed for this purpose. The effects of Al2O3 concentration and Na2O/B2O3 ratio on phase separation behavior and optical properties of the films were investigated. The addition of Al2O3 above a certain critical concentration effectively suppresses the formation of crystalline phases in the 66SiO2–27B2O3–7Na2O glass film under the air-quenching condition. Both the refractive index and birefringence of SBSG films increase linearly with increasing amounts of Al2O3 added. The film was annealed at a temperature below the glass transition point to reduce the birefringence caused by a tensile stress developed between the film and the Si substrate. After annealing at 470oC for 72 h, the birefringence of the SBSG film was reduced to 2×10−4. It was shown that both the degree of crystallization and refractive index increased with increasing ratios of Na2O/B2O3.