Fabrication of pure silica films for planar optical waveguides using colloidal suspensions

• Published in: Journal of non-crystalline solids Vol. 342; no. 1-3; pp. 18 - 24
• Main Authors: Kim, Deok-Yang, Kowach, Glen R., Johnson, David W., Bhandarkar, Suhas, Du, Henry
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.08.2004; Elsevier
• Subjects: Applied sciences; Circuit properties; Electric, optical and optoelectronic circuits; Electronics; Exact sciences and technology; Integrated optics. Optical fibers and wave guides; Optical and optoelectronic circuits; 81.05.Kf; 78.66.Nk; T200; O120; S160; 83.80.Hj; Thickness; Colloidal suspension; Refraction index; Reflectometry; Optical material; Spin-on coating; Optical waveguide; Manufacturing; Silica; Optical glass; Inorganic compound
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2004.06.015

In this work, colloidal suspensions are used as a precursor to the formation of layers of optical quality glass on silicon substrates. The colloidal suspensions were made by dispersing a high concentration of fumed silica (particle diameter of 40±30 nm) in water with tetramethylammonium hydroxide (TMAH) as a base to stabilize the suspension. Spin-coating was used as the film deposition method to prepare porous silica films. These films were then consolidated at 1300 °C in an atmosphere of helium and oxygen. Dense silica films with thicknesses up to 1.4 μm could be made this way from a single spin-coating step. The refractive index, as measured by reflectometry, of the densified film at a wavelength of 632.8 nm is 1.4577±0.0005. This is comparable to that of a thermal oxide on a silicon wafer confirming that the film is fully densified. Also, fully dense, defect-free films with thicknesses in the order of 10 μm were fabricated with multiple spin-coating steps to meet the dimensional requirements of planar optical waveguides.