Synthesis and characterization of poly(methyl silsesquioxane)–titania optical thin films

Abstract

Poly(methyl silsesquioxane) (MSQ)–titania optical thin films were synthesized and characterized in this study. An MSQ precursor with a mixed cage and network structure was prepared first, which had end groups of Si–OH and Si–OCH₃. Then, it was reacted with titanium(IV) n-butoxide, followed by spin-coating and multi-step curing to form the optical thin films. The FTIR spectra suggest successful bonding of MSQ and titania. The prepared films were very uniform with an amorphous nanoscale titania segment from the results of FE-SEM, AFM, and XRD. Excellent thermal stability was found for the prepared MSQ–titania materials. The optical properties of the prepared MSQ–titania films could be tuned by the titania content. By increasing the titania content from 10.6 to 41.6 wt.%, the absorption edge and refractive index were increased from 291 to 310 nm, and from 1.394 to 1.561, respectively. These results are attributed to the growing size effect of the titania segment. Optical planar waveguides were fabricated from the synthesized MSQ–titania films on top of a thermal oxide using a silicon wafer as the substrate. The optical loss of the studied planar waveguide decreased from 0.31 to 0.18 dB cm⁻¹ with increasing titania content. This resulted from a reduction of the C–H bonding density due to the increasing titania composition.