Nanostructured high refractive index titanium oxide films

Titanium oxide due to its optical properties, such as high refractive index, transparency to visible light and photocatalytic properties is being used in a large number of devices such as micro-optical elements and solar cells. The fabrication of TiO2 micro and nano-patterns however requires costly clean-room technology involving a number of fabrication steps. Alternatively titania can be prepared using low cost chemical solution deposition technique using sol-gel process. Sol-gel methods, on the other hand, suffer from high densification temperatures and therefore poorer performance. We present an advanced sol-gel process based on high titanium oxide content synthesis and its one-step patterning using nanoimprint lithography. TiO2 sol-gel films were prepared using titania precursors, titanium isopropoxide (90%) and silica precursor (10%) modified by organic moieties. TiO2 nano-particles were either added (Ø20nm) to the solution or formed in-situ (Ø5nm). The films up to 1 um were spin coated and imprinted at temperatures ranging from 80 to 130C. After this process, the films were cured with UV irradiation and shrank up to 50% leaving patterned areas free of cracks. The patterns from 50 nm to 2 um size and up to 300 nm deep were obtained. Refractive index of the films after UV irradiation increased from 1.6 to 2.1. Directly patternable and UV curable, crack-free and high purity TiO2 films up to 0.5 um thick are suitable for the fabrication of high efficiency micro-components.