Groove-Buried Optical Waveguides Based on Metal Organic Solution-Derived Amorphous Ba0.7Sr0.3TiO3 Thin Films

Abstract

Dielectric optical waveguide systems with large high index contrast Δ offer a size advantage over low index contrast systems because the photonic device size scales down with increasing Δ. In this study, we report the amorphous Ba0.7Sr0.3TiO3 (BST0.7) thin film groove-buried waveguides with 90° bent structure fabricated on Si substrates with 1.65-µm-thick SiO2 thermal oxide layers. The design, fabrication, and optical losses of amorphous BST0.7 optical waveguides are presented. The amorphous BST0.7 thin films were grown on the SiO2/Si substrates with grooves about 400 nm deep using metal organic decomposition from barium 2-caprylate Ba(C8H15O2)2 and 3-methylbutyl acetate CH3COOC2H4CH(CH3)2-based precursors. The film surface was comparatively smooth. The root mean square surface roughness of the thin film about 200 nm thick that was evaluated from the AFM image over an area of 1 µm2 was 1.74 nm. Most light was confined in the BST0.7 core layer on the groove. The optical propagation losses were about 12.8 and 9.4 dB/cm, respectively, for the 5- and 10-µm-wide waveguides at a wavelength of 632.8 nm. The 90° bend losses were about 1.2 and 0.9 dB, respectively, for 5- and 10-µm-wide waveguides at a wavelength of 632.8 nm.