Properties of CVD alumina-titania composite films grown at different CO2/H2 inputs

Amorphous alumina-titania (Al₂O₃-TiO₂) films were prepared on silicon substrates by low-pressure chemical vapor deposition (CVD) using a mixture of aluminum tri-sec-butoxide (ATSB) and titanium tetrachloride (TiCl₄) at different CO₂/H₂ inputs (the ATSB/TiCl₄/CO₂/H₂ system). The films had increased Al contents at higher temperatures and CO₂/H₂ inputs. The `splotchy' deposits were observed. The higher compressive internal stress at higher temperature was attributed to the films with a thinner thickness. Higher compressive internal stress and more Al-O bonding resulted in higher specific critical load. Films deposited at low temperature of 350 °C have a defected structure and a higher dielectric property, due to the non-stoichiometric nature at the Ti-rich composition. Resistivity decreased from 10¹¹ to 10⁸-10⁹ Ω cm after annealing. Breakdown voltages increased slightly with substrate temperature and were in the range of 2.3-6.4 MV/cm. Refractive indices were in the range of 1.71-2.28. Greater than 60% transmittance was observed at visible range for all films.