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 `splotchyʹ 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.