Controlling Thermal Conductivity of Amorphous SiO_<i>x</i> Films through Structural Engineering Utilizing Single Crystal Substrate Surfaces

Development of thin films with low thermal conductivity (κ) and high dielectric breakdown strength is essential to engineer insulating materials for electronics packaging and other application domains, such as power electronics. Silica glass (SiO₂) has extremely high dielectric breakdown strength but a relatively high κ compared to multicomponent silicate glasses. This study reveals that a large and systematic decrease in κ can be obtained by shorter intermediate ordering distances controlled by stronger constraints from the substrate surface atoms. The largest effect on κ is observed for SiO_<i>x</i> films on Si substrates, which can reach one-third of the bulk value. The change in ordering is observable by the shift of the main halo measured by grazing incidence X-ray total scattering. The improved understanding of the κ of SiO_<i>x</i> films presented herein could enable new materials design for electronic devices including wide-bandgap semiconductors.