Thermal conductivity of sputtered oxide films

The thermal conductivity of oxide thin films deposited using dc, rf, and ion-beam sputtering is measured in the temperature range 80–400 K using the 3ω method. Thermal conductivity data for amorphous thin films of ${\mathrm{SiO}}_2$ are nearly identical to bulk a-${\mathrm{SiO}}_2$. Data for amorphous ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$, while having a magnitude and temperature dependence similar to bulk amorphous oxides, show a dependence on deposition method; rf sputtering of an ${\mathrm{Al}}_2$ ${\mathrm{O}}_3$ target produces films with a thermal conductivity 35% smaller than films prepared by ion-beam sputtering. Microcrystalline thin films show a rich variety of behavior: the conductivity of ${\mathrm{TiO}}_2$ films depends on the substrate tempreature ${\mathit{T}}_{\mathit{s}}$ and approaches the thermal conductivity of bulk ${\mathrm{TiO}}_2$ ceramics when ${\mathit{T}}_{\mathit{s}}$≃400 °C; ${\mathrm{HfO}}_2$ films show glasslike thermal conductivity independent of annealing temperature up to 900 °C; and MgO films display a crystalline thermal conductivity that is greatly reduced relative bulk values.