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 80400 K using the 3 method. Thermal conductivity data for amorphous thin films of SiO2 are nearly identical to bulk a-SiO2. Data for amorphous Al2O3, while having a magnitude and temperature dependence similar to bulk amorphous oxides, show a dependence on deposition method; rf sputtering of an Al2O3 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 TiO2 films depends on the substrate tempreature Ts and approaches the thermal conductivity of bulk TiO2 ceramics when Ts 400°C; HfO2 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.