LAUSR

On Si and sapphire substrates, 6–45 nm thick films of atomic layer-deposited Al$$_{2}$$2O$$_{3}$$3 were grown. The thermal conductivity of ALD films has been determined from a linear relation between film thickness and thermal resistance measured by the 3$$\omega $$ω method. ALD films on Si and sapphire showed almost same thermal conductivity in the temperature range of 50–350 K. Residual thermal resistance was also obtained by extrapolation of the linear fit and was modeled as a sum of the thermal boundary resistances at heater–film and film–substrate interfaces. The total thermal resistance addenda for films on sapphire was close to independently measured thermal boundary resistance of heater–sapphire interface. From the result, it was deduced that the thermal boundary resistance at ALD Al$$_{2}$$2O$$_{3}$$3–sapphire interface was much lower than that of heater–film. By contrast, the films on Si showed significantly larger thermal boundary resistance than films on sapphire. Data of $$< 30$$<30 nm films on Si were excluded because an AC coupling of electrical heating voltage to semiconductive Si complicated the relation between 3$$\omega $$ω voltage and temperature.