Thermal conductivity of atomic layer deposited Al2 O3 films on sapphire
Seung-Min Lee, Junsoo Kim, Wonchul Choi, Jung Yoon Kwon, Hyuck Jin Kim, Taekwang Kim, Sol Yee Im, Jaewoo Lee and Seung Eon Moon
The thermal conductivity of atomic layer deposited (ALD) Al2 O3 films was measured using the 3w method in the temperature range of 50 K–320 K. The ALD films were deposited onto 0.43 mm thick sapphire (1000) substrates in the thickness range of 5 nm – 40 nm. For the heater and thermometer, ~330 nm thick Au with ~3 nm thick adhesion layer of Ti was deposited by e-beam evaporation and lift-off patterned into lines of 8 mm width and 0.8 mm length. The temperature oscillation of the heater on the samples was modeled as a series sum of the temperature responses of sapphire substrate, ALD film and thermal addenda due to thermal boundary conductance at heater metal-film and film-substrate interfaces. The thermal resistance of films was separated from the response of substrate and interfacial thermal addenda by linear interpolation of the heater temperature against film thickness. Sample to sample variation of the heater width was considered before the linear interpolation. In the temperature range of 100 K–320 K, the thermal conductivity of sapphire substrate was obtained from the logarithmic frequency dependence of the measured data and used for the series thermal resistance model equation. Below 100 K, effective thermal conductivity value was used because the thermal wavelength is longer than the substrate thickness in our measure frequency range. The measured film thermal conductivity was larger than that of other ALD films or sputtered films. The temperature dependence was similar to those of amorphous materials and was in good agreement with previous reports and theoretical minimum.
Keywords: atomic layer deposition, Al2 O3 film, thermal conductivity, 3w method, thermal boundary, thermal wavelength.