STRUCTURAL AND MICROSTRUCTURAL EFFECTS ON THE THERMAL CONDUCTIVITY OF ZIRCONIA THIN FILMS

Thermal properties of thin films involve in a large number of applications such as electronic and electro-optical devices, thermal barrier coating. It's known that structure and microstructure of thin solid films have a strong impact on the thermal conductivity and this one may be considerably lower than bulk material ones.
The aim of this article is to highlight the role of structure and microstructure on the thermal conductivity of Zr0₂ thin films (stabilized with Y₂0₃ or not). Investigations have been focused on the influence of the film thickness, substrate roughness and crystallites size. Results are obtained by using a new photo-thermal method, that we have developed, which enables the determination of the thermal conductivity of the dielectric films, on various kind of substrates, with an accuracy better than 10%.
First, we observe, that a decrease in the dielectric thickness leads to a drastic drop of the apparent thermal conductivity k_α, whatever the Zr0₂ phases. k_α is affected by an additional thermal resistance R_ƒs, especially between Zr0₂ and alumina substrate. Next, we highlight that R_ƒs depend linearly with the substrate roughness. In final section, we show the influence of crystallite size and estimate the value of a joint grain.
In the future, we intend to study more in detail interfacial structures of the interfaces.