Integrated Computational Materials, Process and Product Engineering – IC-MPPE 2022

Energy efficiency and saving in microelectronic devices goes along with thermal management, as their failure rate increases exponentially and their efficiency decreases linearly with the operating temperature. Due to the continuous trend of miniaturization, thermal management additionally gains importance and leads to an increase in device packing density. This triggers the need for heat dissipation and the development of heat dissipation strategies, which requires knowledge of the temperature-dependent thermophysical and structural properties.
Here, a closer look was taken at nm-thin $\text{Nb}_2\text{O}_5$ films, predominantly used in devices for optical, electrochromic, and sensing applications. Due to their geometrical restrictions, the thermal conductivity of such nanometre thin films can differ from their bulk counterpart, and it is strongly affected by their processing. E.g. depending on the applied substrate temperature, the $\text{Nb}_2\text{O}_5$ film grows either in the amorphous or crystalline form. Within this work, the thermal transport properties and the crystallographic structure of the $\text{Nb}_2\text{O}_5$ films were interrelated. The thermal conductivity of both amorphous and crystalline $\text{Nb}_2\text{O}_5$ was determined by the Time Domain Thermoreflectance. The average and local structure are determined by in-situ high-temperature X-ray diffraction and in-situ high-temperature Raman spectroscopy, respectively. The crystalline $\text{Nb}_2\text{O}_5$ film showed a decrease in thermal conductivity with increasing temperature. In contrast, the amorphous $\text{Nb}_2\text{O}_5$ film had a constant thermal conductivity of 2.2 ± 0.2 W/mK at temperatures below 275°C. Above that temperature, an abrupt increase in thermal conductivity to 2.8 ± 0.2 W/mK was recorded. This substantial increase in thermal conductivity cannot be linked to any macroscopic phase change but rather to a local phase rearrangement near the crystallization temperature evidenced by the Raman spectra analysis. This study serves as a guide to engineer future $\text{Nb}_2\text{O}_5$ based thin film devices and for their reliability and efficiency optimization.