High thermal conductivity materials show promise for thermal mitigation and heat removal in a variety of devices. However, shrinking the length scales of these materials often leads to significant reductions in thermal conductivities, thus invalidating their applicability to functional devices.
Phonon−phonon scattering drives the in-plane thermal transport of these AlN thin films, leading to an increase in thermal conductivity as temperature decreases. This is the opposite of what is observed in traditional high thermal conductivity thin films, where boundaries and defects that arise from film growth cause a thermal conductivity reduction with decreasing temperature.
Steady-state thermoreflectance can provide precise measurements of high in-plane thermal conductivities of 3.05, 3.75, and 6 μm thick aluminum nitride (AlN) film. At room temperature, the AlN films possess an in-plane thermal conductivity of ∼260 ± 40 W m−1 K−1, one of the highest reported to date for any thin film material of equivalent thickness. At low temperatures, the in-plane thermal conductivities of the AlN films surpass even those of diamond thin films
This study provided valuable insight into the interplay among boundary, defect, and phonon−phonon scattering that drives the high in-plane thermal conductivity of the AlN thin films and demonstrates that these AlN films are promising materials for heat spreaders in electronic devices. This realization was enabled from SSTR measurements, which allow for unique sensitivities to in plane thermal conductivity.