Thermal Conductivity Comparison of Indium Gallium Zinc Oxide Thin Films: Dependence on Temperature, Crystallinity, and Porosity

The cross-plane thermal conductivity of InGaZnO (IGZO) thin films was measured using the 3ω technique from 18 to 300 K. The studied morphologies include amorphous (a-IGZO), semicrystalline (semi-c-IGZO), and c-axis-aligned single-crystal-like IGZO (c-IGZO) grown by pulsed laser deposition (PLD) as well as a-IGZO deposited by sputtering and by solution combustion processing. The atomic structures of the amorphous and crystalline films were simulated with ab initio molecular dynamics. The film quality and texturing information was assessed by X-ray diffraction and grazing incidence wide-angle X-ray scattering. X-ray reflectivity was also conducted to quantify film densities and porosities. All the high-density films exhibit an empirical power-law temperature dependence of the thermal conductivity K ~ T0.6 in the specified temperature range. Among the PLD dense films, semi-c-IGZO exhibits the highest thermal conductivity, remarkably exceeding both films with more order (c-IGZO) and with less order (a-IGZO) by a factor of 4. The less dense combustion-synthesized films, on the other hand, exhibited lower thermal conductivity, quantitatively consistent with a porous film using either an effective medium or percolation model. All samples are consistent with the porosity-adapted Cahill-Pohl (p-CP) model of minimum thermal conductivity