Non-diffusive behavior of aluminum and yttrium dopants in ZrO2/Al2O3 and ZrO2/Y2O3 bilayer thin films

This study investigates the diffusive and non-diffusive behaviors of Al and Y dopants in ZrO2/Al2O3 and ZrO2/Y(2)O(3 )stacked thin films grownviaatomic layer deposition (ALD), focusing on their interaction withthe film's crystallization and grain growth. Contrary to the conventional diffusion theory, this workreveals that the diffusion in these nano-scale thin films is strongly influenced by the formation ofthrough-grain structures rather than concentration gradients. Various thin film stacks analyzed bygrazing incidence X-ray diffraction confirm this phenomenon. In the bilayer configurations, the Al and Ydopant layers do not diffuse into the adjacent ZrO(2 )lattice since they do not necessarily interfere withthe continuous grain growth of the ZrO2 layer. However, when the dopant layers are embedded withinthe ZrO2, which disrupt ZrO(2 )grain growth at the insertion site, they must diffuse away to form thethrough-grains and thus lower the grain boundary energy. These findings indicate that the primarydriving force for the Al and Y dopant diffusion in ZrO2thin films is lowering the grain boundary energy,not the concentration gradient. In contrast, thicker (40.3 nm) Al-O layers maintain structural integrityand inhibit through-grain formation, resulting in no Al diffusion. These results offer insights forimplementing dopant layers in various thin film applications.