Hidden structural phase transition assisted ferroelectric domain orientation engineering in HfZrO films.

The polarization of HfO-based ferroelectrics originates from the metastable orthorhombic phase formed during the tetragonal to monoclinic phase transition and is typically controlled by tuning the phase content. However, another way to control polarization via modulating ferroelectric domain orientations remains underexplored. This work uncovers a hidden tetragonal-orthorhombic phase transition pathway to engineer domain orientations and further polarization in polycrystalline HfZrO using single-crystalline TiN substrates. Specifically, (001) and/or (010) domains, which fully contribute to remanent polarization under an electric field, are controllable in HfZrO on TiN (001) and (111), enhancing remanent polarization compared to that on TiN (110). The key is the hidden transition from the tetragonal phase's longest c-axis to the orthorhombic phase's shorter b/c-axis, alongside the reported one to the longest a-axis, assisted by periodic dislocations at the TiN/HfZrO interface. These findings shed light on governing the polarization of HfZrO films by controlling the interface dislocations and further domain orientations.