Effect of stress on fluorite-structured ferroelectric thin films for semiconductor devices

Ferroelectricity, i.e., the characteristic of polar crystals whose spontaneous polarization can be reversed by the application of an appropriate electric field, originates from the formation of a crystallographic phase with noncentrosymmetry and is widely exploited in numerous devices. In particular, fluorite-structured ferroelectrics (FFs) are promising components of semiconductor devices and are typically present as components of compli-cated multistacks containing electrodes and semiconductors. Given that the formation of the ferroelectric phase and the magnitude of its spontaneous polarization are mainly affected by the lattice distortion or sub-unit-cell displacement of ions, the ferroelectricity of FF thin films formed during device fabrication should be strongly influenced by their stress/strain state. Thus, a deep understanding of the stress/strain states of these films and their effects on material properties and device performances is required; however, this topic has not yet been extensively reviewed despite its significance and important reports related to stress/strain effects. To fill this gap, we herein discuss the mechanisms of stress/strain development in FF thin films and their impacts on material properties and device performances based on fundamental thin-film mechanics and relevant theoretical and experimental studies.