Structural Properties of Hf_0.5Zr_0.5O₂Integrated on Silicon

Miniaturization of ferroelectric materials is complicated due to depolarization fields that come into play at small length scales. Hf_0.5Zr_0.5O₂(HZO) has been shown to retain its ferroelectric properties down to the nanoscale, which makes it a promising candidate material for future ferroelectric applications. However, integration of HZO with silicon is needed for its further applicability. The discovery of a polar, rhombohedral HZO phase in HZO thin films grown on top of single-crystal STO substrates opens a way to make HZO compatible with silicon. We report upon one possible way of integrating HZO on silicon using a SrTiO₃-buffered silicon substrate (Si:STO) and investigate its structural properties. We show that HZO crystallizes following the same epitaxial relationship and domain structure as it would on a single-crystal STO substrate, but the rhombohedral distortion is absent or strongly reduced. This dissimilarity may be explained by the difference in thermal expansion coefficients of silicon and STO. Persistent switching is observed in piezoresponse force microscopy and Kelvin probe microscopy, which could be indicative of ferroelectricity or ionic migration.