Improved polarization and endurance in ferroelectric Hf_0.5Zr_0.5O₂ films on SrTiO₃(110)

Abstract

The metastable orthorhombic phase of Hf_0.5Zr_0.5O₂ (HZO) can be stabilized in thin films on La_0.67Sr_0.33MnO₃ (LSMO) buffered (001)-oriented SrTiO₃ (STO) by intriguing epitaxy that results in (111)-HZO oriented growth and robust ferroelectric properties. Here, we show that the orthorhombic phase can also be epitaxially stabilized on LSMO/STO(110), presenting the same out-of-plane (111) orientation but a different distribution of the in-plane crystalline domains. The remanent polarization of HZO films with a thickness of less than 7 nm on LSMO/STO(110) is 33 μC cm^-3, which corresponds to a 50% improvement over equivalent films on LSMO/STO(001). Furthermore, HZO on LSMO/STO(110) presents higher endurance, switchable polarization is still observed up to 4 × 10¹⁰ cycles, and retention of more than 10 years. These results demonstrate that tuning the epitaxial growth of ferroelectric HfO₂, here using STO(110) substrates, allows the improvement of functional properties of relevance for memory applications.