Incipient Ferroelectricity in Al‐Doped HfO₂ Thin Films

TLDR

Incipient ferroelectricity occurs in perovskites such as SrTiO₃, KTaO₃, and CaTiO₃. The study investigates the origin of ferroelectricity in Al‑doped HfO₂ thin films via structural analysis using grazing incidence X‑ray diffraction. The authors use grazing incidence X‑ray diffraction to identify an orthorhombic Pbc2₁ phase that provides the non‑centrosymmetric structure needed for ferroelectricity in low‑Al‑doped HfO₂. Al‑doped HfO₂ thin films display ferroelectricity, with an antiferroelectric‑to‑ferroelectric transition governed by annealing and Al content, offering high potential for ferroelectric, piezoelectric, and pyroelectric devices and immediate relevance given the extensive HfO₂ dielectric research.

Abstract

Abstract Incipient ferroelectricity is known to occur in perovskites such as SrTiO 3 , KTaO 3 , and CaTiO 3 . For the first time it is shown that the intensively researched HfO 2 thin films (16 nm) also possess ferroelectric properties when aluminium is incorporated into the host lattice. Polarization measurements on Al:HfO 2 based metal–insulator–metal capacitors show an antiferroelectric‐to‐ferroelectric phase transition depending on annealing conditions and aluminium content. Structural investigation of the electrically characterized capacitors by grazing incidence X‐ray diffraction is presented in order to gain further insight on the potential origin of ferroelectricity. The non‐centrosymmetry of the elementary cell, which is essential for ferroelectricity, is assumed to originate from an orthorhombic phase of space group Pbc2 1 stabilized for low Al doping in HfO 2 . The ferroelectric properties of the modified HfO 2 thin films yield high potential for various ferroelectric, piezoelectric, and pyroelectric applications. Furthermore, due to the extensive knowledge accumulated by various research groups regarding the HfO 2 dielectric, an immediate relevance of ferroelectric hafnium oxide thin films is anticipated by the authors.