Incipient Ferroelectricity in Al‐Doped HfO₂ Thin Films

Abstract Incipient ferroelectricity is known to occur in perovskites such as SrTiO₃, KTaO₃, and CaTiO₃. For the first time it is shown that the intensively researched HfO₂ thin films (16 nm) also possess ferroelectric properties when aluminium is incorporated into the host lattice. Polarization measurements on Al:HfO₂ 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 Pbc2₁ stabilized for low Al doping in HfO₂. The ferroelectric properties of the modified HfO₂ 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 HfO₂ dielectric, an immediate relevance of ferroelectric hafnium oxide thin films is anticipated by the authors.