Thickness effect on the ferroelectric properties of La-doped HfO2epitaxial films down to 4.5 nm

Abstract

Stabilization of the orthorhombic phase of HfO2with La allows very high polarization and endurance to be achieved. However, these properties have not been confirmed yet in films having a thickness of less than 10 nm. We have grown (111)-oriented La (2 at%) doped epitaxial HfO2films on SrTiO3(001) and Si(001) substrates, and report on the thickness dependence of their ferroelectric properties. Films of less than 7 nm thickness show a high remanent polarization of about 30 μC cm−2, slight wake-up, an endurance of at least 1010cycles and a retention of more than 10 years, with the endurance and retention measured at the same poling voltage. La-doped HfO2films even as thin as 4.5 nm also show robust ferroelectric properties.