Synthesis and Characterization of La-Doped Hafnium Oxide Thin Films by Sol–Gel Method

In this article, the effect of lanthanum-doped HfO2 structure is investigated in order to verify the ferroelectric property as a candidate for the next generation of FeRAM. The xLa-doped HfO2 thin films with x equals to 0.0, 0.2, 0.4, 0.5, 0.6, and 0.8 were prepared by sol–gel method. Hafnium chloride and lanthanum chloride were employed as starting materials which were initially dissolved in ethanol and ethylene glycol, respectively. Diethanolamine was applied as a stabilizer. The ratio between moles of metals, solvent, and stabilizer was initially varied to obtain gel and it was found that 1:80:4 is the most suitable ratio. After spin coated on a substrate (Si), the gel of La-doped HfO2 was annealed to make thin films at 300–1000 °C under atmosphere. Phase formation and microstructure were characterized using Grazing Incidence X-ray diffraction and Field Emission Scanning Electron Microscope (FE-SEM). XRD results showed that a monoclinic phase of HfO2 was found when the films were annealed at 600 °C for 3 and 5 h. Homogenous surfaces were observed in SEM images. Distribution of Hf and La existed on the surface of all samples were also revealed by EDS. The experimental results showed that La-doped HfO2 thin films were successfully synthesized using the sol–gel method. Mole ratios and annealing temperature played a significant role in phase formation and homogeneity of La-doped HfO2 thin films.