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 degrees 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 degrees 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.