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

Abstract

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.

Keywords:

• Hafnium oxide
• thin film
• sol–gel
• spin coating

Acknowledgments

This work was supported by the Suranaree University of technology (SUT) by Office of the Higher Education Commission under NRU Project of Thailand and Synchrotron Light Research Institute (Public Organization) at BL 6A, SLRI, Thailand, for all facilities and financial supports. The authors also acknowledging the XRD at BL1.1W scientists and technicians for their help throughout the experiment.

Additional information

Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.