Thickness-dependent phase evolution and dielectric property of Hf0.5Zr0.5O2 thin films prepared with aqueous precursor

Hf0.5Zr0.5O2 thin films were prepared on silicon substrates by sol–gel method. The crystallization temperature, thickness, density, surface morphology, crystalline structure, and chemical bonding features of the films were investigated using TGA, DSC, XRR, AFM, GIXRD, and XPS techniques. The results showed that the crystallization temperature was 496 °C, the film surfaces were smooth and flat, and no pores and micro-cracks were discernable. The density increased significantly from 5.1 to 8.0 g/cm3 after annealing at 700 °C. The crystalline structure depends strongly on the film thickness. The tetragonal phase could be stabilized in Hf0.5Zr0.5O2 films thinner than 12.9 nm. An increase in the thickness led to a gradual appearance of the monoclinic phase, which ultimately became the dominant phase for films thicker than 46.1 nm. The results could be explained by the surface energy effect. Measured at 1 MV/cm, the leakage current density was about 3.5 × 10−6 A/cm2, further indicating high quality of the thin films derived from aqueous solution precursor.