ZrO 2 films are deposited on bare silicon, silicon with a pre-sputtered ultrathin Zr metal layer, and plasma oxynitrided Si surface by reactive sputtering and the growth of interface layer between ZrO 2 and Si is investigated. The ZrO 2 /Si dielectric stacks, before and after annealing in oxygen ambient, are characterized by grazing incident angle X-ray diffraction, Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, transmission electron microscopy, capacitance–voltage and current–voltage measurements. The results reveal that as-deposited ZrO 2 films contain nanocrystallites embedded in the amorphous matrix. ZrO 2 films deposited on an ultrathin Zr metal layer show a thinner interface layer but contain a greater amount of oxide traps. ZrO 2 films deposited on SiO x N y grown by NH 3 plasma oxynitridation are found to retard the growth of the interface layer effectively, and they also exhibit fewer oxide traps and lower leakage currents.