We have developed a simple method for the preparation of ZrO2 ultrathin films; it involves a sequence of ZrCl4 precursor preparation in an ice bath, sol-gel spin-coating processing, baking, and annealing. The film thickness was controllable and tunable by altering the ZrCl4/hexanol ratio. High-resolution transmission electron microscopy (TEM) and thermal desorption spectrometry indicated that the fabricated ultrathin film was thermally stable at annealing temperatures as high as 900 degrees C. Diffraction patterns of TEM indicated that the films obtained at various annealing temperatures were amorphous. Electron spectroscopy for chemical analysis (ESCA) demonstrated an increase in the intensity of the signal for the Zr-O bonds upon increasing the annealing temperature, whereas those for the signals of carbon and chlorine decreased. The ESCA and TEM analyses also suggested that the thickness of the silicon dioxide film increased upon increasing the annealing temperature. The electrical properties, such as the breakdown field (12.5 MV/cm) and the gate current density (<10(-7) A/cm(2)), of the sol-gel-derived ZrO2 ultrathin films obtained after annealing at 900 degrees C suggested that they were good electrical insulators. These ZrO2 thin films are expected to behave as capacitors and as coatings for insulating films. (C) 2006 The Electrochemical Society.