The electrical and reliability characteristics of ultrathin ZrO2 prepared by thermal oxidation of a sputter deposited Zr-metal layer in a H2O and a D2O ambient were investigated. For the case of lightly oxidized zirconium oxide, an anomalous high capacitance and dispersion characteristics were observed, which can be explained by space charge polarizations of metallic zirconium in zirconium oxide. Based on x-ray photoelectron spectroscopy analysis, the lightly oxidized ZrO2 samples show metallic Zr peaks. By optimizing the wet oxidation conditions, excellent characteristics of ZrO2, such as a capacitance equivalent oxide thickness of 11 Angstrom, negligible dispersion characteristics and leakage current density less than 10 mA/cm(2) at 1 V below the flatband voltage were obtained. Compared with the H2O oxidation of Zr, D2O wet oxidation improves the reliability characteristics of ZrO2.