This work investigates the effects of postannealing on the bulk and interfacial characteristics of ultrathin ZrO2 films on Si substrates. The films were prepared by metalorganic chemical-vapor deposition and were subsequently annealed in N-2 or O-2 ambient at 500-900 degreesC. Partial crystallization of the ZrO2 film and growth of an interfacial layer (IL) were found by the increase of the annealing temperature. The IL is mainly composed of Zr-silicate for annealing in N2, but it is mostly SiO2, for annealing in O-2. The annealing also effectively reduces the oxide trapped-charge density in ZrO2, as demonstrated by the reduction of hysteresis in the capacitance-voltage relation, but not for the specimen annealed in 02 at 900 degreesC, in which excessive oxygen diffused into the film and IL was found. Lower leakage current from substrate injection in association with the reduction of depletion layer, which provides less generation current, was found due to the growth of Zr-silicate IL in N2 annealing, but the leakage from gate injection increased in conjunction with the crystallization of the ZrO2 layer. In contrast, the relatively thick SiO2 IL formed in 02 annealing reduces the leakage for both substrate and gate injection. There is also a significant shift of the turn-around- voltage in the current-voltage relation with voltage swept from inversion to accumulation, but not with voltage swept back. (C) 2004 American Vacuum Society.