Zirconia (ZrO2) thin films were deposited by metal organic chemical vapor deposition (MOCVD) on (10 0) Si over temperature and pressure ranges from 700 to 900 degrees C and 100 to 2000 Pa, respectively. The oxide films were characterized. by field emission microscopy and X-ray diffraction so that microstructure and ratios of monoclinic and tetragonal phases could be estimated according to the process conditions. The mechanical behaviour of the substrate-film systems was investigated using Vickers micro-indentation and Berkovitch nano-indentation tests. The characteristics of silicon are not modified by the presence of a thin film of silicon oxide (10 nm), formed in the reactor during heating. Young's modulus and the hardness of tetragonal zirconia phase, 220 and 15 GPa, respectively, are greater than values obtained for monoclinic phase, 160 and 7 GPa, respectively. The zirconia films are well adherent and the toughness of tetragonal zirconia phase is greater than that of monoclinic phase. (c) 2006 Elsevier B.V. All rights reserved.