The aim of this work was to prepare ultra thin and dense zirconia films by electrostatic spray deposition to be applied in microelectronic devices. in this paper, the influence of the precursor solution was investigated on the morphology of zirconia films, in terms of salt concentration starting from zirconium acetylacetonate and solvent composition based on butyl carbitol and/or ethanol. The microstructure of zirconia films was studied by Scanning and Transmission Electron Microscopies. The as-deposited films, less than 20 nm in thickness, were found to be amorphous. A film densification, leading to its thickness decrease to 7 nm, occurred through a thermal treatment at 600 degrees C under helium. A partial crystallization was observed and the structure of the film was found to be mainly tetragonal, according to electron diffraction. An appearance of 6 mol% monoclinic phase was detected by Raman microspectrocopy. (C) 2009 Elsevier B.V. All rights reserved.