Zirconium-aluminum oxide thin films with different aluminum/zirconium ratios (Al/Zr) have been prepared by ultrasonic spray pyrolysis, using metallic acetylacetonates as source materials. The effect of variations of substrate temperature (T-s), carrier gas flow rate (F-g), and aluminum concentration in the start solution [(Al/Zr)(s)] on the Al/Zr ratio, the deposition rate (R-d), and refractive index of deposited films is analyzed. The Al/Zr ratio increases when the T-s and [(Al/Zr)(s)] ratios increase, but it diminishes as F-g is augmented. Moreover, R-d grows when the deposition parameters are incremented. Refractive index acquires values around 1.85 in all cases. X-ray photoelectron spectroscopy results indicate that the Zr 3d and O 1s core levels shift toward low binding energies when aluminum is incorporated. The location of line Al 2p and its symmetry indicates that aluminum atoms are completely oxidized, forming a ternary oxide with zirconium atoms. Infrared transmittance spectra show small absorption bands related with Zr-O and Al-O bonds in a ternary (ZrAlO) oxide. X-ray diffraction spectra show that all the films containing aluminum are amorphous, except that deposited at the highest T-s. In all other studied cases the films are amorphous. The dielectric constant has values between 11.84 and 20.96 depending on the deposition conditions. (c) 2005 The Electrochemical Society. All rights reserved.