Ultrathin (Nb1-xTax)(2)O-5 films, with thicknesses from similar to 3 to similar to 25 nm, were deposited by chemical solution deposition starting from aqueous precursor solutions. The film's dielectric properties were characterized by capacitance-voltage and current-voltage measurements. Permittivities ranged from 20 to 31 after annealing at 600 degrees C, with the highest value obtained for pure Nb2O5. With increasing Nb content, increasing leakage currents were observed. The crystallization temperature was determined by in situ X-ray diffraction measurement for films with similar to 15 nm thickness: Nb2O5 was crystalline as deposited (600 degrees C), while the crystallization temperature of solid solutions increased with increasing Ta content, up to 875 degrees C for pure Ta2O5. NbTaO5 showed a marked increase in permittivity from 27 to 38 after crystallization anneal at 600 and 800 degrees C, respectively. For Nb2O5, no significant difference in permittivity was observed between amorphous and crystalline layers. (C) 2009 The Electrochemical Society. [DOI: 10.1149/1.3247348] All rights reserved.