Thin films of erbium doped lead zirconate titanate (PZT) of different thickness were deposited by sol-gel technique on Pt/TiO2/SiO2/Si substrates. Capacitance-voltage measurements show that the dielectric constant continuously increases with the thickness. This is interpreted in terms of effects due to a low permittivity interfacial layer in series with the ferroelectric bulk. The linear fit of the reciprocal of capacitance vs. thickness leads to a true dielectric constant of the ferroelectric of 774 and interfacial capacitance of 14.6 nF. The leakage current properties also depend on thickness and temperature. The calculated interfacial potential barrier height amounts to 0.81 and 0.74 eV, respectively for erbium doped and pure PZT thin films. (C) 2003 Elsevier Science B.V. All rights reserved.