The effect of the amorphous insulator layer on conduction behavior of spin coated silica/sputtered indium tin oxide two-layer film was studied in terms of impedance spectroscopy measurements, and current-voltage characterizatics. I-V characteristics of the two-layer films have shown that the conduction mechanism changes from direct tunneling to space-charge-limited conduction, when zinc cations are added to the silica layer. An addition of the ionic dopant leads to a large decrease in sheet resistance of the two-layer film as shown in the Cole-Cole plot. Consequently, the conductivity enhancement of the two-layer film without a reduction in transparency was achieved by the introduction of zinc cations into the amorphous silica layer. (C) 2003 Elsevier Science B.V. All rights reserved.