Oxide double-layer systems have recently attracted much attention, owing to their excellent performance as nonvolatile bipolar resistance memory. In this study, we measured the time required to form conducting channels (i.e., the forming time) in double-layer Pt/Ta2O5/TaOx/Pt cells and single-layer Pt/TaOx/Pt cells by applying a pulse-waveform voltage signal. The voltage amplitude dependence of forming times in both samples revealed nonlinearities with nine orders of magnitude. By investigating their temperature dependence, we found that channel formation for both samples can be attributed to thermally assisted dielectric breakdown. (C) 2013 Published by Elsevier B.V.