We investigated the resistive switching behavior of a Pt/CuC/buffer oxide(BO)/Pt stack. By inserting an ultrathin BO layer, the resistance value at the off-state was increased, resulting in improved on/off resistance ratio. Furthermore, no high forming voltage was required because the Cu atoms diffused into the BO layer through the post metal annealing process, and changed in the effective switching layer into the ultrathin BO layer, where the actual formation and rupture of the Cu filaments take place. On the basis of results, it seems to be a promising candidate for FPGA applications, considering the forming-free operation and high on/off ratio. (C) 2011 The Electrochemical Society. [DOI: 10.1149/1.3591363] All rights reserved.