Abstract
Generally, a resistance change effect in transition metal oxides appear after the forming process. Here, a conducting filamentary path in which resistive switching occurs is formed in the forming process. However, there are resistive random access memory devices which do not need the forming process. These devices are initially in the low resistance state and start with a reset process, where reset means the switching from a low resistance state to a high resistance state. In these devices, the filaments are considered to be formed already in an initial state and, therefore, we call this kind of filaments “native filaments (NFIs)”. The initial resistance of devices containing NFIs and the probability that NFI is observed in as-prepared devices, PNFI, as a function of the device area were measured. As a result, it was suggested that NFIs exist in a certain averaged interval around the electrode. On the other hand, the memory layer thickness dependence of PNFI suggests that NFI consists of metal or oxygen vacancies which connect top and bottom electrodes. These vacancies are considered to be introduced during the reactive ion etching process of the top electrode and the memory layer fabrication.
