Study on fabrication method of forming-free resistance random access memory

In general, the resistance change effect in transition metal oxides appears after a forming process, which is similar to the soft breakdown. However, there exist resistive random access memory cells which do not need the forming process. These cells are initially in the low resistance state and start with a reset process, which is a switching from a low resistance state to a high resistance state. Therefore, filaments are considered to be formed already in an initial state and, therefore, we call this kind of filaments "native filaments (NFIs)". The first I-V characteristics of pristine memory cells with the Pt/NiO/Pt structure, which were formed by using reactive ion etching (RIE), were measured as functions of cell area, S, and NiO thickness, t. As a result, it was shown that the number of NFIs increased with increasing S and with decreasing t. In addition, it was suggested that NFIs exist at the fringe area of the memory cell. These results suggested that an NFI consists of oxygen vacancies which connect top and bottom electrodes, and that vacancies are introduced during the RIE process of the top electrode and the NiO memory layer. Universal relation between a reset current, I-reset, and a total resistance of all NFIs contained in one memory cell was found, providing us a guiding principle to reduce the value and variation of I-reset. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim