Ion irradiation: a tool to understand oxide RRAM mechanism

Abstract

Recently observed resistive random access memory (RRAM) effects in mixed oxides have opened up new horizons for a potential viable alternative to the existing flash non-volatile memory devices. Capacitor structures consisting of simple binary transition metal oxides and perovskite manganites have been shown to possess electric pulse-induced resistance switching (RS). Despite intense research activity in this area, the mechanism governing this switching remains elusive. An interesting finding common to almost all of the oxide RRAM candidate materials is their disordered bulk and/or surface structure offering better switching characteristics than their epitaxial counterpart. Swift heavy ion (SHI) irradiation was used as a unique tool to selectively create controlled defects in several oxide films possessing metal/oxide/metal-like planar structures. Using widely-investigated binary oxides, namely NiO and TiO2 thin film nanostructures, it is shown that the RS in these materials can be induced by SHI irradiation. More than 100% enhancement in the RS ratio has been achieved in these oxides. Using the online elastic recoil detection analysis, it is demonstrated that gross defects contributing to metallic filaments away from the Ag/NiO interface have a major role to play when compared with the interface effects and oxygen electromigration. The role of SHI in improving the RS in the case of TiO2 has been successfully verified. This is an attempt to show that SHI irradiation has unique qualities on offer to the modern and fast emerging field of “oxide electronics”.