EFFECTS OF ARGON⁺ ION BOMBARDMENT ON A PLATINUM/ZIRCONIUM DIOXIDE/IRIDIUM RESISTIVE SWITCHING MEMORY CELL

Abstract

We have fabricated Pt/ZrO 2 /Ir memory cells with pristine and Ar + ion bombarded ZrO 2 films, which show unipolar resistive switching behaviors. Ar + ion bombardment induces change in surface morphology and chemical states of ZrO 2 films. We have found that forming voltage significantly decreases in a Pt/ZrO 2 /Ir memory cell whose Ar + ion bombarded ZrO 2 film shows oxygen vacancy like defects and the largest root-mean-square (RMS) roughness. It seems that forming process may be more easily induced in an Ar + ion bombarded ZrO 2 film with higher RMS roughness mainly due to locally enhanced electric field in a region with oxygen vacancy like defects.Resistive switching (RS) memory using oxide material has been widely studied due to its outstanding benefits -simple device structure, high density, high speed, low power, and so on -for the application in next generation nonvolatile memory. In particular, it has been reported that 3-dimensional cross-point structure is compatible with unipolar RS materials whose reset switching from low resistance state (LRS) to high resistance state (HRS) and set switching from HRS to LRS are induced by external voltages with same polarity. Although the detailed explanations are unclear, there is a general agreement that unipolar RS phenomena may result from the formation and rupture of filamentary conducting path 1,2 through Joule heating 3,4 or migration of ions under an applied electric field. 5−7 Therefore, it is expected that unipolar RS behaviors can be modified by local change where filamentary path is formed.Before reproducible and bistable RS process, each memory cell has to experience a forming process caused by an electric field in a unipolar switching case. During the forming process, soft breakdown can easily form a percolative network of the conducting path, consisting of crystalline defects and/or grain boundaries in memory devices. 1,2,8 If the forming voltage is high, the device may be easily damaged and broken by the high voltage and accompanied high current and also * , † Corresponding Authors. need a huge operation power. Therefore, it has been tried to decrease the forming voltage 9−11 and thus to save the power consumption and to prevent the breakdown during the forming process. However, it has been hard to control the forming voltage artificially since forming process randomly takes place in crystalline defect, grain boundary or weak point. Among many oxide materials, ZrO 2 thin films showing RS phenomena has a good retention property and a high on/off ratio than other binary transition metal oxide materials. 12 Because of its simple chemical composition, high breakdown field and superior thermal stability, ZrO 2 thins films are promising candidates for nonvolatile memory devices using RS phenomena. In addition, it has been reported that phase transformations can be induced in ZrO x thin films with Ar + ions bombardment of relatively low energy and the oxidation state of zirconium increases with depth from the film surface. Treated thin layers are related wit...

Enhancement of resistive switching under confined current path distribution enabled by insertion of atomically thin defective monolayer graphene

“…During the modified fabrication process, Ar + ions bombarded on MLG/NiO may induce defects in the NiO layer as well as on the MLG. According to a previous study about ReRAM treated using IAR 48 , resistive switching characteristics was improved by chemical or structural defects in an oxide layer resulting from Ar + bombardment. It was found that the forming voltage could be controlled by modification of surface roughness and oxygen vacancy concentration of an oxide layer, which depended on kinetic energy of the bombarded Ar + ion.…”