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To implement a cross-point memory array successfully, it is highly required to develop nonlinear selector devices. Insulator-metal transition (IMT) devices are promising candidates for selector applications. Although IMT characteristics of SmNiO 3 with a high transition temperature of 130 °C have already been reported, the film deposition conditions following high-pressure oxygen annealing at high temperatures are not practical for high-density memory applications. In this report, we propose a simple electrical method to form a localized IMT SmNiO 3 region in a sputterdeposited SmNiO x film. The nanoscale IMT device formed by the electro thermal effect shows promising selector characteristics such as switching uniformity, switching endurance (>10 5 cycles), and high temperature stability. The feasibility of good selector characteristics is also investigated by serially connecting the selector device (SmNiO 3 IMT) to a Ta/Ta 2 O 5 /Pt resistive random access memory (ReRAM) device.

In this study, we demonstrate a systematic way to obtain a bidirectional selector for cross point Resistive Random Access Memory (ReRAM) application by engineering material's properties. The nitrogen doping can control carrier density and increase electrical resistivity of zinc oxide. By introducing nitrogen at the both ends of ZnO film, Pt/N-ZnO/ZnO/N-ZnO/Pt structure was fabricated which exhibits very stable selector characteristics. An intensive analysis was performed to analyse the effect of nitrogen percentage and the thickness of N-ZnO on selector characteristics.ZnO has gained substantial interest for many potential applications such as optoelectronics, sensors, transparent transistor, light emitting diode, piezoelectric devices, varistors, nanowires and solar cells. 1 Moreover, because of its high bandgap (3.4 eV), it is possible to moderate the material properties by addition of several doping materials. For example, aluminum, indium, phosphorous doping can make ntype and nitrogen doping can make p-type ZnO. [2][3][4][5] Recently, ZnO has been reported as an attractive material in the field of resistive random access memory (ReRAM) because of its high scalability, high temperature stability and low process temperature. 6-8 Due to simple device structure of ReRAM, the 3D stacking to form high density cross-point memory was proposed. However, the sneak path leakage from unselected cells in passive cross-point architecture is one of the main challenges. 9,10 In this case, researchers have proposed several two terminal selector devices, such as diodes, 11 mixed electronic ionic conductor (MIEC), 12 insulator metal transition (IMT), 13 ovonic threshold switching (OTS) 14 and multi-layer tunnel barrier based selector 15 etc. In 3D cross point architecture, the selector should have some specific requirements such as high on-current with low off-current (current at 1 2 read voltage (V read )) and selectivity (ratio of current at V read to 1 2 V read ) properties. In particular, oxide diodes are suffering from lower on-current density, while IMT and OTS have higher leakage current. Moreover, multi-layer tunnel barrier is proposed with low off-current and high on-current density. But it suffers from complex fabrication processes and complex material properties. In addition, Complementary Resistive Switching (CRS) is another probable solution for cross point application. 16 But this device needs destructive reading and high power consumption.In this study, we proposed Pt/N-ZnO/ZnO/N-ZnO/Pt bidirectional selector with high selectivity and reasonable current density by engineering material property. In this device stack, ZnO layer is sandwiched between the nitrogen doped ZnO (N-ZnO) layers and forms a symmetric structure. It is reported that nitrogen doping can decrease the carrier density and increase the resistivity in ZnO. 17 The N-ZnO layer in this device stack is working as a insulating thin film compared to ZnO film. We proposed a bidirectional selector device having TaO x (conducting)/TiO 2 (insulating)/TaO x...