Fabrication And Performance Of NiO_x-Based Resistive Switching Memory

Resistive switching random access memory (ReRAM) based on resistive switching(RS) of oxide films is one of highlighted candidates for the next generation of nonvolatile memory due to its high writing/read speed, low power consumption, simple structure and high integration density. NiOx is one of oxide materials early observed resistive switching behaviors. Due to the differences on fabrication methods and technologies, NiOx-based ReRAM cells present various kinds of RS behaviors, including unipolar, bipolar and non-polar RS behavious. There are a lot of reports on their switching performance, while discussions on their switching directions are rare.In this paper, oxygen-rich NiOx polycrystalline films have been deposited under optimized conditions on Pt-covered p-Si (100) substrates by using radio frequency magnetron sputtering. Microstructure investigations reveal that NiOx polycrystalline films exhibit a [200] preferred orientation and a columnar configuration vertical to the substrate. Dependences of the switching characteristics, especially for switching direction, on the oxygen partial pressure, scanning voltage, film thickness and measure temperature have been investigated in this paper. Their conduction and resistive switching mechanisms have also been discussed.Current-voltage measurements indicate that the NiOx films deposited at the 20%-oxygen partial pressure present excellent bipolar RS characteristics:the ratio of high/low resistance is higher than 10 at the reading voltage of 0.9 V, which can be well maintained for more than 1.5x103 cycles. On the other hand, it is found that the RS direction of polycrystalline NiOx films is dependent on scanning voltage amplitude as well as film thickness. For the same Ag/NiOx/Pt memory cell, it presents the anticlockwise current-voltage loops when applying a scanning voltage lower than ±2 V, while exhibits clockwise current-voltage loops once the scanning voltage increases to ± 2 V.60 nm-thick NiOx films achieve the anti-clockwise current-voltage loops, while 20 nm-thick NiOx fihns present the clockwise current-voltage loops. On the other hand, the leakage current increases with the increase of measure temperature.Theoretical fitting results show that the Schottky conduction is responsible for the electric transport on the high resistance state, and an ohmic conduction dominates on the low resistance state. Filamentary conducting paths are responsible for the anti-clockwise resistive switching behaviors, while redox processes of Ag ions diffused in NiOx fihns result in the clockwise current-voltage loops.