Abstract
Because RRAM has many advantages such as low cost, low power, fast programming speed (twr < 100 ns), simple structure, shrinkage of cell size and nondestructive operation, it has attracted much attention for many researchers. Besides, in order to decrease the cell area and raise the density, nanowires were used to replace the thin film materials. In the literature, they usually synthesize the Ni nanowires and then oxidize the nanowires to form Ni/NiO core-shell structures. In our research, we report the growth and structural characterization of the core-shell Ni/NiO nanowires in one step. In addition, the electrical and resistance switching properties were also investigated. The Ni/NiO core-shell nanowires were synthesized by NiCl2 sources on Si substrates at 800 ℃ in source region (I) and 700 ℃ in substrate region (II) under Ar carrier gas in two-region furnace via oxide-assisted growth (OAG) mechanism. Due to the OAG mechanism, the SiO2 layer was formed outside of Ni/NiO core-shell nanowires. Then, we used HF vapor to etch away the SiO2. By different reaction temperature and flow gas, we can control the diameters and length of the nanowires. The crystal structure, morphology and chemical composition were analyzed by scanning electron microscope (SEM) and transmission electron microscope (TEM). Besides, due to fabrication of nanodevice, we use the optical microscope (OM) and a series of standard electron beam lithography (EBL). Finally, we used the Keithley 4200 to measure the I-V curve and resistive switching behaviors of core-shell Ni/NiO nanowires. Also, we designed different electrode distances of nanodevices to investigate the possible conduction path. First, different resistive switching modes such as unipolar or bipolar switching mode were observed in different electrodes, nickel and titanium. Secondly, the endurance of the Ni/NiO core-shell nanowires can be modified and the cycle number can be over 100. Finally, because the resistive switching current could be operated at micro amp (A) and lower power, the Ni/NiO core-shell nanowires have potential to become energy efficient random access memory (ReRAM).