Abstract
The combination of nonvolatile memory switching and volatile threshold switching functions of transition metal oxides in crossbar memory arrays is of great potential for replacing charge-based flash memory in very-large-scale integration. Here, we show that the resistive switching material structure, (amorphous TiOx)/(Ag nanoparticles)/(polycrystalline TiOx), fabricated on the textured-FTO substrate with ITO as the top electrode exhibits both the memory switching and threshold switching functions. When the device is used for resistive switching, it is forming-free for resistive memory applications with low operation voltage (<±1 V) and self-compliance to current up to 50 μA. When it is used for threshold switching, the low threshold current is beneficial for improving the device selectivity. The variation of oxygen distribution measured by energy dispersive X-ray spectroscopy and scanning transmission electron microscopy indicates the formation or rupture of conducting filaments in the device at different resistance states. It is therefore suggested that the push and pull actions of oxygen ions in the amorphous TiOx and polycrystalline TiOx films during the voltage sweep account for the memory switching and threshold switching properties in the device.
Highlights
In the near future, the present charge-based flash memories will face the limits to their applications in the very-large-scale integration (VLSI) technology[1,2,3]
We show that the memory switching and threshold switching can both be operated in a particular/(Ag nanoparticles)/(polycrystalline titanium oxide (TiOx)) structure sandwiched between indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) electrodes
When a current compliance (Icc = 10 μA) is subsequently applied on the device of Fig. 1(b), the image. (b) Current-voltage (I-V) relation shows the characteristics of threshold switching mode, as shown in Fig. 1(c) (linear I-V relations are plotted in Supplementary Fig. S1(b))
Summary
The present charge-based flash memories will face the limits to their applications in the very-large-scale integration (VLSI) technology[1,2,3]. When the resistive switching material is used for TS applicaitons, the “ON” and “OFF” states of the device are switchable by adjusting the voltage[32,33] Such TS devices typically exhibit bi-directional switching property, useful for suppressing the sneak current paths between memory cells[34,35,36,37,38,39,40]. We show that the memory switching and threshold switching can both be operated in a particular (amorphous TiOx)/(Ag nanoparticles)/(polycrystalline TiOx) structure sandwiched between indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) electrodes When this device is used for memory switching, it exhibits good electrical properties, especially, the self-compliant driving current, which is beneficial for ultralow programming energy in RRAM applications. The results suggest that, under voltage sweeps, the push and pull actions on the oxygen ions in the amorphous TiOx layer and polycrystalline TiOx layer can account for both the memory switching and threshold switching operations in the device
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