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Memory-state [low-resistance state (R L ) and highresistance state (R H )] dependence of random telegraph noise (RTN) of Ta 2 O 5 /TiO 2 resistive random access memory is investigated. The conduction mechanism of both memory states and a limit of resistance controllability are also investigated to clarify the difference in the RTN mechanism of both states. The boundary between the R L and R H states was found at 5-20 kΩ, and the conduction mechanism much depended on the memory state. The noise also depended on the memory state. The noise amplitude in the R H state was larger than that in the R L state. In the R H state, a tunnel barrier was generated to cut off a conduction path (filament), and traps inside the tunnel barrier were supposed to increase the noise amplitude. Moreover, the composition of the following degraded the noise distribution in the R H state: 1) capture and emission of charges with traps and 2) instability of these traps against the bias temperature stress.Index Terms-Filament, noise, random telegraph noise (RTN), resistive random access memory (ReRAM), resistive switch, RRAM, Ta 2 O 5 , TiO 2 .

We investigated the conduction mechanism of a Ta2O5/TiO2-stacked resistance random access memory (ReRAM) device and found that its highly resistive state can be attributed to tunnel barriers induced in the filament, since single-electron tunneling phenomena was observed in the current–voltage characteristics at low temperatures and the resistance depended only slightly on temperature. We also found that the largest tunnel barrier, whose resistance is more than 1000 times larger than the second largest one, is located at the interface between the Ta2O5 layer and TiO2 layer and that variation in the resistance was caused by variation in the tunnel barrier width.

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We propose a new approach for improving the operating margin of Ta 2 O 5 /plasma oxidized TiO 2 stacked unipolar ReRAM. It was found that the reset voltage (switching from low resistance state to high resistance state) can be minimized by using local minimum against the resistance of the low resistance state. In addition, weakening the plasma oxidation condition reduced the power consumption and the variation of reset voltage. Excellent operating margin and more than 10 5 switching cycle times was successfully demonstrated using the integrated device.