We have successfully achieved high speed (~50 ns) unipolar operation in RRAM devices comprised of titanium oxynitride (TiON) combined with a control resistor connected in series. For unipolar switching, programming and erasing pulses can be the same width, typically, a few tens of nano-seconds. This enables high speed and high density cross-point RRAM memory arrays.In addition, we demonstrate how switching characteristics can be controlled by a series resistor. IntroductionResistance RAM (RRAM

We demonstrate a new memristive device (IL-Memristor), in which an ionic liquid (IL) serve as a material to control the volatility of the resistance. ILs are ultra-low vapor pressure liquids consisting of cations and anions at room temperature, and their introduction into solid-state processes can provide new avenues in electronic device fabrication. Because the device resistance change in IL-Memristor is governed by a Cu filament formation/rupture in IL, we considered that the Cu filament stability affects the data retention characteristics. Therefore, we controlled the data retention time by clarifying the corrosion mechanism and performing the IL material design based on the results. It was found out that the corrosion of Cu filaments in the IL was ruled by the comproportionation reaction, and that the data retention characteristics of the devices varied depending on the valence of Cu ions added to the IL. Actually, IL-Memristors involving Cu(II) and Cu(I) show volatile and non-volatile nature with respect to the programmed resistance value, respectively. Our results showed that data volatility can be controlled through the metal ion species added to the IL. The present work indicates that IL-memristor is suitable for unique applications such as artificial neuron with tunable fading characteristics that is applicable to phenomena with a wide range of timescale.

We present first-principles current-voltage calculations for the models of a HfO 2 -based resistive random access memory cell as a function of electrode materials, W, Ta and TiN. For bias voltage within ±0.5 V, the ON current values depend on electrode, suggesting that the ON state is a joint property of electrode and HfO 2 . The OFF currents are dominated by the wavefunctions near the Fermi energy effusing from the interface into HfO 2 . We identify that enhancement of metallic character at the electrode/HfO 2 interface is necessary for a substantial ON current to flow. Especially, when using the TiN electrode, the ON current flows if the Hf buffer layer is embedded at the TiN/HfO 2 interface. This result is in agreement with a recent experiment.

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