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Voltage-current (I-V) measurements in a wide temperature range from 88 to 573 K demonstrated the effects of temperature on the switching behavior of a Cu/Ta2O5/Pt resistive memory cell that is referred to as a gapless-type atomic switch. After the forming process, the cells were SET from the OFF state to the ON state at a positive bias to the Cu electrode and then RESET from the ON state to the OFF state at a negative bias. In a previous study (Tsuruoka et al 2010 Nanotechnology 21 425205), it was demonstrated that the SET process corresponds to the reformation of a metal filament between the electrodes by the inhomogeneous nucleation and subsequent growth of Cu whereas the RESET process can be attributed to the Joule-heating-assisted dissolution of the metal filament. In the work described here, we observed that the voltages at which the cells are SET and RESET (SET and RESET voltages) decreased in magnitude with an increase in temperature. From calculations of the nucleation rate of Cu nuclei based on the classical nucleation theory, it was found that the observed temperature variation of the SET voltage is primarily determined by supersaturation in the vicinity of the Pt electrode, which is controlled by the application of positive bias. The supersaturation required for spontaneous growth of a Cu nucleus decreases with increasing temperature, resulting in lower SET voltages at higher temperatures. The RESET voltage is determined by the thermal stability of the metal filament formed. Moreover, using the temperature variation in cell resistances of the ON state, the growth speed of the Cu nucleus after the nucleation was found to decease with increasing temperature. These results are consistent with our switching model. [ABSTRACT FROM AUTHOR]

We report the observation of two resistance switching modes in certain 50 nm x 50 nm crossbar TiO2 memristive devices that have been electroformed with a low-current process. The two switching modes showed opposite switching polarities. The intermediate state was shared by both modes (the ON state of the high-resistance mode or the OFF state of the low-resistance mode) and exhibited a relaxation to a more resistive state, including an initial transient decay. The activation energies of such a decay and ON-switching to the intermediate state were determined to be 50-210 meV and 1.1 eV, respectively. Although they are attributed to the coexistence of charge trapping and ionic motion, the ionic motion dominates in both switching modes. Our results indicate that the two switching modes in our system correspond to different switching layers adjacent to the interfaces at the top and bottom electrodes. [ABSTRACT FROM AUTHOR]