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The resistance switching characteristics of the La0.7Ca0.3MnO3-based devices with the top electrodes of Ag, Ag–Al alloys with the atomic ratios of Ag:Al=2:1 (2AgAl) and Ag:Al=1:2 (Ag2Al), and Al have been investigated. The device with 2AgAl top electrode shows excellent endurance, where more than 1000 cycles of reproducible current-voltage hysteresis with stable high and low resistance states have been observed. Based on Auger electron spectroscopy measurement and the detailed investigation of current-voltage curves of these devices, it is suggested that the oxygen affinity of the metal electrode, which is determined by the chemical component of Ag and Al, has an important influence on the interface structure and the resistance switching endurance. The present work provides a possible way for the improvement of the resistance switching endurance by modulating oxygen affinity of the electrode. [ABSTRACT FROM AUTHOR]

Single-phase (Bi2O3)0.7(Y2O3)0.3 (BYO) films are obtained by pulse laser deposition under the temperatures from 300 to 500 °C and the oxygen pressure of 90 Pa. Electric field-induced resistance switching is observed in the Ag/BYO/Pt structure. Postannealing in 750 °C improves the repeatability of the resistance switching and narrows the distribution of the set and reset voltages triggering the resistance switching. A linear variation of reset current with resistance is obtained for the Ag/BYO/Pt systems, either as-prepared or postannealed, despite the great dispersion of these two quantities. A reduction in the activation energy, from ∼0.63 to ∼0.33 eV, for the migration of oxygen vacancies is observed after the forming process. Possible mechanisms are discussed. [ABSTRACT FROM AUTHOR]

Resistance switching property induced by pulsed electric-field in metal-oxide-metal sandwiches attracted much interest due to its potential application in nonvolatile memory devices. In this paper, the influence of the crystallinity of La0.7Ca0.3MnO3 (LCMO) film on the resistance switching of Ag-LCMO-Pt sandwiches has been investigated. LCMO films were grown on Pt/Ti/SiO2/Si substrates using pulsed laser deposition technique at different substrate temperatures. The crystallinity of LCMO films were characterized by x-ray diffraction, atomic force microscopy, transmission electron microscopy, and x-ray photoelectron microscopy. The results show that the crystallinity of LCMO films changed from the amorphous phase to (200) oriented nanocrystalline grains by varying the deposition temperature from 500 to 700 °C. The amorphous LCMO films were crystallized through rapid thermal annealing process under oxygen atmosphere. The coexistence of crystalline grains and grain boundaries results in the inhomogenous conductivity in LCMO films. Current-voltage characteristics and pulsed bias measurements indicate that nonvolatile resistance switching only takes place in the crystallized LCMO films and the resistance change ratio depends on the grain size of LCMO films. These results were described as the electric field induced oxygen vacancy annihilation/generation combined with the change of electron/hole trap density at the local interface between the Ag electrode and the crystalline grains in the LCMO film. [ABSTRACT FROM AUTHOR]

Current-voltage characteristics, conduction mechanisms, and resistive switching properties are investigated in Al/Pr0.7Ca0.3MnO3 (PCMO)/Pt junctions. The junction resistance exhibits an irreversible increase from 2 to 90 MΩ in the forming process, the first several repeated bias sweeps. In contrast to the PCMO junctions involving inert top electrode (TE), the active Al-TE-based junctions show very large junction resistance and opposite cycling directions. It is found that the junction resistance sequence is qualitatively consistent with the standard Gibbs energies ΔG0 for the formation of corresponding TE oxides, rather than the Schottky barrier heights. Current-voltage fits indicate that the conduction processes in high and low resistance states are controlled by Poole–Frenkel emission and space-charge-limited conduction, respectively. The junctions show asymmetric switching thresholds with the minimal switching voltages are +1 V at the positive and -4 V at the negative side. Resistance retention tests indicate that the low resistance state is unstable and it gradually relaxes to higher resistance values. All the properties are discussed by the oxidation/reduction reaction at the Al/PCMO interface. [ABSTRACT FROM AUTHOR]

We report a memristive switching effect in Pt/CuOx/Si/Pt devices prepared by the rf sputtering technique at room temperature. Differently from other Cu-based metal filament switching systems, a gradual electroforming process, marked by a gradual increase of the device resistance and a gradual decrease of the device capacitance, was observed in the current-voltage and capacitance characteristics. After the gradual electroforming, the devices show a uniform memristive switching behavior. By Auger electron spectroscopy analysis, a model based on the thickness change of the SiOx layer at the CuOx/Si interface and Cu ion migration is proposed for the gradual electroforming and uniform memristive switching, respectively. This work should be meaningful for the preparation of forming-free and homogeneous memristive devices. [ABSTRACT FROM AUTHOR]

“Negative” electric-pulse-induced reversible resistance (EPIR) switching phenomenon was found in In/PCMO/Pt sandwich, in which the high resistance can be written with positive voltage pulses, and the low resistance can be reset using negative voltage pulses (the positive voltage direction is defined as going from the top electrode to the bottom electrode). This is just the opposite from the “positive” EPIR effect in Ag/PCMO/Pt sandwich, in which the high resistance can be written only with negative voltage pulses, and the low resistance can be reset using positive voltage pulses. The I–V hysteresis curves of In/PCMO/Pt and Ag/PCMO/Pt sandwiches also show opposite directions, i.e., counterclockwise and clockwise under a negative voltage region for indium and Ag electrode systems, respectively. C–V characteristics show that the barrier does not exist in Ag/PCMO/Pt sandwich, while In/PCMO/Pt sandwich exhibits an obvious Schottky-like barrier. We suggest that in the negative EPIR behavior in In/PCMO/Pt structure, the resistance states are mainly controlled changing the Schottky-like barrier at the interface with the weak effect of carrier trapping process, while the positive EPIR behavior in Ag/PCMO/Pt sandwich mainly depends on the carrier trapping process at the interface. [ABSTRACT FROM AUTHOR]

Ag/Ln 1- x Ca x MnO 3 /Pt (Ln = Pr, La, X = 0.3) sandwich structures showing electric-pulse induced reversible resistance switching properties provide a route for a new resistance random access memory (RRAM), because the electric-pulse induced high-resistance state and low-resistance state can be assimilated to logic 1 and 0 in RRAM systems, respectively. In this work the fatigue and the retention behavior of the electric-pulse induced resistance states have been studied. It is found that the retention properties of the EPIR materials can be modified by post-annealing of the materials and by the inner adjusting of the pulse applied mode. Moreover, the EPIR devices can be optimized by initializing using voltage sweep or pulse sweep circles before application to possess the appropriate original resistance and the stable resistance switching behavior. [ABSTRACT FROM AUTHOR]

Influence of temperature on the La1-xCaxMnO3/SrTiO3:Nb heterojunctions with the Ca content ranging from 0 to 0.75 has been experimentally studied. Obvious temperature effect occurs in the junction with a Ca content of 0.1. As experimentally shown, the interfacial barrier is insensitive to temperature below 340 K, and experiences a decrease from ∼1.24 to 0.85 eV as temperature grows from 340 to 375 K. However, the temperature effect in other junctions is weak, and the energy barrier change is typically ∼0.03–0.08 eV. In the scenario of temperature-driven orbital order-disorder transition in the La0.9Ca0.1MnO3 film, the temperature effect can be qualitatively understood. [ABSTRACT FROM AUTHOR]

Bipolar resistance switching behaviors in the M/La0.7Ca0.3MnO3/Pt (M=Pt, Ag, Cu, Al, Ti, and W) junctions were investigated. We found that the switching polarities of the junctions for M=Pt, Ag, and Cu were opposite to those for M=Al, Ti, and W. This phenomenon was attributed to the different Gibbs free energy of the metal oxide formation. Based on Auger electron spectroscopy measurement of the M/La0.7Ca0.3MnO3 interfaces, the switching mechanisms were further discussed in terms of metal electrode redox reaction for M=Al, Ti, and W and oxygen vacancy generation/annihilation in the La0.7Ca0.3MnO3 film for M=Pt, Ag, and Cu, respectively. [ABSTRACT FROM AUTHOR]

Current-voltage characteristics and colossal electroresistance (CER) have been experimentally investigated in the temperature range from 293 to 454 K for the Schottky junctions Au/SrTiO3:0.5 wt % Nb and Au/SrTiO3:0.05 wt % Nb. Both junctions show electron tunneling-dominated transport behavior. Postannealing of SrTiO3:0.05 wt % Nb in oxygen atmosphere causes a transition of the transport behavior from electron tunneling to thermionic emission. The CER effect appears in the junctions with the transport behavior dominated by electron tunneling and greatly weakens when thermionic emission prevails after postannealing. This result reveals the presence of a close relation between CER and electron tunneling. [ABSTRACT FROM AUTHOR]

A systematic study on photovoltaic effects has been performed for the Schottky junction Au/SrTiO3:0.05 wt %Nb, the resistance of which can be tuned, by applied electric pulses, between ∼1 and ∼200 MΩ. It is found that, despite the great change in junction resistance, the photocurrent across the junction is constant when the power and wavelength of incident light are fixed. The corresponding Schottky barrier, deduced from the photoresponse data is ∼1.5 eV, independent of junction resistance. This result suggests the invariance of the interfacial barrier during resistance switching and the occurrence of filamentary conduction channels. [ABSTRACT FROM AUTHOR]

Temperature dependence of the current-voltage characteristics of Ag–La0.7Ca0.3MnO3–Pt heterostructures was investigated and the related current conduction mechanism was discussed. Poole-Frenkel emission and trap-controlled space charge limited current mechanisms are employed to explain the carrier transport at low and high temperature regions, respectively. Obvious hysteresis is observed only in the region dominated by space charge limited current with traps exponentially distributed in energy. This can be explained by the retention behavior of trapped carriers at the Ag/La0.7Ca0.3MnO3 interface layer. It is proposed that the resistance switching can be optimized for device application by the electrode/film interface defect engineering. [ABSTRACT FROM AUTHOR]

Materials showing reversible resistance switching at room temperature are attractive for today’s semiconductor technology with its wide interest in nonvolatile random access memories. In this letter, the retention behavior of the electric-pulse-induced reversible (EPIR) resistance change effect in Ag–La0.7Ca0.3MnO3–Pt sandwiches was demonstrated. The results suggest that the retention property of the EPIR materials depends on both the resistance states and the resistance switching history, and it can be modified using the proper modes of applied electric pulse. [ABSTRACT FROM AUTHOR]