Resistive switching (RS) characteristics of a Pr0.7Ca0.3MnO3 (PCMO) film sandwiched between a Pt bottom electrode and top electrodes (TE) made of various metals are found to belong to two categories. Devices with TE made of Al, Ti, and Ta exhibit a large I-V hysteresis loop and bipolar RS, but those with TE made of Pt, Ag, Au, and Cu do not. Transmission electron microscopy reveals that a thin metal-oxide layer formed at the interface between the former group of TE and PCMO, but not for the latter group of TE. Analysis shows that the categorization depends on the Gibbs free energy of oxidation of the TEs with respect to that of PCMO.
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.
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